Simulated Canals Research Articles

Shaping Ability of Different Nickel-Titanium Systems in Simulated S-shaped Canals with and without Glide Path

IntroductionThe objective of this study was to compare the shaping ability of different rotary and reciprocating nickel-titanium file systems with and without previous glide path preparation in simulated S-shaped canals. MethodsOne hundred twenty S-shaped canals in resin blocks were prepared to an apical size 25 by using Reciproc, WaveOne, HyflexCM, F360, and OneShape systems either with or without previous glide path preparation (Pathfile) (12 canals/group). Material removal was measured at 20 measuring points, beginning 1 mm from the end point of preparation. Incidence of canal aberrations (zip/elbow, ledge formation), preparation time, and instrument failures were also recorded. Statistical analyses were performed by using analysis of variance and Tukey and χ2 tests. ResultsFor all systems, glide path preparation exerted no significant effect on preparation times (P > .05). Glide path preparation had no influence on the incidence of canal aberrations and instrument fractures (P > .05), with no significant differences between the 5 systems (P > .05). Glide path preparation had no influence on the centering ability of all systems (P > .05). On average, canals prepared with F360, OneShape, and HyflexCM remained better centered compared with those enlarged with WaveOne and Reciproc. ConclusionsUnder the conditions of this study, glide path preparation had no significant impact on canal straightening. Less tapered instruments maintained the original canal curvature better than instruments having greater tapers.

Comparing the Fracture Rate of Hero 642, FlexMaster and Mtwo in the Simulated Canals.

File fracture is one of the main procedural mishaps in endodontic treatment. The aim of this in vitro study was to compare the fracture rate of three NiTi rotary systems; Hero 642, Mtwo and FlexMaster in artificial canals. In this study, bovine long bone was used. After primary preparation of bones, longitudinal sections with 4-cm diameter were cut and encoded. Subsequently, semicircular sections were prepared. A total number of 500 canals were created in the same way; the upper 3 mm of the canals were initially prepared with orifice shapers and then canals were filed with FlexMaster files sizes 25/0.02 and 25/0.04 to 13 mm of canal length. The prepared canals were assigned into 3 groups of the following systems: Hero 642, Mtwo and FlexMaster. Six selected instruments were used from each system; the files were applied 13 mm along the canals for 10 sec with manufacturer's suggested speed and torque. The number of the canals prepared by each file before its separation was recorded; finally the data was analyzed with ANOVA test. Mean number of prepared canals in Mtwo, FlexMaster and Hero groups before file separation was 15, 25 and 32, respectively. RESULTS of this study showed that the number of prepared canals by Hero 642 was more than FlexMaster and Mtwo systems.

A novel methodology providing insights into removal of biofilm‐mimicking hydrogel from lateral morphological features of the root canal during irrigation procedures

To introduce and characterize a reproducible hydrogel as a suitable biofilm mimic in endodontic research. To monitor and visualize the removal of hydrogel from a simulated lateral canal and isthmus for the following: I) Ultrasonic-Activated Irrigation (UAI) with water, ii) UAI with NaOCl and iii) NaOCl without UAI. A rheometer was used to characterize the viscoelastic properties and cohesive strength of the hydrogel for suitability as a biofilm mimic. The removal rate of the hydrogel from a simulated lateral canal or isthmus was measured by high-speed imaging operating at frame rates from 50 to 30,000 fps. The hydrogel demonstrated viscoelastic behaviour with mechanical properties comparable to real biofilms. UAI enhanced the cleaning effect of NaOCl in isthmi (P < 0.001) and both NaOCl and water in lateral canals (P < 0.001). A greater depth of cleaning was achieved from an isthmus (P = 0.009) than from a lateral canal with UAI and also at a faster rate for the first 20 s. NaOCl without UAI resulted in a greater depth of hydrogel removal from a lateral canal than an isthmus (P < 0.001). The effect of UAI was reduced when stable bubbles were formed and trapped in the lateral canal. Different removal characteristics were observed in the isthmus and the lateral canal, with initial highly unstable behaviour followed by slower viscous removal inside the isthmus. The biofilm-mimicking hydrogel is reproducible, homogenous and can be easily applied and modified. Visualization of its removal from lateral canal anatomy provides insights into the cleaning mechanisms of UAI for a biofilm-like material. Initial results showed that UAI improves hydrogel removal from the accessory canal anatomy, but the creation of stable bubbles on the hydrogel-liquid interface may reduce the cleaning rate.

Cyclic fatigue resistance of ProTaper Next nickel‐titanium rotary files

To compare the cyclic fatigue resistance of ProTaper Next files (PTN; Dentsply Maillefer, Ballaigues, Switzerland) with Twisted Files (TF; SybronEndo, Orange, CA, USA), HyFlex CM (HF; ColténeEndo/Whaledent, Inc, Cuyahoga Falls, OH, USA) and ProTaper Universal (PT; Dentsply Maillefer). Size 25, .06 taper for PTN X2, TF, HF and PT F1 size 20, .07 taper were rotated in simulated canals until failure, and the number of cycles to failure (NCF) was recorded to evaluate their cyclic fatigue resistance. A scanning electron microscope was used to characterize the topographic features of the fracture surfaces of broken files. The data of the NCF and fragment length values were analysed statistically using one-way analysis of variance and Tukey post hoc tests. Statistical significance level was set at P<0.05. Twisted Files had a significantly higher resistance to cyclic fatigue than the other instruments (P<0.05). No significant difference was found in NCF between PTN and HF (P>0.05); however, there was a significant difference (P<0.05) of both these systems with PT, which exhibited the lowest mean NCF. The ranking in the NCF values was: TF>PTN>HF>PT. The fracture cross-sections of all brands revealed similar fractographic features, including crack origins, fatigue zone and an overload fast fracture zone. The new ProTaper Next had greater resistance to cyclic fatigue compared with ProTaper and HyFlex CM but not the Twisted Files.

Push-out bond strength of self-adhesive methacrylate resin-based sealers to root dentin

This study examined the adhesive strength of two self-adhesive methacrylate resin-based sealers (MetaSEAL and RealSeal SE) to root dentin and compared them with RealSeal and AH Plus in properties. A total of 48 extracted human single-rooted teeth were used to prepare the 0.9-mm thick longitudinal tooth slice (each per tooth). Standardized simulated canal spaces of uniform dimensions were prepared in the middle of radicular dentin. After treated with 5.25% sodium hypochlorite (NaOCl) and 17% EDTA, tooth slices were allocated randomly to four groups (n=12) in terms of different sealers used: MetaSEAL, RealSeal SE, RealSeal, and AH plus groups. The simulated canal spaces were obturated with different sealers in each group. There were 10 slabs with 20 simulated canal spaces (n=20) used in each group for push-out testing. The failure modes and the ultrastructures of fractured sealer-dentin interfaces were examined. The remaining 2 slabs in each group underwent partial demineralization for observation of the ultrastructure of resin tags. The results showed that the push-out bond strength was 12.01±4.66 MPa in MetaSEAL group, significantly higher than that in the other three groups (P<0.05). Moreover, no statistically significant differences were noted in the push-out bond strength between RealSeal SE (5.43±3.68 MPa) and AH Plus (7.34±2.83 MPa) groups and between RealSeal SE and RealSeal (2.93±1.76 MPa) groups (P>0.05). Mixed failures were predominant in the fractured sealer-dentin interfaces in MetaSEAL and AH Plus groups, while adhesive failures were frequently seen in RealSeal SE and RealSeal groups. In conclusion, after complete removal of the smear layer, MetaSEAL showed superior bond ability to root dentin. The RealSeal SE is applicable in clinical practice, with its adhesive strength similar to that of AH Plus. The self-adhesive methacrylate resin-based sealer holds promise for use in endodontic treatment.

Comparative evaluation of a novel smart-seal obturating system and its homogeneity of using cone beam computed tomography: In vitro simulated lateral canal study.

Aim:The aim was to evaluate and compare a novel polyamide polymer based obturating system and Gutta-percha and sealer in filling simulated lateral canals and their homogeneity when used for obturating the root canals.Materials and Methods:A total of 60 freshly extracted human single rooted teeth with fully formed apices were selected for this study. Teeth were de-coronated, and roots were standardized to a working length of 15 mm. Root canal preparation was carried out with rotary Protaper file system in all groups. The specimens were then randomly divided into three groups A, B, and C (n = 20). Ten samples from each group were decalcified and simulated lateral canals were made at 2, 4, and 6 mm from the root apex. Remaining ten samples from each group were maintained calcified. Group A was obturated with SmartSeal system (Prosmart-DRFP Ltd., Stamford, UK). Group B was obturated with sectional backfill method. Group C was obutrated with cold lateral compaction method (control). Decalcified samples from the respective groups were analyzed with digital radiography and photography and the measurement of the linear extension and area of lateral canal filling was done using UTHSCSA (UTHSCSA Image Tool for Windows version 3.0, San Antonio, TX, USA) software. Calcified samples were subjected to cone beam computed tomography image analysis sectioned axially.Results:Group A 92.46 ± 19.45 showed greatest extent of filling in lateral canals and denser homogeneity of oburation, followed by Group B 78.43 ± 26.45 and Group C 52.12 ± 36.67.Conclusions:Polyamide polymer obturation proved to have greater efficiency when compared with Gutta-percha system, when used for obturation with regards to adaptation of the sealer and penetration into the simulated lateral canals.

Filling of simulated lateral canals with gutta percha or resilon when using thermomechanical compaction.

Aims:To evaluate the filling of simulated lateral canals with gutta-percha or Resilon when using thermomechanical compaction.Setting and Design:Forty-five human single-rooted teeth were subjected to tooth decalcification and clearing.Materials and Methods:After root canal preparation, artificial lateral canals were made at 2, 5, and 8 mm from the working length (WL), corresponding to the apical, middle, and cervical thirds, respectively. The specimens were divided (n = 15) according to the filling material: Dentsply gutta-percha (GD), Odous gutta-percha (GO), and Resilon cones (RE). Root canals were obturated by thermomechanical compaction using a #45 compactor and no sealer. Lateral canals were analyzed by digital radiography and digital images after tooth decalcification and clearing using the Image Tool software.Statistical Analysis Used:Data were subjected to the Kruskal-Wallis and Dunn tests at 5% significance.Results:In the coronal third, RE and GO presented more filling ability than GD (P < 0.05). In the middle and apical thirds, RE presented the best results.Conclusions:Resilon demonstrated filling ability as material for root canal obturation by using thermomechanical compaction.

Shaping Ability of Nickel-titanium Single-file Systems in Simulated Canals with Different Angles

Shaping Ability of Nickel-titanium Single-file Systems in Simulated Canals with Different Angles

Canal shaping with one shape file and twisted files: a comparative study.

The aim of this study was to compare the shaping ability of two different rotary Nickel -Titanium (Ni-Ti) files, One shape file and Twisted files in a simulated artificial canals. A total of 40 endodontic training blocks were used in this study and divided in two groups consisting of 20 each ( n = 20) and the shaping ability was accessed based on the left over ink stain in the artificial canal. Image proplus analysis software and stereomicroscope were used for analysing the shaping ability of the files and statistical analysis was done by SPSS software. Twisted files showed better shaping ability compared to one shape file both experimentally and statistically. It can be concluded that twisted files shaped the canals better then one shape file.

Mineral Trioxide Aggregate Mixed with Normal Saline, Calcium Chloride or KY Jelly as Apical Plug in Simulated Open Apices: An In vitro Microleakage Study.

Mineral trioxide aggregate (MTA) mixed with normal saline has short working time, delayed setting time, and poor consistency when used as an apical plug. A preliminary study suggested that substituting normal saline with KY Jelly or 5% calcium chloride (CaCl2) as a vehicle expedites the setting time of MTA. The present in vitro study compared the microleakage of ProRoot MTA mixed with normal saline (MS) to that of ProRoot MTA mixed with KY Jelly and/or 5% CaCl2 in simulated canals with open apices. Thirty six single-rooted extracted human teeth were cleaned and shaped with ProTaper rotary system to make 36 standardized artificially created open apices. Teeth were randomly divided into three experimental groups (n=10) and two control groups (n=3). In group 1, MTA was mixed with normal saline (MS) and placed into the canals to form 4 to 5 mm apical plugs. In group 2, MTA was mixed with 5% CaCl2 (MC) and in group 3, MTA was mixed with KY Jelly (MK). The other two groups served as positive and negative controls. The remaining canal spaces in the experimental groups were backfilled with thermoplasticized gutta-percha without sealer. Dye penetration and clearing was used to evaluate the sealing ability of each group. The samples were then examined under stereomicroscope to measure the microleakage of different MTA mixtures in mm. Data were statistically analyzed using One-Sample Kolmogorov-Smirnov test for determination of normal distribution and then by one-way ANOVA and Tukey's tests to detect any significance. Positive and negative controls responded as expected. The MS group showed the least mean dye penetration value. There was a significant difference between MS with other groups (P<0.05) but no difference was found between MC and MK groups. Within the limitations of this in vitro study, we can conclude that among these three vehicles, normal saline mixed with ProRoot MTA has the least amount of microleakage in canals with open apices.

Comparison of the shaping ability of GT® Series X, Twisted Files and AlphaKite rotary nickel-titanium systems in simulated canals

BackgroundEfforts to improve the performance of rotary NiTi instruments by enhancing the properties of NiTi alloy, or their manufacturing processes rather than changes in instrument geometries have been reported. The aim of this study was to compare in-vitro the shaping ability of three different rotary nickel-titanium instruments produced by different manufacturing methods.MethodsThirty simulated root canals with a curvature of 35˚ in resin blocks were prepared with three different rotary NiTi systems: AK- AlphaKite (Gebr. Brasseler, Germany), GTX- GT® Series X (Dentsply, Germany) and TF- Twisted Files (SybronEndo, USA).The canals were prepared according to the manufacturers’ instructions. Pre- and post-instrumentation images were recorded and assessment of canal curvature modifications was carried out with an image analysis program (GSA, Germany).The preparation time and incidence of procedural errors were recorded. Instruments were evaluated under a microscope with 15 × magnifications (Carl Zeiss OPMI Pro Ergo, Germany) for signs of deformation. The Data were statistically analyzed using SPSS (Wilcoxon and Mann–Whitney U-tests, at a confidence interval of 95%).ResultsLess canal transportation was produced by TF apically, although the difference among the groups was not statistically significant. GTX removed the greatest amount of resin from the middle and coronal parts of the canal and the difference among the groups was statistically significant (p < 0.05). The shortest preparation time was registered with TF (444 s) and the longest with GTX (714 s), the difference among the groups was statistically significant (p < 0.05). During the preparation of the canals no instrument fractured. Eleven instruments of TF and one of AK were deformed.ConclusionUnder the conditions of this study, all rotary NiTi instruments maintained the working length and prepared a well-shaped root canal. The least canal transportation was produced by AK. GTX displayed the greatest cutting efficiency. TF prepared the canals faster than the other two systems.

Evaluation of a New Filing System's Ability to Maintain Canal Morphology

IntroductionThe manufacturer of the Hyflex CM endodontic files claims the files remain centered within the canal, and if unwound during treatment, they will regain their original shape after sterilization. The purpose of this study was to evaluate and compare the canal centering ability of the Hyflex CM and the ProFile ISO filing systems after repeated uses in simulated canals, followed by autoclaving. MethodsSixty acrylic blocks with a canal curvature of 45° were stained with methylene blue, photographed, and divided into 2 groups, H (Hyflex CM) and P (ProFile ISO). The groups were further subdivided into 3 subgroups: H1, H2, H3; P1, P2, P3 (n = 10). Groups H1 and P1 were instrumented to 40 (.04) with the respective file system. Used files were autoclaved for 26 minutes at 126°C. After sterilization, the files were used to instrument groups H2 and P2. The same sterilization and instrumentation procedure was repeated for groups H3 and P3. Post-instrumentation digital images were taken and superimposed over the pre-instrumentation images. Changes in the location of the center of the canal at predetermined reference points were recorded and compared within subgroups and between filing systems. ResultsStatistical differences in intergroup and intragroup transportation measures were analyzed by using the Kruskal-Wallis analysis of variance of ranks with the Bonferroni post hoc test. There was a difference between Hyflex CM and ProFile ISO groups, although it was not statistically significant. Intragroup differences for both Hyflex CM and ProFile ISO groups were not significant (P < .05). ConclusionsThe Hyflex CM and ProFile ISO files equally maintained the original canal's morphology after 2 sterilization cycles.

The evaluation of two rotary instrumentation techniques under "operator-related variables" standardized conditions.

Objective:We aimed here to evaluate the enlargement characteristics of two nickel-titanium rotary instrument systems that use two different preparation techniques, in simulated root canals under “operator-related variables” standardized conditions.Materials and Methods:A total of 40 simulated canals in resin blocks were divided into two groups as the Mtwo group for use with a single-length technique and the ProTaper instrument system group for use with crown down technique. To standardize the operator-related variables, all preparations were carried out with a computer controlled device that was developed and used previously as described in a published study. The pre- and post-operative digital images of the canals were superimposed and measured at 11 levels from the apical tip. The distances between the pre- and post-operative outer lines of the root canals were measured at both the inner and outer sides of the curve. The amount of removed material and the symmetry of the preparations were evaluated. Statistical analyses were performed with Mann-Whitney test.Results:Significantly more material was removed by Mtwo at 9 levels and by ProTaper at 2 levels (P < 0.05) while no significant difference was determined at 11 levels. The preparations made with ProTaper were more symmetrical at 4 levels while no significant difference was determined at 7 levels.Conclusion:Mtwo removed significantly more material than ProTaper at different levels of the curved root canals. Mtwo and ProTaper made symmetrical preparations and maintained the original shape of the root canal at different levels under controlled operator-related variables.

Filling of simulated lateral canals using different obturation techniques: analysis through IDA digital radiograph system

Lateral canals are part of the root canal system and may be related to periodontal-endodontic diseases. The filling techniques that employ thermoplasticized gutta-percha have demonstrated better results in filling lateral canals. Objective: The aim of this study was to evaluate, through digital radiographs, three techniques of root canal obturation (Lateral Condensation, Obtura II System, Tagger’s Hybrid) regarding to the ability of filling artificial lateral canals. Material and methods: 30 extracted human lower premolars were used in this study. The crowns were removed and artificial laterals canals were prepared on the coronal, medium and apical thirds of the roots by using a reamer made of a K 10 file. The root canals were instrumented and obturated by the following techniques: Lateral Condensation, Obtura II System, and Tagger’s Hybrid. The teeth were radiographed with IDA digital radiograph system and the filling of the lateral canals was evaluated by scores for further statistical analysis. Results: No significant difference was found in the filling of lateral canals between Lateral Condensation and Obtura II, but a significant difference was found among these two and Tagger’s Hybrid technique. Conclusion: Tagger’s Hybrid technique promoted the highest numbers of obturated lateral canals. In the three groups, the root thirds presenting greater number of filled lateral canals were coronal and middle, regardless of the obturation technique employed.

Effect of Torsional Loading of Nickel-Titanium Instruments on Cyclic Fatigue Resistance

IntroductionThe aim of this study was to evaluate the effect of torsional preload on the cyclic fatigue life of nickel-titanium rotary instruments. MethodsProFile (#25/0.06) (Dentsply Maillefer, Ballaigues, Switzerland) and ProTaper (F1; Dentsply Maillefer) were used. Each file was preloaded at 4 conditions (ie, no preloading and 25%, 50%, and 75% of mean ultimate torsional strength) of torsional prestress before the fatigue test. The torsional preloads were applied by securing 5 mm of the file tip while keeping the file straight, rotating it clockwise until the preset torque, and then returning to the original position. This motion was repeated until a preset number (10, 30, or 50) of repetitions were reached (n = 12). After torsional preloading, the number of cycles to failure was evaluated in a simulated canal. Data were analyzed using 2-way analysis of variance and the Duncan post hoc comparison. The fractured fragment surfaces were examined under a scanning electron microscope for the topographic features of fractured instruments. ResultsFor both instruments, there was a significant effect because of the extent of torsional preloads. The 50% and 75% torsionally preloaded ProFile and all ProTaper preloading groups had a higher number of cycles to failure than the other group(s). There was little difference in the lateral view appearance between new and torsionally preloaded files. After cyclic fatigue testing, all preloaded instruments showed numerous microcracks adjacent to the fracture site on lateral view examination. The microcracks did not seem to follow the machining grooves on the instrument surface but rather ran irregularly. ConclusionsThe torsional preloads within the superelastic limit of the material may improve the cyclic fatigue resistance of nickel-titanium rotary instruments.

In Vitro Assessment of Torque and Force Generated by Novel ProTaper Next Instruments during Simulated Canal Preparation

IntroductionThe purpose of this study was to assess torque and force for simulated canal preparation with a new root canal instrument, ProTaper Next. MethodsSix sets of ProTaper Next Instruments (X1–X5) were used to prepare 36 artificial canals. Files were divided into 6 groups. Different settings of rotations per minute (250, 300, and 350 rpm) and numbers of in-and-out movements to reach working length (3 or 4 insertions [ins]) were applied in each group (250 rpm/3 ins, 250 rpm/4 ins, 300 rpm/3 ins, 300 rpm/4 ins, 350 rpm/3 ins, and 350 rpm/4 ins) by using an automated torque bench. Peak torques (Ncm) as well as positive and negative forces (N) were registered. Analysis of variance and Tukey post hoc tests were applied. Preliminary data for angle and stationary torque at failure were also obtained and compared with peak torque for each instrument. ResultsSignificant differences in peak torque (P < .0001), positive force (P < .002), and negative force (P < .0001) were found for ProTaper Next instruments overall. X2 showed the highest torque with all settings. X5 showed the highest positive force in all groups. X1 and X2 showed the highest negative forces for all groups except for 350 rpm/4 ins. Significantly lower torque (P < .0001) and positive force (P < .007) were measured in the group 350 rpm/4 ins for all instruments except for X4. In contrast, X1 showed a significantly lower negative force for 350 rpm/4 ins. Torque at failure according to American Dental Association no. 28/ISO 36030-1 was lower for X1, X2, and X3 than torque during simulated canal preparation (P < .0001). ConclusionsUnder the conditions of this study, using ProTaper Next at 350 rpm and with 4 in-and-out movements resulted in lowest levels of peak torque as well as positive and negative forces.

Influence of rotational speed on the cyclic fatigue of Mtwo instruments

To evaluate the effect of rotational speed on cyclic fatigue of Mtwo nickel-titanium files. A total of 120 new Mtwo rotary instruments sizes 10, 0.04 taper; 15, 0.05 taper; 20, 0.05 taper; and 25, 0.06 taper were randomly divided into three groups on the basis of the rotational speed used to shape nine standardized simulated canals: group A=350rpm; group B=250rpm; group C=150rpm. Each group consisted of 40 instruments, 10 for every size. The average preparation time (in seconds) and the average correlated numbers of cycles to instrument (NCI) the nine standardized canals were recorded for each file. The resistance to cyclic fatigue was determined by counting numbers of cycles to failure (NCF) with a rotational speed of 300rpm in a 60° curve with a 5-mm radius. Data were analysed by two-way anova. Preparation time was significantly longer at 150rpm than at 250 or 350rpm. The average number of cycles needed for each file to instrument nine standardized canals was significantly higher at 350 and 250rpm, than at 150rpm. There were no significant differences in the NCF (P>0.05) between A, B and C groups for instruments of the same size. Speed did not affect the cyclic fatigue of Mtwo instruments with the same size and taper. Preparation time was shorter at 350 or 250rpm rather than at 150rpm. However, there was no significant difference between 350 and 250rpm rotational speed, neither in the preparation time of simulated canals nor in the resistance to fatigue fracture.

Tube Education Device (TED) Simulator for Myringotomy with Tube Insertion for Resident Training Purposes

Objectives: 1) Implement a training device to train otolaryngology residents to perform myringotomy with tube insertion. 2) Analyze data on the performance of medical students with this device. Methods: After approval by University of Texas Medical Branch Institutional Review Board, medical students were recruited to partake in the study from June 2012 to present. An instructional video on this procedure was shown to each subject before each trial. In the operating room, the subjects performed the procedure 5 consecutive times while being recorded through the ear microscope. An otolaryngology resident performed the duties of a surgical tech. The videos were then all randomized and reviewed by 3 attending otolaryngologists with the following criteria: average time, number of errors, and subjective numerical grading of each attempt. Results: To date, 7 subjects have participated. From the first attempt to the fifth attempt, the average time for procedure decreased from 160 seconds to 80 seconds. The average times the myringotomy knife touched the sides of the simulated ear canal dropped from over 2.6 to 0.7 times. The average percentage of instances the grader would allow the subject to perform procedure on a real patient increased from 38% to 91%. The success of the procedure determined by the grader increased from 52% to 95%. Conclusions: No standardized training is available for myringotomy with tube insertion. Training with this device can decrease procedure time by 50%, reduce errors, and increase the confidence of attending otolaryngologists of trainees. These results show potential benefits to translate to real patients.

The Horizontal Angular Vestibulo-Ocular Reflex: A Nonlinear Mechanism for Context-Dependent Responses

Studies of the vestibulo-ocular reflex (VOR) have revealed that this type of involuntary eye movement is influenced by viewing distance. This paper presents a bilateral model for the horizontal angular VOR in the dark based on realistic physiological mechanisms. It is shown that by assigning proper nonlinear neural computations at the premotor level, the model is capable of replicating target-distance-dependent VOR responses that are in agreement with geometrical requirements. Central premotor responses in the model are also shown to be consistent with experimental observations. Moreover, the model performance after simulated unilateral canal plugging also reproduces experimental observations, an emerging property. Such local nonlinear computations could similarly generate context-dependent behaviors in other more complex motor systems.

In vitro evaluation of wear and canal transportation using reciprocating instruments: RECIPROC® vs WaveOne® files

AimTo evaluate the degree of wear and transport index associated with the use of RECIPROC®versus WaveOne®. Materials and methods30 Acrylic cubes with simulated canals were used, all geometrically identical. These were identified and photographed, being randomly assigned to two groups: G1-RECIPROC® using R25 file, and G2-WaveOne® using the Primary file. In both groups the canals were previously catheterized with K10, K15 and K20. The instrumentation was always followed by 2.5% NaOCl irrigation. After the instrumentation, the cubes were photographed again in the stereomicroscope and the resulting images were superimposed using Photoshop CS5 (v12.1, Adobe®), evaluating the differences between the two preparations with ImageJ (v1.45, NIH®) by means of comparative measurements in the apex and at 1, 2, 3, 4, 5 and 6mm. ResultsAll data was evaluated using ANOVA repeated-measurements test after verification with Kolmogorov–Smirnov test. The degree of wear obtained by RECIPROC® (M=201182) was superior and significantly different (p<0.001) than the preparation obtained by WaveOne® (M=148506). The dimension of the effect was very high (ηp2=0.544) being the confidence interval 95%. The transport index for RECIPROC® (M=−68522) was superior and significantly different (p<0.029) than the transport obtained with WaveOne® (M=−39506), being the dimension of the effect moderate (ηp2=0.160) for an IC of 95%. ConclusionsWith the limitations of this pre-clinical study, we conclude that WaveOne® accounts for lower canal wear and superiorly centered preparation when compared with RECIPROC®.