Marginal adaption of Class V restorations with and without "softstart-polymerization"

Area of Science:

• Dental Materials Science
• Restorative Dentistry
• Polymer Chemistry

Background:

• Polymerization shrinkage in light-cured dental restorations leads to marginal gap formation, compromising restoration longevity.
• Soft-start polymerization, a technique involving initial low-intensity light curing followed by high-intensity curing, is proposed to mitigate shrinkage stress.
• The effectiveness of soft-start polymerization on marginal integrity for different dental restorative materials remains under investigation.

Purpose of the Study:

• To evaluate the influence of soft-start polymerization on the marginal integrity of polyacid-modified resin and composite resin restorations.
• To compare the marginal adaptation of different restorative materials under conventional and soft-start polymerization protocols.
• To assess the impact of thermomechanical loading on the marginal integrity of these restorations.

Main Methods:

• Sixty Class V cavities were prepared and restored with either composite resin (Spectrum + Prime & Bond 2.1) or polyacid-modified resins (Dyract + Prime & Bond 2.1; Hytac + OSB Primer).
• Restorations were subjected to either conventional curing (40s, 800 mW/cm²) or soft-start polymerization (10s, 150 mW/cm² followed by 30s, 800 mW/cm²).
• Marginal integrity was quantitatively analyzed before and after thermomechanical loading; microleakage was assessed using dye penetration.

Main Results:

• Soft-start polymerization did not significantly influence gap formation for any material before or after thermomechanical loading.
• After loading, composite resin showed significantly fewer marginal gaps at the enamel interface compared to polyacid-modified resins.
• At the dentin interface, polyacid-modified resins exhibited superior marginal adaptation and less swelling compared to composite resin, with no significant differences in gap formation between materials.

Conclusions:

• Soft-start polymerization, using a low initial intensity, did not enhance marginal adaptation for either polyacid-modified resins or composite resins in Class V cavities.
• Composite resin demonstrated superior marginal adaptation at the enamel-restoration interface, particularly when using an acid-etch technique.
• Polyacid-modified resins showed better marginal adaptation at the dentin-restoration interface, suggesting material-specific performance in different cavity locations.