The microanatomy of the rhesus monkey temporomandibular joint

Age-related changes in the articular cartilage of the mandible of rats

This study investigated the effects of aging on the articular cartilage of the mandible. Wistar rats were divided in two groups (n = 10/per group): 3-months-old group (young group); and 13-months-old group (aged group). After euthanasia, the head of the mandible was collected and stained with hematoxylin and eosin (HE) to evaluate the thickness of the articular layer and cartilage. Sections stained with Picrosirius red and Safranin O were used to evaluate the collagen and proteoglycans deposition, respectively. First, aging has decreased the articular layer thickness. Second, the results suggest a decrease of chondrocytes followed by an increase of the matrix to maintain the mandible homeostasis. Finally, both collagen and proteoglycans increased with aging. Aging displayed important effects to the mandible of aged rats.

Qualitative study of young, adult, and aged Wistar rats temporomandibular synovial membrane employing light, scanning, and transmission electron microscopy

The aim of this study was to analyze the rat temporomandibular joint (TMJ) synovial membrane at different ages using light, scanning, and transmission electron microscopy. Under light microscopic analysis, the TMJ structures were observed such as condyle, capsule, disk, the synovial membrane collagen type, and cells distribution. In the scanning electron microscopy, the synovial membrane surface exhibited a smooth aspect in young animals and there was an increase with ageing in the number of folds. The transmission electron microscopic analysis showed more synoviocytes in the synovial layer in the young group and still a great number of vesicles and cisterns dilation of rough endoplasmic reticulum in the aged group. In the three groups, a dense layer of collagen fibers in the synovial layer and cytoplasmic extensions were clearly seen. It was possible to conclude that synovial membrane structures in aged group showed alterations contributing to the decrease in joint lubrication and in the sliding between disk and joint surfaces. These characteristic will reflect in biomechanics of chewing, and may cause the TMJ disorders, currently observed in clinical processes.

Recombinant adeno-associated virus serotype 2 (rAAV2)-An efficient vector for gene delivery in condylar cartilage, glenoid fossa and TMJ disc in an experimental study in vivo

OBJECTIVE

To elaborate whether rAAV2 can be used for future TMJ gene therapy, we examined the infection efficiencies of rAAV2 in vitro, and the transgene expression pattern mediated by rAAV2 in glenoid fossa, TMJ disc and condylar cartilage in vivo.

MATERIALS AND METHODS

Different dosages of rAAV2-eGFP (MOI: 5 x 10(4), 1 x 10(4), 5 x 10(3)) were applied to primary cultured condylar chondrocytes of rats. Infection efficiencies were analysed by FACSCalitur at different time points. Vastatin, a molecule not naturally expressed in TMJ, was used as a reporter for detection of rAAV2 mediated transgene expression in vivo. Thirty SD rats were injected with either rAAV2-sec-Vastatin (experimental group) or rAAV2-eGFP (control group) into both sides of TMJ. They were sacrificed at the indicated time (7, 14, 21, 30 and 60 days of injection) and the TMJ samples were collected for RT-PCR and immunostaining analysis.

RESULTS

High dosage (MOI 5 x 10(4)) of rAAV2-eGFP can achieve desirable transduction efficiencies in vitro after 5 days. Transgene expression of rAAV-sec-Vastatin persisted for about 21 days in glenoid fossa, around 7 days in TMJ disc and at least 60 days in condylar cartilage in vivo. In condylar cartilage, transgene expression was found in the proliferative layer and chondroblast layer (day 7), chondrocyte layer (day 14), pre-hypertrophic and hypertrophic layer (day 21), hypertrophic layer and deep hypertrophic layer (day 30 and 60).

CONCLUSION

Recombinant AAV2 could be considered as a promising vector for gene therapy in TMJ which can mediate therapeutic gene expression in glenoid fossa, articular disc and condylar cartilage in vivo.

Surgical Induction of Temporomandibular Joint Ankylosis: An Animal Model

PURPOSE

The aim of this study was to develop an animal model of temporomandibular joint (TMJ) bony ankylosis for future evaluation of surgical reconstructive methods.

MATERIALS AND METHODS

An animal model was selected on the basis of 2 sequential experiments. Four goats and 4 minipigs were used in the first experiment, in which 1 goat and 1 minipig served as control animals. Condylectomy with disc preservation was performed on 1 side of 3 animals in each group. On the contralateral TMJ, condylectomy with discectomy was performed, and the arthroplasty gap was filled with the autogenous bone chips. In the second experiment, TMJ ankylosis was induced bilaterally in 3 additional animals of the species that achieved better ankylosis results in the first experiment. All animals were killed postoperatively at 3 months, and the TMJ complexes were examined by plain radiography, computed tomography, and histological evaluation.

RESULTS

In the first experiment, only fibrous ankylosis was observed in the bone-grafted side of 2 goats and 3 minipigs, whereas fibro-osseous ankylosis was achieved in the remaining goat. The extent of ankylosis was found to be more severe in the goats than the minipigs. Hence, goats were selected for bilateral surgery in the second experiment, which achieved consistent bony ankylosis of the TMJ in all animals.

CONCLUSIONS

Goats provide a better TMJ bony ankylosis model than minipigs. Consistent bony ankylosis can be induced by bilateral condylectomy, disectomy, and bone grafting of the arthroplasty gap.

Reconstruction of Mandibular Condyle by Transport Distraction Osteogenesis: Experimental Study in Rhesus Monkey

PURPOSE

This study investigated histomorphologic changes in the newly formed condyle reconstructed by transport distraction osteogenesis through a nonhuman primate model.

MATERIALS AND METHODS

Six adult rhesus monkeys were used in this study. Bilateral condyles and articular discs were extirpated, and the technique of transport distraction osteogenesis was carried out to reconstruct the condyles. X-ray and 3-dimensional (3D) computed tomography (CT) scanning films were taken at various intervals. Two monkeys were killed respectively at 4, 12, and 24 weeks after completion of distraction; the transport segments and the distracted calluses were harvested and processed for histologic examination. The original condyles removed at surgery served as normal control.

RESULTS

Open bite was seen in all animals postoperatively and diminished at the end of distraction. Bone regeneration was perfect in the distraction gap between the transport disc and the pre-existing mandible. The bony transport disc gradually remodeled to a neocondyle that was similar to the original condyle in the appearances and structures. The head of neocondyle was covered with a fibrous cap, which might play the role of an articular disc.

CONCLUSION

A neocondyle with functional shape can be created by transport distraction osteogenesis. This suggests that this technique is an alternative method for reconstruction of the mandibular condyle.

Nutrition pathways to the symphysis pubis

The blood supply of the symphysis pubis is still the subject of some debate. Classic anatomy books state that this joint is avascular, whereas some published works have shown blood vessels in young specimens. As several articular discs such as the knee menisci are known to have blood vessels in their peripheries, we decided to investigate the possible nutrition pathways to the interpubic disc and ligaments. We used 60 Wistar rats, male and female, aged between 28 and 32 days, or between 90 and 100 days. Samples were processed using a variety of techniques: regular histology, immunohistochemestry, India ink injection and corrosion casting. The interpubic disc consisted of an inner bearing portion and an outer fibrous rim. The interpubic ligaments and the fibrous rim were well vascularized in all groups. Marrow contacts between the interpubic disc and the subchondral bone were also observed. Blood vessels formed an authentic arterial circle embracing the joint, from which blood vessels branched into capillary loops facing the avascular inner bearing portion of the disc. These results confirm the need for future studies on the human symphysis pubis, to provide more details on its structure, which would enable clinicians such as physiotherapists to improve prognosis and treatment design. Future studies may also explain the pathways down which the hormone relaxin reaches its targets within this joint.

Temporomandibular joint in miniature pigs: anatomy, cell replication, and relation to loading

The mechanical environment is a regulator of growth and adaptation of the musculoskeletal system, including joints. Although pigs (Sus scrofa) are used frequently as models for temporomandibular joint (TMJ) dysfunction, no systematic description of microanatomy exists for this species. We injected the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) into 10- to 11-month-old miniature pigs that were undergoing measurements of TMJ bone strain. Ten hr later, the animals were sacrificed and their heads were perfused. Histological sections were used to map the distribution of replicating cells. Additional observations were made on gross dissections of jaw joints obtained from an abattoir. The pig TMJ is better supported than that of humans laterally and medially, but more vulnerable posteriorly. The posterior attachment area of the intra-articular disc is fibro-fatty rather than vascular, as in humans. Cartilage lines the articular eminence as well as the condylar surface. At the posterosuperior region of the condyle, the cartilage ends abruptly and is replaced by an invaginating, actively replicating periosteum. Almost all of the BrdU-labeled cells resided in the prechondroblastic zones. The condyle had more replicating cells than did the eminence (P < 0.02), but lateral and medial locations did not differ in either element. In sagittal sections, the condyle had more replicating cells posteriorly (P < 0.001), but no A-P differences were seen in the eminence. Comparisons of these data with data on bone strain indicate that increased loading is negatively associated with cell replication.