A method for the construction of simulated root canals in clear resin blocks

Precision-milled simulated curved root canals in bovine dentine for the assessment of chemo-mechanical root canal preparation

AIM

The aim was to develop a standardized curved root canal model in bovine dentine and to assess whether that natural substrate would behave differently from the resin in standard plastic training blocks when prepared chemo-mechanically. The impact of substrate microhardness on simulated canal transportation was considered.

METHODOLOGY

High-precision computer numerical control (CNC) milling was used to recreate a simulated root canal from a resin training block (Endo Training Bloc J-Shape, size 15) in longitudinally sectioned, dis- and re-assembled bovine incisor roots. Optical overlays obtained from 10 resin blocks were used to identify an average canal and program the CNC milling apparatus accordingly. Resin and dentine microhardness were measured. Simulated root canals in resin training blocks and their bovine counterparts were then instrumented at 37°C using Reciproc R25 instruments (VDW) with water or 17% EDTA (n = 10). Open-access image processing software was used to superimpose and analyse pre- and postoperative images obtained with a digital microscope. Centering ratios were averaged to indicate canal transportation. The effects of substrate and irrigant on canal transportation were assessed by two-way anova.

RESULTS

Superimposed images showed that resin blocks under investigation varied considerably in terms of simulated canal length and curvature, whilst the milled canals were highly similar. The microhardness of dentine was more than three times higher than that of the resin. Conversely, canal transportation was considerably greater in dentine compared to resin, and in dentine had a tendency to be increased by EDTA. There was a strong effect of substrate on canal transportation (p < .001), no overall effect of irrigant, and a marginally significant interaction between irrigant and substrate (p = .077).

CONCLUSIONS

CNC milling allows to create standardized simulated curved root canals in bovine dentine. These models may be useful to test and compare materials and concepts of chemo-mechanical root canal instrumentation. Microhardness is a bulk feature that does not predict the response to chemo-mechanical instrumentation of a composite material such as dentine.

A critical analysis of research methods and experimental models to study root canal fillings

Canal filling materials and techniques have been one of the most studied topics in Endodontics. A simple search using the mesh term "root canal filling" in PubMed revealed more than 11,000 articles, an impressive number that is much higher than "root canal disinfection" (5,544 articles) or even the popular "root canal preparation" (8,527 articles). The overriding importance attributed to root filling procedures is not merely intuitive. It derived from the appealing relevance given by the appearance of the white lines in common radiographs grounded on retrospective clinical data that had identified the quality of a root filling as one of the major causes of treatment failure (lack of healing). Since the publication of the Washington study, impressive efforts have been made for the release of new materials and techniques, as well as, for the development of a plethora of laboratory methods to assess the quality of root filling procedures. This narrative review aims to address and discuss the most relevant laboratory methods to assess the root canal filling. Since filling quality improvements have not translated into higher success rates, as reported in longitudinal clinical studies, more than to deliver a simple methodology-based review, this paper aims to present an in-depth critical view on the assessment of laboratory methods used to study the filling materials and techniques. Recent data indicate that the long-term dimensional stability/degradation over time of endodontic sealers plays a central role in the treatment outcome. In this context, laboratory methods should be developed focusing on predicting, at least to some degree, the long-term clinical behaviour of root canal fillings, rather than simply ranking different materials or techniques.

An Investigation of the Accuracy and Reproducibility of 3D Printed Transparent Endodontic Blocks

Due to a broad spectrum of endodontic rotary instruments on the market and no standardised protocol for comparing their mechanical properties, it can be challenging for clinician to choose proper instruments. In vitro studies using resin blocks with artificial canals can offer many valuable information because of their uniformity compared to studies performed on extracted teeth. To improve precision and reproducibility of artificial canals, 3D printing was used in this study to manufacture endodontic test block samples. 20 commercially available endodontic blocks Endo-Training-Bloc-J by Dentsply Sirona were tested. The mean values of the measured parameters were used for a 3D CAD model of their replicas. 20 copies of the endodontic training blocks were printed from acrylic resin (VeroClear-RGD810, Stratasys, Eden Prairie, USA) using the 3D printer Objet30 Pro (Stratasys, Eden Prairie, USA). The key dimensions of the commercial blocks and the 3D printed blocks were measured under and compared using t – test and Levene’s test for equality of variances. The profiles of the 3D printed artificial canals showed significantly lower dimensional variability when compared with the commercial blocks. 3D polyjet printing proved to be a precise and reproducible method for production of blocks for testing endodontic rotary instruments.

A critical appraisal of research methods and experimental models for studies on root canal preparation

It is the aim of this review to present a critical overview and summary on the contemporary possibilities, limitations and challenges of research related to root canal preparation. Frequently used research tools and contemporary research designs will be presented and discussed critically focussing on shortcomings and benefits with special regard to clinical relevance and scientific evidence. A plethora of experimental set-ups for assessing the shaping of root canals have been described in the endodontic literature using a considerable number of techniques and instruments. Nevertheless, it can be stated that scientific evidence demonstrating the clinical impact of many investigated topics is questionable or even missing. Instead of technical, radiographic and geometrical parameters, further research should focus on biological aspects and clinical evidence of the impact of root canal preparation on the outcome of root canal treatment.

Perception of a modular 3D print model in undergraduate endodontic education

AIM

To evaluate a modular 3D print training dental model with embedded human teeth and electronic working length determination for undergraduate endodontic education.

METHODOLOGY

Cone-beam volume tomography data of a human skull were transferred into stereolithographic (STL) data, and a customizable modular 3D print model with individually removable sextants and teeth was generated for the use in commercially available phantom heads. Each of sixty-eight students performed a complete root canal treatment on an extracted human tooth. Working lengths were determined with electronic apex locators (EAL) and verified radiographically. Subsequently, an evaluation was carried out with regard to the difficulty of the working steps access cavity preparation, working length determination, root canal preparation/irrigation and canal filling, and these steps were compared to commonly used benchtop models. Additionally, the agreement of electronic and radiographic working length determination was assessed and analysed statistically with the chi-square test.

RESULTS

A total of 68 teeth (20 incisors, 26 premolars and 22 molars) with 127 root canals were treated. In total, 87% of the students considered the modular 3D print model considerably more demanding than the conventional benchtop model. Overall, 96% felt better prepared for the clinical situation, 92% felt markedly reduced stress levels during endodontic practice in the subsequent clinical courses, and 93% of the students suggested the model should be used in future preclinical endodontic training. The preradiographic use of EAL resulted in 85% of the cases having radiographically acceptable working length determination within 0-2 mm from the radiographic apex. Readings more than 2 mm from the apex or beyond were significantly more common in molars than in premolars and incisors (P < 0.05).

CONCLUSIONS

The vast majority of students rated the modular 3D print training model positively despite it being more demanding. They also recommended its use in preclinical teaching and training. The model allowed a more realistic simulation of the clinical situation with a simultaneous use of EALs and led to reduced stress levels in endodontic treatment in the subsequent clinical courses.

Assessment of Different Root Canal Preparation Techniques with Rotary Nickel-Titanium Instruments by Novice Students

This study investigated which preparation strategy for root canals leads to the best technical preparation quality, and moreover, which is perceived to be performed best by novice students. Sixty-four students were recruited to prepare one simulated root canal with each of the following: FlexMaster files (F), Mtwo files (M), and Reciproc files (R). After preparation, the students assessed the different instrument systems through a questionnaire. The technical quality of the root canal preparations was evaluated by the centering ratio of the preparation. A total of 186 prepared root canals were submitted for evaluation. With R, significantly better centered preparations were achieved when compared to M and F (p < 0.001). The students evaluated R faster than M and F, and evaluated F significantly (p < 0.05) slower than R and M. M was rated as the easiest system to learn and to handle, as well as the best at reaching the working length; therefore, it was evaluated as the overall favorite of the students. A difference was found between the students' perceptions and their achieved technical quality of root canal preparations.

Shaping ability of four root canal instrumentation systems in simulated 3D-printed root canal models

Introduction

The aim of this study was to compare the shaping ability of four root canal preparation systems in newly developed 3D-printed root canal models.

Materials and methods

For this study, 1080 3D-printed acrylic resin blocks with nine different root canal configurations were produced. They were prepared with Reciproc R25 (#25), F6 SkyTaper (#25 and #30) F360 (#25 and #35) and One Shape (#25) (N = 30 per system). Pre- and post-instrumentation images were superimposed for evaluation of the centering ratio of the different systems. Ledges, instrument fractures and preparation times were also recorded. Analysis of variance (ANOVA) and post-hoc Tukey tests were conducted, comparing the mean canal centering ratios and the mean preparation times.

Results

There were significant differences between all systems regarding the centering ratios in the different root canal configurations (ANOVA p < 0.001). The root canal configuration had considerable effect on the centering ratio of the instruments. The best overall mean centering ratios were achieved with F6 SkyTaper #25 instruments especially in canal configurations with big curvature angles and radii, while F360 #35 was least centered especially in canals with small curvature angles and radii. Most ledges occurred with OneShape, while it was the significantly (p < 0.001) fastest preparation system (86.7 s (SD 13.53)) and Reciproc the significantly (p < 0.001) slowest (103.0 s (SD 20.67)).

Conclusion

3D-printed root canals are suitable to produce challenging canal configurations and to investigate the limitations of root canal instruments. We found that all instruments caused canal transportations. However, F6 SkyTaper #25 files had better overall centering ratios than the other instruments. In canal configurations with small curvature radii, the centering ratio of some instruments is low and the probability for ledges is increased.

Root canal volume change and transportation by Vortex Blue, ProTaper Next, and ProTaper Universal in curved root canals

Objectives

The aim of this study was to compare root canal volume change and canal transportation by Vortex Blue (VB; Dentsply Tulsa Dental Specialties), ProTaper Next (PTN; Dentsply Maillefer), and ProTaper Universal (PTU; Dentsply Maillefer) nickel-titanium rotary files in curved root canals.

Materials and Methods

Thirty canals with 20°-45° of curvature from extracted human molars were used. Root canal instrumentation was performed with VB, PTN, and PTU files up to #30.06, X3, and F3, respectively. Changes in root canal volume before and after the instrumentation, and the amount and direction of canal transportation at 1, 3, and 5 mm from the root apex were measured by using micro-computed tomography. Data of canal volume change were statistically analyzed using one-way analysis of variance and Tukey test, while data of amount and direction of transportation were analyzed using Kruskal-Wallis and Mann-Whitney U test.

Results

There were no significant differences among 3 groups in terms of canal volume change (p > 0.05). For the amount of transportation, PTN showed significantly less transportation than PTU at 3 mm level (p = 0.005). VB files showed no significant difference in canal transportation at all 3 levels with either PTN or PTU files. Also, VB files showed unique inward transportation tendency in the apical area.

Conclusions

Other than PTN produced less amount of transportation than PTU at 3 mm level, all 3 file systems showed similar level of canal volume change and transportation, and VB file system could prepare the curved canals without significant shaping errors.

Evaluation of four instruments with different working motion using artificial plastic model with C-shaped single canal

The purpose of this study was to evaluate four instruments with different working motion for preparation of a C-shaped single canal wall using the same artificial plastic models reproduced from a human tooth. One tooth with root canal morphology C1 (the shape is an uninterrupted “C” with no separation or division) was selected among three-dimensional micro-computed tomography (micro-CT) imaging data of extracted human teeth. Imaging data were then converted into STL form data, and twenty-four C-shaped root canal model blocks were manufactured using this STL form data. These blocks were randomly divided into four groups of six blocks each and instrumented as follows: stainless steel K-files (SSK), Self-Adjusting File (SAF), ProTaper NEXT (PTN) and RECIPROC (REC). Micro-CT images taken before and after canal preparation were superimposed, and instrumented canal area, percentage of instrumented canal area, part of instrumented canal area, volume of instrumented canal and time taken for instrumentation were evaluated for each group. The greatest instrumented canal area, percentage of instrumented canal area and volume of instrumented canal were as follows (in decreasing order): SSK > SAF > PTN > REC (P < 0.05). The longest time taken for instrumentation was as follows (in decreasing order): SAF > SSK > PTN > REC (P < 0.05). The conscious shaping of SSK and the lattice structure of SAF were instrumented all root canal walls equally. PTN and REC required less time taken for instrumentation, but showed unequal instrumentation.

Use of artificial primary teeth for endodontic laboratory research: experiments related to canal length determination

Background

Due to the scarcity of exfoliated/extracted human primary teeth with complete roots, artificial teeth were developed as an alternative to be used for educational and laboratory research purposes. This study aimed to assess the feasibility of using artificial primary teeth for conducting laboratory research through an experiment related to canal length determination, comparing artificial teeth with natural teeth.

Methods

Thirty anterior and 21 posterior artificial teeth, and the same number of natural primary teeth were selected. After preparing the access cavity, the root canal length was determined by two examiners twice using three different methods: radiography and two electronic apex locators. Then, the actual root canal length was measured by inserting a K-file up to the apical foramen (reference standard). Accuracy was calculated using Bland-Altman analysis and intraclass correlation coefficient (ICC). The inter- and intra-examiner reproducibility was also calculated using the ICC.

Results

The methods using the electronic apex locators showed better accuracy in both artificial and natural teeth. Trends observed with artificial primary teeth were similar to those observed with natural teeth, except for the results in artificial anterior teeth.

Conclusions

The model of artificial teeth might be a good alternative for educational purposes; however, improvements are necessary to employ these teeth for research purposes when considering experiments for canal length determination.

Electronic supplementary material

The online version of this article (10.1186/s12903-017-0420-3) contains supplementary material, which is available to authorized users.

Students' perceptions of pre-clinical endodontic training with artificial teeth compared to extracted human teeth

PURPOSE

Artificial teeth have several advantages in pre-clinical endodontics training. This study aimed to compare artificial resin teeth with extracted human teeth, from a student's perspective, during a pre-clinical undergraduate endodontic course for three consecutive academic years (2011-2014).

METHODS

At the end of the course, students completed a questionnaire that included questions about their perceptions of the difficulty of artificial teeth vs. natural teeth and ranked the perceived advantages of artificial teeth.

RESULTS

Participants expressed that all procedures, except obturation, were more difficult to perform on artificial teeth than on natural teeth, a result that was due to the hardness of the resin. They ranked the fairness and availability as the best advantages.

CONCLUSION

Artificial teeth have multiple advantages but cannot replace natural teeth. The physical characteristics through the manufacturing material of artificial teeth should be enhanced to increase wider use and acceptance.

A novel anatomical ceramic root canal simulator for endodontic training

INTRODUCTION

Endodontic therapy is often complicated and technically demanding. The aim of this study was to develop a reproducible biomimetic root canal model for pre-clinical and postgraduate endodontic training.

MATERIAL AND METHODS

A specific ceramic shaping technique (3D printing and slip casting of a root canal mould) was developed to reproduce canal systems with the desired shape and complexity using a microporous hydroxyapatite (HAp)-based matrix. The microstructural morphology, pore size and porosity, as well as the Vickers microhardness of the ceramic simulators (CS) were assessed and were compared with natural dentin and commercial resin blocks. The reproducibility of the root canal shapes was assessed using the Dice-Sørensen similarity index. Endodontic treatments, from refitting the access cavity to obturation, were performed on the CS. Each step was controlled by radiography.

RESULTS

Many properties of the CS were similar to those of natural dental roots, including the mineral component (HAp), porosity (20%, porous CS), pore size (3.4 ± 2.6 μm) and hardness (120.3 ± 18.4 HV).

DISCUSSION

We showed that it is possible to reproduce the radio-opacity of a tooth and variations in root canal morphology. The endodontic treatments confirmed that the CS provided good tactile sensation during instrumentation and displayed suitable radiological behaviour.

CONCLUSIONS

This novel anatomic root canal simulator is well suited for training undergraduate and postgraduate students in endodontic procedures.

Noncontact three-dimensional evaluation of surface alterations and wear in NiTi endodontic instruments

The aim of this study was to undertake a qualitative and quantitative assessment of nanoscale alterations and wear on the surfaces of nickel-titanium (NiTi) endodontic instruments, before and after use, through a high-resolution, noncontact, three-dimensional optical profiler, and to verify the accuracy of the evaluation method. Cutting blade surfaces of two different brands of NiTi endodontic instruments, Reciproc R25 (n = 5) and WaveOne Primary (n = 5), were examined and compared before and after two uses in simulated root canals made in clear resin blocks. The analyses were performed on three-dimensional images which were obtained from surface areas measuring 211 × 211 µm, located 3 mm from their tips. The quantitative evaluation of the samples was conducted before and after the first and second usage, by the recordings of three amplitude parameters. The data were subjected to statistical analysis at a 5% level of significance. The results revealed statistically significant increases in the surface wear of both instruments groups after the second use. The presence of irregularities was found on the surface topography of all the instruments, before and after use. Regardless of the evaluation stage, most of the defects were observed in the WaveOne instruments. The three-dimensional technique was suitable and effective for the accurate investigation of the same surfaces of the instruments in different periods of time.

A comparison of the shaping ability of three nickel-titanium rotary instruments: a micro-computed tomography study via a contrast radiopaque technique in vitro

Background

Micro-CT (μCT) studies that combine simulated canals with meglucamine diatrizoate to evaluate the shaping ability of nickel-titanium (NiTi) rotary instruments are lacking in the literature. The purpose of this study was to evaluate the shaping ability of three new different nickel-titanium rotary instruments in simulated root canals using μCT.

Methods

Thirty simulated root canals with a curvature of 60° were randomly allocated into the following 3 groups (n = 10): Group 1, ProTaper Universal (PTU) rotary system; Group 2, Reciproc single-file system; and Group 3, K3XF rotary system. Pre- and post-instrumented images of simulated canals were scanned with μCT via a radiopaque contrast technique to build a 3-dimensional (3D) model. Canal transportation, volumetric change and centring ability were evaluated in each group. Instrument failure and preparation time were also recorded. The Kruskal-Wallis test was used for statistical analysis and the significance level was set at p = 0.05.

Results

Reciproc produced greater volume change in the apical part of the canals compared with PTU and K3XF (p < 0.05). K3XF exhibited less transportation and better centring ability at the 2- and 3-mm levels from the apical foramen compared with PTU and Reciproc (p < 0.05). There were no significant differences in the centring ratio and transportation between PTU and Reciproc. Preparation time was significantly shorter in the Reciproc group (p < 0.05).

Conclusions

Under the conditions of our study, all of the canals were 3D reconstructed successfully via the radiopaque contrast technique. Reciproc showed enhanced apical volume changes and K3XF exhibited better centring ability when compared with other groups.

Electronic supplementary material

The online version of this article (doi:10.1186/s12903-016-0326-5) contains supplementary material, which is available to authorized users.

Various heat-treated nickel-titanium rotary instruments evaluated in S-shaped simulated resin canals

Background/purpose

Heat treatment of nickel–titanium (NiTi) alloy produces a better arrangement of the crystal structure, thereby leading to increased flexibility and improved fatigue resistance or plastic behavior. This study aimed to assess the performance of various heat-treated NiTi rotary instruments in S-shaped resin canals.

Materials and methods

Forty S-shaped resin canals were instrumented (10/group) with either Twisted Files (R-phase), WaveOne (M-wire), Hyflex CM, or V Taper 2H (CM-wire) with the same apical size and taper (25/0.08). Each S-shaped resin canal was scanned both before and after instrumentation with microcomputed tomography. Changes in canal volume and transportation were evaluated at regular intervals (0.5 mm). Differences between instruments at the apical curve, coronal curve, and straight portion of the canals were analyzed statistically.

Results

All tested instruments caused more transportation at the coronal rather than apical curvatures, with the exception of Twisted Files for which apical transportation was the highest for any instrument or location (P < 0.05). The transportation was mostly influenced by the alloy type rather than their cross-sectional characteristics (P < 0.05). The volumetric increase after instrumentation was similar for all tested instruments at the apical curve (P > 0.05), whereas Hyflex CM created the most conservative preparations at the coronal curve (P < 0.05). At the straight portion, volumetric changes were largest for Twisted Files and smallest for V Taper 2H (P < 0.05).

Conclusion

Amongst heat-treated NiTi instruments, the CM-wire based instruments created the most favorable preparations in S-shaped resin canals.

Comparison of canal transportation in simulated curved canals prepared with ProTaper Universal and ProTaper Gold systems

Objectives

The purpose of this study was to assess the ability of ProTaper Gold (PTG, Dentsply Maillefer) in maintaining the original profile of root canal anatomy. For that, ProTaper Universal (PTU, Dentsply Maillefer) was used as reference techniques for comparison.

Materials and Methods

Twenty simulated curved canals manufactured in clear resin blocks were randomly assigned to 2 groups (n = 10) according to the system used for canal instrumentation: PTU and PTG groups, upto F2 files (25/0.08). Color stereomicroscopic images from each block were taken exactly at the same position before and after instrumentation. All image processing and data analysis were performed with an open source program (FIJI). Evaluation of canal transportation was obtained for two independent canal regions: straight and curved levels. Student's t test was used with a cut-off for significance set at α = 5%.

Results

Instrumentation systems significantly influenced canal transportation (p < 0.0001). A significant interaction between instrumentation system and root canal level (p < 0.0001) was found. PTU and PTG systems produced similar canal transportation at the straight part, while PTG system resulted in lower canal transportation than PTU system at the curved part. Canal transportation was higher at the curved canal portion (p < 0.0001).

Conclusions

PTG system produced overall less canal transportation in the curved portion when compared to PTU system.

A new technique to make transparent teeth without decalcifying: description of the methodology and micro-hardness assessment

Diaphanisation and other in vitro endodontic models (i.e., plastic blocks, micro-CT reconstruction, computerised models) do not recreate real root canal working conditions: a more realistic endodontic model is essential for testing endodontic devices and teaching purposes. The aim of this study was to describe a new technique to construct transparent teeth without decalcifying and evaluate the micro-hardness of so treated teeth. Thirty freshly extracted teeth were randomly divided into three groups as follows: 10 non-treated teeth (4 molars, 3 premolars, 3 incisors; control group - G1), 10 teeth were diaphanised (4 molars, 4 premolars, 2 incisors - G2) and 10 teeth were treated with the new proposed technique (2 molars, 6 premolars, 2 incisors - G3). Vickers hardness tester (MHT-4 and AxioVision microscope, Carl Zeiss, 37030 Gottingen, Germany - load=50 g, dwell time=20s, slope=5, 50× magnification) was used to determine microhardness (Vickers Hardness Number - VHN). Statistical analysis was performed using the Intercooled Stata 8.0 software (Stata Corporation, College Station, TX, USA). Only groups 1 and 3 could be tested for hardness because diaphanised teeth were too tender and elastic. Differences in enamel VHN were observed between G1 (mean 304.29; DS=10.44; range 283-321) and G3 (mean 318.51; DS=14.36; range 295.5-339.2) - (p<0.05); differences in dentine VHN were observed between G1 (mean 74.73; DS=6.62; range 63.9-88.1) and G3 (mean 64.54; DS=5.55; range 51.2-72.3) - (p<0.05). G3 teeth presented a slightly lower VHN compared to G1, probably due to some little structural differences among groups, and were dramatically harder than the diaphanised teeth. The described technique, thus, can be considered ideal for testing endodontic instruments and for teaching purposes.

Restoflex--a revolutionary change in preclinical practice for restorative dentistry and endodontics

Preclinical exercises are very important for the dental students in order to master various dental techniques. The objective of this article is to introduce a new preclinical working model named Restoflex. It is especially designed for the students to carry out various restorative and endodontic procedures in an environment that closely simulate clinical situations. This will help them to provide a smooth transition from preclinical environment to the clinical one. It would also mean an increased confidence level and the efficiency with which the students would deal with their cases.

Single file reciprocating technique using conventional nickel-titanium rotary endodontic files

This study was aimed to evaluate the applicability of a reciprocating movement technique with conventional nickel-titanium files for root canal preparation. Forty-four simulated canals in resin blocks were used in this study and divided as following four groups according to the instruments used and preparation methods. Group CP (n = 12) and CR (n = 12) were instrumented with continuous rotation using four files of ProFile and RaCe, respectively. Group RP (n = 10) and RR (n = 10) were instrumented with a reciprocation movement by using a single ProFile and RaCe file, respectively. The resin blocks were scanned before and after instrumentation, and the images were superimposed. To compare the efficiency of canal shaping, the preparation time, and centering ratio were calculated. Morphologic changes of tested files were examined by scanning electron microscopy (SEM). Data were analyzed by ANOVA and Duncan's post hoc test at p < 0.05. The preparation time was markedly shorter in Groups RP and RR than in Groups CP and CR. No significant difference in the centering ratio was noted between groups. Although the files used for Groups CP and CR showed no distortion under the SEM evaluation, the files used for Groups RP and RR had considerable torsional distortion. This study suggests that the reciprocating instrumentation technique using conventional nickel-titanium rotary file systems might have a comparable efficacy for the root canal shaping with reduced shaping time. Although the reciprocating technique seems to be an effective alternative to the conventional rotation technique, the risk of torsional distortion and fracture should be considered before clinical application.

Comparison of the centering ability of Wave·One and Reciproc nickel-titanium instruments in simulated curved canals

Objectives

The aim of this study was to evaluate the shaping ability of newly marketed single-file instruments, Wave·One (Dentsply-Maillefer) and Reciproc (VDW GmbH), in terms of maintaining the original root canal configuration and curvature, with or without a glide-path.

Materials and Methods

According to the instruments used, the blocks were divided into 4 groups (n = 10): Group 1, no glide-path / Wave·One; Group 2, no glide-path / Reciproc; Group 3, #15 K-file / Wave·One; Group 4, #15 K-file / Reciproc. Pre- and post-instrumented images were scanned and the canal deviation was assessed. The cyclic fatigue stress was loaded to examine the cross-sectional shape of the fractured surface. The broken fragments were evaluated under the scanning electron microscope (SEM) for topographic features of the cross-section. Statistically analysis of the data was performed using one-way analysis of variance followed by Tukey's test (α = 0.05).

Results

The ability of instruments to remain centered in prepared canals at 1 and 2 mm levels was significantly lower in Group 1 (p < 0.05). The centering ratio at 3, 5, and 7 mm level were not significantly different.

Conclusions

The Wave·One file should be used following establishment of a glide-path larger than #15.

Comparison of root canal preparation using reciprocating Safesiders stainless steel and Vortex nickel-titanium instruments

OBJECTIVE

The aim of the present study was to assess several parameters related to the clinical usage of 2 root canal preparation instruments: Vortex .06 rotary nickel-titanium instruments, and Safesiders reciprocating stainless steel instruments.

STUDY DESIGN

Fifty extracted mandibular molars with mesial root canal curvatures between 20° and 50° were divided into 2 groups and embedded in acrylic resin inside a modified Bramante muffle system. All root canals were prepared to ISO size 40 using either Vortex .06 rotary nickel-titanium-instruments in a low-torque motor or Safesiders stainless steel instruments in a proprietary reciprocating handpiece. The following parameters were evaluated: straightening of curved root canals, working safety issues (perforations, instrument breakages, canal blockages, loss of working length), postpreparation root canal cross-section, and working time.

RESULTS

The Vortex .06 instruments maintained canal curvatures well, with the mean degree of straightening recorded as 0.72°. Safesiders instruments demonstrated significantly more canal straightening, with the mean degree of straightening recorded as 15.5°. More than 90% of the root canals prepared with the Vortex .06 instruments resulted in a round or oval cross-section, whereas the Safesiders instruments produced round or oval cross-sections 60% of the time. Neither of the 2 instruments could effectively prepare 100% of the root canal circumference. The area of dentin removed and the remaining dentin thicknesses from each region were similar for the 2 groups. Six procedural incidents were recorded for the Vortex .06 group, compared with 19 for the Safesiders group. There were no instrument fractures recorded in either group. Mean working time was significantly shorter for Vortex .06 (279 s) than for Safesiders (324 s).

CONCLUSIONS

Vortex .06 maintained the original root canal curvatures well, whereas Safesiders instruments demonstrated significant straightening and irregular preparation shapes when used in sizes larger than ISO 20. Preparation of the complete circumference of the root canal was not possible with either system. Fewer procedural errors occurred with the Vortex instruments.

Calcium phosphate cement augmentation of cancellous bone screws can compensate for the absence of cortical fixation

An obvious means to improve the fixation of a cancellous bone screw is to augment the surrounding bone with cement. Previous studies have shown that bone augmentation with Calcium Phosphate (CaP) cement significantly improves screw fixation. Nevertheless, quantitative data about the optimal distribution of CaP cement is not available. The present study aims to show the effect of cement distribution on the screw fixation strength for various cortical thicknesses and to determine the conditions at which cement augmentation can compensate for the absence of cortical fixation in osteoporotic bone. In this study, artificial bone materials were used to mimic osteoporotic cancellous bone and cortical bone of varying thickness. These bone constructs were used to test the fixation strength of cancellous bone screws in different cortical thicknesses and different cement augmentation depths. The cement distribution was measured with microCT. The maximum pullout force was measured experimentally. The microCT analysis revealed a pseudo-conic shape distribution of the cement around the screws. While the maximum pullout strength of the screws in the artificial bone only was 30±7N, it could increase up to approximately 1000N under optimal conditions. Cement augmentation significantly increased pullout force in all cases. The effect of cortical thickness on pullout force was reduced with increased cement augmentation depth. Indeed, cement augmentation without cortical fixation increased pullout forces over that of screws without cement augmentation but with cortical fixation. Since cement augmentation significantly increased pullout force in all cases, we conclude that the loss of cortical fixation can be compensated by cement augmentation.

Critical analysis of artificial teeth for endodontic teaching

The purpose of this study was to evaluate the use of artificial teeth for endodontic teaching. A questionnaire was prepared and submitted to 18 professors of Endodontics from different Brazilian universities to evaluate the following features of five cloudy resin artificial teeth: internal and external anatomy; coronal chambers regarding their size, shape and canal path; root canal regarding their size, shape and position; fulfillment of the pulp chamber and root canals by considering the texture, quantity, color, and ease of handling; resin hardness and visualization of the radiographic image. The results presented favorable opinions, in terms of internal and external anatomy, coronal pulp chambers and root canal and handling and radiographic imaging. The contents of the pulp space and hardness of the teeth were considered satisfactory. The average grade assigned to the artificial tooth quality was 8.4, in a 0-10 scale. In conclusion, the artificial teeth have potential to replace the natural teeth in endodontic teaching; however, improvements are still necessary to reach a better quality model.

Comparison of shaping ability of RaCe and Hero Shaper instruments in simulated curved canals

OBJECTIVE

This study compared the shaping ability of Hero Shaper and RaCe instruments in simulated curved canals.

STUDY DESIGN

Forty simulated canals in resin blocks were divided into 2 experimental groups, each comprising 20 resin blocks, and prepared with Hero Shaper and RaCe using the crown-down technique. Preoperative and postoperative photographs, recorded using a digital camera, were superimposed and aberrations were recorded. Material removal was measured at 10 points beginning 1 mm from the end point of the canal. Mean total widths, outer and inner width measurements, were determined on each central canal path and differences were statistically analyzed using Student t test.

RESULTS

The Hero Shaper and RaCe instruments removed almost the same amount of material from the inner side of the simulated canals. On the outer canal wall, the RaCe instruments removed significantly more material from the first 3 mm (P < .05). However, Hero Shaper removed more material from the middle and coronal aspects of the canal and the differences were statistically significant (P < .01).

CONCLUSION

RaCe instruments removed more resin from the outside of the curvature at the apical thirds, while Hero Shaper removed more material from the middle and coronal thirds on the outer canal wall. Hero Shaper instruments showed better centering ability and fewer aberrations. No instrument fractures but some deformations were observed for both systems.

Development of a Finite Element Analysis Model With Curved Canal and Stress Analysis

This study aimed to establish a model of a curved canal by finite element analysis (FEA). To develop a repeatable and comparable model, simulated curved canals with uniform shape were selected as prototype canals, and a suitable extracted single-root tooth was chosen as the outline. Subsequent combinations and modifications were performed by using the analysis program ABAQUS. By using a series of imitational occlusive forces loaded onto the incisive edge of the model, color plots and the maximal stresses at the apical region were analyzed. Stresses increased when the angle of the loads rose, and loads in the distal and mesial directions induced more stresses in the target region than did loads in the buccal and lingual directions. This study has established a standardized FEA model with a curved canal. Consequently, this model may be applied for future estimations in endodontic procedures for a curved canal.

Comparison of the shaping ability of RaCe and FlexMaster rotary nickel-titanium systems in simulated canals

The aim of this study was to compare the shaping ability of RaCe and FlexMaster rotary nickel-titanium instruments in simulated canals. A total of 80 canals with four different shapes were prepared with either RaCe or FlexMaster instruments. Pre- and postoperative images of each canal were recorded and combined using image analysis software. The development of canal aberrations and transportation was assessed. There was a significant difference (p < 0.001) between the systems for time of preparation to apical size 30, .06 taper; FlexMaster instruments took on average 1.86 min and RaCe 1.66 min. One RaCe and two FlexMaster instruments fractured. No zips, elbows, or danger zones were created. One perforation and eight outer widenings were created using FlexMaster instruments; RaCe instruments created two outer widenings. No differences were found between the instruments for direction of transportation. RaCe and FlexMaster nickel-titanium instruments prepared canals rapidly with few aberrations.

A comparative study of root canal preparation with NiTi-TEE and K3 rotary Ni-Ti instruments

AIM

To evaluate and compare several parameters of curved root canal preparation using two different Ni-Ti systems: NiTi-TEE (Sjöding Sendoline, Kista, Sweden) and K3 (Sybron Endo, Orange County, CA, USA).

METHODOLOGY

Fifty extracted mandibular molars with mesial root canal curvatures ranging from 20 to 40 degrees were divided into two groups. In one group, 50 root canals were instrumented using NiTi-TEE files to an apical size 30; 0.04 taper (the largest available size at the time of this study). In the other group, 50 root canals were prepared with K3 instruments to an apical size 45; 02 taper. Both systems were used in a crowndown manner, with copious NaOCl (3%) irrigation and a chelating agent (Calcinase Slide, lege artis, Dettenhausen, Germany), employing torque-controlled motors. For assessment of shaping ability, pre- and postinstrumentation radiographs and cross-sectional photographs of canals were taken and changes in canal curvature and root canal diameter documented. Cleaning ability was evaluated by investigating specimens of the apical, medial and coronal third of the root canal wall under a scanning electron microscope using 5-score indices for debris and smear layer. Procedural errors (instrument separations, perforations, apical blockages, loss of working length) and working time were recorded. Nonparametric anova was used to compare straightening of canal curvatures, canal cross-sections and canal wall cleanliness (P < 0.05), whereas working time was analysed using the parametric anova (P < 0.05).

RESULTS

Both Ni-Ti systems maintained curvature well: the mean degree of straightening was 0.2 degrees for NiTi-TEE and 0.4 degrees for K3 with no statistical significance between the groups. Post-instrumentation cross-sections of the root canals revealed an acceptable contour (round or oval) in 50.6% of cases for the NiTi-TEE group and in 65.3% of cases for the K3 group. The difference was not significant. The SEM investigation of canal walls showed equally good debris removal for both systems: NiTi-TEE prepared canal walls in 74.7% of cases with scores I and II; K3 achieved these scores in 78.7% of cases. For smear layer, NiTi-TEE and K3 only received good scores (I and II) in 38.7% and 40% of canal wall specimens, respectively. For both parameters, no significant differences were found between groups. File fractures did not occur, but loss of working length was observed in one case following the preparation with NiTi-TEE and in three cases during K3 instrumentation. Mean working time was significantly shorter for NiTi-TEE (170 s) than for K3 (208 s).

CONCLUSIONS

Both systems maintained original canal curvature well and were safe to use. Whilst debridement of canals was considered satisfactory, both systems failed to remove smear layer sufficiently.

Shaping Ability of RaCe Rotary Nickel-Titanium Instruments in Simulated Root Canals

This study assessed the shaping ability of RaCe rotary nickel-titanium instruments in simulated root canals. Forty simulated root canals consisting of four different shapes were prepared with RaCe rotary nickel-titanium instruments in a crowndown approach. Preoperative images were taken at the outset and postoperative images at various stages of preparation including at the conclusion of the shaping procedure. The combined images enabled assessment of aberrations and resin removal at various positions along the canal length. Overall, mean preparation time to size 40, .02 taper was 1.36 min. Thirty-three canals (83%) maintained the working length, three instruments deformed and no zips, perforations, or ledges were created. Under the conditions of this study RaCe rotary nickel-titanium instruments prepared simulated canals rapidly and successfully, with little change in working length and with few aberrations or instrument deformities.

Effect of Pitch Length on the Behavior of Rotary Triple Helix Root Canal Instruments

The behavior of nickel-titanium instruments depends largely on the cross-section of the working part. The effect of pitch length was evaluated using two instruments with the same cross-section (triple helix; 0.6% taper). One had a short pitch (0.5 mm at the tip to 0.9 mm at 16 mm at the end of the working part). The other had a long pitch (1.18 mm/2 mm). A dynamometer recorded tensional stress (MHz) and the tendency to screw in (Fz) during simulated canal preparations. Rotational speed was kept constant, and a continuous pecking movement was used. At the end of the preparations, the average Fz was 5.02 N for the short-pitch instrument and 1.47 N for the long-pitch instrument (p < 0.001). The average Mz varied from 0.88 N (short pitch) to 0.35 N (long pitch). Increasing the pitch decreased torsional load sharing and the tendency to screw in.

Shaping ability of ProTaper nickel-titanium files in simulated resin root canals

AIM

To determine the shaping ability of ProTaper instruments in simulated root canals.

METHODOLOGY

Forty canals with four different shapes in terms of angle (20 degrees and 40 degrees) and position of curvature (straight section before curve: 8 and 12 mm) were enlarged according to the recommendations of the manufacturer with the finishing files F1, F2 and F3 to full working length. Preoperative and postoperative pictures, recorded using a digital camera, were superimposed and aberrations recorded. Measurements were carried out at five different points: at the canal orifice (O); half-way to the orifice in the straight section (HO); beginning of the curve (BC); apex of the curve (AC); end-point (EP).

RESULTS

Ten instruments deformed (nine F3 and one S1, all in canals with straight section of 8 mm), one instrument fractured. There were significant differences between the various canal shapes for the amount of resin removed from the inner curve at all points (O: P < 0.05; HO: P = 0.001; BC, AC and EP: P < 0.001); and for the resin removed on the outer curve at points HO, AC and EP (P < 0.001). Mean transportation was towards the inner aspect of the curve in all canal types at points BC, towards the outer aspect at the end-point of preparation (EP) in all canals with 12 mm straight section. In 8 mm straight section canals, four danger zones were found; in 12 mm straight section canals three zips were present. The canal aberrations were produced following the use of the F2 and F3 instruments. There were no aberrations following the use of the F1 instrument.

CONCLUSIONS

Under the conditions of this study, ProTaper instruments performed acceptable tapered preparations in all canal types. When using F2 and F3 in curved canals, care should be taken to avoid excessive removal at the inner curve, leading to danger zones. In addition, care should also be taken to avoid deformation of the F3 instrument.

Shaping ability of GTTM Rotary Files in simulated resin root canals

AIM

The aim of this study was to determine the shaping ability of GT Rotary Files in simulated root canals.

METHODOLOGY

Forty canals with four different shapes in terms of angle (40 degrees and 60 degrees) and position of curvature (straight section before curve: 8 and 12 mm) were prepared using a crown-down/stepback technique. Pre-operative and post-operative pictures, recorded using an image analysis system, were super-imposed and aberrations recorded. Measurements were carried out at 5 different points: at the canal orifice (0): half-way to the orifice in the straight section (HO); the beginning of the curve (BC); the apex of the curve (AC): the endpoint (EP).

RESULTS

Two instrument fractures occurred and 9 instruments were deformed. Overall, eight zips and one ledge were created. There were significant differences (P < 0.001) for the total width of the canals between the various canal shapes at AC, BC and HO. There were significant differences (P < 0.001) for the amount of resin removed from the outer aspect of the curve at AC, BC and HO; and for the amount of resin removed from the inner aspect of the curve at all five measuring points (0, AC and EP (P < 0.05) and HO and BC (P < 0.001)). Mean transportation was towards the inner aspect of the canal in canals with straight sections of 12 mm regardless the curve angle; towards the outer aspect in canals with straight sections of 8 mm and 40 degrees curves at all the five measuring points, and at AC, BC and HO when the curve was 60 degrees.

CONCLUSIONS

Under the conditions of this study, GT Rotary Files produced acceptable canal shapes. In narrow and curved canals, the length of the straight section of the canal determines the direction of transportation more than the angle of the curve. In the 60 degrees curves, a high incidence of instrument deformation was found when using the 0.04 tapered instruments.

The use of computed tomography when comparing nickel-titanium and stainless steel files during preparation of simulated curved canals

AIM

The aim of this study was to compare canal preparations completed with Hedstrom and K-files of ISO size 15 - 40, made of nickel-titanium (Ni-Ti) and stainless steel (SS).

METHODOLOGY

Eighty simulated canals with 200 and 30 degrees C curvatures were prepared using the step-back technique and quarter turn/pull instrument manipulation. Middle and apical level canal sections were taken using computed tomography.

RESULTS

No significant difference was found between any of the file types at either level with respect to canal curvature (20 degrees or 30 degrees). At the middle level, the stainless steel files caused more enlargement toward the inner part, compared to nickel-titanium files. At the apical level, nickel-titanium canal files caused more enlargement toward the inner part, whereas more outward enlargement was caused by stainless steel instruments. No significant difference could be observed at the middle level (P > 0.05) related to the enlargement toward the outer side of the canal curvature. Transportation at both levels was significantly less (P < 0.001) for the Ni-Ti files than the SS ones. Centring ratios of the file types at the middle level were low, but not significantly different (P > 0.05), whereas at the apical level the centring ratios were significantly higher for the Ni-Ti files (P < 0.001).

CONCLUSIONS

Ni-Ti instruments produced preparations with adequate enlargement, less transportation, and a better centring ratio.

Canal shapes produced sequentially during instrumentation with Quantec SC rotary nickel-titanium instruments: a study in simulated canals

AIM

The aim of this study was to determine the shaping ability of Quantec SC nickel-titanium rotary instruments in simulated root canals.

METHODOLOGY

Forty simulated canals consisting of four different shapes in terms of angle and position of curvature were prepared with Quantec SC instruments. Sequential still images were taken of the canals using a video camera attached to a computer with image analysis software. Images were taken preoperatively, and then after instrument 7 (Size 25, 0.05 taper), instrument 8 (size 25, 0.06 taper), and instrument 10 (size 45, 0.02 taper) were taken to length. Each sequential postoperative image was superimposed individually over the preoperative image in order to highlight the amount and position of material removed during preparation.

RESULTS

Overall, the mean preparation time to size 10 was 3.6 min with 12 mm canals taking on average less time than 8 mm canals. There was a highly significant difference between the canal types (P < 0.0001). No instruments fractured within the canal or deformed, although one instrument separated from the latch grip. All canals remained patent. Following preparation to size 10, 19 canals (48%) retained their length, eight (20%) lost length, and 13 (32%) gained length; the magnitude of the change in length was always 0.5 mm or below. Following preparation to size 7 instruments all canals showed aberrant shapes. Excess removal of material along the outer aspect of the curve between the beginning of the curve and the end-point (outer widening) was found in 26 canals (65%) after instrument 7. At the same stage of preparation six canals (15%) had zips, three (8%) had ledges and five (13%) had perforations. Following preparation to size 10, 27 (68%) canals were perforated.

CONCLUSIONS

Under the conditions of the study, Quantec SC instruments consistently produced aberrations when canals were enlarged to size 7 (size 25, 0.05 taper) or above. Care should be exercised when using these instruments in real teeth.

Canal shapes produced sequentially during instrumentation with Quantec LX rotary nickel-titanium instruments: a study in simulated canals

AIM

The aim of this study was to determine the shaping ability of Quantec LX nickel-titanium rotary instruments in simulated root canals.

METHODOLOGY

Forty simulated canals consisting of four different shapes in terms of angle and position of curvature were prepared with Quantec LX instruments. Sequential still images were taken of the canals using a video camera attached to a computer with image analysis software. Images were taken preoperatively; after, instrument 7 (Size 25, 0.05 taper), instrument 8 (size 25, 0.06 taper), and instrument 10 (size 45, 0.02 taper) were taken to length. Each sequential postoperative image was superimposed individually over the preoperative image in order to highlight the amount and position of material removed during preparation. Intra-canal impressions after preparation to size 10 were taken to evaluate three-dimensional canal form.

RESULTS

Overall, the mean preparation time to size 10 was 4.7 min; canal shape did not have a significant effect on speed of preparation. No instruments fractured within the canal, but 7 instruments separated from the latch grip, and a further 3 instruments deformed. All canals remained patent. Following preparation to size 10, 29 canals (72%) retained their length, 7 (17%) lost length, and 4 gained length; the magnitude of the change in length was always below 1 mm. Zips were created in 3 canals (7%) after use of size 10 instruments, but no perforations or danger zones were produced. Excess removal of material along the outer aspect of the curve between the beginning of the curve and the end-point (outer widening) was found in 22 canals (55%) after instrument 7, in 30 (75%) canals after size 8 and in 35 canals (88%) after size 10. There was a significant difference (P < 0.0001) between canal shapes for the incidence of this aberration at all sizes.

CONCLUSIONS

Under the conditions of the study, Quantec LX instruments tended to remove excess material from the outside of the curve between the beginning of the curve and the end-point. These aberrations increased in prevalence and severity following the use of larger instruments when they were taken to length. Size 8, 9 and 10 Quantec LX instruments should be used with care and short of length, especially in severely curved canals.

Shaping ability of Hero 642 rotary nickel-titanium instruments in simulated root canals: Part 1

AIM

To determine the general efficacy and shaping ability of Hero 642 nickel-titanium rotary instruments during the preparation of simulated canals. Part 1 of this two-part report describes the efficacy of the instruments in terms of three-dimensional canal form.

METHODOLOGY

A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by Hero 642 instruments using a crown-down preparation sequence. The efficacy of the instruments was assessed in terms of preparation time, instrument failure, canal blockages and loss of canal length. Intra-canal impressions were taken of the prepared canals in order to assess three-dimensional canal form.

RESULTS

The mean time for canal preparation was 8.6 min and was influenced significantly (P < 0.05) by canal shape. Two instruments fractured and eight instruments deformed; significant differences were observed between canal shapes (P < 0.05). All of the canals remained patent. Fifteen canals (39.5%) maintained the correct working distance, 15 lost distance and eight canals gained length. Examination of intracanal impressions demonstrated that the majority of canals (79%) had apical stops; canal shape had a significant influence (P < 0.001) on the quality of apical stops. With one exception all canals had smooth canal walls and all of the canals showed good flow characteristics. Taper was poor in 30 canals (79%) and good in eight canals (21%).

CONCLUSIONS

Hero 642 rotary nickel-titanium instruments prepared simulated canals rapidly but with a three-dimensional form that lacked adequate taper.

Shaping ability of Hero 642 rotary nickel-titanium instruments in simulated root canals: Part 2

AIM

To determine the shaping ability of Hero 642 nickel-titanium rotary instruments during the preparation of simulated canals.

METHODOLOGY

A total of 40 simulated root canals made up of four different shapes, in terms of angle and position of curvature, were prepared by Hero 642 instruments using a crown-down preparation sequence. Pre- and postoperative images of the canals were taken using a video camera attached to a computer with image analysis software. The pre- and postoperative views were superimposed to highlight the amount and position of material removed during preparation. This report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and overall postoperative shape.

RESULTS

Four zips and four elbows were created during preparation, all in canals with 40 degrees, 12 mm curves. No perforations or danger zones were created. Highly significant differences (P < 0.001) were apparent between the canal shapes in total canal width at the apex and beginning of the curve, and in the amount of resin removed from the inner and outer aspects of the curve at the orifice. Canal transportation was most frequently directed toward the outer aspect of the curve at specific points along the canal, except at the orifice, where it was apparent that canals with 20 degrees curves transported toward the inner. Overall, mean absolute transportation was always less than 0.15 mm; however, significant differences occurred between canal shapes at the end-point (P < 0.01), apex of the curve (P < 0.01) and at the orifice (P < 0.01).

CONCLUSIONS

Under the conditions of this study, Hero 642 rotary nickel-titanium instruments created canals with few aberrations and no perforations. The relatively high proportion of aberrations in canals with short, acute curves may indicate that instruments with increased taper should be used with caution at or near the full working distance. Further research in real teeth is necessary to elucidate the full potential of these new rotary instruments for use in root canal preparation.