歯科用合金と床用レジンとの接合性に関する研究

抄録

As it is well known, the connection between the artificial teeth and metal plate in cast metal plate dentures is made by a resin material which is also used for the alveolar part of the denture for esthetic reasons. The bonding mechanism between alloy and resin involves a mechanical union between the two which requires an undercut or any other retentive device that can strengthen the force of adhesion.
However, in dentures used for a long time, the finishing line (the line formed by the connection of alloy and resin) will develop a crevice, with alloy and resin separating due to external forces such as masticatory pressure. Also, discoloration results and the crevice may develop bacterial contamination. All of these are a part of the problem which exists in the connection of resin and metal surface in the denture.
Considering the problem, the author tried a method of etching the metal to strengthen the mechanical union between metal and resin and to prevent their separation.
Three alloys were used in these experiments: Co-Cr, Ni-Cr, and Ni-Co-Cr.
The resin used was a heat-curing type known an URBAN.
The results of experiments were as follows:
1. Bonding strength between the etched surface and resin: Surface roughness increased as the etching time was prolonged. An increase in tensile strength was also noted with increasing etching time. For example, the Co-Cr alloy tested at 201 ± 14 kg/cm² (max. value after 120 minutes); Ni-Cr, 101 ± 9 kg/cm² (max. value after 120 minutes); and Ni-Co-Cr, 202 ± 10 kg/cm² (after 30 minutes etching).
2. SEM observations and EPMA and ESCA analysis; Different surface conditions of the three alloys were revealed after the etching process. Only the chromium component of the various alloys remained after the etching process. Acid treatment of the three alloys revealed differing resistance to corrosion by these alloys.
3. Inhibition of dye penetration: The specimens were soaked in a 0.25% basic fuchsin solution for 2 weeks. With Co-Cr and Ni-Co-Cr alloys, the dye did not penetrate, while in the case of the Ni-Cr alloy, there was some staining.
4. Effect of thermal cycling: The tensile strength value after 18 cyclings of the specimen was 167 kg/cm² for the Co-Cr alloy; 68 kg/cm² for the Ni-Cr alloy; and 198 kg/cm² for the Ni-Co-Cr alloy. The results indicated a decreasing bonding strength with increasing numbers of thermal cycles.
5. SEM photographs showed different shaped, corroded areas of 50 μm deepth in the connection region of each specimen. The Co-Cr and Ni-Co-Cr alloys had columnar-shaped corrosion areas, whereas the corrosion sites of the Ni-Cr alloy had the appearance of smooth hills and valley.
6. Clinial application: The effect of etching the metal plates in dentures was tested in 16 cases. After 2 1/2 years, the etched portion of the dentures showed a better inhibition of dye penetration than the control (non-etched) parts. This suggests that etching may be of value in clinical dentistry.