Comparison of different standardized bond strength tests and the influence of glycine powder treatment in composite resin repairs

Abstract

Aim: The repair of restorations is an eligible method to extend the survival rates of intraoral restorations. There is a consensus that the old surface has to be removed before repair by the use of a sandblaster or rotating instruments. This study aimed to investigate whether a glycine powder can be used successfully in composite repair by measurement of shear and tensile bond strength according to dental standards. Methodology: The influence of mechanical preparation by no powder, 25 µm glycine powder or 50 µm aluminium-oxide powder and chemical conditioning by the use of bonding, phosphoric acid and bonding or bonding, phosphoric acid and a silane on the repair bond strength of an artificially aged nano-hybrid composite was tested according to the guidelines of DIN 13990 (2017), ISO 29022 (2013) and ISO/TS 11405 (2015). The fracture modes were evaluated by adhesive, cohesive or mixed failures. Results: There was no significant difference in the performance of the different mechanical and chemical treatments. The shear bond test according to DIN 13990 (2017) produces higher repair bond strengths (26.0±8.9 MPa) than the test described in ISO 29022 (17.9±6.3 MPa). The tensile bond strength according to ISO/TS 11405 (6.9±1.8 MPa) was the lowest. Most adhesive failures occurred with the shear test according to ISO 29022 (41%), followed by DIN 13990 (18%) and the tensile test (4%). Conclusion: For evaluating the bond strength of composites the test described in ISO 29022 is recommended, because it produces the highest percentage of adhesive failures. Nano-hybrid-composites are robust to different repair protocols.