Effects of Resin-Modified Glass Ionomer Cement and Flowable Bulk-Fill Base on the Fracture Resistance of Class II Restorations: An Original Laboratory Experimental Study

Abstract

Aim and objective: The purpose of this study was to investigate the fracture resistance of marginal ridges restored using different techniques (amalgam, open sandwich technique, and incremental placement) and to compare these with smart dentin replacement (SDR) bulk-fill. Materials and methods: Amalgam, dispersalloy; a nanohybrid resin composite (Tetric N Ceram), a resin-modified glass ionomer cement (RMGIC) base (Fuji II LC), and flowable bulk-fill composites (SureFil SDR) were used. Standardized class II (occluso-distal) OD cavities were prepared on 60 (n = 12) extracted premolars, and five different protocols were used to restore the teeth: group 1, dispersalloy; group 2, dispersalloy with 4 mm Fuji II LC base; group 3, incrementally placed Tetric N Ceram; group 4, Tetric N Ceram with 4 mm Fuji II LC base; and group 5, Tetric N Ceram with SureFil SDR. The restorations were thermocycled then fractured using a universal testing machine, the maximum fracture load of the specimens was measured (N), and the type of fracture was recorded. Statistical analysis was carried out using one-way analysis of variance. Results: Amalgam groups showed the lowest fracture resistance, with no significant difference between the based and nonbased groups. The highest fracture resistance was displayed by Tetric N Ceram with SDR base, and it was significantly higher than all the groups except the Tetric N Ceram nonbased group. The RMGIC based Tetric N Ceram displayed intermediate fracture resistance. The majority of the restorations showed mixed types of fracture except for nonbased amalgam, which mostly failed cohesively through amalgam. SDR-based composite was the only group that showed severe tooth failures. Conclusions: The use of a 4 mm thick RMGIC base had no detrimental effect on the fracture resistance of class II amalgam and composite restorations. Clinical significance: Bulk-fill SureFil SDR placed under a conventional resin-based composite had similar fracture resistance to incrementally placed composite but higher than amalgam and composite restorations based on RMGIC.