The Effects on Microtensile Bond Strength in the Absence of Oxygen-Inhibited Layer and method of Etching

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Mikhlin, Dmitry
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Objective: Dental adhesives are relied upon to provide a strong and durable bond that will last, while also resisting dissociating forces, such as those experienced during polymerization shrinkage of composite resin restorations. The aim of this study is to determine the effects of anaerobic photo-curing of dental adhesives, by eliminating the oxygen-inhibited layer, on their mechanical properties; specifically, microtensile bond strength (μTBS). Materials and Methods: Forty permanent molars were divided among eight groups determined by a combination of one of two universal adhesive systems (Prime and Bone Elect, Scotchbond Universal), etching type (self-etch, total-etch), and curing conditions (aerobic, anaerobic). All bonded specimens were incubated in distilled water, half of which were stored for one month, and half for one year. Each specimen was cut into 1mm x 1mm in cross-section sticks, that were then used to test the μTBS of the adhesive. The specimens were subsequently evaluated under a light microscope to determine the location and type of failure. Results: Etching technique and curing conditions had a greater effect, while adhesive type has less influence, on the μTBS of the adhesive systems. Total-etch resulted in better bond strength under anerobic conditions, but performance decreased after one year. Prime Bond Elect presented the highest mean when used in aerobic curing technique associated with total etch (40.17MPa). The lowest value was observed with Scotchbond (SB) under anaerobic conditions and self-etching pre-treatment (11.58MPa). Conclusion: Within the limits of this study we can conclude that etching system and curing condition require further evaluation according to the adhesive system used in order to get the best adhesion results. As it stands, bond strength tends to be comparable, or better, under aerobic conditions. But improvements for better control of an anerobic environment could provide more accurate answers. Clinical significance: The evolution of universal adhesive represents the effort of manufacturers to facilitate the clinical procedures of adherence, but through these results, the choice of pre-treatments as well the curing process should be better evaluated