[Superficial and internal adaptations of a new self-curing composite resin restored class Ⅴ cavity]

Objective: To investigate the superficial and internal adaptations of a new self-curing composite resin in Class Ⅴ cavities. Methods: Class Ⅴ cavities were prepared in 56 caries-free human maxillary premolars (collected from Department of Oral and Maxillofacial Surgery, Capital Medical University School of Stomatology) extracted for orthodontic reasons, and these premolars were assigned into two groups (28 specimens each group). Experimental group were restored with a pretreating agent (Tooth primer) and a new self-curing composite resin (Bondfill SB). Control group were restored with a self-etching adhesive (Scotchbond Universal) and a light-curing composite resin (Z100). The restored teeth were subjected to a fatigue test to simulate temperature change and occlusal load in oral environment: mechanical cycles (1 200 000 cycles at 49 N with a frequency of 1 Hz) and thermocycles (3 000 cycles from 5 ℃ to 55 ℃ with a dwelling time of 1 min each). Before and after fatigue test, restored teeth were immersed in an 50% ammoniacal silver nitrate solution and reduced. Superficial perfect margin percentage value and length of silver deposit along the internal interface were quantified by scanning electron microscopy (SEM). Ultrastructure of dentin bonding interface was analyzed by transmission electron microscope (TEM). Results: Before fatigue test, superficial gaps at dentin side in the specimens in experimental group were narrower than those in control group, and length of silver deposit at enamel side [(0.67±0.15) μm] in specimens in the control group was significantly lower than that in the experimental group [(33.54± 10.27) μm] (P<0.05). After the fatigue test, control group showed higher perfect margin percentage value to enamel [(55.08±15.20)%] than experimental group [(25.15±12.47)%] did (P<0.05). After the fatigue test, cohesive failures could be more easily found in experimental group than in control group at surficial and internal interfaces. In TEM results, more silver deposits were found at dentin bonding interface in control group than in experimental group before the fatigue test. After the fatigue test, the deterioration at dentin bonding interface mostly happened at the bottom of the hybrid layer in control group, while in experimental group it could be found at the bottom of the hybrid layer and in the restorative material. Conclusions: When restored in Class Ⅴ cavity, the studied light-curing composite shows better superficial and internal adaptations for enamel than the new self-curing composite resin and the new self-curing composite resin shows good superficial and internal adaptations for dentin.