Tabriz University of Medical Sciences Journal of Dental Research, Dental Clinics, Dental Prospects 2008-210X 19 4 2025 12 31 Influence of composite resin type and curing method on the fracture resistance of class II restorations: An in vitro comparison 242 249 10.34172/joddd.025.43966 EN Gianella Haydee Vidal-Castillo https://orcid.org/0009-0005-3902-1612 Fredy Hugo Cruzado-Oliva https://orcid.org/0000-0003-1575-0077 Luis Felipe Alarco-La Rosa https://orcid.org/0000-0002-9296-8312 Journal Article 10.34172/joddd.025.43966 2025 08 03 2025 11 10 Background. The selection of the restorative material and the use of inadequate curing protocols can affect the mechanical performance of composite resin restorations. This in vitro study aimed to determine the influence of restorative material type and curing method on the fracture resistance of restorations with proximal involvement. Methods. A total of 120 extracted human molars were selected, and Cl II cavities (OM) were prepared, maintaining consistent dimensions across all teeth. The samples were randomly divided into two experimental groups: teeth restored with a nanohybrid composite resin (Filtek Z350XT) and teeth restored with Ormocer-based composite resin (Admira Fusion). Each group was further subdivided according to the curing method: pre-curing, co-curing, and simultaneous curing. In addition, two control groups were included: a negative control consisting of prepared but unrestored teeth, and a positive control consisting of intact, sound teeth. Fracture resistance was evaluated using a universal testing machine. Data were analyzed using two-way ANOVA and post hoc Tukey tests (α=0.05). Results. Two-way ANOVA revealed significant effects of both the composite resin type (F=1750.4, P<0.001) and the curing method (F=210.6, P<0.001) on fracture resistance, with a significant interaction between the factors (P=0.002). The Ormocer-based composite resin exhibited higher fracture resistance than the nanohybrid composite resin across all curing methods. Within each composite type, the simultaneous curing method showed the highest fracture resistance, followed by co-curing and pre-curing. Conclusion. The fracture resistance of Cl II composite resin restorations was significantly influenced by both the composite formulation and the curing protocol.