Effect of pre-heated composites and flowable liners on Class II gingival margin gap formation

Purpose: To evaluate the effect of preheated composites (PHC) and flowable liners (FL) on the gingival margin gap formation of Class II composite restorations compared to the placement of room temperature composites (RTC). Materials and Methods: Class II composite restorations were prepared on 40 extracted mandibular third molars, with the gingival margin located 1 mm below the CEJ in dentin. Optibond FL (Kerr), microhybrid Filtek Z-250 (3M ESPE) and Flow-It (Jeneric Pentron) were used to evaluate five study groups: 1) PHC, 130°F/54.4°C; 2) PHC, 155°F/68.3°C; 3) FL cured prior to the first increment composite; 4) FL cured simultaneously with the first increment composite and 5) RTC (Control). Impressions were taken with quick set polyvinyl siloxane impression material, and epoxy resin replicas were evaluated under SEM (200x). Gingival margin adaptation was quantitatively evaluated in terms of percentage of gap formation according to a modified ordinal scoring criteria. All margins were evaluated twice for reliability assessment. A non-parametric Kruskal-Wallis test was used to determine whether significant differences in gap formation existed among the study groups. Results: A high level of agreement was observed between duplicate measurements of the percentage of gap formation (intra-class correlation = 0.956, p<0.0001). There was no evidence of a difference among groups defined by placement technique (p=0.82). Overall, the mean gap-percentage for the 40 margins evaluated was 6.3 (Median=l.l; SD=14.8). Conclusions: Gingival margin adaptation was not improved relative to the control by any of the placement techniques tested. No significant differences in gap formation were found among the study groups. A high degree of intra-examiner reliability was confirmed.