Effects of heat in the properties of NaOCl alone and mixed with etidronate and alkaline tetrasodium EDTA.

AIM: To assess the free available chlorine concentration (FAC), organic tissue dissolution and smear layer removal capacity of sodium hypochlorite (NaOCl) alone and when mixtured with etidronate (HEDP) and tetrasodium EDTA (Na4 EDTA), and heated to different temperatures. METHODOLOGY: Mixtures at 1 : 1 ratio of 5% NaOCl with distilled water (considered NaOCl alone), 18% HEDP or 10% Na4 EDTA were heated to 25 °C, 37 °C, 48 °C and 60 °C. The FAC in the mixtures was assessed at 5, 10, 20, 30, 60 and 120 min. Samples of bovine muscle tissue (n = 10) were prepared with similar size and weighed before and after 5, 10 and 15 min of immersion in the mixtures heated to the different temperatures to verify organic matter dissolution. The intergroup results were compared statistically using one-way analysis of variance (anova) and intragroup by two-way analysis of variance (anova), both followed by Tukey's multiple-comparison test (α < 0.01). Bovine dentine blocks (n = 10) were analysed by scanning electron microscopy before and after immersion in the mixtures, and the time taken to remove the smear layer from the surfaces of the samples was determined. The Friedman test was used to compare the scores of the same group (α < 0.01), and the Kruskal-Wallis test with Dunn's post hoc was used to compare the different groups (α < 0.01). Saline solution was used as a control in the experiments of tissue dissolution and smear layer removal, RESULTS: Heating NaOCl alone did not affect its FAC. The higher the temperature of the mixtures with the chelators, the lower the FAC. Organic tissue dissolution was improved by increases in temperature of NaOCl alone and its mixture with HEDP (P < 0.01); however, the mixture with Na4 EDTA had no improvement (P > 0.01). Smear layer removal by NaOCl alone was enhanced by heating resulting in lower scores in some samples and became more rapid in the mixtures with the chelators. The saline solution did not promote tissue dissolution nor smear layer removal (P > 0.01). CONCLUSION: In this laboratory study, heating NaOCl alone or when mixed with HEDP improved its capacity to dissolve organic matter and remove the smear layer. However, the mixture with HEDP required frequent refreshment to retain these effects when heated. Due to the acceleration in the reaction between the irrigants, very rapid reductions in the free available chlorine in the mixtures with Na4 EDTA heated to the different temperatures occurred.

Effect of larger apical size on the quality of preparation in curved canals using reciprocating instruments with different heat thermal treatments.

AIM: To evaluate the influence of larger apical canal enlargement in curved canals using reciprocating systems subjected to various heat treatments. METHODOLOGY: Ninety mandibular premolars with root curvatures ranging from 20° to 30° were selected and scanned by microcomputed tomography (micro-CT) before and after root canal preparation with reciprocating systems (n = 30): Reciproc Blue (RB size 25, .08 taper and size 40, .06 taper; VDW, Munich, Germany), WaveOne Gold (WOG size 25, .07 taper and size 35, .06 taper; Dentsply Sirona, Ballaigues, Switzerland) and ProDesign R (PDR size 25, .06 taper and size 35, .05 taper; Easy Dental Equipment, Belo Horizonte, Brazil). Canal transportation, untouched areas, and apical and total root canal volumes were measured. Statistical analysis was performed with the nonparametric Kruskal-Wallis and Dunn's tests and a significance level set at 5%. RESULTS: The between-group comparison revealed no significant difference in untouched areas, canal transportation, and apical root canal volume among the groups (P > 0.05). However, WOG size 35, .06 taper was associated with a significant increase in the percentage of total canal volume in comparison to the PDR size 35, .05 taper (P < 0.05). The within-group comparison revealed a significant decrease in untouched areas, increase in apical and total root canal volume for all groups when using a larger instrument (P < 0.05). There was no significant difference in transportation among the groups and when a larger apical preparation was created (P > 0.05). CONCLUSIONS: Larger apical enlargement of curved canals was associated with a decrease in untouched areas, an increase in root canal volume and maintenance of canal trajectory. In addition, all systems were safe and provided similar root canal shapes.