Evaluation of polymerization shrinkage of bulk-fill resin composites using microcomputed tomography

Objectives This study evaluated the influence of cavity depth on polymerization shrinkage of bulk-fill resin composites with and without adhesive resin. Materials and methods Standardized box-shaped cavities (width, 4 mm; length, 5 mm, depth, 2 mm or 4 mm) were made on occlusal surfaces of extracted human third molars (N = 60). The teeth were assigned to 3 groups to receive bulk-fill resin composites (low-viscosity bulk-fill, SDR; high-viscosity bulk-fill; Filtek Bulk-Fill-FB; and TetricEvo Ceram Bulk-Fill-TB) in the prepared cavities with and without adhesive resin (Clearfil S3 Bond). Each specimen (n = 5 per group) was scanned twice using microcomputed tomography (micro-CT): once after application of the resin composite to the cavity prior to polymerisation and once after polymerisation. The shrinkage of volumetric loss (%) was measured using micro-CT. Data were analysed using Kruskal-Wallis and Mann-Whitney U tests (alpha = 0.05). Results The material type (p < 0.05), application of adhesive resin (p < 0.05) and cavity depth (p < 0.05) significantly affected the shrinkage values. The interaction terms were also significant (p < 0.05). All the bulk-fill resin composites tested showed significantly less shrinkage when applied in cavities with adhesive resin (0.94-2.55) compared with those without (2.01-3.45) (p < 0.05) and presented significantly more shrinkage after polymerisation (p < 0.05). At a 2-mm cavity depth without (2 mm, 2.28; 4 mm, 2.41) and with adhesive (2 mm, 0.94; 4 mm, 1.67), significantly less shrinkage was observed with FB compared with SDR and TB (p < 0.05). At a 4-mm cavity depth without (3.14) and with adhesive (2.55), SDR showed significantly higher shrinkage compared with FB and TB (p < 0.05). Conclusions The bulk-fill composites tested presented less shrinkage when used in conjunction with adhesive resin application on dentin. Overall, the low-viscosity bulk-fill resin SDR showed more shrinkage compared with high-viscosity resins tested.