Shigeru Hanatani

Wear resistance of experimental Ti-Cu alloys.

After using cast titanium prostheses in clinical dental practice, severe wear of titanium teeth has been observed. This in vitro study evaluated the wear behavior of teeth made with several cast titanium alloys containing copper (CP Ti+3.0 wt% Cu; CP Ti+5.0 wt% Cu; Ti-6Al-4V +1.0 wt% Cu; Ti-6Al-4V+4.0 wt% Cu) and compared the results with those for commercially pure (CP) titanium, Ti-6Al-4V, and gold alloy. Wear testing was performed by repeatedly grinding upper and lower teeth under flowing water in an experimental testing apparatus. Wear resistance was assessed as volume loss (mm(3)) at 5kgf (grinding force) after 50,000 strokes. Greater wear was found for the six types of titanium than for the gold alloy. The wear resistance of the experimental CP Ti+Cu and Ti-6Al-4V+Cu alloys was better than that of CP titanium and Ti-6Al-4V, respectively. Although the gold alloy had the best wear property, the 4% Cu in Ti-6Al-4V alloy exhibited the best results among the titanium metals. Alloying with copper, which introduced the alpha Ti/Ti(2)Cu eutectoid, seemed to improve the wear resistance.

Present status of titanium removable dentures--a review of the literature.

Although porcelain and zirconium oxide might be used for fixed partial dental prostheses instead of conventional dental metals in the near future, removable partial denture (RPD) frameworks will probably continue to be cast with biocompatible metals. Commercially pure (CP) titanium has appropriate mechanical properties, it is lightweight (low density) compared with conventional dental alloys, and has outstanding biocompatibility that prevents metal allergic reactions. This literature review describes the laboratory conditions needed for fabricating titanium frameworks and the present status of titanium removable prostheses. The use of titanium for the production of cast RPD frameworks has gradually increased. There are no reports about metallic allergy apparently caused by CP titanium dentures. The laboratory drawbacks still remain, such as the lengthy burn-out, inferior castability and machinability, reaction layer formed on the cast surface, difficulty of polishing, and high initial costs. However, the clinical problems, such as discoloration of the titanium surfaces, unpleasant metal taste, decrease of clasp retention, tendency for plaque to adhere to the surface, detachment of the denture base resin, and severe wear of titanium teeth, have gradually been resolved. Titanium RPD frameworks have never been reported to fail catastrophically. Thus, titanium is recommended as protection against metal allergy, particularly for large-sized prostheses such as RPDs or complete dentures.

An Experimental Study on the Relationship between the Denture Structural Designs and Pressure Distribution. The Effect of Retainer Designs.

Removable partial dentures should be designed to ensure efficient distribution of masticatory loads over the abutment teeth and alveolar ridge. The relationship between the denture stiffness and the various clasp designs on the pressure distribution to a single abutment tooth and the alveolar ridge was investigated in this study.The results were as follows:1. Regardless of the retainer designs, the pressure on the alveolar ridge was less when using a double structure than a skeleton type, and the pressure on the abutment tooth in the vertical direction was greater when supported by a double structure than a skeleton type.2. When a Konus telescope was applied as a retainer the pressure on the abutment tooth in the vertical direction was greater than an Akers or an RPI clasp.3. When an RPI clasp was applied as a retainer the amount of pressure on the alveolar ridge was maximum.4. The pressure on the abutment tooth in the lateral direction showed a greater tendency when an Akers clasp was applied.5. The displacement and strain of the denture were the least when a double structure design was applied.6. When a double structure design with Konus telescope was applied, the displacement of the denture was the least.

Fatigue Strength of the Metal Framework Structures for Removable Partial Dentures.

The structural design of the metal alloy framework for removable partial dentures is critical. A double structure framework was the representative of these designs, which enables the mechanical strength and durability to improve and the abutment teeth and alveolar ridge to protect. In this study, several structural designs (double structure, T-shapes, trussed structure, rectangular column, nonuniform section) including resin block as control were subjected to a load-controlled fatigue test. The benefits on fatigue strength of five types of structures were evaluated to record the number of cycles at catastrophic failure, to measure continuously displacement and strain under loads repeatedly, and to observe the fracture patterns.The results were as follows:1. Maximum stiffness of double structure and T-shapes was approximately 20 times that of rectangular column and nonuniform section by theoretical calculations.2. Fatigue strength of double structure was the highest, followed by that of trussed structure and T-shapes.3. Double structure was found to be the significantly lowest of both displacement and strain.4. Packed resin fracture was observed in all specimens except double structure.5. The interface of fractured specimen frameworks were revealed inherently with fatigue.