Setting characteristics and cavity adaptation of low-shrinking resin composites

The aim of this study was to evaluate the setting characteristics of low-shrinking resin composites and examine the possible interactions with curing efficiency and marginal adaptation in dentin cavities.

The materials tested were Ceram X Mono/CM, Premise/PR, Clearfil Majesty/CM, ELS/EL, and Filtek Silorane/FS. Polymerization shrinkage strain (%S), strain rate (%S(r)) and time at maximum strain rate (t(max)) were measured using the bonded disk method. Curing efficiency was measured on the top and bottom surfaces of composites with ATR-FTIR spectroscopy. Marginal adaptation was measured in unbonded (%VVF) and bonded (%XVF) specimens by computerized X-ray microtomography (micro-XCT). The % linear length of the interfacial gaps along the cavity margins (%LD) and the maximum gap width (WD(max)) were calculated under optical microscopy on sectioned specimens. Statistical analysis was performed with one- and two-way ANOVA, Bonferroni's post hoc test and Pearson's correlation coefficient.

The %S values ranged from 1.34% (FS) to 2.29% (CX), while %S(r) ranged from 0.06%s(-1) (FS) to 0.15%s(-1) (CX). %VVF values extended from 1.9% (FS) to 5.3% (CX) and for %XVF from 1.98% (FS) to 3.35% (CX). The values for %LD ranged from 36.52% (FS) to 81.28% (CX). Linear regression showed strong positive correlation for %S(r) and t(max) with %VVF (r(2)=0.884 and r(2)=0.927) and also for %S(r) and t(max) with %LD (r(2)=0.823 and r(2)=0.869).

%S(r) and t(max) are more representative than %S in determining the setting pattern of the materials and are strongly correlated to marginal adaptation. The silorane material showed better behavior than the dimethacrylate materials in setting shrinkage and marginal adaptation.