The Effects of Primers and Surface Bonding Characteristics on the Adhesion of Polyurethane to Two Commonly Used Silicone Elastomers

Purpose: When restoring facial defects, maxillofacial prosthodontists and anaplastologists are often limited by material deficiencies. Silicone elastomers bonded to a polyurethane liner best satisfy the functional and esthetic requirements necessary for facial prostheses; however, patients using silicone prostheses with polyurethane liners often experience varying degrees of debonding at the polyurethane-silicone interfaces. This may result in failure of such prostheses. The purpose of this investigation was to evaluate the effects of five primers on bonding between polyurethane and two commonly used silicone elastomers. Material and Methods: Six bonding regimens were used to join polyurethane and silicone materials. Each treatment group consisted of 12 specimens. Bonding regimens included (1) a 40: 60 mixture of MDX4-4210 and Silastic Medical Adhesive Type A, in conjunction with Dow Corning 1205 primer (Udagama's technique); (2) silicone A-2000 with Dow Corning 1205 primer; (3) silicone A-2000 with A-330-G primer; (4) silicone A-2000 with Mucopren primer; (5) silicone A-2000 with Sofreliner T primer; and (6) silicone A-2000 with Sofreliner MS primer. Following fabrication, specimens were attached to a universal testing machine and separated in tension at a crosshead speed of 25.4 mm/min. One examiner performed the assessment of T-peel strength (N/mm), peak load (N), and peel distance (mm) for all specimens. Mean data were analyzed using one-way ANOVA followed by Fisher's protected significant difference multiple comparison of the means (alpha = 0.05). Results: A statistically significant difference (p < 0.05) in T-peel strength was found among specimen groups. Post hoc analysis indicated that Sofreliner MS primer (1.32 +/- 0.13 N/mm) and Sofreliner T primer (1.25 +/- 0.11 N/mm) increased the bond strengths significantly compared to A-330-G primer (0.91 +/- 0.10 N/mm) and Udagama's technique (0.13 +/- 0.02 N/mm). Cohesive failure between silicone A-2000 and polyurethane liner was observed when Sofreliner MS primer and Sofreliner T were used. Conclusion: Within the limitations of this study, the use of Sofreliner MS primer and Sofreliner T primer produced significant increases in the bond strength of silicone elastomer to polyurethane liner material. Based on T-peel strength, peel distance, and peak load data, the combination of silicone A-2000 and Sofreliner MS primer resulted in the greatest mean bond strength for silicone-to-polyurethane applications.