A reconstructed computerized tomographic comparison of Ni-Ti rotary GT files versus traditional instruments in canals shaped by novice operators

AIM: The aim of this study was to compare the effects of preparation with conventional stainless steel Flexofiles and Gates Glidden burs versus nickel-titanium GT rotary files in the shaping of mesial root canals of extracted mandibular molars. METHODOLOGY: A total of 54 canals from 27 mesial roots of mandibular molar teeth were prepared using one of two methods by novice dental students. One canal in each root was prepared by a crown-down approach. utilizing stainless steel Flexofiles and Gates Glidden burs. The other canal was prepared using nickel-titanium GT rotary files in a crown-down fashion as recommended by the manufacturer. Preoperative CT scans of each root were recorded and 50 canal specimens were available for postoperative comparisons. Following canal shaping, postoperative scans were superimposed on the original images. Changes in canal area, canal transportation and thickness of remaining root structure at strategic levels of the root were analyzed. The time taken for each method was also noted. RESULTS: At the coronal and mid-root coronal one-third sections, the rotary GT files produced a significantly smaller postoperative canal area (P < 0.05). In the mid-root sections there was significantly less transportation of the root canal toward the furcation, and less thinning of the root structure with GT files compared to the stainless steel files (P < 0.05). Overall, there was greater conservation of structure coronally and more adequate shape in the mid-root level. The GT rotary technique was significantly faster than the stainless steel hand-held file technique (P < 0.0001). Two GT instruments fractured during the study. CONCLUSIONS: Under the conditions of this study, novice dental students were able to prepare curved root canals with Ni-Ti GT rotary files with less transportation and greater conservation of tooth structure, compared to canals prepared with hand instruments. The rotary technique was significantly faster.     

Comparison of fracture rate, deformation rate, and efficiency between rotary endodontic instruments driven at 150 rpm and 350 rpm

Two groups of 30 mature molars each (S and F) were instrumented with Profile .04 taper Series 29 rotary instruments. Group S molars were instrumented at 150 rpm and group F at 350 rpm. The number of fractures, deformed files, and instrumentation time were recorded for each tooth. No instrument fractures occurred in either group. In group S the mean deformation rate and instrumentation time were 1.1 deformed files and 8.0 min per molar. In group F they were 0.57 deformed files and 4.6 min per molar. Both differences were significant (p < 0.05). The results indicate that Profile .04 taper Series 29 rotary instruments should be used at 350 rpm to nearly double efficiency and halve the deformation rate, compared with 150 rpm. Because no instrument fractures occurred while instrumenting 60 mature molars, both speeds should be considered safe.     

Effect of rotational speed on nickel-titanium file distortion

Separation of instruments while performing root canals is something that has plagued all practitioners. The purpose of this study was to evaluate the effect of rotational speed on nickel-titanium file distortion and separation. Forty extracted human molars were instrumented with Profile (Dentsply Tulsa Dental Products, Tulsa, OK) ISO .04 rotary nickel-titanium instruments at 166.67 or 333.33 rpm. The instruments were evaluated after instrumentation for separation and/or distortion. The results of this study were statistically significant and indicate that file distortion and/or separation is four times as likely to occur at 333.33 rpm vs. 166.67 rpm.     

Inferior alveolar nerve transposition--an in vitro comparison between piezosurgery and conventional bur use

An in vitro comparison between a new ultrasound-based piezoelectric device and a conventional bur was performed for lateralization or transposition of the inferior alveolar nerve to evaluate the effects on soft and hard tissue. Transposition of the inferior alveolar nerve was performed in the cadaver mandibles of 10 sheep: the left nerve was uncovered with a saline-cooled diamond-coated spherical bur (2000 rpm), and the right nerve was uncovered with the piezoelectric device mounted with a spherical diamond tip. The surface, the zone of bone defect, and the nerve were examined by light microscopy and laser microscopy. Bone treated with the rotary bur showed significantly smoother surfaces and shallower defect zones (50 microm) in comparison with the piezoelectric device (150 microm). Lesions of the epineurium and an increased amount of bone particles were found in the lesions prepared with the piezoelectric device. In vitro preparation with the piezoelectric device was more invasive to the bone than was a conventional diamond bur. Touching the inferior alveolar nerve resulted in roughening of the epineurium without affecting deeper structures. The degree of injury was lower than when using the conventional rotary bur.     

Efficiency of rotary nickel-titanium FlexMaster instruments compared with stainless steel hand K-Flexofile--Part 1. Shaping ability in simulated curved canals

AIM: The purpose of this study was to compare the shaping ability of FlexMaster rotary nickel-titanium instruments with stainless steel hand K-Flexofiles. This part of the two-part report describes the efficiency of these two instruments in simulated curved root canals. METHODOLOGY: Simulated 28 degree- and 35 degree-curved canals were prepared by the FlexMaster instruments with a rotational speed of 250 rpm using a crown-down preparation technique. and by the K-Flexofiles using a reaming motion (n = 24 canals in each case). All canals were prepared up to size 35. The pre- and post-instrumentation images were recorded and assessment of the canal shape was completed with a computer image analysis program. The material removal was measured at 20 measuring points, beginning 1 mm away from the apex. Incidence of canal aberrations, preparation time,changes of working length and instrument failures were also recorded. RESULTS: In comparison with stainless steel K-Flexofiles, the rotary FlexMaster instruments achieved bet-ter canal geometry, showed less canal transportation and created fewer canal aberrations in both the canal types. Two FlexMaster instruments were separated, and 15 FlexMaster instruments and 11 K-Flexofiles were permanently deformed during preparation. However, these differences were not significant (P > 0.05).Between both the canal types, FlexMaster was significantly faster (P < 0.001) than K-Flexofiles. Both instruments maintained a good working distance. CONCLUSIONS: FlexMaster instruments prepared curved canals rapidly, and with minimal transportation towards the outer aspect of the curve.     

Physical dimensions, torsional performance, and metallurgical properties of rotary endodontic instruments. 3. Peeso drills.

A laboratory study was performed on Peeso drills to determine their physical dimensions, torsional performance, and metallurgical properties. Samples were measured from each of sizes #1 to #6 of Peeso drills (type P) and sizes #009 to #023 of Peeso drills (type B-1) from the two manufacturers that distribute these instruments in the United States. They were also tested in clockwise and counterclockwise torsion using a digital torque meter instrument. It was not possible to evaluate completely some type P drills of size #4 and larger or type B-1 drills of size #016 and larger because the torsional moments exceeded the capacity of the test instrument. Scanning electron microscopic examination confirmed visual observations that the stainless steel Peeso drills exhibited ductile torsional fracture, in contrast to the carbon steel Peeso drills which fractured in a relatively brittle manner. The carbon steel Peeso drills exhibited a much greater tendency for torsional fractures in the bur head, along with considerably smaller values of angular deflection at separation compared to the stainless steel Peeso drills. This study is part of a continuing investigation to establish standards for all rotary endodontic instruments.     

Comparison of removal times of Thermafil plastic obturators using ProFile rotary instruments at different rotational speeds in moderately curved canals

The purpose of this study was to compare the time required for removal of small Thermafil plastic carriers in moderately curved MB roots of mandibular molars using the ProFile rotary system at 300 and 1,500 rpm. MB roots of 40 mandibular molars were instrumented and obturated with size 30 Thermafil plastic obturators. Teeth were divided into two groups. In group 1, sizes 55 to 25 ProFile 0.04-taper instruments were used in a crown-down manner at 300 rpm. In group 2, size 25 ProFile 0.04-taper instruments were used at 1,500 rpm. Time of carrier removal and the number of instrument separations were recorded. The Student's t test demonstrated a significant difference between groups: 4 minutes 12 seconds for group 1 and 1 minute 28 seconds for group 2 (p < 0.001). However, a trend for greater separation of instruments was found with the higher rpm group.     

Influence of Rotational Speed on the Cyclic Fatigue of Rotary Nickel-Titanium Endodontic Instruments

IntroductionDuring the preparation of curved canals, rotary nickel-titanium (NiTi) instruments are subjected to cyclic fatigue, which can lead to instrument fracture. Although several factors may influence the cyclic fatigue resistance of instruments, the role of the rotational speed remains uncertain. This study was intended to evaluate the effects of rotational speed on the number of cycles to fracture of rotary NiTi instruments.MethodsProTaper Universal instruments F3 and F4 (Maillefer SA, Ballaigues, Switzerland) were used in an artificial curved canal under rotational speeds of 300 rpm or 600 rpm. The artificial canal was made of stainless steel, with an inner diameter of 1.5 mm, total length of 20 mm, and arc at the end with a curvature radius of 6 mm. The arc length was 9.4 mm and 10.6 mm on the straight part. The number of cycles required to fracture was recorded. Fractured surfaces and the helical shafts of the fractured instruments were analyzed by scanning electron microscopy.ResultsThe results showed approximately a 30% reduction in the observed number of cycles to fracture as rotational speed was increased from 300 to 600 RPM (p < 0.05). The morphology of the fractured surface was always of ductile type, and no plastic deformation was observed on the helical shaft of fractured instruments.ConclusionsThe present findings for both F3 and F4 ProTaper instruments revealed that the increase in rotational speed significantly reduced the number of cycles to fracture.     

The deterioration of rotary nickel-titanium files under controlled conditions

It has been shown that rotary nickel-titanium files cannot be used indefinitely. Researchers and clinicians have not been able to agree on how many times a file can be used before being discarded, except if a file has fractured or become visibly distorted. This study used ISO size 20 files of 0.04 taper in the curved canals of extracted mandibular molars. The canals had been previously instrumented to an ISO size 15 with stainless steel hand files. The irrigant used during rotary and hand instrumentation was Glyde. The rotary files were closely examined with scanning electron microscopy before use to detect any defects. They were then reexamined after each of five uses to document deterioration. An electric handpiece was configured to rotate at 150 rpm and secured to the testing device, which also held the extracted tooth. The testing device controlled the load at 8 N, the depth of penetration for each canal and the rate of penetration (12 mm/min). Used instruments demonstrated surface fatigue wear and cracking. Torsional moment at failure was determined on a torsiometer for used and new instruments. Data (n = 10) were analyzed by analysis of variance. The torsional moment for used and new instruments was not affected by use (p = 0.25).     

Comparisons of discomfort among cutting instruments for removal of carious dentine in children

To determine the properties of cutting instruments used objectively in dental treatment for children, a comparative study of erbium-doped yttrium aluminium garnet (Er-YAG) laser, air abrasion system and a rotary cutting steel bur was conducted, focussing on discomfort such as pain, vibration, noise, odour and other types of discomfort during removal of carious dentine. The subjects were 60 children and 60 adults. The visual analogue scale (VAS) was used for evaluation, yielding the following conclusions.With respect to pain, discomfort during the removal of carious dentine using the steel bur was found to have the highest VAS value, while it was milder using the laser treatment, followed by that using the air abrasion treatment. There was no significant difference in pain between children and adults. Vibration increased significantly when the steel bur was used in both groups. In addition, vibration caused more discomfort to child patients than to adults. Noise increased significantly in the air abrasion treatment and steel bur treatment in both groups. However, noise caused more discomfort to child patients than to adults. Discomfort due to odour increased significantly in the laser treatment. Other types of discomfort increased significantly in the air abrasion treatment. The degree of discomfort was significantly higher in the child patients.In conclusion, these results suggest that there were differences in the degree of discomfort between child and adult patients. Children showed characteristic responses to the discomfort in relation to mechano-chemical stimulations, while pain elicited characteristic responses in adults.     

Apical displacement produced by rotary nickel-titanium instruments and stainless steel files

The aim of this study was to evaluate the apical displacement produced by different rotary nickel-titanium instruments, testing the hypothesis that rotary systems with nickel-titanium instruments produce lower mean values of apical displacement than stainless steel hand instruments. A total of 100 maxillary permanent first molars were selected for the study. The mesiobuccal roots were sectioned at the top cervical third and embedded in blocks of self-curing resin. The specimens were randomly divided into 5 groups and the root canals were prepared using the following nickel-titanium instruments: Group 1 - Quantec system 2000 (Analytic Endodontics, Mexico); Group 2 - Pro-File T.0.04 (Dentsply/Maillefer, Switzerland); Group 3 - Pro-File Series 29 T.0.04 (Dentsply Tulsa, Switzerland); Group 4 - Pow-R T.0.02 (Moyco-Union Broach, USA). Specimens in Group 5 were prepared using stainless steel hand instruments Flexofile (Dentsply/Maillefer, Switzerland). All root canals were previously submitted to cervical preparation using Orifice Shaper instruments #1, 2, 3 and 4 (Dentsply/Maillefer, Switzerland). After odontometry, the remaining root canal was shaped employing increasingly larger instruments, so that the final instrument corresponded to Quantec #9, Pro-File Series 29 #6, and #35 for the other groups. Specimens in Groups 1 to 4 were prepared using an electric handpiece with 16:1 reduction at 350 rpm. The specimens in Group 5 were manually prepared. Apical displacement was measured and recorded by means of radiographic superimposition on a specific desk. Statistical analysis (ANOVA) of the results revealed that all groups presented apical displacements. Considering only the nickel-titanium instruments, Group 4 showed the lowest mean value while Groups 2 and 3 produced the highest mean apical displacement values (p<0.001).     

三种根管预备器械在老年人狭窄根管预备时推出根尖孔物质的体外对比研究

目的：比较手用不锈钢K锉、Protaper机用镍钛锉与Mtwo机用镍钛锉在离体老年人狭窄根管预备过程中推出根尖孔物质的质量。方法：将90颗60岁以上老年人狭窄单根管离体下颌中切牙随机分为3个组,每组30颗,分别用手用K锉,Protaper机用镍钛锉与Mtwo机用镍钛锉对离体老年人细窄根管进行预备。预备过程中观察从根尖孔推出的牙本质碎屑与液体,用预先称量的离心管收集,测量推出根尖孔液体的质量与牙本质碎屑的质量。结果：推出根尖孔外的牙本质碎屑及冲洗液的质量：Protaper机用镍钛锉组少于手用K锉组（P〈0.05）;Mtwo机用镍钛锉组少于手用K锉组（P〈0.05）;Mtwo机用镍钛锉组少于Protaper机用镍钛锉组,但差异无统计学意义（P〉0.05）。结论：Mtwo机用镍钛锉与Protaper机用镍钛锉在离体老年人狭窄根管预备过程中推出根尖孔物质的质量均少于手用K锉。     

A scanning electron microscopy evaluation of microfractures, deformation and separation in EndoSequence and Profile nickel-titanium rotary files using an extracted molar tooth model

The development of microfractures in the EndoSequence nickel-titanium rotary (NTR) file (Brassler USA, Savannah, GA) and Profile NTR file was evaluated by using scanning electron microscopy (SEM). Seventy-three maxillary buccal roots and 53 mandibular mesial roots with an average canal curvature of 37 degrees were randomly assigned to one of three groups and prepared with 21-mm .06 taper NTR files as follows: (1) EndoSequence at 300 rpm, (2) EndoSequence at 600 rpm, and (3) ProFile at 300 rpm. File sizes .45 to .20 were used in a crown-down technique to a master apical file (MAF) size of .35/.06. The MAF instruments were evaluated by SEM before use, after completion of 7 canals, and after completion of 14 canals. All EndoSequence instruments developed microfractures by the seven-canal evaluation. The ProFile instruments showed no microfractures at the 7- or 14-canal evaluations. EndoSequence files separated at a higher rate than ProFile instruments. Under the conditions of this study, unique file design and electropolishing did not inhibit the development of microfractures in EndoSequence NTR.     

The machining of cobalt-chromium alloy in partial denture construction

PURPOSE: To investigate the performance of different rotary instruments when machining cobalt-chromium alloy. MATERIALS AND METHODS: One tungsten carbide bur, 1 diamond bur, and 2 aluminum oxide abrasive points (pink stones) of different diameter were used to machine cobalt-chromium alloy under standardized conditions. The rate of metal removal was determined and the resulting surfaces and bur wear were investigated using scanning electron microscopy and energy dispersive analysis. RESULTS: Although the larger diameter pink stone was shown to be the most efficient instrument, the tungsten carbide bur produced the smoothest surface. CONCLUSION: Because of its low cost and high cutting efficiency the pink stone is well suited for laboratory use. The tungsten carbide bur is the preferred instrument for clinical use.     

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° 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.     

Canal preparation with Hero 642 rotary Ni-Ti instruments compared with stainless steel hand K-file assessed using computed tomography

AIM: To compare ex vivo root canal preparation with conventional stainless steel K-files and Hero 642 rotary Ni-Ti instruments. METHODOLOGY: Mesiobuccal canals of 20 maxillary first molars (with angles of curvature between 25 degrees and 35 degrees ) were used. After preparation with Hero 642 rotary instruments and stainless steel K-files, the amount of transportation that occurred was assessed using computed tomography. The teeth were scanned by computed tomography before instrumentation. One millimetre thick slices were prepared from the apical end point to the pulp chamber. The first two sections were 3 mm from the apical end of the root (apical level) and 3 mm below the orifice (coronal level). A further section (mid-root level) was recorded, dividing the distance between the sections of apical and coronal levels into two equal lengths. Ten teeth were instrumented using Hero 642 rotary instruments and another 10 teeth were instrumented using stainless steel K-files. Following the completion of the instrumentation, the teeth were again scanned and compared with the cross-sectional images taken prior to canal preparation. Amount of transportation and centreing ability was assessed. Student's t-test was used for statistical analysis. RESULTS: Less transportation occurred with Hero 642 rotary instruments than stainless steel K-files at the mid-root and coronal levels (mid-root: P < 0.05 and coronal: P < 0.001). Hero 642 rotary instruments had better centreing ability than K-files at all three levels (apical: P < 0.05, mid-root: P < 0.05 and coronal: P < 0.001). CONCLUSIONS: Hero 642 rotary instruments transported canals less, especially at the middle and coronal thirds of the root canals than stainless steel K-files. Hero 642 instruments had better centreing ability.     

An evaluation of polymer rotary instruments' ability to remove healthy, non-carious dentine

The aim of this study was to confirm that Smartprep burs do not cut non-carious, healthy dentine. Twenty non-carious extracted molars were trimmed with a diamond bur to remove enamel and to create a flat dentine surface. A new Smartprep bur (RA # 4) was applied to each tooth for 30 seconds. As a control, a new number three round stainless steel bur was applied to each tooth. The mean dentine loss was 4.25 mg (range 1.4 - 9 mg) for Smartprep burs and 12.21 mg (range 7.6 - 16.5 mg) for stainless steel burs. The Smartprep burs remove significantly less dentine than stainless steel burs.     

The effects of cyclical axial motion on rotary endodontic instrument fatigue

A potential problem with the use of rotary engine-driven files to flare canals is metal fatigue and subsequent breakage. This study analyzes the effects of cyclical axial motion on instrument failure by fatigue testing of endodontic files with and without cyclical axial motion. Eighteen new instruments, sizes 15 to 45, were mounted in a lathe and turned at 1650 rpm in the lubricated lumen of a curved Pyrex capillary tube until failure occurred. Nine instruments of each size were turned with cyclical axial motion and nine were turned without it. The results indicated that cyclical axial motion can significantly extend the life span of rotary engine files. Torsional forces were not considered in this study.     

Surface roughness and bond strength of enamel to composite.

OBJECTIVES: The aim of the study was to assess the influence of pretreating enamel by different rotary instruments on shear-bond strength of composite to enamel after the acid etch technique. METHODS: Ninety human enamel specimens with transversely and longitudinally sectioned prisms were ground flat, and half of the enamel area of each specimen was prepared with one of the eight different rotary instruments: a 120 microns diamond bur, three finishing diamonds (30, 15 and 8 microns), two tungsten carbide finishing instruments (8- and 30-fluted) and two stones (Dura green and Dura white). The other half of the enamel area was left untreated. Enamel roughness was measured by laser-stylus profilometry. Two cylinders filled with the hybrid composite Pertac were adhesively fixed on each enamel surface, one on the prepared side and the other on the untreated side. After seven days of water storage, shear-bond strength was measured with a Universal testing machine. RESULTS: Rz values of the treated enamel surfaces were between 4.14 and 17.75 microns. The shear-bond strength data varied between 16.8 and 29.4 MPa and were similar for transversely and longitudinally orientated prisms. The different roughness data had no significant influence on shear-bond strength of composite to enamel. Additional SEM investigation showed that the surface geometry caused by the rotary instruments largely persisted after acid etching. SIGNIFICANCE: With regard to shear-bond strength, there was no advantage in using a special bur for finishing enamel surfaces prior to the acid etch technique. Burs causing extreme roughness should not be used for this purpose.     

The influence of a manual glide path on the separation rate of NiTi rotary instruments

The dual purpose of this study was, to evaluate the fracture rate of Ni-Ti rotary instruments when following a manual glide path and using stainless steel hand files before carrying out instrumentation by means of rotary files and, to compare the results in this study with those obtained in two previous analyses, in which the glide path technique was not used. A total of 208 canals obtained from a pool of freshly extracted human mandibular and maxillary molars was divided into three groups corresponding to; K3, ProFile and ProTaper. The coronal 2/3 of each tooth were used. In all three groups the apical portion of the samples was prepared with size 10-20 stainless steel K-type hand files. The apical stops were prepared using K3, ProFile and ProTaper rotary instruments. Logistic regression model analysis indicated that breakage was significantly associated with the angle of curvature of the canal (OR = 1.078; 95% CI = 1.032-1.12; p = 0.001), and with the number of clinical uses (files used more than eight times broke more frequently that those used 1 or 2 times; OR: 22.686; 95% CI: 2.6-191.3; p = 0.004). The breakage rate obtained in the present study is significantly lower than in our previous studies, in which the angle of curvature was also greater than 30 degrees and rotational speed a constant 350 rpm, but in which the canals were not first prepared with hand files (25/205 = 12% versus 16/61 = 26%, p = 0.007). Based on the results of this study, we recommend the use of stainless steel hand files to prepare the apical 1/3 of curved canals before introducing rotary files.