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 360h 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 360h 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 8.22N/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 8.22N/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 1.00MPa 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 (0.59–0.65MPa) at baseline, and the Z004 with any of the primers (611, A304, and A330-G) showed greater bond strengths (0.89–1.00MPa) (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: 0.42–1.00MPa for shear and 0.51–8.22N/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.