Ikuo Yonemitsu

Mechanical loading leads to osteoarthritis-like changes in the hypofunctional temporomandibular joint in rats.

OBJECTIVES Temporomandibular joint (TMJ) hypofunction secondary to feeding a liquid diet in the growing period leads to morphological hypoplasia. However, few studies have evaluated the results of mechanical loading on the hypoplastic TMJ. This study investigated whether TMJ hypofunction in rats causes osteoarthritis (OA)-like changes when exposed to mechanical loading. DESIGN Male 21-day-old Wistar rats were divided into four groups. The first group (C) served as the control. In the second group (W), mechanical loading was applied to the TMJ by continuous steady mouth opening (3h/day for 5 days) from 63 days of age. A jaw-opening device was used to hold the mandible open in the maximal mouth-opening position with a cobalt-chromium (Co-Cr) wire (φ: 0.9mm). Groups C and W both received a normal hard diet. The third group (L) and fourth group (LW) were fed a liquid diet and group LW were subjected to the same loading as group W. We evaluated the TMJ using micro-CT, toluidine blue staining and immunohistochemistry of matrix metalloproteinase (MMP)-13. RESULTS In group LW in the superior and posterior regions of the condyle, bone volume fraction, trabecular thickness and trabecular number were significantly decreased and trabecular spacing was significantly increased. The ratio of MMP-13 immunopositive cells was significantly higher than in the other groups. OA-like changes were also observed, including reduced thickness of the cartilage, irregularities in the chondrocytic layer, and cell-free areas. CONCLUSIONS TMJ hypofunction in rats is likely to lead to OA-like changes when exposed to mechanical loading.

Functional Lateral Shift of the Mandible Effects on the Expression of ECM in Rat Temporomandibular Cartilage

OBJECTIVE To test the hypothesis that the effects of mechanical stress from a functional lateral shift of the mandible have no effect on the expression of two main condylar cartilage extracellular matrix components, type II collagen and aggrecan, in rats from early puberty to young adulthood. MATERIALS AND METHODS Functional lateral shift of the mandible was induced in experimental groups of 5-week-old male Wistar rats, using guiding appliances. The rats were sacrificed at 3, 7, 14, and 28 days post appliance attachment. The condyles were immunohistochemically evaluated for type II collagen and aggrecan (the immunoreactive areas were quantified). RESULTS As compared with the control group, on the contralateral condyles, the immunoreactivity of the experimental groups was significantly increased from 7 to 14 days. While on the ipsilateral condyles, the immunoreactive areas were significantly decreased throughout the experimental period. CONCLUSION A functional lateral shift of the mandible modulated the condylar cartilage extracellular matrix differently on each side of the condyle, which affected condylar morphology, growth, biomechanical properties, and even the susceptibility of the condylar cartilage to pathogenesis.

Intermittent posterior displacement of the rat mandible in the growth period affects the condylar cancellous bone

OBJECTIVE To examine whether intermittent posterior condylar displacement causes changes in cancellous bone in the mandibular condyle during the growth period. MATERIALS AND METHODS Sixteen 5-week-old male Wistar rats were divided into experimental and control groups. In the experimental group, an appliance was attached to the maxillary incisors to induce posterior displacement of the condyles in the occluded condition. Untreated rats served as the control group. Animals were sacrificed at 14 days, and the condyles were removed to analyze the three-dimensional cancellous bone structure by microcomputed tomography (micro-CT). Serial sagittal paraffin sections of the condyles were used for hematoxylin and eosin staining to investigate histomorphological changes and for tartrate-resistant acid phosphatase (TRAP) staining to identify osteoclastic cells. RESULTS Micro-CT analysis showed that in the experimental group, the bone volume fraction and the degree of anisotropy were significantly decreased compared with those in the control group in the anterior region of the condyle. Moreover, the number of TRAP-positive cells was significantly greater in the same region in the experimental group than in the control group. CONCLUSION Intermittent posterior displacement of the mandible can cause region-specific changes in the profile and microarchitecture of the condylar cancellous bone.

Effect of functional shift of the mandible on lubrication of the temporomandibular joint

Lubrication of synovial joints reduces the coefficient of friction of the articular cartilage surface. To investigate the effect of malocclusion on the lubrication of the temporomandibular joint (TMJ), we evaluated lubricin expression in the rat TMJ immunohistochemically, under conditions of functional lateral shift of the mandible, during period of growth. Thirty 5-week-old male Wistar rats were divided into experimental, recovery, and control groups. Each rt in the experimental and recovery groups was fitted with an acrylic-plate guiding appliance. The rats in the experimental and control groups were killed at 14 and 28 days after the appliance was attached. Each rat in the recovery group was detached from the appliance at 14 days, and was killed 14 days after the appliance was removed. In the experimental group, the expression of lubricin staining in TMJ cartilage was significantly decreased during the experimental period. In the recovery group, the expression of lubricin staining in TMJ cartilage was significantly greater than in the experimental group, and there was no significant difference at 28 days between the control and recovery groups. Analysis of these data suggests that a functional lateral shift of the mandible during the growth period influences lubrication of the TMJ.

Influence of liquid diet feeding on calcitonin gene-related peptide-like immunoreactive nerve fibers in rat temporomandibular joints during growth period

Abstract Biomechanical factors of masticatory functions are related to the development of the temporomandibular joint (TMJ) components during growth. However, the effects on nerve fibers have not been fully clarified. We investigated the influence of masticatory muscle activity on nerve fibers in the TMJ during growth by changing the consistency of diet. Twenty 3-week-old male Wistar rats were divided into two groups. The experimental group was fed a liquid diet, while the control group had a normal hard diet. Rats were sacrificed at 6-, and 9-week-old. We investigated the expression of calcitonin gene-related peptide-like immunoreactive (CGRP-LI) nerve fibers, which are most abundant in the TMJ and have a nociceptive function, using immunohistochemistry for CGRP. No significant difference in the number of CGRP-LI nerve fibers was detected in 6-week-old rats, but in 9-week-old ones the number in the experimental group was significantly greater than that in the control. We concluded that masticatory muscle activity in the TMJ closely correlates with peripheral sensory nerve fibers during growth.

Severe unilateral scissor bite and bimaxillary protrusion treated by horseshoe Le Fort I osteotomy combined with mid-alveolar osteotomy

This report describes an orthognathic surgical case employing horseshoe Le Fort I osteotomy (HLFO) combined with mid-alveolar osteotomy and bilateral sagittal split ramus osteotomy (BSSRO) for a patient with severe unilateral scissor bite and bimaxillary protrusion. A female patient (aged 26 years, 2 months) presented with a chief complaint of dysmasesis caused by scissor bite on the right side. The clinical examination revealed difficulty in lip closure and a convex profile. Overerupted right maxillary premolars and molars and lingual tipping of the right mandibular premolars and molars were indicated before treatment. After 3 months of presurgical orthodontic treatment, two-jaw surgery involving a combination of HLFO with mid-alveolar osteotomy and BSSRO was performed. A good interdigitation in the right side was established by superior-posterior-medial movement of the dento-alveolar segment of the maxilla. Next, both the maxilla and mandible were moved superiorly and posteriorly to correct the improper lip protrusion, thereby improving the patients profile. Our results suggest that this new orthognathic surgery technique-achieved by combining HLFO with mid-alveolar osteotomy and BSSRO-is effective for adult patients exhibiting severe unilateral scissor bite and bimaxillary protrusion.

Unilateral nasal obstruction induces morphological changes of the mandibular condyle in growing rats

Abstract Purpose Chronic nasal obstruction is known to decrease blood oxygen saturation. Mouth breathing in association with chronic nasal obstruction leads to the collapse of the buccinator mechanism and to a clockwise rotation of the mandible, which causes mandibular retrusion. This study aimed to investigate the influences of nasal obstruction on the morphological and histological changes of the mandible in growing rats. Materials and methods Thirty 8-day-old male Wistar rats were randomly divided into the control and experimental groups. The experimental group underwent unilateral nasal obstruction by cauterization of the external nostrils at 8 days of age. Pulse oxygen saturation (SpO2) was monitored every week. Rats were sacrificed at 9 weeks of age. The mandibular changes were analyzed via lateral cephalometric radiographs and micro-CT scans. We utilized toluidine blue and tartrate-resistant acid phosphatase (TRAP) staining for histological analysis. Immunohistochemical staining of hypoxia induced factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), osteoprotegerin (OPG) receptor activator of nuclear factor kappa-B ligand (RANKL) were also performed to reveal the mechanism of the morphological changes. Results SpO2 was significantly lower in the experimental than in the control group. In the experimental group, length, bone mineral density and cartilage layer thickness of mandibular condyle were decreased. The number of TRAP-positive cells in the condyle, HIF-1α-positive cells, VEGF-positive cells and RANKL-positive cells in the condylar cartilage was significantly increased. In contrast, a reduced expression of OPG protein was observed in the experimental group. Conclusions Our findings suggest that unilateral nasal obstruction in the growth period affects mandibular morphology.

Effects of unilateral nasal obstruction on the characteristics of jaw-closing muscles in growing rats

OBJECTIVES: Mouth breathing caused by nasal obstruction (owing to abnormal pressure of masticatory muscles) affects craniofacial growth and development. The influence of unilateral nasal obstruction on jaw-closing muscles was investigated in rats to reveal one of the etiologic mechanisms. MATERIALS AND METHODS: Forty 8-day-old male Wistar rats were used in this study. Experimental rats were subjected to left-sided nasal obstruction by burning the external nostril tissue at the age of 8 days. Pulse oxygen saturation was recorded each week. Morphologic changes were evaluated by staining with hematoxylin and eosin (to assess the cross-sectional area) and by adenosine triphosphatase activity staining (to assess the myosin heavy chain isoform composition). Immunohistochemical and reverse transcription quantitative real-time polymerase chain reaction analyses of tumor necrosis factor-α and glucose transporter 4 were carried out at 5 and 9 weeks of age. RESULTS: The cross-sectional area of the jaw-closing muscles was lower in the experimental group at 9 weeks of age. The percentage of myosin heavy chain-2a in masseter muscles was increased in the experimental group compared with the control group. An increase in the tumor necrosis factor-α messenger RNA and protein levels and a decrease in the glucose transporter 4 messenger RNA and protein levels at 5 and 9 weeks of age in the jaw-closing muscles in the experimental group were noted. CONCLUSIONS: Unilateral nasal obstruction could affect the morphology and contractile characteristics of jaw-closing muscles during growth in rats.

The imbalance of masticatory muscle activity affects the asymmetric growth of condylar cartilage and subchondral bone in rats.

OBJECTIVE To examine the effects of imbalance of masticatory muscle activity of the rat mandible on the condylar cartilage and subchondral bone during the growth period. DESIGN Forty 5-week-old male Wistar rats were randomly divided into experimental (n=20) and control (n=20) groups. In the experimental group, the left masseter muscles were resected. The rats were sacrificed at 7 or 9 weeks of age in both groups. Microcomputed tomography was used to determine the three-dimensional morphology and cancellous bone structure. For histological and histochemical examination, 5-μm-thick serial frontal sections of the condyle were stained with toluidine blue and immunostained with asporin and TGF-β1 to evaluate the promotion and inhibition of chondrogenesis. RESULTS In the experimental group, microcomputed tomography analysis showed asymmetric growth; the resected side condyles showed degenerative changes. Histological analysis showed that the total cartilage in the central region of the resected side was significantly thinner than in the non-resected side in the experimental group, as well as in the control group. Compared with the control group, the expression of asporin was significantly higher in the resected side, and significantly lower in the non-resected side. In contrast, the expression of TGF-β1-immunopositive cells in the non-resected side was significantly higher than in the resected side and the control group. CONCLUSIONS These findings imply that lateral imbalance of masseter muscle activity lead to inhibition of chondrogenesis and induce asymmetric formation of the condyle during the growth period.