Shrinkage-induced cuspal deformation and strength of three different short fiber-reinforced composite resins.

Objective: The aim of this study is to assess the shrinkage-induced cuspal deformation and strength of large MOD restorations using three different short fiber-reinforced composite resins (SFRC).

Materials And Methods: Twenty-seven typodont teeth #30 (Columbia) received a standardized slot-type preparation (5-mm by 5-mm depth and bucco-palatal width). Three types of SFRCs (everX Posterior, everX Flow, and a 50/50 mixture of both materials) were used with the Optibond FL bonding system. The intercuspal distance of each specimen (n = 9) was measured after preparation, immediately after restoration and at 3, 18, and 24 h. Each specimen was then subjected to simulated mastication (30° angulation with cyclic loading of buccal cusp at 5 Hz), starting at 100 N with 100 N increase every 100 cycles until fracture. Failure mode was determined as re-restorable versus nonrestorable failures. Cusp deformation data were analyzed by two-way repeated measures ANOVA and the fracture performance by Kaplan-Meier survival analysis.

Results: Shrinkage-induced cuspal deformation ranged from 27-34 microns (immediately) to 33-43 microns (24 h). The largest deformations were observed for everX Flow and the 50/50 mixture (up to 43 microns at 24 h), which also demonstrated the lowest average strength (1456 to 1511 N). everX Posterior demonstrated the least amount of shrinkage-induced cuspal deformation (27 microns, up 33 microns at 24 h) and the higher average strength (1744 N). everX Flow tended to demonstrate more repairable partial fractures while everX Posterior induced mainly catastrophic failures.

Conclusions: Large direct MOD restorations were most favorably restored with everX Posterior (less shrinkage, higher strength) at the expense of failure mode. everX Flow induced more friendly failure modes but more shrinkage-induced cuspal deformation.

Clinical Significance: When a low-cost restoration must be chosen, EverX Posterior will significantly improve the performance but not the failure mode of directly layered restorations. Because of its increased shrinkage values, everX Flow is best indicated as a limited liner to cover the IDS layer and improve geometry for semi-(in)direct restorations.