High C-factor Influences Dentin uTBS and Hardness of Conventional and Bulkfill-composites
Objectives: (1) To evaluate the dentin µTBS of a bulk fill and conventional resin-based composite in high C-factor cavity using two different layering techniques; and (2) the Knoop hardness of both composites in different restoration depths.
Methods: Forty Class I cavities (4-mm depth) were prepared in sound human third molars. RBC restorations were layered either with conventional microhybrid resin composite (Z250, 3M ESPE) or bulk-fill resin composite (Tetric EvoCeram Bulk Fill; Ivoclar Vivadent, TBF). The following groups were tested: manufacturer’s layring technique (MT): MT-Z250 — two 2-mm increments; and MT-TBF — one 4-mm increment, and inverted layering technique (IT): IT-Z250 — one 4-mm increment; and IT-TBF — two 2-mm increments. After 24h in water storage, the restorations were sectioned. The first slice (0.7-mm thickness) was taken from the proximal area of the restoration and submitted to Knoop hardness and measured in five depths. Additional sections on x-y directions were performed to obtain beams (0.75 mm x 0.75 mm) that were tested for µTBS.
Results: MT-TBF showed the lowest µTBS mean when compared to MT-Z250 (p<0.05). IT-TBF had the best µTBS mean when compared to IT-Z250 (p<0.05). When the techniques were compared, for TBF, the IT showed best means when compared to MT (p<0.05). Z250 had best performance when MT was used (p<0.05). For Knoop hardness (KHN), MT-Z250 and IT-TBF showed no difference regardless of the depth. However, for IT-Z250 and MT-TBF the depth did influence the KHN (p>0.05). When techniques were compared, MT and IT did not differ up to 1-mm depth for Z250 and 2-mm for TBF (p>0.05). From 2-mm for Z250, MT-Z250 showed best means when compared to IT-Z250 (p<0.05). Above 3-mm, the IT-TBF showed best results when compared to MT-TBF (p<0.05).
Conclusions: The 2-increments restoration technique in high C-factor cavities revealed better µTBS and hardness for both resin composite materials.