Shear Bond Strength of Bioactive Cement versus Resin Cement to Tooth Structure in Two Humid Conditions : (In Vitro Study)

Abstract

Cementation is a critical step that determines the success and longevity of the indirect ceramic restorations anteriorly or posteriorly such as, ceramic inlays, onlays, veneers and complete crowns. Retention and durable seal of the gap between the prepared tooth substrate and the restoration is one of the main functions of the cement that governs the success of the overlying restoration that finally enhances the optical properties of the restored tooth. There is a myriad of cementing agents that have been used in dentistry starting from zinc phosphate cement and were followed by zinc polycarboxylate, glass ionomer, resin modified glass ionomer and resin cement. Success of adhesive bonding in dentistry is multifactorial; it depends on type of substrate, type of adhesive substance, operator skills to bond the restoration successfully and humidity of the working area. Regarding the different substrates for instance, enamel is highly mineralized, which facilitates bonding procedure. On the other hand, dentin is not as of harmonious structure as enamel, it is composed of inorganic, organic components and water that demands ideal moisture conditions to ensure proper bonding by avoidance of collapse of the organic part of the dentin (collagen fibers). Humid condition of the substrate affects majorly the bond strength between the restorations and tooth substrate. There are many contaminants that could interfere with the process of bonding such as saliva, gingival fluid, blood and handpiece lubricant. Glass ionomer cements were introduced with great ease of usage without need for additional step, but it had one main disadvantage that was inadequate strength and toughness. That is the reason why resin modified glass ionomer was presented to improve the mechanical properties of conventional glass ionomer with enhanced strength like that of resin cements. For resin cements, using resin cements for bonding is a technique sensitive procedure because it requires multi-step protocol of primer acid etching and finally bond to establish effective bond joint between the tooth and restoration. To solve this drawback, self-adhesive resin cement was introduced which requires only single-step application, reduces manipulation time and improves bond effectiveness. Despite of the development of cements, there was lack of bioactivity potential of the existing cements and self-sealing ability against bacterial leakage that eventually prevent secondary caries and failure of the restoration. Diverse formulas of bio-active cements were submitted like calcium aluminate and calcium silicate products to form hydroxy apatite and maintain the tooth- restoration interface for a durable and successful restoration. Due to the increase demands for esthetic restorations, ceramic materials have evolved including the glass ceramic and zirconia-based ceramic restorations. Zirconia is a polycrystalline material with better mechanical and physical properties that is used in different dental prosthesis such as, single crowns, adhesive bridges and fixed partial dentures.

Bonding zirconia-based restorations is a critical issue; it cannot be etched with hydro-floric acid because of its polycrystallinity composition. It can be sandblasted which increases the mechanical bond strength. Another method of enhancing bond strength is, silane coupling agents with tribochemical treatment. Self-adhesive resin cements are used with zirconia restorations without a preceding step to prepare the surface.

The aim of this study was to evaluate the bond strength of the bioactive resin modified glass ionomer cement when bonded to enamel and dentin in wet and dry conditions in comparison to self-adhesive resin cement.