EFFECT OF COBALT-60 RADIATION ON RESPONSE TO
ENDODONTIC THERAPY IN MONKEYS
JOHN E. MATSON, DDS,*'$ SAMUEL s PATTLKSON, I)DS, MSD,*'§
ABDEL H. KAFKAWY,
BDS, MSD,*aIl NED R. HOKNBACK,
Response of teeth that had received therapeutic doses of Cobalt-60 radiation
to endodontic therapy were investigated in three monkeys. The results in-
dicated no appreciable effect of the irradiation on the response to root canal
treatment aside from reduction in osteoblastic activity.
Cancer 42:2581-2590, 1978.
R tion of radiation therapy of head and
neck malignancies. The lesions may appear
within a few months or may develop a
number of years later. They may progress to
the point of fracture of the crown and ex-
posure of the pulp with subsequent necrosis.x
Management of such teeth with infected
pulps is often a problem. Prophylactic anti-
biotic therapy followed by atraumatic extrac-
tion has generally been advocated,2 although
allowing the roots to exfoliate over an ex-
tended period has also been ~uggested.~ A few
have proposed endodontic therapy as an al-
ternative in selected case^.^'^'^ Two years after
irradiation therapy had been completed,
Cavallo4 did endodontic therapy on a man-
dibular molar in an area that had received
5100 rad of 250 Kv and Cobalt-60 radiation.
Radiographic examination six months later
indicated a decrease in the size of the periapi-
cal lesion of the involved tooth. The present
study investigated the response to endodontic
therapy of monkeys' teeth that had received
therapeutic doses of Cobalt-60 radiation.
ADIATION CARIES is a common complica-
Three young adult Macaca speciosa mon-
keys were used. Before each experimental
From the *Indiana University School of Dentistry
and the tIndiana University School of Medicine.
f Currently a Commander in the U. S. Navy.
0 Professor and Chairman, Department of Endodontics.
" Associate Professor, Department of Oral Diagnosis/
# Chairman and Professor of Radiation Therapy.
(r Associate Professor of Radiation 7 herdpy.
Address for reprints: Dr. Samuel S Patterson, Depart-
ment of Endodontics, Indiana University School of
Dentistry, Indianapolis, IN 46202.
Accepted for publication February 23, 1978.
procedure the animals were tranquilized by
intramuscular injection of 5 mg of phencycli-
dine hydrochloride,** and then anesthetized
by intravenous injection of sodium pento-
barbital?? in the dose of 22 mg/kg body weight.
Clinical and radiographic examination showed
that all animals had a full set of healthy
permanent teeth except for unerupted third
An alginatekl impression of the maxillary
arch of each animal was taken and stone casts
were made. Upon these casts quick cure
acrylic§§ stents were constructed which ex-
tended across the occlusal surfaces, filling the
palatal vault from the lingual of the anterior
teeth to the posterior of the second molar. To
help direct the Cobalt-60 beam so as to
irradiate the desired area, wire was cemented
along the midline of the stent, extending
about 22.5 cm beyond the anterior teeth. The
acrylic stent itself was designed to produce a
more homogenous distribution of the radia-
tion. Using a quick-cure acrylic tray, an
alginate impression of the muzzle of each
animal was taken from which a stone cast was
made. A matrix was placed upon the cast and
melted paraffin was poured in to form a block,
3.5 cm thick, which extended forward to the
muzzle of the animal for 2.5 cm, and laterally
for 4 cm from the midline. Like the acrylic
stent, this paraffin block was intended to pro-
duce a more homogenous distribution of the
** Sernylan, Bio-Ceutic Laboratories, Saint Joseph,
tt Nembutal Sodium, Abbott Laboratories, North
$$ Jeltrate, I>. D. Caulk Company, Milford, Delaware.
$8 Kerr Formtray, Kerr Manufacturing Co., Romulus,
0008-543)3178/1200/2581 $1.00 0 American Cancer Society
FIG. 3. Pallor of the labial mucosa 56 weeks after
irradiation. The irradiated side appears less vascular.
palatal stent and wax block were inserted and
the mouth was propped open. The Cobalt-60""
source was adjusted at 100 cm above the wax
block and the beam was collimated to cover the
target area on the left half of the block while
the right half was shielded with lead blocks
three inches thick (Fig. 1). Each animal was
then exposed to Cobalt-60 Source which had an
output of 48 rad per minute for a period of 9.8
minutes during each of the radiation therapy
sessions. The dose delivered at each session
was 470 rad, and the animals were irradiated
three times a week for a total of 20 treatments
over a period of seven weeks. The total given
dose at the surface of the wax bolus was 9408
rad and the tumor dose in the area of the root
apices was 6300 to 7000 rad, depending upon
the distance of the individual apices from the
surface of the wax block.
Five weeks after irradiation was completed,
teeth number 3, 5, 7, 10, 12 and 14 of each
animal were opened, the coronal pulps re-
moved and the remaining radicular portion of
the pulp macerated with a fine barbed broach
contaminated with adjacent saliva. These
teeth were then left open to the oral
environment to insure contamination and
were periodically examined radiographically
for the development of periapical lesions.
When none were apparent after six weeks, the
contaminants were sealed within the canals
with zinc oxyphosphate cement for four weeks
to enhance lesion formation.
FIG. 1. A monkey during a radiation therapy session.
rhe paraffin block over the left maxilla helped to produce
a more homogenous distribution of the radiation. The
right maxilla was shielded with a lead block. The wire
in the midline helped in directing the Cobalt-60 beam.
To minimize variation in responses to the
experimental procedures which might result
from the use of different animals, the left
maxilla of each animal in this study was
irradiated, while the right maxilla served as
controls. Before each irradiation session, the
FIG. 2. Epilation and edema of the left upper lip one
1 1 " Eldorado Cobalt-60 Teletherapy Unit, Atomic En-
ergy of Canada, Ltd., Ottawa, Canada.
CANCER December 1978
endodontic therapy, aside from reduced osteo-
blastic activity resulting in a high incidence
of fibrous healing.
It should be emphasized that the findings
of the present study cannot be directly extrap-
olated to man. The monkeys used were young
adults with healthy dentition, in contrast to
older patients who usually need radiation
therapy and who may have their dentition in
a poor state of repair. Furthermore, the major
salivary glands were not in the field of irradia-
tion, and as a result reduction of salivary flow
and dental caries did not subsequently de-
velop. In addition late complications of the
radiation therapy could possibly have been
masked by sacrifice of the animals. However
the encouraging results of the present study,
warrant further investigation in humans.
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