The Influence of Metal Coping Design on Fracture Resistance of Porcelain-Fused-to-Metal Crown

Abstract

The porcelain-fused-to-metal crown is the most popular indirect restoration in dentistry due to its high fracture resistance and low cost. However, unaesthetic labial margin is unacceptable to patients. Metal collar causes dark discoloration, which is worsened by gingival recession. Modification in metal collar coping has been developed to combine high fracture resistance of metal and high aesthetic of porcelain. Modification in crown fabrication including structure and composition of both nickel chromium alloy and feldspathic porcelain; application of self-cured resin cement and digital method; is meant to improve aesthetics without compromising fracture resistance. This study was an experimental laboratory research to evaluate fracture resistance of porcelain-fused-to-metal crowns with different metal coping designs. A total of 20 samples were used and divided into 4 groups according to different coping designs: (1). full metal collar; (2). full metal collarless; (3). modified metal collarless with 1.5 mm reduction; (4). modified metal collarless with 2 mm reduction. Universal Testing Machine (LRXPlus, Lloyd) was used to measure fracture resistance of all crowns. Average fracture resistance value for group 1 was 988.42 N; Group 2 was 1180.15 N; Group 3 was 1089.47 N; Group 4 was 1202.61 N. The results of statistical analysis showed that there was a difference in fracture resistance among porcelain-fused-to-metal crowns with different coping designs, although the value was not statistically significant. The higher coping reduction at labial margin, the higher the fracture resistance and standard deviation.