Considering the clinical aspects of dental materials used for cast restoration, the presents experiments was undertaken using the original methods to establish the relation beteen tooth and cast restorations under sliding abrasion at the marginal region. The following results were obtained.
1. Abrasion phase was observed using sliding abrasion test machine where the experimental abrasion phase resembled to those occuring inside the mouth. In addition prolonged use of the machine showed no instrumental fatigue.
2. SEM photograph indicated that in type-I cast gold alloy of other metals (Type-IV cast gold alloy with heat-hardening treatment, gold-silver-palladium alloy, silver-indium alloy) the sliding abrasion of tooth was due to extension of metal which maintained the marginal seal.
3. Volume of abrasion in type-I cast gold alloy at the margin was minimum and the tendency of abrasion in tooth and metal surface was well-balanced.
4. Surface form of type-I cast gold alloy after abrasion test depicted smooth margin which indicated better adaptation of the cast restorations to the tooth.
5. The results of this experiments suggested that proper selection of metal for cast restoration can minimize the occurence of secondary caries even after slight attrition at the margin of the restoration.