Difference in Adhesion between Flowable and Universal Resin Composites Applied to Cervical Restorations

Abstract

 Purpose: The cervical region is one of the well-known predilection sites of dental diseases, such as dental caries and abrasion lesions. Recently, flowable resin composites have been widely applied to cervical restoration as an easy-to-handle aesthetic restorative, instead of universal resin composite. The purpose of this study was to examine the difference in adhesion between flowable and universal resin composites applied to cervical restoration under thermo-mechanical cyclic stress condition simulating the intra-oral environment.
 Methods: Prior to this study, suitable experimental conditions, i. e., the number of thermo-mechanical stress cycles and type of resin adhesive system, had been investigated. A standardized V-shaped cavity was prepared in the bucco-cervical region of 30 extracted human mandibular premolars. The cavities were pretreated by an etch-and-rinse adhesive system, Adper Single Bond Plus (3M ESPE), according to the manufacturer's instructions. A flowable resin composite, Filtek Supreme Ultra Flowable Restrative (F; 3M ESPE), or a universal resin composite, Filtek Supreme Ultra Universal Restrative (U; 3M ESPE), was filled into the cavities and then light-cured. Restored specimens were subjected to a combination stress simulating the intra-oral environment: thermal cycling (5°C/55°C×200 sets) and simultaneous repeated load (118 N×10⁴ times). Two slabs 1.0 mm thick were obtained from each specimen, and were trimmed and shaped into a standardized dumbbell-form specimen having a bonded area onto the gingival dentin wall of the restored cavity. Micro-tensile bond strengths (μ-TBS) of the dumbbell-form specimens were measured. The data of μ-TBS (n=30) were examined using the t-test and Weibull analysis.
 Results: Mean μ-TBS in MPa/Weibull modulus value (Wm) of the dumbbell-form specimens were F: 30.1/2.9, U: 24.4/1.2. There was no significant difference between the μ-TBS of F and that of U. However, Wm of F was significantly greater than that of U at p<0.01. The μ-TBS of F (15.4 MPa) at 10% probability of failure was statistically greater than that of U (4.5 MPa) at p<0.01. The μ-TBS of F (45.1 MPa) at 90% probability of failure was statistically similar to that of U (56.3 MPa).
 Conclusion: The adhesion of F applied to cervical restoration was significantly superior in the bonding reliability to that of U-restoration. Especially at the 10% probability of failure, which was considered to be a clinically significant condition, cervical restoration using F might require greater external stress to cause debonding compared with U-restoration.