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All systems tested were effective to remove cultivable bacteria and endotoxin in endodontic retreatment. As no differences among systems were observed, it is possible to suggest that clinicians should choose the preferred technique to perform endodontic.

There was no NaOCl extrusion in nine specimens in P1, but all of these teeth had irrigant extrusion in P2. The 5.25% NaOCl used as an endodontic irrigant showed great capacity to extrude beyond both intact and small-sized apical foramina of MB root canals of maxillary first molars.

- The pH values of the external aqueous medium, relative to the roots of 41 human premolar teeth filled with Ca(OH)2 in to several vehicles, were evaluated in the present study. After root canal biomechanical preparation and smear-layer removal, the teeth were stored individually, immersed in flasks containing 800 ml of ultra-pure deionized water for a period of 118 days. A pH meter was used to analyse the pH values as a function of time. The measurements were divided into phase 1: dissolution, in which all canals remained empty and open in the absence of medicament for 48 days, and phase 2: diffusion, in which the specimens were divided into 10 groups which consisted of three control groups: group 1, water control; group 2, sealing control; and group 3, opened canal dissolution control, and seven experimental groups, with five teeth each, whose canals were filled with Ca(OH)2 paste associated with the following vehicles: group 4, saline solution; group 5, polyethylene glycol (Calen); group 6, glycerin and parachlorophenol (PMCC); group 7, PMCC; group 8, glycerin; group 9, glycerin and formo cresol (FC); and group 10, anesthetic solution. This phase lasted for 70 days. A total of 1058 measurements of the pH values were made. Regression analysis was used for statistical evaluation. The results show that all groups containing polyol in the composition of the paste had a trend to acidification in the interval between filling and 14 days later (therapeutic period) and, at the end of the experiment (1687 h to 70 days after canal filling), the pH was slightly alkaline. We conclude that polyhydroxy alcohol (glycerin and polyethylene glycol, Calen) diffusion enhances acidification of the aqueous medium.