Shigeto Koyama

Dynamic changes in bone metabolism in the rat temporomandibular joint after molar extraction using bone scintigraphy

Functional adaptation with reformation of bone tissue structure occurs after changes in mechanical stress distribution. To examine how occlusal changes affect the dynamics of bone metabolism in the mandibular condyle, bone scintigraphy of rat condyles was taken using (99m)technetium-methylene-diphosphonate (99mTc-MDP) after extraction of maxillary molars resulting in unilateral loss of occlusal support. Accumulation of 99mTc-MDP was significantly higher in the condyles on the extracted side than on the intact side 3 d after molar extraction. In addition, bone mineral density (BMD) and osteoprotegerin expression in extracted-side condyles were significantly increased while osteoclast numbers were significantly decreased when compared with intact-side condyles. These differences were not detected 28 d after molar extraction. These findings suggest that occlusal change transiently results in changes in the dynamics of bone metabolism at the mandibular condyles through the downregulation of osteoclastogenesis. These changes may be involved in functional adaptation of the temporomandibular joint.

The Potential of Cohesive Silicone for Facial Prosthetic Use: A Material Property Study and a Clinical Report

PURPOSE Prosthetic reconstruction of a facial defect can help to reduce disfigurement and restore the social functioning of the patient. Several methods for holding a prosthesis in place exist, including the use of osseointegrated implants and medical adhesive agents; however, since the treatment options for some patients may be restricted by various health conditions and other limitations, including allergies to adhesive agents, a history of radiation therapy, and financial issues, other options that suit individual demands are required. The objectives of this study were to test the hypothesis that adhesive characteristics could be bestowed on silicone elastomers by altering their catalyst/base silicone ratios (CBR) and to examine the effect of the thickness of the cohesive silicone layer of a prosthesis on its initial adhesive strength. MATERIALS AND METHODS The adhesive strengths of specimens with CBRs ranking from 1/10 to 1/70 were examined by the rolling ball tack test. A tensile test was used to evaluate the tensile adhesive strengths of specimens made of layers of cohesive silicone (CBR 1/60) and normal silicone (CBR 1/10) with different thicknesses. Auricular prostheses containing cohesive silicone on the skin side were applied to a 50-year-old man with defects in both auricular regions and with reduced manual dexterity due to serious burns. RESULTS The rolling distance was reduced with a decrease in CBR, and a thinner cohesive silicone (CBR 1/60) layer demonstrated a higher peak load. On clinical application, the adhesion of the auricular prosthesis containing cohesive silicone was improved by expanding the adhesive area and altering the thickness of the cohesive silicone layer, resulting in sufficient adhesion and easier handling than that achieved using an adhesive agent 1 year post delivery. CONCLUSION These results suggest that cohesive silicone can be used as a glueless retentive material for facial prostheses.

Clinicopathological features of melanotic neuroectodermal tumor of infancy: Report of two cases.

Melanotic neuroectodermal tumor of infancy (MNTI) is an extremely rare, pigmented neoplastic entity of neural crest origin. Histological and immunohistochemical profiles indicate the presence of two components, small rounded neuroblast-like cellular areas and areas with large melanin-containing cells which consist of combination of neural, melanocytic, and epithelial cell types. Here we present two interesting cases of infants with MNTI which have different clinicopathological features. The first case is a 3-month-old female with rapidly growing MNTI involving the lacrimal sac and inferior wall of the orbital cavity, treated with total maxillectomy without orbital exenteration followed by chemotherapy. The second case is a 7-month-old male with slow-growing maxillary MNTI treated with complete surgical excision. In the female patient, histological findings revealed a predominance of neuroblast-like cellular areas and a high Ki67 index indicating rapid cellular proliferation. In the male patient however, large melanin-containing cells were dominant in this slow-growing tumor. These findings support the presence of two different types of MNTI, rapid-growing and slow-growing types, determined by the component of neuroblast-like cellular areas.

Influence of maxillary obturator prostheses on facial morphology in patients with unilateral maxillary defects

STATEMENT OF PROBLEM Facial asymmetry is prominent with individuals with unilateral bone resorption and can lead to decreased quality of life. PURPOSE The purpose of this study was to investigate the influence of maxillary obturator prostheses on facial morphology of individuals with unilateral maxillary defects by using 3-dimensional digital stereophotogrammetry. MATERIAL AND METHODS The facial data of 8 participants with unilateral maxillary defects were acquired with a noncontact 3-dimensional digitizer, both with and without maxillary prostheses. The mid-facial plane was established by overlapping an original facial image with its mirror image. Displacement at 18 measurement points, including 7 bilateral pairs, was compared between the 2 sides, with and without the prostheses. Asymmetry indices of these 7 pairs also were calculated. Multivariate repeated-measures ANOVA was used to determine differences. RESULTS Displacements of the lateral and inferior points at the ala of the nose were significantly greater on the defect side than on the normal side. The distances between the ideal and defect side points at the superior ala, the upper lip, and the angle of the mouth decreased significantly with the prosthesis. No significant differences were found in asymmetry indices, but the angle of the upper lip line to the mid-sagittal plane increased significantly with the prosthesis. CONCLUSIONS The 3-dimensional analyzing method developed in this study can be useful in evaluating facial reconstruction with maxillary obturator prostheses with individuals with unilateral maxillary defects. The prostheses affect the region of the nasal ala, the upper lip, and the angles of the mouth.

Biomechanical analysis of bone remodeling following mandibular reconstruction using fibula free flap

Whilst the newly established biomechanical conditions following mandibular reconstruction using fibula free flap can be a critical determinant for achieving favorable bone union, little has been known about their association in a time-dependent fashion. This study evaluated the bone healing/remodeling activity in reconstructed mandible and its influence on jaw biomechanics using CT data, and further quantified their correlation with mechanobiological responses through an in-silico approach. A 66-year-old male patient received mandibular reconstruction was studied. Post-operative CT scans were taken at 0, 4, 16 and 28 months. Longitudinal change of bone morphologies and mineral densities were measured at three bone union interfaces (two between the fibula and mandibular bones and one between the osteotomized fibulas) to investigate bone healing/remodeling events. Three-dimensional finite element models were created to quantify mechanobiological responses in the bone at these different time points. Bone mineral density increased rapidly along the bone interfaces over the first four months. Cortical bridging formed at the osteotomized interface earlier than the other two interfaces with larger shape discrepancy between fibula and mandibular bones. Bone morphology significantly affected mechanobiological responses in the osteotomized region (R2 > 0.77). The anatomic position and shape discrepancy at bone union affected the bone healing/remodeling process.

A preliminary report on dental implant condition among dependent elderly based on the survey among Japanese dental practitioners

BackgroundThe objective of this study was to ascertain the situation relevant to implants, the status of oral self-care, the status of aftercare provided by the dentist who placed the implant, and the usage status of the implant card, in homebound or institutionalized older adults who are receiving home-visit dental care due to the inability to visit a dental clinic on their own.MethodsA survey questionnaire was sent by post mail to 2339 people who are representative members or dental specialists belonging to any of the following three academic societies: Japanese Society of Oral Implantology, Japanese Society of Gerodontology, and Japan Prosthodontic Society. The survey questions asked were about provision/no provision of implant treatment, provision/no provision of home-visit dental care, the situation of patients after implant treatment, the situation of implants in the context of home-visit dental care, and the usage status and recognition of the implant card.ResultsNo less than 30% of the dentists had patients who were admitted to the hospital or became homebound after receiving implant treatment at their clinic. Twenty-two percent of the dentists had been consulted about the implants. Dentists who continued to provide post-operative implant care through home-visit dental care accounted for approximately 80%. On the other hand, however, 40% of the dentists did not know the post-implantation status of their implant patients. Of the patients receiving home-visit dental care, approximately 3% had implants (identified mainly by visual inspection). It was found that more than 50% of the dentists offering implant treatment did not use the implant card, and even in cases where it was used, most of the cards were not in the standardized format.ConclusionsWithin the limitation of low response rate to the questionnaire in this preliminary study, we concluded that many of practitioners including specialists indicated the need of universal record of implant for dependent elderly cares.

Evaluation of water absorption properties and fabrication of hollow obturator model using 3D digital dentistry

Fluid accumulation in the hollow spaces of obturator is a continuing problem when fabricating hollow obturator prostheses using the conventional method. To address this problem, the three-dimensional (3D) digital technology was used to evaluate water absorption in the inner hollow obturator spaces. Solid and hollow obturator specimens were fabricated using a 3D printer with photocurable resin. Then, the hermeticity was examined by leak testing. These specimens were immersed in distilled water at 37°C. Each specimen was weighed every 24 h for 120 days, and weight changes between each group were compared. Water accumulation in the hollow obturator was not visually observed. Although water absorption was significantly higher in solid specimens, the weight increase rate was also significantly higher in hollow specimens. Applying a laminating 3D photo fabrication made the fabrication of a completely unified hollow obturator model possible.

Practice-Based Longitudinal Study of Multifactorial Risk Assessment for Periodontal Condition and Survival of Remaining Teeth in Patients with Removable Partial Dentures

PURPOSE This retrospective cohort study examined factors affecting the periodontal condition and survival of remaining teeth 5 years after removable partial denture (RPD) placement using multivariate analyses. MATERIALS AND METHODS Of 231 patients who received RPDs at Tohoku University Hospital, 108 patients who had agreed to undergo a 5-year follow-up were examined. The outcomes of RPD treatment were assigned to one of three categories: successful (n = 58), remake (n = 36), and failure (n = 14). A total of 80 patients in the successful and remake groups were included in this study. The parameters analyzed to evaluate the periodontal condition were probing depth, Miller index of tooth mobility, and bone resorption level. Criterion variables were the outcome of each periodontal condition, deterioration, and tooth loss. Independent variables were sex, age, smoking habit, number of periodic maintenance appointments, location of RPD, number of abutment teeth, denture base material, design, and existence of a denture in the opposite jaw. Bivariate analyses were performed using chi-square test, and multivariate regression analysis was used to assess significance. RESULTS Sex and frequency of maintenance care were independently associated with deterioration of the periodontal condition. Sex and existence of a denture in the opposite jaw were independently associated with tooth loss. CONCLUSION The findings suggest that periodic maintenance care and condition of the opposite jaw are essential for maintaining the condition of the remaining teeth.

Influence of Loading on Bone Metabolism Around Dental Implants in Rat Tibia

This article reviewed the bone metabolic activity around titanium implants in rat tibia under the mechanical loading condition on the implant.

Quantification and Identification of Bacteria in Maxillary Obturator-prostheses

The aims of this study were to quantify and identify bacteria in the in-use acrylic resin maxillary obturator-prostheses. Aspiration pneumonia-associated or airborne bacteria such as Klebsiella and Pseudomonas species as well as oral bacteria were detected at 5.0 × 10–2.5 × 106 colony forming units (CFU)/mL. This study revealed that several species of viable bacteria are present within the obturators. It is suggested that the inner space of obturator can act as bacterial reservoirs.