Effects of traumatic occlusion upon the temporomandibular joints of Rhesus monkeys
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An investigation was undertaken to study the effects that prosthetic appliances, provided with occlusal interferences in the normal path of closure, and with increased vertical dimension of occlusion, could produce on the temporomandibular joint structures of the Rhesus Monkeys. Seven female adult Rhesus Monkeys were chosen. The animals were divided into three groups: Group one: Monkey #1, was a normal monkey and used to help define normalcy. Group two: Monkeys #2, #3, #4. Monkeys #2 and #3 were experimental monkeys, and Monkey #4 was the control monkey. The experimental period for this group was 15 days. Group three: Monkeys #5, #6, #7. Monkeys #5 and #6 were experimental monkeys, and Monkey #7 was the control monkey. The experimental period for this group was 55 days. Perfusion with filtered Pelikan carbon black suspension (Gunther Wagner), was done at the time of sacrifice in order to visualize the blood vessels. The animals were decapitated after sacrifice, and the skin was completely dissected away. The heads were fixed for 6 weeks in 10% buffered formalin with the appliance in place. The right condyle of each animal was tagged for routine histologic sections which were stained with Trichrome (Goldman-Bloom modification) and hematoxiline-embedding eosin techniques. The left side was tagged for epoxy resin/(Mereco Products, 530 Wellington Ave., Cranston, R.I. 02910). The appliances consisted of gold castings over the maxillary and mandibular teeth of the Rhesus Monkeys. The lower castings, with the interferences placed on the occlusal surfaces of the first molars were hitting against a flat plane on the upper appliances. This area was between the second premolar and first molar. The appliances were designed so that a rocking action of the condyles and meniscus were expected to result in a forward and downward displacement. Then, due to muscular action, the condyle and meniscus were expected to be pushed back and upward. The appliances for the control animals (Monkeys #4 and #7) were prepared in such a way as to increase the vertical dimension of occlusion to 4 mm at the level of the first molars. There were no interferences in these appliances. The following observations were made on the overall histologic study of the right condyles: the experimental monkeys (#2 and #3) showed a greater cellular activity in the fibrocartilage covering the head of the condyle than the control monkeys. The experimental animals (#2, #3, #5, #6) showed a marked osteoclastic activity at the anterior neck of the condyle. Monkeys #2 and #6 also showed resorptive areas at the posterior neck of the condyle. In the left condyles, which were embedded in epoxy resin, there were vascular alterations characterized by vessel dilation and vessel disruption in the experimental animals as well as in the control animals. This experiment corroborates the statements of Ricketts (22) and the findings of Cimasoni (6). The results of this experiment appear to be due to the traumatic action of the appliances, which, in turn, precipitated degeneration (18, 19, 28, 29, 30, 31, 32). This seems to have been caused by the fulcrum appliances which forced the mandible to pivot upward and posteriorly. The histologic findings were significant and indicate that all the structures of the temporomandibular joint of the Rhesus Monkeys are susceptible to mechanical stresses. Of all the structures of the temporomandibular articulation of the Rhesus Monkeys, the glenoid fossa was the least affected by mechanical stresses.
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