Mandible protraction alters Type I collagen, osteocalcin and osteonectin gene expression in adult mice condyle

Mandible condyle remodeling is a great challenge on craniofacial growth studies. The great majority of the reports deals with growing period. However, there is a great necessity to clarify the importance of functional stimulation on adult mandible condyle remodeling. By using an adult mouse model, we investigated the influence of mandible forwarding on condyle remodeling and gene expression by bone forming cells. Tomographic and scintigraphic evaluations showed sagittal growth and cell activity enhancement. RT-PCR showed that Type I collagen, osteocalcin and osteonectin expression level can be altered. We showed that functional stimulation is necessary to maintain the regular gene expression by condyle bone forming cells in adult mice. It opens new frame for further investigations aiming new clinical approaches to temporomandibular joint problems treatment, as well as mandible retrusion treatment.

Calcitonin and vitamin D3 have high therapeutic potential for improving diabetic mandibular growth

The goal of this study was to assess the effect of the intermittent combination of an antiresorptive agent (calcitonin) and an anabolic agent (vitamin D₃) on treating the detrimental effects of Type 1 diabetes mellitus (DM) on mandibular bone formation and growth. Forty 3-week-old male Wistar rats were divided into four groups: the control group (normal rats), the control C+D group (normal rats injected with calcitonin and vitamin D₃), the diabetic C+D group (diabetic rats injected with calcitonin and vitamin D₃) and the diabetic group (uncontrolled diabetic rats). An experimental DM condition was induced in the male Wistar rats in the diabetic and diabetic C+D groups using a single dose of 60 mg·kg⁻¹ body weight of streptozotocin. Calcitonin and vitamin D₃ were simultaneously injected in the rats of the control C+D and diabetic C+D groups. All rats were killed after 4 weeks, and the right mandibles were evaluated by micro-computed tomography and histomorphometric analysis. Diabetic rats showed a significant deterioration in bone quality and bone formation (diabetic group). By contrast, with the injection of calcitonin and vitamin D₃, both bone parameters and bone formation significantly improved (diabetic C+D group) (P < 0.05). These findings suggest that these two hormones might potentially improve various bone properties.

Influence of immediate and early loading on bone metabolic activity around dental implants in rat tibiae

OBJECTIVES

The aim of this study was to examine the influence of immediate and early loading on dynamic changes in bone metabolism around dental implants using bone scintigraphy.

MATERIAL AND METHODS

Two titanium implants were inserted in the right tibiae of 21 rats. Closed coil springs with 4.0-N loads were applied parallel to the upper portion of the implants for 35 days. According to the load application timing, rats were divided into three groups: immediate loading (IL) group, early loading 1 day after implant insertion (1-D early loading [EL]) group, and loading 3 days after implant insertion (3-D EL) group. Rats were intravenously injected with technetium-99 m-methylene diphosphonate (Tc99 m-MDP) (74 MBq/rat) and scanned by bone scintigraphy at 1, 4, 7, 11, 14, 21, 28, and 35 days after load application. The ratio of accumulation of Tc99 m-MDP around the implants to that of a reference site (uptake ratio) was calculated to evaluate bone metabolism.

RESULTS

In every group, the uptake ratio increased until 7 days after load application and then gradually decreased. It was significantly higher than baseline at 4, 7, 11, and 14 days (P < 0.001). The uptake ratio in the 1-D EL and 3-D EL groups were significantly higher than that in the control group and also that in the IL group (P < 0.001).

CONCLUSIONS

Bone metabolism initially increased and then gradually decreased to baseline despite differences in load timing. Increases in bone metabolic activity differed according to load application timing; the later the load application, the more enhanced the bone metabolism.

Influence of unilateral tooth loss in the temporomandibular joint and masseter muscle of rabbits

OBJECTIVE

The purpose of this study was to evaluate the influence of the masticatory system in patients with missing teeth.

STUDY DESIGN

The influence of tooth loss on the masticatory system was analyzed with the use of bone scintigraphy ((99m)Tc-MDP) and histochemistry. Eight white rabbits (New Zealand, 12 weeks old) were used. The rabbits were divided into 2 groups: 6 weeks and 12 weeks. Teeth were extracted unilaterally in each rabbit under general anesthesia. Six and 12 weeks after extraction, scintigraphy was conducted, and the rabbits were killed and their masseter muscles removed for histochemical analysis.

RESULTS

The results of bone metabolism (relative ratio) measured by bone scintigraphy were 48.27% at extraction sites and 51.73% at nonextraction sites at 6 weeks and 39.96% at extraction sites and 60.04% at nonextraction sites at 12 weeks. There was a significant difference at 12 weeks (P < .05). Tissue calcium contents and osteoclast counts showed different results between the extraction and nonextraction sites, but these differences did not reach statistical significance.

CONCLUSIONS

The bone metabolism of temporomandibular joints and histochemical aspects of masticatory muscles may be associated with occlusal alterations following tooth loss.

Alterations in intermediate filaments expression in disc cells from the rat temporomandibular joint following exposure to continuous compressive force

The articular disc in the temporomandibular joint (TMJ) that serves in load relief and stabilizing in jaw movements is a dense collagenous tissue consisting of extracellular matrices and disc cells. The various morphological configurations of the disc cells have given us diverse names, such as fibroblasts, chondrocyte-like cells and fibrochondrocytes; however, the characteristics of these cells have remained to be elucidated in detail. The disc cells have been reported to exhibit heterogeneous immunoreaction patterns for intermediate filaments including glial fibrillary acidic protein (GFAP), nestin and vimentin in the adult rat TMJ. Because these intermediate filaments accumulate in the disc cells as tooth eruption proceeds during postnatal development, it might be surmised that the expression of these intermediate filaments in the disc cells closely relates to mechanical stress. The present study was therefore undertaken to examine the effect of a continuous compressive force on the immunoexpression of these intermediate filaments and an additional intermediate filament - muscle-specific desmin - in the disc cells of the TMJ disc using a rat experimental model. The rats wore an appliance that exerts a continuous compressive load on the TMJ. The experimental period with the appliance was 5 days as determined by previous studies, after which some experimental animals were allowed to survive another 5 days after removal of the appliance. Histological observations demonstrated that the compressive force provoked a remarkable acellular region and a decrease in the thickness of the condylar cartilage of the mandible, and a sparse collagen fiber distribution in the articular disc. The articular disc showed a significant increase in the number of desmin-positive cells as compared with the controls. In contrast, immunopositive cells for GFAP, nestin and vimentin remained unchanged in number as well as intensity. At 5 days after removal of the appliance, both the disc and cartilage exhibited immunohistological and histological features in a recovery process. These findings indicate that the mature articular cells are capable of producing desmin instead of the other intermediate filaments against mechanical stress. The desmin-positive disc cells lacked α-smooth muscle actin (α-SMA) in this study, even though desmin usually co-exists with α-SMA in the vascular smooth muscle cells or pericytes. Because the precursor of a pericyte has such an immunoexpression pattern during angiogenesis, there is a further possibility that the formation of new vessels commenced in response to the extraordinary compressive force.

Unilateral maxillary molar extraction influences AQP5 expression and distribution in the rat submandibular salivary gland

OBJECTIVE

Mastication has been regarded as a crucial factor for maintaining the morphology and function of secretion in salivary glands. Although it is known that occlusion affects mastication, the detailed process for how occlusal changes affect the secretory function of salivary glands is still unknown. Aquaporin 5 (AQP5) is a membrane protein that forms water channels, and plays an important role in water transport. In this study, we investigated the structural changes and alterations in the expression and distribution of AQP5 in the rat submandibular salivary gland (SMG) under occlusal hypofunction after unilateral molar extraction.

METHODS

Seven-week-old male Wistar rats (n = 36) were used in the study. In the experimental group, all of the right maxillary molars were extracted. Rats with no molar extraction were used as the control group. The rats were euthanized at 7, 14 or 28 days after the procedure, and the right SMGs were isolated and subjected to histological analyses. The expression and distribution of AQP5 were detected by immunohistochemistry.

RESULTS

Morphological analyses revealed hypertrophic changes in the acinar cells in the experimental group. Immunohistochemical staining of AQP5 was detected in the apical membrane (APM) and intercellular secretory canaliculi of acinar cells in both groups. On the other hand, the AQP5 expression in the APM and intercellular secretory canaliculi of acinar cells was less prominent in the experimental group than in the control group.

CONCLUSIONS

The present findings suggest that unilateral molar extraction has significant influences on the function of water transport in the rat SMG.