Dynamic versus static bond-strength testing of adhesive interfaces

A static bond-strength test is often regarded as clinically less relevant, since such abrupt loading of the adhesive-tooth bond clinically never occurs. Therefore, dynamic fatigue testing is often claimed to better predict the clinical effectiveness of adhesives.ObjectivesTo measure the micro-tensile fatigue resistance (μTFR) of adhesives bonded to dentin, and to compare their μTFR to their micro-tensile bond strength (μTBS).MethodsThe bonding effectiveness (including fracture analysis) of three adhesives (OptiBond FL, Kerr: 3-step etch-and-rinse adhesive or 3-E&Ra; Clearfil SE, Kuraray: 2-step self-etch adhesive or 2-SEa; G-Bond, GC: 1-step self-etch adhesive or 1-SEa) was measured by means of both a dynamic μTFR and a static μTBS approach. Preparation and test set-up of the micro-specimens were identical for both tests. In fatigue, specimens were tested with a wide range of selected loads at 2 Hz and at 10 Hz until failure, or until 104 cycles were reached. At 2 Hz, the μTFR was also measured after 3-month water storage. The μTFR was determined using a logistic regression model. Two-way ANOVA and Tukey HSD multiple comparisons test were used to determine statistical differences in μTBS.ResultsThe 1-SEa recorded significantly lower values in μTFR at 10 Hz and in μTBS than the 2-SEa and 3-E&Ra. The 1-SEa and the 2-SEa performed significantly lower in μTFR than the 3-E&Ra, when tested at 2 Hz after 3-month water storage. Fatigue testing at 2 Hz after 1-week water storage did not reveal any differences in μTFR between the three adhesives.SignificanceThe 3-E&Ra performed best in terms of bonding effectiveness, irrespective of the experimental condition or test used. The μTBS test proved once more to be a reliable laboratory test in ranking contemporary adhesives on their bonding effectiveness.