Introduction

Longevity and performance of resin-based restorations depend largely on the efficiency of monomer-to-polymer conversion, known as the degree of conversion. This conversion critically influences the physical, mechanical, and biological properties of light-cured composite resins.

Objectives

This study aimed to evaluate and compare the degree of conversion of different bulk-fill composites at superficial and deep layers, and to assess the effect of varying high-intensity light-curing durations.

Material and methods

Four bulk-fill composites, including Beautifil Bulk Restorative, Beautifil Bulk Flowable, Tetric N-Ceram Bulk Fill, and Tetric N-Flow Bulk Fill were polymerized using a high-intensity light-curing unit (2300-2500 mW/cm²) for 1, 3, and 6 seconds. The degree of conversion was analyzed at the top and bottom surfaces for each curing duration.

Results

A significant difference was observed in the degree of conversion between the top and bottom surfaces, where the top surface had higher degree of conversion values than the bottom surface. Between different curing times across several tested groups, the 6 sec group showed the highest degree of conversion, indicating variability in polymerization efficiency within the samples.

Conclusions

All tested composites exhibited higher degrees of conversion at the top surface compared to the bottom. Samples cured for 6 seconds achieved greater conversion than those cured for 1 second. Flowable composites demonstrated higher conversion values than their high-viscosity counterparts. These findings suggest that high-intensity light-curing units can achieve adequate polymerization in as little as 1-6 seconds, supporting their clinical applicability for efficient bulk-fill composite curing.