Fracture Resistance of Nano Hybrid Ceramic versus Lithium Disilicate Endocrowns Cemented with Twoo Bonding Approaches : An In Vitro Study /

Abstract

Endodontically treated molars are considered a challenge in restorative dentistry. Such teeth are more susceptible to fracture because of their inherently poor structural integrity by the carious lesions, trauma and extensive cavity preparation. There are a lot of debates about the ideal treatment for endodontically treated teeth. Although dowels are used to retain coronal buildup materials, nowadays it is agreed that dowel do not reinforce remaining tooth structure and may even lead to excessive weakening. The endocrown restoration is an alternative for restoring endodontically treated molars which presented in 1999 by Bindl and Mörmann. This monolithic, ceramic adhesive restoration needs specific preparation designs to satisfy criteria aiming for the success of these restorations. The endocrown restorations are achieving a biomechanical concept by a cervical margin in the form of a butt joint and preparation of the pulp chamber that does not reach the root canals conserving root dentin. The remaining tooth structure helps in increasing the durability and strength. Recently there are new dental ceramic materials and new processing techniques, specifically CAD/CAM and milling technology that facilitated the development and application of recently introduced dental ceramics. CAD/CAM helps in using different materials that cannot be used by conventional dental processing techniques. Perfectly controlled industrial ceramic processing can allow for producing of increased microstructural uniformity, higher density, and lower porosity and decreased residual stresses in restorations. Such improvements have the potential to improve clinical predictability and satisfactory outcome. For chairside cases where strength is a consideration, lithium disilicate CAD restorations offer the strength of 400 Mpa as compared with the leucite-reinforced ceramic, with Mpa ranging from 120 to 160, and still having good esthetic results. Lithium disilicate ceramic material used in the form of monolithic material and provide better strength. (5) Recently introduced CAD/CAM block based on the integration polymer network and ceramics. Hybrid material offers the ease of handling of a composite material with the surface gloss and optimum finish similar to porcelain. The microstructural analyses suggested that this hybrid material composed of interconnected networks: a dominant ceramic and a polymer. Endocrowns restricted to the silica-based ceramic material, which can be acid etched ceramic to obtain a good bond to the prepared tooth structure by using of adhesive cementation system, and ensure the stability of this monolithic restoration. Pressed or machined lithium disilicate ceramic showed favorable results. As they have high mechanical strength and satisfactory esthetic results. The bond strength of hybrid ceramics to composite resin cement is thought to be superior to that found with ceramics. The presence of resin matrix in blocks of hybrid ceramics facilitates bonding to resin composite luting materials, giving more even and uniform distribution of forces when compared to feldspathic and reinforced ceramics and therefore better fracture resistance. The recently introduced dentin adhesives allowed for increased bond strength and claimed by the manufacture to be eighth generation dentin bonding agent (Futurabond DC, Voco, Germany). These bonding agents contain valuable amounts of highly functional nano- sized cross- linking agents, silica particles and offer the advantage to be dual -cured and having higher bond strength than sixth and seventh generations.