Serial Study On Bonding Of Silicone Elastomers To Acrylic Resin

This study is one part of studies on SY-1 room temperature vulcanizing silicone elastomer. It is one of important practices to restore the maxillofacial defects with maxillofacial prostheses in which retentive technique for maxillofacial prostheses is the first thing. Acrylic resin is used to construct a framework or substructure over which a silicone skin-like facial prosthesis is constructed. The bond of the silicone elastomer prosthesis to acrylic resin is the weakest link in the restoration, and experience has demonstrated partial to complete dedonding of the acrylic resin from the prosthesis.Connecting techniques depend only on mechanical connecting technique in the early silicone elastomer prostheses based on acrylic resin. The connection can be enhanced with primers combined with adhesives. Now primers have been used to enhance the bond generally. Both silicone elastomer and acrylic resin are low surface energy polymers and the bond between them is different. The purpose of this study is to develop a new primer in bonding SY-1 silicone elastomer to acrylic resin and to find the best application technologies of bonding of silicone elastomer to acrylic resin systematically. This paper includes two parts: PartⅠStudy on the development of new prime and relevant capabilityBased on pilot study, we developed a new primer to bond SY-1 silicone elastomer to acrylic resin. A reliable bonding can be achieved only with the primer. The different stage products of the new primer were subjected to Fourier transform infrared spectroscopy to analyze the hydrolysis and condensation mechanism. From the spectroscopy analysis and the shear bond strength, we can infer the bonding mechanism of the primer in bonding silicone elastomer to acrylic resin. The shear bond strengths of another 3 kinds of silicone elastomers were tested to compare with SY-1 silicone elastomer. The haemolytic test, cytotoxicity test and skin irritation test were investigated to study the biological safety of the new primer. The results are showed as follows:1. The new primer is composed with two kinds of silane coupling agents: VTMS andγ-MPS, acid catalyst and solvent. When the concentration of VTMS is 12.5% andγ-MPS is 2% we can get the highest shear bond strength between SY-1 silicone elastomer and acrylic resin. The best shear strength reached 2.20MPa.2. The different stage products of the new primer were subjected to Fourier transform infrared spectroscopy to analyze the hydrolysis and condensation mechanism. The analysis of infrared spectrograph showed that acid reaction system can cause hydrolysis and condensation of VTMS andγ-MPS molecules. We can infer the bonding mechanism of the primer in bonding silicone elastomer to acrylic resin combining with the shear bond strength.3 The shear bond strengths of 4 kinds of silicone elastomer to acrylic resin were tested. The silicone elastomers and corresponding primers include: SY-1/SA-1, CosmesilM521/CosmesilG621, CosmesilM511/ CosmesilG611, A-2186/ A-330- G. The SY-1/SA-1 group gave the highest shear bond strength 2.20 MPa. The shear bond strength were 1.63, 1.44, 1.51 MPa respectively for the other three groups. The shear bond strengthes increased after 60d accelerated heat aging for every group. Especially, the shear bond strength increased significantly for SY-1/SA-1 group and A-2186/ A-330-G group after 30d and 10d. The 2-way ANOVA indicated a significant influence of both silicone elastomer , primer type and their interaction. Optimisation of adhesive bonding can be achieved by proper selection of the system silicone elastomer/primer. The compatibility of the components of these systems can be attributed to various physicochemical interactions taking place during application.4. New primer has good biological safety. No acute haemolyticus, skin irritation and cytotoxicity were found.PartⅡStudy on different application technologies on bonding of silicone elastomers to acrylic resinBonding between silicone elastomer and acrylic resin relies on the primer mainly. Bond is a complex problem. Beside the component of primer, the surface structure does much to the bond. There are no generally accepted application technologies of bonding silicone elastomer to acrylic resin now. Mechanical treatment of the acrylic resin cause different roughness and microstructure on the acrylic resin surface and Chemical treatment have much effect on the surface of acrylic resin, too. Curing temperature and curing time are essential for the mechanical properties of the silicone elsastomers. We selected different application technologies in order to find the best way to bond silicone elastomer and acrylic resin. The results are shown below:1 The effect of the different mechanical pretreated surfaces was determined by a surface analyzer and scanning-electron microscopy (SEM). SiC paper finished specimens, polished specimens and sandblasted specimens showed different roughness and microstructure. The shear bond strengthes were positive relative to the roughness of the resin surface roughness in the present study. Sandlasted group gave the highest shear bond strength 2.46 MPa, Significantly higher than the other group. The results indicated that we can treat the acrylic resin surface by sandbalsting in the fabrication of maxillofacial prostheses.2 The effect of the different chemical pretreated surfaces was determined by SEM.MMA and acetone treatments produced significant surface texture changes of the acrylic resin and improved the bond strength between silicone elastomer and acrylic resin. The treatments had different effect on bond of the different silicone elastomer and acrylic resin. The shear bond strength of SY-1 silicone elastomer and acrylic resin reached 2.67 MPa and 2.31 MPa for A-2186 after chemical treatments .The results indicated that we can treat the acrylic resin surface with MMA or acetone in the fabrication of maxillofacial prostheses.3 SY-1 silicone elastomer was cured in three curing ways. The curing ways include room temperature 24h,heat 70 oC 1.5h,and microwave 700W 3min. The results showed the curing ways had no effect on SY-1'mechanical properties (tensile strength, elongation at break, the permanent deformation, tear strength and Shore A hardness) and the shear bond strength to acrylic resin. The results indicated that we can use microwave curing way to accelerate the fabrication of maxillofacial prostheses and meet with the patient's demand.