A preliminary investigation into the longevity and causes of failure of single unit extracoronal restorations

Four types of single unit restoration, including porcelain jacket, full and partial veneer, and metal ceramic crowns provided at the Prince Philip Dental Hospital in Hong Kong were investigated for evidence of failure. Of the 4658 units of restoration provided between 1981 and 1989, 100 restorations of each type were selected at random by computer. The relevant patient were identified and invited to return for a review appointment. A total of 132 patients attended and 152 crowns were examined. The average length of service was 34 months at the date of examination. Using strict criteria, 21 (14 per cent) restorations were deemed to have failed. Technical failure was the most prevalent cause of failure, followed by aesthetic complaints and endodontic problems. The failure rates ranged from 2.4 to 7.8 per cent per year for the different crowns in order of: partial veneer less than full veneer less than metal ceramic less than porcelain jacket crowns. Fracture of restoration, which affected metal ceramic and porcelain jacket crowns, was the single most frequent cause of failure observed in this study.