Bonding of maxillofacial silicone elastomers to an acrylic substrate

Objective: To investigate the effect of three different primers on shear and peel bond strengths between three maxillofacial silicone elastomers and an acrylic resin after 360 h of accelerated daylight-aging. Materials and methods: Peel and shear-bond strengths of three maxillofacial silicone elastomers (TechSil S25, Cosmesil M511, Cosmesil Z004) to acrylic denture resin bases using three adhesive primers (611, A304, A330-G) were assessed at baseline and after 360 h of accelerated artificial light-aging. Data were collected and statistically analyzed by two-way ANOVA, one-way ANOVA, and Bonferroni post hoc tests (α = 0.05). Independent t-test was used to investigate the effect of light-aging on bond strengths (α = 0.05). Modes of failure were visually analyzed and categorized as adhesive, cohesive, or mixed. Results: In the peel bond test, at both baseline and after aging, there was a significant influence of primers and silicones on bond strength (p <0.001) and a strong interaction was also found between primers and silicones (p <0.05). Peel bond strengths ranged from 0.85 to 5.31 and 0.76 to 8.22 N/mm at baseline and after aging, respectively. The Z004 and 611 and Z004 and A330-G combinations showed the highest peel bond strength (5.31 and 8.22 N/mm, respectively) (p <0.05), as baseline and after aging. In the shear-bond test, there was only a significant influence of silicones on shear-bond strength (p <0.001), whereas primers did not affect it (p > 0.05), and no interaction between primers and silicones was found (p > 0.05). Shear-bond strengths ranged from 0.42 to 0.66 and 0.48 to 1.00 MPa at baseline and after aging, respectively. The combinations of Z004 and 611, Z004 and A304, Z004 and A330-G, M511 and A304, M511 and A330-G exhibited the highest bond strength (0.59-0.65 MPa) at baseline, and the Z004 with any of the primers (611, A304, and A330-G) showed greater bond strengths (0.89-1.00 MPa) (p <0.05) after aging. All the silicone elastomers at baseline, regardless of the adhesive primers, failed predominantly by cohesive debonding under peel and shear forces (68.9% and 100% respectively). However, after light-aging, peel and shear forces predominantly exhibited adhesive (79.5%) and cohesive (84.4%) failures, respectively. Conclusions: Shear and peel test-regimes were both relevant and suitable for studying bonding and debonding characteristics of maxillofacial silicone elastomers bonded to an autopolymerising acrylic resin. The silicone/acrylic bond strengths were different for shear versus peel tests: 0.42-1.00 MPa for shear and 0.51-8.22 N/mm for peel. Cohesive failures were predominant with shear-tests, whereas peel-tests showed predominant cohesive failures at baseline but adhesive failures after light-aging. The optimum bonding achieved (best bonding at baseline that increased or was unaffected after light-aging) varied between shear and peel. For shear, it was achieved using Cosmesil Z004, with any primer, and M511 (but only with A304, and 330-G primers). For peel, it was achieved using both Cosmesil Z004 and TechSil S25 bonded using A330-G primer. Consequently, Cosmesil Z004 along with primer A330-G was the optimum silicone/primer combination to select on the basis of bond strengths. Significance: A wide variety of new maxillofacial silicone elastomers and primers used in this study gave serviceable bond strengths. However, Cosmesil Z004 along with primer A330-G gave the optimum silicone/primer combination to select on the basis of bond strengths. © 2010 Academy of Dental Materials.