Effect of immersion in sodium hypochlorite on torque and fatigue resistance of nickel-titanium instruments

This study investigated the effect of immersion in sodium hypochlorite (NaOCl) on torque and fatigue resistance of two nickel-titanium files. Size 25 .04 ProFile and RaCe files were immersed in 5.25% NaOCl for 1 or 2 hours at temperatures of 21 degrees C and 60 degrees C. Torque and angle at failure were measured according to ISO 3630-1. Resistance to cyclic fatigue was determined by counting rotations to breakage in a 90 degrees curve with a 5-mm radius. Data were analyzed by 2-way analysis of variance. Torsional resistance of both rotaries was not significantly affected by immersion in NaOCl, except after 2 hours of immersion at 60 degrees C. Resistance to cyclic fatigue decreased significantly for ProFile and RaCe instruments after immersion in NaOCl. Spontaneous fractures occurred in 28 of 160 files during immersion in NaOCl. In conclusion, nickel-titanium rotaries have reduced resistance to cyclic fatigue after contact with heated NaOCl and may then be considered single-use instruments.     

高压蒸汽灭菌对3种机用镍钛器械形貌及抗力的影响

目的 比较高压蒸汽灭菌对3种机用镍钛器械（K3、Mtwo、ProTaper）形貌及循环疲劳抗力的影响。方法 分别选取3种不同品牌的机用镍钛器械K3、Mtwo、ProTaper各36根。首先取各品牌器械24根,分为4组（n=6）,分别进行循环高压蒸汽灭菌0、1、5、10次后,在人工根管内自由旋转至器械折断,记录折断前的旋转时间和折断尖端长度,采用SPSS13.0 软件包对数据进行单因素方差分析,比较其循环疲劳抗力的差别。再将剩余的器械各12根分为2组（n=6）,第1组不予处理,第2组循环高压蒸汽灭菌10次,扫描电镜观察各器械尖端外表面形貌及横截面形貌的改变。结果 未灭菌组中,循环疲劳抗力K3大于Mtwo,并大于ProTaper(P<0.05);K3组5、10次组较未灭菌组均表现出抗力增强趋势,仅10次组与未灭菌组间差异有显著性(P<0.05);ProTaper组所有灭菌组较未灭菌组均显著增强(P<0.05),其中,5次组抗力最大;Mtwo组中,随着灭菌次数的增加,循环疲劳抗力逐渐增强(P<0.05)。扫描电镜观察发现,镍钛器械外表面和内部的不规则缺陷在多次灭菌后均显著增加。结论 不同品牌器械之间循环疲劳抗力不同,高压蒸汽灭菌在一定程度上可增加镍钛器械的循环疲劳抗力,但却使器械表面的粗糙度增加,横截面微观缺陷增多。     

A comparison of cyclic fatigue resistance in reciprocating and rotary nickel-titanium instruments

The cyclic fatigue resistance of four nickel-titanium endodontic instruments was compared. K3, ProFile and GT Series X rotary instruments were examined along with SafeSiders reciprocating instruments. 30/0.04 instruments at 25 mm length were compared. Cyclic fatigue testing was conducted by operating instruments in artificially constructed stainless steel canals with 30° and 45° angles of curvature and 5 mm and 7.5 mm radii of curvature. The time and cycles to failure were recorded for 192 samples. Statistical analysis was performed with three-way anova and the Student-Neuman-Keuls multiple comparisons testing. With a 5 min maximum running time, no SafeSiders samples were observed to separate. ProFile and GT Series X instruments were found to be significantly more resistant than K3 instruments (P < 0.001) for all experiment groups. There was no statistical difference between ProFile and GT Series X files (P < 0.582).     

Influence of sterilization on mechanical properties and fatigue resistance of nickel-titanium rotary endodontic instruments

AIM: To evaluate the effect of repeated sterilization cycles in dry oven or autoclave, on the mechanical behaviour and fatigue resistance of rotary endodontic Ni-Ti instruments. METHODOLOGY: New Ni-Ti instruments were subjected to five consecutive sterilization cycles in a dry oven or steam autoclave. Microhardness was measured in the nonmachined parts of the shanks of instruments using a Vickers indenter. Specimens of Ni-Ti wires were submitted to the same sterilization protocol and tensile tested until rupture. A group of instruments were fatigued to one half of their average fatigue life and then sterilized. New and sterilized instruments were fatigue tested until rupture. anova tests at alpha = 0.05 were used for statistical analysis. RESULTS: Sterilization procedures resulted in no significant changes in Vickers microhardness, nor in the parameters describing the mechanical behaviour of the wires. However, the number of cycles to failure was statistically higher for all instruments after dry heat or autoclave sterilization cycles. In the instruments previously fatigued to one half of their fatigue life, autoclave sterilization gave rise to an increase of 39% in the remaining number of cycles to failure. CONCLUSIONS: Changes in the mechanical properties of Ni-Ti endodontic instruments after five cycles of commonly used sterilization procedures were insignificant. The sterilization procedures are safe as they produced a significant increase in the fatigue resistance of the instruments.     

Cyclic fatigue resistance of three rotary file systems in a dynamic model after immersion in sodium hypochlorite

Odontology - To evaluate the effect of immersion in 3% sodium hypochlorite solution in the resistance to cyclic fatigue of three nickel–titanium (NiTi) rotary file systems, ProTaper Next...     

Influence of sodium hypochlorite and EDTA on the microtensile bond strength of a self-etching adhesive system

Chemical substances used during biomechanical preparation of root canals can alter the composition of dentin surface and affect the interaction with restorative materials.

Objective

The purpose of this study was to evaluate the microtensile bond strength (µTBS) of a self-etching adhesive system to dentin irrigated with sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (eDTA).

Material and Methods

Thirty human third molars were sectioned 3 mm below the occlusal surface, polished with 600- to 1200-grit silicon carbide papers, and randomly divided into 3 groups: G1 (control): no irrigating solution; G2: 1% NaOCl; and G3: 1% NaOCl followed by the application of 17% eDTA. The specimens received the self-etching adhesive system (XeNO III - Dentsply), restored with microhybrid composite resin (Z250 - 3M ESPE), sectioned and trimmed to create 4 hourglass-shaped slabs of each tooth. The slabs were tested in microtensile strength in a universal testing machine (emic DL 2000) at a crosshead speed of 0.5 mm/min until fracture. The results were analyzed statistically by ANOVA and Newman-Keuls test.

Results

Mean µTBS values and standard deviations in MPa were: G1 = 11.89 ± 4.22; G2 = 19.41 ± 5.32; G3 = 11.34 ± 4.73. 1% NaOCl increased the adhesive resistance significantly (p<0.001/ F=22.5763). The application of 1% NaOCl/17% eDTA resulted in statistically similar µTBS to the control group.

Conclusions

None of the irrigants affected negatively the µTBS of XeNO III to dentin. The use of 1% NaOCl alone resulted in higher bond strength than the other treatments. The combination of 1% NaOCl and 17% eDTA produced similar bond strength to that of untreated dentin.     

Cyclic fatigue resistance of new and used Mtwo rotary nickel-titanium instruments in two different radii of curvature

The fracture of nickel-titanium rotary instruments is a serious problem that can jeopardise the outcome of root canal treatment. The aim of this study was to compare the cyclic fatigue resistance of new and used Mtwo rotary nickel-titanium instruments in artificial canals with two different radii of curvature. Four hundred and twenty Mtwo instruments were used in the present study. Thirty new and 30 used instruments of each size were tested for cyclic fatigue in artificial canals with radii of curvature of 5 or 10 mm. Each instrument was rotated until fracture occurred and the number of cycles to fracture was calculated by multiplying time to fracture and rotational speed. Data were analysed using a t-test. According to the results of the study, radius of curvature was an important factor on cyclic fatigue resistance and clinical use significantly reduced the instrument lifespan.     

Surface roughness and cyclic fatigue resistance of reciprocating and novel rotary instruments after use in curved root canals

This study evaluated surface wear and resistance to fracture of reciprocating and novel rotary instruments after use in curved canals. Twenty new instruments (n = 5/each group): Reciproc Blue, WaveOne Gold, XP-endo Shaper (XPS) and TruNatomy were used twice for the instrumentation of simulated curved canals in plastic blocks. The instrumentation was performed according to the manufacturer's instructions at body temperature. Surface roughness was evaluated, using a profilometer, before instrumentation and twice after the instrumentation. Instruments were, then, subjected to a cyclic fatigue test to evaluate the time to failure. Differences were assessed using ANOVA and post hoc tests (α = 0.05). The XPS instruments showed significantly higher values of roughness compared with TruNatomy at every stage, especially after the second use (p < 0.008). Reciprocating instruments showed superior cyclic fatigue resistance compared with novel rotary instruments (p < 0.05). TruNatomy showed minimal surface roughness, and XPS exhibited significantly higher surface roughness.     

机用和手用ProTaper预备中度弯曲根管后的器械损伤情况评价

目的:评估机用和手用ProTaper镍钛器械预备中度弯曲根管后的损伤情况,为临床安全使用ProTaper镍钛器械提供理论指导。方法:使用机用和手用ProTaper镍钛器械各6套预备中度弯曲的下颌第一磨牙近中颊根。每预备1个根管后,在立体显微镜下观察并记录器械分离和螺纹松解情况。预备完成后,分别以扫描电镜观察全新、预备5次、15次和20次的SX和F1表面,观察其表面和切割刃的磨损情况。结果:预备中度弯曲根管时,SX、S1、F1、F3易发生器械分离,断裂位置一般位于距离锉尖3～4 mm处。机用ProTaper器械在使用15次后,可观察到明显的裂纹和损伤,手用ProTaper器械在使用20次后,可观察到明显的微裂纹和切割刃的损伤。使用相同的次数,机用ProTaper镍钛锉的损伤比手用ProTaper镍钛锉严重。结论:推荐机用ProTaper镍钛锉可以安全使用15次,手用ProTaper镍钛锉可以安全使用20次,每次使用后,应重点观察SX、F1和F3的锉尖位置,以便及早发现安全隐患,防止镍钛锉断裂。     

Dynamic cyclic and torsional fatigue resistance of TruNatomy compared with different nickel–titanium rotary instruments

This study evaluated the dynamic cyclic and torsional fatigue resistance of recently introduced TruNatomy instruments (TRN) and compare with HyFlex CM (HFC), Vortex Blue (VB) and FlexMaster (FM) instruments. Size 20, 0.04 taper of TRN, HFC, VB and FM instruments was tested for dynamic cyclic and torsional fatigue resistance. Dynamic cyclic fatigue resistance was evaluated using an artificial canal with a radius of 5 mm and a 90° angle of curvature. The number of cycles to failure (NCF) was calculated. The dynamic torsional fatigue resistance was evaluated by holding a 5 mm of the tip of each instrument in a metal block with composite resin. Torsional fatigue resistance was recorded by counting the number of load applications before fracture for each instrument. The HFC instruments had greater fatigue resistance than VB, TRN and FM. FM had a higher resistance to torsional stress than TRN, HFC and VB instruments.     

Evaluation of cyclic flexural fatigue resistance of 25/0.04 and 25/0.06 twisted file rotary nickel‐titanium endodontic instruments

Twisted files (TFs) are rotary nickel‐titanium (NiTi) instruments that are produced with a newly developed manufacturing process that is supposed to improve their properties, especially flexibility and resistance to cyclic flexural fatigue failure. The aim of this study was to study the cyclic flexural fatigue failure resistance of tip size International Standards Organization 25 TFs with two tapers 0.04 and 0.06 and to compare them with the Profile (PF) rotary NiTi files of similar tip size and taper. Four groups of fifteen files were used in this study. TF (25/0.04), TF (25/0.06), PF (25/0.04) and PF (25/0.06) were tested using the cyclic flexural fatigue testing device. The time to failure during cyclic flexural fatigue testing was recorded. The mean time required for the instrument to fail under cyclic flexural fatigue testing was 235.5 ± 68 s for 25/0.04 TF, 188.5 ± 75 s for 25/0.06 TF, 180.3 ± 102 s for 25/0.04 PF and 156.3 ± 17 s for 25/0.06 PF. The difference between the time to failure of 25/0.04 TF and 25/0.06 TF was not statistically significant. The difference between the time to failure of TF and PF of similar tip size and taper was not statistically significant. The findings of this study indicate that size 25/0.04 and 25/0.06 TFs had similar resistance to cyclic flexural fatigue failure. In addition, TFs were not superior, in terms of resistance to cyclic flexural fatigue failure, to PF of similar tip size and taper.     

Surface hardness evaluation of different composite resin materials: influence of sports and energy drinks immersion after a short-term period

Objectives:

This study evaluated the effect of sports and energy drinks on the surface hardness of different composite resin restorative materials over a 1-month period.

Material and Methods:

A total of 168 specimens: Compoglass F, Filtek Z250, Filtek Supreme, and Premise were prepared using a customized cylindrical metal mould and they were divided into six groups (N=42; n=7 per group). For the control groups, the specimens were stored in distilled water for 24 hours at 37º C and the water was renewed daily. For the experimental groups, the specimens were immersed in 5 mL of one of the following test solutions: Powerade, Gatorade, X-IR, Burn, and Red Bull, for two minutes daily for up to a 1-month test period and all the solutions were refreshed daily. Surface hardness was measured using a Vickers hardness measuring instrument at baseline, after 1-week and 1-month. Data were statistically analyzed using Multivariate repeated measure ANOVA and Bonferroni''s multiple comparison tests (α=0.05).

Results:

Multivariate repeated measures ANOVA revealed that there were statistically significant differences in the hardness of the restorative materials in different immersion times (p<0.001) in different solutions (p<0.001). The effect of different solutions on the surface hardness values of the restorative materials was tested using Bonferroni''s multiple comparison tests, and it was observed that specimens stored in distilled water demonstrated statistically significant lower mean surface hardness reductions when compared to the specimens immersed in sports and energy drinks after a 1-month evaluation period (p<0.001). The compomer was the most affected by an acidic environment, whereas the composite resin materials were the least affected materials.

Conclusions:

The effect of sports and energy drinks on the surface hardness of a restorative material depends on the duration of exposure time, and the composition of the material.