Effect of thermal cycling and filling technique on leakage of composite resin restorations.

The objective of this study was to evaluate in vitro the effect on leakage of two incremental filling techniques and two composite resins with different elastic modulus and similar polymerization shrinkage. Eighty Class V cavities (4x4x2mm) were prepared in bovine incisors and were randomly restored with Z-250 (Z) or Durafill VS (D) + Single Bond in axial (a) or oblique (o) increments. The restorations were divided into two groups: Not Aged - N (4-hour-storage in water at 37ºC) and Aged - A (1-week storage in water at 37ºC + 1000 x - 5º-55ºC / 1-min dwell time). The specimens were covered with 2 coats of nail varnish so that only the restoration margins were exposed to silver nitrate 50% (2h) and developed under fluorescent light (8h). After they were sectioned twice in buccal-lingual direction, the four exposed surfaces were digitized (Vidcap) and the silver nitrate penetration was measured (ImageLab) at the incisal and gingival walls. Data were analyzed by a 3-way ANOVA (Resin, Filling Technique and Aging) separately for incisal and gingival walls (alpha=0.05). Resin and Aging were statistically significant either for the incisal and the gingival walls. The microfill composite resin infiltrated more than the hybrid composite. The thermal cycling caused an overall increase in silver nitrate penetration. The filling technique affected leakage depending on the composite resin and aging regimen.