Although there is an increase in clinical

Although there is an increase in clinical use of zirconia ceramics due to improved mechanical properties, further evidence regarding the adhesive cementation of Y-TZP restorations is necessary for the clinical success and the long-term performance of such restorations through establishing the most reliable bonding technique [46]. Bond strengths are influenced by several factors one of which is the luting cement type [47,48]. Resin cementation seems to be the favorable choice for cementing zirconia restorations [46,47]. Multilink Automix resin cement was used in this study. It contains dimethacrylate, HEMA and silica fillers which provide the improved mechanical properties of the cement represented by high flexural strength (70 MPa) according to the manufacturers. These improved mechanical properties could be responsible for high bond strength results of Multilink Automix [39]. There is some evidence that improved adhesive bonding to Y- TZP ceramics might be achieved using materials with a chemical affinity for metal oxides [22,49–51]. Phosphate ester monomers, such as MDP (10-methacryloyloxyi- decyl-dihydrogenphosphate), chemically react with zirconium dioxide, promoting a water-resistant bond to densely sintered zirconia ceramic [22]. So Metal/Zirconia Primer which contains MDP and other monomers, including VBATDT (6-[4-vinylbenzyl-n-propyl]amino-1,3,5-tri- azine-2,4-dithione), MEPS (thiophosphoric methacrylate) and MTU-6 (6-methacryloyloxyhexyl-2-thiouracil- 5-carboxylate) [52,53] was also used. According to Heikkinen [54], and Blatz et al., [55] silane coupling agent in the present study was mixed together with zirconia primer. Monobond Plus not only act as hybrid inorganic-organic bifunctional molecules that copolymerize with the organic matrix of the resin cement [56], but also improve the surface (S)-Crizotinib cost and wettability of zirconia to resin cements [57]. Thermocycling was performed to simulate thermal changes that occur in the mouth and act as a fastened aging process [37,42,51,58]. Samples were subjected to 3000 thermal cycles between 5 and 55C°. It is considered as an important factor that has been shown to decrease the bond strength in in-vitro studies [55,59]. Shear bond strength test is one of the most widely used for evaluation of adhesion in dentistry [43,46,49,59–62], because of being easy, fast and reflects the clinical situation. The stresses applied during the shear test were directed mainly at the zirconia/cement interface resulting in a relatively uniform distribution of inter-facial stresses because non-uniform distribution may cause mainly cohesive failure within the cement or the ceramic, which may lead to erroneous conclusions [23]. In the present study and in order to improve the bond strength between composite resin cement and zirconia ceramic surface, not only chemical retention was performed through using a mix of silane agent and metal/zirconia primer, but also different surface treatments of zirconia were performed to provide micromechanical retention [39,63, 64].The mean values of bond strength of resin cement to Y-TZP zirconia ceramic presented in somatostatin study varied between 6.5 and 19.6 MPa depending on the surface treatment method applied It was noticed that untreated, control (group (1)) samples showed the statistically significantly lowest mean shear bond strength, (6.5 MPa). These data were also supported by SEM evaluation (Fig. 7) which showed that the control group samples have slight roughness produced during milling procedures caused by diamond burs. This finding concurs with Blatz et al., [59] Al Hussaini and Wazzan [64] and Hummel and kern [65], Because such slight roughness was not enough to produce a retentive surface in comparison with other surface treatments (groups (2), (3) & (4)), and 3D-optical profilometer control group samples recorded the lowest mean values of irregularities; 0.74 μm. The shear bond strengths of sandblasted samples (group (2)) in the present study showed statistically significantly higher mean values than those of control group, (13.7 MPa). Sandblasting was recommended as a preferred surface treatment method for densely sintered oxide ceramics by Nothdurft et al., [39] Cavalcanti et al., [63] and Zhu et al. [67], Moreover, in this study deposition distance was controlled using a specially constructed device as recommended by Ozcan et al. [66].