Abstract
The aim of the present study was to evaluate the microtensile bond strength and the microleakage of a bulk-fill composite resin compared with a conventional incremental composite resin, in permanent molars and under cariogenic challenge using a Streptococcus mutans model. Permanent human third molars (n = 60) with an occlusal cavity of 5×3×2 mm were randomly allocated into four subgroups of restorative treatments: conventional composite resin with (n = 15) and without (n = 15) cariogenic challenge (Z350-E and Z350-C experimental and control groups, respectively), and bulk-fill composite resin with (n = 15) and without (n = 15) cariogenic challenge (Bulk Fill-E and Bulk Fill-C, respectively). Ten specimens from each subgroup were submitted to microtensile strength, and 5, to microleakage. The cariogenic challenge was conducted using the Streptococcus mutans strain (ATCC) for 7 days. The stickers obtained (1 × 1 × 2 mm) were submitted to a microtensile strength test, followed by classification of the fracture mode. Microleakage was performed using a scoring system. The data were analyzed by Kruskal-Wallis and Mann-Whitney tests (p < 0.05). Filtek Z350 XT resin presented higher microtensile bond strength than Bulk Fill resin without (19.02 ± 4.90 and 8.76 ± 3.94MPa, respectively; p < 0.001) and with cariogenic challenge (22.69 ± 7.86 and 13.31 ± 3.38MPa, respectively; p < 0.02). Z350-C and Bulk Fill-C resins presented a higher prevalence of mixed fractures (23 and 14%, respectively) in the specimens submitted to cariogenic challenge than those of the control groups, whereas microleakage was similar (p = 0.85). The conventional composite resin had higher microtensile bond strength than the bulk-fill resin, but both resin types had similar adhesion quality and microfiltration scores.
Highlights
Composite resins have posed many problems ever since they were introduced in routine clinical practice, including polymerization contraction, lack of adaptation to cavity walls, sensitivity, pulpitis, fracture and restoration loss.[1,2] This concern has called for solutions to overcome its disadvantages by improving its properties and its insertion techniques.[1,2,3] The most widely accepted insertion techniqueBraz
The specimens were randomly allocated into four groups (G1, G2, G3 and G4) and each code of each group (Z350-Control, Z350-Experimental, Bulk Fill-Control, Bulk Fill-Experimental, respectively) was registered in an Excel file
At the end of the 7-day cariogenic challenge using the commercial strain of Streptococcus mutans, white spot lesions could be observed in all the permanent teeth of the experimental groups, demonstrating the validity of this cariogenic biofilm-based model
Summary
Composite resins have posed many problems ever since they were introduced in routine clinical practice, including polymerization contraction, lack of adaptation to cavity walls, sensitivity, pulpitis, fracture and restoration loss.[1,2] This concern has called for solutions to overcome its disadvantages by improving its properties and its insertion techniques.[1,2,3] The most widely accepted insertion techniqueBraz. Composite resins have posed many problems ever since they were introduced in routine clinical practice, including polymerization contraction, lack of adaptation to cavity walls, sensitivity, pulpitis, fracture and restoration loss.[1,2] This concern has called for solutions to overcome its disadvantages by improving its properties and its insertion techniques.[1,2,3] The most widely accepted insertion technique. Bulk-fill resins were developed as an alternative to conventional resins, inserted with up to 2 mm increments, because the bulk-fill variety features effective photopolymerization in increments of up to 4 mm.[3] These 4-mm increments gained the attention of pediatric professionals in their dental practice, because of the shorter clinical time associated with reduced shrinkage. When used in routine practice, bulk-fill resins present advantages compared with conventional resins, owing to their reduced, uncompromised clinical time, like polymerization contraction. Several studies have observed that bulkfill resins show average microtensile bond strength comparable or superior to conventional enamel or dentin composites of deciduous or permanent teeth; bulk-fill resins have been found to have more gaps in formation along gingival walls than conventional resins.[11,12,13]
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