Relationship between degree of polymerization and enamel bonding strength with self-etching adhesives

To investigate the relationship between the degree of conversion of double bonds of all-in-one adhesives and their shear bond strength on ground human enamel.

Six commercially available systems and one experimental adhesive were tested: Absolute (ABS; Dentsply-Sankin), Clearfil S3 Bond (CSB; Kuraray), G-Bond (GBO; GC), Hybrid Bond (HYB; Sun Medical), iBond (IBO; Heraeus Kulzer), Xeno IV (XEN; Dentsply Caulk), and experimental iBond NG (ING; Heraeus Kulzer). Conventional shear bond strengths (SBS, n=8) of adhesive-coated enamel specimens bonded to Venus composite (Heraeus Kulzer) and degrees of conversion (DC) (FTIR, n=5) were determined after 1 and 10 min, 1, 2, and 24 h of storage. Data were statistically analyzed using ANOVA and Duncan's post hoc test (0 < 0.05).

The adhesives' SBS (MPa) and DC (%) by testing time followed logarithmic regression lines established by the least square method. Mean shear bond strengths after 1 min/24 h were: ABS 9.8/14.9; CSB 14.7/23.4; GBO 14.8/22.0; HYB 9.7/17.0; IBO 11.3/22.3; XEN 9.1/17.3; ING 9.7/25.6. The corresponding mean DC values were: ABS 51.3/66.2; CSB 83.1/90.8; GBO 75.8/87.7; HYB 49.6/67.2; IBO 72.6/93.7; XEN 61.6/74.1; ING 64.9/89.1. Linear regressions for the relationship DC vs. SBS were significant with coefficients of determination (r2) between 0.72 and 0.97.

Despite similar acidity, the adhesives showed different SBSs on enamel. Based on the relationships between DC and SBS, the cohesive failure patterns observed, and the composition-property relations discussed, it is concluded that the percentage DC is the main parameter influencing an adhesive's bonding efficacy to ground enamel.