Impacto da fibra de polietileno na resistência à fratura e propagação de trincas em restaurações de resina composta MOD

Abstract

Class II cavities represent a clinical challenge due to the loss of dental structure and the consequent reduction in fracture resistance. The presence of cracks can further weaken this structure. It is believed that resin composites can protect these teeth. The use of polyethylene fiber (PF) could increase the resistance of restorations and prevent crack propagation; however, there is no robust evidence. This in vitro study evaluated the fracture resistance and crack propagation of mesio-occluso-distal (MOD) restorations using nanohybrid (NH) and bulk fill (BF) resin composites, with and without PF, after simulating five years of clinical service through thermal and mechanical cycling. After approval by the Ethics Committee of the Federal University of Santa Maria, 40 intact molars were selected and distributed into four groups: Nanohybrid (NH), Nanohybrid with PF (NH+PF), Bulk fill (BF), and Bulk fill with PF (BF+PF). MOD cavities were prepared and restored according to each group. The largest visible crack on each tooth surface (buccal, mesial, lingual, and distal) was measured with a stereomicroscope (Discovery V20, Carl Zeiss, Germany) at 7.5x magnification, after restoration and after 25.000 thermal cycles and 1.250.000 mechanical cycles to evaluate its propagation. Fracture resistance was assessed using a universal testing machine, and the failure moment was recorded in Newtons (EMIC DL1000, Brazil). The mode of failure was classified as favorable or unfavorable. Statistical analyses were performed using Jamovi software. The fracture resistance and crack propagation were analyzed using two-way ANOVA. Fracture modes (favorable or unfavorable), were analyzed using Fisher's Exact test. The Spearman's correlation test was used to analyze the association between fracture resistance and crack propagation. Fracture resistance was not significantly influenced by the type of resin composite (p = 0.41) or the presence of PF (p = 0.89), and no interaction between these factors was observed (p = 0.23). Failure modes were similarly unaffected by resin composite type or PF presence (p = 0.74). Crack propagation varied among the surfaces: on the buccal surface, PF showed a trend toward increasing crack propagation (p = 0.054), while on the mesial surface, PF significantly increased crack propagation (p = 0.04). The type of resin composite did not significantly affect crack propagation on the mesial, buccal, or lingual surfaces, however, BF presented significantly reduced crack propagation on the distal surface (p = 0.02). No significant interactions between resin composite type and PF were observed for crack propagation on any surface. Incorporating PF into resin composites did not affect fracture resistance or fracture mode; however, the presence of PF was associated with increased crack propagation on the mesial surfaces. Both composites demonstrated similar fracture resistance and failure modes, while BF showed reduced crack propagation on the distal surface.