An In vitro Comparative Evaluation of the Effect of Preheating of EverX Posterior, Bulk Fill and G-aenial Posterior Composite Resins on Their Microhardness and Depth of Cure

Introduction: With increasing demand for aesthetic dentistry and advancements in materials, composite resins are crucial. Bulk-fill composites, allowing thicker increments (up to 4 mm), save time but raise concerns about cure depth and hardness. Preheating composites improves flow, polymerisation and mechanical properties by reducing viscosity and increasing monomer conversion. While research on preheating conventional composites exists, its impact on Bulk-fill resins, particularly regarding microhardness and depth of cure, remains limited. This study aims to compare the micro-hardness and depth of cure of preheated EverX Posterior, Beautifil Bulk Restorative and G-aenial Posterior (GP) composite resins. Materials and Methods: Sixty dental composite resin discs were made using Teflon moulds with a standardised size of 10 mm in diameter and 3 mm in height. All samples were evenly divided into 3 groups of 20 each. Group 1 ( n = 20): EverX Posterior, Group 2 ( n = 20): Beautifil Bulk-fill Restorative and Group 3 ( n = 20): GP composites. Each group was further divided into two subgroups, with 10 samples each: Subgroup A: composite resin used at room temperature (37°C), Subgroup B: pre-heated composite resin (55°C). The microhardness of both the top and bottom surfaces of all composite discs was measured using a Vickers microhardness tester, and the depth of cure was calculated by the test ratio of the bottom surface Vickers Hardness Number (VHN) to the top surface VHN. Results: Pre-heated composite resin samples showed higher VHN than samples at room temperature. Group 1 (EverX Posterior); Subgroup B showed higher VHN and depth of cure. Whereas Group 2 (Bulkfill): Sub-group A showed the least VHN and depth of cure. VHN was maximum on the top surfaces and minimum on the bottom surfaces among samples in all three groups. Conclusion: Pre-heating (55°C) of composite resin resulted in higher microhardness and depth of cure compared to composite resins used at room temperature (37°C). Pre-heated EverX Posterior showed maximum microhardness and depth of cure, whereas Beautifil Bulk Restorative showed the least microhardness and depth of cure.