Tadashi Onizuka

Study on Adhesion Fixed Partial Denture Applied Composite Resin Teeth as Pontic. In vitro Measurement of Bonding Durability.

The adhesion fixed partial denture applied resin teeth as pontic, i.e., adhesionpontic bridge, is effective prosthodontic treatment to conserve the tooth substrate of intact abutment teeth.The purpose of this study was to improve the bond strength and durability between adhered pontic applied composite resin teeth and abutment teeth. At first, the bond strength of resin teeth pontic bonded to extracted human teeth with two self-curing resin adhesives were measured after thermocycling test up to 50, 000 times, and the specimen bonded with Super-Bond C & B showed higher bond strength than with Enamagic. However, the bond strength with Super-Bond C & B after thermocycling 50, 000 times decreased to about30% of the value before thermocycling, and the failure of all specimens occurredat the adhesion interface between composite resin teeth and Super-Bond C & B.Then some methods to reinforce the bonding durability of Super-Bond C &B to composite resin teeth were evaluated. The highest bond strength was obtained in the specimen with the hole in the proximal plane of composite resin teeth.The results suggested that the combination of mechanical retention and bond applied resin adhesives is effective to achieve the durable bond and lengthen thelife of adhesion pontic bridge.

Basic Study of Sintered Metal Restoration. Part 1. Fitness Accuracy and Surface Roughness.

Sintered metal restorations, made from powder metallurgy developed by Degussa Co., Ltd., and conventional cast restorations were prepared by using a metal modelfor MOD inlay. A comparative study was carried out, and the results were as follows:1. As for surface roughness, no significant difference of Rz could be observed both on the polished surface and cavity floor. In the graphs of Rz on the cavity floor, the picture was rough for cast restorations and sink hole-like gas cavities were locally recognized on the surface of sintered metal restorations with a roughness of 3 μm on average. As the results of the corrosion test, roughness of the polished surface of both restorations rose and the increase was larger in cast restorations. Sintered restorations showed better corrosion resistance.2. The fitness test showed no significant difference in the margin, butthe fitness of sintered metal restorations was inferior to cast restorations on the inner surface.3. The surface hardness of sintered metal restorations was lower than the values indicated by the manufacturer.Based on these results, it was considered that powder metallurgy was not suitable for the preparationof a thick abutment tooth with sharp angles such as MOD.

A Study on Adhesion of Dental Porcelain to Castable Glass Ceramics. Part II Fabrication of Tensile Test Pieces and Tensile Test.

Castable glass ceramics-porcelain jacket crown, in which castable glass ceramics are used as a coping and dental porcelain is partially or completely fired, is recommended from an aspect of esthetics. The adhesive strength between two ceramic materials is considered to be important for this jacket crown. The purposes of this study were to evaluate the adhesion of two ceramic materials under tensile load and to establish fabrication of tensile test pieces.The following results were obtained.1. Established method for fabricating tensile test pieces and tensile test are adequate to know the behavior of ceramic materials under a tensile load.2. Dental porcelain used in this study showed favorable adhesion to castable glass ceramic, without detracting the inherent physical properties of castable glass ceramic.3. The white layer, which shows the formation at the surface of castable glass ceramic after the ceraming process, does not affect the adhesion of dental porcelain to castable glass ceramic.4. Reinforcement of the white layer is expected to be obtained by firing dental porcelain.

Studies on the retentive strength of polycarboxylate cements and pulp reaction.

In order to determine the clinical assessment of the polycarboxylate cements, some test were made on four commercially available polycarboxylate cements and one zinc phosphate cement as control.The findings are as follows:1. Tensile strength of the polycarboxylate cements obtained with the crown model was similar or stronger than that of zinc phosphate cement. Tensile strength with taper 1/10 crown model was significantly stronger than that with taper 2/10 crown model.2. In case of the shear strength at dentine-polycarboxylate interface on smooth surface was stronger than on rough surface, and the result showed that adhesion was due to chelate bond. While the shear strength at dentinecement interface obtained with polycarboxylate cements was variable, it was certainly superior to that obtained with zinc phosphate cement.3. The shear strength of polycarboxylate cements was more than twice that of zinc phosphate cement.4. The polycarboxylate cements were not irritant to dental pulp.5. The properties obtained with these test made the polycarboxylate cement the material of choice for cementing full crown restorations and bridge work on vital teeth.