A 3D finite element analysis of stress distribution on different thicknesses of mineral trioxide aggregate applied on various sizes of pulp perforation.

OBJECTIVES: The aim of this study was to evaluate the stress distribution on different thicknesses of mineral trioxide aggregate (MTA) placed on various widths of pulp perforations during the condensation of the composite resin material. MATERIALS AND METHODS: The mandibular molar tooth was modeled by COSMOSWorks program (SolidWorks, Waltham, MA). Three finite elemental analysis models representing 3 different dimensions of pulp perforations, 1, 2, and 3 mm in diameter, were created. The perforation area was assumed as filled with MTA with different thicknesses, 1, 2, and 3 mm for each pulp perforation width, creating a total of 9 different models. Then, a composite resin material was layered on MTA for each model. A 66.7 N load was applied and an engineering simulation program (ANSYS, Canonsburg, US) was used for the analysis. Results were presented considering von Mises stress criteria. RESULTS: As MTA thickness increased, the stress values recorded within the area between pulp and MTA decreased. Strain was decreased when the thickness of MTA increased. CONCLUSIONS: Stresses at MTA-pulp interface and strain on MTA decreased with the increase in MTA thickness. CLINICAL RELEVANCE: In clinical practice, when MTA is required for pulp capping, using a thick layer of the material seems to be a better option in order to reduce the stress under forces of hand condensation of overlying restorative materials.

In vitro comparison of induction capacity and biomineralization ability of mineral trioxide aggregate and a bioceramic root canal sealer.

AIM: To compare the effect of mineral trioxide aggregate (MTA) and iRoot SP, a bioceramic root canal sealer, on the cell viability, hard tissue deposition capacity and odontogenic differentiation of human tooth germ stem cells (hTGSCs). METHODOLOGY: The dental materials MTA, iRoot SP and Dycal were packed into Teflon rings and placed on transwell inserts for toxicity evaluations by the MTS assay on days 3 and 7. Dycal was used as a positive control for the cell viability assay. Teflon rings were cocultured with hTGSCs, followed by the induction of odontogenic differentiation. The odontogenic differentiation of hTGSCs and biomineralization ability of the materials were evaluated by analysing the mRNA expression levels of dentine sialophosphoprotein (DSPP) and collagen type 1A (COL1A) by real-time polymerase chain reaction expression analysis, measurement of alkaline phosphatase (ALP) activity and visualization of calcium deposits by von Kossa staining. RESULTS: MTA and iRoot SP exhibited no cytotoxicity, but Dycal caused cytotoxicity (P < 0.05) of almost all of the cells after 7 days. MTA significantly stimulated (P < 0.05) the odontogenic differentiation of hTGSCs compared with iRoot SP. MTA and iRoot SP increased (P < 0.05) the mRNA levels of COL1A and DSPP mRNA compared with noninduced hTGSCs, which served as a negative control (NC). iRoot SP, however, significantly decreased (P < 0.05) COL1A and DSPP mRNA expression levels compared with the PC. CONCLUSION: MTA and iRoot SP induced hTGSC differentiation into odontoblast-like cells, but MTA might provide more inductive potential and hard tissue deposition compared with iRoot SP.

An investigation of current endodontic practice in Turkey.

OBJECTIVES: The aim of this study was to gather information about the quality and quantity of root canal treatments carried out by general dental practitioners in Turkey. METHODS: Questionnaires were given to 1400 dentists who attended the 16th National Congress organized by the Turkish Dental Association. The participants were asked to answer 34 multiple-choice questions. The questions were subdivided into 3 main topics; general information; general approach to endodontic treatment; and cleaning, shaping, and obturation of root canals. The statistical analysis was carried out by an χ²-test to compare the means at a significance level of P < 0.05. RESULTS: The response rate for this study was 43%. There was a wide variation in the number of root canal treatments completed per month. Nearly 92% of practitioners stated that they never used rubber dam. The most commonly used working length determination technique was radiographic evaluation (P < 0.05). Sodium hypochlorite was the irrigant of choice with varying concentrations and AH Plus was the sealer of choice (P < 0.05). Resin composite was the most frequently used material for final restorations. CONCLUSIONS: Endodontic procedures in general practice in Turkey have differences from widely acknowledged quality guidelines. Despite the introduction of new instruments and techniques, most of the general practitioners chose conventional methods.

Comparison of the force required to fracture roots vertically after ultrasonic and Masserann removal of broken instruments.

AIM: To evaluate the force required to fracture roots vertically after the removal of broken instruments using ultrasonic tips and a Masserann kit. METHODOLOGY: Thirty-nine extracted human anterior teeth with single and straight roots were used. The crown of each tooth was removed until the full length of the tooth was 13 mm. All canals were instrumented with the step-back technique to a size 25 K-file. The teeth were randomly divided into three groups: two experimental groups and a control group. The size 30 K-files used for the test were notched to a depth of half of the instrument with a No. 2 round bur at a point 3 mm from the tip to facilitate breakage of the file at this point. The fractured instruments were removed from the canals using ultrasonic tips or a Masserann kit. The samples were subjected to a continual vertical loading, using a universal testing machine. For each root, the force at the time of fracture was recorded in Newtons. The results were analysed statistically using one-way anova and Tukey HSD test. RESULTS: The force required to fracture the roots vertically was significantly higher in the control group than the experimental groups (P < 0.01). The roots from which the broken instruments had been removed using ultrasonic tips required more force to fracture than roots in the Masserann group; however, the difference was not statistically significant. CONCLUSION: Removal of a fractured instrument from the middle third of the root decreased the force required to fracture the root vertically, regardless of the technique used for instrument removal. There was not difference between the ultrasonic technique and the Masserann technique.

Effect of acid-etching procedure on selected physical properties of mineral trioxide aggregate.

AIM: To evaluate the effect of acid-etch procedures on the compressive strength and surface microhardness of tooth-coloured mineral trioxide aggregate (MTA). METHODOLOGY: White ProRoot MTA (Dentsply Tulsa Dental) was mixed and packed into cylindrical tubes of 4 mm in diameter and 6 mm in height. Three groups, each of 15 specimens were subjected to an acid-etch procedure either 4, 24 or 96 h after mixing. The compressive strength was measured and compared with unetched control groups. Differences between groups were analysed using the Kruskall-Wallis test. A further batch of cylindrical specimens of 6 mm in diameter and 12 mm in height were prepared for testing surface microhardness. Three groups of 15 specimens were subjected to the acid-etch procedure at either 4, 24 or 96 h following mixing. Data were subjected to one-way anova. Changes in the surface microstructure before and after the acid-etch procedures were analysed using a scanning electron microscope (SEM). RESULTS: There was a general trend for the compressive strength and surface microhardness of specimens to increase with time. In terms of compressive strength, the increase was significant between 4 h and the other time periods for both experimental and control groups (P < 0.0001); however, there was no significant difference between 24 and 96 h. The increase in surface microhardness was significant between 4, 24 and 96 h (P < 0.0001). In addition, there was a significant difference between experimental and control groups at all time periods (P < 0.0001). SEM examination revealed morphological differences between the intact and the etched MTA surfaces. CONCLUSIONS: Acid-etch procedures affected the compressive strength and surface microhardness of ProRoot MTA. This indicates that it may be better to postpone restorative procedures for at least 96 h after mixing MTA. Etching created surface changes that might have the potential to enhance bonding of resinous materials.