Efficacy of final irrigation--a scanning electron microscopic evaluation.

The purpose of this in vitro study was to determine the degree of removal of pulpal remnants and smear layer from root canals after final irrigation with three different solutions. During instrumentation the step-back preparation and 1% NaOCl were used. The final 4-min, 30-ml irrigation varied as follows: group I, 10 ml of 1% NaOCl + 10 ml of 10% citric acid + 10 ml of distilled water; group II, 15 ml of 0.5% NaOCl + 15 ml of EDTA-T; and group III, 10 ml of 5% NaOCl + 10 ml of 3% H2O2 + 10 ml of 5% NaOCl. Scanning electron microscopic photomicrographs were evaluated for the mean number of visible open dentinal tubules by three observers. The largest number of visible tubules in the three groups was in the cervical third, followed by the middle and apical thirds. There was no statistically significant difference between groups I and II when third was compared with third; however, groups I and II had significantly more visible dentinal tubules than group III.

The use of Histoacryl in endodontics.

The oral environment is one of the most complex systems of the human body. It is populated by a variety of microorganisms, with some of the species still not classified. Tissue adhesives, such as cyanoacrylates, have been used in dentistry and in medicine because of their adhesiveness potential to the human tissue, even in the presence of moisture, their biological compatibility, surface isolation, hemostatic properties and bacteriostatic features. Based on these observations, the authors investigated the use of a tissue adhesive (Histoacryl; Laboratório Braun, RJ, Brazil) with the purpose of sealing the remaining dentin, especially in endodontically treated molars and premolars. The results strongly suggest that Histoacryl controls micro-leakage of oral fluids at the filling/tooth interface.

Morphologic study of tissue changes occurring in the apical third and periapex of rat molars after endodontic treatment performed under different occlusal conditions.

The purpose of the present study was to carry out a histologic study of the periapical changes of the maxillary first molar of rats submitted to endodontic treatment under different occlusal conditions. The experiment was carried out under conditions analogous to those used in clinical practice. Pulpotomy, pulpectomy and chemomechanical preparation of the mesial root canal were carried out according to previously established techniques and the mesial root canal was filled with cement and gutta-percha. A glass ionomer cement was used as restorative material under conditions of subocclusion, normal occlusion and excessive occlusal forces. No inflammatory reaction of periapical tissue was observed under the three conditions used, and active closing of the root canal was observed 15 days after the procedure, with the formation of cementum replacing the pulpar remnant.

The effect of the renewal of calcium hydroxide paste on the apexification and periapical healing of teeth with incomplete root formation.

AIM: To evaluate the influence of renewing calcium hydroxide paste on apexification and periapical healing of teeth in dogs with incomplete root formation and previously contaminated canals. METHODOLOGY: Forty premolars from four 6-month-old dogs were used. After access to the root canals and complete removal of the pulp, the canal systems remained exposed to the oral environment for 2 weeks. Canal preparation was then carried out using Hedströem files, under irrigation with 1% sodium hypochlorite, 1 mm short of the radiographic apex. After drying, the canals of one premolar in each dog were left empty (group 4-control), and those of the other nine teeth in each animal were filled with a calcium hydroxide-propylene glycol paste. All teeth were restored with reinforced zinc oxide cement (IRM) or IRM and amalgam (group 4). The paste was renewed and the teeth restored again 1 week later. Then, the nine teeth in each animal were divided into three experimental groups: group 1 - paste not changed; group 2 - paste renewed every 4 weeks for 5 months; and group 3 - paste renewed after 3 months had elapsed. The teeth were restored with IRM and amalgam (groups 1 and 3) or IRM (group 2). The animals were killed 5 months later, and blocks of the teeth and surrounding tissues were submitted to histological processing. The sections were studied to evaluate six parameters: apical calcified tissue barrier, inflammatory reaction, bone and root resorption, paste extrusion and microorganisms. Results of experimental groups were analysed by Kruskal-Wallis nonparametric tests and by the test of proportions. The critical value of statistical significance was 5%. RESULTS: Significant differences (P < 0.05) were found in relation to the presence of bone resorption and paste in the periradicular area, the formation of a calcified tissue barrier at the apex, and the intensity of the apical inflammatory reaction. Bone resorption was more evident in group 1 (medicament not changed), and the presence of paste in the periodontal tissues was more common in groups 2 and 3. Renewal of the paste reduced the intensity of the inflammatory reaction (groups 2 and 3), but the formation of apical calcified tissue was more noticeable in the teeth where the paste had not been renewed. CONCLUSIONS: Replacement of calcium hydroxide paste was not necessary for apexification to occur, however, it did reduce significantly the intensity of the inflammatory process. Monthly renewal of calcium hydroxide paste reduced significantly the occurrence of apexification.

Heat stress-induced life span extension in yeast.

The yeast Saccharomyces cerevisiae has a limited life span that can be measured by the number of times individual cells divide. Several genetic manipulations have been shown to prolong the yeast life span. However, environmental effects that extend longevity have been largely ignored. We have found that mild, nonlethal heat stress extended yeast life span when it was administered transiently early in life. The increased longevity was due to a reduction in the mortality rate that persisted over many cell divisions (generations) but was not permanent. The genes RAS1 and RAS2 were necessary to observe this effect of heat stress. The RAS2 gene is consistently required for maintenance of life span when heat stress is chronic or in its extension when heat stress is transient or absent altogether. RAS1, on the other hand, appears to have a role in signaling life extension induced by transient, mild heat stress, which is distinct from its life-span-curtailing effect in the absence of stress and its lack of involvement in the response to chronic heat stress. This distinction between the RAS genes may be partially related to their different effects on growth-promoting genes and stress-responsive genes. The ras2 mutation clearly hindered resumption of growth and recovery from stress, while the ras1 mutation did not. The HSP104 gene, which is largely responsible for induced thermotolerance in yeast, was necessary for life extension induced by transient heat stress. An interaction between mitochondrial petite mutations and heat stress was found, suggesting that mitochondria may be necessary for life extension by transient heat stress. The results raise the possibility that the RAS genes and mitochondria may play a role in the epigenetic inheritance of reduced mortality rate afforded by transient, mild heat stress.

[Evaluation of the histocompatibility of endodontic cement in subcutaneous connective tissue using three methods]. / Estudo da histocompatibilidade de cimento endodôntico no tecido conjuntivo subcutâneo utilizando três methodologias.

It was employed three methods to evaluate the histocompatibility of a root canal filling cement, as the N-Rickert paste: implantation of round glass cover slips, polyethylene tubes and pellets of the cement. The results demonstrated qualitative and quantitative differences among the methods utilized indicating as a good toll the use of glass cover slips covered by the cement, since they provide good conditions of work, major areas of study, as also facilities in obtaining the specimens for study. The pellets didn't simulate the clinical conditions of the cement and the very small areas of study of the polyethylene tubes don't give definitive conclusions.