Assessment of Microhardness of Conventional and Bulk-Fill Resin Composites Using Different Light-Curing Intensity

Area of Science:

• Dental Materials Science
• Polymer Chemistry
• Biomaterials Engineering

Background:

• This study investigates the impact of two light-curing protocols on dental resin composites.
• Evaluated were a conventional/low-voltage (LV) protocol (10s, 1340 mW/cm²) and a high-voltage (HV) protocol (3s, 3440 mW/cm²).
• Five resin composites were tested, including conventional and bulk-fill types.

Purpose of the Study:

• To evaluate the effect of LV and HV light-curing protocols on the microhardness (MH) of five resin-based composites (RBCs).
• To determine the correlation between filler content (weight % and volume %) and the MH of RBCs.
• To assess the depth-dependent curing effectiveness using the bottom/top ratio of initial MH.

Main Methods:

• Laboratory preparation of cylindrical composite specimens (diameter 6 mm, height 2 or 4 mm).
• Measurement of initial microhardness on top and bottom surfaces 24 hours post-curing using a digital microhardness tester.
• Analysis of filler content (wt%, vol%) and calculation of the bottom/top MH ratio for curing effectiveness.

Main Results:

• Microhardness of RBCs was found to be more dependent on material composition than the light-curing protocol used.
• Filler weight percentage (wt%) demonstrated a greater influence on microhardness values compared to filler volume percentage (vol%).
• Bulk-fill composites exhibited bottom/top ratios over 80%, indicating good depth-of-cure, while conventional composites showed borderline or suboptimal values.

Conclusions:

• Material composition is a more critical factor than the light-curing protocol for achieving adequate microhardness in dental resin composites.
• Filler weight percentage significantly influences the microhardness of resin composites.
• Bulk-fill composites demonstrate superior depth-of-cure compared to conventional sculptable composites under the tested conditions.