Laboratory Effectiveness of Adhesives: A Meta-Statistical Approach

Most current adhesives can bond predictably to dental tissues. On the longer term, however, some adhesive techniques are clearly superior to others. In this lecture, we will concentrate on how dental adhesive bonds do fail and what we can learn from literature. Worldwide, bond-strength tests are used to screen bonding effectiveness of dental adhesives. The objective was to systematically collect bond-strength data, to identify the primary parameters affecting the outcome of bond-strength tests, and to attempt to disclose trends in adhesive performance of different adhesive approaches. We identified 1019 studies by entering the search term ‘dentin bond strength AND "published last 5 years"[Filter]' in PubMed. 296 studies met the inclusion criteria, yielding 2140 individual bond-strength tests. The bond-strength test used most often was the micro-tensile bond strength test (µTBS: 61%), followed by the macro-shear (SB: 22%), macro-tensile (8%) micro-shear (6%), and push-out bond strength test (3%). Different tests yielded different outcomes (for example µTBS versus SB: 31.5 versus 15.2 MPa respectively, p=0.0002), so that separate analyses for µTBS and SB are indicated (other tests were excluded). Because of the inheterogeneity of the data, a meta-modelling analysis based upon artificial neural networks was employed. This allowed us to build a statistical model based upon 10 predicting variables. Variables like ‘research group' and ‘adhesive brand' appeared most determining. Weighted means derived from this analysis confirmed the high sensitivity of current adhesive approaches (especially of all-in-one adhesives) to long-term water-storage and substrate variability. In summary, despite the lack of a standard bond-strength protocol, this meta-analysis allowed, thanks to the vast amount of data available, to draw some clear conclusions with regard to the bonding effectiveness to dentin of different adhesive approaches.