The effect of different insertion techniques on the depth of cure and vickers surface micro-hardness of two bulk-fill resin composite materials

BACKGROUND The aim of this study was to evaluate the Vickers surface micro-hardness and the depth of cure of two bulk-fill resin composites and one incremental-fill resin composite. MATERIAL AND METHODS Two Bulk-fill dental resin composites (X-tra Fil, Voco; Sonic-FillTM 2, Kerr Corporation) and an incremental-fill dental resin composite (Filtek™ Z250 XT, 3M ESPE) were used. Sixty cylindrical specimens of 4 mm thickness were prepared using split Teflon moulds. Specimens were divided into six groups (n=10) according to the type of the material used and according to the insertion technique applied (bulk or incremental). Prepared specimens were stored dry in complete darkness at 37°C for 24 hours. All specimens were tested for their Vickers surface micro-hardness, on their top and bottom surfaces. The depth of cure of the tested specimens was assessed by calculating the hardness ratio for each specimen. The Vickers surface micro-hardness and depth of cure data were analyzed for normality using Kolmogorov-Smirnov and Shapiro-Wilk tests. Independent sample-t test was used to compare between two groups while One-way ANOVA was used to compare between more than two groups. RESULTS Significant difference in the Vickers surface micro-hardness and depth of cure values was demonstrated among the tested materials (P<0.0001). X-tra Fil recorded the highest mean Vickers micro-hardness value (94.05±1.05). Bulk-fill dental resin composites X-tra Fil and Sonic-Fill showed 0.980±0.005 and 0.921±0.020 depth of cure values (bottom/top hardness ratio) respectively while Z250 XT recorded 0.776±0.141. CONCLUSIONS X-tra Fil showed highest Vickers surface micro-hardness values on both top and bottom surfaces, whether inserted in increments or bulk. Both bulk-fill resin composites showed higher depth of cure for both insertion techniques. Key words:Depth of cure, Vickers surface micro-hardness, bulk-fill resin composite, insertion techniques.