Abstract
The present study aimed to evaluates polymerization shrinkage (PS) using microcomputed tomography (μCT) and microtensile bond strength (μTBS) in bulk fill composites (BFC) and conventional class I restorations as well as the correlation between these factors. Class I cavities (4 x 5 x 4 mm), factor-C = 4.2, were created in third molars that were free of caries, which were randomly divided in 4 groups (n = 6): XTI (Filtek Supreme XTE: incremental technique); XTB (Filtek Supreme XTE: single fill technique); TBF (Tetric Bulk Fill); and SF (SonicFill). Each tooth was scanned twice in μCT: T0 was after filling the cavity with composite, and T1 was after light curing. The data were analyzed by subtracting the composite volume for each time (T1 - T0). After 1 week, the teeth were sectioned crosswise in the buccolingual and mesiodistal directions to obtain specimens with approximately 1 mm² thickness and fixed in a universal testing machine to perform μTBS. The Kruskal-Wallis and Dunn tests showed a statistically significant difference for shrinkage in µCT among the XTI and XTB and between the SF and XTB. Regarding the μTBS, all the groups differed from XTB. Bulk fill composites type presents a PS similar to that of the conventional nanoparticulate composite inserted using the incremental technique, but the bond strength was higher for the incremental group, which presented a lower number of pre-test failures when compared to BFC. No correlation was observed between the polymerization shrinkage and bond strength in the studied composites.
Highlights
Modifications in the organic matrix of composites have allowed for the evolution of new materials known as bulk fill composites (BFCs)
Polymerization Shrinkage Analysis by μCT The results for μCT were expressed in percentage volume of polymerization shrinkage (VS)
The results of this study verified that the incremental insertion technique (XTI) and the sonic bulk fill technique (SF) presented lower volumes of polymerization shrinkage (PS) and higher bond strength than the single insertion of conventional composite (XTB), but no correlation was found between these two factors
Summary
Modifications in the organic matrix of composites have allowed for the evolution of new materials known as bulk fill composites (BFCs). These materials have been indicated for use in a single layer in deep cavities (4 to 5 mm) and with a high-factor cavity configuration (Factor-C), simplifying the steps in the clinic [1]. There is significant evidence that the stress of PS in the composites can lead to deleterious effects, such as marginal leakage, gap formation, cuspal deflection, tooth cracking, reduced resin-dentin bond strength, and lowered mechanical properties, which cause great concern about the control of these effects and make the phenomenon clinically relevant [5]. The most obvious concern with respect to the PS stresses is the detrimental effect on marginal integrity and sealing of the composite restoration to the tooth [5], which may lead to tooth/composites interface failure, but these failures can be minimized by performing the incremental insertion technique, with the decrease of the C-factor [4]
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