RESUMO
The objective of this study was to evaluate the effects of glycolic acid (GA) (with pH 1.2 and 5) and ethylenediaminetetraacetic acid (EDTA) on the chemical and mechanical properties of dentin to investigate the potential use of GA as final irrigant in the root canal therapy. Specifically, changes in microhardness, smear layer removal, erosion, mineral content distribution, apatite/collagen ratio and flexural strength of mineralized dentin treated with GA were assessed. Saline solution was used as a negative control. Knoop microhardness (KHN) was measured on the root canal lumen of root segments. Dentin beams were used for 3-point flexural strength (σ) test. Scanning electron microscopy (SEM) images of root sections were obtained for evaluation of smear layer removal and dentin erosion on root segments and energy dispersive X-ray spectroscopy (EDS) was used for mineral content distribution. The apatite/collagen ratio (A/C) in dentin powder were examined by Fourier transform infrared (FTIR) spectroscopy. KHN, σ and A/C results were statistically analyzed with ANOVA and Tukey tests (α = 0.05). Smear layer and dentin erosion scores were analyzed with Kruskal-Wallis and Dunn tests (α = 0.05). Root dentin treated with EDTA and GA presented similar KHN regardless of the pH (p > 0.05). However, KHN was significantly reduced in EDTA and GA groups when compared to control group (p<0.001). GA showed the same ability to remove the smear layer and to cause dentin erosion as EDTA. EDS results showed that the GA and EDTA solutions did not alter the dentin mineral content distribution. The apatite/collagen ratio reduced with all irrigant solution and was the lowest with GA pH 5 (p<0.001), while σ was not significantly affected by the experimental solutions (p = 0.559). It can be concluded that GA has similar ability to remove the smear layer than EDTA. GA does not affect negatively the chemical/mechanical properties and it does not increase dentin erosion. The use of GA with low pH seems to promote less change in collagen/apatite ratio, but further studies are needed to establish an ideal clinical protocol. Therefore, this study supports the potential use of GA as an alternative final irrigation solution for root canal preparation.
RESUMO
To investigate the influence of post system and amount of remaining root tissue on the fracture resistance of endodontically treated teeth. Seventy upper canine teeth were divided into seven groups (n=10), one control (sound teeth) and six experimental groups resulting from the interaction between the two study factors: post system (FB, fiber post; FPC, fiber post relined with resin composite; CPC, cast Ni-Cr alloy post and core) and amount of remaining root tooth tissue (2 or 1mm of thick root). All teeth were restored with metal crowns and exposed to 250,000 cycles in a controlled chewing simulator. The samples were submitted to the fracture resistance test in a universal testing machine, at an angle of 135° and speed of 0.5mm/min, until fracture occurred. Failure modes were observed, and the data of fracture resistance, in Newtons, were submitted to the analysis of variance (ANOVA), followed by Tukey's test (α=0.05). Roots restored with FPC had the highest fracture strength of the experimental groups, being statistically similar to the intact teeth group (P>0.05). FP and CPC did not differ statistically (P>0.05) and were statistically lower than those of FPC (P<0.05). No statistically significant difference was observed between amounts of remaining root tooth tissue to the same post systems (P>0.05). A prevalence of irreparable failures was observed in specimens restored with CPC, whereas FP and FPC posts showed more repairable failures. The post system had an influence significant on fracture resistance. However, the remaining dentine with 2- or 1-mm thickness was not an important factor for the fracture resistance.