Basic Research—Technology
Periapical Inflammation after Coronal Microbial
Inoculation of Dog Roots Filled with Gutta-Percha
or Resilon
Guy Shipper, BDS, MDent, MS, Fabricio B. Teixeira, DDS, MSc, PhD, Roland R. Arnold, PhD,
and Martin Trope, BDS, DMD
Abstract
A dog model was used to assess and compare in vivo
the efficacy of gutta-percha and AH26 sealer versus
Resilon with Epiphany primer and sealer [Resilon
“Monoblock” System (RMS)] filled roots in preventing
apical periodontitis subsequent to coronal inoculation
with oral microorganisms. There were 56 vital roots in
the premolars of seven adult beagle dogs aseptically
instrumented, filled, and temporized. The roots were
randomly divided into four experimental groups (Coronal Leakage Model) and one negative control group
and filled as follows: group 1—lateral condensation of
gutta-percha and AH26 sealer (n ! 12); group 2—vertical condensation of gutta-percha and AH26 sealer
(n ! 12); group 3—lateral condensation of RMS (n !
12); group 4 —vertical condensation of RMS (n ! 10);
negative control (n ! 10)— gutta-percha and AH26
sealer or RMS root fillings using lateral or vertical
condensation techniques as in groups 1 to 4. Positive
control—57 additional premolar roots were instrumented, infected and not filled (beginning of the Entombment Model experiment). The premolars in groups
1 to 4 were accessed again, inoculated with dental plaque
scaled from the dog’s teeth, and temporized. This fresh
innoculum of microorganisms was repeated on two more
occasions at monthly intervals. The teeth in the negative
control group were not accessed again and remained
undisturbed. On the 14-wk postcoronal inoculation, dogs
were euthanized, and jaw blocks prepared for histologic
evaluation under a light microcope. Mild inflammation
was observed in 82% (18 of 22) of roots filled with
gutta-percha and AH26 sealer that was stastistically more
than roots filled with RMS (19% or 4 of 21) and roots in
the negative control (22% or 2 of 9) (McNemar paired
analysis, p " 0.05). The Resilon “Monoblock” System was
associated with less apical periodontitis, which may be
because of its superior resistance to coronal microleakage.
Drs. Shipper, Trope and Teixeira are affiliated with the
Department of Endodontics, University of North Carolina
School of Dentistry, Chapel Hill, NC. Dr. Roland R. Arnold is
Professor, Departments of Diagnostic Sciences and Periodontology, and Director of Oral Microbiology, UNC School of
Dentistry, Chapel Hill, NC.
Address requests for reprints to Dr. Martin Trope, Department
of Endodontics, School of Dentistry, University of North Carolina,
Chapel Hill, NC, 27599; E-mail: martin_trope@dentistry.unc.edu.
Copyright © 2005 by the American Association of
Endodontists
JOE — Volume 31, Number 2, February 2005
A
pical periodontitis is caused primarily by microorganisms or their by-products in
the root canal system (1–3). The aim of endodontic treatment is to prevent or
eliminate microbial challenge to the surrounding periodontal structures. Disinfecting of
the root canal space is achieved through mechanical and chemical means (4, 5) and if
the microbial flora is controlled, predictable success will result (6 – 8).
After the microbial control phase of endodontic therapy, a root canal filling is
placed to seal the root canal system from the external environment. This filling should
serve 3 principal functions: entombing most surviving bacteria; stopping the influx of
periapical tissue-derived fluid from reaching surviving bacteria in the root canal system;
and acting as a barrier, thereby preventing re-infection of the root canal (9). However,
the present root filling materials and techniques fail in all three requirements mentioned above (10, 11).
Torabinejad et al. (12) examined the microbial coronal leakage of single-rooted
extracted root-filled teeth and found that 50% of the teeth were contaminated along the
whole length of the root filling after 19 and 42 days depending on the organism.
Additional in vitro studies have confirmed the high leakage rate of gutta-percha and
sealer root fillings within 30 days using either lateral or vertical condensation techniques (13, 14).
Coronal seal has been shown to be critical for periapical health after root canal
treatment. Ray and Trope (15) recognized that the integrity of the coronal part of the
root canal system is paramount for success, and concluded that the technical quality of
the coronal restoration was significant and perhaps more important than the technical
quality of the root canal filling to ensure prevention or healing of apical periodontitis.
Tronstad et al. (16) confirmed that the coronal restoration was critically important for
success in endodontic therapy, but stated the technical quality of the root filling was also
highly significant.
It appears that a root filling containing gutta-percha is the weak point in endodontic therapy (10 –14). Filling of the root canal with gutta-percha and sealer even by the
most technically proficient operator will not result in a seal that is dependable. In fact
as stated before, the coronal restoration is more likely the reason for success over the
long term than the gutta-percha fill. Many different materials have been proposed as
root canal fillings, but none have replaced gutta-percha that is universally accepted as
the gold standard filling material. Although gutta-percha has been used for a long time,
most agree that it would be advantageous to replace it with a filling material that
provides a superior seal (than gutta-percha) at all levels of the root canal system.
Adhesive resins have been used for many years in operative dentistry. In recent
years the seal and bond strength of these resins has been improved significantly (17).
Resilon (Resilon Research LLC, Madison, CT), a thermoplastic synthetic polymer based
root canal filling material, has been developed that performs like gutta-percha, has the
same handling properties, and for retreatment purposes may be softened with heat or
dissolved with solvents like chloroform. Based on polymers of polyester, Resilon contains bioactive glass, bismuth oxychloride and barium sulfate. The sealer used is Epiphany Root Canal Sealant (Pentron Clinical Technologies, Wallingford, CT), which is a
dual curable dental resin composite sealer. This sealer when used with the Resilon
filling material forms a bond to the dentin wall and the core material making the filling
resistant to bacterial penetration (18). Thus, the Resilon core filling with Epiphany
In Vivo Assessment of Resilon
91
Basic Research—Technology
sealer is considered as a single entity and in this report will be referred
to as the Resilon “Monoblock” System (RMS). The importance of the
Resilon core material is illustrated by the fact that when the Epiphany
sealer is used with gutta-percha the seal created is not better than all
gutta-percha systems tested (18).
In addition to a final rinse with 17% EDTA, Epiphany primer is
applied to the dentin walls of the root canals. The preparation of the
dentin through these chemical agents may prevent shrinkage of the resin
filling away from the dentin wall and aid in sealing the roots filled with
the RMS.
Shipper et al. (18) tested the resistance to bacterial penetration of
the RMS in extracted single-rooted teeth, and compared it to guttapercha with sealer filled roots. Streptococcus mutans or Enterococcus faecalis penetration were tested over a 30 day period through
gutta-percha with sealer and RMS using two filling techniques, namely
lateral and warm vertical condensation or a continuous wave of condensation (System B). In this study as in previous ones (10 –14), guttapercha and sealer allowed bacterial penetration in a high proportion of
cases. The RMS groups with self etch primer and resin sealer resisted
bacterial penetration to both test bacteria. In addition lateral condensation and vertical condensation of softened Resilon were equally effective in resisting bacterial penetration. This excellent sealing capability of
Resilon may be attributed to the “monoblock” described above.
The in vitro experiments of Torabinejad et al. (12) and Shipper et
al. (18) evaluated and compared the sealing abilities of different materials or techniques. However, it is not possible to relate leakage in the in
vitro experiments with disease in vivo (19). Even minimal penetration of
bacteria into the lower chamber broth in the in vitro leakage studies will
result in a “failure” when the bacteria multiply in the medium. The
minimum inoculum of microorganisms for disease in vivo is unknown.
Because the results from the in vitro microbial leakage model were
so favorable, it is important to test the RMS and gutta-percha with sealer
in an in vivo model where the host defense response also plays a role
and where a histological evaluation can determine the presence/absence of apical periodontitis, the disease of interest in endodontics.
The purpose of this study was to assess and compare in vivo the
efficacy of gutta-percha and AH26 sealer versus RMS filled roots in
preventing apical periodontitis subsequent to coronal inoculation with
oral microorganisms.
Materials and Methods
Seven adult beagle dogs were selected for this research. There
were 10 premolars used in each dog, half were used for another experimental model whereby the roots were infected, apical periodontitis
induced and then filled (Entombment Model). This manuscript addresses the Coronal Leakage Model where vital roots were instrumented, filled immediately, and then challenged by coronally placed
oral microorganisms. The study protocol was approved by the University of North Carolina Institutional Animal Care and Use Committee
(IACUC). There were 56 vital roots of premolars (excluding the most
posterior premolars of the mandible) randomly selected.
The anesthetic induction was achieved by intravenous administration of thiopental (13.2 mg/kg body weight) followed by administration
of 1 to 2% isoflurane via an endotrachial tube. The dogs additionally
received a local anesthetic (bupivacaine 0.5 ml/ quadrant) to provide
regional nerve block anesthesia. Constant monitoring of the animals
during treatment determined when additional anesthesia was necessary
to assure that the procedure was carried out painlessly. Preoperative
radiographs were taken before any endodontic treatment was performed.
92
Shipper et al.
To minimize any postoperative discomfort for the dogs during the
study, three pharmacological approaches were taken: (a) Rimadyl (2.2
mg/kg orally every 12 h) was given preoperatively beginning 24 h before
the surgical session. (b) Upon termination of the surgical sessions, the
dogs received an immediate subcutaneous injection of butorphanol
(0.2 mg/kg) for postoperative analgesia. (c) The dogs were given Rimadyl postoperatively (2.2 mg/kg orally) every 12 h for 48 h to control
inflammation or pain. The dogs were fed their normal soft diet after root
canal treatment. The mouth of the dogs were inspected daily for signs of
obvious infections or ulcers. Food intake was also monitored.
All procedures were performed under strict asepsis. Before treatment, the teeth were radiographed, pumiced, isolated with rubber dam,
and wiped with 10% povidone-iodine solution. The central cusp of each
tooth was slightly reduced and a mesiodistal access cavity was prepared
with a sterile bur at high-speed, under sterile saline irrigation. The root
canals were instrumented with ProFile rotary files (Dentsply Tulsa Dental, Tulsa, OK) and a #40 K file (Kerr, Romulus, MI) to working length.
A total of 15 ml of 1.25% sodium hypochlorite (NaOCl) was used for
irrigation between instruments with a syringe and a 27-gauge Monoject
endodontic irrigation needle (Sherwood Medical, St Louis, MO). There
were 5 ml of 17% EDTA rinses used during and after instrumentation.
The root canals in the experimental and the negative control were
dried with sterile paper points and filled immediately after instrumentation. Each root canal was randomly allocated for filling with either
RMS or gutta-percha and AH26 sealer, using either a lateral or a continuous wave of condensation (System B, Analytic Endodontics, Orange,
CA) and an Obtura II (Obtura Spartan, Fenton, MO) backfill technique.
To ensure no cross-contamination of the filling materials and their
sealers, separate instruments including System B pluggers and Obtura II
systems were used.
In each dog the roots were randomly divided into four experimental groups (Coronal Leakage Model), one positive control group (Entombment Model) and one negative control group, and filled as follows
(see Table 1):
Group 1: Lateral Condensation of Gutta-Percha—12 Roots
After instrumentation the canals were rinsed with EDTA. These
roots were filled with gutta-percha and AH26 sealer (Dentsply Maillefer,
Tulsa, OK) using a cold lateral condensation technique. An ISO size 40
gutta-percha master cone (Kerr, Romulus, MI) was coated with AH26
sealer and placed into the root canal to working length. A size 30 finger
spreader (Dentsply Maillefer) was then inserted into the canal to a level
approximately 1 mm short of working length. Lateral condensation with
fine accessory gutta-percha cones (Kerr) coated with sealer was performed until the root canal was filled. A sterile cotton pellet was placed
in the access cavity and the crown was temporized with a glass ionomer
(Fuji IX, GC Corporation, Tokyo, Japan) restoration.
Group 2: Vertical Condensation of Gutta-Percha—12 Roots
After instrumentation the canals were rinsed with EDTA. An ISO
size 40 gutta-percha master cone (Obtura Spartan) was coated with
AH26 sealer and was fitted apically and then vertically thermoplastisized
using a continuous wave of condensation technique (System B). A backfill with Obtura gutta-percha was carried out using the Obtura II system.
A sterile cotton pellet was placed in the access cavity and the crown was
temporized with a glass ionomer (Fuji IX) restoration.
Group 3: Lateral Condensation of Resilon—12 Roots
After instrumentation, the canals were rinsed with EDTA. A selfetching primer (Epiphany Primer), (Pentron Clinical Technologies,
Wallingford, CT) was placed into the canal with a sterile paper point
(soaked with the primer). Roots were filled with lateral condensation of
JOE — Volume 31, Number 2, February 2005
Basic Research—Technology
TABLE 1. Periradicular inflammation of mandibular premolars of beagle dogs.
Group
Experimental
1
2
1$2
3
4
3$4
1!2!3!4
Negative
1
2
3
4
1!2!3!4
Inoculation
No. of Roots
Yes
Yes
Yes
Yes
Yes
Yes
11
13
24
12
10
22
46
(10)*
(12)*
(22)*
(11)*
No
No
No
No
2
4
2 (1)*
2
10 (9)*
(21)*
(43)*
Treatment
Lateral gutta-percha
Vertical gutta-percha
Lateral $ vertical gutta-percha
Lateral Resilon
Vertical Resilon
Lateral $ vertical Resilon
Lateral gutta-percha
Vertical gutta-percha
Lateral Resilon
Vertical Resilon
Periapical
Inflammation
(roots)
Mild
%
8
10
18
2
2
4
22
80
83
82
18
20
19
51
1
1
0
0
2
50
25
0
0
22
* ! Number in parenthesis represents samples available for analysis after exclusion of exposed roots and those damaged in histology.
Experimental groups: three separate inoculations of plaque coronal to the root fillings with monthly intervals (14 wk after 1st plaque inoculation and a 6 month observation period). Negative control group: roots
were filled and no plaque was inoculated coronally (6 month observation period).
McNemar paired analysis test (p " 0.05): groups (1 $ 2) and negative control–p ! 0.016; groups (3 $ 4) and negative control–p ! 0.5; groups (1 $ 2) and (3 $ 4)–p ! 0.00018; lateral and vertical
gutta-percha–p ! 0.5; lateral and vertical Resilon–p ! 1.0.
Resilon and Epiphany sealer. The sealer was placed according to manufacturer’s instructions with a lentulo spiral instrument (Dentsply
Maillefer, Johnson City, TN). An ISO size 40 Resilon master cone was
placed to length and a size 30 finger spreader (Dentsply Maillefer) was
then inserted into the canal until resistance was felt. The space created
was filled with a fine Resilon accessory point coated with Epiphany
sealer. The process was repeated until it was felt that the canal was
completely filled. A sterile cotton pellet was placed in the access cavity
and the crown was temporized with a glass ionomer (Fuji IX) restoration.
Group 4: Vertical Condensation of Resilon—10 Roots
After instrumentation the canals were rinsed with EDTA. The roots
were prepared with the primer as in group 3. Roots were filled with an
ISO size 40 Resilon master cone and Epiphany sealer using the continuous wave of condensation (System B) technique and backfilled with
Resilon in an Obtura II system. The sealer was placed according to
manufacturer’s instructions with a lentulo spiral instrument. A sterile
cotton pellet was placed in the access cavity and the crown was temporized with a glass ionomer (Fuji IX) restoration.
Negative Control—10 Roots
Roots were filled with gutta-percha and AH26 sealer or RMS using
lateral or vertical condensation techniques as in groups 1 to 4. The floor
of the access cavity was filled with Cavit (ESPE America Inc., Norristown,
PA) (2-mm thick) and then a glass ionomer final restoration (Fuji IX)
was placed coronally.
Positive Control—57 Roots (beginning of the Entombment
Model experiment)
Roots were instrumented and irrigated with saline solution. A cotton pellet coated with isologous plaque scaled from the dog’s teeth was
placed in the access cavity. A glass ionomer restoration (Fuji IX) was
placed coronally.
After 14 wk, the teeth assigned in the experimental group were
accessed again and the cotton pellets removed. The pulp chambers in
the experimental group were then inoculated with isologous plaque
scaled from the dog’s teeth. A cotton pellet soaked in the dog’s plaque
JOE — Volume 31, Number 2, February 2005
was replaced in the access cavity and the teeth were sealed with Fuji IX.
The innoculum of plaque and placement of the glass ionomer restoration in the experimental groups of the Coronal Leakage Model were
repeated monthly on two more occasions. Anaerobic cultures were
obtained from pulp chambers in 14 randomly selected teeth (two teeth
per dog) before the 2nd and 3rd stages of coronal inoculation of microorganisms and in 14 randomly selected teeth before root fillings in
the positive control group (two teeth per dog). The teeth in the negative
control group were not accessed again and remained undisturbed. After
6 wk, all the teeth in the positive control group showed distinct areas of
radiolucencies (while the experimental and negative control groups did
not). The teeth in the positive control were used in a different experiment model (Entombment Model) and were also not accessed again
after root canal filling and coronal restorations had been placed. All
teeth, were examined each month to verify the integrity of the restorations. Standardized radiographs utilizing pretreatment bite-blocks with
Regisil 2# bite registration material (Dentsply Caulk, Milford, DE)
were taken after the teeth were initially prepared. Additional radiographs were taken at 1, 3, and 6 months postoperatively and observed
for apical periodontitis.
A period of 14 wk had passed since the initial application of plaque
in the experimental teeth and 6 months for the control teeth, before the
sacrifice of the dogs. Deep anesthesia was attained with the use of
pentobarbital (iv administration), using a dosage of 30 mg/kg body
weight. The left and right common carotid arteries were then exposed
and the jaws perfused with 4% neutral buffered formaldehyde. Jaw
blocks containing the treated teeth were resected, fixed in 10% phosphate-buffered formalin, decalcified in 10% EDTA and embedded in
paraffin. and prepared for histologic evaluation. Serial longitudinal sections of 5 to 7 microns in a mesio-distal orientation to include the entire
root canal system and at least 1 mm of peripaical tissue were cut and
hematoxylin and eosin stained.
The periradicular tissues were examined histologically under a
light microscope at #10 magnification. The evaluators, one endodontist and one oral pathologist, were blinded to the treatment groups and
evaluated the histological sections according to the following predetermined scale:
In Vivo Assessment of Resilon
93
Basic Research—Technology
Fig 1. Radiograph taken 14 wk after coronal inoculation of plaque, showing
mandibular premolars filled with Resilon and Epiphany sealer using a lateral
condensation technique (2nd premolar—P 2) and a vertical condensation
technique (3rd premolar—P 3). The 4th premolar was missing in this dog. A
cotton pellet soaked in plaque was placed coronal to the root fillings and the
teeth were temporized with a glass ionomer restoration. No periradicular lucencies are evident.
Fig 2. Photomicrograph of the mesial root of a mandibular premolar in a beagle
dog 14 wk after 1st inoculation of plaque coronal to the root filling. High power
view showing healthy periodontium (original magnification #50; H&E).
0 ! No inflammation and normal width of the periodontal ligament
(PDL) space
1 ! Mild inflammation and widened PDL space
2 ! Moderate inflammation and detectable loss of apical bone
3 ! Severe inflammation and severe destruction of apical and cortical
bone
McNemar paired analysis was used to compare the incidence of inflammation in the four experimental groups and the negative control (p "
0.05).
Results
All dogs tolerated the operative procedures well throughout the
observation period. There was no evidence of swelling or sinus tract
associated with any of the treated teeth. One tooth fractured and was
excluded from the study (two roots filled with gutta-percha and AH26
sealer). One root filled with RMS using the lateral condensation technique was lost in histological sectioning. The overall results are summarized in Table 1.
94
Shipper et al.
Fig 3. Photomicrograph of the distal root of a mandibular premolar in a beagle
dog 14 wk after 1st inoculation of plaque coronal to the root filling. High power
view showing inflamed periodontal ligament, resorption of bone and abundant
inflammatory cells (original magnification #50; H&E).
Radiographic observations at all time intervals revealed no signs of
apical periodontitis in the experimental (Fig. 1) and negative control
groups. The positive control teeth all showed distinct radiolucencies 6
wk after placement of the plaque. Anaerobic cultures of the recovered
cotton pellets from the teeth in the experimental group and positive
controls were all positive for microbial growth. Histological evaluations
were not performed on the positive control roots since after distinct
radiolucencies were seen radiographically they were used for an entombment study. Histological outcomes showed normal periodontium
(score ! 0) (Fig. 2) or mild inflammation with localized inflammatory
cell infiltrate (score ! 1) (Fig. 3). No specimens showed moderate or
severe inflammation with significant loss of apical bone.
Mild inflammation was observed in 82% (18 of 22) of roots filled
with gutta-percha and AH26 sealer (groups 1 and 2) and 19% (4 of 21)
of roots filled with RMS (groups 3 and 4). This difference was statistically significant (p ! 0.00018). In the negative control group, mild
inflammation was observed in 22% (2 of 9) of the roots. The two roots
that had mild inflammation in the negative control group were filled with
gutta-percha and AH26 sealer. The difference in mild periapical inflammation between the roots filled with gutta-percha in the experimental
groups (groups 1 and 2) and the negative control was statistically significant (p ! 0.016) (Table 1). However, the roots filled with RMS in
the experimental groups (groups 3 and 4) had a similar incidence in the
absence of mild periapical inflammation to the negative control group
(p ! 0.05) (Table 1). There was no difference in periapical inflammation between lateral and vertical techniques in the gutta-percha (p !
0.05) or RMS groups (p ! 1.0) (Table 1).
Discussion
This in vivo study is a continuation of the evaluation of this new
RMS to assess if the superior bacterial leakage resistance found in our
in vitro model (18) is related to apical periodontitis, the disease of
interest in endodontics. While the RMS was clearly superior in the in
vitro model, that model is unable to determine if the leakage found
relates to disease. This study was designed to assess if the apparent
superiority of the material can be duplicated under physiologic functional stresses and if a difference in the incidence of apical periodontitis
could be determined.
Twenty-two percent (2 of 9) of the negative control teeth that were
not challenged by coronal microorganisms showed mild inflammation
JOE — Volume 31, Number 2, February 2005
Basic Research—Technology
TABLE 2. Periradicular inflammation of roots 14 wk after coronal inoculation of plaque (Friedman et al. 1997 vs Shipper et al. 2004).
Study
Friedman et al. (1997)
Shipper et al. (2004)
Shipper et al. (2004)
Weeks post 1st
plaque inoculation
Root Filling
(Sealer)
n
(Roots)
14 wk*
14 wk*
14 wk*
Gutta-percha $ Kerr Pulp Canal
Gutta-percha $ AH26
Resilon $ Epiphany
9
22
21
Periapical Inflammation (roots)
None
Mild
Severe
3 (33%)
4 (18%)
17 (81%)
6 (67%)
18 (82%)
4 (19%)
0 (0%)
0 (0%)
0 (0%)
*Friedman et al. (1997) had only one inoculation of plaque while our study (Shipper et al. 2004) had three separate inoculations of plaque with monthly intervals.
at the 6 month evaluation period. Both of the teeth that showed inflammation were filled with gutta-percha and AH26 sealer. The inflammation
may have been the result of inflammatory stimulators other than bacteria, a break in the aseptic chain while performing the root canal treatments or a break down in the coronal restorations over the 28-wk
period. While it is disappointing that the negative control teeth showed
some inflammation in roots after vital pulp therapy, the incidence is
much lower than if gutta-percha filled teeth are challenged by microorganisms.
A previous study was performed by Friedman et al. (20) using the
same experimental model with gutta-percha and Kerr sealer placed with
a lentulo spiral and a lateral condensation technique. Two weeks after
completion of the root canal therapy, they placed plaque coronally and
found at a 14-wk histological evaluation (postplaque inoculation), mild
inflammation in 67% of the roots. In this study we found mild inflammation in 82% of the roots filled with gutta-percha and AH26 sealer
using a lateral or a vertical condensation technique. We did not find a
statistical difference in apical inflammation between those roots filled
with a lateral or vertical gutta-percha technique. While the differences in
inflammation rates of Friedman et al. (20) and our study (67% versus
82%) are unlikely to be statistically significant (Table 2), our higher
inflammation rate may be explained by the fact that we replaced the
coronal microorganisms every month while in the Friedman study (20),
they were placed at the beginning of the experiment and not replaced.
We felt that replacing the microorganisms every month was important
because this would more accurately simulate a clinical situation with a
lost or leaky coronal restoration where the filling of the root canal is
continually challenged by new microorganisms. We are also confident
that our inflammation rates are not an aberration because of a small
number of teeth. There were 56 roots used in this experiment, which is
in fact the number that Friedman et al. (20) suggested because their
numbers were much smaller.
While our study cannot be absolutely compared to the Friedman
study (20) because the sealer type and placement method were different, both our and Friedman’s results are in accordance with what is
expected from a root canal filled with any gutta-percha method and
sealer type. Most importantly either 67% or 82% periapical inflammation for a gutta-percha filled root canal is totally unacceptable from a
material whose primary function is to resist microbial penetration.
In both studies the inflammation was mild. We feel that if we had
continued to provide fresh microorganisms coronally and waited longer
before sacrificing the animals that moderate or severe inflammation
would have been seen in some of the specimens making the difference
discernable with radiographic evaluation (Fig. 1).
The RMS is based on the same principles as adhesive restorations
and as such is a completely different concept from gutta-percha and
sealer. Gutta-percha and sealer rely on the sealer filling the gap between
the gutta-percha and the root wall. Whereas, the RMS uses a primer to
enhance bonding of the dual curable resin to the dentinal walls and then
the sealer bonds to the fully polymerized core material. Thus one block
is formed unlike the layers of gutta-percha and sealer.
The RMS as with the gutta-percha groups showed no statistical
difference between those groups filled with lateral or vertical techJOE — Volume 31, Number 2, February 2005
niques. However the incidence of apical periodontitis for the RMS was
significantly lower than the gutta-percha and sealer groups and was not
different from the negative control group. Thus, we deduce that the low
incidence of apical periodontitis in the roots filled with RMS is a result
of a resistance to microbial penetration. This we feel is primarily because of a superior seal of the material, although a possible antibacterial
effect of the material itself cannot be discounted. Future studies will
evaluate the possible antibacterial effect of this material. Although statistical analysis was not performed between the RMS groups in this study
and the gutta-percha with Kerr sealer groups placed with a lentulo spiral
instrument in the Friedman study (20), the results of this study are
clearly superior to that of Friedman study (Table 2).
Presently we are awaiting analysis of the roots in these dogs used to
assess entombment of remaining microorganisms in the root canal. We
feel that the results of this in vivo study in addition to the published in
vitro study justify a prospective human outcome study that is presently
ongoing at the Department of Endodontics, University of North Carolina.
Acknowledgment
This study was supported in part by the Endodontic Research
Grant of the American Association of Endodontists Foundation.
The authors thank Eric Simmons (Department of Oral Microbiology, University of North Carolina, Chapel Hill, NC) for his assistance in culturing the microbiological specimens.
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JOE — Volume 31, Number 2, February 2005