Akihiko Nakasima

Effects of Static Magnetic Fields on Bone Formation in Rat Osteoblast Cultures

Although the promotional effects on osteoblasts of pulsed electromagnetic fields have been well-demonstrated, the effects of static magnetic fields (SMF) remain unclear; nevertheless, magnets have been clinically used as a ’force source’ in various orthodontic treatments. We undertook the present investigation to study the effects of SMF on osteoblastic differentiation, proliferation, and bone nodule formation using a rat calvaria cell culture. During a 20-day culture, the values of the total area and the number and average size of bone nodules showed high levels in the presence of SMF. In the matrix development and mineralization stages, the calcium content in the matrix and two markers of osteoblastic phenotype (alkaline phosphatase and osteocalcin) also showed a significant increase. Accordingly, these findings suggest that SMF stimulates bone formation by promoting osteoblastic differentiation and/or activation.

Hereditary factors in the craniofacial morphology of Angle's Class II and Class III malocclusions

We attempted to assess the role of heredity in the development of Angles Class II and Class III malocclusions by comparing craniofacial morphologic differences between parents with Class II offspring and those with Class III offspring and by analyzing the parent-offspring correlations within each Class II and Class III malocclusion group. Lateral and frontal roentgenographic cephalograms were obtained for ninety-six patients with Class II malocclusion, 104 patients with Class III malocclusion, and their respective parents. Mean cephalometric profile diagrams were superimposed between the two groups of parents as well as between their offspring. Within the two groups, the parent-offspring correlation coefficients were computed for nineteen variables connecting cephalometric landmarks. The differences in the craniofacial complex were evident in the two groups of parents as well as in their offspring. High correlation coefficient values were seen between parents and their offspring in the Class II and Class III groups. Thus, there appears to be a strong familial tendency in the development of Class II and Class III malocclusions. We conclude that the hereditary pattern must be taken into consideration in the diagnosis and treatment of patients with these classes of malocclusion.

Root Resorption and Immune System Factors in the Japanese

The objective of this study was to determine whether there is an association between excessive root resorption and immune system factors in a sample of Japanese orthodontic patients. The records of 60 orthodontic patients (18 males, age 17.7 +/- 5.7 years; 42 females, age 16.4 +/- 6.0 years) and 60 pair-matched controls (18 males, age 15.9 +/- 4.5 years; 42 females, age 18.5 +/- 5.2 years) based on age, sex, treatment duration, and the type of malocclusion were reviewed retrospectively. The validity of our hypothesis was tested using the logistic regression analysis. The pretreatment records revealed that the incidence of allergy and root morphology abnormality was significantly higher in the root resorption group (P = .030 and .001), with a mean odds ratio of 2.794 and 6.317 and 95% confidence interval of 1.107-7.053 and 2.043-19.537, respectively. The incidence of asthma also tended to be higher in the root resorption group. From these results, we concluded that allergy, root morphology abnormality, and asthma may be high-risk factors for the development of excessive root resorption during orthodontic tooth movement in Japanese patients.

Expression of the type I collagen gene in rat periodontal ligament during tooth movement as revealed by in situ hybridization

The in situ hybridization technique used digoxigenin-labelled oligodeoxynucleotide. In untreated molars, cells expressing a positive signal for type I collagen mRNA were distributed uniformly in the periodontal ligament space. After experimental tooth movement, the density of cells expressing a positive signal appeared to be much greater in the tension side than the pressure side. In both sides the distribution of the positively hybridizing cells was uniform along the principal fibres of the ligament. This characteristic distribution appeared at 12 h after the initiation of tooth movement, reached a maximum at 1-3 days, and persisted for about 14 days during the treatment. These results indicate that the remodelling of collagen fibres in periodontal ligament occurs in an orderly manner throughout the principal fibres, mainly on the tension side, and that the recovery of gene expression for type I collagen occurs within the first 14 days in response to experimental tooth movement.

Neurotrophic factor neurotrophin-4 regulates ameloblastin expression via full-length TrkB

Neurotrophic factors play an important role in the development and maintenance of not only neural but also nonneural tissues. Several neurotrophic factors are expressed in dental tissues, but their role in tooth development is not clear. Here, we report that neurotrophic factor neurotrophin (NT)-4 promotes differentiation of dental epithelial cells and enhances the expression of enamel matrix genes. Dental epithelial cells from 3-day-old mice expressed NT-4 and three variants of TrkB receptors for neurotrophins (full-length TrkB-FL and truncated TrkB-T1 and -T2). Dental epithelial cell line HAT-7 expressed these genes, similar to those in dental epithelial cells. We found that NT-4 reduced HAT-7 cell proliferation and induced the expression of enamel matrix genes, such as ameloblastin (Ambn). Transfection of HAT-7 cells with the TrkB-FL expression construct enhanced the NT-4-mediated induction of Ambn expression. This enhancement was blocked by K252a, an inhibitor for Trk tyrosine kinases. Phosphorylation of ERK1/2, a downstream molecule of TrkB, was induced in HAT-7 cells upon NT-4 treatment. TrkB-FL but not TrkB-T1 transfection increased the phosphorylation level of ERK1/2 in NT-4-treated HAT-7 cells. These results suggest that NT-4 induced Ambn expression via the TrkB-MAPK pathway. The p75 inhibitor TAT-pep5 decreased NT-4-mediated induction of the expression of Ambn, TrkB-FL, and TrkB-T1, suggesting that both high affinity and low affinity neurotrophin receptors were required for NT-4 activity. We found that NT-4-null mice developed a thin enamel layer and had a decrease in Ambn expression. Our results suggest that NT-4 regulates proliferation and differentiation of the dental epithelium and promotes production of the enamel matrix.

Effect of Facial Convexity on Antero-posterior Lip Positions of the Most Favored Japanese Facial Profiles

Soft tissue analyses are basic tools in planning orthodontic treatment. However, the perception of a well-balanced Japanese facial profile has not yet been established, particularly with respect to changes in facial convexity. The purpose of this study was to assess and determine the range of antero-posterior (A-P) lip positions of the top three most favored, well-balanced profiles from a series of various facial silhouettes with changing facial convexity. The average profile was constructed from the profiles of 30 Japanese males and females with Class I occlusions. Changes in facial convexity were established by altering the A-P chin position by protruding or retruding the chin in increments of 5 degrees and 10 degrees from the average profile. A series of 11 profiles were developed from each of the four changes in facial convexity. The lips were then protruded or retruded in one-mm increments from the average profile. Forty orthodontists were asked to rate the top three most favored, well-balanced profiles. We found that the raters tended to prefer more retruded lip positions as facial convexity decreased, for both males and females. The raters also tended to prefer slightly more protruded lip positions as the facial convexity increased. Because chin position is inherent in each patient, others may equate a retrusive or protrusive chin with certain personalities, thus, it is important for orthodontists to take into account the balance between the lips and the chin.

Characteristics of craniofacial structures of parents of children with cleft lip and/or palate

We looked for possible differences in craniofacial morphology between parents of children with celft lip (CL) and/or cleft palate (CP) and normal controls. Fifty measurements were obtained from lateral and frontal roentgenographic cephalograms of these subjects. The means of all measurements were tested for significant statistical differences, and a discriminant analysis was carried out to distinguish the craniofacial structures in the experimental subjects from those in the controls. Facial shape of parents of children with CL and/or CP differed from that of control subjects. Shorter height and greater width in the upper face were the main characteristics of facial shape of parents of CL and/or CP children. Craniofacial morphology was considered to be related to susceptibility to these facial deformities.

Three-dimensional analysis system for orthognathic surgery patients with jaw deformities

INTRODUCTION Traditionally, lateral and frontal cephalograms are used with facial photographs to evaluate a patients maxillofacial skeletal and facial soft-tissue morphology. However, the enlargement and distortion of 2-dimensional radiography made it difficult to accurately conceptualize the patients anatomy. The purpose of this article was to introduce a new method for comparing 3-dimensional (3D) standard values of the maxillofacial skeletal and facial soft-tissue morphology before and after orthognathic surgery. METHODS Normative 3D standard values of the maxillofacial skeletal and facial soft-tissue morphology were calculated from normal women. The pre- and postoperative morphology of one woman who underwent orthognathic surgery was compared with the normative data. RESULTS This 3D analysis has clinical value to evaluate patients before and after surgical treatment. CONCLUSIONS This quantitative assessment of 3D maxillofacial morphology can evaluate the area and degree of displacement and rotation of the facial skeleton and facial soft tissues. This method is sufficiently useful for routine clinical applications.

Relationship Between Congenitally Missing Lower Third Molars and Late Formation of Tooth Germs

In this investigation, we used longitudinal panoramic radiographs from 96 subjects (47 boys, 49 girls) who did not have any congenital disease. The subjects were selected based on their age at the initial radiograph and the number and frequency of radiographs. Lower left premolars and second molars were used as parameters to identify factors that influence the age of formation of the third molar. We classified teeth into eight formation stages according to the method of Demirjian. The age at the beginning of formation of the lower third molar was determined with a regression equation of longitudinal data. The highest correlation existed between the age at the beginning of formation of the third molar and the formation stage of the second molar. We conclude that late formation of tooth germs is one of the factors that leads to the congenital absence of lower third molars. Furthermore, we assume that when the tooth germ of the lower third molar has not appeared at stage 7 of formation of the second molar, the probability of the third molar being missing is 100%.

Hard and soft tissue stability of orthognathic surgery.

OBJECTIVE To test the hypothesis that there is no difference in the stability of the hard and soft tissue changes following a surgical mandibular setback using a sagittal split ramus osteotomy or an intraoral vertical ramus osteotomy. MATERIALS AND METHODS The samples consisted of 45 female patients with mandibular prognathism, who were divided into two groups. Twenty-three underwent a sagittal split ramus osteotomy (SSRO) with rigid fixation by titanium mini-screws and maxillomandibular fixation (MMF) for 14.0 +/- 0.7 days. Twenty-two underwent intraoral vertical ramus osteotomy (IVRO) without rigid fixation, and MMF was released 21.5 +/- 3.3 days after surgery. Data were collected from standardized cephalometric radiographs taken at the start of preoperative orthodontic treatment (T1), immediately after surgery (MMF, T2), and the completion of postoperative treatment (T3). Angular measurements were compared on each of T1, T2, and T3. RESULTS There were no significant differences in the pretreatment hard and soft tissue morphology between the SSRO and IVRO. However, when fixation was released, the mandible was posteriorly positioned in the IVRO group. In the soft tissue profile, the mental region was located backward in the IVRO group at postoperative stage (T3). CONCLUSIONS The hypothesis is rejected. The soft tissue profile of the IVRO group especially showed a retromandibular position after postoperative treatment in comparison with the SSRO group. This tendency of the IVRO group would contribute to the database for treatment planning and prediction.