Effect of Flowable Resin Liner Thickness on Damage at the Tooth–Restoration Interface: A Finite Element Study

This study aims to employ a cohesive zone model (CZM) with finite element analysis to investigate the effect of flowable liner thickness on adhesive damage in Class V resin composite restorations. 3D finite element models of Class V restorations on the mandibular first premolar were created, featuring three distinct cavity shapes: box-shaped, U-shaped, and V-shaped. Each cavity geometry was modeled with four liner conditions (0.00, 0.05, 0.10, and 0.15 mm). The adhesive damage between the restoration and the tooth was characterized using CZM. The loading conditions encompassed both polymerization shrinkage and occlusal forces. The analysis focused on the adhesive damage induced by polymerization shrinkage, occlusal forces, and their combined effects, quantified using the maximum value of the stiffness degradation scalar (SDEG) and the percentage of damage area (PDA). After polymerization shrinkage, peak SDEG and PDA decreased as liner thickness increased. During subsequent occlusal loading, increasing liner thickness was associated with a greater peak SDEG increment, higher PDA at the enamel interface, and lower PDA at the dentin interface. After the full loading sequence, overall PDA decreased with increasing liner thickness, while overall peak SDEG varied only slightly. Within the investigated thickness range, increasing flowable liner thickness reduced polymerization-shrinkage-induced adhesive damage but increased peak SDEG increments during subsequent occlusal loading. These numerical findings highlight a load-dependent mechanical trade-off associated with liner thickness.