Final irrigation with 6% NaOCl accelerates dentinal erosion following treatment with 15% EDTA.

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Background:The initial electronic apex locator (EAL) length measurement is generally established with a small-sized file. It is not known whether file size would be interfering with the reading accuracy of the EAL. This study aimed to evaluate the effect of file size on the accuracy of Root ZX apex locator using an agar model when sodium hypochlorite solution or blood was present during electronic measurements in enlarged root canals. Methods: A total of 36 extracted lower premolars were used. In stage 1, the canals were instrumented using size 10-40 K-files with a size 40 K-file as the master apical file (MAF). The teeth were then divided randomly into two groups of 18 teeth each. In group A, the teeth were mounted in one per cent agar and irrigated with six per cent sodium hypochlorite solution (NaOCl), while in group B the teeth were mounted in agar and irrigated with human blood. In stage 2, the canals were enlarged using a size 60 K-file as the MAF. In stages 1 and 2, the apical portions of the canals were instrumented using the step-back sequence (up to a size 80 K-file). In stage 3, the canals were enlarged using a size 80 K-file as the MAF. In each stage, the length was measured with a Root ZX until the meter value reached 'APEX' using small and large size files. Results: Three-way ANOVA and Bonferroni test showed that file size, stage of preparation and type of irrigant all had a significant influence on the measurement error (P<0.0001), with all the interactions between these three factors being significant (P<0.0001). Conclusions:As the diameter of the root canal increased, the measured length with the smaller size files became shorter. A file of a size close to the prepared canal diameter should be used for root length measurement in the presence of blood. In the presence of NaOCl, the Root ZX was highly accurate even when the file was much smaller than the diameter of the canal. The agar model was effective and suitable for testing EALs in vitro.Key words: Agar, blood, electronic apex locator, file size, root length determination, root canal preparation, sodium hypochlorite.Abbreviations and acronyms: EAL = electronic apex locator; MAF = master apical file; NaOCl = sodium hypochlorite solution.

Irrigation using the intracanal aspiration technique allowed more effective removal of the smear layer than that performed by the conventional method in an apically resected canine tooth. The intracanal aspiration technique produced limited extrusion of the irrigant beyond the apical foramen.

Both magnification (stage 2) and dentine removal under magnification (stage 3) were effective in detecting the presence of the MB2 canal. However, MB2 canals could not be detected in 13% of the teeth because of canal calcification or branching located more apically.

The purpose of this study was to examine the accuracy of radiographic evaluation of root canal multiplicity in mandibular first premolars in vitro. One hundred thirty-nine extracted human mandibular premolars were used. Buccolingual radiographs were taken, and the number of canals in each tooth was determined on radiographs by four dentists using a view box. A sudden narrowing of the main canal was interpreted as a sign of multiple canals. After the radiographic evaluation, the tooth crown was removed. India ink was injected into the root canal system, and the root was cleared to observe the canal morphology. There was no statistically significant difference among the four dentists with respect to the coincidence rate (93%-96%) of the canal number evaluated on radiographs with that identified by cleared teeth observation (p > 0.05, one-way analysis of variance). A sudden narrowing of the main canal on the radiograph was a good criterion to judge root canal multiplicity.

The precise distribution of various immunocompetent cells in rat molar pulp was immunohistochemically examined by use of seven anti-rat monoclonal antibodies. It was demonstrated that rat molar pulp contained many OX6 (anti-Ia antigen)-positive cells and a large number of ED1 (anti-monocytes, macrophages, and dendritic cells)-positive, ED2 (anti-tissue macrophages)-positive, and/or OX35 (anti-macrophages and CD4+ lymphocytes)-positive cells. Macrophage-like cells predominated in the central portion of the pulp, while cells of dendritic appearance usually existed in the periphery of the pulp. Double-immunoperoxidase staining revealed that these cells showed some heterogeneity, but the majority could be classified as ED1+/OX6-/ED2+ cells, which may be Ia-histiocytes. Findings also suggested that true dendritic cells may be included in the ED1+/OX6+/ED2- category of cells. A small number of T lymphocytes and plasma cells were also detected. These results suggest that the normal dental pulp contains a variety of immunocompetent cells, with macrophages as the most dominating. Following the exogenous invasion of pathogenic stimuli in the pulp, these cells may participate in the defense reaction by acting as phagocytes or antigen-presenting cells, which are essential for the initiation of immune responses.

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