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The effect of loss of molar occlusion upon the mandibular joint

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The effect of loss of molar occlusion upon the mandibular joint

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Content THE EFFECT OF LOSS OF MOLAR OCCLUSION
UPON THE MANDIBULAR JOINT
by
Lawrence Furstman, D.D.S.
A Thesis Presented to the
DEPARTMENT OF ANATOMY, SCHOOL OF MEDICINE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(Anatomy)
August 1964
UMI Number: EP54675
All rights reserved
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UNIVERSITY OF SOUTHERN CALIFORNIA
GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANGELES 7, CALIFORNIA
T h is thesis, w ritte n by
L a w r e n c e L. F u r s t m a n
u nd e r the d ire c tio n o f h..Ï3.....Thesis C om m itte e,
and a p p ro v e d by a ll its m em bers, has been p re
sented to and accepted by the D e a n o f the
G ra d u a te S cho ol, in p a r tia l fu lfillm e n t o f re
quirem ents f o r the degree o f
M a s t e r of S c ie n c e
Dean
Da/g......
THESIS COMMITTEE^
^ ...
I . Chmrman
' - ' ) -
/
6-61— 2 M — HI
ACKNOWLEDGMENTS
I wish to express my slncerest thanks to Dr. Paul
R. Patek, chairman of the Department of Anatomy, for
accepting me as a graduate student and for affording me the
opportunity of working in his department.
Words cannot adequately express my feelings toward
Dr. Sol Bernick who has proven himself to be a stimulating
teacher, an exciting Investigator and a sincere friend.
The help of Dr. W. J. Paule who read the original
manuscript and gave me many valuable suggestions Is deeply
appreciated.
A final word of thanks must be extended to Mr.
Lloyd Matlofsky of the photographic department of the Los
Angeles County General Hospital who took the many photo
micrographs that were required.
Without the constant friendly help and encourage
ment of these men, this work would not have been possible.
11
TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS .......................... il
LIST OF TABLES.......................... iv
INTRODUCTION ............................ 1
REVIEW OF THE LITERATURE............... 3
MATERIALS AND METHODS ................... 16
OBSERVATIONS (Normal) ................... 21
OBSERVATIONS (Experimental) ............. 31
DISCUSSION.............................. 44
SUMMARY.................................. 55
CONCLUSIONS.............................. 58
BIBLIOGRAPHY ............................ 60
APPENDIX................................ 65
111
LIST OF TABLES
Table Page
1, Age of Normal Animals......... 17
2. Experimental Procedures .... 18
IV
INTRODUCTION
Clinicians and research workers in all phases of
Dentistry have become increasingly aware of the many prob
lems associated with the Human Temporomandibular Joint.
Pain either direct or reflected in nature, plus
other associated problems such as muscle spasm, grating and
clicking in the joint cavity or subluxation of the joint,
comprise a large group of varied clinical entities. These
symptoms have been classified loosely as the "Temporoman
dibular joint pain dysfunction syndrome."
While the causative factors that create pain, dis
comfort and other problems in this area are not completely
understood, a strong suspicion is being evidenced by the
Dental Profession that the occlusion of the teeth is a
critically responsible factor.
These various joint problems are being treated
experimentally with many different approaches that vary
from the mechanical correction of the dental articulation
to the use of sclerosing solutions injected directly into
the joint cavity.
Considerable success in the relief of pain and
associated symptoms has been found in empiric treatment
2
that first places the joint at rest by means of splinting,
followed by restorations that correct the occlusion of the
teeth and establishes their proper articulation.
If incorrect occlusion can truly create these prob
lems, it follows that a malocclusion of the teeth, or a
change from the correct or normal occlusion regardless of
the cause, or a complete loss of occlusion, can also create
the same problems.
One can postulate further that if the conditions
outlined above are correct, it should be possible to create
and demonstrate morphologic changes in one or more of the
component parts of the mandibular joint, namely the con
dyle, the articular disc or the joint fossa upon an experi
mental basis.
This investigation is to determine whether the
removal of selected quadrants of molar teeth can create a
morphologic change in the temporomandibular joint that
could be considered a causative factor in the temporoman
dibular joint pain dysfunction syndrome.
REVIEW OF THE LITERATURE
A great many studies on experimentally created
problems In the Temporomandibular Joint area are found in
the literature. These procedures range in method from
dietary control (Barber, 1963) to orthodontic tooth move
ment (Breitner, 1940); or from the severing of one or more
of the muscles of mastication (Horwitz, 1951) to unilateral
or bilateral condylectomy (Hayes, 1961). Very few of these
investigations included the microscopic examination of the
involved structures. For the most part these studies were
limited in scope to those of a gross anatomic or radio-
graphic nature.
The study of the experimental changes in this
investigation was histologic in nature ; therefore studies
of a similar character will be primarily considered in this
review. However, many investigators have studied gross
changes in the mandible and in the joint area that are of
considerable interest. Great care had to be exercised in
their interpretations of gross changes in experimental
animals as small as a rat or a mouse because of possibili
ties of error. Even though these studies are not pertinent
to the histologic evaluation that is presented here, some
4
of these investigations should be considered because of
their importance in an over-a11 evaluation of the problem.
As an example of this type approach we have the
work of Baker (1941) who demonstrated changes in skull
growth of the Rodent, Carnivore and Omnivore by the removal
of various dental formative organs. Following removal of
the maxillary molars he demonstrated considerable deformity
in the mandible after a nine-month period.
Watts and Williams (1951) made an extremely good
gross study of the rat following strict dietary control.
Their work utilized 60 young growing rats. Thirty were
given a vigorous diet and 30 were kept on a soft diet.
In addition they also studied a group of 38 old rats.
Nineteen were given a vigorous diet and 19 were kept on a
soft diet. Both the young and old groups were kept under
strict dietary control for four months and were then sacri
ficed. They demonstrated increased thickness of supporting
bone about the first molars, increased wear on the teeth in
the vigorous diet groups and an increase in the weight,
volume, density and area of the buccal aspect of the
mandible plus increased width of the maxilla in the vigor
ous diet group. Their conclusion was that "function as
influenced by differences in the physical consistency of
food is an important factor in the growth and development
of the Maxilla and Mandible of the rat."
Horwitz and Shapiro (1951) removed the Temporalis
5
muscle In rats and found that modifications of the outer
form and the internal architecture of the mandible resulted
from the removal of the temporalis muscle in one-month-old
rats. Gross examination showed no evidence of a Coronoid
process of the Mandible, the normal insertion site of the
temporalis muscle. Changes were also noted in the form and
direction of the neck and head of the condyle on the
operated side. Modifications of the internal architecture
were revealed by means of Grenz ray examination.
Sarnat (1957) removed the mandibular condyle in the
Macaca Rhesus monkey in order to demonstrate changes in
Facial and Neurocrania1 growth. In his opinion "mandibular
growth can be considered to be a leading component of
facial growth." In addition he felt that "the condyle is
the most active growth center of the mandible. It is the
pacemaker and organizer of mandibular growth." Following
removal of the mandibular condyle he demonstrated that not
only was there a severe lack of growth of the mandible on
the operated side but also that facial and neurocranial
bone complexes were less developed on the operated side.
Consequently there was a marked asymmetry of the skull in
all of its aspects.
Hayes (1961) performed unilateral condylectomies on
young rats and made gross studies plus X-ray tracings. In
addition he did unilateral condylectomies in two animals
and left the resected condyles in situ. He also created
6
simulated operative trauma to the condyle by surgical
trauma to the masseter muscle. His findings were that
unilateral condylectomy resulted in a modification of the
mandibular fossa. The fossa seems to be positioned ante
riorly and inferiorly, and also seems to be shallower and
flatter. The slope of the long axis changes from downward
and backward to downward and forward. This, according to
Hayes, indicates the importance of function in the forma
tion of the mandibular fossa.
Barber, Green and Cox (1963) studied the changes in
the condyle of rats following certain diets. They fed rats
whole pellets and ground pellets of food with the same
nutritional values. Mandibular length and weight was sig
nificantly greater after eighteen weeks if the animals were
given whole pellets of food that required vigorous chewing.
Differences in the condylar area were highly significant,
the areas of the whole pellet group being larger. Their
results indicated that physical diet consistency affected
condylar growth of the mandibular condyle of the rat.
In 1941 Cabrini and Erasquin published the first
comprehensive study on the development of the rat mandib
ular joint. Because the articulating surface of the
squamosal bone consists of two levels, they very carefully
adjusted the dentition of their animals after sacrifice.
By doing this the joint could be studied while at rest, in
molar occlusion or with the incisors in function.
7
The year 1946 saw the publication by Collins and
his co-workers of a normal study of the development of the
mandibular condyle of the female rat. Their work was the
preface to a group of studies concerning the effects of
various vitamin deficiencies on this animal, as well as a
study of the effects of thyroxin upon the condyles of hypo-
physectomized animals. Generally, they agreed in their
concept of the normal development of the mandibular articu
lation with the findings of Cabrini and Erasquin.
Collins and his co-workers (1946) did, however,
describe a cartilage-like mass between the fibrous tissue
of the squamosal articulating surface and the bone itself.
Their feeling was that this mass never ossified, and there
fore the fossa could remodel itself throughout life in
response to function.
In the hypophysectomized rats they found that
chondrogenesis was considerably slowed within four days
after the operation, and that the transformations following
this operation were similar to those occurring in aging
rats. They also found that growth processes in the
senescent mandibular joints of hypophysectomized rats may
be restored to juvenile vigor by the administration of
pituitary growth hormone.
Becks and Evans created an atlas of the skeletal
development of the rat in 1953. This was a complete devel
opmental study rather than a study of condylar development
8
only, as was done for the female rat in 1946 by the same
individuals in association with Collins and Simpson.
Weinman (1946) also reported changes in the mandib
ular condyle of the rat. He first studied the changes in
experimental rickets and in experimental hyperparathyroid
ism. He found that lack of calcification of the condylar
growth cartilage inhibits its resorption during "endochon
dral” growth. The normally thin cap of cartilage is thick
ened to such a degree that the entire condyle seems to
consist of cartilage. The bone deposited during experi
mental rickets does not calcify and therefore is resistant
to resorption. Lack of modeling resorption at the mandib
ular neck causes it to be disfigured to a plump, club-
shaped bone. If injections of Parathyroid hormone are
given for a prolonged period, a process of healing sets in.
His findings on the rachitic mandibular condyle are, in
principle, identical with those of the rachitic epiphyseal
or articular cartilages.
Levy (1948) made a study of the normal development
of the mandibular joint of the mouse. His work encompassed
a range from 1 to 540 days and was to establish a standard
on which to base future studies of the mandibular joint in
mice. It is interesting to note that Levy states that the
gross anatomic structure of the mandibular joint of the
mouse is identical to that of the rat, with the exception
of the size of the structure and normal age changes. One
9
other point he emphasizes is that the cranial portion of
the joint shows no evidence of the cartilage-like tissue as
described by Collins.
Following his establishment of a standard, Levy
(1949) next studied the effect of pantothenic acid defi
ciency on the mandibular joint of the mouse. He found that
mice deficient in pantothenic acid showed an inhibition of
proliferation and a hypertrophy of the growing cartilage of
the condyle. Restoration of the animal to an adequate diet
proved that the change was not permanent. Following this
procedure, chondrogenesis was renewed.
Levy (1949) also reported on the effect of ribo
flavin deficiency on the growth of the mandibular condyle
of the mouse. His findings were that the growth cartilage
of the condyle became markedly narrower than normal. These
changes, however, were reversible, and with the refeeding
of adequate diets the condylar cartilage assumed its normal
width.
Bhaskar (1953) studied the growth pattern of the
rat mandible from thirteen days insemination age to thirty
days after birth. In this study he based his investiga
tions upon 41 "ia" mutant rats and 43 heterozygous litter-
mates. The "ia" mutant strain is characterized by the
absence of bone resorption, so that the appositional growth
pattern is easily determined in the bones of "ia" animals.
Structures of the "ia" rats and their normal littermate
10
controls could be compared. This comparison revealed the
areas and extent of bone resorption during normal develop
ment . One of Bhaskar*s determinations was that the direc
tional proliferation of the condylar cartilage plays an
important role not only in the growth, but also in the
determination of the final shape of the mandible.
In another study Bhaskar (1953) examined the role
of Meckel* s cartilage in the development of the rat
mandible. He determined that the articulation between the
squamosal bone and the mandible was fully established by
twenty-one days insemination age.
Cunat, Bhaskar and Weinman (1956) studied the
development of the Squamoso-mandibular articulation in the
rat. Once again normal and "ia** mutant rats were used, and
the scope of the study was from sixteen days of insemina
tion age until thirty days after birth. Important among
their findings was the structure of the articular disc and
the time of its formation. The superior slit forms at the
nineteenth day of insemination age while the inferior or
mandibular cleft is not completely formed until after
birth. They carefully described the apposition and resorp
tion pattern in the articular fossa.
In addition they described the growth process tak
ing place in the mandibular condyle both before and after
birth. They described the articular fossa as being formed
by the zygomatic process and the inferior half of the
11
squama of the squamosal bone. The articulation between the
rat mandible and the skull was discussed from the stand
point of nomenclature. Some authorities refer to this
articulation as the mandibular joint or as the temporo-
maxillary joint. Since the temporal bone does not exist in
the rat, and since the mandibular condyle articulates with
the zygomatic process and the squama of the squamosal bone,
these authors agree with Collins and Becks and feel that
the joint should be referred to as the Squamoso-mandibular
articulation.
The year 1936 saw one of the first studies on the
effect of extraction of rat molars reported by Anderson,
Smith, Arnim and Orten. These investigators raised the
question of whether certain changes in bone could be
related to the extraction of teeth. Since these changes
were only seen in rats that had been subjected to extrac
tion procedures, the removal of teeth was held responsible
for the occurrence of the changes. Their study emphasizes
the far-reaching effects of alteration in masticatory
stress and strain.
Breitner (1940) performed Orthodontic tooth move
ment on monkeys; then after sacrifice he did histologic
studies on various areas. These areas included the Tem
poromandibular Joint. Following four different orthodontic
procedures, he concluded that changes take place in the
mandibular fossa and the head of the condyle following the
12
application of orthodontic forces to the teeth. His find
ings were documented with histologic sections that showed
either deposition or resorption of bone in the articular
fossa or the condyle in direct relationship to the pull
force that had been applied to the teeth.
Avant, Averill and Hahn (1952) were interested in
changes in the Mandibular joints of rats caused by altera
tions in the intermaxillary relationship of the teeth.
They extracted various molar teeth or ground the teeth to
relieve them from their proper occlusal contact. This was
done in various combinations. They demonstrated disturb
ances in the anterior portion of the condyle that consisted
of replacement fibrosis of subchondral bone, hemopoietic
marrow spaces and cartilage cap, atrophy and rarefaction of
condylar cartilage and cessation of bone growth. Morpho
logic changes were evidenced by flattening of the condylar
head and loosening and fraying of the articular disc.
Histopathology of the component tissues of the glenoid
fossa was limited. The degree of pathologic disturbances
of the joint were in direct relation to the severity of the
intermaxillary disturbance.
Applebaum and Levy (1954) created changes in the
mandibular condyle of mice by using cast gold bite plates.
They observed that the individual animals that had worn
bite plates lost up to 25 per cent of their body weight
during the experiment. From this fact the authors felt
13
that the form of the developing condyle was influenced not
so much by the mechanical effect of a bite plate as by
malnutrition resulting from impaired mastication.
Baume, Haupl and Stellmach (1959) reported on the
growth and transformation of the Temporomandibular Joint in
an orthopedically treated case of Pierre Robins syndrome.
Since this child died two months following the correction,
they were able to make histologic studies of the joint.
They claim to show a forward displacement of the articular
fossa as evidenced by coordinated processes of bone deposi
tion and resorption. The condylar head showed growth
activity in the vertical and horizontal direction exceeding
the normal rate. Their histologic findings are identical
with those seen by Breitner in the monkey.
Baume and Derichsweiler (1961) experimented with
bite blocks in monkeys in order to determine if the con
dylar growth center was responsive to orthodontic therapy.
They contend that the condylar cartilage responds to func
tional therapy. They further state that transformation of
the joint structures of the Temporal Bone remained at
microscopic levels.
Bavetta, Bernick and associates (1954) studied the
effect of tryptophane deficiency on the jaws of rats. In
this study they found a retardation of osteogenesis and
chondrogenesis with a subsequent flattening of the condyle
after seven weeks of tryptophane deficiency. The inner
14
cartilaginous layer at the condylar head was only two or
three cells thick with no hypertrophic cartilage cells
present. Also no bony spicules were seen in the subchon
dral area.
Bavetta and Bernick (1935) investigated the effect
of lysine deficiency on dental structures and again found a
marked narrowing of the cartilage layers in the head of the
condyle as well as an absence of trabeculae in the subcon-
dral region. They found that retardation and inhibition of
growth was similar to that found in the epiphyseal plate.
These degenerative changes, however, were reversible.
A further study by Bavetta, Bernick and Ershoff
(1958) considered the effect of growth hormone on the bone
and peridontium of Vitamin A depleted rats. Here once
again it was demonstrated that the condylar cartilage is a
barometer for vitamin deficiencies. In the animals with
Vitamin A free diet, plus saline injections, the cartilag
inous zone was narrowed with a loss of trabeculae and
myeloid elements. The fibrous capsule of the condyle
itself was thicker than is seen normally. With the same
diet, supplemented by growth hormone in place of the saline
injection, a wider cartilaginous layer was seen. In the
animals fed a Vitamin A adequate diet, there was a wider
cartilaginous layer and denser bony structure. The bony
trabeculae were undergoing enlargement as indicated by
osteogenic tissue occupying the marrow spaces. Fat cells
15
were being replaced by myeloid elements.
Cimasoni and Becks (1963) studied the growth of the
Rat mandible as related to function. Their method was to
remove the upper right quadrants of molar teeth from three
groups of animals: Normals, hypophysectomized animals that
were receiving injections of growth hormone, and hypo
physectomized animals. In general, the form of the
mandible was not affected. The condylar cartilage showed
no significant difference between the functioning and non-
functioning side. They did demonstrate that injection of
growth hormone in the hypophysectomized animals created
marked changes.
Later in 1963, Cimasoni reported on Histopathology
of the Temporomandibular Joint following bilateral extrac
tion of molars in the rat. Two quadrants of upper molars
were extracted and the animals were kept 200, 270 and 300
days before sacrifice. Group 1 (200 days) showed no abnor
malities. Group 2 (270 days) and Group 3 (300 days) demon
strated lesions consisting of Perichondrocytal calcifica
tions in the Glenoid Fossa, necrosis of cartilage of the
fossa, structural alteration of the meniscus and pannus.
MATERIALS AND METHODS
One hundred eleven male rats of the Holtzman strain
were used in this investigation. Animals were fed a stock
diet with water ad libitum. Young litters were kept with
the mother before weaning.
Seventy-five animals in fifteen arbitrarily
selected age groupings, ranging from one day to two years,
were used to determine normal changes due to aging. Cer
tain of these age groups were identical with those of
post-experimental groups and could thus be used as litter
mate controls. Five animals per age group were studied
(see Table 1).
Thirty-six animals, age 2 months, comprised the
experimental material. These animals were divided into six
groups of six animals. Each group underwent a different
operative surgical procedure (see Table 2).
Two animals of each group were sacrificed at two-,
four- and six-month intervals following operative surgical
procedures.
Operative equipment was constructed after the
methods of Maurice and Schour (1955).
Animals were anesthetized with Sodium Pentothal;
16
17
TABLE 1
AGE OF NORMAL ANIMALS
Group
1 1 day
Group
6 40 days
Group
11 10 months
2 7 days 7 2 months 12 12 months
3 14 days 8 4 months 13 16 months
4 21 days 9 6 months 14 20 months
5 30 days 10 8 months 15 24 months
18
TABLE 2
EXPERIMENTAL PROCEDURES
Group 1.
Group 2.
Group 3.
Group 4.
Group 5.
Group 6.
Upper right molar quadrant extracted.
Lower right molar quadrant extracted.
Upper right and left molars quadrants extracted.
Upper right and lower left molar quadrants
extracted.
Upper right and lower right molar quadrants
extracted.
All four molar quadrants extracted.
Each group contained 6 animals, divided into sub
groups A, B and C of 2 animals each.
surgery
surgery
surgery
Sub-group A was sacrificed at 2 months after
Sub-group B was sacrificed at 4 months after
Sub-group C was sacrificed at 6 months after
Two animals. Group 6 C, lived 5-1/2 months post
operative ly but were lost before the correct sacrifice
date.
All other animals survived until sacrificed.
19
0.1 c.c. per 100 grams of body weight was injected intra-
peritoneally. Following extraction of the selected quad
rants of molar teeth, each animal was given 50,000 units of
penicillin by intra-peritoneal injection. Metrazol, 0.1
c.c. per 100 grams of body weight, was injected intra-
peritoneally as an immediate post-operative stimulant to
dispel anesthetic effects as quickly as possible. Sodium
Pentothal affects the respiratory center, and it was felt
that this procedure would help prevent post-operative cage
deaths from pneumonia.
Tissues of all animals, both control and experi
mental, were prepared in the same manner. Following
sacrifice, the heads and jaws of all animals were fixed in
acetic acid, alcohol, formalin fixative. After fixation,
all heads and jaws were split mid-sagitally.
Lateral and ventral radiographs were taken of each
lateral half of each head to determine normal findings and
whether the operative surgical procedures would show gross
radiographic changes in the condylar area.
Following X-ray procedures, all heads and jaws were
decalcified in 10 per cent nitric acid in 10 per cent
formalin. All material was then processed in the usual
manner for embedding in nitrocellulose. Right and left
lateral halves were segregated and processed independently.
All tissues were sectioned in the coronal plane at a thick
ness of from 22-24 miera.
20
Alternate cut sections were stained with Haema-
toxylln and TriosIn^ Mallory’s Connective Tissue Stain,
Alclan Blue or with Periodic Acid Schlff counter-stained
with Haematoxylln. Sections were then mounted for micro
scopic examination.
OBSERVATIONS
The No rma 1 An ima 1
1 Day Old
The squamosal bone is not completely formed over
the superior surface of the joint cavity. Two different
centers of ossification are seen, one on the medial aspect
that Is arising from the Inferior half of the squama of the
squamosal bone, and the second observed on the lateral
aspect that is arising from the zygomatic process of the
same bone. Bony spicules from both lateral and medial
centers of ossification are oriented toward each other
(Fig. 1).
The articular disc consists of cellular connective
tissue. The superior or squamosal compartment of the joint
cavity Is completely formed; however, the Inferior or
mandibular compartment Is still not complete at this
period. Cleft formation has started on the lateral sur
face, but the articular disc Is still attached to the
superior medial aspect of the condyle.
The condyle Is a well defined oval mass of embry
onic cartilage (Fig. 1). The long axis of this oval
cartilaginous mass Is oriented In a superior-inferior
21
22
direction with a lateral tip of the long axis of about 10
degrees at the superior aspect. A thick fibrous cover
encases the entire condyle. Evidence of bone formation Is
seen along the Inferior border of the cartilaginous mass.
Bone can be followed superiorly on both the medial and
lateral surfaces of the condyle for approximately two
thirds the superior-Inferior height. The earliest bone
formation was on the lateral surface. The bony development
In this area Is further advanced than on the Inferior or
medial surfaces. All bone formation Is Immediately sub
jacent to the fibrous tissue that encases the condyle.
7 Days Old
Bone formation has been rapid In the squamosal por
tion so that the medial and lateral centers of ossification
have now united and the superior portion of the joint Is
now completely formed. The squamosal portion of the joint
now completely covers the articular disc and the condyle.
The Inferior or joint surface of this bone Is covered with
embryonic fibrous connective tissue (Fig. 2).
The articular disc is thick and Is composed of
embryonic connective tissue. Cleft formation has been
completed and both compartments of the joint cavity are
formed.
The condyle has not changed In shape and Is still
covered by fibrous connective tissue. The embryonic
23
cartilage at the superior aspect of the condyle shows aging
as you pass Inferiorly. First signs of endochondral bone
formation are seen.
14 Days Old
The squamosal bone Is now well formed and the
surface forming the superior portion of the joint cavity
Is covered with fibrous connective tissue.
The articular disc Is still thick but Is now becom
ing fibrous in character.
The shape of the condyle Is unchanged but the
fibrous covering along the peripheral surface Is becoming
thinner. More endochondral bone Is seen In the Inferior
one third of the condyle (Fig. 3).
21 Days Old
The squamosal bone is now well calcified and large
marrow spaces are seen. The articular surface is covered
with dense fibrous connective tissue that Is considerably
thicker than was seen previously.
The articular disc is composed of embryonic connec
tive tissue but Is becoming fibrous In character.
The condyle Is now changed In shape (Fig. 4). It
is becoming more flattened superiorly and Is slightly
broader In this area. The cartilage at the superior aspect
of the condyle now forms a cap and Is divided Into three
zones :
24
1. Fibrous connective tissue.
2. Embryonic cartilage.
3. Older cartilage.
Next, Inferlorly endochondral bone Is seen. This
bone now shows large marrow spaces. A space appears
between the older cartilage and the bone Itself. The
endochondral bone formation extends to the superior one
fifth of the condyle. The superior portion of the condyle
Is tilting laterally. Attachment of the external pterygoid
muscle Is seen. The attachment of the squamoso-mandibular
ligament Is seen on the lateral aspect of the condyle.
30 Days Old
The squamosal bone Is now well formed and calcified
and shows large marrow spaces. The articular surface Is
covered with dense fibrous connective tissue (Fig. 5).
The cellular elements of the articular disc are
still primarily embryonic In character. Fibers of the
External Pterygoid muscle are seen entering the disc on its
medial aspect.
The condyle Is now covered with a thin layer of
dense fibrous connective tissue. The cartilaginous layer
or cap Is divided Into three zones :
1. Embryonic cartilage.
2. Older cartilage.
3. Vacuolated cartilage cells just superior to the
endochondral bone.
25
Bony lamellae in the condyle run in a superior-
inferior direction In a fairly parallel pattern. Large
marrow spaces are seen between the bony trabeculae.
40 Days Old
The squamosal bone Is considerably denser than
before and the articular surface Is covered by a thin layer
of connective tissue. This fibrous connective tissue on
the articular surface of the squamosal bone shows an
Increase In thickness when compared to younger specimens.
Immediately above this tissue Is a layer of osteoid bone
(Fig. 6).
The articular disc Is now not so embryonic In
character. It Is becoming fibrous, with the long axis of
the fibers being oriented In a meslo-lateral direction.
The condyle Is covered with a thin layer of fibrous
connective tissue with a cartilaginous layer Immediately
subjacent. The cartilaginous cap of the condyle Is now
considerably thinner than was seen In younger animals.
Vacuolated cartilage cells are now only two deep just above
the bone formation. Inferior to the cartilaginous layer Is
an Inner bony trabecular core that comprises the remainder
of the condyle. Bone formation Is advanced and the marrow
spaces are filled.
26
2 Months Old
The squamosal bone is well calcified. Marrow
spaces are filled with Hemopoietic marrow. The articular
surface Is lined with dense fibrous connective tissue
(Fig. 7).
The articular disc Is now composed of dense fibrous
connective tissue and has assumed Its characteristic
shape--thin In the center. Increasing In thickness as the
peripheral regions are reached.
The condyle has flattened medio-laterally and has
assumed Its mature morphology. Zoning In the cartilaginous
area Is quite definite :
1. Dense fibrous connective tissue.
2. Embryonic cartilage.
3. Older cartilage.
4. Vacuolated cartilage cells.
Infiltration of layer 4 by blood vessels Is seen as
well as the subsequent destruction of layer 4. Numerous
bone lamellae are seen running parallel to the long axis of
the condyle (Fig. 7).
4 Months Old
The squamosal bone is very dense and compact;
otherwise it remains unchanged. Fewer marrow spaces are
seen.
The articular disc is composed of a thin layer of
27
dense fibrous connective tissue.
The condyle is covered by dense fibrous connective
tissue. The cartilaginous layers are becoming indistinct
as compared to the two-month animal (Fig. 14). (Compare
with Fig. 7.) Fibrous connective tissue and embryonic
cartilage comprise the first two layers, but the older
cartilage and the vacuolated layer seem to be combined.
The vacuolated layer Is less distinct and the cells are
smaller. The whole cartilage cap Is thinner. Lamellae are
quite dense and large marrow spaces are seen. Bone forma
tion Is well advanced and Is considerably higher than has
been seen previously. The entire condyle Is more rounded
on Its superior aspect and Is considerably narrower at the
neck (Fig. 14).
6 Months Old
The squamosal bone Is quite dense with fewer marrow
spaces. The osteoid border on the Inferior surface Is
Increased In thickness.
The articular disc Is unchanged.
The condyle Is now high and rounded. The cartilag
inous cap extends over the periphery from neck to neck.
This cap of cartilage Is thin and Is similar to that seen
In the four-month animal. The subjacent bony trabeculae
are larger and denser and few marrow spaces are seen
(Fig. 8).
28
The primary differences seen in this age group as
compared to the four-month group are due to the normal
aging process.
8 Months Old
With the exception of denser bone in the squamosal
area and in the condyle, there Is practically no change.
The fibrous connective tissue Is slightly thicker on the
articular surface of the squamosal bone and osteoid bone Is
seen Immediately superior to this tissue.
The older cartilage cells In the third layer of the
cartilage cap are now arranged In rows at right angles to
the surface of the condyle (Fig. 9).
10 Months Old
The squamosal bone and the articular disc are
unchanged.
The cartilaginous cap of the condyle Is much
thinner and considerable spacing Is seen between the
vacuolated cells. The bone of the condyle Is quite dense
with fewer marrow spaces (Fig. 10).
12 Months Old
The cartilaginous cap of the condyle Is now con
siderably thinner on the peripheral areas. The squamosal
bone and articular disc are unchanged.
29
16 Months Old
No changes are seen In the squamosal bone or the
articular disc.
The condyle now consists of solid bone. This bone
is sealed off from the cartilage In the condyle.
20 Months Old
No changes are seen (Fig. 11) .
24 Months Old
No changes are seen.
Summary of Findings In the Normal Animal
The growth and transformation of the mandibular
joint of the normal rat from one day through two years of
life has been described. Marked changes occur In the
articular fossa, the interartlcular soft tissue and the
condyle.
The bone forming the fossa is formed primarily from
intra-membranous ossification. A layer of osteoid tissue
is found between the compact bone of the squamosa and the
fibrous connective tissue that lines the articular cavity.
The synovial membranes and the articular disc
become more fibrous and less cellular with advancing age.
At birth the mandibular condyle is composed
entirely of hyaline cartilage. This cartilage continues
to grow but is also being eroded by endochondral bone
30
formation from the center of ossification. By twenty-one
days, the cartilage cap has become reduced In thickness to
300 mlcra. The cartilage can be differentiated Into three
different zones: (1) embryonic cartilage, (2) older
cartilage, and (3) vacuolated cartilage just superior to
the endochondral bone formation. In older animals the
zones of cartilage other than the embryonic zone disappear
or become calcified. A thin remnant of the cartilaginous
cap that measures 90 mlcra can be seen In the oldest
animals examined In this series.
The condylar trabeculae, which are thin and deli
cate In the young animal, become progressively coarse and
fuse with advancing age. By sixteen months of age the
condyle consists of solid bone which appears to be sealed
off from the thin cartilaginous cap.
OBSERVATIONS
Experimental Material
Group 1. Upper Right Molar Quadrants Extracted
A. 2 Months Post Surgery
Operated side. The squamosal bone is considerably
denser than is seen in the control and presents a thick
fibrous covering on the articular surface.
The articular disc is unchanged.
The cartilaginous layer of the condyle is decreased
in thickness from 90 mlcra In the control to 45 mlcra.
Osteosclerosis Is seen In the condyle (Fig. 12). (Compare
with Fig. 14.)
Unoperated side. Layers of new bone are seen in
the articular area of the squamosal bone.
The articular disc seems thicker than normal.
The cartilaginous layer of the condyle is about one
half the thickness seen in the normal animal. Osteoscle
rosis is seen in the condyle (Fig. 13). (Compare with
Fig. 14.)
31
32
B. 4 Months Post Surgery
Operated side. The squamosal bone is denser than
normal with a thick fibrous covering on the articular
surface.
The articular disc Is thicker than normal.
The condyle now consists of dense bone, osteoscle
rotic in character, and is almost solid. The cartilaginous
layer Is very thin, averaging only 35 miera as compared to
90 miera in the control animal, and is sealed off from the
bone. The vacuolated cells of the cartilaginous layer are
now only two or three cells thick (Fig. 15). (Compare with
Fig. 17.)
Unoperated side. The squamosal bone is denser than
is normally seen but the fibrous connective tissue layer
lining the articular surface is thin and of normal thick
ness .
The articular disc is thicker than normal.
The condyle has a thin fibrous cover similar to
that seen in the normal but the cartilaginous layer is
considerably thinner than normal. Average width Is 30
mlcra compared to 90 micra in the normal animal. The
cartilaginous cap Is thinner on the lateral surface and
thicker on the medial surface of the condyle. The bone is
considerably denser than normal and is almost solid
(Fig. 16). (Compare with Fig. 17.)
33
C. 6 Months Post Surgery
Operated side. The squamosal bone is quite dense,
much denser than normal, and shows an osteoid border that is
greatly increased in thickness when compared to the
unoperated control.
No change is observed in the articular disc and It
Is still composed of dense fibrous connective tissue.
The condyle appears to be quite osteosclerotic in
character with a marked absence of marrow spaces. By com
parison, the normal eight-month animal shows definite bony
trabeculatlon with a good many marrow spaces. There Is
also a marked decrease In the thickness of the cartilagi
nous layer, averaging 25 mlcra as compared to 90 mlcra In
the control animal.
Unoperated side. The same changes were noted as
were seen on the operated side.
Group 2. Lower Right Molar Quadrant Extracted
A. 2 Months Post Surgery
Operated side. The squamosal bone shows a thick
ened layer of osteoid bone in the joint area.
The articular disc is thicker than normal.
The condyle shows a wider border of fibrous connec
tive tissue than is seen normally. There is a thickened
34
cellular layer and the older cartilage cells are not as
highly vacuolated as are seen in the control animal. There
is an infiltration of cartilage into the bone. Lamellae
of the endochondral bone subjacent to the cartilage are now
at right angles to the long axis of the condyle. Fat is
seen in the marrow spaces of the condyle. No fat Is seen
in the normal animal. Osteosclerosis is seen in the con
dyle (Fig. 18). (Compare with Fig. 19.)
Unoperated side. Layers of new bone are seen on
the articular surface of the squamosal bone.
The articular disc is unchanged.
The cartilage of the condyle is thicker than normal
and the bone of the condyle is denser than normal and is
osteosclerotic in character.
B. 4 Months Post Surgery
Operated side. The squamosal bone shows a thicker
layer of osteoid bone than is seen in the control.
The articular disc is thicker than normal.
The condyle shows a narrower cartilaginous cap than
is seen normally and marked osteosclerosis is seen (Fig.
20). (Compare with Fig. 22.)
Unoperated side. The osteoid layer on the surface
of the squamosal bone is thinner than that of the operated
side.
35
The articular disc is thinner than on the operated
side.
The cartilaginous cap of the condyle is thinner
than on the operated side, while the bone is osteosclerotic
(Fig. 21). (Compare with Fig. 22.)
C. 6 Months Post Surgery
Operated side. The squamosal bone is denser than
normal and has a thick fibrous covering on the articular
surface.
The articular disc is thicker than normal and dis
organization can be seen in its fibrous structure.
The condyle is almost solid bone. The bone is
sealed off from the cartilage. More bone deposition is
seen on the lateral surface. The normal control animal at
this age level shows dense bone and marrow spaces but this
experimental animal resembles a 16-month normal control.
Unoperated side. The squamosal bone is denser than
normal with a thicker fibrous covering on the articular
surface.
The articular disc is thicker than normal and
disorganization can be seen in its fibrous structure.
The condyle is almost solid bone that is sealed off
from the cartilage. More bone deposition is seen on the
medial surface. The normal animal of 8 months shows dense
bone and marrow spaces but this experimental group can be
36
compared to the 16-month normal animal.
Group 3. Either Both Lower Molar Quadrants or
Both Upper Molar Quadrants Were Extracted
Since extraction procedures were bilateral, right
and left joint areas will be considered together.
A. 2 Months Post Surgery
The squamosal bone is thicker than normal and shows
a thicker layer of fibrous connective tissue lining the
articular surface. Lamellae of new bone being laid down
can be easily seen.
The articular disc is thicker than normal. The
fibers seem to be oriented in an anterior-posterior direc
tion and seem to be cut in cross section.
The condyle has a thicker fibrous connective tissue
covering than is seen normally. The cartilaginous cap is
thin, being only 45 micra as compared to the 90 micra width
seen in the control. The bone is osteosclerotic and dense,
and is sealed off from the cartilage. Very few marrow
spaces are seen. This is quite different than the normal
animal where the bony trabeculations are thin with many
marrow spaces (Fig. 23). (Compare with Fig. 24.)
B. 4 Months Post Surgery
The squamosal bone is denser than normal. Its
outer fibrous layer is thinner than was seen in the animal
37
that survived only 2 months post surgery.
The articular disc is unchanged in character.
The condyle shows denser bone than has been seen
previously with a further narrowing of the condylar car
tilage . Conditions seen here can be compared to the normal
12-month animal.
C. 6 Months Post Surgery
The density of the squamosal bone is greater than
is seen in the 4-month post surgical animal. A thicker
fibrous connective tissue covering is seen on the articular
surface.
The articular disc is considerably thicker than
normal and its fibers are oriented in a medio-lateral
direction.
The condyle now consists of very dense bone with
very few marrow spaces. It is comparable to that seen in
the normal 16-month animal. There is considerable car
tilage activity on the medial surface of the condyle while
less is noted on the lateral surface (Fig. 25). (Compare
with Figs. 26 and 27.)
Group 4. Upper Right and Lower Left Molar
Quadrants Were Extracted
Since extraction procedures were bilateral although
in different jaws, the right and left joint areas will be
considered together.
38
A. 2 Months Post Surgery
The squamosal bone shows a thicker layer of dense
fibrous connective tissue than is seen normally. This
tissue covers a thick layer of newly formed bone in the
area of the articular surface.
The articular disc seems to be thicker than normal
and there is evidence of disorientation of the usual fiber
position.
Sclerosis is seen at the head of the condyle, with
a narrowing of the cartilaginous layer to approximately
half its usual thickness. This bone is sealed off from the
cartilaginous cap. The cartilaginous layer is narrowed but
all layers can be easily differentiated.
B. 4 Months Post Surgery
The squamosal area is the same as seen in the
2-month material.
The articular disc is the same as is seen in the
2-month material.
The condyle is the same as in the 2-month material,
except for a slight widening of the cartilaginous layer and
a progression of osteosclerosis (Figs. 28 and 29). (Com
pare with Fig. 30.)
C. 6 Months Post Surgery
No changes were observed from the 4-month material
(Figs. 31 and 32). (Compare with Fig. 33.)
39
Group 5. Upper Right and Lower Right Molar
Quadrants Were Extracted
A. 2 Months Post Surgery
Operated side. The squamosal bone is denser than
normal and shows a well defined layer of fibrous connective
tissue on the articular surface.
The articular disc is thicker than is seen in a
control animal of comparable age.
Sclerosis is seen in the head of the condyle. The
cartilaginous layer of the condyle is reduced to half the
thickness seen in the normal animal. More cartilage activ
ity is seen on the medial surface. While this animal is
only 4 months old, it is comparable to an 8-month control
animal.
Unoperated side. The only difference found between
the operated and unoperated side was that more cartilage
activity was seen on the lateral surface of the condyle in
the unoperated animal.
B. 4 Months Post Surgery
Operated side. The squamosal bone is denser than
normal and presents a thicker layer of fibrous connective
tissue on the articular surface.
The articular disc is thicker than normal and some
disorientation of the fibers is noted.
40
The bone of the condyle is denser than normal and
is osteosclerotic in character with large marrow spaces.
Osteoclastic activity is seen on the medial surface of the
condyle. The changes seen in this animal make it compara
ble to a normal 12-month animal (Fig. 34). (Compare with
Figs. 35 and 36.)
Unoperated side. With one exception, the observa
tions were identical with those seen on the operated side.
More cartilaginous activity is seen on the lateral surface
of the condyle while osteoclastic activity is seen on the
medial surface of the condyle (Fig. 35). (Compare with
Figs. 34 and 36.)
C. 6 Months Post Surgery
Operated side. The fibrous covering of the articu
lar surface of the squamosal bone is now considerably
thinner than is seen in the normal animal.
The articular disc is thicker than is seen in the
normal control.
There is a marked thinning of the fibrous layer at
the superior aspect of the condyle. Sclerosis of the con
dyle is complete and the cartilaginous layer cannot be
seen. This animal can be compared to a 16-month control
animal.
Unoperated side. All observations were identical
41
with those of the right side.
Group 6. All Four Molar Quadrants
Were Extracted
Since extraction procedures were bilateral, both
right and left joints will be considered together.
A. 2 Months Post Surgery
The squamosal bone is much denser in character than
is seen in the normal animal. The fibrous connective
tissue lining the articular surface is thicker than normal.
The articular disc is thicker than normal and there
appears to be some change from the normal orientation of
the fibers at its superior aspect.
Osteosclerosis at the head of the condyle is com
plete . Only a thin cartilaginous cap remains covering the
superior surface. These animals show advanced changes when
compared to the normal and can be compared to a normal
12-month animal.
B. 4 Months Post Surgery
The only changes noted were in degree. The bone in
both the squamosal bone and in the condyle is denser than
was seen in the 2-month post surgical material. Although
these animals are only 6 months old, they can be compared
to a 16-month normal animal (Fig. 37). (Compare with
Fig 36.)
42
C. 6 Months Post Surgery
There were no survivors in this group.
Radiographic Findings
No differences could be found between normal and
experimental animals of the same age groups by X-ray study.
To be certain of this, all radiographs were enlarged four
magnifications for examination and study.
Summary of Findings in the
Experimental Animal
All experimental animals showed marked changes in
the squamosal area, the articular disc and in the condyle.
The squamosal bone was considerably denser than
that observed in the normal control animal. In most cases
a thickening of the fibrous connective tissue lining of the
articular surface was seen. Also in most cases there was a
concomitant widening of the layer of osteoid bone between
the fibrous connective tissue and the compact bone of the
squamosal.
The articular disc was usually thicker than normal
and some disorganization of its fibrous elements was seen.
The most dramatic changes occurred in the mandib
ular condyle where a marked thinning of the cartilaginous
cap was seen decreasing in thickness from 90 micra in the
normal animal to from 30 to 45 micra in the operated
43
animal. The longer the animal lived following surgery, the
thinner the cartilaginous cap. In addition, signs of
osteosclerosis were seen as early as ten days after
surgery. This osteosclerosis was progressive in nature,
and by six months after surgery the condyle was usually
solid bone.
DISCUSSION
The articulation of the mandible with the cranium
has been the object of much study. It is a ginglimo-
arthrodial type joint whose function is similar in lower
animals to that of man. In the human this joint is called
the temporomandibular articulation. Because many of the
lower animals do not have a temporal bone and have the
cranial portion of the joint located in the squamosal bone,
this area is frequently called the squamosal mandibular
articulation. For the purposes of this discussion, the
term mandibular joint will be used.
The rat is a monophydont with the dental formula
Incisor 1, Molar 3. The fossa of the mandibular articula
tion is on two different levels, an anterior-inferior level
and a posterior-superior level. With the mandibular con
dyle functioning on the anterior-inferior plane, only the
incisor teeth are in function or occlusion. With the
mandibular condyle retracted to the posterior-superior
level, only the molar teeth are functional. The rat,
therefore, can be considered to have two different types of
dentitions--the incisors which are used primarily for
prehension, gnawing and biting, and the molars which are
44
45
used only for grinding.
The mandibular joint of normal rats has been
studied by Cabrini (1941), Collins (1946), Becks (1953),
Bhaskar (1953) and Cunat (1956). In addition, a study of
the normal development of this joint, in the mouse, was
made by Levy (1948) who found a remarkable similarity
between the mandibular joints of the rat and the mouse.
Cabrini and Erasquin (1941) stated that "the
glenoid fossa is composed of compact bone covered by
fibrous tissue." The present study demonstrates that the
squamosal portion of the joint is covered with fibrous
connective tissue. Immediately adjacent to this connective
tissue is a layer of osteoid bone. Adjacent to the osteoid
bone is the compact bone of the squamosal.
Collins and his co-workers (1946) describe the
cranial portion of the joint or the squamosal region and
state, "A cartilage-like mass of tissue lies adjacent to
the articular surface of the fossa, separated from the
joint cavity by only a thin layer of fibrous tissue." They
also claim that this tissue can be found in old rats even
at 465 days of age. In their opinion the presence of this
cartilage-like mass at older age levels gives the articular
fossa the ability to remodel itself or change its shape in
response to pressure.
This is contrary to the findings of Cabrini and
Erasquin as well as the findings of this study. No such
46
cartilage-like mass was described by Cabrini, nor was any
evidence of cartilage or a cartilage-like mass found in
this study.
Levy in his study on mice also disputed the pres
ence of this so-called "cartilage-like mass" as described
by Collins. However, Levy worked with mice so his chal
lenge is open to question.
Breitner (1940) forcibly repositioned the mandible
by inserting bite blocks in monkeys. He was able to show
bony changes in the glenoid fossa and the condyle. His
findings were based upon a very small number of experi
mental animals and perhaps may be open to question. Even
though his work was limited by an insufficient number of
animals, European orthodontic clinicians were impressed
enough to develop a whole new system of orthodontic treat
ment designed specifically to stimulate bone growth.
Baume (1959) tried to confirm these findings by
also inserting bite planes into a small number of monkeys.
In addition. Baume (1961) reports a case of an infant of
two months that had Pierre Robins syndrome. This infant
was treated orthopedically for three months before it
expired. Baume then showed histologic changes in the
glenoid fossa and the condyle. It is the feeling of this
investigator that Baume's evidence in both reports was
sparse and incomplete.
There has been a scarcity of studies relating the
47
loss of teeth or the loss of occlusion to possible sequelae
in the temporomandibular joint.
The question of the effect of loss of occlusion due
to the extraction of molar teeth was first mentioned by
Anderson (1936). He and his co-workers subjected a number
of animals to extraction procedures. At that time all
gross changes in symmetry were considered to be the effect
of these extractions. Since all their animals were sub
jected to extraction procedures, they had no control group.
Without further study they did speculate as to whether
extraction procedures could create a change in the joint.
Avant and co-workers (1952) described changes in
the rat mandibular joint following loss of occlusion
created either by extraction of molar teeth or by the
grinding of teeth until they were removed from occlusion.
Some of these disturbances were ; replacement fibrosis in
the anterior portion of the condyle affecting subchondral
bone, hemopoietic marrow spaces and the cartilage cap.
They also described a loosening and fraying of the articu
lar disc.
None of those findings were observed in this study.
However, the atrophy and rarefaction of the condylar carti
lage plus a flattening of the condyle as described by these
authors was observed. Avant also describes a cessation of
bone growth. Osteosclerosis was a primary finding in the
condyle in this study. In another instance Avant felt that
48
changes in the articular fossa were limited, while the
findings of this study showed they were quite marked and
definite.
Unfortunately, a detailed report of Avant*s find
ings is not available in the literature. The only informa
tion found on this subject was in the form of a very short
abstract.
Cimasoni and Becks (1963) subjected rats to extrac
tion procedures. After removing the upper right quadrants
of molar teeth, they examined the joint histologically.
They state, *'The condylar cartilage averages 14.75 mm. on
both the functioning and non-functioning side." They
further state that rats hypophysectomized at twenty days
that were subjected to extraction of an upper molar quad
rant at forty days, and then given injections of growth
hormone from age 150 days to 210 days, showed a condylar
cartilage that measured 33.5 mm. on the extracted side and
31.2 ram. on the unextracted side.
Presuming that the measurements given above should
read *'micra,’* they are still far beyond the range of varia
tion of thickness of the cartilaginous cap as found by this
investigator. In this study, thickness of the cartilag
inous cap averaged 165 micra for the 60-day rat, 90 micra
for the 120-day rat and 90 micra for the 150-day rat. In
the experimental group in this study, the cartilaginous cap
diminished in thickness to approximately 30-45 micra within
49
a period of six months after surgery.
Cimasoni and Becks make no mention of the thickness
of the condylar cartilage in their hypophysectomized
animals that had been given no growth hormone.
Becks (1946) in an earlier report did state that
chondrogenesis was considerably slowed within four days
following hypophysectomy, and that juvenile vigor could be
restored to senescent mandibular joints by the administra
tion of growth hormone.
On the basis of findings in this study, they would
have to revert to animals with a chronologic age of thirty
to forty days. This may or may not be possible. A sudden
growth of the condylar cartilage as seen with the injection
of growth hormone is possible. The question is the amount.
Since the histologic sections in the Cimasoni and Becks
study were in the sagittal plane, it is possible that some
of these sections were cut more obliquely than was
expected, and a variation in thickness of the condylar
cartilage was due to the plane of sectioning.
Cimasoni (1963) also reported on histopathology of
the rat mandibular joint following bilateral molar extrac
tions. His findings showed no abnormalities at 200 days
after surgery but showed severe changes 270 and 300 days
after surgery.
In this study, bilateral molar quadrant extractions
were performed in two different groups of animals.
50
Findings showed definite changes in the articular fossa,
the articular disc and the condyle at 60, 120 and 180 days
after surgery. Since marked changes such as development of
osteoid bone in the articular fossa and a thinning of the
cartilaginous cap of the condyle, coupled with the appear
ance of osteosclerotic bone in the condyle were found 60
days after surgery, the findings of Cimasoni are confusing.
The osteoarthritic lesions and pannus as described by
Cimasoni were not seen in this study. The fact that no
experimental animals were permitted to live past 240 days
may be the reason.
The question of what histologic changes would fol
low experimental functional disturbances has been partially
answered by this investigation. Basically, changes took
place in the squamosal portion of the joint where increased
density of the squamosal bone plus large additional incre
ments of osteoid bone and fibrous tissue were observed.
The articular disc was affected since it was usually
increased in thickness, and the fibrous structure of the
disc showed evidence of disorientation.
A marked change was also found in the mandibular
condyle where severe alterations were seen. These were
evidenced by a change in the structure of the cartilaginous
cap and a generalized reduction in the thickness of this
cap. In terms of averages, the width of the cartilaginous
cap was reduced from 90 micra in the normal animal to 45
51
micra in the experimental animal at four months of age
(two months post surgery), from 90 micra to 32 micra at
six months (four months post surgery) and from 90 micra to
25 micra in the eight-month animal (six months post sur
gery). Sclerosis was seen in the bone of the condyle.
This increased in degree as the post-operative survival age
of the animals increased.
Rapid senescence of the mandibular joint following
removal of quadrants of molar teeth is seen when one com
pares the operated animal with the unoperated control.
Conditions found in the operated animal two months after
surgery are comparable to those seen in the eight-month
unoperated control. Those four months after surgery are
similar to a twelve-month unoperated control, and those
animals who were retained for six months after surgery can
be likened to a sixteen-month control animal.
The senescence of the mandibular joint can be
either the true aging process or a process similar to
aging. The true aging process is not reversible. Changes
in the condyle are reversible in most studies of nutri
tional or hormonal problems. A determination as to whether
the changes produced in this study were reversible could
not be made. If such reversibility were possible it could
only be accomplished at a very early age, during the period
when the condyle was growing quite rapidly.
Another factor that must be considered is whether a
52
nutritional deficiency could be partially responsible for
the findings of this study. While the animals used in the
experimental procedures in this study were not weighed,
their growth pattern was similar to those used in the con
trol group. No variations were noted in size, and it is
assumed that there was a minimal amount of nutritional
disturbance.
Normal function is extremely important in the gross
development of the mandibular joint as well as of all
skeletal structures. In experimental loss of function one
would expect overdo sure of the mandible on the operated
side and a thinning of the articular disc. This was not
the case. Inevitably, the side that had not lost function
because of the extractions showed as much evidence of
change as did the operated side.
In the results observed in this problem the ques
tion arises whether local or systemic effects were the
causative factors. Morphologic changes can be due to
either local or systemic effects. These morphologic
changes are similar in character even though they are
functionally dissimilar. Since studies of nutritional
disturbances (for example, tryptophane deficiencies) showed
osteoporosis in the condyle, it appears that the osteoscle
rotic bone found in this study is due to a localized
mechanical factor such as a change in muscle pull.
In some instances a skewing of the mandible toward
53
the operated side was evidenced by bone growth on the
lateral surface and bone resorption on the medial surface
of the condyle of the unoperated side, with bone deposition
on the medial surface and bone resorption on the lateral
surface of the operated side (Figs. 34 and 35).
To extrapolate findings in the rat or in any exper
imental animal to the human is a step that should be taken
with great care. However, it is not unreasonable to
hypothesize that similar changes can be effected in the
human condyle, even though the morphology and mechanics of
the temporomandibular joint are considerably different from
those of the rat. It should be kept in mind that major
changes can only be seen in experimentally produced pathol
ogy in the young growing condyle and joint.
Marked changes were seen in the mandibular condyle
by various investigators following nutritional or hormonal
disturbances. Severe alterations of the condyle were also
found following the removal of selected quadrants of molar
teeth and the subsequent functional disturbances. Thus,
marked changes can be created experimentally in the rat
mandibular joint by nutritional, hormonal, or functional
imbalances.
All the experimental procedures mentioned in the
review of the literature or performed in this study show
some effect on the condyle. The condyle, therefore, can be
considered a mirror that reflects changes caused by
54
nutritional, hormonal or functional disturbances.
Changes in the occlusion of the teeth due to loss
of occlusion created by the removal of selected quadrants
of molar teeth have created dramatic changes in the fossa
of the mandibular joint as well as in the articular disc
and the condyle itself. The sum total of these changes is
to experimentally create a condition similar to one that is
normally brought about by the aging process. It is felt
that these changes are a factor that could lead to symptoms
of the mandibular joint pain dysfunction syndrome.
SUMMARY
An investigation was made to determine whether the
removal of selected quadrants of molar teeth would create
a morphologic change in the mandibular joint that could be
considered a causative factor in the mandibular joint pain
dysfunction syndrome.
Seventy-five white male rats of the Holtzman strain
were used to determine the normal age changes in the
squamoso-mandibular articulation. Fifteen arbitrarily
selected age groups ranging from one day to two years were
used. Certain of these age groups were used as control
animals for the second part of this investigation.
Thirty-six, two-month-old, white male rats of the
Holtzman strain were subjected to various surgical proce
dures in which one, two or four quadrants of molar teeth
were extracted. Animals were sacrificed at two, four and
six months after surgery.
Each squamoso-mandibular articulation of each
animal, both normal and experimental, was examined indi
vidually by means of X-ray as well as microscopic
techniques.
The squamoso-mandibular joint of the rat does not
55
56
reach its mature morphologic pattern until approximately
the fiftieth day of life. This is about two and one-half
weeks after the eruption of the third molars and the estab
lishment of clinical occlusion for these teeth. At this
time the cartilaginous cap of the condyle has decreased to
approximately 90 micra in thickness. Minute variations
occur in the width of this cartilage with normal aging, but
even at the age of two years there is very little variation
from this dimension.
During the normal aging process, the bone of the
mandibular condyle becomes increasingly more dense until
the sixteenth month, at which time the condyle consists of
solid bone.
Following the removal of selected quadrants of
molar teeth, the following changes are seen:
1. The squamosal portion of the joint is consider
ably denser than normal and shows a large
increase in thickness of fibrous connective
tissue as well as large additional increments
of osteoid bone.
2. The articular disc increases in thickness and
disorientation of the fibers of the disc is
seen.
3. A thinning of the cartilaginous cap of the
condyle is observed, as well as osteosclerotic
changes in the condyle.
57
No differences conId be found between normal and
experimental animals of the same age group by X-ray study.
All films were magnified four times for this purpose.
CONCLUSIONS
The condyle of the mandible can be considered a
mirror that will reflect functional disturbances of the
occlusion of the teeth, as well as hormonal or nutritional
disturbances.
Changes can be created experimentally in the rat
mandibular joint by the removal of quadrants of molar
teeth. Increased calcification of the squamosal bone plus
deposition of new bone on its articular surface, thickening
of the articular disc plus disorientation of its fibers and
a thinning of the cartilaginous cap of the condyle in addi
tion to osteosclerosis in the bone of the condyle are seen.
These changes from the normal morphology can be
considered signs of premature aging. The morphologic
changes noted can be considered a causative factor in the
mandibular joint pain dysfunction syndrome.
58
BIBL I OG R AP H Y
BIBLIOGRAPHY
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A. V. Changes in Molar Teeth and Their Supporting
Structures of Rats Following Extraction of Upper Right
First and Second Molars. Yale Jnl. Biol. & Med.
9:189, 1936.
Applebaum, E., and Levy, H. P. Changes in the Mandibular
Condyle of Mice Following the Use of Orthodontic Bite
Plates. Am. Jnl. Orth. ^:775, 1954.
Avant, F. B., Averill, C. J., and Hahn, W. E. Changes in
the Temporomandibular Joint of Rats Caused by Altera
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J. Dent. Res. ^:500, Aug. 1952.
Baker, L. W. The Influence of the Formative Dental Organs
on the Growth of the Bones of the Face. Am. J. Orth.
2J7:488, 1941.
Barber, C. J., Green, L. J., and Cox, G. J. The effects of
the physical consistency of diet on the condylar
growth of the rat mandible. Abstracts I.A.D.R. #246,
page 97, 1963.
Baume, L. J., Haupl, K., and Stellmach, R. Growth and
Transformation of Temporomandibular Joint in an Ortho
pedically Treated Case of Pierre Robins Syndrome.
A Histologic Study. Am. J. Orth. ^:901, 1959.
Baume, L. J., and Derichsweiler, H. Is the Condylar Growth
Center Responsive to Orthodontic Therapy? Oral Surg.;
Oral Med.; Oral Path. jA :347, 1961.
Bavetta, L., Bernick, S., Geiger, E., and Bergen, W. The
Effect of Tryptophane Deficiency on the Jaws of Rats.
J.D.R. ^:309, June 1954.
Bavetta, L., and Bernick, S. Lysine Deficiency and Dental
Structures. J.A.D.A. 50:427, Apr. 1955.
60
61
Bavetta, L. A., Bernick, S., and Ershoff, B. Effect of
Growth Hormone on the Bone and Periodontium of Vit. A
Depleted Rats. Arch. Path. ^:610, Nov. 1958.
Becks, H., Collins, D. S., Simpson, M. E., and Evans, H. M.
Growth and Transformation of the Mandibular Joint in
the Rat; III. The Effects of Growth, Hormone and
Thyroxin Injections in Hypophysectomized Female Rats.
Am. J. Orth, ^;447, 1946,
Becks, H., Collins, D. A., Asling, C, W., Snow, R. 0.,
Simpson, M. E., and Evans, H, M. The Growth and
Transformation of the Mandibular Joint in the Rat.
IV. The Effects of Thyroidectomy at Birth. Oral
Surg. 1^:315, 1948.
Becks, H., and Evans, H. Atlas of the Skeletal Development
of the Rat. Amer. Inst, of Dent. Med. Berkeley,
Calif., 1953.
Bernick, S. The Vascular and Nerve Supply of the Temporo
mandibular Joint of the Rat. Oral Surg., Oral Med.,
Oral Path. ^;488, 1962.
Bhaskar, S. N. Growth Pattern of the Rat Mandible from 13
Days Insemination Age to 30 Days after Birth. Am.
Jnl. Anat. 9^:#1,1, Jan. 1953.
Bhaskar, S. N., Weinman, J. P., and Schour, I. Role of
Meckel*s Cartilage in the Development and Growth of
the Rat Mandible. J. Dent. Res. ^:#3,398, June 1953.
Bourne, G. H. The Biochemistry and Physiology of Bone.
Academic Press, Inc., New York, 1956.
Breitner, C. Bone Changes Resulting from Experimental
Orthodontic Treatment. Am. Jnl. Orth. & Oral Surg.
26:521, 1940.
Cabrini, R., and Erasquin, J. La Articulacion Temporo-
raaxilar de la Rata. Rev. Odontol. de Buenos Aires
29:385, July 1941.
Cimasoni, G., and Becks, H. Growth Study of Rat Mandible
as Related to Function. A.O. ^:#1,27, Jan. 1963.
Cimasoni, G. Histopathology of the TMJ Following Bilateral
Extraction of Molars in the Rat. O.S., O.M., and O.P.
j^:613. May 1963.
62
Collins, D. A,, Becks, H., Simpson, M. E., and Evans, H. M.
Growth and Transformation of the Mandibular Joint in
the Rat. I. Normal Female Rats. Am. Jnl. Orth, and
Oral Surg. ^:431, 1946.
Growth and Transformation of the Mandibular Joint
in the Rat. II. Hypophysectomized Female Rats. Am.
Jnl. Orth. 12:443, 1946.
Cunat, J. J., Bhaskar, S. N., and Weinman, J. P. Develop
ment of the Squamosal-Mandibular Articulation in the
Rat. Jnl. Dent. Res. 35;#4,533, Aug. 1956.
Farris, E. J., and Griffith, J. Q. The Rat in Laboratory
Investigation. Hafner Publishing Co., New York, 1962.
Furstman, L. The Early Development of the Human Temporo
mandibular Joint. Am. Jnl. Orth. 672, Sept. 1963.
Hayes, A. M. Changes in the Mandibular Fossa of the Rat
Following Unilateral Condylectomy. J. Can. Dent. Ass.
22:647, 1961.
Horwitz, S. Y., and Shapiro, H. H. Modification of Mandib
ular Architecture Following Removal of the Temporalis
Muscle in the Rat. J. D. R. 2Q.*276, 1951.
Levy, B. M. Growth of Mandibular Joint in Normal Mice.
J.A.D.A. 36:177, 1948.
The Effect of Riboflavin Deficiency on the Growth
of the Mandibular Condyle of Mice. Oral Surg. 2:89y
1949.
Effects of Pantothenic Acid Deficiency on the
Mandibular Joints and Periodontal Structures of Mice.
J.A.D.A. ^:215, 1949.
Maurice, C. G., and Schour, I. Experimental Cavity Prepa
ration in the Molar of the Rat. Jnl. Dent. Res.
34:429, 1955.
Sarnat, B. G. Facial and Neurocranial Growth after Removal
of the Mandibular Condyle in the Macaca Rhesus Monkey.
Am. Jnl. Surg. 94:#1,19, July 1957.
Watts, D. G., and Williams, C. H. M. The Effects of the
Physical Consistency of Food on the Growth and
Development of the Mandible and the Maxilla of the
Rat. Am. Jnl. Orth. 37:895, 1951.
63
Weinman, J. P. Rachitic Changes of the Mandibular Condyle
of the Rat. J. D. Res. Z3:509, 1946.
Nutritional and Hormonal Changes of the Mandib
ular Condyle. J. D. Res. 22* 157, 1946
AP PENDIX
65
■
mm
Fig. 1.--1 Day Old Rat (Normal) 75x
The condyle consists of cartilage with a thick
fibrous covering. The articular disc is still not
completely separated from the condyle in the region
of the inferior or mandibular compartment. The
disc is composed of cellular connective tissue.
Two centers of ossification are seen in the squa
mosal bone--one lateral and one medial.
66
###
' -iJM:
^msmrnsmm. «
Fig. 2.--7 Day Old Rat (Normal) 75x
First signs of endochondral bone ossification
are now seen at the head of the mandibular con
dyle . Both the inner and outer compartments of
the articular disc are well defined. The articular
disc is still composed of cellular connective
tissue. The squamosal bone ossification centers
have now joined and the articular fossa now com
pletely covers the condyle and the articular disc.
67
Fig. 3.--14 Day Old Rat (Normal) 35x
Attention is invited to the change in magnifica
tion from the two previous figures. The squamosal
bone is now well formed and has greatly increased
in thickness. The articular disc is well formed
and has assumed its typical shape. The condyle is
still mainly cartilage but endochondral bone forma
tion is well established at the inferior area.
68
m-. -«aw: fe
la
Fig. 4.--21 Day Old Rat (Normal) 35x
The squamosal bone is becoming denser and
better organized. The articular disc is still
composed of cellular connective tissue. The
condyle is flattened medio-laterally on its
superior aspect. The cartilage of the condyle
is now in two layers embryonic and vacuolated.
Much endochondral bone is seen.
69
I
ma
Fig. 5.-“30 Day Old Rat (Normal) 35x
The squamosal bone is increasing in size and
density. The articular disc is unchanged. The
condyle has continued to enlarge and more bony
trabeculae are seen. Cellular elements of the
cartilaginous cap are now well differentiated.
70
miÉM
mm
Fig, 6.--40 Day Old Rat (Normal) 35x
There is an Increased thickness of the fibrous
connective tissue covering the head of the con
dyle. The condyle shows an increase in denseness
and there is a thickening of the bony trabeculae.
A decrease is noted in the size of the marrow
spaces. There is a narrowing of the cartilaginous
layer at the head of the condyle. No change is
noted in the articular disc. The squamosal bone
is becoming more dense in character.
71
Fig. 7.--2 Month Old Rat (Normal) 35x
The mature morphology of the condyle has been
reached. Zoning in the cartilaginous area is
quite definite :
1. Dense Fibrous Connective Tissue.
2. Embryonic Cartilage.
3. Older Cartilage.
4. Vacuolated Cartilage.
The articular disc is now composed of dense fibrous
connective tissue and has assumed its characteris
tic shape.
72
#
Fig. 8.--6 Month Old Rat (Normal) 35x
Bone is much denser in the condyle due to the
normal aging process. The condyle is high and
rounded. The cartilaginous cap is now quite thin,
measuring only 90 micra.
73
Fig. 9.--8 Month Old Rat (Normal) 35x
With the exception of denser bone in the squa
mosal area and in the condyle, there is practically
no change.
74
&%-%«;!'. L«,
----- - j l ' . m
.1 -' ' ( U , r
Fig, 10.--10 Month Old Rat (Normal) 35x
The only changes seen are due to the normal
aging process. Denser bone is noted in the
squamosal area and in the condyle, with fewer
marrow spaces being seen.
75
i
Fig. 11.--20 Month Old Rat (Normal) 35x
The condyle now is composed of solid bone. The
cartilaginous layer has remained constant at a
thickness of 90 micra since the fourth month of
life. The squamosal bone is also very dense and
well calcified. The articular disc has remained
unchanged.
76
Fig. 12.--EX 1 AR. Right mandibular joint of
an animal that had upper right molar quadrants
extracted and was sacrificed 2 months after
surgery at age of 4 months (35x).
The squamosal bone is quite dense with a thick
fibrous covering on the articular surface. The
articular disc is unchanged. The cartilaginous
layer of the condyle is slightly decreased in
thickness. Sclerosis can be seen in the condyle.
Compare with 4-month control animal. Fig. 14.
77
g
Fig. 13.--Ex 1 AL. Left mandibular joint of an
animal that had the upper right molar quadrant
extracted and was sacrificed 2 months after
surgery at age 4 months (35x).
Layers of new bone are seen in the articular
area of the squamosal bone. The articular disc
seems thicker than usual. The cartilaginous cap
of the condyle is thinner than on the operated
side. Sclerosis can be seen in the condyle.
Compare witn 4-month control animal. Fig. 14.
78
P
K ' " t / J
4
Fig, 14.--Control animal, age 4 months (35x)
The squamosal bone is dense and compact with
few marrow spaces. A thin layer of fibrous con
nective tissue lines the articular cavity. The
articular disc consists of a thin layer of dense
fibrous connective tissue. The cartilaginous cap
of the condyle is thin, about 90 to 120 micra,
and the older cartilage cells and the vacuolated
cartilage cells seem to be combined. Bone forma
tion is well advanced in the condyle and lamellae
are quite dense with large marrow spaces.
79
0
Fig. 15.--Ex 1 BR. Right mandibular joint of an
animal that had the upper right molar quadrant
extracted and was sacrificed 4 months after surgery
at age 6 months (35x).
The squamosal bone is dense with a thick fibrous
covering on the articular surface. The articular
disc is thick. The condyle now consists of dense
bone and is almost solid. The cartilaginous layer
is very thin and is sealed off from the bone. The
vacuolated cells in the cartilaginous layer are now
only 2 or 3 cells thick. Compare with 6-month con
trol animal. Fig. 17.
80
g,/ "
J ' “
#i {
#- ;
a# *
Fig. 16.--Ex 1 BL. Left mandibular joint of an
animal that had the upper right molar quadrant
extracted and was sacrificed 4 months after surgery
at age 6 months (35x).
The squamosal bone is dense but the fibrous
connective tissue layer lining the articular surface
is thin. The articular disc is thick. The condyle
has a thin fibrous cover and the cartilaginous
layer is thin. The cartilage cap is thinner on the
lateral surface and is thicker on the medial surface
of the condyle. Advanced sclerosis is seen in the
condyle. Compare with 6-month control animal.
Fig. 17.
81
Fig. 17.--Control animal, age 6 months (35x)
The squamosal bone is quite dense, with few
marrow spaces. The osteoid border of the artic
ular cavity is increased in thickness. The
articular disc is composed of dense fibrous con
nective tissue. The condyle is high and rounded.
Its cartilaginous cap is thin, about 90 micra.
Bony trabeculae of the condyle are large and dense,
with few marrow spaces.
82
w v i
f Y a b i % ü t f = ? 4 f : g k
■ -^mk
■ m â ■ :
Fig. 18.--Ex 2 A. Mandibular joint of an animal
that had the lower right molar quadrant extracted
and was sacrificed 2 months after surgery at age
4 months (35x).
The squamosal bone shows a thick hyalinized
layer of developing bone in the joint area. The
articular disc is thick. The condyle shows a wide
border of fibrous connective tissue with a thickened
cellular layer. The older cartilage cells are not
as highly vacuolated as expected. Sclerosis is
developing in the bone of the condyle. Fat is seen
in some of the marrow spaces. Compare with 4-month
control animal. Fig. 19.
83
0
Fig. 19.--Control animal, age 4 months (35x)
The squamosal bone is dense and compact, with
few marrow spaces. A thin layer of fibrous con
nective tissue lines the articular cavity. The
articular disc consists of a thin layer of dense
fibrous connective tissue. The cartilaginous cap
of the condyle is thin, about 90 to 120 micra,
and the older cartilage cells and the vacuolated
cartilage cells seem to be combined. Bone forma
tion is well advanced in the condyle and lamellae
are quite dense with large marrow spaces.
84
m i.
Fig. 20.--Ex 2 BR. Right mandibular joint of
an animal that had the lower right molar quadrant
extracted and was sacrificed 4 months after surgery
at age 6 months (35x).
The squamosal bone shows a thick layer of osteoid
bone. The articular disc is thicker than normal.
The condyle shows a reduction in thickness of the
cartilaginous layer and this cartilage is sealed
off from the bone. Osteosclerosis is well advanced
in the bone of the condyle. Compare with 6-month
control animal, Fig. 22.
85
Fig. 21.--Ex 2 BL. Left mandibular joint of an
animal that had the lower right molar quadrant
extracted and was sacrificed 4 months after surgery
at age 6 months (35x)•
A thinner layer of osteoid bone is seen in the
articular area of the squamosal bone when compared
to the operated or right side. The articular disc
is thinner. The cartilaginous cap of the condyle
is thinner than on the operated side. Here, too,
the cartilage is sealed off from the bone. Osteo
sclerosis is well advanced in the bone of the
condyle. Compare to 6-month control animal. Fig.
22.
86
Fig. 22.--Control animal, age 6 months (35x)
The squamosal bone is quite dense, with few
marrow spaces. The osteoid border of the articular
cavity is increased in thickness. The articular
disc is composed of dense fibrous connective tissue.
The condyle is high and rounded. Its cartilaginous
cap is thin, about 90 micra. Bony trabeculae of
the condyle are large and dense, with few marrow
spaces.
87
Fig. 23.--Ex 3 A. Mandibular joint of an animal
that had both quadrants of lower molar teeth removed
and was sacrificed 2 months later at age 4 months
(35x).
The squamosal bone is dense and lamellae of new
bone being laid down in the area of the articular
cavity can be plainly seen. The articular disc is
thick and there is a disorientation of fibers. The
condyle show a thick covering of fibrous connective
tissue. The cartilaginous cap is quite thin. The
bone of the condyle is quite dense and is sealed
off from the cartilage. Very few marrow spaces are
seen. Osteosclerosis is proceeding rapidly in the
condyle. Compare with 4-month control. Fig. 24.
88
m m i
mmm
Fig. 24.--Control animal, age 4 months (35x)
The squamosal bone is dense and compact, with
few marrow spaces. A thin layer of fibrous
connective tissue lines the articular cavity. The
articular disc consists of a thin layer of dense
fibrous connective tissue. The cartilaginous cap
of the condyle is thin, about 90 to 120 micra, and
the older cartilage cells and the vacuolated car
tilage cells seem to be combined. Bone formation
is well advanced in the condyle and lamellae are
quite dense with large marrow spaces.
89
Fig. 25.--Ex 3 CR. Right mandibular joint of an
animal that had both lower molar quadrants removed
and was sacrificed 6 months later at age 8 months
(35x).
The squamosal bone is quite dense and presents
a thick fibrous covering on the articular surface.
The articular disc is thick. Osteosclerosis is
advanced in the condyle. Very few marrow spaces
are seen. More cartilage activity is seen on the
medial surface of the condyle than can be found on
the lateral surface. Compare with normal 8-month
animal. Fig. 27.
90
rSrMM".
y Bar
Fig. 26.--Ex 3 CL. Left mandibular joint of an
animal that had both lower molar quadrants removed
and was sacrificed 6 months later at age 8 months
(35x).
The squamosal bone is quite dense and shows few
marrow spaces. The articular disc is thinner than
on the opposite side. Osteosclerosis is advanced
in the condyle. Few marrow spaces are seen. The
cartilaginous layer of the condyle appears to be
sealed off from the bone. Compare with normal
8-month animal. Fig. 27.
91
%
1
m s
Fig. 27.--Control animal, age 8 months (35x)
The squamosal bone is quite dense, with very
few marrow spaces. The articular cavity is lined
with a very thin layer of dense fibrous connective
tissue adjacent to the osteoid bone. The articu
lar disc is composed of dense fibrous connective
tissue. The cartilaginous layer of the condyle is
thin, about 90 micra. Bone of the condyle is quite
dense and shows fewer marrow spaces than are seen
in the 6-month animal. The denser bone and smaller
number of marrow spaces can be attributed to the
normal aging process.
92
V ''\t
^ w .
Fig, 28,--Ex 4 BR. Right mandibular joint of an
animal that had the upper right and lower left
molar quadrants extracted and was sacrificed 4
months later at age 6 months (35x).
The squamosal bone shows a thick layer of newly
formed bone lining the articular cavity. Disori
entation is seen in the fibers of the articular
disc. Sclerosis is seen at the head of the condyle
with a narrowing of the cartilaginous layer. The
bone of the condyle is sealed off from the cartilag
inous layer. Compare with 6-month control animal.
Fig. 30.
93
Fig. 29.--Ex 4 BL. Left mandibular joint of an
animal that had the upper right and lower left
molar quadrants extracted and was sacrificed 4
months later at age 6 months (35x).
Not as much new bone is seen in the articular
area of the squamosal bone as is seen in the right
joint. Some disorientation is seen in the articu
lar disc. Sclerosis is seen in the condyle. There
is a narrowing of the cartilaginous layer and it
appears to be sealed off from the bone. Compare
with 6-month control animal, Fig. 30.
94
I
Fig, 30.--Control animal, age 6 months (35x)
The squamosal bone is quite dense, with few mar
row spaces. The osteoid border of the articular
cavity is increased in thickness. The articular
disc is composed of dense fibrous connective tissue.
The condyle is high and rounded. Its cartilaginous
cap is thin, about 90 micra. Bony trabeculae of
the condyle are large and dense, with few marrow
spaces.
95
5:^
Si)
Fig. 31.--Ex 4 CR. Right mandibular joint of
an animal that had the upper right and lower left
molar quadrants extracted and was sacrificed 6
months later at age 8 months (35x).
The only changes between this specimen and the
younger animals in this series were in degree.
Osteosclerosis is much farther advanced in the con
dyle. Compare with Ex 4 BR, Fig. 28, and with
8-month control animal, Fig. 33.
96
f.
Fig. 32,--Ex 4 CL. Left mandibular joint of an
animal that had the upper right and lower left
molar quadrants extracted and was sacrificed 6
months later at age 8 months (35x).
The only changes between this specimen and the
younger animals in this series was in degree of
aging. Osteosclerosis is much farther advanced in
the condyle. Compare with Ex 4 BL, Fig. 29, and
with 8-month control animal. Fig. 33.
97
Fig. 33.— Control animal, age 8 months (35x)
The squamosal bone is quite dense, with very few
marrow spaces. The articular cavity is lined with
a very thin layer of dense fibrous connective tissue
adjacent to the osteoid bone. The articular disc is
composed of dense fibrous connective tissue. The
cartilaginous layer of the condyle is thin, about
90 micra. Bone of the condyle is quite dense and
shows fewer marrow spaces than are seen in the
6-month animal. The denser bone and smaller number
of marrow spaces can be attributed to the normal
aging process.
98
Fig. 34.--Ex 5 BR. Right mandibular joint of an
animal that had the upper and lower right molar
quadrants extracted and was sacrificed 4 months
later at age 6 months (35x).
The squamosal bone is dense and shows a thick
fibrous connective tissue layer on the articular
surface. There is some disorientation of the
fibers of the articular disc. The bone of the
condyle is osteosclerotic in character, but some
large marrow spaces can be seen. More cartilage
is seen on the medial surface of the condyle. The
cartilage is sealed off from the bone of the
condyle. Compare with normal 6-month animal. Fig.
36.
99
Fig, 35.--Ex 5 BL. Left mandibular joint of an
animal that had the upper and lower right molar
quadrants extracted and was sacrificed 4 months
later at age 6 months (35x).
The squamosal bone is dense and shows a thick
fibrous connective tissue layer on the articular
surface. There is some disorientation of the fibers
of the articular disc. The bone of the condyle is
osteosclerotic in character but some marrow spaces
can still be seen. More cartilage is seen on the
lateral surface of the condyle. Compare with Fig.
34 which shows the right mandibular joint of this
same animal, and with a normal 6-month animal,
Fig. 36.
100
«m
m:\r
#
Fig. 36.--Control animal, age 6 months (35x)
The squamosal bone is quite dense with few
marrow spaces. The osteoid border of the articular
cavity is increased in thickness. The articular
disc is composed of dense fibrous connective tissue.
The condyle is high and rounded. Its cartilaginous
cap is thin, about 90 micra. Bony trabeculae of
the condyle are large and dense, with few marrow
spaces.
101
' F ' #
Fig. 37.-“Ex 6 B. Mandibular joint of an animal
that had all four molar quadrants extracted and
was sacrificed 4 months later at age 6 months (35x)
The squamosal bone is quite dense and few marrow
spaces are seen. Disorganization is seen in the
fibers of the articular disc and it is thicker than
normal. Osteosclerosis is well advanced in the
condyle. The cartilaginous layer is thin and is
sealed off from the bone.
102
WIDTH OF CONDYLAR CARTILAGE 300 _
Normal animal ________
Experimental animal —
270
80
90
micra
months
Fig. 38.--Graph Illustrating the varying thick
ness of the condylar cartilage as related to age.
103
r
Fig. 39.--Diagrammatic representation of the
changing morphology of the mandibular condyle from
7-60 days (70x).
The medio-lateral midplane of the condyle was
used as the plane of reference registered on the
most superior portion of the condyle. Note chang
ing angulation of the condyle to the ramus and the
decrease in size between 40 and 60 days when the
mature morphology is reached.
104
Fig. 40.--Diagrammatic representation of the
changing morphology of the articular fossa from
7-60 days (70x).
The medio-lateral midplane of the glenoid fossa
was used as a plane of reference registered on the
most superior portion of the concave surface of
the articular fossa.

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Asset Metadata

Creator Furstman, Lawrence (author)

Core Title The effect of loss of molar occlusion upon the mandibular joint

School School of Medicine

Degree Master of Science

Degree Program Anatomy

Degree Conferral Date 1964-08

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag biological sciences,OAI-PMH Harvest

Format application/pdf (imt)

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c37-192322

Unique identifier UC11637716

Identifier EP54675.pdf (filename),usctheses-c37-192322 (legacy record id)

Legacy Identifier EP54675.pdf

Dmrecord 192322

Document Type Thesis

Format application/pdf (imt)

Rights Furstman, Lawrence

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA