Assesment of Cohesive and Adhesive Failures Using Stereomicroscope

Objectives: Volumetric changes of composite during polymerization give rise to stress in bonding interface. If the bond strength of composite surpasses that of stress, cracks in hard dental tissues around the filling will appear. We assessed those cracks using stereomicroscope. Methods: On crowns of 72 intact human premolars 144 proximal cavities were prepared using four different composites; two pacable composites, Tetric Ceram HB (Vivadent) and Filtec P60 (3M Dental Products) and two hybrid composites; Tetric Ceram (Vivadent,) and Filtec Z250 (3M Dental Products). Half of the cavities were filled with flowable composite. Two types of flowable composites were used, Tetric Flow and Filtec Flow. Vivadent composites were treated with Excite (Vivadent) and self-etching adhesive system Clearfill SE Bond (Kuraray). For 3M composites Single bond (3M Dental Products) and Clearfill SE Bond were used. Each filling was cured using two modes (ECS high intensity and puls mode) of Astralis 10, Lux-o-Max and LED curing units. The teeth were then inserted into moulds which were filled with acrylic resin. Samples were cut transversally into two halves and observed with stereomicroscope Olympus SZX-12 as well as photographed using Olympus DP-12 digital camera. On all the images depth and width of cavity, thickness of enamel, cohesive cracks, irregular hybrid layer and adhesive failures were marked and measured using Olympus DP-Soft 3.2 picture imaging program. Results: Cohesive failures were seen in 85 cavities and adhesive in 77. No statistical significance can be found regarding the type of curing or the type of adhesive system used. More cohesive failures were found in fillings made without flowable composite while samples containing pacable composite fillings had more enamel cracks. Conclusion: To minimize the stress an elastic layer of flowable composite is desirable. Cracks too small to ease penetration of enamel are not considered to be a treatment failure.