Influence Of Different Conditions On The Bonding Effect Between Root Canal And Resin Sealer

Objectives:The purpose of this study was to evaluate the bonding effect between resin sealer and root canals which were conditioned with 35% phosphoric acid solution and 17% EDTA solution for different periods; then provide experimental basis on further research of resin sealer applied in root canal therapy.Methods:Sixty-four single-rooted premolar teeth, extracted because of orthodontic reasons, were selected for this study. They were all prepared by using a combination of Nickel—Titanium files and crown—down technique. The teeth were then randomly divided into six test groups of 10 each and one control group of 4.The canals were treated with the following conditions as the final irrigation:groupP1,1mL of 35% phosphoric acid for 5 seconds;groupP2,1mL of 35% phosphoric acid for 10 seconds; groupP3:1mL of 35% phosphoric acid for 15 seconds; groupE1:1mL of 17% EDTA for 30 seconds; groupE2:1mL of 17% EDTA for 60 seconds; groupE3:1mL of 17% EDTA for 90 seconds; groupC:1mL of distilled water for 90 seconds. After the removal of the smear layer, all teeth were irrigated with 5mL of distilled water. Fifty specimens from 8 of each text group and 2 of control group were longitudinally sectioned in labio-lingual direction, then examined under SEM to evaluate the values of smear layer removal at the cervical, middle, and apical thirds of root canals. Kruskal-Wallis H test, Mann-Whitney U test and two-way (solution versus time) analysis of variance (ANOVA) were used for the values of smear layer removal.Fourteen remaining specimens from 2 of each test group and 2 of control group were obturated by a combination of LuxaCore-Dual and gutta percha. After obturation, the specimens were placed in deionized water at 37℃for 7 days before observation. The teeth were cut transversely 2 mm coronal to the cementoenamel junction and lmm apical portion, then each root was transversely sectioned into three equal parts:cervical, middle, and apical segments, according to the final length of each tooth (10-12mm).The flat surface dentine-cement interfaces of the three segments were etched with 35% phosphoric acid solution for 30 seconds, deproteinated with 5% NaCIO for 5min, rinsed with distilled water for 1min, and ultrasonically cleaned for 3min. The evaluation of resin tags and hybrid layer at the cervical, middle and apical segments of the root canals were examined under SEM.Results:1. Comparing the values of smear layer removal, the specimens irrigated with 35%phosphoric acid solution for 15 seconds were significantly lower than 5 seconds and 10 seconds (P0.01),17%EDTA solution for 60s and 90s were significantly lower than that 30s (P<0.01), and all of test groups were lower than control group. The conditions of phosphoric acid for 15 seconds, EDTA for 60 seconds and 90 seconds could completely remove the smear layer with no statistical difference (P>0.05),when excessive demineralization of dentin was seen except EDTA for 60 seconds.2. Conditioned with 35%phosphoric acid solution for 15 seconds, 17% EDTA solution for 60s and 90s, many long resin tags and uniform hybrid layer were observed. However the bonding effect performed by EDTA was a little better than phosphoric acid. In other groups, fewer and short resin tags were found, with no hybrid layer formed.3. Comparing the values of three portions, the apical portion was higher than cervical and middle portions (P<0.01), yet there was no statistical difference between the latter two (P>0.05).After the obturation, the bonding effect of apical third between the root canals and resin cement was also worse than that of cervical third.Conclusions:1. A good surface cleanness in root canal can be achieved with the final irrigation with 35%phosphoric acid solution for 15 seconds and 17%EDTA solution for 60s or longer.2. The complete removal of smear layer can contribute to improve the bonding effect between root canal and resin sealer; the condition of 17% EDTA solution for 60 seconds can benifit effective bonding, comparing with 35% phosphoric acid solution for 15 seconds.3. The particular structure of apical portion caused adverse bonding effect between root canal and resin sealer.