Atmospheric moisture effects on the testing rate and cementation seating load following resin-strengthening of a soda lime glass analogue for dental porcelain

Objectives

To investigate if resin-cementation of a soda lime glass dental analogue could elucidate information regarding the pattern of resin-reinforcement when coated in an environment actively scavenged of moisture.

Methods

192 soda lime disc-shaped specimens (alumina particle air abraded, hydrofluoric acid-etched and silane coated) were randomly assigned to eight groups (n = 24 per group) prior to resin-coating at seating loads of 5 N (Groups A–D) and 30 N (Groups E–H) in an environment where moisture was actively scavenged and maintained below 15 ppm. Following one week storage the discs were tested in biaxial flexure at crosshead rates of 0.01, 0.1, 1 and 10 mm/min. Analysis of group means was performed utilising a general linear model univariate analysis and post hoc all paired Tukey tests (P < 0.05).

Results

The general linear model univariate analysis identified the mean biaxial flexure strength (BFS) was significantly influenced by the factors resin-cementation seating load (P < 0.001) and crosshead speed of the applied load (P < 0.001) with a significant interaction (P = 0.008) between both factors. The linear logarithmic regression curves fitted to the group mean BFS data plotted against the crosshead speed highlighted significant differences between the pattern of resin-strengthening for the cementation loads and testing conditions.

Conclusions

The decrease in resin-penetration expected within the ‘resin-ceramic hybrid layer’ following removal of the 30 N seating load was proposed as the modifying resin-strengthening parameter. These observations are supported by the viscoelastic and creep behaviour of resins at slow testing rates which becomes the dominant or determining phenomenon.