Hiroki Sugiyama

Effects of Bisphosphonate on the Remodeling of Rat Sagittal Suture After Rapid Expansion

The purpose of this study was to investigate the effects of bisphosphonate (BP), an inhibitor of bone resorption, on the remodeling of the rat sagittal suture after rapid expansion. Wistar strain male rats were divided into 4 groups and subjected to rapid mechanical expansion with an initial force of 60 g for 3 days. Immediately after the sutural expansion, the appliance was removed in 2 of the groups. In the S group, half of the animals were injected with saline solution daily for 3 days and the other half were injected daily for 7 days prior to sacrifice. In the B group, half of the animals were injected with bisphosphonate daily for 3 days and the other half were injected daily for 7 days prior to sacrifice. The remaining 2 groups underwent 7 days of mechanical retention before the appliance was removed. In the SR group, half of the animals were injected with saline solution daily for 3 days and the other half were injected daily for 7 days prior to sacrifice. In the BR group, half of the animals were injected with bisphosphonate solution daily for 3 days and the other half were injected daily for 7 days prior to sacrifice. The calvariae were fixed in 4% neutral formalin, decalcified, and embedded in paraffin. The amount of relapse and the relevant bone remodeling were evaluated in terms of a relapse ratio and the number of osteoclasts. The relapse ratio was 54.11% in the S group and 32.53% in the B group 7 days after the injection. This ratio was 25.13% in the SR group and 9.60% in the BR group. The number of osteoclasts 3 days after injection was 15.47 in the S group, which was significantly greater than the 5.26 present in the B group. This number was 7.08 in the SR group, which was significantly greater than the 1.83 in the BR group. These results demonstrate that the injection of BP after rapid expansion, if combined with mechanical retention, may produce more secure retention by inhibiting bone resorption, indicating a possibility of employing a pharmaceutical aid to decrease the skeletal relapse after mechanotherapy in clinical orthodontics.

Influences of vertical occlusal discrepancies on condylar responses and craniofacial growth in growing rats.

The present study was conducted to investigate the influence of vertical occlusal discrepancies on condylar remodeling and the subsequent craniofacial growth in growing rats. Thirty 4-week-old male Wistar strain rats were used. A 1-mm-thick metal plate was bonded onto the occlusal surface of the maxillary molars to increase posterior dentoalveolar height. During the early phase of the experiment, the thickness of the proliferative and maturative/hypertrophic zones in the anterior and superior portions of the condyle was significantly smaller in the experimental group than in the controls. The number of TRAP-positive cells was significantly greater in the experimental group than in the controls. At the end of the experiment, decreased ramus height and a large gonial angle were found in the experimental group. Changes in the intra-articular environment associated with vertical occlusal discrepancies may influence condylar and craniofacial growth in growing individuals, although some adaptive response of the condyle may be induced if growth potential remains.

Changes in Urinary Bone Resorption Markers (Pyridinoline, Deoxypyridinoline) Resulting from Experimentally-Induced Osteoarthritis in the Temporomandibular Joint of Rats

ABSTRACT The purpose of this study was to quantify the urinary bone resorption markers, pyridinoline (Pyr) and deoxypyridinoline (Dpyr), excreted from experimentally-induced osteoarthritis (OA) in the temporomandibular joint (TMJ) of rats. Osteoarthritic lesions were induced by intra-articular injection of collagenase into the right TMJs of 16-week-old male rats. The whole days urine was collected from each animal one day before the injection and 5,7,11 and 14 days after the injection. Urine samples were analyzed by high-performance liquid chromatography and fluorescence spectroscopy. Histological changes in condyle were examined by using paraffin sections with toluidine blue staining. Degenerative changes were observed in the articular cartilage of the experimental group on day 7 and day 14 after the injection of collagenase. The concentration of Pyr was remarkably high in the experimental group, and consequently the Pyr to Dpyr ratio was significantly higher (p<0.05) in the experimental group than in the control group from 7–14 days after the injection. These findings suggest that a urinary Pyr/Dpyr ratio would be available for the detection of degenerative changes in condyle relevant to temporomandibular joint osteoarthritis (TMJ OA).

Transplantation of new autologous biomaterials into jaw cleft

This study compared bone-marrow grafting using chondroid or fibula bone grafts transplanted into simulated alveolar bone defects in mice. The osteogenic procedure was also investigated. As an experimental model of the maxillary alveolar bone cleft, suitable for testing bone-inductive materials, a surgical trephine with a low-speed dental engine was used to form critical-sized defects in the pre-maxillary bones of male mice. Distraction osteogenesis was performed using an external fixation device. The osteotomy site was surrounded by an external callus, consisting of hyaline cartilage, that contained a large quantity of chondroid bone. Transplanted bone within chondroid bone was characterized by bone formation and remodelling 30 days post-transplantation, and bone adhesion following chondroid bone grafting was better than adhesion following fibula grafting. The present findings are the first to demonstrate the potential of chondroid bone transplantation as a new therapeutic system of bone grafting, suitable for bone substitution in craniofacial bone defects.

Sexual dimorphism in the trigeminal motor neurons innervating the mouse masseter muscle

The extrafusal and intrafusal muscle fibers in the masseter muscle are innervated by motoneurons in the trigeminal motor nucleus (Mo 5). In the present study, we found that the number of trigeminal motor neurons in the male mouse was significantly larger than that in the female. However, we could not detect any significant difference between male and female mice in the number of sensory neurons in the trigeminal mesencephalic nucleus (Me 5). This is the first report on sexual dimorphism in masticatory motoneurons of mammals.

Long-Term Granular Diet May Lead to Declined Resistance to Trauma of the Temporomandibular Joint

This study was carried out to determine the effect of food texture on the response to trauma of the temporomandibular joint in mice. Animals were fed either a solid or granular diet after weaning. At 8 weeks old, condylar hypermobility was induced by forcing the mouth wide open ten times under ether anaesthesia. This procedure was repeated 10 times once daily for 10 consecutive days. The temporomandibular joint tissues were observed microscopically on day 0 and then 2 days, 5 days, 2 weeks, 3 weeks and 5 weeks after the last forced opening. Eighteen male mice were used in total, three for each timepoint. A proliferation in synovial surface cells and an increased number of capillaries were seen at day 2 in the mice fed a granular diet, but not in those fed a solid diet. Multiple cell layers of the synovial membrane, dilated capillaries and fibrin deposits were expanded further between day 2 and week 5 in the mice fed a granular diet, but not until day 5 to week 5 in the mice that had been fed a solid diet. At week 3, the mice fed a granular diet showed erosion of the anterior articular disc. This was observed in both dietary groups at week 5. This study suggests that, in advanced countries, people who habitually eat easily chewable food should be advised that such practice may lead to a decline in the resistance to trauma of the masticatory system.