Effects Of Different Pretreatments To Post-space On Bonding Strength Of Fiber Posts After Root Filling With Resilon

By advantages such as good aesthetics, mechanical properties to match the dentine and non-interference to magnetic resonance et.al, fiber posts are widely used in dental repair after the treatment of pulp. Fiber posts are luted into post-space by resin cement, the bond strength depend on resin-dentine interdiffusion zone (RDIZ), resin tags and its mechanical strength. The smear layer in the surface of dentine and residues in the dentin tubule may obstruct the bond of resin cement and dentine. Therefore, physical and chemical irrigation before the cementation of fiber posts is very important and useful. Previous studies mainly focused on the cleaning effects of different irrigants to the smear layer of dental surface and the bond strength at the resin cement-dentine interface. However, the smear layer of post-space dental surface is consist of dentine debris and/or the residues of paste filling, and it is different from the smear layer of the original dentine before the filling, thus, the cleaning effect of traditional irrigants remain controversial. The contemporary root canal therapy using the warm vertical condensation technique and resin filling materials, these materials adhered to dentine closely and formed a "monoblock" structure, they can improve the hermetic seal of root canal system and reduce micro leakage. The research about the effect of pretreatment (irrigation) to post-space on bond strength of fiber posts was few, to study this subject, we used warm vertical compaction by Resilon/RealSeal to treat the invitro premolars, then researched the cleaning effect of different irrigants and their effect on bond strength of fiber posts.In the first experiment, twenty-eight premolars were obturated by Resilon using warm vertical compaction and randomly divided to receive4flushing methods (distilled water, NaOCl, EDTA/NaOCl, EDTA/NaOCl/UA). Subsequently, coronal and radicular dentin surfaces were observed under scanning electron microscopy (SEM). As a result, the group of EDTA/NaOCl/Ultrasonic irrigation showed the maximum effectiveness in removing the smear layer and debris on the dentinal surface, small part of the dentinal tubule was filled with materials, and the orifices were widely opened and slightly eroded, while the other groups had different degrees of smear layer. The result showed that Ultrasonic agitation had an additional effect on the cleanness of pile cavity.In the second experiment, luting the RelyX fiber posts into the remaining pretreated canals with RelyX U100, then each specimen was transversely sectioned into thin-slices, and the slices were divided into the coronal and apical portions, took the thin-slice push-out test and observed the specimen by SEM. The data were analyzed by ANOVA and Tukey's HSD posthoc, and the percentage of failure type was calculated. As a result, the group of EDTA/NaOCl/Ultrasonic showed the highest push-out strength value (2.18±1.26MPa),but no significant difference was noted when compared with the other2experimental groups(NaClO group,1.62±0.84MPa; EDTA/NaCIO group,1.66±0.74; P>0.05). This study showed that the cleanness of post-space didn't significantly improve the bond strength of fiber posts.In the third experiment, spraying the thin-slice gold, then observed the shape of RDIZ and resin tags by SEM, analyzed the effect of different pretreatments to post-space on bonding strength of dentine and cement. As a result, manifest RDIZ and resin tags weren't formed on the cement-dentine interface. As a self-adhesive resin cement, RelyX Unicem had superficial reaction with dentine, may influenced the formation of RDIZ and resin tags.In brief, ultrasonic agitation had an additional effect on the cleanness of pile cavity after the process of warm vertical compaction by Resilon, it also improve the bond strength of fiber posts, but the effect was not significant, this may because that Resilon/RealSeal changed the micro structure of root canal wall, and it can't infiltrated into the dentinal tubule as a self-adhesive resin cement so that influence the formation of RDIZ and resin tags, and further influence the bond strength of fiber posts.