Marginal Adaptation of In Vitro Class II Restorations Made Out of Bulk or Conventional Composite Using Single- or...

Area of Science:

• Dental Materials Science
• Restorative Dentistry
• Biomaterials Engineering

Background:

• Direct composite restorations are widely used for large Class II cavities.
• Marginal integrity is crucial for restoration longevity and preventing secondary caries.
• Sub-gingival margins present unique challenges for achieving and maintaining adaptation.

Purpose of the Study:

• To evaluate the influence of different restorative materials (conventional vs. bulk-fill composites) and layering techniques (single vs. multi-layered) on the marginal adaptation of Class II direct composite restorations.
• To assess the impact of thermomechanical loading (TML) on the marginal integrity of restorations with supra- and sub-gingival margins.
• To compare the types of marginal defects (cohesive vs. interfacial) occurring in enamel and dentin under fatigue conditions.

Main Methods:

• Forty prepared teeth were divided into five groups using various conventional and bulk-fill composites with different layering strategies.
• Specimens underwent staged thermomechanical loading (TML) simulating intraoral conditions.
• Scanning electron microscopy (SEM) was used to quantitatively assess marginal adaptation at enamel and dentin margins at multiple timepoints (T0, T1, T2, T3).

Main Results:

• TML significantly reduced continuous marginal adaptation in all groups, with percentages decreasing from 75.2–91.8% at baseline to 21.3–73.9% after fatigue.
• Both composite systems and layering protocols significantly influenced marginal adaptation, with time-dependent effects observed.
• Enamel margin defects were primarily cohesive (micro-fractures), while dentin defects were mainly interfacial gaps.

Conclusions:

• Long-term in vitro fatigue testing revealed significant degradation of marginal adaptation for direct composite restorations, even with high-viscosity conventional materials and proper layering in sub-gingival cavities.
• No significant differences in adaptation were found at cervical dentin margins across the tested groups.
• A tendency towards better enamel margin adaptation was observed with higher modulus materials applied using a multi-layered technique.