Effect of autoclave sterilisation and heat activated sodium hypochlorite irrigation on the performance of nickel-titanium rotary files against cyclic fatigue

The present study aims to assess the impact of heat-activated sodium hypochlorite (NaOCl) and/or autoclave sterilisation on the cyclic fatigue resistance (CFR) of heat-treated nickel-titanium rotary files used in root canal treatment. The CFR of One Curve (OC) files was evaluated under the following conditions: as received (Group 1; control), immersion in NaOCl at 23 ± 1ºC (Group 2), immersion in NaOCl at 60 ± 1ºC (Group 3), autoclave sterilisation at 135 1ºC (Group 4), combined treatment of autoclave sterilisation and immersion in NaOCl at 23 ± 1ºC (Group 5), and combined treatment of autoclave sterilisation and immersion in NaOCl at 60 ± 1ºC (Group 6). A simulated root canal in a zirconia block was utilised to test the performance of the files. All the types of treatments resulted in significant reductions in fracture resistance of the OC files. Immersion of the files in NaOCl at 23ºC revealed the smallest reduction, while combined treatment of autoclaving and immersion in NaOCl at 60ºC caused the greatest reduction. Autoclave sterilisation or exposure of OC files to 2.5% NaOCl adversely affect the cyclic fatigue life and increasing solution temperature or combined treatment caused additionally significant reduction in CFR

p38 MAP Kinase-Mediated Odontogenic Differentiation of Dental Pulp Stem Cells

The multipotent nature of dental pulp stem cells (DPSCs) promises regenerative endodontic potentials. Alterations in microenvironment have been shown to control the differentiation phenotypes of DPSCs. Understanding the biological mechanisms and finding the optimal DPSC differentiation protocols are crucial for successful DPSC engineering strategies in pulp and dentin healing. The aim of this study is to identify the role of p38 mitogen-activated protein kinase (p38) under normal and oxygen-deprived conditions (2%) to reveal its effect on odontogenic DPSC differentiation. Human DPSCs were isolated from healthy molars and underwent odontogenic differentiation in regular and osteogenic media treated with SB203580, a p38 inhibitor, for 72 hours, and then swapped with osteogenic media for 21 days under hypoxic condition. Immunochemistry and PCR analysis for the various odontogenic differentiation genes and proteins were performed. Our PCR data demonstrate that p38 inhibition resulted in a significant upregulation in odontogenic gene expressions such as DMP-1, DSPP, RUNX, and OSX in normal conditions. Under hypoxia, this effect was reversed. These results were further supported by DSPP immunohistochemistry. The DSPP expression under hypoxia was significantly weaker compared to the control. Our results indicate that p38 represents a negative regulator of the odontogenic DPSC differentiation in normoxia. Under hypoxia, p38 exerts a positive function of DPSC differentiation. Taken together, we identified the p38 and oxygen level as crucial factors to control odontogenic DPSC differentiation providing their essential roles in designing for successful pulp-dentin complex engineering strategies.</jats:p

Factors contributing to the separation of endodontic files

Cleaning and shaping of the root canal system is essential for successful endodontic treatment. However, despite improvements in file design and metal alloy, intracanal file separation is still a problematic incident and can occur without any visible signs or permanent deformation. Only a few studies have reported high success rates of fractured file removal using contemporary techniques. Conflicting results have been reported regarding the clinical significance of retaining separated files within root canals. An understanding of the mechanisms of, factors contributing to, file fracture is necessary to reduce the incidence of file separation within root canals. This article reviews the factors that are of utmost importance and in light of these, preventive procedures and measures are suggested

Experimental evaluation of cyclic fatigue resistance of four different nickel-titanium instruments after immersion in sodium hypochlorite and/or sterilization

NiTi instruments have a high risk of separation due to torsional or flexural fatigue (cyclic fatigue). Chemomechanical preparation, cleaning procedures, chemical disinfection and sterilization cause the corrosion of endodontic instruments that may weaken the fracture resistance of the instruments. OBJECTIVE: To assess the effects of NaOCl immersion and autoclave sterilization on the cyclic fatigue resistance of ProFile, FlexMaster, Mtwo and TwistedFiles NiTi instruments (tip size 25, 0.06 taper, n=160). MATERIAL AND METHODS: The instruments (n=10 for each subgroup) were dynamically immersed in NaOCl; immersed in NaOCl and sterilized in one autoclave cycle; 5 cycles immersed in NaOCl and sterilized in autoclave and not immersed in NaOCl and not sterilized (control group). Dynamic cyclic fatigue resistance was tested. The number of cycles to failure (NCF) were statistically analyzed (P<0.05). RESULTS: Kruskall-Wallis test indicated significant differences among the tested instruments in terms of NCF (P=0.000). The mean NCF of Mtwo (556.75) was higher than that of the Twisted File, Flexmaster and ProFile, 483.1, 376.12, 365.25, respectively. NaOCl immersion and autoclave sterilization have no effect on the NCF values of the tested instruments (P>.05). CONCLUSIONS: Cyclic fatigue resistance of the tested NiTi instruments cannot be adversely affected by NaOCl immersion and autoclave sterilization. Production process (TwistedFiles) or design (Twisted Files, FlexMaster, Mtwo and ProFile) of the instruments can influence their cyclic fatigue resistance