Survival Rate of Metal Crowns Covered by Public Health Insurance System in Japan: A Quality-of-Care Perspective

Rather than focusing solely on cost-effectiveness and accessibility, it is also important to assess the quality of treatments available under Japan's Public Health Insurance System (PHIS). The purpose of this retrospective study was to assess the survival rate of metal crowns used to replace first molars in a clinical setting. Only metal crowns made of 12% gold-silver-palladium alloy placed on first molars and available under the PHIS were included. The endpoint was removal/separation of a crown or extraction of the tooth. A total of 603 crowns fitted at 20 dental offices were investigated. During the observation period, 133 of these crowns showed failure. The crown survival rate was 92.5% at 5 years, 80.8% at 10 years, 70.5% at 15 years, and 54.0% at 20 years as estimated using the Kaplan-Meier method. The estimated mean survival period was 20.6 years. The analysis revealed 3 risk factors: male (hazard ratio [HR]: 1.51), low gonial angle (HR: 1.74), and deep pockets around the abutment teeth (HR: 1.53). The main reasons for crown failure were extraction of an abutment tooth (22.6%), separation from an abutment tooth (21.8%), root fracture (18.8%), and caries (15.8%). The results showed that metal crowns available under the PHIS at dental offices have a long survival period, and that plaque control and measures to prevent separation from the abutment teeth are important for their longterm survival.