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.
COBALT-60 AND ENDODONTIC THERAPY
. Mntson et a[.
FIG. 4A. A non-
irradiated apex at 18
weeks after endodontic
treatment. Particles of
sealer and debris were
pushed beyond the
apex (A) and are asso-
ciated with an inflam-
matory reaction. Notice
the osteoblastic activity
and new bone formation
(H & E, original mag-
Endodontic therapy using generally ac- canals. The canals were irrigated with 4%
cepted aseptic techniques was started 15 weeks Chloramine T,## and dried with sterile
after irradiation had been completed (10 paper points. A cotton pellet dampened
weeks after the teeth were opened to induce with camphorated paramonochlorophenol
lesions). With the rubber dam in place, the
first treatment to each tooth was gross
debridment and determination of length of the Wisconsin.
## Chlorazine, Badger Pharmaceuticals, Cedarburg,
FIG. 4B. Higher
magnification of the
area enclosed within
the upper rectangle in
Fig. 4A showing osteo-
blastic activity and new
bone formation (Origi-
FIG. 4C. Higher
magnification of the
area enclosed within
the rectangle on the
right in Fig. 4A showing
with debris and particles
of sealer that were
pushed beyond the api-
cal foramen (Original
magnification, x 100).
FIG. 5. An irradiated apex (A) at 18 weeks
after endodontic treatment. Reduced osteo-
blastic activity resulted in fibrous healing (F)
(H & E, original magnification, X 100).
COBALT-60 AND ENDODONTIC THERAPY
Matson et al.
FIG. 6. A nonirradkated apex at 39 weeks
after endodontic treatment. The root canal
filling was overextended. Root resorption
is evident (large arrows). Particles of sealer
are dispersed in the adjacent connective
tissue (small arrows) (H & E, original mag-
(CMCP)lln was sealed in the pulp chamber with
zinc oxyphosphate cement.***
At the second session the canals were
opened and cultures were taken and in-
cubated in brain heart infusion broth with
.Ol% agar. The canals were further in-
strumented to the desired length and diameter
at this time with sterile instruments, irrigated
and sealed with CMCP as before. At the third
session, if the culture was negative, the canals
were lightly instrumented and a master gutta
percha cone was fitted and each canal was
filled with a combination of Kerr Tubli-
seal??? and laterally condensed gutta percha
cones. Excess gutta percha was removed from
the pulp chamber with a hot instrument. The
chamber and access opening were then
cleaned with a chloroform dampened cotton
CMCP, King’s Specialty Co., Fort Wayne, Indiana.
*** Flecks, Mizzy Inc., Clifton Forge, Virginia.
ttt Kerr Manufacturing Co., Romulus, Michigan.
pellet and air dried. The entire chamber and
access opening were filled with zinc oxyphos-
phate cement and the occlusion was adjusted.
Clinical and radiographic examinations
were done periodically. The monkeys were
sacrificed with an overdose of sodium pento-
barbital at 37, 58 and 75 weeks after
irradiation (18, 39 and 56 weeks after root
canal therapy was completed). Blocks of the
maxillae containing the teeth and their
supporting tissues were fixed in 10% formalin
and decalcified with 55% formic acid. Semiserial
paraffin sections 7 pm thick were prepared
and stained with hematoxylin and eosin.
Selected sections were stained with the Brown
and Brenn method for bacteria.
Clinically, at about the 3500 rad level the
skin on the irradiated side of the animal’s
muzzle became dry and scaly with pigment
change. This was followed within two weeks