Layering Technique and Operator Experience on In-Vitro Marginal Adaptation

Objectives: To evaluate/compare composite/marginal interface characteristics of proximal surfaces in Class II restorations, in-vitro.
Methods: Forty, freshly extracted, intact, unrestored human molars were prepared for a controlled-size Class II slot preparation by a single, calibrated operator (5mm B/L, 4mm O/G, 3mm axially). Prepared teeth were secured in a dentoform and restored by 2 operators (faculty/student) using either horizontal or oblique incremental layering techniques: acid-etch 15s, OptiBond-FL dentin bonding (Kerr), Premise (Kerr), 10-s incremental exposure with LED (VALO, Ultradent). Finishing was performed wet while in the dentoform using flame-shaped carbide burrs and the Enhance system (Dentsply) was used. Greyscale digital images of the proximal surfaces were captured, and subjectively evaluated independently by 4 individuals for 7 separate parameters using a pre-defined scoring sheet. Chi-square analysis (p=0.05) was applied within each parameter to observe possible differences between operator experience or layering technique on the outcome measure.
Results: No significant differences were noted between operator experience or between incremental layering technique for the following parameters: (A) percentage of cavosurface gap formation (B) evidence of long, continuous gap formation (C) evidence of peripheral enamel fracture (D) correlation between incremental layering method and peripheral enamel fracture. Significant differences were noted in the following parameters: (E) horizontal layering showed less marginal gaps (p=0.3542) but no effect of operator (F) layering technique had no significant effect on bubbles/voids on proximal surface, but student performance showed fewer (p=0.0075) (G) proximal surface showing visual evidence of incremental layering technique used - no difference between operators, but oblique technique demonstrated significantly greater incidence (p=0.0306).
Conclusions: Overall, few differences were noted in marginal gap and proximal surface characteristics between incremental layering technique used, or experience of the operator. However, the horizontal technique did demonstrate fewer gaps, and oblique method left more visual indicators of layering technique on the proximal surface.