Comparing the shear bond strength between universal and fifth-generation adhesives in direct restorations: a randomized controlled laboratory study

BACKGROUND: Evaluation of the clinical effectiveness of an adhesive system based solely on bond strength testing is insufficient. Additional laboratory studies are recommended, including assessment of restoration retention loss after thermocycling and testing of marginal adaptation of restorations in extracted teeth. AIM: This study aimed to compare the shear bond strength of composite restorations to tooth hard tissues after thermocycling when using a universal adhesive system and a fifth-generation adhesive system. METHODS: Shear bond strength was determined using a universal adhesive system (group 1) and a fifth-generation adhesive system (group 2). Laboratory tests were performed at the Department of Propaedeutics of Dental Diseases, Medical Institute of the Peoples’ Friendship University of Russia (Moscow), and at Technodent LLC (Belgorod). The study included specimen preparation, laboratory testing (thermocycling and shear bond strength testing), and statistical analysis using SPSS Statistics software. Extracted teeth without carious lesions or large restorations, removed for periodontal indications, were used for specimen preparation. The specimens were tested in accordance with GOST R 56924-2016 Dentistry — Polymer-based Restorative Materials. RESULTS: The mean shear bond strength in group 1 (universal adhesive system) was 17.48 ± 3.30 MPa, exceeding the GOST R 56924-2016 requirements by 2.5 times. In group 2 (fifth-generation adhesive system), the mean shear bond strength was 16.54 ± 3.91 MPa, exceeding the standard requirements by 2.4 times. The shear bond strength in the universal adhesive group was 1.05 times higher compared with the fifth-generation adhesive group. The difference between groups 1 and 2 was statistically significant (p 0.05). CONCLUSION: The shear bond strength of the universal adhesive system exceeded that of the fifth-generation adhesive system by 1.05 times and was 17.48 ± 3.30 MPa (p 0.05), indicating high clinical effectiveness of both adhesive systems, particularly for restorations located in the cervical area.