Survival of ceramic onlays placed with and without metal reinforcement

All-ceramic molar onlays continue to have higher failures from bulk fracture than similar cast metal onlays.

The purpose of this retrospective study was to compare long-term failure rates and causes for posterior sintered feldspathic ceramic (Mirage) onlays placed with and without metal substructure reinforcement.

Nineteen onlays were placed with and 78 without metal reinforcement in 50 older adolescent and adult patients treated by 2 prosthodontists in a private practice. All onlays opposed occluding tooth surfaces. Clinical judgment determined the type of onlay placed. Observational factors included patients, clinicians, onlay sites, and failure modes. Acrylic resin maxillary splints were generally provided for patients with multiple onlays or parafunctional habits. Thirty-six dies were also available for comparison of the occlusal thickness and taper of intact and failed molar onlays. The chi-square test or Fisher exact test, Student t test, and life table survival statistics were used to evaluate the data (alpha=.05).

Over 6 years, failures occurred in 21.1% of onlays placed with metal reinforcement and in 26.9% without metal reinforcement. Cumulative survival estimates (+/- standard error) were 62.4% +/- 14.7% and 60.5% +/- 6.3%, respectively (P=.84). Bulk fracture occurred in 16.5% of molars, independent of metal reinforcement (P=1.00). Overall, 11.4% of premolar and 33.9% of molar onlays failed. Irreversible pulpitis occurred in 6.2% of all teeth. From the dies, there were no clear relationships between either the thickness of occlusal ceramic material or the internal preparation taper and molar onlay failures, for onlays placed with or without metal reinforcement.

Sintered ceramic onlays placed with and without metal reinforcement showed a similar incidence of bulk fracture in molars. Preparations for both types of onlays were similar.