A method for assessing force/work parameters for stickiness of unset resin-composites

To evaluate the stickiness of unset resin-composites, at different speeds and temperatures, in terms of maximum probe separation-force (F(max)) and work-of-separation (W(s)).

Eight commercial light-cured resin-composites were selected. Each material was placed in a cylindrical mold (φ=7 mm × 5 mm depth) held at 25 °C or 37 °C. The maximum force (F(max), N) and work probe separation (W(s), N mm) were measured by using a texture analyzer to register force/displacement. A flat-ended stainless-steel probe (φ=6mm) was mechanically lowered onto and into the surface of the unset sample. When a 'trigger' compressive force of 0.05 N was registered, data-acquisition commenced. Descent continued until a compressive force of 1N was reached, which was held constant for 1s. Then the probe was moved vertically upward at constant speed. This was varied over the range 2, 4, 6 and 8mm/s. The tensile force produced on the probe by the sticky resin-composite was plotted against displacement and the maximum value was identified (F(max)). W(s) was obtained as the integrated area. Data was analyzed by multivariate ANOVA and multiple pair wise comparisons was done by using a Tukey post hoc test to establish homogenous subsets (at p=0.05).

F(max) and W(s) were taken as potential measures of stickiness. They ranged from 0.47 to 3.68 N and from 0.11 to 2.84 N mm, respectively. Multivariate ANOVA showed a strong interaction of withdrawal speed, temperature and materials on both F(max) and W(s) (p<0.001).

F(max) and W(s) are useful parameters for characterizing the handling-stickiness of resin-composite materials, additional to previously reported stickiness-strain or 'peak-height'. The resin-composites investigated could be differentiated, mostly showing increases in F(max) and W(s) stickiness with increased temperature and probe-withdrawal speed.