Cusp Deflection During Polymerization of a Silorane or Control Materials

Objectives: The shrinkage of resin composites during polymerization creates stress and deflection of the cusps. A novel material using ring opening polymerization (Silorane) was reported to feature lower shrinkage. The present study compares this material to conventional controls regarding cusp deflection during polymerization.

Methods: Extracted human molars were divided into eight groups of 6 teeth matched for equivalent size. MOD cavities (occlusal box: 3.5mm deep, 4mm wide; one interproximal box 2mm above, one exactly at CEJ) were prepared and restored using four restorative systems: 1) Silorane Self Etch Adhesive / Filtek Supreme Flowable XT / Filtek Silorane (3M ESPE) [SIL]. 2) Adper Scotchbond 1 XT / Filtek Supreme Flowable XT / Filtek Supreme XT (3M ESPE) [SUP]. 3) Clearfil SE Bond / Clearfil Liner Bond 2 Protect Liner F / Clearfil AP-X (Kuraray) [APX] 4) AdheSE / Tetric Flow / Tetric EvoCeram (Vivadent) [EVO]. In every other group a thin layer of flowable restorative material was applied covering the dentine surfaces of the cavity. Using the high viscosity material two horizontal increments were placed on the cavity floor. The interproximal and occlusal boxes were restored using two oblique increments, respectively. Each increment was irradiated for 20s using an LED curing light (Freelight 2, 3M ESPE). During polymerization, the cusp deflection was measured using inductive displacement transducers. The data were analysed using two-way ANOVA and the Tukey test.

Results:

	Cusp deflection [µm] (mean±SD)
Restorative system	w/o flowable	with flowable
SILa SUPc APXc EVOb	9.5±2.4 15.1±4.5 17.5±2.6 12.8±3.0	9.2±1.6 17.0±3.5 16.0±1.0 11.3±2.2

SIL produced the lowest, SUP and APX the highest cusp deflection (ANOVA: P<0.001).  Equivalent cusp deflection was observed with or w/o flowable (ANOVA: n.s.).

Conclusion: Low shrinking restorative materials may reduce cusp deflection during polymerization.