Dr. Vinit Shah
Junior Resident
Prosthodontics
FODS, KGMU
















PART - I
Introduction
Physical principles
Interaction of radiation and tissues
Fractionation
Brachytherapy
Indications for treatment of head and neck tumours
Use of prosthetic stents and splints during therapy
Radiation effects
Part - II
Dental management – dentulous patients
Osteoradionecrosis
Prosthetic management – edentulous patients
Implants in irradiated tissues
Irradiation of existing implants
Conclusion
John Beumer III, Tohomas A. Curtis, and Russel Nishimura:

Radiation therapy is defined as the therapeutic use of ionizing radiation.

Two categories of radiation ;
 Electromagnetic
 Particulate

Electromagnetic wave of wavelength less than 1 angstrom are called
photons.
They have neither mass nor charge. Measured in electron volt. eg xrays and gamma rays.


Particulate radiation have mass and are charged negatively (electrons),
positively ( protons, alpha particles) or are neutral (neutrons)





Radiation absorption by tissues
Biologic effects
Reoxygenation
Repopulation
Accelerated repopulation
Radiation absorption by tissue
Direct ionizing
Indirect Ionizing

When Charged particles have sufficient energy , they are
directly ionizing.
( pass through target matter, and disrupt the atomic
structure by producing chemical and biological changes).

Photons and neutrons (uncharged particle) are indirectly
ionizing .(give up their energy to produce fast moving
charged particles.)



The primary effect of radiation is confined to the
intranuclear structures such as DNA and mitotic apparatus.
Damage to intranuclear structures may be;
1. lethal
2. sublethal (may not be apparent until atleast one
cellular division is attempted).
If enough time passes between the sublethal event and
cellular division, the damage may be corrected, process
known as repair of sublethal damage.


The indirect action of photon beam on target tissues is
dependent on the level of oxygenation concept known as
reoxygenation.
Anoxic tissues - 3 times more resistant to radiation effects
oxygen+ organic free radicals = organic peroxides

This reaction leaves more hydroxyl free radical which can
then interact with target molecules that would otherwise
react with hydrogen to form inactive molecules of water.

The radiation effect on individual cells may vary according
to the position they occupies in the cell cycle at the time of
irradiation.

More vulnerable during G1 and in mitotic phase
Relatively radioresistant at the beginning and the end of
DNA synthesis.


Radiation given during these phases, increased cell killing,
known as redistribution.

In a given enough overall treatment time, cell in the
irradiated tissue can proliferate and repopulate known as
repopulation.

It has been observed that any cytotoxic agent, including
radiation, can trigger colonogenic surviving cells to divide
faster than before. This is called accelerated repopulation.

Estimated to occur about 4 weeks after the initiation of the
treatment.

Thus in order to keep pace with the more rapid growth of
tumor cell, a more rapid delivery of treatment may be
needed.

Biologically Equivalent Treatment Schedules

As dose increases, tissue changes become more profound
and irreversible  increased complications.
Important variables:
Number of fractions
Dose per fraction
Total dose
Time period

1.
2.
3.
4.

Radiation therapy is delivered in the series of treatment or
fractions.
“Conventional fractionation” (in US)




total dose - 6500 to 7200cGy
daily fractions -180-200cGy
period- 7weeks
given Monday through friday
Advantages:
 Allows regular reoxygenation of the tumor during the
course of treatment, making it more radiosensitive.

Offers radiation to effect more tumor cells during the
radiosensitive phase of their cell cycle.

Normal cell seems to recover more completely between
fractions from sublethal damage than do tumor cells.

Method of radiation treatment in which sealed radioactive
source is used to deliver the dose to a short distance by
interstitial(direct insertion into tissue),
intracavitary(placement within a cavity) or surface
application(molds).
(Boost for advanced tumors or primarily for small lesions)

Most commonly used radioisotope in head and neck regions
are iridium 192, cesium137 and radium 226.

Radiation sources may be form of needles, narrow tubes,
wires or small beads.
Advantages –

Rapid decrease in dose with distance from radiation
source (inverse square law).

Thus a high radiation dose can be given to the tumor
while sparing surrounding normal tissues.

Also dose rate is low relative to external beam therapy, it
can be considered a highly fractionated form of
irradiation

Thus continuous low dose irradiation tends to
synchronize the cell cycle and allows sublethal damage
repair.
Disadvantages –
 Inhomogeneity.

Requires the operator to have adequate technical and
conceptual skills to achieve good dose distribution.

Exposure to room personnel and to therapist specially with
the use of radium needles.

Decision regarding the use of radiation and/or surgery for
the control of primary lesion is a function of the location and
extent of the tumor.

carcinoma of nasopharynx, base of tongue, soft palate,
tonsillar fossa radiation therapy is the treatment of choice
because of surgical morbidity, difficult access, and high risk
of regional lymph node involvement.

Carcinoma of salivary gland and alveolar ridge should be
treated surgically followed by radiotherapy due to potential
for bony infiltration.

Early carcinoma of glottic larynx and tongue are equally well
controlled by radiation or surgery but radiation offer a
better functional result

Hard deeply infiltrated carcinoma of tongue are less likely to
be controlled by radiation. (Due to fixation to the vocal
cord)
( superficial / exophytic lesions have higher cure rate with
radiation than deeply infiltrated lesions)
These are used to optimize the delivery of radiation while
reducing the associated morbitity.
stents
splints
carriers
shields
positioners

Used to rearrange tissue topography within the radiation
field and displace normal tissues outside the radiation field.
Useful in;
 tongue and floor of
the mouth lesions.
 inferior positioning of tongue
and mandible enabling to lower the radiation field.
(sparing to parotid gland – more salivary output )





For dentulous patients.
Interocclusal stent prepared
that extends lingually from
both occlusal tables with a
flat plate ff acrylic resin.
Serves to depress the tongue
A hole is made in the
anterior horizontal segment
Serves as an orientation hole
for reproducible tongue
position.






For edentulous patients
Impressions
Interocclusal record at half/ two-thirds of maximum
opening
Mounting
Base plate wax attached to mandibular record base
to form the portion which will depress the tongue.
Occlusal index for comfort and stability




use to boost radiation over Small
superficial lesions (T1 or T2 in sizes)
in accessible locations in the oral
cavity.
The tumor site > adjacent vital
structures
useful in;
lesions like floor of mouth,
hard palate, soft palate, or
tongue.
(Spares vital adjacent tissues such
as mandible, teeth and salivary
gland.)




Helpful if patient is to receive
unilateral dose of radiation.
Useful in;
Buccal mucosa, skin and
alveolar ridge.
It has been reported that; 1
cm thickness of Cerrobend
alloy will prevent
transmission of 95%of an 18
Mev electron beam radiation
exposure to normal
structures.







Lipowitz metal or
cerrobend alloy is
commonly used to
shield.
Cerrobend Alloy:
Low fusing alloy
50% bismuth
26.7% lead
13.3% tin
10% cadmium

Use of a stent to flatten the lip and corner of the mouth,
thereby placing the entire lip in the same plane to deliver
uniform dosage of radiation.
Useful in;

treating skin lesions
associated with upper and lower lips.
Radioactive source
(cesium132 or iridium 192).
Preloaded


After loaded
Preloaded (RS position within prosthesis prior to carrier
insertion) medical staffs receives some exposure.
After loading technique, isotopes are threaded into the
hollow tubing after the carrier is in predesigned location
reduces the radiation exposure to medical staff.
Direct implantation of the radioactive source in the tumor.
useful in;
Lesion of the tongue and anterior floor of the mouth.


Used to position the source and also determine the proper
depth of insertion.
Once prosthesis is secured , tissue conditioning material is
flowed over the implants to maintain them in proper
position during the treatment period.

Irregular tissue = uneven radiation dose

A bolus is a tissue equivalent material placed directly onto
or into irregular tissue contours to produce a more
homogenous dose distribution.
commonly used materials are- saline, wax, acrylic resins.
This method optimizes the dosimetry by restoring tissue
density throughout the defect and ensures uniform
delivery of radiation and also protects friable healing tissue
such as skin graft.

Following orbital
exenteration and
maxillectomy

Irregular contours and air
spaces

Tissues at greatest risk of
radiation injury: skin
grafts, areas of thin
mucosa over bone and
brain tissue









Oral mucous membrane
Taste
Olfaction
Edema
Trismus
Salivary glands
Bone
Periodontium
Teeth
ORAL MUCOUS MEMBRANE Initially an erythema appears, epithelium becomes thin,
less keratinized, vascularity decreases and mucosa becomes
more fibrotic leading to extensive ulceration and
desquamation.




Pain and dysphagia resulting in weight loss .
Mucositis begins to appear
2-3 weeks after the start of therapy
and reaches peak toward the end of therapy.
Soft palate> hypopharynx> floor of the mouth > buccal
mucosa> base of the tongue> dorsum of tongue
Healing is rapid and usually complete in 2-3 weeks.

After therapy, changes in tissues in the field of therapy
predispose to tissue breakdown and delayed healing

Epithelium thin and less keratinized

Submucosa less vascular and fibrotic

These changes make fabrication and tolerance of prosthesis
difficult.

Taste bud shows signs of degeneration and atrophy at 1000
cGy and at cancericidal dose the architecture of taste bud is
completely obliterated.
Alteration in taste are discovered during the second week
and continue throughout the course of treatment.

Perception of bitter and acid flavors are more impaired than
salt and sweet.

Taste gradually return to normal levels after therapy is
completed.
Xerostomia  decreased recovery of taste


Since the olfactory epithelium is high in nasal passage and
not included within the radiation field, the sense of smell is
less affected.

Edema of tongue, buccal mucosa, submental and
submandibular area is occasionally clinically significant.

Apparent during the early postradiation period when scaring
and fibrosis are common
(Impairs patency of both lymphatic and venous channel
resulting in obstruction.)

Occasionally, edema reaches proportion which compromise
tongue mobility, impairs salivary control, make denture
utilization and speech articulation more difficult.





Most noticeable following
treatment of
nasopharyngeal, parotid,
palatal and nasal sinus
tumors in which TMJ and
muscles of mastication are
in radiation field.
Maximum mouth opening
may be reduced upto 1015mm.
Treatment
Exercise
Dynamic bite openers

Saliva changes in volume, viscosity, pH, inorganic and
organic constituents, predisposing to caries, periodontal
disease, impairment of taste acuity, poor tolerance of
prosthetic restoration, and difficulty in swallowing.

Bone is 1.8 times as dense as soft tissue , thus, it absorbs a
large proportion of radiation than does a comparable
volume of soft tissue.

Mandible absorbs more than maxilla because of increased
density, plus reduced vascularity accounts for increase
incident of osteoradionecrosis.



Periodontal ligament thickens and fibres become
disoriented.
Exhibit decreased cellularity and vascularity
cementum capacity for repair and regeneration is also
compromised.
Evidence in changes of crystalline structure of enamel,
dentin, or cementum following RT is unclear.
 Pulp shows decrease in vascular elements, with
accompanying fibrosis and atrophy.
 Pulpal response to infection, trauma, and various dental
procedures appears compromised.
Level as low as 2500 cGy can have marked effect on tooth
development.
Exposure

before calcification completion - tooth bud may be
damaged .

At later stage of development - may arrest growth.


Radiation field that include substantial portions of salivary
glands leads to significant changes in the composition of
oral flora.

Increase in the population of streptococcus mutans,
lactobacillus and actinomyces predisposing to dental caries.
Brown has reported upto 100 fold increase in fungal
populations.
Post therapy candidiasis of corner of mouth and beneath
prosthetic appliance is common.


















PART - I
Introduction
Physical principles
Interaction of radiation and tissues
Fractionation
Brachytherapy
Indications for treatment of head and neck tumours
Use of prosthetic stents and splints during therapy
Radiation effects
Part - II
Dental management – dentulous patients
Osteoradionecrosis
Prosthetic management – edentulous patients
Implants in irradiated tissues
Irradiation of existing implants
Conclusion





Criteria for pre-radiation ExtractionFollowing factors should be considered before making
decisions regarding extraction or retention of teeth.
They are divided into 2 categories:
.Dental Disease Factors - Condition of residual dentition
-Dental compliance of patient
Radiation Delivery Factors
-Urgency of treatment
-Mode of therapy
- Radiation fields
-Mandible versus maxilla
- Dose to bone

Dentition in optimal condition (high risk dental procedures
will not have to be performed in the post treatment period).

Extraction of all teeth with questionable prognosis before
radiation.

Periodontal status in healthy condition. (Furcation
involvement of mandibular molar teeth in the radiation field
is ground for preradiation extraction) .
Becomes difficult to maintain after treatment;
 reduced salivary output.
 Trismus,
 impaired motor functions,
 and surgical morbidities
(The patient’s oral hygiene at initial examination is often a
reliable indicator of future performance.)





Urgency of treatment
Mode of therapy
Radiation fields
Mandible versus maxilla
Dose to bone
 The status and behavior of tumor may preclude pre-radiation
dental extractions, since delay secondary
significantly compromise control of disease.
healing could
 The dentist, radiation therapist and patient must accept the
risk of complications and must attempt to maintain oral health
at optimum level. Control of tumor obviously is the most
important consideration.
 When external beam therapy is used in combination with
radioactive sources implanted( brachytherapy) - dose to
adjacent tissues is reduced and more confined.
 When external radiation is the sole mean of radiation
delivery - close scrutiny of the dentition is mandatory.
 Nasopharynx and posterior soft palate, (includes both parotid
glands) – xerostomia and postradiation caries.
 Lateral tongue and floor of mouth, (encompass the entire
body of mandible ) - osteoradionecrosis is high.
 Tonsillar, soft palate , or retromolar trigone carcinomas,
(major salivary glands and a significant portion of body of
mandible.) - caries and osteoradionecrosis is high in this
group.

Osteoradionecrosis in maxilla is rare - conservative approach
is justified.

Almost all osteoradionacrosis occur in mandible - more
aggressive approach is advocated, Particularly mandibular
molars (common site of osteoradionecrosis). when they are
in radiation beam.

For tissues treated to the high level of `tolerance, more
aggressive program of extracting teeth prior to therapy is
indicated .
The type of tumor will also dictate the radiation levels used
in treatment. Eg;- Hodgkin's disease -4000 to 4500 cGy,
-Squamous cell carcinoma of oral cavity-6500 to 8500cGy.


Extraction of impacted mandibular third molars prior to
radiation is not advocated for most patients. (create large
defects requiring prolonged periods for healing).

Patients with partially erupted mandibular third molars
represent a particularly difficult and perplexing problem
because of risk of pericoronities. Operculectomy is useful in
selected cases.

Factors to be observed for extraction in the preradiation
period for best results.
1.
Radical alveoectomy should be performed, edges of the
tissue flaps averted, and primary closure obtained .
2.
Teeth should be removed in segments. (When individual
teeth are extracted, closure is difficult to obtain without
excessive tension on tissue flaps).

3. Administration of antibiotics during the healing period Is
effective when extraction results in excessive trauma.

4. 7 to 10 day for adequate healing before therapy is begun.
Can be shortened or extended depending upon progress made
by the patient.


5. Periosteum is the predominant source of vascularity and all
efforts should be made to avoid mishandling it during surgical
procedure.

The risk of bone necrosis secondary to dental extractions in
postradiation period has been debated by many clinicians.


Following definitive course of radiation therapy -vascular
changes in bone and oral mucosa impair blood supply and
predispose to tissue breakdown and secondary infections of
bone and soft tissue.
Best indicator of potential risk is the radiation dose to
bone in the area of the dentition being considered for
removal.

If the dose to bone locally is below 5500cGy, conventional
therapies for tooth or teeth in question can be employed,
including root planning and curettage, crown lengthening
and root canal therapy. However, Periodontal flap surgery is
not recommended.

When tumor dose exceeds 6500cGy, options are dependant
upon the radiation treatment modality used.

If the dental infection involved the molar region adjacent to
implant in absence of exposed bone, dental extractions are
employed only as last resort.

Endodontic therapy is recommended in order to maintain
mucosal integrity.

If the infection is periodontal and/ or into the bifurcation area
following the root canal therapy, the crown can be amputated
, thereby providing access for oral hygiene to this area .

If the implant increases the dose in these regions above
5500cGy, hyperbaric oxygen maybe considered .

Difficulties;

Rubber dam isolation is complicated by minimal coronal tooth
structure and risk of tissue trauma and resultant bone
exposure.

Oropharyngeal reflexes compromised , translating into
greater risk for aspiration of files.

Trismus and small pulp canals make the access for
instrumentation and filling difficult.

Is not primarily an infectious process, it is exposure of bone
within radiation treatment volume of 3 months or longer in
duration.

It may progress to intractable pain and pathological fracture
of mandible, often accompanied by orocutaneous fistula and
requiring resection of major portion of mandible.
The dose to bone is probably the best predictor of risk .


In a study by Morrish, in
which dose to bone was
calculated on all patients,
mandibular bone necrosis
developed in 85% of
dentulous patients who
received 7500cGy or more
to bone.

None of the patients who
received
less
than
6500cGy to mandibular
bone develop necrosis.

Osteoradionecrosis associated with external beam;

Dose less than 6500cGy and localized exposure - local
irrigation and packing of idoform gauze, impregnated with
tincture of benzoin.

Dose to bone above 6500cGy and exposure extends beyond
the mucogingival junction, or in association with teeth hyperbaric oxygen combined with surgical sequestrectomy
should be considered.

If external beam dose to the bone is below 5500cGy,
conservative therapy are excellent,
Hyperbaric oxygen ;
2.4 atmospheres with 100%oxygen

Stimulates neovascular proliferation in marginally
necrotic tissues , enhances fibroblastic prolifiration,
enhances the bactericidal activity of white blood cells and
increases production of bone matrix.

Marx stated that hyperbaric oxygen is a valuable
therapeutic modality not only in treatment of
osteoradionecrosis but, also, in preventing
osteoradionecrosis.
Marx protocol for treatment of osteoradionecrosis;

Stage I- Osteoradinecrosis but without pathological
fracture, orocutaneous fistula or radiographic evidence of
bone resorption to the inferior border of mandible.
2.4 atmospheres, 100%oxygen for 90 minutes for 30
treatments.
End of 30 treatments
improvement
20 treatments
are added.
No clinical improvement
non- responder and advanced
to stage II
Stage II- Surgical sequestrectomy, wound closed primarily in
3 layers over a base of bleeding bone.
Additional 10 hyperbaric treatments
wound dehisces
non -responder and advanced to stage III.

Stage II Nonresponder with orocutaneous fistula,
pathologic fracture or radiographic evidence of bone
resorption to inferior border of mandible are considered
stage III patients.




Stage III- Nonvital mandibular bone are resected transorally
with the aid of tetracycline fluorescence under ultraviolet
light. External fixation of mandibular segment, orocutaneous
fistulae closed and soft tissue deficits restored with local or
distant flaps.
Another 10 hyperbaric treatments are given and the patient
is advanced to stage IIIR.
Stage IIIR- Ten weeks after resection, the mandible is
reconstructed with bone grafts , using transcutaneous
exposure. Mandibular fixation is achieved and maintained for
8 weeks.
10 hyperbaric treatments are given postoperatively.


Contraindications to Hyperbaric oxygen;
Persistent tumor

Optic neuritis

Active viral disease states

Untreated pneumothorax
Complications include barotrauma of ear, temporary
myopia and in rare instances pulmonary fibrosis .




Non neoplastic mucosal ulceration occurring in the
postradiation field and which does not expose bone. Occurs
most often following treatment with interstitial implants and
peroral cone modalities .
Most of these necrosis occurs within 1 year after completion
of radiation therapy.
Intense local discomfort is a clinical symptom that is
sometimes useful in differentiating this lesion from persistent
disease.
A tumor recurrence usually presents with irregular
indurated margins whereas soft tissue necrosis present with
regular , non indurated margins

If the radiation fields cover little of denture bearing surfaces
(eg; nasopharyngeal carcinoma ), dentures can be inserted
as soon as mucositis resolves.

Most prosthodontists advised the construction of dentures
be deferred for at least 1year after radiation therapy had
been completed.

The status of the residual ridge is an important clinical
factors to be carefully appraised.

Regular/ irregular mandibular ridge
Denture base should ensure distribution of pressure as
widely and as equally as possible.
Occlusal scheme should be to minimize lateral
movement of mandibular denture base.




Examination;
Information of site of the tumor, mode of therapy
employed, total dose ,dates of treatment, radiation fields,
tumor response and prognosis for disease control should
collected.
Oral examination,
Appearance of oral mucous membranes, scarring and
fibrosis at tumor site, degree of trismus, presence and
nature of lymphodema, and status of salivary function.





Impression;
Conventional border molding, using custom tray and
modeling plastic is advocated for making impression.
In xerostomia ,thin coating of petrolatum may be applied
over the soft modeling plastic to avoid sticking to dry mucosa.
Peripheral seal is virtually impossible to obtain in these
patients because of curtailment of salivary flow. Efforts should
be to gaining stability and support rather than retention
Edema of floor of mouth and tongue (radical neck
dissection), will limit the extent of the lingual flange.

vertical dimension;
Consideration for reduce vertical dimension of occlusion.
1.
Reducing the vertical dimension may limit the extent of
the forces applied to the supporting mucosa and bone
during a forceful closure.
2.
In patients with clinically significant trismus, entrance of
bolus is more easily accomplished by increasing the
interocclusal space.



Occlusal form;
Lingualised or monoplane occlusal schemes.
In arranging posterior teeth, careful attention should be
directed toward attaining a proper buccal horizontal overlap.
Some clinicians use only 3 posterior teeth, 1 bicuspid and
2 molars in order to avoid trauma to the posterior buccal
mucosa.


Delivery and post insertion;
Occlusal discrepancies caused by processing errors should
be eliminated prior to removing the dentures from the cast.
After removal any rough projections on tissue surface
should be smoothed..
Instructions concerning removal of prosthesis if soreness
develops, the necessity for periodic return visits, and initial
limited use of prosthesis are provided.

Irradiation predisposes changes in bone, skin, mucosa which
affect the predictability of Osseointegrated implants.

Careful consideration to risk of osteoradionecrosis

Osseointegration is impaired in bone that has received >
5000 cGy

Results in backscatter.

Dose is increased about 15% at 1mm from the implant

It is recommended that all abutments and superstructures
be removed prior to radiation.

Skin/mucosa closed over implant till healing is complete

The cancer patient who is to receive curative doses
of radiation to the head and neck presents an
interesting challenge to the dentist.

Dental management of the irradiated patient is a
serious undertaking since the standard of care has
an effect on the patient’s quality of life.