Bond strength of a 3-step total-etch bonding system to dentine - An improved approach.

BACKGROUND: Generally, the bonding of one material to another is important for function, and especially in so-called 'adhesive dentistry'. However, there are concerns about the clinical relevance and the discriminatory power of currently employed tests of bond strength. OBJECTIVE: Develop and validate a test protocol based on 4-point bending that may be used to examine the bonding of various dental materials to a range of substrates. The bonding of a resin-based composite (RBC) to dentine is taken as an example. METHODS: Slices of dentine 'coupons' (5.0 x 2.0 x approximately 4-6 mm(3)) from extracted molars were prepared using a diamond saw under running water. Pairs of RBC bars (5.0 x 2.0 x approximately 24 mm(3)) (Z250) were bonded symmetrically either side of a dentine coupon using all combinations of the following treatments: E: acid-etched (Scotchbond Universal Etchant), P: primer (Adper Scotchbond Multipurpose Adhesive); A: adhesive (Adper Scotchbond Multipurpose Primer) (all 3 M) as well as N: no treatment. Following retrieval from the mould, test pieces were immediately subjected to 4-point bending at 23 degrees C, cross-head speed 0.5 mm/min, until fracture. Three-way analysis of variance on log(flexural strength): etch x primer x adhesive, was applied. Scanning electron microscopy (SEM) was used to examine fracture surfaces and identify failure origins. RESULTS: Flexural strengths in MPa: N: 1.38 +/- 0.56; P: 9.82 +/- 0.89; A: 5.12 +/- 0.73; E: 9.39 +/- 1.78; E + P: 21.03 +/- 2.63; E + A: 12.80 +/- 1.53; P + A: 17.16 +/- 3.03; E + P + A: 20.84 +/- 3.93. The treatment main effects (all, p < 10(-12)) were not additive, there being significant two-way (p < 10(-5)) and three-way (p = 0.037) interactions. There was no significant difference between E + P + A and E + P (p = 0.86). CONCLUSION: With good reproducibility (low scatter), discriminatory power (clear treatment effects), economy with regard to substrates, the method has the potential to be adaptable to many systems.