The effect of mechanical vibration (Acceledent 30Hz) applied to the hemimaxilla on root resporption and tooth movement after application of orthodontic force. A micro CT study

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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
The Effect of Mechanical Vibration
(Acceledent, 30Hz) applied to the hemimaxilla on Root Resorption Associated with
Orthodontic Force
A Micro-CT Study
Daniel Tan BDS (Hons) FRACDS
Discipline of Orthodontics
Faculty of Dentistry
University of Sydney
Australia
A thesis submitted in partial fulfilment of the requirements for the Doctor of Clinical
Dentistry in Orthodontics
1
Discipline of Orthodontics, Faculty of Dentistry
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Dedication
To my loving wife, Sabina for all of your patience, support and encouragement.
To my boys, Jayden and Harrison, for giving me a pleasant distraction from writing this
thesis.
2
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Acknowledgements
Sincere gratitude is expressed to the following:
Professor M Ali Darendeliler, Head of Department, Discipline of Orthodontics, University of
Sydney for his supervision and the opportunity to have a career in orthodontics.
Dr Carmen Gonzales, Senior Lecturer, Discipline of Orthodontics, University of Sydney for
her supervision of the project.
Dr Oyku Dalci, Lecturer, Discipline of Orthodontics, University of Sydney for her supervision
of the project.
Dr Qiang Fei Li, Discipline of Orthodontics, University of Sydney for her assistance with the
statistical analysis.
Dr Peter Petocz, Department of Mathematical Sciences, Macquarie University for his
assistance with the statistical analysis.
3
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Associate Professor Allan Jones, Australian Centre for Microscopy and Microanalysis,
University of Sydney, for his help with the micro-CT and VG Studio Max.
Mr Dennis Dwarte, Australian Centre for Microscopy and Microanalysis, University of
Sydney, for his help with the micro-CT and VG Studio Max.
To my colleagues, Drs Saad Almozy, Riaan Foot, Johnathan Grove and Tiffany Huang for their
continuous support and friendship over the last three years.
The Australian Society of Orthodontics Foundation for Research and Education Inc for
providing funding for this project.
4
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Declaration
CANDIDATE CERTIFICATION
This is to certify that the candidate carried out the work in this thesis in the Orthodontic Department
at the University of Sydney, and this work has not been submitted to any other university or
institution for a higher degree.
5
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Table of Contents
1
Introduction .................................................................................................................................... 9
2
Literature review........................................................................................................................... 11
2.1
Cementum ............................................................................................................................ 11
2.2
Orthodontic tooth movement and OIIR................................................................................ 12
2.3
Classification of root resorption ........................................................................................... 13
2.4
Orthodontically induced root resorption.............................................................................. 15
2.4.1
Mechanism of root resorption ...................................................................................... 16
2.4.2
Repair processes ........................................................................................................... 18
2.5
Incidence and prevalence of root resorption ....................................................................... 19
2.5.1
2.6
Orthodontically treated populations .................................................................................... 20
2.7
Aetiology and risk factors associated with OIIR .................................................................... 22
2.7.1
Biologic factors .............................................................................................................. 22
2.7.2
Habits ............................................................................................................................ 27
2.7.3
Mechanical factors ........................................................................................................ 31
2.8
Management of OIIR ............................................................................................................. 38
2.9
Research methodologies....................................................................................................... 40
2.9.1
2.10
Methods for measuring OIRR........................................................................................ 40
Micro Computed tomography .............................................................................................. 43
2.10.1
History and development of 3D microtomography ...................................................... 43
2.10.2
SkyScan 1172 Desktop X-ray Micro Tomograph ........................................................... 44
2.10.3
Previous research OIIR investigations using Micro CT technology ............................... 45
2.11
3
Untreated populations .................................................................................................. 19
Disinfection and Storage medium of experimental teeth .................................................... 48
Vibration ....................................................................................................................................... 49
3.1
Whole body vibration ........................................................................................................... 49
3.2
The use of vibration in dentistry and orthodontics .............................................................. 51
3.2.1
Vibration and the rate of orthodontic tooth movement .............................................. 51
3.2.2
Acceledent device ......................................................................................................... 54
3.2.3
Pain and vibration ......................................................................................................... 55
3.2.4
Conclusion ..................................................................................................................... 56
References ............................................................................................................................................ 57
Manuscript ............................................................................................................................................ 71
4
ABSTRACT ...................................................................................................................................... 74
6
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Introduction .......................................................................................................................................... 74
Materials and Methods......................................................................................................................... 74
Results ................................................................................................................................................... 75
Conclusions ........................................................................................................................................... 75
Introduction and literature review ....................................................................................................... 76
Materials and methods ......................................................................................................................... 79
Statistical analysis ................................................................................................................................. 82
Results ................................................................................................................................................... 83
Discussion.............................................................................................................................................. 85
Conclusions .......................................................................................................................................... 88
Acknowledgement ................................................................................................................................ 88
References ............................................................................................................................................ 89
5
Appendix ....................................................................................................................................... 93
Study design .......................................................................................................................................... 93
Figure 1 (a&b) - Appliance Design......................................................................................................... 94
Figure 2 (a&b) - Acceledent device ....................................................................................................... 95
Sky Scan 1172 Desktop X-ray Microtomograph.................................................................................... 96
Specimen Mounting on the SkyScan 1172 Desktop Microtomograph ................................................. 97
Skyscan 1172 x-ray images ................................................................................................................... 98
Nrecon version 1.4.2 Aartsellaar Belgium ............................................................................................ 98
Images from Cone Beam Reconstruction with NRecon (Aartsellaar, Belgium Version 1.4.2) .............. 99
Figure 3: 3D reconstruction images using VG Studio Max (Volume Graphics, GmBh, Heidelberg,
Germany) .............................................................................................................................................. 99
Convex Hull 2D .................................................................................................................................... 100
Table I (a&b) - Paired T tests ............................................................................................................... 101
Figure 4: Graph - Vibration vs. Non-vibration ..................................................................................... 101
Table II (a&b) - Regression Analysis of mean volume difference (improvement) on non-vibration root
resorption volume. ............................................................................................................................. 102
Figure 5: Graph – Improvement vs. Non-vibration ............................................................................. 103
Raw Data – Patient information and total root resorption Volumes ................................................. 104
Future directions ................................................................................................................................. 107
7
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Abbreviations
2D
Two dimensional
3D
Three dimensional
ANOVA
Analysis of Variance
BMP
Bitmap
CT
Computed tomography
EARR
External Apical Root Resorption
g
Grams
H&E
Haematoxylin and Eosin
Hz
Hertz
IL-1
Interleukin-1
IL-1β
Interleukin – 1 beta
ISO
International organisation for standardisation
LM
Light Microscopy
mm
Millimetres
µm
Micrometer
Nd-Fe-B
Neodymium
PEMF
Pulsed Electromagnetic Field
TIFF
Tagged Image File Format
TA
Thermoplastic aligner
RANKL
Receptor activation of nuclear factor kappa β ligand
SEM
Scanning electron microscopy
TEM
Transmission electron microscopy
TRAP
Tartrate resistant acid phosphate
8
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
1 Introduction
Root resorption is the destructive process of the cementum and/or dentine layers of a tooth root
due to clastic cell activity which leads to a subsequent loss root structure of a tooth. This process
may be physiological or pathological. Physiological root resorption of deciduous teeth naturally
occurs when the permanent teeth begin to erupt. It may also occur to a small degree in the
permanent dentition associated with physiological tooth movement.1 Pathological root resorption
has been related to orthodontic tooth movement, trauma, and ectopic eruption of adjacent teeth
and in association with other pathology.
Bates2 was the first to describe root resorption of permanent teeth in 1856. The link between
orthodontics and root resorption was identified in 1914 by Ottolengui. The term “Orthodontically
induced root resorption (OIIRR)” was introduced by Brezniak and Wasserstein to describe the type of
root resorption experienced during orthodontic treatment.3 It is a pathological surface or transient
inflammatory root resorption that occurs due to the presence of an orthodontic force on a tooth. It
is accepted that most individuals will experience some degree of root shortening after orthodontic
treatment. Fortunately the presence of severe root shortening is relatively uncommon after
orthodontic treatment4.
The exact aetiological factors of OIIRR are still unclear. These factors can be either patient biological
related or treatment mechanics related5. Biological factors described in the literature include genetic
factors, dental age, root morphology, bone density and a previous history of root resorption.
Treatment mechanic factors that have been suggested to cause an increase in root resorption are
force magnitude, duration of treatment, the amount of tooth movement, direction of tooth
movement, the type of bone.
9
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Vibration in orthodontics has been applied with the main aim of increasing the rate of orthodontic
tooth movement by accelerating the periodontal and bony tissue modelling and remodelling
processes. This has the benefit of decreasing the duration that a patient has fixed appliances on their
teeth. In the literature, increased treatment duration has been associated with an increased risk of
caries6, periodontal problems7 as well as a higher risk of root resorption8-10.
Vibration has the advantage of minimal side effects in comparison to other methods of accelerating
tooth movement such as local or systemic medicines and has proven to be a safe low impact
alternative that enhances bone remodelling in the medical field.
A new device called Acceledent has been introduced to the market and aims to achieve an increased
rate of tooth movement by enhancing bone remodelling using pulsating forces. Invented by Dr
Jeremy Mao, it is intended to be used by a patient in conjunction with fixed orthodontic appliances
or removable sequential aligner treatment for 20 mins per day. It vibrates at a frequency of 30Hz
and has force amplitude of 20 grams.
Although vibration in conjunction with orthodontics may accelerate bone and periodontal tissue
remodelling, there is very limited research on the effect of this accelerated remodelling on the root
surface of teeth.
The aim of this study is to compare the root resorption that occurs on human upper first premolar
teeth following the application of a buccally directed force (150g) with and without vibration from
Acceledent. The experimental teeth were extracted after four weeks of force application and
examined using Micro-computed tomography. This method has been shown to be more accurate
and reliable at quantitative measurements than previous studies using two dimensional radiographs,
light microscopy and scanning electron microscopy and transmission electron microscopy.11-14
10
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
2 Literature review
2.1 Cementum
The tissues that support a tooth consist of the gingiva, cementum, periodontal ligament and alveolar
bone. Tooth Cementum, first described in 185315, is a mineralised tissue formed by cementoblast
cells on the entire surface of root dentine. It is derived from dental follicular connective tissue that
forms subsequent to Hertwig’s root sheath disintegration.16
Cementum has been classified into five different subtypes based on the presence (cellular) or
absence (acellular) of cells and the source of collagen (extrinsic vs. intrinsic).17 Although cementum
has many similarities with bone, it contains considerably higher fluorine content, is non-innervated
and avascular and generally exhibits little or no remodelling. It contains approximately 45%
mineralised inorganic material (hydroxyapatite crystals), 33% organic material and 22% water.
Cementum increases in thickness from 20-50µm at the cementoenamel junction to approximately
150-200µm towards the root apex18. Cellular cementum also continues to increase in thickness
throughout life.
The major role of cementum is to provide anchorage of the tooth in its alveolus. Acellular cementum
serves to anchor the periodontal ligament fibre bundles to the tooth while cellular cementum has an
adaptive and reparative role. Another function of the cementum is to assist in maintaining occlusal
relationships19. With increasing wear of the occlusal and incisal surfaces of the teeth, compensatory
eruption of the tooth and cementum deposition occurs. The deposition of new cementum is thought
to maintain the width of periodontal ligament space at the root apex. Although cementum is
deposited throughout life, there does not appear to be any predictable correlation between
functional forces and the thickness of cementum.19
11
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Orthodontic tooth movement is possible because of the greater resistance of cementum than bone
to resorption.20 The high rate of turnover of bone results in tissue that is newer and more immature
than the adjacent cementum. Thus the cementum is surrounded by older and more mature collagen
which is more resistant to chemical changes than the bone.21
2.2 Orthodontic tooth movement and OIIR
Orthodontic Tooth movement is made possible by remodelling changes that occur in the dental and
paradental tissues including the dental pulp, periodontal ligament (PDL), alveolar bone and the
gingiva22. Research by Sandstedt, Oppenheim23 and Schwarz24 has lead to the classic pressuretension theory of orthodontic tooth movement. It occurs when forces applied to a tooth creates
areas of compression and tension within the PDL25 which alters the blood flow. A change in the PDL’s
vascularity results in local synthesis and release of key molecules such as inflammatory mediators.
This induces an acute inflammatory response which is necessary for tissue deposition on the tension
side and resorption on the pressure side.
Bone resorption is crucial to orthodontic tooth movement by removing alveolar bone from the path
of the moving tooth root.22
With light forces on a tooth and associated maintenance of vascular patency, clastic cells adjacent to
the lamina dura start to remove bone in the process of direct (or frontal) resorption. Tooth
movement begins soon after.26
Indirect (or undermining) resorption is associated with heavy forces which occlude the blood vessels
and cut off blood supply to areas within the PDL. A sterile necrosis called the hyalinzation zone
develops. When this occurs, remodelling of bone bordering the necrotic area of the PDL must be
performed by osteoclasts which attack the underside of the bone immediately adjacent to the
12
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
necrotic tissues. Undermining resorption is associated with a delay in tooth movement as well as
pain for the patient.26-27
It is desirable to achieve orthodontic tooth movement with as much frontal resorption as possible as
it is more efficient. However, in practice, even light forces have been associated with areas of
hyalinisation and direct and indirect resorption appear concurrently.28
During the resorption of bone process, clastic cells may also attack the outer cementum layers of the
tooth root. If there was no difference between bone and cementum, orthodontic tooth movement
would cause them to resorb equally. Although bone and cementum have many similarities, they
behave very differently. Cementum is more resistant to resorption than bone which results in
preferential bone resorption and orthodontic tooth movement.20,29
If the reparative capacity of cementum is exceeded by root resorption, it will present as the
permanent loss of root structure.30
2.3 Classification of root resorption
Andreasen31 defined three types of external root resorption:
1. Surface resorption – involves small outlining areas followed by spontaneous repair from adjacent
intact parts of the periodontal ligament. This is a self limiting process.
2. Inflammatory resorption – initial root resorption has reached dentinal tubules of an infected
necrotic pulpal tissue.
3. Replacement resorption - bone replaces the resorbed tooth material and then leads to ankylosis
13
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Tronstad32 in 1988 classified root resorption into inflammatory or replacement resorption.
Inflammatory resorption occurs in the presence of denuded cemental areas which are colonised by
multinucleated cells. Inflammatory resorption can be either transient or progressive. Transient
inflammatory resorption is usually undetectable on radiographs and occurs when damaging
stimulation is minimal or for a limited time. Resorption is repaired by cementum like tissue.
If the damaging stimulation is for a longer period of time, progressive inflammatory resorption will
occur. This can be observed radiographically.
Replacement resorption occurs when extensive necrosis of PDL leads to bone formation onto a
denuded area of the root surface (ankylosis). As the tooth becomes part of the bone, remodelling
will eventually lead to destruction of the tooth by the bone.
Root resorption occurring from orthodontic treatment is either a surface resorption or transient
inflammatory resorption. Replacement resorption is not normally seen after orthodontic
treatment.33
Brezniak and Wasserstein3 suggested the term orthodontically induced inflammatory root resorption
(OIIR) to distinguish this type of resorption from others such as those caused by trauma, periapical
lesions of periodontal disease. They then described three degrees of severity:
1. Cemental or surface resorption with remodelling – only the cemental layers are resorbed and then
fully regenerated.
2. Dentinal resorption with repair – cemental and the outer layers of dentine are resorbed and
usually repaired with cementum material. This process may alter the shape of the root from its
original form.
14
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
3. Circumferential apical root resorption – full resorption of all hard tissues of the root apex occurs.
This leads to irreversible root shortening. External surface repair and remodelling of sharp edges
occurs in the cemental layer.
2.4 Orthodontically induced root resorption
Root resorption is commonly seen on dental radiographs as the permanent shortening of the tooth
root.
Normally, the cementum layer of a tooth root does not undergo appreciable resorption. However,
with orthodontic force application on a tooth, sometimes excessive resorption of root cementum
and dentine is induced which will eventually lead to the irreversible shortening of a tooth root’s
length. 22
Root resorption in orthodontics has been referred to by many terms in the literature such as apical
root resorption, external apical root resorption (EARR) or orthodontically induced inflammatory root
resorption (OIIRR). It has long been recognised in the field of dentistry, especially in orthodontics.
Over a century ago in 1856, Bates2 discussed root resorption in permanent teeth as a result of
trauma. Ottolengui34, in 1914 was able to relate root resorption specifically to orthodontic
treatment. However, it was in 1927, when Ketcham35 demonstrated root resorption with
radiographic evidence after orthodontic treatment, that root resorption began to become a great
concern.
At this time, the terms absorption and resorption were used interchangeably to describe the loss of
apical root. This issue was put to rest by an article written by Becks and Marshall36 in 1932.
Becks and Marshall36 preferred the resorption over absorption as tissues constituting a tooth such as
calcium or phosphorous are first absorbed by the blood from the food and then deposited as a
15
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
tooth. Occasionally the calcium and phosphorous in a tooth are “absorbed again” from the root by
the blood. The term “resorb” means, by its derivation, “absorb again”37. They initially defined root
resorption as the destruction of formed tooth structure.
More recently, root resorption has been defined as the active removal of mineralised cementum and
dentine.38
To describe root resorption that specifically occurs in association with orthodontic treatment,
Bresniak and Wasserstein suggested the term orthodontically induced inflammatory root
resorption.3
However, even when no radiographic signs of root resorption can be visible, it is accepted that most
teeth undergoing orthodontic tooth movement will experience some degree of root resorption
followed by repair.39 The clinical significance of root resorption will depend on individual
susceptibility and biological reaction to orthodontic treatment.
2.4.1
Mechanism of root resorption
Root resorption as a result of orthodontic tooth movement is associated with a local over
compression of the periodontal ligament with the development of a sterile necrosis (hyalinised
zone). Historically, Swartz40 hypothesised that the ideal force to move a tooth would be those which
just overcome capillary blood pressure (20-26 grams per square centimetre). If the force placed on a
tooth exceeded the capillary blood pressure, the capillary would collapse, cut off blood circulation
and lead to areas of tissue necrosis and thus root resorption. It is thought that when resorption
processes exceed the reparative capacity of cementum, OIRR will ensure.41
16
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Much of what we know about the cellular processes involved is from mice and rat studies. Brudvik
and Rygh38,42-46 in a series of resorption studies found OIIR is part of the hyaline zone elimination
process and follows a consistent pattern.
OIIR starts in the circumference of the main necrotic hyalinised tissue and continues a few days later
with the removal of the main hyalinised zone. 42
Two different cell populations are involved in the root resorption process.
Cells involved in the initial phase of resorption (1-3 days) are not odontoclasts as they lack tartrate
resistant acid phophatase (TRAP) enzyme. They are macrophage –like cells whose role is to
eliminate the necrotic tissues. 47
During removal of the hyaline zone, the nearby cementoid layer can be damaged, exposing the
underlying cementum. Rygh21 suggested the cementoid layer acts as defence against resorption
describing it as a resorption-resistant “coating”. Reitan48 confirmed this by demonstrating that the
presence of a cementoid or predentine layer on the root delays the resorption process.
The initial phase of cells are followed by multinucleated (odontoclasts) as well as mononucleated
TRAP positive cells which invade into the hyalinised tissue from the periodontal membrane as well as
the adjacent alveolar bone. They attack the cementum and eventually dentine.43 According to Shaza
and Hartsfield30, Kvam49 was the first to describe resorption lacunae penetrating the cementum into
dentin in human premolar teeth.
The root surface under the main hyaline zone resorbs several days later. This resorption process
continues at the same time repair processes in the periphery are taking place. It stops when no
hyaline tissue is remaining and/or the force level decrease.
17
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
2.4.2
Repair processes
Repair of root resorption craters begins when the force applied is discontinued or reduced below a
certain level.21 This has been recorded to begin as early as the first week of retention50. The
reparative process increases with time51-52 and especially during the first 4 weeks of retention.50
However, by the 5th and 6th weeks, repair seems to slow and reach a steady state.53
Brudvik and Rygh described the process of repair beginning from the periphery in the resorbed
lacunae where the PDL has been re-established while active resorption still occurs beneath the main,
more centrally located over compressed hyalinised zone46.
After 10 days of tooth movement multinucleated resorptive cells and collagen producing fibroblastlike cells occupy the same resorption lacuna. The fibroblasts invade the lacunae from the
circumference indicating a transition of resorption to repair.45
Approximately two weeks after force is removed, different phases of repair can be observed with
the placement of new cementum or coverage of root dentine with fibrillar structures.
By three weeks, mineralised cementum fills the resorption lacunae and PDL attachment is restored.
Light Microscopy (LM) studies also demonstrate that repair of resorption lacunae can occur in the
presence of active force at the peripheries of the resorbed areas.44,46
In contrast, to this, Barber and Sims51 found repair to proceed from the centre of the resorption
cavity and moving outwards. Owman-Moll and Kurol54 also found early repair initially began only on
the bottom of the resorption cavities with occasional reparative cementum extending onto the
lateral walls. No reparative cementum was found on the lateral walls alone. The repair process of
root resorption was achieved mainly by deposition of cellular cementum with acellular cementum
only at the initial phase of healing.
18
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Both repair patterns from the periphery and the centre were observed by Sismanidou and Lindskog55
in adolescents. They also found that onset of reparative cementum appeared after 2 weeks of force
discontinuation and initially only involved acellular cementum formation. Gradually this changed to
cellular cementum at the more advance stages of healing.
2.5 Incidence and prevalence of root resorption
2.5.1
Untreated populations
Root resorption is a necessary natural process for deciduous teeth during the eruption of their
permanent successors. Permanent teeth also undergo a certain amount of apical root resorption.
This may be a normal physiological process similar to continuous bone remodelling.1
Root resorption of teeth has been reported in both orthodontically treated subjects as well as in
untreated populations56, however, orthodontically treated patients are more likely to have severe
shortening of the root.57
Henry and Weinman58 used a histological study of 261 non orthodontically treated teeth and found
90.5% displayed evidence of root resorption. Root resorption seemed to affect the apical region the
most followed by the mesial, buccal, distal and lingual surfaces. They also reported that resorption
increased with increasing age.
19
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
2.6 Orthodontically treated populations
The incidence of orthodontically induced root resorption varies widely in the literature. This can be
explained by the various study methodologies, which historically, has looked at root resorption
either by histological sectioning or radiographic images.
Diagnosis can be by panoramic or periapical radiographs. Clinical diagnostic radiographic studies
generally report a lower incidence than histological studies.
Ketcham35 was the first to show radiographic evidence of root resorption after orthodontic
treatment. While 1% of the untreated population had some root resorption, he found 21% of five
hundred patients had evidence of root resorption. In contrast, Rudolph in 1940 found treated teeth
displaying root resorption had an incidence of 75% and 100% compared to a non treated sample
which had an incidence of 5%59-60
Massler and Malone also reported relatively high numbers with 86.7% of non treated patients and
more than 90% of treated patients presenting with signs of root resorption.61
Levander and Malmgren studied the root resorption pattern of 610 upper incisors after treatment
with either an edgewise or Begg technique. They found only 1% of teeth had severe root resorption
and that this was related to minor resorption after the initial 6-9 months of treatment.
Sameshima and Sinclair in 2001 using full mouth periapical films reported that greater than 2 mm of
OIIR was seen in 25% of the 868 treated patients. Killany reported a similar frequency of 30% with
OIIR greater than 3mm. Only 5% of treated patients were found to have >5 mm of root resorption57.
With panoramic or periapical radiographs, apical root resorption is usually less than 2.5 mm and
varies from 6% to 13% for different teeth4.
20
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Histology of orthodontically moved teeth in animal and human studies tends to report a greater
incidence of OIIR ranging from 0 to 100%4.
An early histological report by Henry and Weinmann58 found 90.5% of untreated teeth showed areas
of resorption, most of which occurred at the root apex. They concluded that it is normal for a tooth
to incur some degree of resorption during its life.
In most cases, the amount of OIRR experienced is considered minimal and not clinically significant. If
this is the case, it can be classified as minor or moderate. This is approximately 2mm from the apex
of the maxillary central incisor, with loss on the lateral incisor being somewhat greater. Severe
resorption is defined as loss of root structure exceeding 4mm, or a third of the original root length.62
Fortunately this is only seen in 1%-5% of teeth4.
21
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
2.7 Aetiology and risk factors associated with OIIR
Although many risk factors have been found, our predictive power in assessing the possibility of
future resorption is still poor. Individual variation in biologic response to orthodontic forces and
genetic predisposition may explain the variation in OIIR that occurs. Brezniak and Wasserstein in
their review of the literature divided risk factors into biological and mechanical factors.
2.7.1
Biologic factors
2.7.1.1 Genetic factors
OIIR tends to have a strong genetic component. Although no definite genetic conclusion has been
found, autosomal dominant, autosomal recessive and polygenic modes of inheritance are
possible.5,62
Harris et al63 used a sib-pair model to examine the genetic influence of EARR. They reported that
genetic predisposition to EARR had high heritability (h² = 70%).
Recently, polymorphism of the pro-inflammatory cytokine Interleukin-1 (IL-1) gene cluster has been
associated with the severity of adult periodontitis and increased tissue resorption64. IL-1β has been
implicated in bone resorption during orthodontic tooth movement. Humans and animals undergoing
orthodontic tooth movement have been reported to have increased levels of IL-1β in their gingival
tissues and gingival crevicular fluid65-68. The speed of tooth movement is also related to IL-1 gene
cluster polymorphisms.69-70
22
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Al-Qawasmi et al71-72 investigated the clinical screening of orthodontic patients for IL-1β genotype by
analysing DNA from a cheek swab. Their analysis indicated that IL-1β polymorphism accounted for
15% of the total variation of maxillary incisor OIIR and patients homozygous for the IL-1β allele 1 had
a 5.6 times increased risk of OIIR greater than 2mm compared to those that did not. These findings
suggest that genetics are just one factor that contributes to the complex aetiology of OIIR.
OIRR of the maxillary central incisors have the highest heritability component and are usually the
most severely affected.63,73
The possibility of genetic testing and screening for patient susceptibility to OIIRR may become a
reality in the future. However, presently, if a child has had previous orthodontic treatment, viewing
of their post treatment radiographs may prove invaluable to the treatment of subsequent siblings.74
2.7.1.2 Race
Sameshima et al in their sample of 868 patients reported that Asian patients were found to
experience significantly less root resorption than white or Hispanic patients. In contrast, Smale et
al75 recruited patients from 3 different centres in 3 countries and found no differences in resorption
among the subsamples. They reported that this justified their decision to combine all patients into
one group for analysis.
2.7.1.3 Systemic factors
It has been proposed that systemic factors such as the inflammatory mediators produced outside of
the PDL may act to enhance cellular interactions involved in root resorption76.
23
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Davidovitch et al applied an orthodontic force on the maxillary molars of guinea pigs. These guinea
pigs were induced with allergic asthma. It was noted that the numbers of alveolar bone osteoclasts
increased in the compressed PDL areas over control guinea pigs which suggested that cell
populations involved in resorption were influenced by inflammatory mediators produced by
asthma.76
Patients with treated as well as untreated chronic asthma have been reported to have an increased
incidence of OIIRR compared with healthy individuals.
McNab et al77 used panoramic films to measure the root resorption on posterior teeth of asthmatics
and healthy patients after fixed appliance treatment. Asthmatics had significantly more external
apical root resorption of posterior teeth compared with the healthy group (P = .0194). Although
increased incidence of OIIRR was reported, both asthmatics and healthy patients had similar
amounts of moderate and severe resorption.
Using the hypothesis that inflammatory mediators enhance root resorption, it was theorised that
OIIRR of the upper first molars in asthmatics may be the result from local sinus inflammation.
It was concluded that although the incidence of OIIRR may be increased in asthmatics, it only tends
to be in the form of increase in root blunting. Therefore asthmatics are only at a minimal risk of
posterior OIIRR that may not adversely affect the function or longevity of these teeth.
Similar findings were reported in a group of 60 Japanese orthodontic patients. Pre-treatment
records revealed that the incidence of allergy and root morphology abnormality was significantly
higher in the root resorption group. Also the incidence of asthma tended to be higher in the root
resorption group. The authors concluded that allergy, asthma and abnormal root morphology may
be high risk factors for excessive OIIRR in Japanese patients.78
24
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
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Owman-moll and Kurol in 2000 analysed factors that might be associated with OIIRR by examining
extracted maxillary premolars of 96 adolescents after buccal movement. A preliminary screening of
possible risk factors such as root morphology, allergy, nail biting, medication etc was performed.
Interestingly, only those subjects with allergies showed an increase risk of root resorption, however,
this result was not statistically significant.
2.7.1.4 Nutrition
Nutrition was suspected to be linked to root resorption in the past. Calcium and vitamin D deficiency
in animals have been reported to have root resorption79.
Brezniak and Wasserstein5, in their review of the literature reported that nutritional imbalance is
not likely to be a major factor in root resorption.
2.7.1.5 Dental age
Orthodontic treatment does not stop root development. The stage of root formation at the onset of
treatment has been discussed in terms of lessening the severity of OIIR. There are some studies
which suggest that incompletely formed roots exhibit less root resorption than in patients treated
when root formation is complete. 80 Although they may have less OIIRR, early orthodontic tooth
movement may also prevent the roots from reaching their “normal” length.81 Although this has been
reported, these teeth reach a significantly greater length than those that were fully developed at the
start of treatment82.
25
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Rosenberg reported that orthodontic treatment increased the dilacerations incidence of roots from
25% to 33% after treatment. This was found to be higher in canines than premolars.83
Brezniak and Wasserstein5 reported in their review of the literature that orthodontic treatment
should begin as early as possible since there is less root resorption in developing roots and young
patients show better muscular adaptation to occlusal changes
2.7.1.6 Chronological age
With increasing age, the periodontal membrane becomes less vascular, aplastic, and narrow, the
bone more dense, avascular, and aplastic, and the cementum wider. Reitan25 suggested that these
age changes may explain why adults have a higher susceptibility to root resorption.
However, most studies have found that chronological age and OIIR to be poorly correlated and that
chronological age may not be a significant factor in the occurrence of OIIRR74.
Sameshima and Sinclair8 reported that root resorption of the mandibular incisor and canine regions
is more in adults than in children; however age was not found to be a statistically significant factor in
the maxillary anterior region.
2.7.1.7 Gender
There are conflicting reports in the literature regarding gender susceptibility to OIIRR.
Some reports suggest there to be no difference in the incidence of OIIR and gender.8-9,63,84-85
26
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Others claim that girls are more susceptible than boys.62,86 Newman62 found females to be more
prone to root resorption than males with the sex ratio of their sample to be 3.7 females to 1 male.
However, this ratio may partially be explained by the fact that orthodontists probably saw a higher
frequency of female patients that were included in the study.
In comparison, studies by Baumrind et al 87, Remington et al88 and spurrier et al89 have reported a
higher incidence and severity of OIIRR in males when compared to females.
2.7.2
Habits
Nail biting and tongue thrust habits have been implicated in causing more severe root
resorption.62,90
Harris and Butler looked at adolescents with open bites and found the roots of permanent maxillary
incisors were significantly shorter than matched deep bite subjects. They explained that tongue
thrusting in association with an anterior open bite produced intrusion and torquing forces on the
incisors. This might explain why roots of the upper anterior teeth were already compromised before
mechanotherapy.91
2.7.2.1 Root morphology
Most studies have found teeth with abnormally shaped roots have a greater risk of OIIR than teeth
with normally shaped roots. Sameshima and Sinclair in a study of 868 cases found the worst
resorption to be on the maxillary lateral incisors and in teeth with pipette, pointed or dilacerated
roots.8
27
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Long roots, narrow roots and deviated root shape have been identified as significant risk factors84
Kjaer found strong associations between root morphology such as invagination, length of root,
taurodontism, and root shapes and increased root resorption.86
Brin et al92 in their study found teeth with unusual morphological roots before treatment were only
slightly more likely to have moderate to severe OIIR when compared to teeth with normal roots.
However, they said that this could not be a significant predictor of OIIR.
2.7.2.2 Previous trauma and endodontically treated teeth
Dental trauma and orthodontic treatment after dental trauma is generally considered a predisposing
factor for OIIR85 9. Linge and Linge80 investigated the incidence and extent of apical root resorption in
maxillary incisors in 719 consecutively treated patients. Of this sample, 110 patients reported
trauma to the incisors prior to treatment. The trauma group had more root resorption in terms of
average root length reduction as well as for the most severely affected incisor when compared to
the rest of the sample. This difference was found to be highly significant (p<0.001). The authors
recommended screening patients prior to treatment with records of previous incisor trauma.
In contrast, other studies such as Brin et al92, Kjaer86 and Mandall et al93 found no difference in the
incidence of OIIR when comparing teeth that had previous trauma and those that had not. Levander
et al94 also found no statistical significant correlation between trauma history and OIIRR.
The correlation between endodontic treatment and OIIRR is not yet conclusive. This may be due to
some bias in the study design which has included teeth that have a history of trauma. Steadman’s37
review in 1942 suggested that roots of the root canal tooth may act as a foreign body and “melt
28
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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away as the years pass”95. Wickwire et al95 reported that orthodontic movement of endodontically
treated teeth exhibited a greater frequency of root resorption than their vital controls.
Other authors have reported no significant differences in the amounts of root resorption
experienced in vital and endodontically treated teeth. 96-97
Spurrier et al89 compared the severity of apical root resorption in endodontically treated incisors and
the contralateral vital tooth as a control. Forty three patients were examined. Surprisingly vital
incisors resorbed to a significantly greater degree than endodontically treated incisors with a mean
difference of 0.77mm. They reported that although it was significant, this difference would be
virtually undetectable at the clinical level.
Mirabella et al’s results agreed that endodontically treated teeth resorb significantly less than their
contralateral controls.89,98
2.7.2.3 Type of malocclusion
Many believe that the presence of an overjet is a strong predictor for OIIRR due to large distances
the anterior teeth have to move for overjet correction.
Increased overjet but not overbite has been significantly associated with greater root resorption.8
The type of malocclusion was found to have a negative correlation by VonderAhe99.
29
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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2.7.2.4 Bone density
Historically, the use of areas of increased bone density such as the labial or palatal cortical plate
were thought to be good for increasing anchorage during treatment mechanics.
Ten Hoeve and Mulie100 were the first to report an association between root contact with the bony
cortical plate and OIIRR. Horiuchi et al101 found root approximation to palatal cortical plate during
retraction of incisors to be factors influencing the amount of root resorption. Narrowing of alveolar
bone width was also influenced apical root resorption.
In contrast, the amount of alveolar bone around the root of a tooth, the thickness of cortical bone
and density of trabecular network have not been found to have significant correlation with the
extent of OIIRR.102 Mirabella and Artun84 reported a few cases in their sample to have root contact
with the palatal cortical plate without significant root resorption. They suggested that resorption
may be more dependent on the amount of tooth movement than pressure on the cortical plate.
2.7.2.5 Specific tooth vulnerability to root resorption
OIIRR can present as localised to particular teeth or as a generalised shortening of all the teeth.
Regardless of genetic or mechanical related factors, it is generally agreed that maxillary incisors
seem to be affected by OIIR more frequently and to a greater extent than the rest of the
dentition62,88. A possible reason is that the maxillary incisor is most often moved the greatest
distance through bone and subjected to longer active force duration than any other tooth.10
Maxillary central incisors are usually quoted as more affected than the maxillary lateral incisors.
However, some studies have reported the lateral maxillary incisor as the most affected tooth5,103.
30
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Sameshima et al suggest that this was due to the lateral incisors having a higher incidence of
abnormal root shape.103
Other teeth vulnerable to OIIRR are the mandibular incisors, distal root of the mandibular first
molars, mandibular second premolars, and maxillary second premolars.5
Peg shaped laterals have not been associated with an increased risk of OIIRR. 84
Root resorption has been reported to range from 0% to 90.5% of examined teeth or 0% to 100% of
examined patients in the untreated population5,35,39,58-59,61,104-108. The presence of root resorption on
teeth prior to orthodontic tooth movement significantly increases the risk of further resorption
during orthodontic treatment.80,91
2.7.3
Mechanical factors
Mechanical risk factors associated with OIIRR are those related to the type of orthodontic treatment
mechanics used to move teeth. Many treatment related risk factors have been studied such as force
characteristics, type and direction of tooth movements, treatment duration and orthodontic
appliance factors. As these factors are under the clinician’s control, knowledge in this area may allow
for minimisation of OIIRR.
2.7.3.1 Force characteristics
Mechanical risk factors which may possibly be preventable such as the magnitude of force used or
the duration of force have been investigated.
31
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Continuous, interrupted continuous and discontinuous forces have been compared. It has been
hypothesised that periods of rest may allow for secondary cementum to repair resorption cavities.27
Harry and Sims39 suggested that duration of force was more crucial than magnitude in regards to
root resorption.
Dermaut and demunck108, however, said there was no significant relationship between duration of
force and root resorption.
Owman-moll109 compared the effect of continuous 24 hours/day vs. interrupted continuous
(interrupted one week every four weeks) forces in adolescents. Histological sections of the
experimental teeth showed no difference in amount or severity of root resorption between the two
forces.
In contrast, Maltha and Dijkman in an animal study found discontinuous forces (16 hours per day)
caused less extensive root resorption when comparing the amount of root resorption after (24hours
per day) forces.
Acar et al110 compared the effect of 100g tipping force on 22 experimental premolars using elastics
continuously for 24 hours vs. 12hours on the discontinuous side. After 9 weeks, the mean
percentage of resorption affected areas was smaller and apical blunting was less severe on the
discontinuous side.
It is generally thought that increasing force magnitude would be associated with an increase in root
resorption as it would lead to more areas of hyalinisation. It is also believed that higher forces cause
more extensive root resorption because the rate of lacuna development is more rapid and the tissue
repair process is compromised.4,10
Dellinger111 and reitan27 reported increased root resorption with increasing force magnitude.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Owman moll et al112 in their histological study did not agree. They found root resorption was not
force sensitive as forces of 50g and 100g applied to maxillary first premolars produced no significant
difference in the severity of root resorption. The same group of researchers also compared 50g with
a four fold larger force of 200g113. No significant differences in the frequency or severity of root
resorption were found between the two forces used.
2.7.3.2 Type of orthodontic movement
All types of orthodontic tooth movement induced some form of root resorption. Tipping, torque and
bodily movement of teeth have been implicated as mechanical risk factors80,99,114. Intrusion of teeth
seems to be the most detrimental movement in terms of root resorption104,108,115 as this movement
concentrates pressure at the tooth apex. Expansion with RME has also been identified to cause root
resorption51.
2.7.3.3 Correction of impacted maxillary canines
Impacted maxillary canine treatment has been identified as a risk factor for apical root resorption of
incisor teeth. This is not just confined to the root of the adjacent lateral incisor and can not be fully
explained by the ectopic eruption path of the canine. Linge et al9 theorised that the extrusive of the
canine would cause a reciprocal intrusive force on the incisors. Intrusion of maxillary incisor teeth
have been associated with considerably more apical root resorption in orthodontic patients.108
33
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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2.7.3.4 Arch wire sequence
Mandall et al93 in a randomised controlled trial aimed of one hundred and fifty four patients
compared the differences between three orthodontic archwire sequences in terms of patient
discomfort, root resorption and time to working archwire. They found no statistically significant
difference between archwire sequences for patient discomfort or upper incisor root resorption.
Begg vs. Straight wire vs. standard edgewise
No statistical difference in tooth length could be found after Begg, Tweed or straight wire
techniques.114
2.7.3.5 Two phase class II treatment
Brin et al92 tested the hypothesis that the maxillary incisors of class II children treated in a single
phase with fixed appliances were more likely to experience moderate to severe OIIRR. It was
thought that single phase treatment would involve a longer time in fixed appliances as well as
greater root movement. A retrospective sample of 138 children compared single phase fixed
appliances with two phases with headgear or bionotar followed by fixed appliances. When
examining the amount of root resorption of central and lateral incisors, significant associations were
made among OIIRR and the magnitude of overjet reduction and the time spent wearing fixed
appliances. They concluded that early growth modification to reduce the severity of an overjet might
play a role in decreasing the incidence of OIIIRR in class II malocclusion patients.
The use of herbst function appliance for treatment of class II malocclusion may deliver unphysiologic
forces to the immediate anchor teeth thereby exposing them to a high risk of root resorption.116
34
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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2.7.3.6 Self ligation
With the introduction of self ligating brackets, many claims have been made about the increased
efficiency of tooth alignment compared to conventional brackets. This is most likely due to lower
friction levels reported with the use of self ligating brackets. Scott et al117 examined the clinical
effectiveness of self ligating versus conventional preadjusted edgewise orthodontic bracket systems
as well as the effect on mandibular incisors. Their randomised controlled trial reported no significant
difference in the initial rate of tooth alignment. Incisor root resorption was not clinically significant
and did not differ between to different bracket types.
These results were also reported by Pandis et al118, who found no difference in the amount of OIIRR
between conventional and passive self ligating brackets.
The use of elastics such as in the case of class II correction may be a risk factor for the teeth that
support the elastics.9,84 Mirabella et al84 suggested that it was probably due to the jiggling
movements that occur on these anchor teeth.
2.7.3.7 Extraction treatment
The literature is inconclusive regarding the effect of extraction treatment on OIIRR. No difference
between extraction and non extraction has been reported by VonderAhe99 from 57 patients.
Some studies have reported that a positive correlation between OIIRR and extraction treatment may
exist. Sameshima and Sinclair103 observed that patients who had undergone all first premolar
extraction experienced more root resorption than patients who had non extraction or only maxillary
first premolar extractions.
35
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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McNab et al119 reported a higher incidence of OIIRR when treatment was performed with Begg
appliances compared to edgewise appliances. When extractions were performed, the incidence of
OIIRR was 3.72 times higher.
Patients who have extraction treatment with the correction of open bite may be more prone to
OIIRR. This may be due to the amount of overjet correction and retraction of central incisor
apices.120
Extraction space closure using 2-step sliding mechanics (canine retraction first then incisor
retraction) and en mass space closure has been investigated in 52 patients by Huang et al. It was
postulated that since two step space closure takes longer to close an extraction space than an en
masse procedure, it may be associated with more frequent and serious OIIRR. Their study, however
found no significant difference in root resorption between two step and en masse space closure
procedures.
Early Serial extraction followed by mechanotherapy has previously been hypothesised to cause less
OIIRR due to the procedure needing less mechanotherapy since crowding of incisors would be
relieved. A qualitative study comparing serial extraction vs. late extraction found the serial
extraction patients to have less OIIRR, however, it was not clinically significant121. Brin and Bollen122
also compared serial extraction vs. late extraction cases with similar amounts of tooth movement.
They concluded that the spontaneous unravelling of incisor crowding with serial extraction
treatment did not prevent OIIRR and that the differences in tooth length reduction between the two
groups were not significant.
36
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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2.7.3.8 Removable vs. fixed appliances
There is still debate in the literature regarding which treatment appliance, fixed or removable, is
associated with more OIIRR.
Linge and Linge reported less root resorption in their removable appliance group than the group
treated with fixed appliances. However, they stated that the risk of root resorption must be weighed
against appliance efficiency and individual treatment objectives.
This use of thermoplastic aligners has increased in popularity as an alternative to treatment with
fixed appliances. In terms of root resorption, Barbagallo et al123 compared sequential removable
thermoplastic aligners with both light and heavy forces from conventional fixed appliances. Root
resorption volumes were measured from data produced by micro ct scans. It was found that
thermoplastic aligners produced similar effects on root cementum as light (25g) forces from fixed
appliances.
2.7.3.9 Treatment duration
Most studies have found a positive correlation between increased treatment duration and the
amount of root resorption experienced by a patient8-10,103.
Liou et al, in a study of 50 adult patients, investigated apical root resorption of maxillary incisors in
cases with en-masse maxillary anterior retraction and intrusion with miniscrews. They reported that
apical root resorption of the maxillary central incisors was significantly correlated to the duration of
treatment and not to the amount of en-masse retraction, intrusion or palatal tipping of the maxillary
incisor teeth. They concluded that since more enmasse anterior retraction was needed with
miniscrew anchorage cases, treatment time increased which might increase the risk of OIIRR.124
37
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Although this factor is most often correlated with apical root loss, publications by Baumrind and
Koran87 and Mirabella and Artun84 have reported no significant association between treatment
duration and OIIRR.
Artun et al125 also reported that treatment duration and time with square arch wires was not related
to the amount of resorption. The best predictor of severe apical root resorption in their sample
seemed to be the amount of resorption experienced by the patient in the initial treatment stages.
Orthodontic patients who experienced detectable root resorption in the first six months of active
treatment seem to be more prone in the following six months than those without.126
2.8 Management of OIIR
Patients must be informed of the risk of root resorption prior to starting orthodontic treatment as
part of informed consent. In most cases, clinically significant shortening of a tooth root is rare.
However, each patient must be made aware that, at present, we can not predict which individuals
will be susceptible to severe root resorption. Significant loss of tooth root structure can lead to an
unfavourable crown to root ratio. Many clinicians fear that the potential consequence is an adverse
effect on the long term prognosis of the affected tooth. Current literature, however, suggests that
even extensive root resorption does not usually affect the functional capacity or greatly compromise
the longevity of the teeth.4 The reason for this may be in the initial stages of root resorption and
crestal bone loss, 3mm of root resorption is approximately equivalent to 1mm of crestal bone loss.
Following more than 2mm of loss, the ratio is closer to 2mm of root resorption equalling 1mm of
crestal bone loss.127
38
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Various authors have suggested methods to minimise OIIRR. These include the use of light
intermittent forces21,39,48, reduction of treatment duration104,128, habit control62,90 and prior
assessment of family and medical history8,62,115. Minimising the use of intermaxillary elastics9 and
high risk tooth movements such as intrusion and root torquing have also been recommended114.
Full radiographic records should be taken prior to commencement of treatment to aid in diagnosis
and assess the preoperative root structures. Progress radiographs taken six to twelve months after
the commencement of orthodontic treatment to detect early signs of OIIR4. Levander and Malmgren
found that root resorption of the upper incisors during the initial six to nine months of treatment
with fixed appliances gives a high risk for continued resorption during the subsequent treatment.128
If severe loss of root structure is detected, treatment objectives for the patient should be reassessed
and a decision made on whether treatment should be stopped early or to reach an occlusal
compromise. Active treatment should cease for 2 to 3 months with passive arch wires to decrease
further root resorption and allow for reparative processes to occur.94 Alternative treatment options
should be sought to decrease the time in fixed appliances such as prosthetic replacements to close
space, and stripping teeth instead of extracting.
After active orthodontic treatment has been completed, further shortening of root structure will
normally cease99. This is to be expected as OIIR is a tissue-pressure response.
Remington et al88 found teeth that resorbed during orthodontic therapy frequently had rough,
jagged, and often notched root contours. After a mean 14.1yrs long-term evaluation, no apparent
increase in root resorption was detected, however, remodelling of rough, sharp resorption areas
was evident.
39
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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2.9 Research methodologies
2.9.1
Methods for measuring OIRR
The methods used to study root resorption include radiography, serial sectioning and light
microscopy48 and scanning or transmission electron microscopy129-130. More recently micro
computered tomography 131-134 has been used for their ability to quantify variables in three
dimensions. The current ‘gold’ standard in the measurement of root resorption volumes is with
micro computed tomography.12-14
Early studies on root resorption craters have used two dimensional methods such as radiographs,
light or scanning electron microscopy to detect root resorption before, during and after orthodontic
treatment. However, these methods have proven to be inaccurate in quantifying resorption craters
due to problems of magnification, angulations and positioning errors and also reproducibility to
allow comparison.
2.9.1.1 Radiography
Reports in the study of root resorption using radiographs have been performed with periapical or
panoramic radiographs or lateral cephalograms. These reports are limited to assessing root
resorption by apical root shortening. Surface resorption is usually very difficult to exam on
radiographs as it must be sufficiently advanced or severe and at the correct angulations. Clinically,
radiographs allow a clinician to detect the presence of root shortening before, during or after
orthodontic treatment. The quantitative value of radiographs remains questionable.11
40
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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Periapical films have been found to be superior to panoramic images for fine detail and less
distortion. Magnification of periapical films tends to be less than 5%135. Ideally positioning of the
periapical radiograph should be performed using the paralleling technique to ensure geometrically
accurate images136. The bisecting angle technique tends to be unsuitable for root resorption
assessment as it is difficult to reproduce views over time. Remington et al reported that root lengths
can not be recorded from non standardised bisecting angle technique radiographs88.
Panoramic radiographs tend to be used as screening tools of the dentition. A possible limitation of
the use of panoramic radiographs is that root shapes such as dilacerations and other abnormal
shapes are much harder to assess on panoramic films when compared to periapical views.
Sameshima and Asgarifar137 in comparing periapical films to panoramic films found panoramic films
to overestimate the amount of root loss by 20%. Mandibular incisors are most likely to be vulnerable
to this distortion. It was concluded that in cases where the apices are obscured, periapical films
should be ordered.
Since root resorption craters are three dimensional in nature, Chan et al11 looked at using 3D scans
to evaluate and quantify the volume of these craters.
In a comparison between periapical radiographs and micro ct images, Dudic et al138 concluded that
apical root resorption may be underestimated when using digitised periapical radiographs.
2.9.1.2 Serial sectioning and light microscopy
This method has been used to study root resorption and repair. It involves embedding and serial
sectioning an extracted tooth parallel to the long axis and histological staining such as with
haematoxylin and eosin. Using a light microscope, quantification of resorption craters is made using
41
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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a micrometer fitted into the eyepiece109. The major limitation of this method is that root resorption
craters may be completely missed due to the sectioning process11. Craters that are found could be
miscalculated.
2.9.1.3 Scanning electron microscopy (SEM)
Reitan48 suggested that scanning electron microscopy provides enhanced visual and perspective
assessment of root surfaces. When recorded in stereo pairs, they provide resolution and detail not
attainable with histological models reconstructed from serial sections.
Kvam129,139 was the first to use SEM when documenting root resorption craters following tooth
movement. Later studies by using SEM to measure root resorption used surface area landmarks
obtained from micrographs39,51,110. The problem with this method is that the root surfaces of the
experimental teeth are curved and an absolute straight on view is difficult to obtain. Parallax errors
in 3D can occur which would induce measurement errors. Also, the composite micrographs obtained
are usually physically pieced together before resorption craters are measured with a digitiser. If
craters occur along the edges of the micrographs, quantitative measurements would be inaccurate11.
2.9.1.4 SEM stereo imaging and 3D measurements
To overcome this problem, Chan et al12 used the SEM as a capturing device and analysed stereo
images of resorption. The pair of stereo images was converted into an 8 bit greyscale depth map.
Volumetric measurements were calculated using specially written software. The planar area of the
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crater was multiplied by the average depth of the nominated crater to give the volume. This method
was calibrated against a Vickers hardness tester indenting on four cylindrical metallic rods140. The
results showed volumetric measurements by the software were both highly accurate and
reproducible.
This method was later used to quantify root resorption in a sample of 36 teeth141.
2.10 Micro Computed tomography
X-ray microtomography is a non destructive imaging method particularly useful in the biomedical
field for assessing hard tissues. It is derived from computerised axial tomography and has a high
spatial resolution in the order of micrometers. The first x-ray microtomography apparatus was
introduced ten years after the CT scanner in 1982 by Elliot and Dover142. It has the ability to
accurately measure and map on a microscopic scale and quantify structures in three dimensions.
Current technology limits the use of microcomputer tomography to mainly small inanimate
specimens such as bone or teeth143.
2.10.1 History and development of 3D microtomography
Wilhelm Conrad Roentgen was to first to discover the new form of radiation which he called xradiation due to its unknown nature. He first presented his findings in 1895 to the Wursburg Physical
Medical society in 1895. Although x-rays allowed non-invasive visualisation of the inside of the body,
interpretation of the x-ray image was not simple. This was due to the loss of depth information as
the features of a 3D object become superimposed as it is mapped onto a 2D image.
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Computed axial tomography, introduced by Hounsfield144 in 1973 was a major advancement in the
medical field as it made it possible for imaging of internal features to be based directly on their x-ray
attenuation coeffiecients143. Tomography involves taking a series of x-ray projections through the
slice at various angles around an axis perpendicular to the slice. A 3D map of object can be obtained
by computing the number of slices together.
The development of microtomography was aimed at scaling down the conventional medical scanner
and allowing for the study of small specimens at high resolution. Current x-ray micro tomography
scanners can produce an image resolution typically at 5 to 10 µm but also as far down as 1 µm.
Besides the scale of the machine, the only other difference between medial CT scanners and
microcomputer tomography is that the specimen moves whilst the x-ray source and detector are
stationary for micro ct systems instead of the x-ray source moving around the subject in medical CT
scanners. The cone beam algorithm introduced by Feldkamp in 1984 allowed for an easier
tomographic reconstruction from 2D projection data. Its performance was shown to be faster and
generally comparable to the standard fan beam algorithm145.
2.10.2 SkyScan 1172 Desktop X-ray Micro Tomograph
This study makes use of the SkyScan 1172 micro tomograph (SkyScan, Aartselaar, Belgium) to
examine the premolar samples. Previous root resorption studies performed at the Sydney University
Orthodontic Department have used this machine in their analysis.
The SkyScan 1172 is a fourth generation compact desktop machine used for microscopy and micro
tomography applications.
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It consists of an X-ray shadow microscope system and tomographic reconstruction software. The
cone beam X-ray source has a spatial resolution of 2 to 5 µm. the recommended image field is 68mm
wide and 70mm high. Samples are placed in the system on a rotating platform which can revolve up
to 360 degrees. Magnification is determined by the distance of the platform from the X-ray source.
The X-ray detector consists of a high resolution 1024 x 1024 pixel charged couple device which can
output generated 16 bit Tagged Image File Format (TIFF) picture files.
After image acquisition is completed, software based on Feldkamp cone beam algorithms145
reconstructs the axial slice by slice images. The resultant axial 2D images are generated as 8-bit
greyscale 1024x1024 pixel bitmap (BMP) images.
Software program VG Studio Max (version 1.2 Volume Graphics, GmbH, Heidelberg, Germany) is
used to collate the axial 2D slices to form 3D reconstructed images.
2.10.3 Previous research OIIR investigations using Micro CT technology
There are numerous studies in the literature using Micro CT technology to analyse OIIR, many of
which have been performed at the Sydney University Orthodontic department.
Harris et al14, in a prospective randomised clinical trial used a split mouth design to intrude upper
first premolar teeth with no force (control), light force (25g) and heavy force (225g) for twenty eight
days prior to extraction. They used the SkyScan – 1072 microcomputed tomograph x-ray system and
specially designed software for direct volumetric measurements of OIIR craters. The volume of
resorption crater was found to be directly proportional to the magnitude of the intrusive force
applied with the light force and heavy force groups experiencing 2 and 4 times greater OIIR craters
than the controls respectively.
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Foo et al13 hypothesised that since fluoride has been reported to be beneficial in preventing root
resorption in dental traumatology, it may perform in a similar fashion in OIIR. Orthodontic force was
used and fluoridated water was given to control and experimental wistar rats. After two weeks, the
animal s were sacrificed and the teeth scanned with the SkyScan 1072. Software analysis of the
scans provided volumetric measurement of the OIIR craters.
Systemic fluoride was found to reduce the size of resorption craters however, this was variable and
statistically insignificant (P>.05).
Barbagello et al123 used Micro CT to quantify the effect of clear sequential removable thermoplastic
appliances (TAs) on OIIR craters. They also compared forces applied by clear sequential removable
plastic aligners and fixed orthodontic appliances. 27 patients with 54 maxillary 1st premolar teeth
were used as the sample. These subjects were randomly assigned to 3 groups consisting of 9
patients each. A split mouth design was used for each group. Group 1 used clear plastic aligners to
move teeth on one side in a buccal direction at a rate of 0.5mm every 2 weeks while the
contralateral side had no tooth movement and acted as the control group. Group 2 used clear plastic
aligners for tooth movement on one side and beta-titanium alloy cantilever spring used to produce a
heavy (225g) buccally directed force on the contralateral side. Group 3 was similar to group 2 except
a light buccally directed force (25g) was used from the cantilever spring. The results found teeth
undergoing orthodontic tooth movement had significantly greater root resorption than the control
group teeth. Heavy forces (225g) produced significantly more root resorption than light forces (25g)
or TA force. Light force fixed appliances and TA force produced similar effects on root cementum.
Continuing from these initiation studies, a series of split mouth studies using similar methodology
and micro ct volumetric analyses looked at continuous vs. intermittent controlled orthodontic forces
on OIIR146, repair of resorption craters 4 and 8 weeks after 4 weeks of continuous light and heavy
forces147, the incidence of physiological root resorption on unerupted third molars148, the amount of
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root resorption after 12 weeks of light or heavy forces and OIRR after 2.5 and 15 degrees of buccal
root torque for 4 weeks.146
These studies reported increase in OIIR with increasing force (more in heavy 225g vs. light 25g) and
increase in force duration over 4,8 and 12 weeks. Maxillary first premolars were more likely to suffer
from OIIR than mandibular first premolars134.
No significant difference in the amounts of repair of resorption craters was found at 4 or 8 weeks
after 4 weeks of continuous force. Repair seemed to be steady after 4 weeks of passive retention
following 4 weeks of light force application, whereas most repair occurred after 4 weeks of passive
retention following 4 weeks of heavy force application.147
Intermittent forces (4 days of force with 3 days rest) produced less root resorption on maxillary first
premolars than continuous force over an 8 week period. Although it may not be clinically practical,
intermittent forces might be a safer method to prevent significant root resorption.146
Physiological root resorption was found in unerupted non-impacted maxillary third molars and
compared with premolar teeth from the other studies which had undergone light and heavy
orthodontic forces. It was found that unerupted third molars had slightly greater cube root volume
per tooth than the erupted first premolars not subjected to orthodontic force and a similar cubic
root volume per tooth as first premolars subjected to light buccal and intrusive forces. It was
concluded that root resorption might occur as part of hard tissue remodelling and turnover.
Third order torque movements have been identified as a mechanical risk factor for OIIR. Increase in
torque was found to produce more OIIR particularly in the apical region.132
Da Silveira et al149 used an in vitro study aimed to evaluate the diagnostic ability of CT to detect
simulated external root resorption defects in 59 human mandibular incisors. Cavities were drilled to
standardised small, medium and large defects in the cervical, middle and apical thirds of buccal
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surfaces. They concluded that CT diagnostic ability revealed high sensitivity and excellent specificity,
however, small cavities in the apical third were more difficult to detect than all other cavities.
Dudic et al 138 compared the use of digitised periapical radiographs in evaluating OIRR against micro
computed tomograph scanning as a criterion standard. 29 premolars from 16 subjects were tipped
buccally for 8 weeks while 19 contralateral premolars not subjected to orthodontic movement acted
as controls. They found that less than half of the cases with root resorption identified using a CT
scanner were identified by radiography and thus concluded that evaluation of OIIR may be
underestimated when evaluating with periapical radiographs.
2.11 Disinfection and Storage medium of experimental teeth
Malek et al150 in 2003 examined the effect of five different disinfection and storage protocols on the
hardness and elasticity modulus of human premolar teeth. They found that Milton’s solution for 10
minutes was an appropriate method for disinfection and removal of the periodontal ligament
remanent; however storage for 24 hours caused a significant decrease in the hardness of cementum.
Storage in 70% alcohol or Milli Q solution was suggested as better alternatives for storage. Milli Q
solution in particular was found to have no significant effect when used to store teeth for up to 9
months. Desiccation of tooth samples should be avoided as it was found that it caused a significant
increase in both hardness and elastic modulus from baseline.
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3 Vibration
Vibration, otherwise known as high frequency, low magnitude stimulation, is defined as a
mechanical stimulus characterised by an oscillatory motion.
The key descriptors of vibration include:
i) Frequency (measured in Hz; the number of Hz indicates the number of complete up and down
movement cycles per second)
ii) Amplitude (the extent of the oscillatory motion, measured in mm)
iii) Direction of the vibration movement.
3.1
Whole body vibration
The study of vibration for achieving therapeutic or physical performance goals in the medical field
has been increasing since the mid 1980s. Studies on the application of whole body vibration on the
skeleton have been carried out in animals and humans; the therapeutic value of vibration being
based on Wolff’s law – that, trabecular bone adapts to its mechanical environment. It is also thought
that extremely small mechanical strains are strong determinants of bone morphology.151
Rubin et al 2001 reported that low magnitude mechanical signals induced at a high frequency can
stimulate bone formation. Vibration therapy has also been used to improve or maintain bone and
muscle mass in cases such as mobility impaired patients152, decreased bone density153-154 and in
surgical healing155-156.
Whole body vibration has been studied as a possible means of decreasing the bone density loss that
occurs in astronauts who have extended periods of time in space, or patients with extended bed rest
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or paralysis157. The advantage of vibration therapy is that it is non invasive, non pharmacological and
can be applied in a low impact manner which is critical in elderly or diseased individuals.
There are currently many devices available for use in the fitness and health care areas. The
frequency of vibration in these devices tends to range from a few Hz to 50 Hz with amplitudes
ranging from a few micrometres to several millimetres.158
The vibration protocol is very important. Stimulation of cortical bone in animal turkey study has
been found to successfully stimulate an increase in cortical bone at high frequency 30Hz, low
amplitude (200 microstrain) while low frequency 1Hz, high amplitude 3000 microstrain signals failed
to anabolic159. In a longer term animal study, 20 minute daily sessions of high frequency (30 Hz) and
low level 0.3g(earth’s gravitational) force, stimulated 43% increase in bone density in the proximal
femur151
The Acceledent is able to produce vibration variables of 30Hz and 20 grams. This is a vibration
protocol is similar to that used by Rubin et al160 in the prevention of postmenopausal bone loss. Also,
the Juvent 1000 vibration plate which works at 0.3G (force of gravity) at 32-37 Hz. This device has
been reported to maintain the musculoskeletal system and is well within the exposure limits
recommended by the international organisation for standardisation (ISO).
A Review by Prisby et al 2008161 looked at the skeletal effects of vibration in animals and humans.
They noted that although the scientific basis of vibration devices is increasing steadily, current
literature is unable to establish an optimal vibration prescription.
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This is due to a lack of standardisation in vibration parameters and methodology. Additionally, the
lack of justification offered for the choice of vibration parameters is a significant limitation in the
current literature. 161-162
Future research is needed to develop the optimal vibration protocol. This optimal protocol is likely to
vary depending on the population using the vibration (e.g. young vs. elderly) due to differences in
patient bone quality and bone remodelling patterns as well as the responsiveness of skeletal tissue
to the vibration stimulus.
3.2
The use of vibration in dentistry and orthodontics
High frequency, low magnitude vibration has been applied in the field of orthodontics with the main
aim of increasing the rate of orthodontic tooth movement by accelerating periodontal and bony
tissue modelling/remodelling. Many authors have also hypothesised that vibration may also be a
means of decreasing orofacial pain or pain associated with orthodontic adjustments.
3.2.1
Vibration and the rate of orthodontic tooth movement
The orthodontist’s aim is to achieve their treatment objectives for a patient as well as limit the
duration of treatment and the amount of time a patient has braces on their teeth. In the literature,
increased treatment duration has been associated with an increased risk of caries6, periodontal
problems7 as well as a higher risk of root resorption80,128.
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Roberts et al163 considered bone resorption at the PDL surface to be the rate limiting factor in
orthodontic tooth movement. A maximal rate of molar translation in the maxilla is approximately
2mm per month of space closure in a rapidly growing child or 1mm per month of space closure in a
non growing adult. 164 Clinically and experimentally there have been many attempts to increase the
rate of orthodontic tooth movement, whether it be by reducing friction in the orthodontic
appliances165, adjunctive medicinal or hormonal therapies (local or systemic)166 and more recently
surgical corticotomy techniques167.
Previous research into these strategies has revealed some disadvantages. Systemic medicines can be
non-specific and may produce unwanted side effects in addition to accelerating tooth movement.
Local injection of drugs can complicate treatment and may cause discomfort for patients.
Corticotomy techniques are invasive and increase patient discomfort.
Vibration has the advantage of minimal side effects in comparison to medicinal treatments. It also
has proven to be a safe low impact alternative that enhances bone remodelling in the medical field.
Research on vibration and orthodontic tooth movement has mainly been applied to animal studies,
in particular, rats.
It is difficult to extrapolate the results of animal studies to humans due to differences in PDL and
alveolar bone morphology and physiology. However, even with these short comings, rats are still
generally considered to be a good model to study orthodontic tooth movement. 168
Darendeliler et al 2007169 studied the effect of high frequency low magnitude vibration in 44 wistar
rats using magnets and a pulsed electromagnetic field. They hypothesised that since the literature
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has noted an increase in anabolic activity in bone from high frequency low magnitude vibration, it
may also increase the rate of tooth movement.
The study was designed to allow a pulsed electromagnetic field to interact with Nd-Fe-B magnets
bonded onto the molar teeth of the rat subjects. This interaction caused a mesiodistal vibration
stimulus on the studied teeth. Having split the sample into 4 groups, they compared the effect of
vibration alone; vibration compared with vibration and coil spring; PEMF alone compared with PEMF
and coil spring; and vibration and coil spring compared with PEMF and coil spring.
The results showed coil springs, either with sham or active magnets move the molar teeth more
than magnets alone regardless if a PEMF was present. Under a PEMF, the coil spring produced
significantly more tooth movement than the coil-magnet group, as did the magnet group compared
to the sham magnet group.
The authors concluded that the PEMF induced vibration may enhance the effect of mechanical and
magnetic forces on tooth movement.
In another laboratory study by Nishimura et al170 in 2008, molar vibration in the rat model
significantly increased the rate of tooth movement when compared to a non vibration control
sample. This study was performed on a sample of 42 wistar rats with an experimental duration of 21
days.
Their vibration protocol (60Hz, 1.0m/s²) was based on measuring the natural frequency of the rat
first molar. The natural frequency or otherwise known as the resonance frequency was defined as
the maximum recorded velocity in the resonance curve and was thought to be the force that applied
the largest amplitude of vibration to the periodontal tissues.
Vibration Stimulation was only applied for 8 minutes which was determined in a previous pilot study
of theirs to be the shortest period required to activate the periodontal ligament.
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In addition to reporting an increased rate of tooth movement, the authors also demonstrated the
activation of the RANK-RANKL signalling pathway in response to the loading of resonance vibration.
The safety of vibration was addressed by investigating the effect on root resorption. No significant
differences in root resorption were found between the vibration and non vibration groups. In fact,
they noted that a trend of less root resorption was found in the vibration group. The authors
theorised that vibration may prevent hyalinisation of tissues in the PDL; however, further research is
necessary to determine the exact mechanisms that take place.
3.2.2
Acceledent device
Following on from the findings of these studies, a device called the Acceledent, has reached the
market and aims to achieve an increased rate of tooth movement by enhancing bone remodelling
using pulsating forces. Its inventor, Dr Jeremy Mao previously investigated the effects of cyclic forces
on suture growth. He based his studies on a model suggested by Meikle et al 1979 which concluded
that cranial sutures models mimic the forces that the periodontal ligament and other sutures of the
cranium are exposed to during orthodontic tooth movement171.
The Acceledent vibration variables are based on Dr Rubin’s studies 172-173 on whole body vibration
with a frequency of 30Hz and amplitude of 20g. The Acceledent is prescribed to be used for 20 mins
per day during orthodontic treatment and can be used as an adjunct to fixed appliance or aligner
treatment.
With the release of this new device, research on the effectiveness and safety of vibration in humans
for orthodontic tooth movement will be performed. Currently, there has been an initial study on the
Acceledent device and its effectiveness on the rate of tooth movement and its effect on root
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
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resorption performed at the UT-Houston in Texas, US. Results from these studies have been
favourable, with the Acceledent groups showing an increased rate of tooth movement over controls
as well as less root resorption when reviewed with cone beam CT images.
3.2.3
Pain and vibration
Pain is a common experience and concern for patients who undergo any form of dental treatment.
Pain following an orthodontic adjustment has been reported to be quite prevalent and may affect
patient compliance with treatment174. Pain associated with orthodontics may also adversely affect
the level of patients’ plaque control.175
The usual method of dealing with discomfort is with the use of analgesics. NSAIDS have been
reported to decrease the rate of tooth movement and thus possibly increase orthodontic treatment
times. In a systematic review on the effect of medicines on orthodontic tooth movement, it was
suggested that paracetamol was the analgesic of choice as it didn’t affect the rate of tooth
movement.166
Other alternatives to analgesics for pain control include chewing gum after adjustments176;
Or the use of lower force levels. Even if lower force levels are used, Lim et al showed that pain was
still experienced by most patients.
More recently low level laser therapy, transcutaneous electrical nerve stimulation and vibratory
stimulation have been shown to be effective post orthodontic adjustment.177
When using Vibratory stimulation it is thought that the vibration acts to interfere with the pain
pathways, in particular, the interaction between large fibres and small pain-carrying fibres.178
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It also appears to re-establish the blood supply and intercept the ischemic response.179
Marie et al179 used a small battery operated vibrating motor with a soft detachable mouthpiece and
observed that the appliance had to be used before the onset of pain for it to be effective. When
used after pain had manifested, vibration did little to decrease it.
They found, with the use of visual analog scales, that discomfort was significantly less at every time
interval for those patients who used the vibratory apparatus.
3.2.4
Conclusion
Vibration in orthodontics is still in its infancy. Initial studies for increasing the rate of tooth
movement have been promising. The reduction of pain associated with orthodontic adjustment
when using vibration is another positive in its use.
With the introduction of the Acceledent device, the use of vibration in orthodontics could become
more widely spread. More clinical trials will be needed to fully access the efficacy of Acceledent as
well as its safety.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
70
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Manuscript
71
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Manuscript
The Effect of Mechanical Vibration (Acceledent,
30Hz) applied to the hemi-maxilla on Root
Resorption Associated with Orthodontic Force
A Micro-CT Study
A condensed version of this manuscript is to be submitted for publication to the American Journal of
Orthodontics and Dentofacial Orthopaedics
72
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Australian Centre of Microscopy &
Microanalysis.
Daniel Tan, BDS (Hons)
Post-graduate student
University of Sydney
Discipline of Orthodontics
Faculty of Dentistry
Peter Petocz PhD
University of Sydney
Associate Professor, Statistician
Department of Statistics
Oyku Dalci, DDS, PhD
Macquarie University
Lecturer
Discipline of Orthodontics
Faculty of Dentistry
M. Ali Darendeliler, BDS, PhD, Dip Ortho,
Certif. Orth, Priv. Doc
University of Sydney
Professor and Chair
Discipline of Orthodontics
Carmen Gonzales, DDS, PhD
Faculty of Dentistry
Senior Lecturer
University of Sydney
Discipline of Orthodontics
Faculty of Dentistry
Address for Correspondence:
University of Sydney
M. Ali Darendeliler
Department of Orthodontics
Qiang Fei Li
Sydney Dental Hospital
Lecturer
Lvl 2, 2 Chalmers Street
Discipline of Orthodontics
Surry Hills, NSW 2010
Faculty of Dentistry
Australia
University of Sydney
Phone +61 2 93518314
Fax +61 2 9351 8336
Allan S. Jones, B.App.Sc, Grad. Dip.
(Biomed.E), PhD
Email: [email protected]
Senior Lecturer (Image Analysis)
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
4 ABSTRACT
Introduction
Root resorption is an unpredictable, unavoidable pathologic consequence that occurs during
orthodontic tooth movement. Fortunately in the majority of cases, root resorption is minimal.
In the pursuit of increasing treatment efficiency and decreasing treatment duration, vibratory
stimulation has been advocated as a possible adjunct to orthodontic appliances to increase the rate
of tooth movement. Following this, a new device called the Acceledent has become commercially
available, and is aimed at decreasing treatment duration by accelerating periodontal and bony tissue
remodelling with low magnitude high frequency vibration. To date, there are few studies on the
effect of vibration on root resorption during orthodontic tooth movement. The aim of this clinical
study was to investigate the effect of Acceledent vibration on the volumetric amount of root
resorption after the application of a controlled force (150g) in a buccal direction for 4 weeks.
Materials and Methods
Fifteen patients requiring bilateral extraction of their maxillary first premolar teeth as part of their
orthodontic treatment were recruited for the study. With ethical approval and informed consent
obtained, the experiment incorporated a split mouth design, with the left and right maxillary first
premolars subjected to a buccally directed force of 150g using partial fixed appliances. Each patient
was issued with an Acceledent device with only half a mouthpiece to use (side randomly assigned)
for 20 minutes per day according to the manufacturer’s instructions. At the end of the 4 week
experimental period, the premolars were extracted and scanned with microcomputer tomography
74
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
(micro CT). Volumetric measurements of the root resorption craters were performed with specially
designed software.
Results
Individual variation was evident in the amount and distribution of root resorption craters. There was
no statistical difference between the Acceledent vibration and non-vibration groups in terms of root
resorption volumes and distribution p =0.67. Regression analysis investigating the relationship
between the amount of root resorption in non-vibrated teeth and the improvement in root
resorption with the use of vibration revealed a statistically significant trend p = 0.029.
Conclusions
The use of Acceledent did not appear to increase the volume of root resorption craters of maxillary
first premolars that had undergone a buccally directed force for four weeks to a statistically
significant degree. Vibration could potentially be more beneficial in patients who are more
susceptible to root resorption during orthodontic tooth movement. Further research is necessary to
validate the full effect of vibration using the Acceledent device on tooth root resorption.
Key words: Root resorption, Acceledent, vibration, x-ray microtomography, volumetric analysis
75
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Introduction and literature review
Root resorption has long been recognised as an undesirable side effect of orthodontic tooth
movement1-2. It is the destructive process of the cementum and/or dentine layers of a tooth root
due to clastic cell activity which may eventually lead to loss of apical root length. The term
“Orthodontically induced root resorption (OIIRR)” was introduced by Brezniak and Wasserstein to
describe the type of root resorption experienced during orthodontic treatment.3 It is an unavoidable
and unpredictable pathological surface or transient inflammatory root resorption that occurs due to
the presence of an orthodontic force on a tooth4. Generally it is accepted that most individuals will
experience some degree of root shortening after orthodontic treatment. Fortunately the presence of
severe root shortening is relatively uncommon after orthodontic treatment5.
Although the exact aetiological factors remain unclear, previous studies suggest possible risk factors
for root resorption could be biological or mechanical in origin6. Biological factors such as genetic
factors7 and ethinicity8, chronological and dental age6,9-11, systemic factors12-13, nutrition12, gender7,1415
, root morphology8,16-17, and a previous history of root resorption9,18 have been indicated.
Treatment mechanic factors that have been suggested to cause an increase in root resorption are
force magnitude19-24, duration of orthodontic force8,25-26, direction of tooth movement27, and the
type of tooth movement9,11,26,28-30.
Increased treatment duration has been suggested as a significant factor in increasing the risk of root
resorption8,26,31. Prolonged treatment time in fixed appliances has also been associated with an
increased risk of caries32 and periodontal problems33. Many attempts have been made to accelerate
orthodontic tooth movement and decrease overall orthodontic treatment times. These include
systemic and local medications34, corticotomy techniques35 and recently, low magnitude, high
frequency vibration stimulation36-37, or “Vibration therapy”.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Vibration therapy has been increasingly studied in the medical field and has been successful in
improving or maintaining bone and muscle mass in cases such as mobility impaired patients38,
decreased bone density39-40 and in surgical healing41-42.
Stimulation of bone in an animal study using high frequency, low magnitude vibration has also been
found to successfully stimulate an increase in cortical bone43. When compared to low frequency 1Hz,
high amplitude 3000 micro strain signals, vibration failed to be anabolic43. In a longer term animal
study, 20 minute daily sessions of high frequency (30 Hz) and low level 0.3g(earth’s gravitational)
force, stimulated 43% increase in bone density in the proximal femur44
The Acceledent is a new device specifically designed to be used in orthodontics. It is able to produce
vibration variables of 30 Hz and 20 grams. This vibration protocol is also similar to that used by the
Juvent 1000 vibration plate which works at 0.3G (force of gravity) at 32-37 Hz used to maintain the
musculoskeletal system.
In orthodontics, early animal studies on high frequency, low magnitude vibration were aimed at
increasing the rate of orthodontic tooth movement by accelerating periodontal and bony tissue
modelling/remodelling36-37. Many authors have also hypothesised that vibration may also be a
means of decreasing dental pain or pain associated with orthodontic adjustments45-46.
Although vibration in conjunction with orthodontics may accelerate bone and periodontal tissue
remodelling, there is very limited research on the effect of this accelerated remodelling on the root
surface of teeth.
The aim of this study is to compare the root resorption that occurs on human upper first premolar
teeth following the application of a buccally directed force (150g) with and without vibration, using
the vibration device called “Acceledent”. The experimental teeth were extracted after four weeks of
force application and examined using Micro-computed tomography. This method has been shown to
be more accurate and reliable at quantitative measurements than previous studies using two
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
dimensional radiographs, light microscopy and scanning electron microscopy and transmission
electron microscopy24,47-49. This study will be included as part of the series of root resorption studies
performed at the University of Sydney.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Materials and methods
The sample consisted of thirty maxillary first premolar teeth which were collected from a total of 15
healthy patients (6 boys, 9 girls; mean age, 15 years 8 months; range, 13 years 5 months – 21 years 7
months) who required these teeth to be extracted as part of their fixed orthodontic appliance
treatment. Subjects were selected using a strict criteria previously described.50
All subjects and their parents or guardians consented to participation after receiving verbal and
written explanations (ethics approval: SLHN No X11-0013 & HREC/11/RPAH/13).
Each subject had partial fixed appliances bonded to their maxillary posterior teeth (Figure 1). These
consisted of 0.022-inch Speed brackets (Strite Industries, Cambridge, Ontario, Canada) bonded on
the maxillary first permanent molar and the first premolar teeth. Self ligating brackets were used to
provide standard ligation of the experimental teeth. Both sides received a buccally directed force of
150g using a 0.017x0.025-in TMA cantilever spring (beta III titanium, 3M Unitek, Monrovia, Calif). All
cantilever springs were made by one clinician (DT) and no reactivation of the spring took place
during the 4 week experimental period.
A strain gauge (Dentaurum) was used to measure the force magnitude and verified with two
members of Sydney Dental Hospital orthodontic staff. The experimental premolar teeth were
relieved of occlusal interferences by placing light cured cement (Transbond Plus light cure band
adhesive, 3M Unitek) on the occlusal surfaces of the mandibular first permanent molar teeth.
Each subject was randomly assigned a side for which they would use the Acceledent device. This
divided the premolar samples into “vibration” and “non-vibration” groups. The Acceledent
mouthpieces were modified by cutting them in half so that the mouthpieces would only vibrate on
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
the side assigned to the subject (Figure 2). The subjects were then instructed to use the Acceledent
according to the manufacturer’s instructions. This involved biting on the mouthpiece (light pressure)
and using Acceledent vibration for 20 mins per day. The compliance with the Acceledent device was
monitored using the inbuilt software of the device which records daily usage, as well as calling the
patient by telephone to remind the patients to use the device.
After four weeks of using Acceledent vibration and force application, the cantilever springs were
removed and the upper first premolars were carefully extracted by one of two surgeons. To
minimise damage to the root cementum, no luxators were used and minimal contact was made
between forceps and the cervical cementum. Each tooth was then immediately stored in separate
specimen sample containers filled with sterilised deionised water (Milli Q, Millipore, Bedford, Mass).
Milli Q has previously been described as an appropriate storage media for root resorption
research.50
To prepare the teeth for analysis, residual PDL and soft tissues were removed by placing the teeth in
an ultrasonic bath for 10 minutes. Any remaining soft tissue fragments were then removed by gently
rubbing the root surface with a damp gauze swab. The teeth were then disinfected with 70% alcohol
for 30 minutes and dried on the bench at ambient room temperature (23°C ± 1°C) for at least 48
hours.
The analysis of the root surfaces involved scanning the sample teeth with the SkyScan 1172 desktop
x-ray microtomograph (SkyScan, Aartselaar, Belgium). This system produces high spatial resolution
2-dimensional x-ray shadow projections which allow for 3-dimensional reconstructed images.
All of the sample teeth were scanned separately from 2 to 3mm coronal to the cemento-enamel
junction through to the root apex. The x-ray tube was operated at 60kV and 167µA. No filter setting
was used with a resolution of 17.2µm pixel size. Teeth were rotated 360° around the long axis of the
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
root at 0.2° rotational steps during the x-ray acquisition process. X-ray absorption radiographs were
acquired at each rotation step producing a total of 1800 x-ray absorption radiographs for each tooth.
Each generated image was saved in 16-bit tagged image file format (TIFF) picture files.
Slice by Slice reconstruction was performed using SkyScan’s volumetric reconstruction software
(Nrecon, version 1.4.2 Aartsellaar Belgium). The software program uses a modified Feldkamp
algorithm to create a set of cross sectional slices through the tooth. Reconstructed slices are 1024
x1024 pixels having an 8 bit gray scale dynamic range, saved in BMP data format.
Visualisation and analysis of CT data is performed using VGStudio Max software (version 1.2, Volume
Graphics, Gmbh, Heidelberg, Germany). This program allows for precise and fast analysis of voxel
data. Root resorption craters are first viewed in the 3D reconstructed images and then verified in
axial cross sections. Individual craters were isolated and then exported as axial slices to specially
designed software (Convex Hull 2D, University of Sydney, Australia) to measure the volume of each
crater (Figure 3).
Root resorption craters were grouped according to their location in the vertical plane e.g. apical,
middle or cervical. This was performed by measuring the total length of the root from the CEJ to the
apex and dividing it into equal thirds. Craters were further separated according to their location
when viewed axially, namely, the buccal, palatal, mesial and distal surfaces. All measurements were
carried out by one operator (DT) to eliminate inter-operator variability.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Statistical analysis
The volumes of the root resorption craters were measured as voxels and then converted to mm³ for
analysis. This was performed according to the methods of previous micro ct root resorption
studies.24,48-49,51
Root resorption crater volumes were summed together to obtain total resorption values per tooth.
They were also grouped according to their position by facial surface (buccal, palatal, mesial, or distal)
as well as by their placement in vertical third of the root (coronal, middle, apical).
Paired t tests compared the non vibration and vibration root resorption crater volumes for each
subject using statistics software SPSS (SPSS for windows version 19; SPSS, Chicago). All tests were
analysed for a statistical significance level of p<0.05.
A regression analysis compared the total volumes of root resorption experienced by the nonvibration experimental teeth to the improvement in root resorption (measured by non-vibration
root resorption volume minus vibration root resorption volume).
The root resorption crater volumes of six randomly selected teeth were remeasured to obtain a
standard error of measurement (SE meas) and a coefficient of variation (CV %).
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Results
The compliance with the Acceledent device was recorded using the inbuilt software of the base unit.
At the end of the experimental period the range of patient compliance with Acceledent usage varied
from 73% to 100% with a mean compliance of 92.5%.
Volumetric measurements of craters were repeated on six randomly selected teeth to obtain a
standard error of measurement (se meas = 0.0056) and a coefficient of variation (CV=3.6%). When
separated into non-vibration and vibration measurements, non-vibration se meas = 0.0045,
CV=2.7%; vibration se meas = 0.0065, CV = 4.4%.
There was a wide variation in response to the Acceledent. The mean total amount of root resorption
of the Acceledent experimental maxillary premolar was 0.1085 mm³. When compared to the nonvibration tooth group (0.095 mm³), the difference in root resorption volume was not found to be
statistically significant, p=0.67 (Table I) (Figure 4).
When the results were analysed for location of the resorption craters according to vertical thirds,
the differences were not statistically significant (p-values buccal = 0.46, mesial = 0.94, palatal = 0.86,
distal =0.35). Facial surfaces of the roots showed little variation in the number and size of the
resorption craters between the two groups (p-values cervical = 0.56, middle = 0.22, apical = 0.80).
A regression analysis was performed of improvement (measured by the difference of vibration from
non-vibration volumes) on the total volumes of root resorption experienced by the non vibration
group. The regression is statistically significant with p = 0.029 (Table II) (Figure 5).
Patients with higher non vibration root resorption volumes showed a significant increase in
improvement of resorption values for buccal (p=0.12), palatal (p<0.001), cervical (<0.001) and apical
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
(p=0.03) surfaces. The mesial (p=0.06), distal (p=0.09) and middle (p=0.07) regions of the root did
not reach statistically significant levels but were all in the same direction.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Discussion
The most commonly affected teeth from orthodontically induced root resorption are the maxillary
incisors7,52. In this study, upper first premolars were chosen as they are frequently extracted as part
of orthodontic treatment planning and buccal tipping force was applied for four weeks to those
teeth. The experimental duration was limited to four weeks due to ethical and practical reasons.
Though this is much shorter than routine orthodontic treatment, this is consistent with studies
performed previously23-24,29-30, and despite the limited duration, root resorption craters were still
evident on both vibration and control groups.
Daily courtesy telephone calls were made to subjects to encourage routine use of the Acceledent.
However, the recordings from the Acceledent device indicated that 100% patient compliance during
the experimental period was not achieved (mean compliance 92.5%). Vibration from Acceledent was
instructed to be applied for 20 mins per day for the four weeks of the experiment. The basis for the
time frame comes from vibration studies by Rubin et al53. Although not related to orthodontics, they
found two 10 minute vibration treatments per day to be effective in inhibiting the decline in bone
mass density. Their main issue was compliance with their vibration plate with the highest quartile of
compliance to be 86% compliant. They suggested compliance may have improved if a single 20
minute session had been used. Compliance with vibration was found to be a problem in this study
even with the single 20 minute daily usage. Future research could possibly be directed at shortening
the vibration period in order to avoid interfering with a patient’s personal schedule to further
improve daily compliance of Acceledent.
Previous root resorption studies have reported a significant amount of resorption on the buccal coronal and apical - palatal regions corresponding to a buccal tipping force23,51,54. Compared to these
findings, this study also found several craters on the mesial and distal surfaces of both the vibration
and non vibration experimental teeth.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
The presence of resorption lesions on the mesial and distal aspects of the teeth could indicate a
rotational or torquing movement occurring concurrently to the buccal tipping of the teeth caused by
the cantilever spring. This may have affected the amounts of root resorption craters experienced by
the experimental teeth as slight differences in the initial malocclusion and root morphology would
have affected which areas of the PDL were compressed and hyalinised by the orthodontic force.
Initial pilot studies on the Acceledent device and its effectiveness on the rate of tooth movement as
well as its effect on root resorption have been performed at the University of Texas, US. Results from
a case report55 have been favourable, with the Acceledent groups showing an increased rate of
tooth movement over controls. Root resorption after 6 months of Acceledent use in conjunction
with fixed appliances were found to be within clinically accepted limits56. However, this cone beam
study used a small sample and no mention was made of the overall compliance rate of the
Acceledent during the 6 month study period.
Nishimura et al37 suggested that low magnitude, high frequency stimuli can accelerate orthodontic
tooth movement with no collateral damage to periodontal tissues. Their animal research reported
no significant difference between vibration and non vibration in terms of root resorption after 21
days. This was similar to the finding of this study; however, comparison is difficult due to differences
in the vibration device and the experimental protocol which were used.
Interestingly, Nishimura et al37 did observe a trend towards less root resorption in the vibration
group. Vibration has the potential to alter tissue perfusion, however the magnitude of this effect is
tissue specific and depends on the vibration regimen57. The authors hypothesised that vibration in
their study may have prevented blood flow obstruction and the development of hyalinization, thus
leading to less root resorption.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Using Micro CT imaging, this study did not produce enough evidence to show a difference between
the vibration and non vibration groups. There was great individual variation in the amount and
severity of root resorption for this study sample. This may possibly be explained by individual
susceptibility to root resorption 7,16,58. Another possibility is differences in response to Acceledent
vibration. The subjects may have different responsiveness of skeletal and periodontal tissues and
cells to vibratory stimuli as well as differences in patient bone quality and bone remodelling
patterns.
Although no statistically significant trends for lower root resorption were found in the Acceledent
vibration group, some subjects did appear to experience much less resorption when compared to
the non vibration teeth.
The regression analysis comparing root resorption volumes in the non vibration teeth to the
improvement in root resorption revealed a statistically significant relationship. It suggests that
patients with initially higher root resorption predisposition (as measured by the root resorption
volumes of the non vibration group) may potentially benefit more from the use of vibration than
those that were less susceptible for root resorption. This finding may be useful in minimising future
orthodontically induced root resorption in cases where patients present with a high amount of risk
factors for root resorption prior to orthodontic treatment.
Further research with a larger sample size and longer study design may be needed to further
investigate the effect of Acceledent vibration on root resorption and its mechanisms.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Conclusions
To date, there have been limited studies on the effect of vibration on orthodontically moved teeth
and root resorption. From our results, we can conclude the following:
1. Individual expression of root resorption on buccally tipped upper first premolars was highly
variable after the daily use of Acceledent for four weeks.
2. Acceledent vibration at the frequency and duration utilised in this experiment did not appear to
increase or decrease the amount of root resorption experienced by teeth that were tipped buccally
after 4 weeks to a statistically significant degree. Further testing is required to determine if
difference frequency levels or daily vibration regimens may be more beneficial.
3. Vibration may potentially be more beneficial in patients more susceptible to orthodontically
induced root resorption.
4. Further research is necessary to determine the full effect of vibration when used in orthodontics.
Acknowledgement
This study was supported by the Australian Society of Orthodontics Foundation for Research and
Education Inc.
We wish to thank AB Orthodontics (Australia) and OrthoAccel Technologies for their generous
donation of the Acceledent units used in this study.
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The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
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application of orthodontic force. A micro−CT study.
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properties of root cementum: part 2. Effect of different storage methods. American Journal of
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discussion 8-9.
52. Remington DN, Joondeph DR, Artun J, Riedel RA, Chapko MK. Long-term evaluation of root
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application of orthodontic force. A micro−CT study.
Daniel Tan
54. Paetyangkul A, Turk T, Elekdag-Turk S, Jones AS, Petocz P, Darendeliler MA. Physical properties of
root cementum: part 14. The amount of root resorption after force application for 12 weeks on
maxillary and mandibular premolars: a microcomputed-tomography study. American Journal of
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58. Smale I, Artun J, Behbehani F, Doppel D, van't Hof M, Kuijpers-Jagtman AM. Apical root
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92
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
5 Appendix
Study design
N=15 patients
Acceledent
vibration (20
mins per day)
Non vibration
n=15
premolars
n=15
premolars
93
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Figure 1 (a&b) - Appliance Design
Figure 1 a. intraoral view of the experimental appliance
Figure 1b.TMA cantilever spring before ligation (left) and after ligation (right)
94
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Figure 2 (a&b) - Acceledent device
Figure 2 a. Acceledent device with modified mouthpiece (mouthpiece side was randomly assigned)
Figure 2 b. Clinical use of Acceledent
95
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Sky Scan 1172 Desktop X-ray Microtomograph
96
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Specimen Mounting on the SkyScan 1172 Desktop Microtomograph
97
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Skyscan 1172 x-ray images
Nrecon version 1.4.2 Aartsellaar Belgium
98
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Images from Cone Beam Reconstruction with NRecon (Aartsellaar,
Belgium Version 1.4.2)
Figure 3: 3D reconstruction images using VG Studio Max (Volume
Graphics, GmBh, Heidelberg, Germany)
99
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Convex Hull 2D
100
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Table I (a&b) - Paired T tests
Paired Samples Statistics
Mean
Pair 1
N
Std. Deviation
Std. Error Mean
nvib
.09525
15
.070974
.018325
vib
.10847
15
.096597
.024941
Paired Samples Test
Paired Differences
95% Confidence Interval of
Mean
Pair 1 nvib -
-.013225
Std.
Std. Error
Deviation
Mean
.116553
the Difference
Lower
.030094
-.077770
vib
Figure 4: Graph - Vibration vs. Non-vibration
101
Upper
.051320
Sig. (2t
-.439
df
tailed)
14
.667
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Table II (a&b) - Regression Analysis of mean volume difference
(improvement) on non-vibration root resorption volume.
ANOVA
Model
1
Sum of Squares
df
Mean Square
Regression
.060
1
.060
Residual
.130
13
.010
Total
.190
14
F
Sig.
5.988
.029
a
a. Predictors: (Constant), nvib
b. Dependent Variable: diff
Coefficients
Standardized
Unstandardized Coefficients
Model
1
B
(Constant)
nvib
Coefficients
Std. Error
Beta
-.101
.044
.922
.377
a. Dependent Variable: diff
102
T
.562
Sig.
-2.285
.040
2.447
.029
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Figure 5: Graph – Improvement vs. Non-vibration
103
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Raw Data – Patient information and total root resorption Volumes
Subj n°
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Total
Subj
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Total
Total resorption per tooth mm³
Non-Vibration
Vibration Group
Group
0.1061
0.1064
0.0330
0.0073
0.2831
0.1538
0.1420
0.0894
0.0865
0.0607
0.0229
0.1548
0.0051
0.0130
0.0542
0.2322
0.0875
0.1329
0.2347
0.0305
0.3133
0.0804
0.0363
0.0063
0.1146
0.0611
0.0561
0.0521
0.0768
0.2218
1.6271
1.4287
Root resorption per tooth surface mm³ - Vibration group
Buccal
Mesial
Palatal
0.0011
0.1052
0
0.0012
0.0020
3.05307E-05
0.0002
0.2317
0
0
0.0004
0.013703298
4.07076E-05
0.0648
0.0145
0.0001
0
0
0.0005
0.0038
0.0007
0.0032
0.0156
0.0328
0.0091
0.0286
0.0435
1.01769E-05
0.1715
0.0215
0.0271
0.0779
0.0237
0.0223
0.0010
0
0.0016
0.0243
0.0218
0
0.0183
0.0221
0
0.0086
0
0.0670
0.7545
0.1948
104
Distal
0
0.0040
0.0511
0.1279
0.0070
0.0227
0
0.0023
0.0060
0.0415
0.1844
0.0129
0.0667
0.0155
0.0681
0.6107
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Root resorption per tooth surface mm³ - Non vibration group
Buccal
Medial
Palatal
0.0009
0.0305
0.0072
0
0.0275
0.0054
0.0002
0.1292
0
0.0207
0.0310
0.0262
0.0007
0.0322
0.0218
0
0.1197
0.0318
0
0.0026
0.0033
0
0.1775
0
0.0142
0.0736
0.0092
0
0.0216
0.0043
0.0352
0.0203
0.0001
0
0.0003
0.0060
0.0063
0.0199
0.0035
0.0011
0.0374
0.0087
0.01541
0.0084
0.0879
0.09507
0.7322
0.2156
Subj
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Total
Subj
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Total
Root resorption per vertical thirds mm³ - Vibration group
Cervical
Middle
Apical
0.0771
0.0281
0.0011
3.05307E-05
0.0071
0.0002
0
0.2828
0.0003
0.0004
0.0286
0.1129
0.0639
0.0222
0.0002
0.0001
0.0227
0
0.0043
0
0.0007
0.0156
0.0385
0
0.0134
0.0453
0.0286
0.0714
0.1297
0.0335
0.0845
0.0206
0.2081
0.0342
0.0020
5.08845E-05
0.0129
0.0814
0.0201
0.0178
0.0148
0.0233
0
0
0.0768
0.3964
0.7243
0.5063
105
Distal
0.0674
0
0.0243
0.0114
0.0059
0.0032
0.0071
0.0547
0.0358
0.0046
0.0246
0
0.0313
0.0048
0.1100
0.3857
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Root resorption per vertical thirds mm³ - Non vibration group
Subj
Cervical
Middle
Apical
1
0.0009
0.0253
0.0798
2
0.0031
0
0.0298
3
0.1292
0.0002
0.0243
4
0.0226
0.0092
0.0575
5
0.0259
0.0239
0.0108
6
0.0032
0.0118
0.1397
7
0.0097
0.0033
0
8
0.0963
0.0811
0.0547
9
0.0335
0.0902
0.0091
10
0
0.0089
0.0216
11
0.0599
0
0.0204
12
0
0
0.0063
13
0.0263
0
0.0347
14
0.0011
0.0327
0.0182
15
0.1254
0.0273
0.0691
Total
0.5377
0.3143
0.5766
106
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Future directions
Vibration is a relatively new field. Although it has been studied increasingly in the medical field for
the treatment of mobility impaired patients, decreased bone density and in surgical healing, little is
known about the potential benefits for the orthodontist. Initial studies on the effect of vibration on
orthodontic tooth movement and the craniofacial structures have so far been limited to animal
studies.
With the introduction of Acceledent, the use of vibration in orthodontics may transfer from the
theoretical, experimental use to common day usage.
This study is one of the first to look at the effect of Acceledent on root resorption while teeth are
undergoing a buccally directed force. Its study design was based on similar methodology used in
previous research work in the Sydney university orthodontic department.
To further assess the clinical safety of Acceledent, further research is needed with possibly a longer
study duration and larger sample size.
This study was limited to extracted premolar teeth. The use of Micro CT limits its use to inanimate
objects. As technology improves a Micro CT scanner may become available for live subjects. If this is
the case, studies on the root resorption of the maxillary incisor teeth may be interesting as these are
the most prone teeth to root resorption.
Different vibration protocols and different vibration devices should be tested. In the medical field,
low magnitude high frequency has been reported to be effective while high magnitude low
frequency has not. Although the Acceledent is based on this work, those previously reported
vibration protocols were not specifically designed for the oral cavity. This may require a different set
of parameters for optimal orthodontic tooth movement and safety.
107
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Likewise, different patients may respond to vibration differently. Older patients and younger
patients exhibit different bone quality, bone remodelling patients and biological response to
vibration stimulation. What may work for an older patient may not be suitable for a younger patient.
Further testing is required to determine which frequency and magnitude provides the most
beneficial results.
Compliance in using the device has been an issue. Currently it is recommended for use 20 minutes
per day. Testing in the field of duration of use for Acceledent could improve compliance if it is shown
that shorter durations of use yield similar benefits.
Nishimura in their rat study hypothesised that vibration could potentially increase vascular flow to
areas of compression thereby inhibiting hyalinisation and decreasing root resorption. Histological or
vascular studies could be performed to test this theory. Previous studies on root resorption have
examined repair of root resorption cavities. If vibration is able to accelerate remodelling of the bony
alveolus around a tooth, it could possibly accelerate the repair of root resorption cavities.
Histological or micro CT studies could be used to determine if vibration is able to decrease root
resorption as well as accelerates healing as well.
In the present study, a statistically significant correlation was made which suggested that patients
with initial high levels of root resorption may benefit more from the use of vibration. Genetic testing
for root resorption susceptibility may eventually become a possibility and thus the theoretical
correlation could be proven or disproven.
The main aim of Acceledent is to increase the rate of orthodontic tooth movement. Future research
in the department is needed to assess the efficacy of its claims with a clinical trial. It must be proven
that Acceledent works to a clinically significant degree before it can be a widely accepted treatment
adjunct.
108
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
Acceledent has been advertised to work with all orthodontic appliances including lingual fixed
appliances, labial fixed appliances and removable thermoplastic appliances. Clinical studies may be
carried out to determine their efficacy is different between the appliances.
Finite element analysis studies of Acceledent vibration may give clues to the potential spread of
vibration not just to the teeth but also to the craniofacial skeleton as a whole. This may allow for
research into the most effective design of the device.
Vibration in orthodontics is still in its infancy. Initial studies for increasing the rate of tooth
movement have been promising. With the introduction of the Acceledent device, the use of
vibration in orthodontics could become more widely spread. More clinical trials will be needed to
fully access the efficacy of Acceledent as well as its safety.
109
The effect of mechanical vibration (Acceledent) on root resorption and tooth movement after
application of orthodontic force. A micro−CT study.
Daniel Tan
110
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