• 2018-07
  • 2018-10
  • 2018-11
  • In contrast to these findings Wang et al Rathke et


    In contrast to these findings, Wang et al. [35], Rathke et al. [36], and Goracci et al. [37] showed the superiority of the “etch & rinse” adhesive system regarding the push-out strength of fiber-reinforced posts when compared to self-adhesive resin cements. Conflicting results could be attributed to differences in luting procedures employed and/or different types of cements used. In the present study, RelyX Unicem was applied into the root canal by means of ‘Elongation Tips’, while Metacem was inserted with its mixing tip, and RelyX Luting was inserted with 50 K file. The elongation tip of Unicem facilitates reaching the cement into the most apical portion of the root canal space, spreading the cement onto the entire walls. In addition, forceful application of the cement inhibits air bubbles or voids formation [38]. Moreover, in Goracci et al[24] study, RelyX Unicem was chemically initiated. Foxton et al[39] have reported a significant reduction in bond strength when polymerization of the dual-cure resin composite was chemically initiated. In this study, gave statistically significantly lower bond strength values compared to RelyX Unicem, Table (1). Two-steps total-etch resin cements are technique sensitive [15]. The delivery of etchants and adhesive materials deep into the post space can be very challenging [15]. Moreover it had been shown that the curing depth of light is limited [40] thus deeper portions of dual-cured cements depend on the chemical curing only. This can reduce the degree of conversion of the cement and consequently affect its mechanical properties [41]. These factors when coupled with difficulty of humidity control in deep root areas may have compromised the bond strength of Metacem cement. Moreover, Gefitinib etching of the dentin surface with phosphoric acid removes the smear layer and the smear plugs, increasing tubule diameter and dentin permeability. Rinsing with water probably results in the retention of a substantial volume of water within the widened tubule entrances. As such water may not be completely removed by absorbent paper points; it may contribute to blister growth at the adhesive/resin cement interface. Considering the evidence that sliding friction is the main factor responsible for fiber post retention, these blisters may have reduced the contact between the resin cement and root canal walls, resulting in lower push-out bond strength values [42]. Blister growth is related to the availability of water and the polymerization rate of the resin cement, which in a slow polymerization reaction results in more water blisters [43]. On the other hand, the significantly lowest bond strength of RelyX Luting, a resin-modified glass ionomer, is probably related to the application over the smear layer because no acid solution is applied before cementation. Thus, the retention provided by RelyX Luting is more dependent on frictional retention than on its bonding to dentin [44]. Because the mechanical properties of this cement are poorer compared with the resin cements, it was expected that this cement would have the lowest retention [45], Table (1). In the present study, the push-out bond strength was reduced after thermocycling. However, statistical results showed no significant differences before and after thermocycling (TC), Table (1). These findings are concordant with Purton et al. [45] who reported that the bond strengths were not susceptible to reduced retention after thermocycling. While, Bitter et al. [19] and Mazzoni et al. [46] observed a significant influence of TC on the bond strength of resin cements to root canal dentin which was contradictory to results of the present study. Bitter et al. [19] observed a significant decrease of the bond strength of resin cements to root canal dentin after 5.000 cycles. However, in another study by the same author, the bond strength was not affected by thermocycling [47]. While, Mazzoni et al. [46] observed a significant reduction in bond strength of resin cements to root canal dentin after 40,000 thermal cycles. The controversy of the results can be attributed to the different thermal cycles employed in each study.