Ana Cecília Diniz Viana

Flexibility and Torsional Strength of ProTaper and ProTaper Universal Rotary Instruments Assessed by Mechanical Tests

The purpose of this study was to assess how the geometric and dimensional changes made on ProTaper Universal (PTU) instruments in comparison with ProTaper (PT) instruments affected their flexibility and torsional strength. Two groups (n = 12) of each type of shaping (S1 and S2) and finishing (F1, F2, and F3) for both PT and PTU instruments were employed. Tip angle, instrument diameter at each millimeter, and cross-sectional area at 3 mm from the tip were the dimensional parameters measured. Flexibility and torsional strength of each instrument (n = 12) were assessed according to specification ISO 3630-1. Data were analyzed using analysis of variance (alpha = 0.05). Flexibility increased for S1 and F1 PTU instruments and decreased for F2 and F3, whereas torsional resistance increased for S2, F2, and F3. Changes in tip angle were accompanied by variation of tip geometry in all instruments.

Flexural Fatigue and Torsional Resistance of ProFile GT and ProFile GT Series X Instruments

INTRODUCTION The purpose of this study was to compare the flexural fatigue and torsional resistance of ProFile GT and GT Series X instruments, taking into account their structural and dimensional characteristics. METHODS Instrument diameter at each millimeter from the tip and pitch length were the dimensional parameters measured. Chemical composition was determined by energy-dispersive x-ray spectroscopy and phase constitution by x-ray diffraction. Vickers microhardness measurements were performed to assess instrument strength. One group of 20/.06 GT and GTX instruments (n = 10 each) was tested until failure in a flexural fatigue test device, whereas another group of 20/.04 files (n = 10 each) was tested in torsion based on ISO 3630-1. RESULTS GT and GTX instruments showed approximately the same chemical composition, namely 51at%Ni-49at%Ti (56wt%Ni-44wt%Ti) and contained mainly the beta-phase. GTX instruments showed higher intensity x-ray diffraction peaks and a statistically higher Vickers microhardness. There was a significant decrease in the diameter of GTX in relation to GT instruments from D6 to D9 for 20/.04 instruments and from D4 to D7 for 20/.06 instruments. Pitch length increased along the active part of both instruments, with a steeper increase in GTX. In general, GT Series X instruments were significantly more resistant to flexural fatigue than were similar GT instruments (p < 0.001) but exhibited lower torsional strength (p < 0.001). CONCLUSIONS Different structural and dimensional characteristics were found in GTX instruments in comparison with GT instruments; this is probably the cause for their higher flexural fatigue resistance and lower torsional strength.

Dimensional characterization and mechanical behaviour of K3 rotary instruments.

AIM To correlate the mechanical behaviour in torsion, bending and fatigue tests of K3 instruments with their dimensional characteristics. METHODOLOGY Instrument length, tip angle, distance between blades (pitch length) and the diameter at each millimetre from the tip of sizes 20, 25 and 30, 0.04 taper and sizes 20 and 25, 0.06 taper K3 rotary instruments were measured in an optical microscope equipped with digital micrometers. The cross-sectional area at 3 mm from the tip of the same instruments was determined using digital image analysis of scanning electron microscopy images. Maximum torque and angular deflection, as well as bending moment at 45 degrees were measured according to specification of ISO 3630-1. Fatigue resistance of instruments size 30, 0.04 taper, and sizes 20 and 25, 0.06 taper was determined in a fatigue test bench device. RESULTS The analysed instruments presented no uniformity in the distance between adjacent blades, but the measured diameters at each millimetre from the tip were regular, showing compliance with manufacturing standards. Torque and bending moment of the tested instruments increased significantly with diameter and cross-sectional area at 3 mm from the instrument tip. The fatigue resistance of the instruments showed a tendency to decrease as the diameter of the instruments increased. CONCLUSIONS The bending moment at 45 degrees and the torsional resistance of K3 instruments can be predicted using instrument diameter and cross-sectional area at 3 mm from the tip. Fatigue resistance decreased as the instrument diameter increased.

Behavior of nickel-titanium instruments manufactured with different thermal treatments.

INTRODUCTION The purpose of this study was to investigate if nickel-titanium instruments with similar designs manufactured by different thermal treatments would exhibit significantly different in vitro behavior. METHODS Thirty-six instruments each of ProTaper Universal (PTU F1; Dentsply Maillefer, Ballaigues, Switzerland), ProFile Vortex (PV; Dentsply Tulsa Dental Specialties, Tulsa, OK), Vortex Blue (VB, Dentsply Tulsa Dental Specialties), and TYPHOON Infinite Flex NiTi (TYP; Clinicians Choice Dental Products, New Milford, CT) (all size 25/.06) were evaluated. Bending resistance, torsion at failure, and dynamic torsional tests were performed with the instruments (n = 12). Analysis of variance and Tukey post hoc tests were applied. RESULTS Flexibility was significantly higher for TYP compared with the other 3 groups (P < .0001). With respect to the maximum torque at failure, PV group showed the highest resistance to twisting (torsional strength) among the analyzed instruments followed by VB, TYP, and PTU. The TYP group exhibited greater angular deflection at failure compared with the other groups (P < .0001). The mean dynamic torque scores during simulated canal preparation were highest for TYP (3.01 ± 0.71 Ncm) and lowest for PV (1.62 ± 0.79 Ncm). However, no significant differences were observed comparing groups PTU with TYP and VB and VB with PV (P > .05). The highest mean forces were recorded with PTU (7.02 ± 2.36 N) and the lowest with TYP (1.22 ± 0.40 N). CONCLUSIONS TYP instruments were significantly more flexible than the other instruments tested. The PV group had the highest torsional strength and TYP, despite being the most flexible, showed similar torsional moments to the other instruments, whereas its angular deflection was the highest among the groups.

Relationship between flexibility and physical, chemical, and geometric characteristics of rotary nickel-titanium instruments.

OBJECTIVE The purpose of this study was to assess the influence of both the metallurgic and the geometric characteristics of nickel-titanium endodontic instruments on their flexibility. STUDY DESIGN ProTaper Universal (PTU), K3, and EndoSequence (ES) instruments were evaluated. Their chemical composition and phase constitution were characterized by conventional analytical techniques. Instrument diameter and cross-sectional area were evaluated by image analysis. Flexibility was evaluated in bending tests according to the ISO 3630-1. RESULTS K3 presented the highest average bending moment (M(B)), followed by PTU and ES. A linear relationship was found between M(B) and the instruments diameter and cross-sectional area at 3 mm from the tip. Alloy chemical compositions were similar among the files, but transformation temperatures were lower for K3 instruments, which presented only austenite as a constituent phase. CONCLUSION Nickel-titanium instruments from different manufacturers have unequal behavior related to their flexibility properties. Manufacturing processes changed the phase constitution and transformation temperatures of the instruments investigated and may also have influenced their flexibility.

Guided Endodontic Access of Calcified Anterior Teeth

&NA; Pulp canal calcification is characterized by the deposition of calcified tissue along the canal walls. As a result, the root canal space can become partially or completely obliterated. Recently, “guided endodontics” has been reported as an alternative solution in cases of partial or completed canal obliteration. Although this technique can enhance minimally invasive access to the calcified canal, it has been shown that the incisal surfaces are often removed during the access of anterior teeth. This report describes 2 cases of guided endodontics using conventional palatal access in calcified anterior teeth and discusses the applicability of this approach in cases of pulp canal calcification with apical periodontitis and acute symptoms. The method demonstrated high reliability and permitted proper root canal disinfection expeditiously, without the unnecessary removal of enamel and dentin in the incisal surface.

Cyclic flexural fatigue resistance of NiTi Controlled Memory and Blue Technology instruments after torsional preloading

Abstract Objective The aim of this study was to evaluate the influence of torsional preloading on the cyclic flexural fatigue resistance of thermally treated NiTi instruments. Material and Methods Ten new instruments New Hyflex CM (HF 30.06; Coltene/Whaladent Inc.), Typhoon CM (TYP 30.06; Clinicians Choice Dental Products) and Vortex Blue (VB 30.06; Dentsply Tulsa Dental) were chosen, based on geometry and specific characteristics of the manufacturing process. The new instruments of each system were tested in a bench device to determine their fatigue resistance through mean value of number of cycles to failure (Nf) (Control Group – CG). Another group of 10 new HF, TYP and VB instruments were submitted to 20 cycles of torsional straining between 0° and 180° (Experimental Group – EG) and then submitted to fatigue until rupture under the same conditions of the CG. Tested instruments were examined by scanning electron microscopy (SEM). Data were analyzed using one-way analysis of variance and post hoc Tukey’s test (α=.05). Results Higher fatigue resistance was accomplished by HF instruments, followed by VB and TYP (p<0.05). During the torsional preloading, the lowest mean torque value was observed for TYP instruments (p<0.05). The torsional preload caused a significant reduction in the Nf values (p<0.05) of about 20%, 39% and 45% for instruments HF, VB and TYP, respectively. Longitudinal cracks, generated during the torsional preloading, were present in VB files, but were not observed in the CM instruments (HF and TYP). Conclusions In conclusion, the flexural fatigue resistance of thermally treated instruments is diminished after cyclic torsional loading.

Comparison between the Flexibility of Three Different Types of Rotary NiTi Endodontic Instruments

The aim of this study was to characterize metallurgical properties and the dimensions of three types of rotary NiTi endodontic instruments and to establish a correlation between these characteristics and the flexibility of the instruments. Their chemical composition and constitution were characterized by energy dispersive spectroscopy (EDX) and X-ray diffraction (XRD). Transformation temperatures were assessed by means of differential scanning calorimetry (DSC). Computer software was used to analyse images of the longitudinal and transverse sections for determining instrument diameter and cross-sectional area at 3mm from the tip. The flexibility of the instruments was evaluated in bending tests performed according to the ISO 3630-1 specification, in which the instruments are clamped at 3mm from their tip and bent by 45° along their longitudinal axis. The values of bending moment at 45° were correlated with instrument diameter and cross-sectional area at 3mm from the tip. The results of EDX, XRD and DSC showed that physical and chemical properties of the materials differed slightly among the files analyzed. A direct relationship was found between bending moment and the geometric characteristics of the instruments. Resistance to bending of NiTi root canal instruments depended on their geometrical shapes and metallurgical properties, but the cross-sectional configuration can be seen as an important parameter affecting this property.