The influence of cement lute, thermocycling and surface preparation on the strength of a porcelain laminate veneering material

Objectives. The purpose of the current study was to examine the impact of thermocycling on the development of surface flaws on the cemented surfaces of PLV restorations prepared by acid-etching or alumina (Al2O3) abrasion. Methods. Sets of 30 Vitadur-alpha dentin porcelain discs (15 mm diameter, 0.9 mm thickness) were prepared by either abrading with 50 μm Al2O3 or hydrofluoric (HF) acid-etching. Further specimen series were coated with a resin luting cement prior to thermocycling to simulate the conditions encountered ‘in service’. Mean fracture strengths, standard deviations and associated Weibull moduli (m) were determined using bi-axial fracture (ball-on-ring). Results. The two-way ANOVA revealed significant differences between the mean strength values of the porcelain specimens abraded with 50 μm Al2O3 compared with the higher strength HF acid-etched specimens. Significant differences were also identified in the mean fracture strength data for the abraded cemented and acid-etched cemented groups with the abraded groups recording the highest strength levels. Significance. Composite resin polymerisation shrinkage may help to strengthen porcelain surfaces by imposing a compressive stress on the porcelain surface. However, the strength of the HF etched cemented groups when bonded to composite resin were weaker than abraded specimens. Etching the porcelain does not only provide the necessary surface roughness conducive to mechanical interlocking but would appear to have a weakening effect on the porcelain surfaces.