Лако-красочные материалы — производство

The luting cements based on silicates, phosphates, ZOE, EBA, and simple methacrylate resins provide little, if any, chemical adhesion, and as pointed out before, the existing bonding forces, for the most part involving micromechanical retention, are weak. However, special biphasic resin compositions are available which, on account of the presence of both hydrophilic and hydrophobic molecular constituents, experience enhanced retention to the enamel and dentinal domains of the tooth substance and to the restoration, although still largely by micromechanical interlocking. This feature is exploited for the luting of porcelain and composite inlays or onlays and for the bonding of porcelain veneers onto buccal tooth surfaces.[36] Resins of the biphasic type find their major use as dentin bonding agents and hence will be explored more thoroughly in Section V. B.3. Only two exemplifying luting agents for porcelain inlays are presented in this section. One of these is based on 4-(2-methacryloyloxyethoxycarbonyl)phthalic anhydride (4-META) as the key monomer. The material consists of a base, a mixture of 4-META and methyl methacrylate (MMA) which is combined with the (preoxidized) tributylborane initiator prior to application. As the material also adheres strongly to etched base alloy, it is an efficacious bonding agent for the attachment of metallic bridges to acid-etched enamel of the tooth structure. Enamel-metal joints with this 4-META-based resin system have been reported to attain mean tensile bond strengths near 26 MPa [9]. Typical shear bond strengths to both dentin and base metal alloys are 20 MPa [10]. With similar values determined for the bond to porcelain, the resin is also useful for the repair of porcelain restorations [11]. The second bonding system consists of a weakly filled, modified phosphate ester of bis-GMA. The application procedure includes etching of the enamel with aqueous phosphoric acid for surface roughening, application of the bonding resin, and placement of the restoration. The resin hardens through chemically initiated polymerization; temporary superficial protection from oxygen is required for proper con­version [12]. In order to achieve acceptable retention, the porcelain surfaces are properly pretreated.*This affords enamel-porcelain joints with representative bond strengths of 14 to 18 MPa. Typical shear bond strength values for the adhesive itself, attached to silanized composite, are in the vicinity of 25 MPa [8]. Adhering strongly to base metal alloys [12-14], this bonding system also finds use in prosthodontics for the fastening of bridges as in the preceding case. Usefulness as an orthodontic bracket adhesive is also indicated

[12] , with shear bond strengths near 16 MPa and fracture in tension observed to occur at the metal surface [15]. For another highly efficacious adhesive-type luting agent, based on a biphenyldimethacrylate (BPDM) primer, the reader is referred to Section V. B.3.