Characterisation Of Commercial Bulk-Fill Resin Composite

Abstract

Background: Bulk-fill resin composites were developed to overcome the limitations of the conventional incremental technique by allowing thicker incremental placement of 4–5 mm. with the aim of simplifying restorative procedures while maintaining acceptable material properties. This can be useful in paediatric dentistry, where shorter treatment time and easier placement are clinically beneficial. However, the behaviour of bulk-fill composites remains material-dependent, and further laboratory testing is needed. Aim: This study aimed to characterise and compare the chemical and physical properties of two commercial bulk-fill resin composites, 3M Filtek One Bulk Fill and Ivoclar Tetric PowerFill, against a conventional composite, Dentsply Ceram.X Spectra ST HV, as a control. Methods: Five physicochemical tests were conducted:1. degree of conversion (DC%) measured at 1–5 mm depths using FTIR spectroscopy, 2. polymerisation shrinkage strain and volumetric shrinkage assessed by the bonded-disc method over 60 minutes, 3. depth of cure evaluated according to ISO 4049:2019, 4. water sorption, desorption, and solubility following Braden's method, 5. acid uptake using acetic acid solution at pH 4.0. All materials were light-cured using a 3M Elipar DeepCure-L unit at 1200 mW/cm² according to the manufacturer's instructions. Data were analysed using one-way ANOVA and Tukey's HSD post-hoc testing. Results: : Ivoclar Tetric PowerFill had the highest DC% at all depths and the lowest solubility (0.14%), which may be linked to its unique polymerisation chemistry. 3M Filtek One Bulk Fill showed adequate DC% up to 4 mm but a notable drop at 5 mm (bottom surface: 31.84%), and had the highest water absorption (1.16%) and acid uptake (0.89%). Dentsply Ceram.X Spectra ST performed well within its recommended 2 mm increment but showed the greatest reduction in conversion at greater depths and the highest solubility (0.31%). Both bulk-fill materials achieved significantly greater depth of cure (5.65 mm and 5.52 mm) than the conventional composite (3.23 mm; p < 0.001). Polymerisation shrinkage was similar across all three materials. Conclusion: Both bulk-fill composites performed well within their recommended increment thicknesses and showed better depth of cure than the conventional material. The results support the clinical use of bulk-fill composites for posterior restorations and highlight the need for further testing, to build a more complete picture of their long-term performance.