Marginal adaptation of Class II composite fillings: guided polymerization vs reduced light intensity

Area of Science:

• Dental Materials Science
• Polymer Chemistry
• Restorative Dentistry

Background:

• Class II composite fillings are prone to marginal adaptation issues.
• A three-sited light-curing technique has shown promise in improving marginal integrity.
• The mechanism behind this improvement, whether guided polymerization or reduced stress, required investigation.

Purpose of the Study:

• To determine if the improved marginal adaptation of Class II composite fillings using a three-sited light-curing technique is due to guided polymerization or reduced polymerization stress.
• To evaluate the role of transdental curing and light intensity in achieving better marginal adaptation.

Main Methods:

• Forty human molars with Class II slot cavities were prepared and filled with composite resin in three increments.
• Light intensity was measured using photodetectors and controlled using an argon laser.
• Curing was performed using occlusal or three-sited techniques with adjusted light intensities (high and low).
• Marginal adaptation was assessed using SEM after water storage and thermocycling.

Main Results:

• No significant difference in marginal adaptation was observed between curing techniques when light energy levels were equal.
• Higher light intensity, regardless of curing technique, resulted in significantly more marginal defects (fracture and opening).
• Lower light intensity, particularly with the three-sited technique, showed better marginal adaptation outcomes.

Conclusions:

• The beneficial effect of the three-sited light-curing technique on marginal adaptation is primarily due to the reduction in polymerization stress achieved by lower light intensity.
• Guided polymerization is not the main factor; rather, managing light intensity is key to improving marginal adaptation in Class II composite restorations.