Takashi Yamashiro

Influences of Ovariectomy on Experimental Tooth Movement in the Rat

Estrogen withdrawal, which is important in the pathogenesis of post-menopausal osteoporosis, accelerates bone metabolism with a negative calcium balance. Therefore, it is hypothesized that estrogen deficiency could affect the rate of experimental tooth movement and alveolar bone remodeling. Six-week-old rats received a bilateral ovariectomy (OVX) or sham operation. Fourteen days later, rats were subjected to lateral tooth movement in the upper molar with nickel-titanium wire of 10 g of force. OVX significantly increased the rate of experimental tooth movement from 12 days after experimental tooth movement (p < 0.001). Eighteen days after the start of tooth movement, bone histomorphometry demonstrated that OVX significantly elevated the osteoblast surface, osteoclast surface, and number of osteoclasts (p < 0.05) in the alveolar bone. These findings indicated that estrogen deficiency caused significantly rapid orthodontic tooth movement, and that the acceleration of tooth movement could be due to the further activation of alveolar bone turnover.

The Effect of Local Application of 1,25-Dihydroxycholecalciferol on Osteoclast Numbers in Orthodontically Treated Rats

Orthodontic tooth movement requires remodeling of periodontal tissues, especially alveolar bone. 1,25-(OH)2D3, the active form of vitamin D 3, is known to be a potent stimulator of osteoclastic bone resorption. The purpose of this study was to investigate the effect of local application of 1,25-(OH)2D3 on osteoclast numbers induced by experimental tooth movement. A piece of orthodontic elastic band was inserted between the first and second upper molars of male Wistar rats weighing about 200 g each. Twenty μL of 1,25-(OH)2D3 (10-12-10 -7 mol/L) was injected locally into the submucosal palatal area of the root bifurcation of the right first molar. The left side was injected with phosphate-buffered saline (PBS). The number of osteoclasts was counted in a 700 x 1050 μm2 area of the interradicular septum. The local injection of 1,25-(OH)2D3 caused a dose-dependent increase in osteoclast number. The effect of 1,25-(OH)2D3 reached a response plateau at 10-10 mol/L when greater than a threefold rise in osteoclast number was attained compared with the PBStreated controls. While the insertion of a piece of elastic band for three days induced a significant increase in osteoclasts in the alveolar bone, daily injections of 20 μL of 10-10 mol/M 1,25-(OH)2D 3 for three days markedly stimulated the numbers of osteoclasts induced by the insertion of an elastic band. 1,25-(OH)2D3 was apparently synergistic with mechanical stimuli, resulting in enhancement of the numbers of osteoclasts induced by mechanical stimuli alone. These findings suggest that the local application of 1,25-(OH)2D 3 acted directly to increase osteoclast number and to potentiate osteoclastic bone resorption induced by mechanical stimuli.

Effect of Age on the Rate of Tooth Movement in Combination with Local Use of 1,25(OH) 2D3 and Mechanical Force in the Rat

The purpose of this study was to compare the amount and rate of tooth movement in young and mature rats administered 1,25(OH)2D3 simultaneous with application of mechanical force. In 30 seven-week-old and 30 28-week-old male Wistar rats, the right maxillary first molar was moved buccally with a fixed appliance. The appliances delivered forces ranging from 5 to 20 g. Twenty μL of 1,25(OH)2 D3 (10-10 and 10-8 mol/L) was injected locally into the submucosal palatal area of the root bifurcation of the right first molar. The left side was injected with phosphate-buffered saline (PBS). In young rats receiving 10-10 mol/L 1,25(OH)2D3 every three days, tooth movement significantly increased to 126% ofthat in PBS-injected control rats on day 20. In 1,25(OH)2D3-injected mature rats, tooth movement was stimulated markedly and increased with 10-10 mol/L to 245% and with 10-8 mol/L to 154% of the amount of tooth movement seen in the PBS-injected controls by the end of the experiment. PBS-injected rats had a plateau stage where tooth movement did not occur at all, while there was no such lag-time in the 1,25(OH)2D 3-injected group which showed continuous tooth movement. The local injection of 1,25(OH)2D3 did not change serum calcium, phosphate, and alkaline phosphatase activity, and there were no apparent clinical or microscopic side-effects.

Isolation of multipotent stem cells in human periodontal ligament using stage-specific embryonic antigen-4

The periodontal ligament (PDL) comprises adult stem cells, which are responsible for periodontal tissue regeneration. In the present study, we investigated the specific profile of the stem cells in the human PDL. Microscopic analysis demonstrated that PDL cells showed a fibroblastic appearance, forming flat and loose aggregates. PDL cells expressed embryonic stem cell-associated antigens (SSEA-1, SSEA-3, SSEA-4, TRA-1-60, TRA-1-81, OCT4, NANOG, SOX2, and REX1, and alkaline phosphatase activity), as well as conventional mesenchymal stem cell markers. When PDL cells were cultured in the presence of all-trans-retinoic acid, the numbers of SSEA-3+ and SSEA-4+ PDL cells were significantly decreased, while that of SSEA-1+ was increased. SSEA-4+ PDL cells showed a greater telomere length and growth rate. SSEA-4+ PDL cells exhibited the potential to generate specialized cells derived from three embryonic germ layers: mesodermal (adipocytes, osteoblasts, and chondrocytes), ectodermal (neurons), and endodermal (hepatocytes) lineages. Our findings demonstrated that SSEA-4, a major antigen to distinguish human embryonic stem cells, could also be used to identify multipotent stem cells in the PDL. Hence, SSEA-4+ human PDL cells appear to be a promising source of stem cells for regenerative medicine.

Distal Movement of Maxillary Molars Using Miniscrew Anchorage in the Buccal Interradicular Region

OBJECTIVE To quantify the treatment effects of interradicular miniscrew anchorage and to confirm the validity of the clinical usage of interradicular miniscrews in the distal movement of maxillary molars in nonextraction treatment. MATERIALS AND METHODS Twenty-four maxillary molars were moved to the distal using miniscrews placed in the interradicular space between the second premolar and the first molar at an oblique angle of 20 to 30 degrees to the long axis of the proximal tooth. The teeth were evaluated as to how the molars were moved to the distal with the use of lateral cephalograms and dental casts. RESULTS Maxillary molars were moved to the distal by 2.8 mm with distal tipping of 4.8 degrees and intruded by 0.6 mm. Maxillary incisors were moved to the distal by 2.7 mm with palatal tipping of 4.3 degrees. Molar extrusion and/or consequent mandibular rotation was not observed in any patient. CONCLUSION Miniscrews placed in the maxillary interradicular space provide successful molar distal movement of 2.8 mm without patient compliance and with no undesirable side effects such as incisor proclination, clockwise mandibular rotation, or root resorption.

Gene and protein expression of brain-derived neurotrophic factor and TrkB in bone and cartilage

Gene and protein expressions of brain-derived neurotrophic factor (BDNF) and TrkB, the high-affinity receptor of BDNF, were investigated in the femur and mandibular condyle of rats by in situ hybridization and immunohistochemistry. BDNF and TrkB mRNA showed overlapped expression in chondrocytes in proliferating and mature zones of the epiphyseal growth plate cartilage and mandibular condylar cartilage, and in cuboidal-shaped active osteoblasts at the site of endochondral and intramembranous ossification and in trabecular bone. Expression of BDNF protein also showed a similar localization. The present study suggests that BDNF may participate in regulating the development and remodeling of bony tissue in the developing rat.

Possible roles of Runx1 and Sox9 in incipient intramembranous ossification

We evaluated the detailed expression patterns of Runx1 and Sox9 in various types of bone formation, and determined whether Runx1 expression was affected by Runx2 deficiency and Runx2 expression by Runx1 deficiency. Our results indicate that both Runx1 and Sox9 are intensely expressed in the future osteogenic cell compartment and in cartilage. The pattern of Runx1 and Sox9 expression suggests that both genes could potentially be involved in incipient intramembranous bone formation during craniofacial development.

Denervation Resulting in Dento-Alveolar Ankylosis Associated with Decreased Malassez Epithelium

Inferior alveolar nerve denervation causes appreciable decreases in the distribution of epithelial rests of Malassez. To explore roles of the Malassez epithelium, we attempted to evaluate possible changes in dento-alveolar tissues surrounding this epithelium by experimental denervation. We found that denervation led to dento-alveolar ankylosis with a decrease in the width of the periodontal spaces. Interestingly, with regeneration of the Malassez epithelium 10 weeks after the denervation, the periodontal space width showed a correspondingly significant increase. These findings suggest that the Malassez epithelium may be involved in the maintenance of periodontal space and that sensory innervation might be indirectly associated with it. In addition, it is of interest that denervation activated root resorption of the coronal root surface and that the consequently resorbed lacunae were repaired by cellular cementum. It is suggested that Malassez epithelium may negatively regulate root resorption and induce acellular cementum formation.

Hormonal, pH, and Calcium Regulation of Connexin 43–Mediated Dye Transfer in Osteocytes in Chick Calvaria

Gap junctional intercellular communication among osteocytes in chick calvaria, their natural 3D environment, was examined using FRAP analysis. Cell–cell communication among osteocytes in chick calvaria was mediated by Cx43 and was regulated by extracellular pH, extracellular calcium ion concentration, and PTH.

A Cineradiographic Study of Deglutitive Tongue Movement and Nasopharyngeal Closure in Patients with Anterior Open Bite

The purpose of this study was to investigate the movement of the tip and the dorsal surface of the tongue during deglutition in patients with anterior open bite using cineradiography. The subjects were 10 female patients with anterior open bites and 10 female controls with normal overbites. By cineradiography we established 7 stages of tongue movement and bolus position during deglutition and analyzed the tongue position, tongue movement and the time. The tongue-tip position was more protrusive during deglutition in anterior open bite than in the controls. After the head of the bolus arrived at the opening of the esophagus, the rear part of the dorsal surface of the tongue demonstrated slower movement in patients with anterior open bite than in controls. The nasopharynx closed earlier in patients with anterior open bite than in controls. It is suggested that anterior open bite patients had compensatory coordination of tongue movement, soft palate movement and pharyngeal constrictor muscle activity during deglutition.