Influence of flowable composite lining thickness on Class II composite restorations

Area of Science:

• Dental Materials Science
• Restorative Dentistry
• Biomaterials Engineering

Background:

• Class II composite restorations are prone to marginal degradation and internal porosity.
• Flowable composites are utilized as liners to improve adaptation and reduce stress.
• Optimal lining thickness for marginal quality and internal integrity remains debated.

Purpose of the Study:

• To evaluate the effect of different flowable composite lining thicknesses on marginal quality and internal porosity of Class II restorations.
• To compare co-cured versus pre-cured lining techniques.
• To assess the impact of thermocycling on restoration integrity.

Main Methods:

• In vitro study on 32 molars with Class II box-only cavities.
• Four groups: no lining, ultrathin co-cured, thin pre-cured, thick pre-cured.
• Thermocycling (1500 cycles, 5-60°C) and dye penetration for microleakage.
• SEM analysis of marginal patterns and internal void assessment.

Main Results:

• Ultrathin co-cured lining (Group 2) showed superior marginal quality and reduced microleakage.
• Thick pre-cured lining (Group 4) exhibited the worst marginal quality and highest openings.
• Pre-cured linings (Groups 3 & 4) reduced internal and cervical voids.
• Thick lining potentially compromises marginal sealing post-thermocycling.

Conclusions:

• Minimally thin flowable composite lining enhances cavity adaptation and marginal sealing.
• Ultrathin, co-cured flowable composite liners offer optimal marginal integrity.
• Thicker linings may impair marginal sealing, necessitating careful material selection and technique.