Effect of Composite Type and Placement Technique on Shrinkage Stress

Objectives: Compare the polymerization shrinkage stress exerted on tooth structure by bulk-fill and conventional composite resins.
Methods: Thirty-five extracted maxillary premolars were divided into 5 groups and mounted into phenolic rings. Strain gauges were bonded to the buccal and lingual cusps. Proximal matrices were made with polyvinyl siloxane. Specimens received standardized MOD cavity preparations and strain gauges were connected to a data acquisition unit. A self-etch adhesive (OptiBond XTR) was applied and the preparations were restored with materials placed and cured as follows: Positive control (n=7): Filtek Supreme Ultra in 2mm oblique increments; Negative Control (n=7): Filtek Supreme Ultra in bulk; experimental group 1 (n=6): SonicFill in bulk; experimental group 2 (n=8): Surefil SDR in bulk, covered with a 2mm occlusal layer of Filtek Supreme Ultra; experimental group 3 (n=7): Tetric EvoCeram Bulk Fill in bulk. A maximum strain value (µs) was obtained from each specimen. Data were subjected to one-way ANOVA and Tukey’s post-hoc test.
Results: The mean maximum strain values and standard deviations were: Positive control: 758.8±90.6µs, negative control 1503.1±1669µs, experimental group 1: 528.2±72.7µs, experimental group 2: 495.6±57.2µs, experimental group 3: 596.4±136.7µs. A significant difference (p<0.02) was found between the positive control group and experimental groups 1 and 2. The negative control group was excluded from the statistical analysis due to the high mean and standard deviation of the group, both the result of cuspal fractures due to shrinkage stress.

Conclusions: Bulk-fill composite resins can reduce shrinkage stress, compared with conventional composites placed incrementally. The ability of bulk-fill materials to reduce shrinkage stress seems to be product-dependent. Bulk-filling with conventional composite resins is unpredictable and contraindicated.