Hideo Mitani

Skeletal anchorage system for open-bite correction

A skeletal anchorage system was developed for tooth movements. It consists of a titanium miniplate that is temporarily implanted in the maxilla or the mandible as an immobile anchorage. In this article, we introduce the skeletal anchorage system to intrude the lower molars in open-bite malocclusion and evaluate the results of treatment in two severe open-bite cases that underwent orthodontic treatment with the system. Titanium miniplates were fixed at the buccal cortical bone around the apical regions of the lower first and second molars on both the right and left sides. Elastic threads were used as a source of orthodontic force to reduce excessive molar height. The lower molars were intruded about 3 to 5 mm, and open-bite was significantly improved with little if any extrusion of the lower incisors. No serious side-effects were observed during the orthodontic treatment. The system was also very effective for controlling the cant and level of the occlusal plane during orthodontic open-bite correction.

Dual Regulation of Osteoclast Differentiation by Periodontal Ligament Cells through RANKL Stimulation and OPG Inhibition

Periodontal ligament (PDL) cells play an important role in maintaining the homeostasis of periodontal tissues. However, it is not known how PDL cells contribute to osteoclastogenesis. In this study, we examined the consequences of cell-to-cell interactions between peripheral blood mononuclear cells (PBMCs) and PDL cells during osteoclastogenesis. PBMCs were co-cultured directly or indirectly with PDL cells for two to four weeks. PBMCs that were directly co-cultured with PDL cells formed significantly more resorption pits on dentin slices than did PBMCs that were cultured alone. However, soluble factor(s) produced from PDL cells inhibited the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. Furthermore, PDL cells expressed both receptor activator nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) mRNA. In conclusion, PDL cells support osteoclastogenesis through cell-to-cell contact. PDL cells might regulate osteoclastogenesis by opposing mechanisms-stimulation of resorptive activity by RANKL and inhibition by OPG-thus affecting processes such as periodontitis and orthodontic tooth movement.

Long-term effects of chincap therapy on skeletal profile in mandibular prognathism

The purpose of this study was to investigate the long-term changes in the skeletal Class III profile subsequent to chincap therapy. The sample consisted of 63 Japanese girls who had skeletal Class III malocclusions before treatment. All underwent chincap therapy from the beginning of treatment. The duration of chincap therapy varied but averaged 4 1/2 years. The samples were divided into the following three groups according to their ages when chincap therapy was started: A group that started at 7 years of age (n = 23), a group that started at 9 years of age (n = 20), and one that started at 11 years of age (n = 20). The data were derived from lateral cephalometric head films, taken serially at the ages of 7, 9, 11, 14, and 17 years. Skeletal facial diagrams were constructed by X-Y coordinates of representative cephalometric landmarks. The data were analyzed statistically. The results of the present study were as follows: (1) The mandible showed no forward growth during the initial stages of chincap treatment in all three groups. (2) Patients who had entered treatment at 7 and 9 years of age appeared to show a catch-up manner of mandibular displacement in a forward and downward direction before growth was completed. (3) There was no statistical difference in the final skeletal profile between the group that had entered treatment at age 7 and the one that had entered at age 11. In conclusion, the skeletal profile was greatly improved during the initial stages of chincap therapy, but such changes were often not maintained thereafter. This finding indicated that chincap therapy did not necessarily guarantee positive correction of skeletal profile after complete growth.

Anchorage and retentive effects of a bisphosphonate (AHBuBP) on tooth movements in rats.

The purpose of this study was to examine the effect of 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP), a potent blocker of bone resorption, on orthodontic tooth movements in rats. In the first experiment, the right and left upper first molars were moved buccally for 3 weeks with a uniform standardized expansion spring under systemic administration of AHBuBP every other day. The total tooth movement during the 3-week experimental period was 40% of that in the control at a dose of 0.5 mg P/kg. In the second experiment, the right and left upper first molars were first moved buccally for 3 weeks without AHBuBP. The spring was then removed and administration of AHBuBP was initiated. The total relapse movement during the 3-week experimental period was 50% of that in the control at a dose of 0.5 mg P/kg. Results of the first and second experiments were both dose dependent. Histologic examination showed that in the experimental animals fewer osteoclasts appeared on the alveolar bone surface, and both bone resorption and root resorption were inhibited. Inhibition of tooth movement was also observed when AHBuBP was applied topically. These results suggest that AHBuBP could be useful in enhancing anchorage or retaining teeth in orthodontic treatment.

Periodontal tissue activation by vibration: Intermittent stimulation by resonance vibration accelerates experimental tooth movement in rats

INTRODUCTION Accelerating the speed of orthodontic tooth movement should contribute to the shortening of the treatment period. This would be beneficial because long treatment times are a negative aspect of orthodontic treatment. In this study, we evaluated the effects of mechanical stimulation by resonance vibration on tooth movement, and we showed the cellular and molecular mechanisms of periodontal ligament responses. METHODS The maxillary first molars of 6-week-old male Wistar rats were moved to the buccal side by using an expansive spring for 21 days (n = 6, control group), and the amount of tooth movement was measured. Additional vibrational stimulation (60 Hz, 1.0 m/s(2)) was applied to the first molars by using a loading vibration system for 8 minutes on days 0, 7, and 14 during orthodontic tooth movement (n = 6, experimental group). The animals were killed under anesthesia, and each maxilla was dissected. The specimens were fixed, decalcified, and embedded in paraffin. Sections were used for immunohistochemical analysis of receptor activator of NF kappa B ligand (RANKL) expression. The number of osteoclasts in the alveolar bone was counted by using TRAP staining, and the amount of root resorption was measured in sections stained with hematoxylin and eosin. RESULTS The average resonance frequency of the maxillary first molar was 61.02 +/- 8.38 Hz. Tooth movement in the experimental group was significantly greater than in the control group (P <.05). Enhanced RANKL expression was observed at fibroblasts and osteoclasts in the periodontal ligament of the experimental group on day 3. The number of osteoclasts in the experimental group was significantly increased over the control group on day 8 (P <.05). Histologically, there were no pathological findings in either group or significant differences in the amount of root resorption between the 2 groups. CONCLUSIONS The application of resonance vibration might accelerate orthodontic tooth movement via enhanced RANKL expression in the periodontal ligament without additional damage to periodontal tissues such as root resorption.

Effects of chincap force on the timing and amount of mandibular growth associated with anterior reversed occlusion (Class III malocclusion) during puberty

The effects of chincap force on the amount and timing of mandibular growth associated with anterior reversed occlusion (Class III malocclusion) were studied during the pubertal period in 26 Japanese girls. Their records consisted of serial lateral cephalometric roentgenograms, wrist-hand roentgenograms, periodic data of standing height, and time records of chincap use. The stage of pubertal growth was first evaluated by the change of ossification events of hand bones and incremental change of standing height. Mandibular measurements were assessed on this maturational basis. The findings indicated that application of chincap force (500 to 600 g, average 11 to 12 hours per day) hardly alters the general pattern of mandibular growth timing at puberty. With regard to inhibition of growth amounts, the effects seem to take place independently in different parts of the mandible. The length of time of force application per day in the range from 6 to 15 hours did not have a significant role in the change of growth amount and/or timing in the clinical use of the chincap. Individual reactions to the chincap force varied in the effects on mandibular growth variables. Further study of the effects of retrusive orthopedic force on the mandible during the rapid growth phase of puberty is indicated.

The Influences of Molar Intrusion on the Inferior Alveolar Neurovascular Bundle and Root Using the Skeletal Anchorage System in Dogs

The skeletal anchorage system (SAS) was developed as intraoral rigid anchors for open-bite correction by intrusion of molars. Since the application of SAS is a new modality in orthodontic treatment, the influences of radical molar intrusion on the root and the inferior alveolar neurovascular bundle were unknown. The purpose of this research is to verify the effect of molar intrusion on the neurovascular bundle, the level of osseointegration of bone screws, and root resorption. The results of this study showed mandibular molars were intruded 3.4 mm on the average over 7 months in dogs. The miniplates were well stabilized with osseointegrated bone screws and the peri-implant soft tissues showed slight inflammatory changes. Neither nerves nor blood vessels were damaged. Root resorption was observed but was repaired with new cementum. We concluded that the SAS utilizing transmucosal titanium miniplates as an immovable orthodontic anchorage could provide a new modality for molar intrusions without serious iatrogenic problems.

Effects of Maxillary Molar Intrusion on the Nasal Floor and Tooth Root Using the Skeletal Anchorage System in Dogs

The skeletal anchorage system (SAS) was developed to provide intraoral absolute anchorage for the intrusion or distalization of molars. The purpose of this study was to verify the effects of remarkable molar intrusion on the tooth root and the maxillary sinus floor. Six adult female beagles with fully erupted dentition were used. Titanium miniplates were implanted bilaterally above the maxillary second premolar root apices using pentobarbital anesthesia. The second premolars were intruded for four or seven months after three months of healing after implantation. Standardized dental radiographs were taken periodically to evaluate the amount of tooth movement and root resorption. After the experimental animals were fixed by perfusion at the end of each experimental period, the second premolars were dissected along with the surrounding alveolar bone. Undecalcified (60 microm thick) and decalcified (five microm thick) sections were prepared. The average extent of intrusion was 1.8 mm after four months and 4.2 mm after seven months. The root apices of the intruded molars penetrated into the nasal cavity. Remodeled bone around the intruded molar toots was rich in woven bone on the buccal side, whereas that on the palatal side was rich in lamellar bone. Nasal floor membrane and a thin layer of newly formed bone, which lifted intranasally, covered the intruded molar root. Root resorption partly reached into the dentine without the formation of reparative cementum, and little or no serious pathological changes were seen in the pulp of the intruded molars. SAS effectively intruded maxillary molars, but some moderate root resorption was observed.

Effect of stretching on gene expression of β1 integrin and focal adhesion kinase and on chondrogenesis through cell-extracellular matrix interactions

Differentiation of skeletal tissues, such as bone, ligament and cartilage, is regulated by complex interaction between genetic and epigenetic factors. In the present study, we attempted to elucidate the possible role of cell-extracellular matrix (ECM) adhesion on the inhibitory regulation in chondrogenesis responding to the tension force. The midpalatal suture cartilages in rats were expanded by orthopedic force. In situ hybridization for type I and II collagens, immunohistochemical analysis for fibronectin, alpha5 and beta1 integrins, paxillin, and vinculin, and cytochemical staining for actin were used to demonstrate the phenotypic change of chondrocytes. Immunohistochemical analysis for phosphorylation and nuclear translocation of extracellular signal-regulated kinase (ERK)-1/2 was performed. The role of the cell-ECM adhesion in the response of the chondroprogenitor cells to mechanical stress and the regulation of gene expression of focal adhesion kinase (FAK) and integrins were analyzed by using an in vitro system. A fibrous suture tissue replaced the midpalatal suture cartilage by the expansive force application for 14 days. The active osteoblasts that line the surface of bone matrix in the newly formed suture tissue strongly expressed the type I collagen gene, whereas they did not express the type II collagen gene. Although the numbers of precartilaginous cells expressing alpha5 and beta1 integrin increased, the immunoreactivity of alpha5 integrin in each cell was maintained at the same level throughout the experimental period. During the early response of midpalatal suture cartilage cells to expansive stimulation, formation of stress fibers, reorganization of focal adhesion contacts immunoreactive to a vinculin-specific antibody, and phosphorylation and nuclear translocation of ERK-1/2 were observed. In vitro experiments were in agreement with the results from the in vivo study, i.e. the inhibited expression of type II collagen and upregulation in integrin expression. The arginine-glycine-aspartic acid-containing peptide completely rescued chondrogenesis from tension-mediated inhibition. Thus, we conclude that stretching activates gene expression of beta1 integrin and FAK and inhibits chondrogenesis through cell-ECM interactions of chondroprogenitor cells.

An immunohistochemical study of regional differences in the distribution of type I and type II collagens in rat mandibular condylar cartilage

The mammalian temporomandibular joint is a highly specialized diarthrodial joint under multidirectional compressive and tensile forces. In such a complicated biomechanical environment, the phenotypic expression of extracellular matrix may vary in different regions of the mandibular condylar cartilage. To test this hypothesis, immunohistochemical techniques were used to examine the localization of type I and type II collagens in various anterioposterior regions of the condylar cartilage of 4-week-old rats. In the posterosuperior region, which is mainly subjected to compressive forces, a strong reaction for type II collagen was observed in the cartilaginous layer (maturative and hypertrophic cell layers), and a rather weak reaction was observed for type I collagen in the precartilaginous and cartilaginous layers, compared with the reactions in other peripheral regions. Proceeding anteriorly, staining for type I collagen increased, while that for type II collagen decreased. In posteroinferior cartilage, which is subjected mainly to tensile forces because of its direct attachment to the retrodiscal pad, staining for type I collagen was strong, and that for type II collagen was faint in the cartilaginous layer. These results demonstrate that marked regional differences exist in the phenotypic expression of two major collagen components in mandibular condylar cartilage, which may reflect the local functional environment and cellular response.