Stickiness of Unset Dental Composites as a Function of Time

Objectives: Maximum-load-force (F_max) and work-of-separation (W_s) have been described in the literature¹ as parameters to describe stickiness of unset resin-composites.

Methods: An experimental composite was prepared by gradually mixing a light activated resin system containing BisEMA/DDCDMA/UDMA monomer mixture with a nanohybrid filler system (80wt%) in a speed-mixing-machine(Flackteck-DAC150). The maximum-load-force (F_max, N) and work-of-separation (W_s, mJ) were measured immediately after sample preparation and at different time intervals, by placing the uncured resin-composite in a cylindrical Teflon mold (Ф = 8mm x 3mm depth) on a mechanical tester (Instron 5943). The sample was centered under a flat-ended stainless-steel-probe (Ф = 6mm) and allowed to rest for 2 minutes. The probe was lowered at a rate of 0.25mm/s onto and into the uncured resin-composite. A force of 1N was reached and held for 2 seconds. The probe was then retracted upward at a rate of 2mm/s. The tensile force exerted on the probe by the unset resin-composite was plotted against displacement and the maximum value identified as F_max. W_s was obtained by the integrated area under the plot. Data was analyzed by ANOVA(Holm-Sidak, p<0.001).

Results:  

Data is shown in the table below. For each parameter, same letters indicate no statistical differences.

	Initial	48hours	1week	2weeks	3weeks	4weeks
Fmax, N	2.08±0.27(a)	2.02±0.05(a)	2.12±0.21(a)	2.24±0.20(a)	2.17±0.18(a)	2.34±0.14(a)
Ws, mJ	0.62±0.05(b)	0.61±0.18(b)	0.56±0.06(b)	0.54±0.20(b)	0.57±0.18(b)	0.65±0.03(b)

Conclusions:

The stickiness of uncured resin-composite was evaluated as a function of time using the F_max and W_s parameters and was determined to be constant (unchanged) over the time period tested and the parameters of this study.

¹ Kaleem, M; Satterhwaite, J.D; Watts,D.C. Dental Materials 27(2011),805-810