Chemical versus dual curing of resin inlay cements

Dual-cure inlay resin cements polymerize both chemically and through light activation; however, clinically some aspects of the cement are not readily accessible to the light source. This study investigated the degree of cement hardening achieved through chemical curing only versus dual curing and the effect of inlay thickness on cement hardness. Disks 6 x 2.5 mm were prepared from seven commercially available cements. Eight specimens were prepared from each material; half of the specimens were cured chemically only, and the remainder were dual-cured. Knoop hardness measurements were then recorded at 1-hour, 1-day, and 1-week intervals. In addition, 24 specimens of the same dimensions were prepared from each cement. Twelve specimens were dual-cured through resin composite spacers of varying thicknesses (1 to 6 mm), and the others were cured through similar ceramic spacers, and hardness measurements were recorded. Multivariate analysis of variance revealed significant differences in hardness of chemically cured versus dual-cured specimens at the 5% level of significance for all examined cements. Significant differences were also found in the hardness of specimens dual cured through ceramic or resin composite spacers 2 to 3 mm in thickness or more versus those that were dual cured without spacer regardless of the spacer material. It is concluded that chemical curing alone was not sufficient to achieve maximum hardening of the examined cements. Cement hardness was significantly reduced when inlay thickness was 2 to 3 mm or more.