Objective: To compare the cuspal strain in Class II restorations made with bulk-fill and conventional composite resins. Materials and methods: Fifty extracted maxillary premolars were mounted into phenolic rings and divided into five groups (n = 10). Specimens received standardized MOD preparations. A two-step self-etch adhesive was applied and the preparations were restored using a custom matrix as follows: Filtek Supreme Ultra in eight 2-mm increments (FSUI); Filtek Supreme Ultra in bulk (FSUB); SonicFill in bulk (SF); SureFil SDR flow in bulk, covered with a 2-mm occlusal layer of Filtek Supreme Ultra (SDR/FSU); Tetric EvoCeram Bulk Fill in bulk (TEBF). Strain gages bonded to the buccal and lingual cusps recorded cuspal strain during restorations. End strain values were determined and data were subjected to Kruskal-Wallis testing, followed by one-way ANOVA and Tukey´s post hoc test. Results: Combined strain values and standard deviations (in µɛ) were: FSUI: 723 ± 102.8, FSUB: 929.2 ± 571.9, SF: 519.1 ± 80.2, SDR-FSU: 497.4 ± 67.6 and TEBF: 604.5 ± 127.1. A significant difference was found between group FSUI and groups SF, SDR-FSU, and TEBF. Group FSUB showed significantly higher mean strain and greater standard deviation than all other groups due to cuspal fractures, and was thus excluded from the statistical analysis. Conclusions: The tested bulk-fill composite resins exerted less strain onto tooth structure than the incrementally placed conventional composite resin, although the magnitude of generated strain was product-dependent. Bulk-filling with conventional composite resins is contraindicated. Clinical significance: Bulk-fill composite resins exerted less strain onto adjacent tooth structure than a traditional composite, even when that composite is was placed incrementally. Bulk-filling with traditional composite resins is unpredictable and contraindicated.
Bibliographical noteFunding Information:
Funded by a research project grant from the Dora Lee and John C. Brauer Dental Research Fund, presented by the Dental Foundation of North Carolina and the Office of the Associate Dean for Research at the School of Dentistry, University of North Carolina at Chapel Hill.
The authors do not have any financial interest in any of the companies whose products are included in this paper. This study was funded by a research project grant from the Dora Lee and John C. Brauer Dental Research Fund, presented by the Dental Foundation of North Carolina and the Office of the Associate Dean for Research at the School of Dentistry, University of North Carolina at Chapel Hill. The authors would like to thank Dr. Ceib Phillips for her help with the statistical analysis. The authors would also like to thank Brasseler USA, Ivoclar Vivadent, 3M-ESPE, Kerr Corporation and Dentsply for providing the materials for this study.
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