Comparative evaluation of surface changes in four Ni-Ti instruments with successive uses - An SEM study

Comparative evaluation of stress distribution against the root canal wall at three different levels using novel NiTi rotary files - A finite element analysis

Background

Recent innovations in the physical and mechanical features of endodontic file systems have diminished the prospect of stress generation and fracture risk in novel endodontic files.

Aim

The purpose of this research was to comparatively evaluate the stress distribution of recently introduced endodontic rotary files with distinct features and metallurgy at three different levels of the root canal wall by finite element analysis.

Materials and Methods

Forty endodontic files were used in this experiment after being inspected through a scanning electron microscope for any surface deformities. Based on their metallurgy and design, the scanned files were divided into four groups, each with 10 samples: Group A-2Shape files, Group B-F360, Group C-One Curve, and Group D-TruNatomy. To assess the mechanical behavior of these files, the stress produced by computer-aided models of these instruments on the dentinal wall of a simulated root canal was numerically analyzed using ANSYS® 15 Workbench finite element software.

Results

A one-way ANOVA was used to assess all the raw data with post hoc Tukey analysis, the Shapiro-Wilk test, and Levene's test. F360 files exerted the maximum stress on the dentinal wall, while TruNatomy files exerted the least stress at all the distinct levels of dentinal walls.

Conclusions

There was no statistically significant variation in the stress generated between the four groups. Therefore, it can be concluded that improvements in rotary file design and metallurgy have the potential to reduce the stress during canal shaping and the risk of instrument breakage during clinical use.

An in vitro comparison of alterations in surface topographies of three different rotary files after root canal preparation with different irrigating solutions: Atomic force microscopic study

Objectives

The objective of the study was to evaluate and compare the surface topographies of WaveOne Gold (WOG), FlexiCON X1, and EdgeOne Fire (EOF) reciprocating files before and after root canal instrumentation using different irrigating solutions.

Materials and Methods

Forty-eight extracted mandibular molars were selected and randomly assigned into three groups (n = 16) based on the file system used and each group was divided into two subgroups based on the irrigants used during root canal treatment. (Group-1: WOG; Group-2: FlexiCON X1; Group-3: EOF; Subgroup-A: 3% sodium hypochlorite [NaOCl] +17% ethylenediaminetetraacetic acid [EDTA]; Subgroup-B: Citra wash as irrigating solutions). The surface topography of the files was analyzed using atomic force microscope before and after instrumentation. Average roughness and root mean square roughness were calculated. Independent and paired t-tests and one-way analysis of variance with Tukey's post hoc were used for statistical analysis.

Results

Atomic force microscopy results showed an increase in surface roughness after instrumentation, EOF showing the highest roughness. Citra wash showed more roughness compared to NaOCl and EDTA together. However, the surface roughness between the experimental groups WOG and EOF are statistically insignificant and this insignificance was also seen among subgroups (P>0.05).

Conclusion

Instrumentation with various irrigating solutions affected the surface topography of EOF, WOG, and FlexiCON X1 reciprocating files.

Healing Abutment Distortion in Implant Prostheses: An In Vitro Study

Little has been studied regarding the repeated usage of healing abutments and their effects on the distortion of dental implant-healing abutment hex surfaces. Additionally, implant manufacturers do not provide specific guidelines on how many times a healing abutment can be used before discarding. Therefore, we evaluated the effect of repeated screwing-unscrewing of implant-healing abutment on the healing abutment hex surface and screw head. A total of 12 Biomate implants with 4 mm diameter and 13 mm length were inserted into a synthetic bone block. The standard healing abutments of 3 mm diameter and 4 mm length were screwed onto each implant using a torque ratchet at a final torque of 30 Ncm. Immediately, the abutments were unscrewed at 30 Ncm. Then, screwing-unscrewing was repeated for 4, 8, 16, 24, 32, 40, 80, 160, 320, and 400 times and the healing abutments were scanned under the scanning electron microscope for any distortion. Distortion was graded as 0, 1, 2, and 3. Data were analyzed using SPSS 24.0. Descriptive statistics were calculated. One-way ANOVA with post hoc using Tukey’s HSD test was performed to analyze the difference in distortion at different screwing-unscrewing times. A significant level was selected at p-value = 0.05. It was found that distortion healing abutments screws were seen after 32 times screwing and unscrewing. There was a significant difference in the distortion (p-value < 0.05) after 24 times of repeated usage of healing abutment and at 160, 320, and 400 times. No surface distortions were observed at the healing abutment screw head at 4, 8, 16, 24, 32, 40, 80, 160, 320, and 400 cycles of screwing-unscrewing. It can be concluded that repeated screwing and unscrewing of the implant-healing abutments causes damage to the healing abutment hex surface. The distortion of healing abutments screws was seen after 32 times screwing and unscrewing. No surface distortions were observed on the healing abutment screw head until 400 times of screwing and unscrewing. Hence, the clinician should be cautious while using the healing abutments repeatedly.

Structural Analysis of NiTi Endodontic Instruments: A Systematic Review

Introduction

Irregularities and defects on NiTi endodontic instruments originating from the manufacturing process can lead to the structural collapse and fracture of these instruments during treatment. To assess the cause of instrument wear and fracture, as well as increasing fracture incidence, destructive and non-destructive methods have been used for the analysis of surfaces and internal structures of new and used NiTi instruments. The aim of this systematic review was to undertake a detailed analysis of the methods used to evaluate the surface and internal microstructure of endodontic instruments.

Methods and Materials

The scientific literature was comprehensively and systematically searched in the MEDLINE (PubMed), Web of Science, Cochrane Library, Scopus, and LILACS/BBO databases for studies published up to June 9, 2019. The eligibility criteria was based on the PICO (Patient, Intervention, Comparison, and Outcome) strategy with the question "What is the best method for structural analysis of endodontic files?" Two aspects were considered for inclusion in this study: (i) endodontic instruments and (ii) methods for structural analysis of NiTi instruments. . The systematic review was performed according to the PRISMA statement.

Results

Based on the inclusion criteria, 94 articles were selected. The results showed that although specific methods have been used for qualitative and/or quantitative structural analysis of NiTi instruments, no study addressed both the surface and internal structure of the instruments at the same time. According to this review, the need to compare the methodologies used in the selected articles has been identified; however, each type of method used has its own limitation on the analysis of both the surface and the internal structure of the instruments.

Conclusions

The comparison between the different types of methodologies used in the studies revealed the reliability and the limitations of the methods employed for structural analysis of endodontic instruments; thus assisting us in determining their validity.

Stereomicroscopic evaluation of defects caused by torsional fatigue in used hand and rotary nickel-titanium instruments

Objective:

The aim of this study was to evaluate defects caused by torsional fatigue in used hand and rotary nickel-titanium (Ni-Ti) instruments by stereomicroscopic examination.

Materials and Methods:

One hundred five greater taper Ni-Ti instruments were used including Protaper universal hand (Dentsply Maillefer, Ballaigues, Switzerland), Protaper universal rotary (Dentsply Maillefer, Ballaigues, Switzerland), and Revo-S rotary (MicroMega, Besançon, France) files. Files were used on lower anterior teeth. After every use, the files were observed with both naked eyes and stereomicroscope at 20× magnification (Olympus, Shinjuku, Tokyo, Japan) to evaluate defects caused by torsional fatigue. Scoring was assigned to each file according to the degree of damage.

Statistics:

The results were statistically analyzed using the Mann-Whitney U test and the Kruskal-Wallis test.

Results:

A greater number of defects were seen under the stereomicroscope than on examining with naked eyes. However, the difference in methods of evaluation was not statistically significant. Revo-S files showed minimum defects, while Protaper universal hand showed maximum defects. The intergroup comparison of defects showed that the bend in Protaper universal hand instruments was statistically significant.

Conclusion:

Visible defects in Ni-Ti files due to torsional fatigue were seen by naked eyes as well as by stereomicroscope. This study emphasizes that all the files should be observed before and after every instrument cycle to minimize the risk of separation.

Deformation and fracture of K3 rotary nickel-titanium endodontic instruments after clinical use

AIM

The aim was to evaluate the incidence and type of defects that occurred with K3 rotary nickel-titanium instruments during routine clinical use.

METHODOLOGY

A total of 2397 K3 (G-PACKS, SybronEndo, West Collins, Orange, CA, USA) instruments were collected from a graduate endodontic clinic over 21 months. All the instruments were limited to a maximum use of 30 canal preparations. The collected instruments were measured by a digital caliper to determine whether any fractures had occurred and then were visually inspected for deformation and fracture under a stereomicroscope. The surfaces of fractured instruments were further evaluated under a scanning electron microscope. Data were analysed using chi-square test and Kruskal-Wallis test.

RESULTS

The incidence of instrument defect was 5.63%, consisting of 3.59% fractures and 2.05% deformations. The defect rates of 0.04 and 0.06 files were statistically higher than the other taper groups (P < 0.003) except for 0.08 files (P > 0.05). For the fractured instruments, 63.95% failed from flexural fatigue, whilst 36.05% failed from torsion.

CONCLUSION

Flexural fracture was the major mode of fracture for instruments with larger taper. A routine check for instrument integrity particularly for 0.04 and 0.06 files at high magnification is recommended after each clinical use.

Comparative evaluation of the effects of multiple autoclaving on cyclic fatigue resistance of three different rotary Ni-Ti instruments: An in vitro study

Aims:

The aim of this in vitro study was to evaluate comparatively the effects of multiple autoclaving on surface topography and cyclic fatigue of three different rotary nickel-titanium (Ni-Ti) instruments.

Materials and Methods:

Twenty-one files each of Twisted Files (TF), Revo-S, and RaCe were used in this study. They were grouped as group 1-TF, group 2-Revo-S, and group 3-RaCe. All the files were autoclaved and subjected for scanning electron microscopic analysis and cyclic fatigue analysis.

Results:

Data were subjected to statistical analysis using one way analysis of variance (ANOVA) and post hoc Tukey's Kramer multiple comparison test. TF exhibited the highest cyclic fatigue resistance followed by Revo-S and RaCe. Scanning electron photomicrographs showed no obvious surface changes in the files after three autoclaving cycles.

Conclusions:

Within the limitation of this study, it can be concluded that Twisted Files was the most fatigue resistant compared to Revo-S and RaCe, and multiple autoclaving cycles did not have any significant alterations in the cyclic fatigue resistance of rotary Ni-Ti files.