Effect of stepped light intensity on polymerization force and conversion in a photoactivated composite

Area of Science:

• Dental Materials Science
• Polymer Chemistry
• Biomaterials Engineering

Background:

• Polymerization shrinkage forces are a critical factor in dental composite restorations, potentially leading to marginal gaps and secondary caries.
• Optimizing light-curing protocols is essential to balance adequate conversion with minimized stress development.

Purpose of the Study:

• To evaluate the impact of stepped light intensity curing on polymerization shrinkage forces and the degree of conversion in a hybrid dental composite.
• To compare stepped vs. standard light-curing methods under varying conditions.

Main Methods:

• Hybrid composite specimens were subjected to four light-curing protocols, including stepped (low to high intensity) and standard high-intensity modes.
• Polymerization shrinkage forces were measured using a universal testing machine.
• Degree of conversion was assessed using Fourier transform infrared spectroscopy (FTIR) at the top surface and 2 mm depth.

Main Results:

• No statistically significant difference in maximum shrinkage forces was observed between stepped and standard curing groups with equivalent total energy delivery.
• Stepped curing protocols resulted in a delayed onset of force development.
• While the mode of curing did not affect overall conversion, both cure duration and depth significantly influenced the degree of conversion.

Conclusions:

• Stepped light intensity curing can be a viable alternative to standard high-intensity curing, potentially mitigating stress without compromising shrinkage forces.
• Optimizing light-curing duration and considering depth of cure are crucial for achieving adequate polymerization of dental composites.