Comparative investigation of two rotary nickel-titanium instruments: ProTaper versus RaCe. Part 2. Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth

Alteration in the inherent metallic and surface properties of nickel-titanium root canal instruments to enhance performance, durability and safety: a focused review

The expanded use of nickel-titanium (NiTi) rotary instruments in root canal procedures has led to the development of a wide variety of shapes, designs and applications. Root canal anatomy has not changed, however, and the same challenges exist in both initial treatment and the revision of unacceptable treatment. These challenges include application with high levels of achievement and low to no levels of adverse effects, such as instrument fracture, root canal wall ledging, dentine wall perforation and so forth. To that end, many manufacturers have been seeking ways to alter the presently available and wide range of root canal instrument designs, with a focus on altering the surface of the alloy or altering the alloy microstructure with post-machining or post-twisting heat treatment. This focused review will address the impact that these modifications have had on instrument flexibility, resistance to cyclic fatigue and cutting efficiency.

Canal-centering ability: An endodontic challenge

During instrumentation of the root canal, it is important to develop a continuously tapered form and to maintain the original shape and position of the apical foramen. However, the presence of curvatures may cause difficulty in root canal instrumentation. The ability to keep the instruments centered is essential to provide a correct enlargement, without excessive weakening of the root structure. Several studies have shown that Ni-Ti instruments remain significantly more centered and demonstrated less canal transportation than stainless steel files. Considerable research has been undertaken to understand the several factors related to an instrument's canal-centering ability. In this article, we have discussed the influence of various parameters such as alloys used in the manufacture of instruments, instrument cross-section, taper, and have given tips on canal-centering ability.

Histological analysis of cleaning efficacy of hand and rotary instruments in the apical third of the root canal: A comparative study

AIM

To compare the cleaning efficiency of manual and rotary instrumentation in the apical third of the root canal system.

MATERIALS AND METHODS

In group 1 (n=10), instrumentation was performed with stainless steel K-file; in group 2 (n=10), it was done with hand ProTaper files; and in group 3 (n=10), instrumentation was done with ProTaper rotary. Distilled water was used for irrigation. The apical third was sectioned transversally and histologically processed. The cross sections were examined under optic microscope and debris was measured using Motic software.

RESULTS

Instrumentation with stainless steel K-files showed minimum amount of debris, followed by ProTaper hand files, and rotary ProTaper files were least effective with maximum amount of debris; however, there were no significant differences between the three experimental groups.

CONCLUSIONS

Both the manual and rotary instrumentation are relatively efficient in cleaning the apical third of the root canal system and the choice between manual and rotary instrumentation should depend on case to case basis.

A comparative evaluation of gutta-percha filled areas in curved root canals obturated with different techniques

The aim of this study was to compare different obturation techniques in severely curved canals in terms of the percentage of gutta-percha filled area and voids. The obturation times and the incidence of extrusion of filling material were also compared. Curved root canals (curvature, 25-35°) of 48 extracted human teeth were enlarged with Mtwo rotary NiTi instruments and obturated as follows: Group A: 0.04/35 matched-single-cone; Group B: cold lateral compaction with 0.04/35 gutta-percha master cone; Group C: warm vertical compaction; Group D: lateral compaction with standardized gutta-percha master cone. In all groups AHPlus was used as sealer. The teeth were sectioned horizontally at 2, 3, 4, 6 and 8 mm from the apex. The total area of each canal segment was measured and the areas of gutta-percha, sealer and voids were converted to percentages of the total area. Data were subjected to the Kruskal-Wallis and post hoc Dunn test. Obturation times were compared using ANOVA and post hoc Student-Newman-Keuls test. The matched-single-cone obturation (group A) was significantly the fastest method while warm vertical compaction (group C) required significantly more time than all other techniques (p < 0.05). No significant differences were obtained between the groups in terms of percentage of voids at any level (p > 0.05). At all levels, groups B, C, and D produced significantly higher gutta-percha filled areas (p < 0.05) and lower sealer-filled areas (p < 0.05) than group A. No significant differences were found between groups B, C, and D (p > 0.05) regarding gutta-percha and sealer-filled areas. Within the limitations of the in vitro study, it can be concluded that lateral compaction of greater taper gutta-percha cones is a fast and efficient method for obturation of curved canals.

The effect of three different rotary instrumentation systems on substance P and calcitonin gene-related peptide expression in human periodontal ligament

INTRODUCTION

The purpose of this study was to quantify the effect of three different rotary root canal preparation systems on substance P and calcitonin gene-related peptide expression in healthy human periodontal ligament.

METHODS

Fifty periodontal ligament samples were obtained from healthy premolars in which extraction was indicated for orthodontic reasons. Before extraction, 40 of these premolars were equally divided into four groups, and root canals were prepared using four different systems: the ProTaper Universal rotary system, the RaCe rotary system, the Mtwo rotary system, and the hand instrumentation technique. The remaining 10 healthy premolars that were extracted without treatment served as a negative control group. All periodontal ligament samples were processed, and SP and CGRP were measured by radioimmunoassay.

RESULTS

Greater SP and CGRP expression were found in the ProTaper Universal group followed by the hand instrumentation group, the RaCe, and the Mtwo groups. The lower SP and CGRP values were for the negative control group. The Kruskal-Wallis test showed statistically significant differences between groups (p < 0.0001). Post hoc Least Significant Difference (LSD) tests showed statistically significant differences in SP and CGRP expression between the negative control group and all the other groups except the Mtwo group. Hand instrumentation also showed statistically significant differences with all the other groups, except the ProTaper Universal group. Differences between the three rotary systems were also statistically significant.

CONCLUSION

SP and CGRP expression in periodontal ligament increases when teeth are prepared with ProTaper Universal and RaCe rotary instrumentation systems as well as with hand instrumentation. Mtwo maintains SP and CGRP levels.

Comparative evaluation of surface characteristics of dentinal walls with and without using plastic finishing file

Aim:

The aim of this in vitro research is to evaluate the debris present on the dentinal walls after instrumentation in mesiobuccal root of maxillary molar with Hand Protapers, Hand Profiles, Hand Hero Shapers, and finishing the dentinal walls with and without rotary plastic files using stereomicroscope.

Materials and Methods:

Sixty freshly extracted human maxillary first molar teeth were divided into two groups of 30 teeth each (group A and B). Both the groups were divided into three subgroups of 10 teeth each (group A had subgroups A1, A2, and A3) and (group B had subgroups B1, B2 and B3). In group A, all the 30 canals were subjected to cleaning and shaping with three different instruments system and kept unfinished. This group was named as unfinished group. In group B, all the 30 canals were subjected to cleaning and shaping with three different instruments system followed by finishing with plastic files. This group was named as finished group. The crown of each tooth was sectioned at the cementoenamel junction. Canals were prepared following conventional principles of crown down technique. After splitting the roots longitudinally, the dentinal debris of each root canal was evaluated in three areas (coronal, middle and apical thirds of the root) by means of numerical evaluation scale, using a stereomicroscope.

Results:

Stereomicroscopic evaluations showed that there was no significant difference in the debris scores between the subgroups when the canals were instrumented with hand Protaper, hand Profile and hand Hero Shaper in all the thirds. There was no significant difference in scores between the unfinished group and the finished group in the coronal third but significant differences were seen in middle third and apical third.

Conclusions:

After instrumentation with different hand instruments, the use of plastic finishing files showed cleaner canal walls.

Shaping ability of four nickel-titanium rotary instruments in simulated S-shaped canals

INTRODUCTION

The purpose of this study was to compare the shaping ability of ProTaper, Mtwo, BioRaCe, and BioRaCe + S-Apex instruments in simulated canals with an S-shaped curvature.

METHODS

Canal transportation and aberrations were assessed by comparing the preinstrumentation and postinstrumentation images under a stereomicroscope. Analysis of variance and post hoc Student-Newman-Keuls test were used for statistical analysis.

RESULTS

ProTaper instruments caused more pronounced canal transportation in the apical curvature (P < .01) than all other instruments. The use of ProTaper, Mtwo, and BioRaCe instruments resulted in more canal aberrations compared with BioRaCe + S-Apex (P < .05).

CONCLUSIONS

NiTi systems including less tapered and more flexible instruments like S-Apex seem to be favorable when preparing S-shaped canals.

A comparative scanning electron microscopic study of the effect of three different rotary instruments on smear layer formation

The aim of this study was to evaluate the effect of RaCe, FlexMaster and ProFile rotary instruments on smear layer formation by scanning electron microscopy. Eighty-four caries-free freshly extracted human single-rooted teeth were selected and divided into three groups, each containing 28 teeth. The teeth were instrumented with rotary instruments sequentially: Group A: ProFile Rotary Instruments; Group B: FlexMaster Rotary Instruments; and Group C: RaCe Rotary Instruments. Instrumentation was performed by the crown-down method and according to the manufacturer's instructions. The specimens were then examined with SEM according to Hülsmann's classification. One-way ANOVA and a post hoc Tukey test were used for statistical analysis. The results showed that there were no statistically significant differences among the three groups in the coronal third (P = 0.39), but at the apical and middle thirds there were statistically significant differences between the RaCe group and the other groups (P < 0.05). Smear layer in the RaCe group was less than that in the ProFile and FlexMaster groups, but the difference between the ProFile group and FlexMaster group was not statistically significant (P > 0.05). It was concluded that RaCe Rotary Instruments produce less smear layer than FlexMaster and ProFile Rotary Instruments.

Radiological evaluation of the morphological changes of root canals shaped with ProTaper for hand use and the ProTaper and RaCe rotary instruments

This study evaluated, by means of the radiography examination, the occurrence of deviations in the apical third of root canals shaped with hand and rotary instruments. Sixty mandibular human molars were divided into three groups. The root canals in group 1 were instrumented with ProTaper (Dentsply/Maillefer, Ballaigues, Switzerland) for hand use, group 2 with ProTaper and group 3 with RaCe. The images obtained by double superimposition of the pre- and postoperative radiographs were evaluated by two endodontists with the aid of a magnifier-viewer and a fivefold magnifier. Statistical analysis was performed using the Fisher-Freeman-Halton. The instrumentation using the ProTaper for hand use showed 25% of the canals with a deviation in the apical third, as did the ProTaper, while the corresponding figure for the RaCe (FKG Dentaire, La-Chaux-de-Fonds, Switzerland) was 20%, but these results were not statistically significant. There was no correlation between the occurrence of deviations in the apical third and the systems used.

In vitro comparative study of manual and mechanical rotary instrumentation of root canals using computed tomography

This in vitro study compared, using computed tomography (CT), the amount of dentin removed from root canal walls by manual and mechanical rotary instrumentation techniques. Forty mandibular incisors with dental crown and a single canal were selected. The teeth were randomly assigned to two groups, according to the technique used for root canal preparation: Group I - manual instrumentation with stainless steel files; Group II - mechanical instrumentation with RaCe rotary nickel-titanium instruments. In each tooth, root dentin thickness of the buccal, lingual, mesial and distal surfaces in the apical, middle and cervical thirds of the canal was measured (in mm) using a multislice CT scanner (Siemens Emotion, Duo). Data were stored in the SPSS v. 11.5 and SigmaPlot 2001 v. 7.101 softwares. After crown opening, working length was determined, root canals were instrumented and new CT scans were taken for assessment of root dentin thickness. Pre- and post-instrumentation data were compared and analyzed statistically by ANOVA and Tukey's post-hoc test for significant differences (p=0.05). Based on the findings of this study, it may be concluded that regarding dentin removal from root canal walls during instrumentation, neither of the techniques can be considered more effective than the other.

Comparison of effects of ProTaper, HeroShaper, and Gates Glidden Burs on cervical dentin thickness and root canal volume by using multislice computed tomography

The purpose of this study was to compare the effects of 3 different instruments used to prepare curved root canals on the remaining cervical dentin thickness and total amount of dentin removed from root canals during instrumentation by using multislice computed tomography. Mesiobuccal canals of 45 mandibular first molars with curvature between 30-40 degrees were divided into 3 equal groups: ProTaper, Hero Shaper, and Gates Glidden Bur with Flex-R hand file. Cervical dentin thickness and canal volume were measured before and after instrumentation by using multislice computed tomography and image analysis software. The results indicated that ProTaper removed significantly less cervical dentin from distal wall of the root (dangerous zone) than HeroShaper and Gates Glidden Bur (P < .05). The total dentin removed during canal instrumentation was significantly more with ProTaper system (P < .05).

Scanning electron microscopic evaluation of debris and smear layer remaining following use of ProTaper and Hero Shaper instruments in combination with NaOCl and EDTA irrigation

OBJECTIVE

The purpose of this study was to evaluate the amounts of debris and smear layer remaining on canal walls after preparation with ProTaper and Hero Shaper instruments in combination with NaOCl and EDTA irrigation in curved root canals.

STUDY DESIGN

A total of 55 root canals were randomly divided into 2 instrumentation groups of 20 canals each and 1 negative control group of 15 canals. The canals in each of the 2 instrumentation groups were prepared with ProTaper or Hero Shaper instruments. Irrigation was performed with 5% NaOCl and 17% EDTA solutions. The control group was not instrumented. The remaining debris and smear layer were evaluated from scanning electron photomicrographs at x200 and x1,000 magnification taken in the coronal, middle, and apical thirds of the canals at both inner and outer canal walls. A 5-category scoring system for debris and smear layer was used. Statistical analysis was carried out using the Kruskal-Wallis and Mann-Whitney rank sum tests.

RESULTS

Completely clean root canals were not found in either instrumentation group. In the coronal and middle thirds, the canal walls of both instrumentation groups were clean, with no or only small areas of debris and smear layer. In the apical region, there were higher scores in terms of debris and smear layer in both instrumentation groups. No significant difference was found at the inner wall of the 2 instrumentation groups in terms of debris mean score. However, the outer canal walls prepared with ProTaper showed lower debris score compared with those prepared with Hero Shaper (P < 0.001). Concerning the smear layer, both the inner and outer canal walls prepared with ProTaper showed lower mean scores compared with those prepared with Hero Shaper (P < 0.001).

CONCLUSIONS

Within the limitations of this study, both instruments in combination with NaOCl and EDTA irrigation produced a clean and debris-free canal surface in the coronal and middle thirds, but were unable to produce a canal surface free from debris and smear layer in the apical third. However, the canals prepared with ProTaper instruments showed smaller amounts of debris and smear layer remaining in the apical region.

Shaping ability of progressive versus constant taper instruments in curved root canals of extracted teeth

AIM

To compare the shaping ability of progressive versus constant taper shaft instruments in curved root canals of extracted human teeth.

METHODOLOGY

A total of 40 root canals of mandibular molars with curvatures ranging between 20 degrees and 40 degrees were divided into two groups of 20 canals each and embedded in a muffle system. The root canals sectioned horizontally at three levels before preparation and then remounted into the mould. All root canals were prepared with ProTaper (progressive taper) or Hero Shaper (constant taper) instruments. Pre- and post-instrumentation radiographs and cross-sectional images were obtained. The parameters evaluated were: working safety (instrument failure, apical blockage and loss of working length) and shaping ability (straightening, cross-sectional area, transportation and centring ability). The data were analysed statistically using Student's t-test.

RESULTS

No instrument fractured during preparation. One Hero Shaper instrument permanently deformed. Both instrument systems maintained working length well. The canals prepared with Hero Shaper instruments were straightened to a lesser degree (P < 0.05). ProTaper instruments removed more dentine in the coronal and the middle sections of the canals. Canals prepared with Hero Shaper instruments had less transportation (P < 0.01) and better centring ability (P < 0.05) in the apical section.

CONCLUSIONS

Both instrument systems were safe to use and maintained working length well. The canals prepared with Hero Shaper had less transportation and were better centred in the apical region, possibly because their smaller taper reduced instrument stiffness.

Fatigue testing of a NiTi rotary instrument. Part 2: fractographic analysis

AIM

To examine the topographic features of the fracture surface of a NiTi instrument after fatigue failure, and to correlate the measurements of some features with the cyclic load.

METHODOLOGY

A total of 212 ProFile rotary instruments were subjected to a rotational-bending test at various curvatures until broken. The fracture surface of all fragments was examined by SEM to identify the crack origins. The crack radius, i.e. extent of the fatigue-crack growth towards the centroid of the cross-section, was also measured, and correlated with the strain amplitude for each instrument.

RESULTS

All fracture surfaces revealed the presence of one or more crack origins, a region occupied by microscopic striations, and an area with microscopic dimples. The number of specimens showing multiple crack origins was significantly greater in the group fatigued under water than in air (P < 0.05). A linear relationship between the reciprocal of the square root of the crack radius and the strain amplitude was discernible (P < 0.001), the slopes of which were not significantly different for instruments fatigued in air and water.

CONCLUSIONS

The fractographic appearance of NiTi engine-files that had failed because of fatigue is typical of that for other metals. The fatigue behaviour of NiTi instruments is adversely affected by water, not only for the low-cycle fatigue life, but also the number of crack origins. There appears to be a critical extent of crack propagation for various strain amplitudes leading to final rupture (akin to the Griffith's criterion for brittle materials).

The influence of various automated devices on the shaping ability of Mtwo rotary nickel-titanium instruments

AIM

To compare the shaping ability of Mtwo rotary nickel-titanium instruments in simulated curved canals and in curved canals of extracted teeth when set into permanent rotation with two different torque-limited automated devices.

METHODOLOGY

Root canal instrumentation was performed with two different torque-limited automated devices (Mtwo direct handpiece and Endo IT motor) using Mtwo rotary nickel-titanium instruments up to size 35. Simulated canals: 28 degrees and 35 degrees curved canals in resin blocks (n = 20 canals in each group) were prepared. Pre- and post-instrumentation images were recorded and assessment of canal shape was completed with a computer image analysis program. Extracted teeth: a total of 40 curved root canals were divided into two groups, which were balanced with respect to the angle and the radius of canal curvature. Straightening of the canal curvatures was determined with a computer image analysis program. Incidence of canal aberrations, preparation time, changes of working length and instrument failures were recorded both in simulated and real canals and were analysed using the t-test and a chi-square test.

RESULTS

In simulated canals, instrumentation with Endo IT was significantly faster than with Mtwo direct (P < 0.05). No significant differences between the two devices were noted when all other parameters were assessed (P > 0.05). Only one instrument separated (Mtwo direct) during the enlargement of 28 degrees curved simulated canals. All systems maintained working distance well.

CONCLUSIONS

Both systems respected original root canal curvature well and were safe, indicating that the Mtwo direct handpiece is suitable for preparing curved root canals with the Mtwo instruments.

The Influence of Canal Curvature on the Mechanical Efficacy of Root Canal Irrigation In Vitro Using Real-Time Imaging of Bioluminescent Bacteria

There are no quantitative data on the mechanical efficacy of irrigation in the removal of bacteria from curved canals. This study quantitatively analyzed the effects of root canal curvature and preparation size on the mechanical efficacy of irrigation using 33 mandibular single-rooted bicuspids allocated to groups according to root canal curvatures, group 1 (straight) 4 to 8 degrees, group 2 (intermediate curvature) 15 to 19 degrees, and group 3 (greatest curvature) 24 to 28 degrees. Teeth were sequentially instrumented to sizes 27/.04, 36/.04, and 46/.04 using a crown-down technique. Suspensions of the bioluminescent reporter strain Pseudomonas fluorescens 5RL (1.5 x 10(6) cells) were inoculated into canals of sterilized teeth after each sequential instrumentation. Canals were irrigated with 6 ml of irrigant delivered 1 mm from working length using a 30-gauge needle. Remaining bacteria were quantified using real-time bioluminescent imaging. Irrigation was significantly less effective in 24 to 28 degrees curvature canals prepared to size 27/.04 compared to 46/.04 (p < 0.007, repeated-measures ANOVA).

Deformation and fracture of RaCe and K3 endodontic instruments according to the number of uses

AIM

To evaluate, by scanning electron microscopy, the deformation and fracture of NiTi RaCe and K3 size 25, 0.04 taper instruments.

METHODOLOGY

Ten sets of instruments from RaCe and K3 NiTi rotary systems were used to prepare 100 simulated canals in epoxy resin blocks with 20 or 40 degree curvatures beginning 8 or 12 mm from the orifice. Each instrument set was used to prepare five simulated canals using a crowndown technique. The size 25, 0.04 taper instruments were analysed by SEM when new and again after each use. Three observers scored images of the instruments after each use for distortion of the spirals (no distortion, distortion of one spiral or distortion of more than one spiral), wear (no wear, small, moderate or severe wear) and fracture (yes or no). Two-way anova was used to analyse differences between instruments for distortion and wear; Fisher's exact test looked for differences related to fracture of instruments.

RESULTS

No fractures occurred with K3 instruments, whereas six RaCe instruments fractured (P = 0.005). A statistically significant difference occurred between RaCe and K3 instruments in terms of distortion of spirals and surface wear (P < 0.001). Distortion of spirals and wear increased with progressive use of RaCe instruments, whereas K3 instruments remained relatively undamaged after their fifth use. The simulated canals with smaller radii of curvature were positively associated with fracture of RaCe instruments.

CONCLUSIONS

A significant difference was found between RaCe and K3 in terms of deformation and fracture of size 25, 0.04 taper instruments; K3 instruments had more favourable results.

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.

Comparative Evaluation of Three Nickel-Titanium Instrumentation Systems in Human Teeth Using Computed Tomography

This study investigated several parameters of root canal preparation with three different rotary NiTi systems: Hero Shaper, ProTaper, and RaCe. The parameters evaluated were: changes in root canal volume and cross-sectional area, canal transportation, and working time. Curved, mesial molar roots were scanned in a computed tomography (CT) unit before and after instrumentation. Cross-sectional views of each canal were obtained at 1 mm intervals. Postinstrumentation volume and cross-sectional area of root canals and the extent of transportation were calculated using image analysis software and, thereafter, subjected to statistical analysis. ProTaper removed significantly more dentin than Hero Shaper (p < 0.05). Instrumentation increased the cross-sectional area at all cutplanes, while the difference between test groups was not significant (p > 0.05). RaCe files significantly transported the canals at the coronal level (p < 0.05). There was no difference between any rotary systems in regards to working time.

Efficacy of different rotary instruments for gutta-percha removal in root canal retreatment

The purpose of this study was to evaluate the efficiency of FlexMaster, ProTaper, and RaCe rotary instruments compared with Hedström files for removal of gutta-percha during retreatment. Sixty mandibular premolars with one single straight canal were instrumented with K-type files and filled using cold lateral compaction and sealer. The teeth were randomly divided into four groups of 15 specimens each. After repreparation with Gates Glidden burs and the test instruments the specimens were cleared. The area of remaining gutta-percha/sealer on the root canal wall was measured from two directions. The RaCe group showed significantly less residual obturation material than FlexMaster and Hedström group (p < 0.05; closed test procedure). There was no difference between ProTaper and all other instruments (p > 0.05). ProTaper and RaCe instruments required significantly less time for retreatment than FlexMaster and Hedström files (p < 0.05). One RaCe file, two ProTaper, and two FlexMaster instruments separated. RaCe cleaned obturated canals more effectively than hand files and FlexMaster files.

Shaping ability and safety of five different rotary nickel-titanium instruments compared with stainless steel hand instrumentation in simulated curved root canals

OBJECTIVE

To compare the shaping ability and safety of engine-driven FlexMaster, GT Rotary, ProFile, ProTaper, and RaCe rotary instrumentation and Hedström hand instrumentation in simulated root canals.

STUDY DESIGN

One hundred fifty simulated colored root canals with a curvature of 20 degrees and a radius of 10 mm were randomly distributed among 6 groups of 25 specimens each. After preparation to apical size 30 the area of remaining color on the canal wall indicating unprepared areas was measured in mm2 using image analyzer software.

RESULTS

Specimens treated with RaCe left least areas of remaining color compared to all other groups (P < .001), followed by ProTaper. Preparation with ProFile left behind the highest amount of unprepared areas. The ProFile group revealed significantly more remaining color than ProTaper, GT Rotary, and FlexMaster (P < .05). Four FlexMaster files separated.

CONCLUSION

RaCe rotary files were safe and more effective compared to the other instruments.

Effectiveness of a hand file and three nickel-titanium rotary instruments for removing gutta-percha in curved root canals during retreatment

OBJECTIVE

This study intended to compare the effectiveness of hand files and FlexMaster, ProTaper, and RaCe rotary instruments for removing gutta-percha in curved root canals during retreatment.

STUDY DESIGN

Sixty curved mandibular premolars were randomly divided into 4 groups of 15 specimens each. The canals were enlarged and obturated using lateral condensation technique. After repreparation with the test instruments the specimens were cleared. The area of remaining obturation material was measured from 2 directions. Statistical analysis was performed using the Kruskal-Wallis test and a closed test procedure.

RESULTS

RaCe instruments revealed significantly less residual obturation material than FlexMaster files (P < .05). No significant difference was found among the hand file, ProTaper, and FlexMaster groups (P > .05). There were 5 fractured instruments in the ProTaper group and 3 in the FlexMaster group.

CONCLUSION

The RaCe system is an efficient and safe device for gutta-percha removal in curved root canals.

Comparative study on the shaping ability and cleaning efficiency of rotary Mtwo instruments. Part 2. Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth

AIM

To compare the cleaning effectiveness and shaping ability of Mtwo, K3, and RaCe nickel-titanium rotary instruments during the preparation of curved root canals in extracted human teeth.

METHODOLOGY

A total of 60 root canals of mandibular and maxillary molars with curvatures ranging between 25 degrees and 35 degrees were divided into three groups of 20 canals. Based on radiographs taken prior to instrumentation with the initial instrument inserted into the canal, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared using a low-torque control motor. Using pre- and post-instrumentation radiographs, straightening of the canal curvatures was determined with a computer image analysis program. The amount of debris and smear layer was quantified on the basis of a numerical evaluation scale. The data established for scoring the debris and the smear layer was separately recorded and analysed statistically using the Kruskal-Wallis test.

RESULTS

During preparation no instrument separated. Completely clean root canals were never observed. For debris removal Mtwo instruments achieved significantly better results (P < 0.001) than K3 and RaCe instruments. The results for remaining smear layer were similar and not significantly different (P > 0.05). Mtwo instruments maintained the original canal curvature significantly better (P < 0.05) than the other instruments. Instrumentation with Mtwo files was significantly faster than with K3 or RaCe instruments (P < 0.05).

CONCLUSIONS

Under the conditions of this study, Mtwo instruments resulted in good cleaning and maintained the original curvature significantly better than K3 or RaCe files.

Effectiveness of hand and rotary instrumentation for removing a new synthetic polymer-based root canal obturation material (Epiphany) during retreatment

AIM

To evaluate the effectiveness of hand and rotary instrumentation for removal of vertically compacted Epiphany and gutta-percha during retreatment.

METHODOLOGY

Sixty extracted single-rooted maxillary central incisors were enlarged to size 40 using FlexMaster instruments. The teeth were randomly divided into four groups of 15 specimens each. The canals of two groups were obturated using vertically compacted Epiphany. The others were filled with vertically compacted gutta-percha and AH Plus sealer. One Epiphany group and one gutta-percha group was reinstrumented with Gates Glidden burs and Hedström files. In the other two groups, obturation material was removed using Gates Glidden burs and RaCe rotary instruments. After clearing the roots, the area of remaining obturation material on the root canal wall was measured using a computer image analysis program. Statistical analysis was performed using Repeated Measures Analysis of Variance and anova.

RESULTS

Retreatment of specimens obturated with gutta-percha showed significantly more remaining obturation material than specimens filled with Epiphany (P < 0.05). No difference was found between the removal with Hedström files and with RaCe instruments (P > 0.05). Regarding the mean time of retreatment and time required for reaching the working length, Hedström files were significantly faster than RaCe instruments (P < 0.05). The times did not depend on the kind of obturation material (P > 0.05).

CONCLUSIONS

Vertically compacted Epiphany in combination with Epiphany Root Canal Sealant was removed more effectively than gutta-percha and AH Plus sealer. Hedström files were more rapid than RaCe rotary instruments.

Comparison of the cleaning efficacy of the FKG race system and hand instrument in molar root canal

Introduction and objective:

The aim of this study was to evaluate the ability of root canal cleaning of the RaCe rotary instrumentation system (FKG Dentaire – La-Cheaux-de Fonds – Switzerland), compared to manual filing with Stainless Steel K-files (Maillefer Instruments – Ballaigues – Switzerland).

Material and Method:

Twenty extracted human teeth (maxillary molars) were selected and their pulp tissue was removed after coronal access. The root canals were filled with a dye (India ink) and allowed to dry for 48 hours, followed by establishment of the working length of the mesiobuccal root; then, half of the specimens were instrumented by the modified Oregon technique and the other half were instrumented by crown-down sequence of the RaCe system. After preparation, the teeth were longitudinally sectioned and evaluated according to the amount of remaining dye.

Results:

Data obtained were registered as numerical scores, and the arithmetic means were compared between groups using the Mann Whitney test. Both techniques were unable to completely clean the interior of the root canals, with a better performance of the manual technique only at the middle third.

Conclusion:

It could be concluded that the RaCe system was able to provide satisfactory cleaning, similar to that obtained by the manual instrumentation technique.

Influence of different types of automated devices on the shaping ability of rotary nickel-titanium FlexMaster instruments

AIM

To compare the shaping ability of rotary FlexMaster nickel-titanium instruments in simulated curved canals and in curved canals of extracted teeth when set into permanent rotation with three different torque-limited automated devices.

METHODOLOGY

Root canal instrumentation was performed with three different torque-limited automated devices (ENDOadvance, SIRONiTi and Endo IT motor) by FlexMaster nickel-titanium instruments up to size 35. Simulated canals: 28 degree and 35 degree curved canals in resin blocks (n = 20 canals in each group) were prepared. Pre- and post-instrumentation images were recorded and assessment of canal shape was completed with a computer image analysis program. Extracted teeth: A total of 60 curved root canals were divided into three groups, which were balanced with respect to the angle and the radius of canal curvature. Straightening of the canal curvatures was determined with a computer image analysis program. Incidence of canal aberrations, preparation time, changes of working length and instrument failures were recorded both in simulated and real canals.

RESULTS

In simulated and real canals, instrumentation with Endo IT was significantly faster than with SIRONiTi (P < 0.05). With respect to canal aberrations in simulated canals, there were no significant differences between the devices (P > 0.05), even though more aberrations were created with ENDOadvance and SIRONiTi. In real canals, the Endo IT motor resulted in significantly less straightening during instrumentation (P < 0.05) than SIRONiTi. A total of three instruments separated (one file in each group) during the enlargement of 35 degree curved simulated canals. All systems maintained working distance well.

CONCLUSIONS

All systems respected original root canal curvature well and were safe, indicating that torque-limited rotation handpieces are suitable for preparing curved root canals.

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.

Comparison of root canal preparation using RaCe and ProTaper rotary Ni-Ti instruments

AIM

To compare various parameters of root canal preparation using RaCe (FKG Dentaire, La-Chaux-de-Fonds, Switzerland) and ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) nickel-titanium (Ni-Ti) instruments.

METHODOLOGY

Fifty extracted mandibular molars with mesial root canal curvatures between 20 degrees and 40 degrees were embedded in a muffle system. All root canals were prepared to size 30 using RaCe or ProTaper rotary instruments in low-torque motors with torque control and constant speed of 300 r.p.m. (ProTaper with ATR Tecnika, Advanced Technology Research, Pistoia, Italy; RaCe with EndoStepper, S.E.T., Olching, Germany). In both groups irrigation was performed with 2 mL NaOCl (3%) after each instrument size. Calcinase-Slide (lege artis, Dettenhausen, Germany) was used as a chelating agent with each instrument. The following parameters were evaluated: straightening of curved root canals, postoperative root canal cross-sections, safety issues and working time. Cleanliness of the root canal walls was investigated under the SEM using 5-score indices for debris and smear layer. Statistical analysis was performed using the following tests: Wilcoxon's test for straightening and working time was used (P < 0.05); Fisher's exact test for comparison of cross-sections and root canal cleanliness (P < 0.05).

RESULTS

Both Ni-Ti systems maintained curvature well; the mean degree of straightening was less than 1 degrees for both systems. Following preparation with RaCe, 49% of the root canals had a round or oval diameter and 50% an irregular diameter, ProTaper preparations resulted in a round or oval diameter in 50% of the cases. For debris, RaCe and ProTaper achieved 47 and 49% scores of 1 and 2, respectively; there was no significant difference. For smear layer, RaCe and ProTaper achieved 51 and 33% scores 1 and 2, respectively; no statistically significant differences were apparent for the coronal and middle sections of the root canals, but RaCe performed significantly better in the apical region (Fisher's exact test, P = 0.0392). Two roots lost working length with RaCe instruments, whilst ProTaper preparation resulted in two roots loosing working length and one fractured instrument. Mean working time was shorter for ProTaper (90.9 s) than for RaCe (137.6 s); the difference was significant (Wilcoxon's test, P = 0.011).

CONCLUSIONS

Both systems respected original root canal curvature well and were safe to use. Cleanliness was not satisfactory for both systems.