Long-term survivals of 'direct-wax' cast gold onlays: a retrospective study in a general dental practice

Compared to other restoration types, indirect cast posterior restorations of partial coverage exhibit one of the longest survivals. The purpose of the current study was to estimate the success rates of 'direct-wax' cast gold onlays. According to the direct wax technique, the wax pattern is shaped intra-orally followed by direct casting without the need for impressions, resulting in low cost and short processing time.

A retrospective survival study was undertaken at a mixed National Health Service and private general dental practice based in London. Patients with direct-wax onlays attending over a period of four months for regular check-ups or dental treatment were recruited. Patient discomfort, pain or sensitivity was recorded. Restoration location, extension, marginal fit, and tooth vitality were also recorded. Restoration failure was defined in the event of recurrent caries, pulp infection for vital teeth, increase in the size of periapical radiolucency for non-vital teeth, and restoration decementation. Survival estimates were calculated using the Kaplan-Meier algorithm.

One hundred and ninety-four onlays in 56 patients were examined. Four restorations (2.1%) had failed, mainly due to recurrent caries. The cumulative survival probability was estimated at 415.3 (95% Confidence Interval: 403.0, 427.7) months (34.6, 95% CI: 33.6, 35.6 years), while the 10-year and 20-year survival rates were 97.0% and 94.1% respectively. Vital teeth, compared to non-vital ones, and onlay extension encompassing both the mesial and distal tooth surfaces exhibited significantly (P <0.05) higher success rates. Variations in marginal fit and restoration location did not affect the survival probability.

Direct-wax cast gold restorations of partial coverage were a highly successful treatment option for posterior restorations in a general dental practice environment.