The aim of this study was to determine the shear bond strength (SBS), etching pattern and depth, and debonding performance of several market-leading, self-etching (SE) adhesives primarily used in restorative dentistry (iBond, Clearfil S(3) Bond, Clearfil Protect Bond, AdheSE, XenoIII), two experimental self-etching adhesives (exp. Bond 1, exp. Bond 2) and one experimental self-etching cement (SE Zement) used with and without prior phosphoric acid-etching, and to compare them to an orthodontic self-etching product (Transbond Plus SE Primer) and to traditional acid-etch technique (Transbond XT Primer, phosphoric acid)
All adhesives were applied on pumiced and embedded bovine incisors following the manufacturers' instructions. Then one bracket each (coated with Transbond XT composite) was bonded (n = 20). Transbond XT was polymerized for 20 s from the incisal and gingival sides using a halogen device positioned at a constant 5 mm from and a 45 degrees angle to the specimen. The specimens were stored in distilled water for 24 h at 37 degrees C before measuring SBS. The ARI (adhesive remnant index) for all specimens was determined from the sheared-off brackets of each. After conditioning, the surface texture was morphologically evaluated from scanning electron microscope (SEM) images, while the etching depth was determined using a confocal laser-scanning microscope (CLSM). All groups were tested for normal distribution and analyzed by applying ANOVA, Kruskal-Wallis or the t test. In addition, a Bonferroni correction was used.
The median values of the SBS tests were: SE Zement 3.0 MPa, SE Zement preceded by phosphoric acid etching 11.2 MPa, experimental bond 1: 7.4 MPa, experimental bond 2: 5.6 MPa, iBond 8.1 MPa, Clearfil S(3) Bond 14.1 MPa, Clearfil Protect Bond 16.6 MPa, Clearfil SE Bond 15.9 MPa, AdheSE 16.0 MPa, XenoIII 16.1 MPa, Transbond SE Primer 20.7 MPa, acid-etching+Transbond XT Primer 21.0 MPa. With the exception of iBond, we observed no significant differences among the self-etching adhesives used in Restorative Dentistry or in comparison to the Transbond Plus SE Primer. No significant differences were apparent even when compared to the Transbond XT Primer after phosphoric acid-etching. Both experimental bonding agents and SE Zement without acid etching performed significantly worse than the products mentioned above, failing to demonstrate sufficient adhesive strength. SEM examination revealed less distinctive enamel-etching patterns for self-etching products than for phosphoric acid-etching. CLSM analysis revealed etching depths between 0.5 and 20 microm depending on the product. When self-etching products were used, less residual composite remained on the enamel surface than after phosphoric acid-etching.
All the adhesives tested are suitable for bonding orthodontic brackets and to reduce the risk of enamel fracture while minimizing etching depth, which in turns means less conditioning-related enamel loss. More development is needed to improve the etching performance of both experimental bonding agents and SE Zement.