Mechanical Properties and Cusp Deflection of Bulk Fill Composite Resins

Objectives: The aim of this study was to evaluate diametral tensile strength (DT), compression strength (CS) and cuspal deformation (CD) of bulk fill composite resins: TBF, Tetric EvoCeram Bulk Fill (Ivoclar Vivadent); VBF, Venus Bulk Fill (Heraeus Kulzer); SDR, Surefil SDR (Dentsply); FBF, Filtek Bulk Fill (3M ESPE); and 3 universal microhybrid composite resins: Z350, Filtek Z350 XT (3M ESPE); CHA, Charisma Diamond (Heraeus Kulzer); EST, Esthet X HD (Dentsply).
Methods: Cylindrical samples (N=10) were made for CS test (6mm thickness, 3mm diameter) and DT test (2mm thickness, 4 mm diameter). The tests were performed at 0.5 mm/min. Molars with standardized class II mesio-oclusal-distal preparations (N=10) were restored with bulk fill composite overlayed occlusally with universal composite from the same manufacturer, except TBF which was used for the whole restoration. Two-increment Z350 restoration was the control (N=10). CD was measured using strain gauges (Excel Sensores) on buccal (B) and lingual (L) cusps during restoration. Data were analyzed by one-way ANOVA and Tukey test (α=0.05).
Results: The CS values (MPa) were: Z350, 257.0±36.1a; EST, 252.9±30.6a; CHA, 250.8±36.0a; FBF, 245.1±37.4a; VBF, 229.1±44.8ab; TBF, 213.3±37.4ab; SDR, 182.3±14.6b. DT values (MPa) were: CHA, 54.2±3.7a; Z350, 47.3±7.5ab; VBF, 43.8±8.2bc; EST, 43.6±5.9bc; SDR, 43.5±3.7bc; FBF, 38.6±5.9c; TBF, 37.8±7.7c. The cusp deflection (μS) were: Z350 B-293±185a; L-536±358b; FBF+Z350 B-284±184a; L-737±230b; SDR+EST B-222±166a; L-572±398b; TBF B-201±95a; L-375±267b; VBF+CHA B-254±90a; L-556±286b. Different letter means significant difference among composite resins for CS and DT and between cusps for CD.
Conclusions: SDR had lower CS than universal composite resins. The bulk fill composites generally had lower DT than universal composite resins. No difference was found for CD among composite resins tested. Buccal cusps had significantly lower CD than Lingual cusps for all restorative materials.