The influence of alumina abrasion and cement lute on the strength of a porcelain laminate veneering material

Abstract

The purpose of the current study was to examine whether alumina abrasion regime influenced the necessary surface roughness conducive to mechanical interlocking prior to composite resin bonding. The impact of alumina abrasion and cement lute on the bi-axial flexure strength and associated Weibull Moduli (m) on the cemented surfaces of disc specimens of porcelain laminate veneer (PLV) materials was therefore investigated. Sets of 20 Vitadur-alpha dentine porcelain discs (15 mm diameter, 1.7 mm thickness) were condensed and prepared by abrading with 25, 50 or 110 microm alumina. Further specimen groups were stored wet or coated with a resin cement. Mean fracture strengths, standard deviations and associated m were determined using a ball-on-ring assembly. The surface roughness was assessed using profilometry and scanning electron microscopy. The one-way ANOVA revealed a significant reduction (P<0.05) between the means of the dry control and alumina abraded specimens. A significant increase in m was identified for 50 and 110 microm alumina abraded cemented specimens (6.1+/-1.4 and 6.0+/-1.3, respectively) compared with the 25 microm alumina abraded cemented and non-alumina abraded cemented controls (3.9+/-0.9 and 3.5+/-0.8, respectively). Increasing the alumina particle size utilised for the abrasion resulted in a decrease in the surface roughness (R(a) value) which is the arithmetic mean of the absolute departures of the roughness profile from the mean line. Alumina abrasion acted to replace surface defects with a narrower distribution of defects. Composite resin polymerisation shrinkage may prevent surface flaws from being extended by healing the key surface defects and would appear to suggest that the use of a resin-based luting material may reduce the potential for crack propagation. Given the arrangement of ions across crack tips it is more likely that the resin composite cement enhanced strength by acting to heal key defects rather than imposing a compressive stress on the porcelain surface as suggested previously.