Calcification patterns of rat condylar cartilage after induced unilateral malocclusion

Changes in the expression of aromatase, estrogen receptor α and β in mandibular condylar cartilage of rats induced by disordered occlusion

BACKGROUND

Estrogens play an important role in modulating the morphology and function of temporomandibular joints (TMJs), which is suggested to act via estrogen receptors (ERs). The present study was to investigate the expression of aggrecan, collagen type II (Col II), Col X, aromatase, ERα and ERβ in degenerative changes of mandibular condylar cartilage.

METHODS

Forty male and 40 female 8-week-old rats were enrolled in this study. In experimental groups, the disordered occlusion was created by moving the first molars mesially and the third ones distally. Immunohistochemistry and real-time PCR were performed at the end of the second or fourth week.

RESULTS

Degenerative changes, characterized by interrupted continuity of hypertrophic layer, pyknotic and eosinophilic lesion with few nuclei, areas filled with eosinophilic nuclei, were observed in more joints from female experimental groups than male ones. However, thickening changes in hypertrophic layer were only found in male experimental groups. The gene expression of Col II, Col X and aggrecan increased in 4-wk male experimental subgroup (both P < 0.01), but decreased in 2-wk and 4-wk female subgroups (P < 0.05). The gene expression of ERα decreased in 2-wk male and female experimental subgroups (both P < 0.01), however, that of ERβ increased except the 2-wk female experimental subgroup (all P < 0.01). The expression of aromatase decreased in both male and female experimental subgroups (all P<0.01).

CONCLUSIONS

Mandibular condylar cartilage responses differently to the disordered occlusion in male and female rats. The levels of locally synthesized estrogen, ERα and ERβ may have limited attribution, if any, to the sex-specific cartilage response.

Retreatment of a patient with Marfan syndrome and severe root resorption

This case report describes the retreatment of a patient with Marfan syndrome whose earlier orthodontic and surgical treatment had been unsuccessful. Marfan syndrome is an inherited connective tissue disorder transmitted as an autosomal dominant trait. The disorder results from molecular defects in the fibrillin gene that are responsible for the impaired structural integrity of the skeletal, ocular, and cardiovascular systems. When she sought retreatment, the patient had an open bite, mandibular anterior crowding, severe root resorption, and temporomandibular joint derangement with some resorption of the condyles. The second treatment, which included extractions and surgery, resulted in balanced and harmonious facial proportions, and a Class I occlusion with normal overjet and overbite. There was no further loss of condylar tissue, and the temporomandibular joints were asymptomatic. More root resorption on the mandibular left canine and the left second premolar was evident after the second treatment.

Retreatment of a patient who presented with condylar resorption

This case report describes the retreatment of a patient whose initial nonextraction treatment several years earlier had been unsuccessful. When she sought new treatment, she had an open bite, proclined incisors, and severe temporomandibular joint derangement with almost complete resorption of the condyles. The new treatment, which included extractions and surgery, gave her balanced and harmonious facial proportions, a Class I occlusion with normal overjet and overbite, and a healthy dentition. There was no further loss of condylar tissue and the temporomandibular joints were asymptomatic.

Microscopic analysis of the temporomandibular joint in rabbits (Oryctolagus cuniculus L.) using an occlusal interference

The purpose of this study was to assess the tissue alterations in the temporomandibular joint (TMJ) of the New Zealand White rabbit (Oryctolagus cuniculus L.), after a unilateral occlusal interference insertion on the animal's right side back teeth. A total of 36 animals were used, thirty of which belonged to the experimental group and six to the control group. We established three experimental periods: 24 hours, three days and seven days. The control group animals were divided two by two; each pair followed the same experimental periods of the former one. The experimental group animals were submitted to the use of a 0.3 mm thick metallic cap with a visor. All animals were euthanized, and the TMJs were removed. Using a microscope for examination we observed, in all experimental periods, the presence of intra-articular hemorrhage in the supra- and infra-disk compartments as well as in the retro-disk zone. There were no inflammatory cells detected. The thickness of the condylar fibrocartilage presented significant alterations among the animals of the three experimental groups. In the left TMJs no inflammatory cells were detected. The results suggest that the insertion of a unilateral occlusal interference in rabbit back teeth does not cause any inflammatory intra-articular process within seven days; however, it does cause bilateral intra-articular hemorrhage and a larger compression of the condylar fibrocartilage in the joint opposite the side where the interference is placed. We also concluded that, in order to do research on the temporomandibular joint using animals, it is necessary have an independent (or separate) group of animals as controls.

Calcifications of the disc of the temporomandibular joint

Calcified lesions of the temporomandibular joint discs obtained from 135 human cadavers were studied. Calcifications were observed in 92 of 250 discs by soft x-ray radiography. Studies by light and electron microscopy and x-ray diffraction revealed that there were two different types of calcification in the discs: apatite crystal deposition with or without ossification, and calcium pyrophosphate dehydrate (CPPD) crystal deposition. Calcifications were recognized more frequently posteriorly than anteriorly, and were related to disc perforation. The results of this investigation suggest that disc degeneration, which may occur as a result of aging or mechanical stress, causes calcifications.

Histopathological changes in rabbit craniomandibular joint associated with experimentally induced anterior disk displacement (ADD)

Several studies have shown that anterior disk displacement (ADD) of human temporomandibular joint (TMJ) can lead to cellular and extracellular alterations in the disk proper, bilaminar zone (BZ), condyle, articular eminence and synovial membrane. Due to lack of an animal model for this disease, it is not known whether the mechanical displacement of the disk could lead to the observed histopathological changes. The purpose of this experiment was to investigate the histopathological changes that occur in the rabbit craniomandibular joint (CMJ) following surgical induction of ADD. The right CMJ was exposed surgically and the discal attachments were severed except for the BZ attachments. Then the disk was displaced anteriorly and sutured to the zygomatic arch. The left joint served as surgical control. The CMJs were removed after 24 h, 1 week, 2 weeks or 6 weeks and stained with H&E or modified Masson stain. The results showed neovascularization, cell clustering and fibrillation of the displaced disk. The BZ showed marked fibrosis. The condyle showed subchondral hemorrhage and fibrosis followed by osteoarthritic changes in the articular cartilage. The articular eminence showed chondrocytic clustering and an increase in the amount of chondroid bone. Synovial membrane exhibited marked hyperplasia. We concluded that surgical induction of ADD in the rabbit CMJ leads to cellular and extracellular alterations in the disk proper, BZ, condyle, articular eminence and synovial membrane similar to those described previously in human ADD. It appears that the mechanical trauma resulting from ADD could lead to a cascade of reparative and degenerative changes of the affected joints similar to those described for osteoarthritis.

Effect of condylotomy on matrix synthesis and mineralization in the rat mandibular condylar cartilage

Little information is available about the influence of biomechanical factors on the rate of matrix synthesis and mineralization in the condylar cartilage. In an attempt to temporarily disrupt articular forces at the temporomandibular joint, bilateral condylotomies were performed on 29 day-old male Sprague-Dawley rats. Animals which underwent a similar surgical procedure except for actual condylotomy comprised a sham-operated control group; a non-operated third group served as further controls. Incorporation of [35S]-sulphate did not differ among the groups at 18 h and 2 days after condylotomy, but was significantly reduced in condylotomy animals at 7 and 14 days. Total alkaline phosphatase activity was reduced at 18 h and increased at 14 days by condylotomy, with no differences at the intermediate time intervals; similarly 45Ca-uptake was increased at the 14-day interval. Thus both matrix synthesis and mineralization of the condylar cartilage were altered in the 2 weeks after condylotomy. The changes are in general similar to those noted in other studies after a lessening or removal of articular forces from the condyle.

Effect of condylotomy on DNA synthesis in cells of the mandibular condylar cartilage in the rat

The role of articular forces and the periosteal envelope in the regulation of condylar cartilage growth is uncertain. Transection of the condylar neck, or condylotomy, influences both by a temporary reduction of articular forces and a transient release of the ramus periosteal envelope. To investigate the effects of this procedure on proliferative activity of the prechondroblast layer of the condylar cartilage, bilateral condylotomies were performed on 29-day-old male Sprague-Dawley rats. A surgical control group underwent identical incision without condylotomy and a non-operated third group also served as controls. Eighteen hours after surgery, there was no difference in [3H]-thymidine incorporation among the different treatment groups. However, by two days after surgery, [3H]-thymidine incorporation was significantly higher in the condylotomy group than in either surgical or untreated controls. Incorporation values remained significantly higher in condylotomy animals at seven days after surgery, but declined to control levels by 14 days after surgery. These findings support other radioautographic and cephalometric evidence of an increased growth rate of the condylar cartilage after condylotomy, but suggest that the increase may be transient and perhaps related to the disruption and restoration of articular function.

Variation in alkaline-phosphatase activity with changing load on the mandibular condylar cartilage in the rat

Biomechanical loads were varied by feeding diets of different consistencies. One group was fed hard diet for eight weeks, a second soft diet for eight weeks, and a third soft diet for four weeks followed by four weeks of hard diet. In all groups, alkaline-phosphatase activity was localized primarily in cells and extracellular matrix of the hypertrophic zone, and in cells lining trabeculae of the subcondylar bone. The staining intensity in the hypertrophic zone was slightly less in the soft-diet and soft/hard-diet groups than in the hard-diet group. The thickness of the cell layer staining positively for alkaline-phosphatase was significantly less in the soft-diet group than in the hard- and soft/hard-diet groups.

Effects of experimental loss of teeth on the temporomandibular joint

A review is presented of the effects of loss of teeth, with impaired occlusal stabilization, on the temporomandibular joint in experimental animals. Loss of teeth, with subsequent abnormal loading of the temporomandibular joint, leads to histomorphological, pathological and pathophysiological changes in the articular cartilages, the articular disc, the synovium, and the bony articular components. The severity of the changes increases with increasing age, and an existing arthritis of the joint is aggravated by impaired occlusal stabilization. The experimentally induced changes resemble those in human subjects with extensive loss or extensive attrition of teeth.