Clinically-relevant Measurements of Depth of Cure of Bulk-fill Composites

Objectives: To determine and compare the depth of cure (DOC) of bulk-fill composite resins measured by a more clinically-relevant procedure versus the standard ISO 4049 measurement and bottom/top hardness ratio (H).
Methods: An OPTILUX 501(Kerr Co.) unit and a radiometer (CURE RITE, Dentsply Caulk) were used in all specimens’ preparation. The clinically-relevant method was carried out by drilling preserved human third molar teeth in the center of the cuspal surface with a 3.2 mm diameter drill pit. The teeth were filled with composites under evaluation to make cylindrical specimens (n=5) and were cured following manufacturer’s directions for use. Immediately after light curing, the specimen was removed from the tooth and the soft, unpolymerized composite material was scraped from the bottom of the specimen with a spatula. The length of the apparently cured composite was measured with a digital micrometer and divided by two in accordance with the standard ISO 4049 to calculate the DOC.
Results: All composites were tested for DOC. The clinically-relevant method met or exceeded the manufacturers’ claimed DOC of all composites tested shown in table. DOC was not a normally distributed variable in this dataset (Shapiro-Wilke p-value: 0.0002). Based on a Kruskal-Wallis test p- value of <0.0001, at least one of the brands had a significantly different depth of cure than the others. Mann-Whitney U tests with False Discovery Rate correction for multiple comparisons were then used.
Conclusions: Quixx and Sonic Fill had the highest and significantly similar depth of cure among all composites tested. The tooth structure allowed light beam transmittance that produced a 20% deeper DOC on average across all products tested compared to the stainless steel mold used in the standard ISO 4049.