Chikahiro Ohkubo’s research while affiliated with Tsurumi University and other places

Additive-manufactured (AMed) Co-Cr and Ti alloy clasps were made with five surface treatments. Either one of a conventional freehand finishing or barrel finishing as a medium finishing process or one of a freehand, dry electrolytic, or magnetic polishings was selected as the final polishing process. After each surface treatment, the polishing efficiencies of the AMed clasps were evaluated as to surface roughness, fitness accuracy, and retentive forces. By surface treatments without using magnetic polishing, sufficient surface smoothness was observed for both alloys. Under all five treatment conditions, better fitness accuracies and sufficient retentive forces were obtained in all Co-Cr and Ti alloy clasps for clinically acceptable results. A combination of barrel finishing and dry electro-polishing can be recommended as the automatic finishing technology, replacing the freehand polishing process by dental technicians. The findings of this study will significantly reduce the workload of dental technicians.

Purpose: The processes and methods of treating and polishing additive-manufactured (AMed) cobalt-chromium (Co–Cr) alloy clasps were assessed in vitro to determine their suitability for constant clinical use and the reduction of dental technician work. Methods: AMed Aker clasps were fabricated by selective laser sintering of approximately 50 μm Co–Cr alloy powders. After the nodules and fins on the inner surface of the AMed clasps were removed and morphological correction was performed, a dental technician manually polished the clasps as a control. Four surface treatments, barrel finishing, shot peening, and wet and dry electropolishing, were performed to obtain smooth surfaces. In addition, hybrid manufacturing, which integrates repeated laser sintering and high-speed milling for one-process molding, was added to this study. After observing the treated surfaces using SEM and Hybrid Laser Microscope (HLM) the surface roughness, fitness accuracy, and retentive forces of the treated AMed clasps were measured, and their polishing efficiencies were compared. Results: Similar to manual polishing, dry electropolishing yielded the smoothest surfaces in all treatments. The fitness accuracy of all clasp regions and treatment methods ranged from 80 to 140 μm, without significant differences among the treatment methods. All treated clasps showed acceptable retentive forces for clinical use, and hybrid manufacturing and wet electropolishing showed significantly higher forces. Conclusions: AMed Co–Cr clasps with all surface treatments could be clinically used if additional slight manual polishing was performed; however, each processing condition should be carefully selected.

In the present study, the soft tissue response toward a fibronectin–immobilized zirconia implant was evaluated by animal experiment. Quartz crystal microbalance (QCM) analyses for atelocollagen adsorption to zirconia were also performed. Cylindrically shaped yttria stabilized tetragonal zirconia polycrystals (Y-TZP) was sandblasted and acid etching–treated (SLA/Y-TZP). Fibronectin–immobilized Y-TZP (Fn/Y-TZP) was obtained using the tresyl chloride–activated method. Implants were placed in the tooth socket of the extracted maxillary teeth of rats. Soft tissue responses 3-weeks after implantation were observed. Long collagen fibers perpendicularly oriented to the Y-TZP implant surface were more abundant in Fn/Y-TZP than in SLA/Y-TZP. The lengths of vertically oriented collagen fibers on the palatal side and the total of the buccal and palatal sides of Fn/Y-TZP were significantly higher than that of SLA/Y-TZP. Fn/Y-TZP showed a significantly higher area of vertically oriented collagen fibers on the buccal side and the total sides as compared to SLA/Y-TZP. There were no significant differences among the ratios of epithelial attachments to fibrous attachments. QCM analyses indicated that the pre–adsorption of fibronectin significantly decreased the amounts of atelocollagen adsorption. In conclusion, the immobilization of fibronectin had a clear effect on the orientation of gingival fibers toward the zirconia implant surface. Atelocollagen adsorption to zirconia was influenced with by fibronectin pre–adsorption.

Refractory cases in removable partial denture (RPD) treatment are defined as “a group of cases in which patient satisfaction cannot be obtained even with normal denture design and fabrication.” The most refractory of these are Eichner classification C1 cases. Eichner classification C1 problems include dealing with remarkably deteriorated remaining teeth, residual ridges, and collapsed occlusion in the pretreatment; the correction of the mandibular position and reconstruction with increased vertical dimension during denture fabrication; and coping with breakage and rotational change of the RPD after delivery. In this paper, the author reconsiders the problems in the treatment of Eichner classification C1 and outlines the classification and characteristics of each type. Also, the design guidelines for RPDs are proposed, and therapeutic precautions, effective implant support, and how to deal with rotational change of the RPD are explained.

Purpose Japan, with an increasing number of elderly people needing long-term care in a super-aged society, urgent needs to develop the clinical guidelines on implant maintenance for elderly people with declining independence. The purpose is to categorize the troubles encountered in the care of patients with dental implants and to indicate actual practices and points of note. Methods From the members of the Japanese Society of Oral Implantology, 12 expert panelists who were experienced with many problems of implant maintenance during dental visits and were familiar with their solutions were selected. Through repeated discussions in the many panel meetings, the problems of implant maintenance during dental visits were distilled. Results During a dental visit, the oral cavity, general conditions, and background of elderly patients who cannot orally care for themselves must be grasped, and medical staff, care managers, and patients should understand the changes in these factors as time goes by. The solutions and responses that can be made differ greatly depending on the medical care facilities, the environment, differences in the experience of medical staff, and the patient’s background. Thus, it is necessary to select safe treatments appropriate to each situation. Conclusions This paper features many opinions based on clinical experiences. However, clinical guidelines on implant management during dental visits should be formulated in the future based on the accumulation of evidence through the implementation of clinical research.

Purpose: To investigate the bone augmentation ability of demineralized bone sheets mixed with allogeneic bone with protein fractions containing bioactive substances and the interaction between coexisting bioactive substances and proteins. Methods: Four types of demineralized bone sheets mixed with allogeneic bone in the presence or absence of bone proteins were created. Transplantation experiments using each demineralized bone sheet were performed in rats, and their ability to induce bone augmentation was analysed by microcomputed tomography images. Bioactive substances in bone proteins were isolated by heparin affinity chromatography and detected by the measurement of alkaline phosphatase activity in human periodontal ligament cells and dual luciferase assays. Noncollagenous proteins (NCPs) coexisting with the bioactive substances were identified by mass spectrometry, and their interaction with bioactive substances was investigated by in vitro binding experiments. Results: Demineralized bone sheets containing bone proteins possessed the ability to induce bone augmentation. Bone proteins were isolated into five fractions by heparin affinity chromatography, and transforming growth factor-beta (TGF-β) was detected in the third fraction (Hep-c). Dentin matrix protein 1 (DMP1), matrix extracellular phosphoglycoprotein (MEPE), and biglycan (BGN) also coexisted in Hep-c, and the binding of these proteins to TGF-β increased TGF-β activity by approximately 14.7% to 32.7%. Conclusions: Demineralized bone sheets are capable of inducing bone augmentation, and this ability is mainly due to TGF-β in the bone protein mixed with the sheets. The activity of TGF-β is maintained when binding to bone NCPs such as DMP1, MEPE, and BGN in the sheets.

Pure titanium is widely used as a material in dental implants. However, it possesses inferior mechanical strength. This study aimed to elucidate the efficacy of acid treated multi-directionally forged (MDF) pure titanium in vivo. We verified the temporal changes until osseointegration in beagle dogs. Using two types of experimental materials (conventional pure titanium or MDF pure titanium), new bone formation was assessed using morphological examinations, and the bone-to-implant contact (BIC) value was evaluated at each time point (14, 30, and 90 days after the operation). As such, new bone formation was observed around the acid-etched MDF group, in which the BIC value was highest, followed by that in the acid-etched pure titanium group. MDF pure titanium implants showed early promotion of new bone formation compared to conventional titanium implants. The new acid-treated MDF made of pure titanium could be applied to humans in the future to prove its practicality.

Since cast titanium prostheses have many drawbacks, multi-directionally forged titanium grade 2 (MDF) was developed, and the application of the milling process was proposed for improving the titanium clasp. This in vitro study evaluated milled titanium clasps, including MDF titanium. Milling clasps were manufactured with commercially pure (CP) titanium grade 2 (CP 2), grade 4 (CP 4), Ti-6-Al-4V, and MDF. As a control, a CP 2 cast titanium clasp was fabricated in the conventional manner. No porosities and catastrophic failures were observed in the four milled titanium clasps. Fitness accuracy and retentive forces of milled CP 2 and CP 4 tended to be worse, and the milled MDF showed the higher retentive forces (12.45 N) than did cast and milled CP 2 clasps (9.32 N and 4.42 N). Milled titanium clasps can be recommended for longer-term clinical use as compared to cast clasps.

Since various factors, namely, the number of missing teeth, the pattern of partial edentulousness, the conditions of abutment teeth and antagonistic teeth, the degree of periodontal disease, the occlusal force, and the patient’s requirements and background, are related to decisions regarding the permanent prostheses, knowing whether to choose a fixed or removable prostheses is often difficult. Prognosis is the most important aspect for prosthetic treatment, and the quality of the treatment cannot be judged by short-term progress; thus, prosthetic rehabilitation can be properly evaluated by long-term observation. Regarding large prostheses, how to choose between a fixed bridge and a removable partial denture is reconsidered in this review. The selection criteria for fixed and removable prostheses and the factors that affected the oral conditions and prosthetic devices at 10 to 20 years after delivery were imagined based on long-term follow-up.