Abstract
Objectives: Resin-based composites are the most widely used dental restorative materials. Bulk-fill resin composites are of rising interest as they can be clinically applied in thicker increments compared to conventional composites. The purpose of the study was to evaluate the flexural fatigue strength of a conventional and bulk-filled resin composite placed incrementally or non-incrementally. Methods: Resin composite specimens were fabricated using either a conventional (Brilliant EverGlow?) or a bulk-fill (Fill-Up!TM) resin composite by either non-incremental filling (2 × 2 × 25 mm3) or in increments of (1 × 2 × 25 mm3). Specimens were stored in distilled water for 24 h or thermocycled for 5000 cycles. The static flexural strength (σ), flexural fatigue limit (FFL) after 105 cycles and post-fatigue flexural strength (PFσ) were measured. Data were analyzed using ANOVA, with a post-hoc Tukey’s test to compare mean FFL (p σ and PFσ compared to conventional composites regardless of incremental cure or thermocycling (p σ and FFL for conventional composites but not bulk-filled composites. There was no significant difference in PFσ compared to σ after 24 h storage, but a significant increase in PFσ after thermocycling (p < 0.05). Conclusions: The type of composite rather than incremental placement had a greater effect on flexural strength, suggesting that operator placement technique had less influence than material selection. Thermocycling in combination with cyclic loading caused a strengthening effect in the composites, likely due to the absorption and dissipation of stresses, thereby enhancing resistance to fracture.
Highlights
Resin-based composites are widely used for dental restorations due to their excellent aesthetics and suitable mechanical properties that can be directly placed using bonding agents, conserving sound tooth tissue [1]
Following thermocycling, the conventional non-incremental (CNI-T) group exhibited lower strength than bulk-filled groups BNI-T and BI-T (p < 0.05). Conventional composites placed both with no increment and incrementally, CNI and CI, showed a significant decrease in flexural strength following thermocycling while bulk-filled composites maintained higher strength values under both storage conditions (p < 0.05)
The fatigue resistance of the bulk-fill and conventional composites in this study demonstrated that the resin composite with the highest static flexural strength did not necessarily exhibit the highest fatigue resistance
Summary
Resin-based composites are widely used for dental restorations due to their excellent aesthetics and suitable mechanical properties that can be directly placed using bonding agents, conserving sound tooth tissue [1]. The polymerisation of the methacrylate monomers present in resin composites is inevitably accompanied by shrinkage that is directly or indirectly related to the contraction stresses that develop causing pain, sensitivity and gap formation resulting in microleakage, all of which may lead to secondary caries and ultimate failure of the restoration [2] [3]. Since bulk-filled resin composites can be cured in increments up to 4 mm deep, it decreases the number of layers in larger cavities but has been reported to lower cuspal strain and deformation [11]. This has the advantage of reducing clinical chair time and technique sensitivity, providing an efficient restorative option for a variety of clinical applications
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