Seating load parameters impact on dental ceramic reinforcement conferred by cementation with resin-cements

Cementation of all-ceramic restorations with resin-cements has been demonstrated to reduce the incidence of fracture in service. The aim was to investigate the influence of loading force and loading duration applied during cementation on the reinforcement conferred by a resin-cement on a leucite reinforced glass-ceramic.

210 glass-ceramic discs (12 mm diameter, 0.8 mm thickness) were allocated to seven groups (n=30). The bi-axial flexure strength (BFS) was determined for 'as-fired' specimens (group A), following HF-acid etching (group B) and following etching and centrally loading on a semi-compliant substrate with 30 N for 300 s (group C). Further etched specimens were coated with Rely-X Unicem resin-cement under cementation loading of 5 or 30 N, for 60 or 300 s (groups D-F) prior to BFS determination using multilayered analytical solutions. BFS data was compared using factorial or one-way analyses of variance and the Weibull analysis.

HF-acid etching of the 'as-fired' surface resulted in a significant reduction in mean BFS (P<0.001) whereas resin-cementation subsequently conferred significant strengthening (P<0.001) ranging from 24 to 38% and dependent on the loading parameters employed. A factorial significance (P=0.004) of seating load (5 or 30 N) and significant factorial interaction (P<0.001) of seating load and load duration (60 or 300 s) on the mean BFS were identified.

The magnitude of resin-reinforcement conferred was sensitive to the loading parameters investigated although the mechanisms underlying the variation appear complex. Similar patterns of variability can be expected clinically impacting on the clinical longevity of resin-cemented glass-ceramic restorations.