A comparison of shaping ability using ProFile, GT file, and Flex-R endodontic instruments in simulated canals

Numeric Evaluation of Innovate Spring Machined Nickel-Titanium Rotary Instruments: A 3-dimensional Finite Element Study

INTRODUCTION

The purpose of this study was to investigate if machined springs in nickel-titanium (NiTi) rotary instruments can improve their mechanical properties. The bending and torsion properties were assessed using finite element (FE) model analysis.

METHODS

A basic 3-dimensional file model without a spring was created with apical size #25, 25-mm full length, and 16-mm cutting flutes. Three other models were created with a spring machined into their shaft portion with different numbers of spring coils: standard (STspr), 10% more (INspr), and 10% less (DEspr). To compare the mechanical responses among the 4 FE models, file bending and torsion were simulated using FE analysis.

RESULTS

Spring machined NiTi rotary instruments showed higher torsional resistance and less bending stiffness than the same instrument without. The spring machined models required more torque to bend or rotate the DEspr model than was required for the STspr and INspr models; however, the STSpr and INSpr models were similar.

CONCLUSIONS

Within the limitations of this study, the FE analysis indicated that machining a spring into the shaft of NiTi rotary instruments improved torsional resistance and bending flexibility. Therefore, spring machining has the potential to increase the durability of the NiTi rotary instruments.

Nickel-Titanium Rotary Instruments: Development of the Single-File Systems

Over the past two decades, the nickel-titanium (NiTi) rotary instruments have highly improved the quality of the cleaning and shaping of the root canals. The superelasticity and shape memory of these instruments reduce the possibility of the canal transportation along with saving the time for both the patients and the clinicians. Several commercial types of these instruments, produced by different manufacturers, have currently become available by modifying the characteristics of the wonder NiTi alloy and also the cross-sectional shapes, cutting edges, tapering and numbers and distances of the flutes of the instruments. Up to this date, five generations for NiTi rotary instruments have been described according to the time of introduction, properties, and method of application. The aim of this article is to review the evolution of these five generations of NiTi rotary instruments since their inception.

Preference of undergraduate students after first experience on nickel-titanium endodontic instruments

Objectives

This study aimed to compare two nickel-titanium systems (rotary vs. reciprocating) for their acceptance by undergraduate students who experienced nickel-titanium (NiTi) instruments for the first time.

Materials and Methods

Eighty-one sophomore dental students were first taught on manual root canal preparation with stainless-steel files. After that, they were instructed on the use of ProTaper Universal system (PTU, Dentsply Maillefer), then the WaveOne (WO, Dentsply Maillefer). They practiced with each system on 2 extracted molars, before using those files to shape the buccal or mesial canals of additional first molars. A questionnaire was completed after using each file system, seeking students' perception about 'Ease of use', 'Flexibility', 'Cutting-efficiency', 'Screwing-effect', 'Feeling-safety', and 'Instrumentation-time' of the NiTi files, relative to stainless-steel instrumentation, on a 5-point Likert-type scale. They were also requested to indicate their preference between the two systems. Data was compared between groups using t-test, and with Chi-square test for correlation of each perception value with the preferred choice (p = 0.05).

Results

Among the 81 students, 55 indicated their preferred file system as WO and 22 as PTU. All scores were greater than 4 (better) for both systems, compared with stainless-steel files, except for 'Screwing-effect' for PTU. The scores for WO in the categories of 'Flexibility', 'Screwing-effect', and 'Feeling-safety' were significantly higher scores than those of PTU. A significant association between the 'Screwing-effect' and students' preference for WO was observed.

Conclusions

Novice operators preferred nickel-titanium instruments to stainless-steel, and majority of them opted for reciprocating file instead of continuous rotating system.

Comparison of single cone obturation performance of different novel nickel-titanium rotary systems

OBJECTIVES

The purpose of this study was to compare several different single-cone obturations in the gutta-percha-filled areas (PGFA), sealer-filled areas (PSFA) and voids, also determining the volumetric characteristics of the tested cones.

MATERIALS AND METHODS

Curved mesial roots of 120 mandibular molars were instrumented using several different systems (ProTaper Next, Twisted File Adaptive, OneShape, ProTaper Universal, WaveOne and Reciproc) and filled with corresponding single cones. The teeth were then sectioned horizontally at 2, 4, 6 and 8 mm from the apex. The area values of each section were calculated and converted to percentages (PGFA, PSFA and voids) of the total area. To determine volumetric characteristics of the tested cones, 20 gutta-percha points of each tested group were scanned with CBCT using the same parameters.

RESULTS

The ProTaper Next and WaveOne groups presented the most PGFA and least PSFA. The Twisted File Adaptive group presented the least PGFA and most PSFA (p < 0.05) and the least gutta-percha volume.

CONCLUSIONS

The Twisted File Adaptive system matched cones had the least volume and the least PGFA in severely curved mesiobuccal canals of mandibular first molars. Single matched cones volume varied.

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.

The quality of single cone and laterally compacted gutta-percha fillings in small and curved root canals as evidenced by bidirectional radiographs and fluid transport measurements

OBJECTIVE

The aim of this study was to examine the quality of root fillings in small and curved root canals using bidirectional radiographs and fluid transport (FT) measurements.

STUDY DESIGN

Root canals in eighty 38 degrees -curved mesial roots of mandibular molars were prepared using a balanced force technique. Samples were divided into 4 groups of 20 each and obturated by either the cold lateral compaction (LC) or the single cone (SC) technique, using either epoxy resin-based or zinc oxide-eugenol sealers. Bidirectional (buccolingual and mesiodistal) radiographs were acquired from each root. The voids along the root filling were assessed. The FT along the root filling was measured using an FT monitoring device. The differences between the groups regarding FT and the bidirectional radiographic score were analyzed by means of a Kruskal-Wallis test. The correlation between the FT values and the radiographic scores were analyzed using a Spearman test.

RESULTS

Three groups of LC or SC fillings containing epoxy resin-based sealers exhibited similar radiographic scores and FT values (P > .05). The group of SC fillings that contained zinc oxide-eugenol sealer had worse radiographic scores than the other groups (P = .047). The bidirectional radiographic scores and the FT values for the 80 filled roots were strongly correlated (r(2) = 0.519; P = .00001).

CONCLUSION

Root fillings of similar quality were confirmed in small and curved root canals filled using either a single cone or laterally compacted gutta-percha and epoxy resin-based sealers.

Comparison of forces generated during root canal shaping and residual stresses of three nickel-titanium rotary files by using a three-dimensional finite-element analysis

The study was aimed to compare the stress distribution during simulated root canal shaping and to estimate the residual stress thereafter for some nickel-titanium rotary instruments. Three brands of instruments (ProFile, ProTaper, and ProTaper Universal; Dentsply Maillefer) were scanned with micro-computed tomography to produce a real-size, 3-dimensional model for each. The stresses on the instrument during simulated shaping of a root canal were analyzed numerically by using a 3-dimensional finite-element package, taking into account the nonlinear mechanical behavior of the nickel-titanium material. From the simulation, the original ProTaper design showed the greatest pull in the apical direction and the highest reaction torque from the root canal wall, whereas ProFile showed the least. In ProTaper, stresses were concentrated at the cutting edge, and the residual stress reached a level close to the critical stress for phase transformation of the material. The residual stress was highest in ProTaper followed by ProTaper Universal and ProFile.

Comparison of root canal preparation with two rotary NiTi instruments: ProFile .04 and GT Rotary

AIM

To compare root canal preparation using ProFile .04 and GT Rotary nickel-titanium instruments (both Dentsply Maillefer, Ballaigues, Switzerland).

METHODOLOGY

Fifty extracted mandibular molars with mesial root canal curvatures between 20 and 40 degrees were randomly divided into two groups and embedded in a muffle system. All root canals were prepared to size 45 using ProFile .04 or GT rotary instruments. The following parameters were evaluated: straightening of root canal curvature, postoperative root canal cross-section, cleaning ability, safety issues and working time.

RESULTS

Both NiTi systems maintained curvature well; the mean degree of straightening was <1 degrees . The majority of the root canals prepared with ProFile .04 (80.8%) and GT (84.0%) postoperatively showed a round or oval cross-section. For debris, ProFile .04 and GT rotary achieved 67.1% and 71.6% scores of 1 and 2, respectively. Concerning the coronal region statistical analysis showed a better result for GT than for ProFile .04. For the middle and apical thirds of the root canals, results did not differ significantly. None of the two systems completely removed smear layer. Ten procedural incidents occurred with ProFile .04 compared with five with GT. Mean working time was shorter for ProFile .04 (131.8 s) than for GT (143.7 s); the difference was not significant.

CONCLUSIONS

Both systems respected original root canal curvature well and were safe to use. Smear layer removal was not satisfactory with either systems.

A Comparative Photoelastic Stress Analysis of Internal Root Stresses between RC Prep and Saline When Applied to the Profile/GT Rotary Instrumentation System

The purpose of this study was to measure and compare the amount of stress produced by GT ProFile (GT) and ProFile (PF) rotary files lubricated with either RC Prep (RCP) or saline (S) on the walls of prepared simulated canals. Twenty-four 10-mm long canals with a 10 mm radius of curvature were prepared in PL-2 photoelastic acrylic blocks which were lubricated with either RCP or S. The files were inserted into a Nouvag handpiece mounted to an Instron 4502 universal testing machine and lowered into the canal at a rate of 60 mm/min and a rotational speed of 300 RPM. The following four GTs and four PFs were sequentially introduced into predetermined depths of each canal: 20/.10, 20/.08, 20/.06, 20/.04, 40/.04, 35/.04, 30/.04, and 25/.04. Total areas of stress created by each file were captured by digital video images and measured using Image J software. Statistical analysis of the data was performed using a two-way ANOVA (p < 0.05, n = 24). The GT/RCP group demonstrated a significant average of 64.22% less stress than GT/S group. The PF (25, 30, and 35)/RCP groups demonstrated a significant average of 27.02% less stress than the same S groups. PF (40) produced a negligible amount of stress regardless of the lubricant type. The results reveal that using RCP as a lubricant when instrumenting curved canals with GT and PF results in less stress when compared to saline.

Comparative evaluation of the preparation efficacies of HERO Shaper and Nitiflex root canal instruments in curved root canals

OBJECTIVES

To comparatively evaluate the shaping efficacies of HERO Shaper rotary instruments and Nitiflex hand files.

STUDY DESIGN

The mesial roots of 40 mandibular molars were used. In 20 teeth, the mesiobuccal canals were instrumented with HERO Shaper and the mesiolingual canals with Nitiflex. In the remaining 20 teeth, the mesiobuccal canals were instrumented with Nitiflex and the mesiolingual canals with HERO Shaper. Pre- and postoperative sections were obtained from the coronal, middle, and apical portions and analyzed. Statistical analysis was performed using the Student t test.

RESULTS

More dentin was removed from the middle portion with HERO Shaper (P < .05). No statistically significant difference was observed in terms of transportation (P>.05). No instrument fracture or deformation was noted.

CONCLUSIONS

Both HERO Shaper and Nitiflex can be recommended for clinical practice. Further studies can focus on the comparison of HERO Shaper with other rotary instruments as there is an increasing trend for the utilization of these systems.

Shaping ability of two rotary instruments in simulated canals: stainless steel ENDOflash and nickel-titanium HERO Shaper

AIM

To compare the shaping ability of two rotary instruments in simulated curved canals: stainless steel ENDOflash Files (KaVo, Biberach, Germany) and the recently introduced nickel-titanium HERO Shaper instruments (Micro-Mega, Besançon, France).

METHODOLOGY

Simulated root canals with 35 degree curves in resin blocks were prepared to size 30, .04 taper (HERO Shaper) using a crowndown technique or size 30, .02 taper (ENDOflash) using a rotary motion and a rotation speed of 400 or 250 rpm respectively. In both groups, irrigation was performed with 1 mL distilled water after each instrument size and Glyde (Dentsply Maillefer, Ballaigues, Switzerland) were used. Canals (n = 17 per group) were scanned before, during and after preparation. The assessment of preparation shape was carried out with a computer image analysis program. Material removal was measured at seven points beginning 1 mm from the end-point of the canal. Statistical analysis was performed using Wilcoxon's test and Fisher's exact test (P < 0.05).

RESULTS

No instrument fractures, apical blockage or loss of working length (WL) occurred. More zips (10 vs. 4) and more strippings (17 vs. 0) were created with ENDOflash compared with the HERO Shaper. There were significant differences in terms of the amount of resin removed on the inner wall of the curvature obtained with the two instruments (P < 0.0001). On average, HERO Shaper instruments removed material more evenly on the outer and inner wall of the curvature. Considering the different points of measurement, there were significant differences between the two systems both on the inner and outer walls at WL-1, 2, 5 and 6 mm (P < 0.05). The HERO Shaper had a more centred enlargement compared with the ENDOflash.

CONCLUSIONS

Stainless steel rotary ENDOflash instruments did not perform as well as HERO Shaper instruments and created an increased risk of root canal transportation. Nickel-titanium rotary HERO Shaper instruments maintained the original curvature significantly better.

An evaluation of .06 tapered gutta-percha cones for filling of .06 taper prepared curved root canals

AIM

To compare the area occupied by gutta-percha, sealer, or void in standardized .06 tapered prepared simulated curved canals and in mesio-buccal canals of extracted maxillary first molars filled with a single .06 gutta-percha point and sealer or lateral condensation of multiple .02 gutta-percha points and sealer.

METHODOLOGY

Simulated canals in resin blocks with either a 30 degrees curve and radius of 10.5 mm (n = 20) or a 58 degrees curve and 4.7 mm radius (n = 20) and curved mesio-buccal canals of extracted maxillary first molars (n = 20) were prepared using .06 ProFiles in a variable tip crown-down sequence to an apical size 35 at 0.5 mm from the canal terminus or apical foramen. Ten 30 degrees and 58 degrees curved resin canals and 10 canals in the extracted teeth group were obturated with .02 taper gutta-percha cones and AH 26 sealer using lateral condensation. The time required to obturate was recorded. The remaining canals were obturated with a single .06 taper gutta-percha cone and AH 26 sealer. Excess gutta-percha was removed from the specimens using heat and the warm mass vertically condensed. Horizontal sections were cut at 0.5, 1.5, 2.5, 4.5, 7.5 and 11.5 mm from the canal terminus or apical foramen. Colour photographs were taken using an Olympus 35 mm camera attached to a stereomicroscope set at x40 magnification, and then digitized using a flatbed scanner. The cross-sectional area of the canal contents was analysed using Adobe PhotoShop. The percentage of gutta-percha, sealer or voids to the total root canal area were derived and data analysed using unpaired Student's t-test and the Mann-Whitney U-test.

RESULTS

In the 30 degrees curved canals the levels had between 94 and 100% of the area filled with gutta-percha with no significant difference (P > 0.05) between the lateral condensation and single cone techniques. In the 58 degrees curved canals the levels had 92-99% of the area filled with gutta-percha, with the single cone technique having significantly (P < 0.05) more gutta-percha fill at the 2.5 mm level only. In the mesio-buccal canals of the teeth the levels had between 72 and 96% of the area filled with gutta-percha with no significant difference (P > 0.05) between the lateral condensation and single cone technique. The time for obturation was significantly (P < 0.05) greater for lateral condensation compared with the single cone technique in all groups.

CONCLUSIONS

The .06 taper single cone technique was comparable with lateral condensation in the amount of gutta-percha occupying a prepared .06 tapered canal. The .06 single cone technique was faster than lateral condensation.

Comparison of Generated Forces and Apical Microleakage Using Nickel-Titanium and Stainless Steel Finger Spreaders in Curved Canals

The purpose of this study was to compare (a) forces generated during lateral compaction and (b) apical microleakage for nickel-titanium (NiTi) and stainless steel (SS) finger spreaders. Twenty-eight extracted human teeth were instrumented using a standardized rotary instrumentation technique. NiTi and SS #30 spreaders were used to obturate molar roots while the forces generated during obturation were measured on a Universal testing machine. Apical microleakage was determined using a fluid filtration method. There was no significant difference in microleakage between spreaders. NiTi spreaders produced significantly less force than SS spreaders in all specimens (p < 0.001).

The efficacy of ultrasonic irrigation to remove artificially placed dentine debris from different-sized simulated plastic root canals

AIM

To investigate the influence of diameter and taper of root canals on the effectiveness of ultrasonic irrigation to remove artificially placed dentine debris from simulated uninstrumented extensions in simulated root canals.

METHOD

Three groups of standard canals were cut in resin blocks using either size 20, .04 taper ProFile instruments, size 20, .06 Greater Taper (GT) rotary instruments or size 20, .08 GT instruments, respectively. Each resin block was then split longitudinally through the canal, forming two halves. In one canal wall, a standard groove 4 mm in length was cut 2-6 mm from the apical end of the canal, to simulate uninstrumented canal extensions. Each groove was filled with dentine debris mixed with 2% NaOCl to simulate a situation when dentine debris accumulates in the uninstrumented canal extensions. Each canal was reassembled by joining the two halves of the resin block by means of wires and sticky wax. In each canal ultrasonic irrigation was performed for 3 min using 2% NaOCl as irrigant. Before and after irrigation, images of each half of the canal with a groove were taken using a microscope and a digital camera, after which they were scanned into a PC as TIFF images. The quantity of dentine debris in the groove was evaluated using a scoring system: the higher the score, the larger the amount of debris remaining. The score data were analysed by means of Kruskal-Wallis and Mann-Whitney U-tests.

RESULTS

After ultrasonic irrigation, the debris score for the size 20,.04 taper group was significantly higher than that for the size 20,.06 group (P = 0.040) and the size 20,.08 group (P = 0.006) groups. However, no significant difference was found between the size 20,.06 and the size 20,.08 groups (P = 0.320).

CONCLUSION

In simulated plastic root canals, the diameter and taper of root canal influenced the effectiveness of ultrasonic irrigation to remove artificially placed dentine debris.

Current Challenges and Concepts in the Preparation of Root Canal Systems: A Review

Nickel-titanium rotary instruments are important adjuncts in endodontic therapy. This review attempts to identify factors that influence shaping outcomes with these files, such as preoperative root-canal anatomy and instrument tip design. Other, less significant factors include operator experience, rotational speed, and specific instrument sequence. Implications of various working length definitions and desired apical widths are correlated with clinical results. Despite the existence of one ever-present risk factor, dental anatomy, shaping outcomes with nickel-titanium rotary instruments are mostly predictable. Current evidence indicates that wider apical preparations are feasible. Nickel-titanium rotary instruments require a preclinical training period to minimize separation risks and should be used to case-related working lengths and apical widths. However, and despite superior in vitro results, randomized, clinical trials are required to evaluate outcomes when using nickel-titanium instruments.

Comparison of Hand Stainless Steel and Nickel Titanium Rotary Instrumentation: A Clinical Study

The aim of this study was to compare the effect of hand instruments and rotary nickel titanium Flex-Master files used by eight experienced dentists in private practice on the extent of straightening of curved root canals. In patients, 110 canals were prepared by FlexMaster instruments, and 84 canals were enlarged using hand instruments. After instrumentation, all canals were obturated. Preoperative and postoperative radiographs were taken of each tooth using customized bite blocks. Straightening of the canal curvatures was determined with a computer image analysis program. Preparation time and size of the master apical file were also recorded. The use of FlexMaster instruments resulted in significantly less straightening and a shorter preparation time (p < 0.0001) compared with hand instrumentation. Master apical file sizes were significantly greater for FlexMaster than for hand instruments (p < 0.01). This clinical study indicates that FlexMaster instruments prepared curved canals rapidly and with only minimal straightening.

Root-canal shaping with manual and rotary Ni-Ti files performed by students

AIM

To investigate root-canal shaping with manual and rotary Ni-Ti files performed by students.

METHODOLOGY

Thirty undergraduate dental students prepared 150 simulated curved root canals in resin blocks with manual Ni-Ti files with a stepback technique and 450 simulated curved canals with rotary Ni-Ti files with a crowndown technique. Incidence of fracture, preparation length, canal shape and preparation time were investigated. Questionnaires were then issued to the students for them to note their experience of the two preparation methods.

RESULTS

Zips and elbows occurred significantly (P < 0.001) less frequently with rotary than with manual preparation. The correct preparation length was achieved significantly (P < 0.05) more often with rotary files than with manual files. Instrument fractures were recorded in only 1.3% of cases with both rotary and manual preparation. The mean time required for manual preparation was significantly (P < 0.001) longer than that required for rotary preparation. Prior experience with a hand preparation technique was not reflected in an improved quality of the subsequent rotary preparation. Approximately 83% of the students claimed to have a greater sense of security in rotary than in manual preparation. Overall 50% felt that manual and engine-driven preparation should be given equal status in undergraduate dental education.

CONCLUSIONS

Inexperienced operators achieved better canal preparations with rotary instruments than with manual files. No difference in fracture rate was recorded between the two systems.