An ideal dental adhesive should provide retentive strength, marginal seal, be relatively simple to achieve and demonstrate clinical durability. Future improvements in adhesive bonding to tooth structure require in vitro test methods that provide reliable data for materials development and/or evaluation of experimental variables. The objective of this project was to identify a test method that is relatively easy to perform, repeatable and ultimately useful for predicting clinical outcomes. The Academy of Dental Materials initiated a project to develop and distribute guidance documents on laboratory test methods that are useful for the evaluation of dental adhesives and cements, composite resins and ceramics. The dental adhesive sub-group has identified the micro-tensile bond strength test, especially after subjecting the specimens to a durability challenge, as currently the best practical surrogate measure of dental composite restoration retention. The following μTBS guidance is meant to aid the researcher in conducting the μTBS test. The authors, while recognizing the limitations of a static, strength-based test method, welcome comments and suggestions for improvements of this guidance document in future revisions.

Besides micro-mechanical interlocking through hybrid-layer formation, self-etch adhesives may benefit from additional chemical interaction between the functional monomer and residual hydroxyapatite. One-step adhesives are commonly associated with lower bonding effectiveness, which must be attributed in part to the dissolution of hydrophilic and hydrophobic monomers in a relatively highly concentrated solvent. In this ‘difficult’ mixture, also water is essential as ionization medium to enable self-etching activity. Due to the high hydrophilicity, one-step self-etch adhesives have been reported to behave as semi-permeable membranes, allowing fluids to pass through and seriously jeopardizing bond durability. Recent research has also revealed that HEMA-free one-step adhesives are prone to phase-separation, which may also account for their lower bonding effectiveness. Employing an appropriate air-drying technique may, however, improve the bonding effectiveness of such phase-separating adhesives by getting rid of substantially more interfacial water than HEMA-containing adhesives, of which water might be more difficult to remove from.