Adhesive luting of all-ceramic restorations - The impact of cementation variables and short-term water storage on the strength of a feldspathic dental ceramic

Purpose: To investigate the impact of resin cement luting variables and short-term water storage on the strength of an adhesively luted all-ceramic restorative material. An understanding of the strengthening mechanisms will result in optimisation of operative techniques and materials selection criteria. Materials and Methods: The "fit" surfaces of 480 disk-shaped feldspathic porcelain specimens were alumina air abraded to introduce a clinically relevant surface texture and consistent surface defect population. Thirty specimens randomly allocated to each of 16 groups were coated with silane, unfilled resin or filled resin cement, or a combination. Eight groups were stored either dry or wet for 24 h prior to bi-axial flexure testing (ball-on-ring). Statistical analysis of the flexure strength data involved a three-factor general linear model (p < 0.05) prior to a Weibull analysis. Results: Resin coating the porcelain surface resulted in a significant increase in the characteristic stress (σ_o), and strengthening was dependent on coating type (p < 0.001). Silane priming resulted in additional strengthening when preceding filled resin cement coating. Water immersion for 24 h resulted in a strength degradation of both the uncoated control and coated specimens, whereby the magnitude of strength degradation was dependent on coating type (p < 0.001). Conclusion: Resin luting of dental ceramics results in significant strengthening likely to impact on clinical performance. The strengthening is dependent on the creation of a resin-ceramic hybrid layer sensitive to cementation variables and clinical placement technique. Short-term water immersion results in a significant degradation of strengthening sensitive to the characteristics of the resin-ceramic hybrid layer.