Abstract
The aim of this research was to study the impact of using a short fiber-reinforced composite (SFRC) core on the fatigue performance and fracture behavior of direct large posterior composite restorations. Moreover, the influence of the consistency (flowable or packable) of occlusal composite coverage was assessed. A total of 100 intact molars were collected and randomly distributed into five groups (n = 20). Deep mesio-occlusal-distal (MOD) cavities were prepared in all groups. After adhesive treatment and rebuilding the missing interproximal walls with conventional composite, the specimens in four experimental groups were restored by an SFRC core (everX Flow), which was applied and cured either in bulk or in oblique layers (each 2 mm thick). Packable (G-aenial Posterior) or flowable (G-aenial Injectable) conventional composites were used as a final occlusal layer. The control group was restored with only packable conventional composite. Fatigue survival was measured for all specimens using a cyclic loading machine until a fracture occurred or a total of 25,000 cycles was achieved. Kaplan–Meyer survival analyses were conducted, followed by pairwise log-rank post hoc comparisons. The static load-bearing capacity of surviving teeth was tested using a universal testing machine. Fracture patterns were evaluated visually. There was no statistically significant (p > 0.05) difference in terms of survival between the tested groups. All groups for which flowable SFRC was used showed statistically significantly higher load-bearing capacities compared to the control group (p < 0.05). There were no significant differences regarding fracture resistance among the fiber-reinforced study groups. Regarding the fracture pattern during the survival analysis, all specimens that received SFRC showed a dominantly restorable type of fracture, while the control specimens presented a dominantly non-restorable type. The use of flowable SFRC as a reinforcing core for large MOD direct restorations showed promising achievements regarding fracture behavior.
Highlights
It was assessed whether the consistency of the composite used for covering the short fiber-reinforced composite (SFRC) material is important in terms of fatigue failure and fracture resistance
The results suggest that neither the use of flowable SFRC nor the consistency of the occlusal conventional composite coverage could significantly improve the fatigue resistance of direct MOD restorations compared to conventional composite fillings
Our results show the superiority of bi-structured direct restorations over conventional composite fillings when tested with extremely high forces
Summary
With the development of adhesive techniques and composite resin restorative materials, composite fillings have come to be routinely used in the posterior region of the mouth [1,2]. The number of direct posterior composite restorations is expected to increase further with the worldwide phasing out of the use of amalgam [3,4,5]. In addition to aesthetic considerations, modern direct restorations must restore function and protect the remaining tooth structure against fractures [6]. The more dentin is missing from posterior teeth (due to caries or trauma), the more challenging it becomes to properly reinforce the complex formed by the remaining tooth material and the restoration. Of the possible cavities in posterior vital teeth, MOD (mesio-occlusal-distal) cavities are the most demanding
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