Comparing apical preparations of root canals shaped by nickel-titanium rotary instruments and nickel-titanium hand instruments

This study measured displacement of canal centers in extracted human teeth after preparation by Lightspeed and nickel-titanium K-files. The specimens were divided into two groups (n = 11), after radiographing the roots from the buccolingual and mesiodistal planes with pathfinding files in situ. More strongly and less strongly curved canals were, respectively, assigned to the Lightspeed and nickel-titanium K-file groups. Using a reassembly technique, cross-sections at 1.25 mm, 3.25 mm, and 5.25 mm from the apices were made of the experimental roots embedded in clear plastic. Stereomicroscopic 35-mm slides were taken of the uninstrumented sectioned canals. The sections were reassembled and then prepared to size 50 Master Apical Rotary and size 40 Master Apical Files, for the Lightspeed and K-file groups, respectively. Similar 35-mm slides of the instrumented canals were taken and electronically superimposed over their uninstrumented counterparts. Displacements of root canal centers after preparation and increases in cross-sectional areas of the prepared root canals were evaluated at specific levels. No significant differences in displacement of canal centers or between the mean cross-sectional areas of the instrumented root canals were recorded between the Lightspeed and K-file groups. Both types of instruments produced similar displacement of canal centers after preparation.     

A comparison of curved canal transportation with balanced force versus lightspeed

The Flex-R file was compared with the Lightspeed nickel-titanium file in respect to canal center movement and final canal area after instrumentation. Thirty-eight root canals in extracted human molars were divided into two equal groups of 19, in all of which the angle of curvature ranged from 20 to 35 degrees. After mounting in a mold, each root was sectioned at two locations, providing an apical and coronal section. Pre- and postinstrumentation 35 mm photographic slides of each section were projected, traced, and then scanned into a computer. From these computerized pre- and postinstrumentation images, the movement of the canal center and the area of each canal were computed at both the apical and coronal sections. Results showed significant difference in the apical canal center movement and postinstrumentation area with the Lightspeed yielding smaller values in both cases. Coronally, the Flex-R Lightspeed instruments demonstrated no significant difference in canal movement or postinstrumentation area. No significant correlation was found between the angle of root curvature and canal movement or the angle of root curvature and postinstrumentation canal area.     

Preparation of curved root canals with rotary FlexMaster instruments compared to Lightspeed instruments and NiTi hand files

AIM: To compare the recently introduced rotary FlexMaster instruments with Lightspeed instruments and NiTi hand files in preparing curved root canals. METHODOLOGY: Root canals of extracted molars were shaped with rotary FlexMaster instruments ('FM': n = 45), Lightspeed instruments ('LS': n = 46), and NiTi hand files (n = 45) using the balanced-force technique. The apical preparation size was 40. Root canal instrumentation was carried out in a phantom head under clinical conditions. A re-assembly technique allowed a comparison of the canal outline before and after preparation. Root sections 2.5 mm short of working length were used to calculate the percentage of prepared canal outline (= PPO) and the amount of root canal transportation. Loss of working length, fracture rate and time spent on complete preparation were also recorded. RESULTS: The highest PPO values were found in the LS group (mean = 63% [95% CI: 55%; 70%]). Although not statistically significant, lower PPO values were detected for FM instruments (mean = 55% [95% CI: 49%; 62%]) and for hand files (mean = 53% [95% CI: 47%; 59%]). The incidence of root canal transportation exceeding 0.1 mm was significantly lower in the LS group than in the FM group. Loss of working length of 0.5 mm occurred in five cases (LS group: 4x; FM group: 1x). Two LS instruments fractured. Half the time was needed for root canal preparation with FM instruments than with hand files. CONCLUSIONS: Rotary FM instruments are suitable for preparing curved root canals. They provided results similar to LS instruments with minimal risk of instrument fracture but increased risk of root canal transportation.     

A comparative study of root canal preparation using Profile .04 and Lightspeed rotary Ni-Ti instruments

AIM: The purpose of this Study was to compare several parameters of root canal preparation using two different rotary nickel-titanium instruments: ProFile .04 (Dentsply/ Maillefer, Ballaigues, Switzerland) and Lightspeed (Lightspeed Technology Inc., San Antonio, TX, USA). METHODOLOGY: Fifty extracted mandibular molars with root canal curvatures between 20 degrees and 40 degrees were divided into two similar groups having equal mean curvatures. The teeth were then embedded into a muffle system as described by Bramante et al. (1987) and modified by Hülsmann et al. (1999b). All root canals were prepared using ProFile .04 or Lightspeed Ni-Ti instruments to size 45 following the manufacturers' instructions. The Lightspeed system was used in a step-back technique: ProFile .04 instruments were used in a crown-down technique. The following parameters were evaluated: straightening of curved root canals (superimposition of pre- and postoperative radiographs), postoperative root canal diameter (superimposition of pre- and postoperative photographs of root canal cross-sections), safety issues (file fractures. perforations, apical blockages, loss of working length) (protocol), cleaning ability (SEM-evaluation of root canal walls using a five-score system for debris and smear layer), and working time (protocol). Statistical analysis was performed using the Wilcoxon test (P < 0.05) for straightening, and Fisher's exact-test (P < 0.05) for comparison of cross-sections, for comparison of contact between pre- and postoperative diameter, root canal cleanliness and working time. RESULTS: Both Ni-Ti systems maintained curvature well; the mean degree of straightening was less than 1 degrees for both ProFile .04 and for Lightspeed with no statistical significance between the groups. Most procedural incidents occurred with Profile .04 instruments (three fractures), Lightspeed preparation was completed without instrument fractures. Loss of working length, perforations or apical blockage did not occur with either instrument. Following preparation with Profile.04. 64.0% of the root canals had a round, 30.7% an oval, and 5.3% an irregular cross-section, Lightspeed preparation resulted in a round cross-section in 41.3% of cases, an oval shape in 45.3% of cases: 13.3% of cases had an irregular cross-section. No significant differences were found between the two systems. Lightspeed instruments enlarged the root canal more uniformly with no specimen showing 50% or more contact between pre- and postoperative diameter. The difference was statistically significant only for the coronal third of the root canals (P = 0.032). Mean working time was significantly shorter for Profile .04 (105 s) than for Lightspeed (140 s) (P = 0.02). For debris removal Lightspeed achieved the best results (68% scores 1 and 2), followed by Profile .04 (48.4%) with no significant differences between the systems. The results for remaining smear layer were similar: the lowest amount of smear layer on the root canal walls was found after preparation with Lightspeed (30.7% scores 1 and 2). followed by Profile.04 (23.1%). In the coronal third of the root canals Lightspeed performed significantly better than Profile .04 (P = 0.029): in the middle and apical third the differences were not significant. CONCLUSIONS: Both systems under investigation respected original root canal curvature and were safe to use. Both systems can be recommended for clinical use.     

The quality of apical canal preparation using hand and rotary instruments with specific criteria for enlargement based on initial apical file size

The aim of this study was to compare the quality of apical enlargement of mesiobuccal canals of mandibular molars using conventional stainless steel hand files (K files) and nickel-titanium (Ni-Ti) rotary instruments (LightSpeed). Thirty freshly extracted mandibular molars were randomly assigned to three equal groups (n = 10 each group). The mesiobuccal canals were instrumented with K file using step-back technique without coronal flaring (control; group 1), K file using step-back technique after coronal flaring (group 2), and LightSpeed instrumentation (group 3). Specific criteria for apical enlargement based on initial apical size were used. For step-back techniques, the master apical file sizes were based on the Grossman criterion of three sizes larger than the first file that bound at working length, without coronal flaring (group 1) and with flaring (group 2). For the LightSpeed (LS) group, the master apical rotary sizes were based on the manufacturer's recommendation. Canal cleanliness, canal transportation, and final canal shapes were determined histologically at 1-mm and 3-mm levels short of the working length. Canals were prepared to significantly larger sizes using LS instrumentation than with either hand instrumentation techniques (15-17 ISO units, p < 0.001). LS instrumentation allowed greater apical enlargement with significantly cleaner canals, less apical transportation, and better canal shape than both hand instrumentation groups at both levels (p < 0.05). None of the three techniques was totally effective in cleaning the apical canal space. It was concluded that greater apical enlargement using LS rotary instruments is beneficial as an attempt to further debride the apical third region in mesiobuccal canals of mandibular molars. Instrument designs, alloy properties, and canal curvature are important factors that determine the feasibility of greater apical enlargement in narrow canals.     

An analysis of canal centering using mechanical instrumentation techniques.

The purpose of this study was to compare canal transportation in moderately curved canals using mechanical instrumentation systems. Mesial roots of mandibular first or second molars were mounted in resin using a modified Bramante muffle system and divided into four groups. The roots were cross-sectioned 2 mm from the working length and at the height of root curvature. Tracings of the canal were made from preinstrumentation slides of the cross-sections. The canals were prepared using ProFile Series 29 rotary instruments, Quantec 2000 rotary instruments, Flex-R files in the Endo Gripper contra-angle handpiece, and Shaping Hedstrom files in the M4 contra-angle handpiece. Tracings of the prepared canals were made onto the originals from postinstrumentation slides. A canal centering ratio was calculated along the line of maximum transportation. Quantec 2000 rotary instruments yielded significantly greater transportation at the apical level when compared with the Profile Series 29 system. There were no other significant differences in transportation at either level. There were no differences in the direction of canal transportation between instrument systems, and the direction of canal transportation was not related to the direction of canal curvature. Canal preparation time was shortest with Profile Series 29 system followed by Flex-R files in the Endo Gripper, Quantec 2000, and Shaping Hedstrom files in the M4.     

Micro-CT评价不同弯曲度根管预备后根尖偏移的实验研究

目的使用Micro—CT评价不同弯曲度根管预备后的根尖偏移。方法选取10颗离体上颌磨牙共30个根管。根据不同的弯曲度分为轻度、中度和重度弯曲共3组根管,每组10个根管。使用不锈钢K型锉采取逐步后退法预备根管,分别于预备前、中和后进行Micro—CT扫描,评价根管的根尖偏移情况。结果根管预备至25号锉时,各弯曲度根管组间的根尖偏移差异有统计学意义;预备至35号锉时,重度弯曲根管组与轻度和中度弯曲根管组间差异均有统计学意义,而轻度和中度弯曲根管组间差异无统计学意义。各组预备至35号和25号时的根尖偏移差异均有统计学意义。结论根管弯曲度越大,根尖偏移度越大;根管预备锉的号码越大,根尖偏移越明显。     

根管偏移对充填材料封闭根管能力的影响

目的 :研究弯曲根管预备后的根管偏移对充填材料封闭根管能力的影响。方法 :选取 73颗下颌单根管前磨牙作为研究对象 ,其中弯根管牙 46颗 ,直根管牙 2 7颗。A组 2 3颗弯根管牙用Lightspeed器械预备根管 ,B组 2 3颗弯根管牙、C组 17颗直根管牙以及对照组牙用K锉预备根管 ,预备方法为逐步后退技术。使用双曝光X线技术和Ehrlich法测量根管偏移指数 (ATI)的大小。使用侧向加压技术充填所有根管后 ,用流体传输模型测量每个根管内微渗漏的量。结果 :A组中有 19%的根管发生根管偏移 ,B组中有 85 %的根管发生根管偏移 ,两组之间ATI的大小有高度显著性差异。当ATI大于 0 .3mm时 ,根管内微渗漏的发生率明显增加。结论 :弯曲根管预备中出现的根管偏移会削弱充填材料封闭根管的效果。     

A comparison of stainless steel hand and rotary nickel-titanium instrumentation using a silicone impression technique

BACKGROUND: Root canal preparation using rotary nickel-titanium instruments has been reported to be superior to hand instrumentation in terms of root canal shape, centring and frequency of procedural errors. The purpose of this study was to evaluate canal preparations using a sequential silicone impression technique to assess root canal morphology. METHODS: Pre-operative canal impressions were obtained from 24 extracted single-rooted premolars. Canals were randomly assigned to be firstly, instrumented with stainless steel K-type files or rotary nickel-titanium instruments (Profile), then further apically enlarged with rotary nickel-titanium instruments (Profile or Lightspeed). Post instrumentation impressions were taken and digitally photographed in a bucco-lingual and mesio-distal orientation at low-power magnification. Images were evaluated for procedural defects, changes in canal curvature, canal enlargement and canal rounding at 1, 3 and 7mm from the working length. RESULTS: Silicone impressions could accurately reproduce the detailed root canal morphology of single-canal premolars. Repeated impressions of each canal using a standardized procedure allowed a detailed comparison of instrumentation techniques at various stages. Hand instrumentation incurred more errors than rotary nickel-titanium instrumentation (Profile). Further apical enlargement using Lightspeed instruments incurred fewer errors than with Profile instruments. Differences among techniques were highly significant (p<0.005). All techniques resulted in slight canal straightening, as well as rounder and enlarged canals particularly in the apical third. CONCLUSIONS: Rotary nickel-titanium instrumentation, especially Lightspeed, may produce better canal shape by reducing procedural errors.     

Preparation of simulated root canals using the Macfile, Canal Master U and K-Flexofile

The efficacy of three different root canal instruments in maintaining the original shape of curved canals was evaluated. Acrylic blocks were prepared to simulate canals with 40° and 60° curvature. K-Flexofiles and Macfiles were used with a step-back technique utilizing an 'in/out' filing motion. The balanced-force technique was used with Canal Master 'U' instruments. Ten 40° and 10 60° canals were prepared with each instrument. The results were evaluated using superimposed photographic slides at ×20 magnification to show the canals before and after the instrumentation. The width of the prepared canals was measured at their convex/concave point to determine the divergence of the instrumented canal shape from the original canal shape. The measurements were taken at the level of the apical foramen and 3 and 6 mm coronal to it. In this way it was possible to recognize all the defects created during the preparation of a canal. Among the tested instruments, the Macfile provoked minimal canal deviation ( P = 0.05). The Canal Master 'U' was similarly effective ( P = 0.05), but had the highest incidence of instrument fracture. The K-Flexofile demonstrated the most defects in canal preparation and canal deviation, particularly at the level of the apical foramen ( P < 0.01).     

A comparative study of seven instruments in shaping the root canal in vitro

The objective of this study was to evaluate the shaping characteristics of various root canal instruments using human teeth. A total of 420 extracted human roots were embedded in resin blocks. The embedded roots were divided into three groups, i.e. roots with (i) straight, (ii) apically curved, and (iii) whole-length curved canals according to the Schneider's angle and the length of the radius of arc fitting the curvature of root canals. Each of the three groups containing 140 roots were randomly divided into seven subgroups prior to preparation. The canals were prepared manually with traditional and flexible instruments, engine driven Racer-type, Giro-type, randomly vibrating instruments and with sonic and ultrasonic instruments. The shortcomings of the seven preparation methods were assessed by the superimposition of projected radiographs taken in bucco-lingual and mesio-distal views before and after the preparation. The prepared straight canals showed a high percentage (75.7%) of apical asymmetry. Coronal transposition of the apical stop was graded with higher scores in all canal forms prepared with Racer-type and Giro-type instruments, which could have occurred through packing of debris towards the apical constriction. The majority of the prepared curved canals were asymmetrical in shape. The location of the aberrations depended on the original shape of the canal but the method of shaping also had a decisive effect on the post-operative form of the canal. Large differences were found between the incidence of elbow (11.7-40.0%) and zip (75.7-80.0%). K-Flex files produced minor canal aberrations and significantly less asymmetry (P < 0.05) than the conventional hand instruments. The MM 1400 handpiece and ultrasonic instruments were associated with less aberration and significantly less asymmetry than the other instruments tested. The Excalibur appeared to be superior to the conventional hand instruments in straight canals, but its shaping characteristics were similar to conventional instruments in curved canals. Under the conditions of this study, canal shaping with Cavi Endo, MM 1400 and K-Flex files appeared to be superior to that achieved with conventional hand instruments Excalibur, Intra Lux Endo Kopf 3LDSY, and 3LD instruments.     

Leakage along apical root fillings in curved root canals. Part I: effects of apical transportation on seal of root fillings

Occurrence of apical transportation (AT) may complicate the root filling procedure and result in a compromised seal. In part I of this study, human mandibular premolars with single, curved (21 to 39 degrees), or straight canals were prepared by Lightspeed or a step-back hand filing technique. An AT index was determined using a double exposure radiographic technique. The prepared canals were obturated using lateral condensation of gutta-percha. Leakage along the apical 3 mm of root filling was measured with a fluid transport model. After hand filing, AT and perforation occurred in 87% of the curved canals. The AT indices were > or = 0.4 mm. After Lightspeed preparation, AT occurred in only 19% of the curved canals. The hand filing/curved group leaked statistically significantly more than the hand filing/straight and Lightspeed/curved groups (p = 0.002). We conclude that occurrence of AT is a factor that negatively influences the apical seal when curved canals are obturated by lateral condensation of gutta-percha.     

Efficiency of hand and rotary instruments in shaping oval root canals

This study was designed to determine the efficiency of hand and rotary instruments in shaping oval root canals. Seventy-five oval canals were equally divided into three groups. The apical third was prepared with rotary LightSpeed instruments either to size 52.5 (mandibular incisors) or to size 57.5 (distal root of mandibular molars). The middle third with an oval cross-section was shaped with Hedstr?m hand files using circumferential technique, with 6% taper rotary Hero files in a circumferential filing movement or with rotary LightSpeed instruments in a step-back technique. Instrumentation was performed under clinical conditions in a phantom head. The teeth were sectioned at two levels in the middle third of the root. An assembly technique allowed comparing the canal outline before and after instrumentation. The photographed root sections were superimposed and traced under a stereomicroscope. The ratio of prepared to unprepared canal outline was calculated for each section. The lowest values were observed in the LightSpeed group (mean: 0.42; 95% confidence interval (CI): 0.37; 0.47). Significantly higher values were recorded in the Hero group (mean: 0.58; 95% CI: 0.53; 0.64) and in the Hedstr?m group (mean: 0.56; 95% CI: 0.49; 0.62). No instrumentation technique was capable of completely preparing dentin walls of oval root canals. Circumferential filing of the middle third of oval root canals with either 6% taper Hero files or conventional Hedstr?m hand files gave comparable results.     

新型机动镍钛器械预备根管的疗效评价

目的:探讨新型机动镍钛器械Hero642预备根管的临床疗效。方法:选取患牙髓炎或根尖周炎的恒磨牙60例(60颗患牙),试验组用机动镍钛器械Hero642及根向预备技术预备根管,对照组用K锉及逐步后退技术预备根管,两组均采用侧向加压充填技术充填根管。根据治疗前后的X线片评价根管预备和充填效果,t检验比较两组根管弯曲度和操作时间,χ2检验比较根管内并发症和术后疼痛的发生率。结果:试验组能维持根管的原走向,无根尖阻塞、台阶、根管偏移及侧壁穿孔等并发症发生,对照组并发症的发生显著多于试验组(P<0.005);试验组操作时间短,术后疼痛发生少。结论:机动镍钛器械Hero642预备根管快速、有效,成形效果好,值得临床推广应用。     

Comparative study of hand-held nickel-titanium dental instruments based on the shape of the prepared root canal

The aim of this study was to compare the shaping characteristics of two hand instruments: the NiTi K-files and the NiTi S-files. A total of 60 extracted human roots were embedded in resin blocks. The roots were divided into three groups according to their shape: straight, apically curved and entirely curved. Each of the three groups was divided into two subgroups for the NiTi K-file and the NiTi S-file instrumentation. The files were used with a step-back technique and enlarged so that the master apical file was size 30, and the canals were stepped back to size 40. The performance of the files was assessed by the superimposition of projected radiographs taken in bucco-lingual and mesio-distal views before and after preparation. The results were analyzed statistically using of analysis of covariance and Duncan's multiple range test. Although canal preparation using NiTi K-files was quicker, there were no statistically significant differences between file types. The NiTi S-file removed significantly more dentine at the most coronal level (p < 0.05). There were minor differences between instruments at the apical level. Only in the proximal view of apically curved canals prepared with NiTi S-files was significantly more dentine removed from the convex side of the wall (p < 0.05). At the middle level the NiTi S-files removed more dentine from the concave wall in apically curved canals. Under the conditions of this study, preparation with NiTi K-files produced more appropriate shapes in roots with apically curved canals than NiTi S-files.     

The effect of maintaining apical patency on canal transportation

Aim To evaluate, ex vivo, the effect of maintaining apical patency on the original canal shape during preparation of curved roots by two different techniques. Methodology Forty extracted human maxillary and mandibular molars were evaluated. Occlusal surfaces were ground and roots sectioned to the level of the cemento‐enamel junction to allow only one root to remain for evaluation in each tooth. Specimens were divided into four experimental groups (10 canals each): Group 1 – root canals prepared using the balanced force technique with stainless steel K‐files, and patency established with size 10 K‐files between each instrument; Group 2 – same as Group 1 but without the use of a patency file; Group 3 – canals instrumented with LightSpeed® instruments and patency established with size 10 K‐files between each instrument; and Group 4 – same as Group 3 but without the use of a patency file. Specimens were mounted and a series of radiographs taken. Initial and post‐preparation digital images were superimposed and the distance between two central axes at 1, 2 and 4 mm from the working length (WL) was measured to obtain an indication of the degree of apical transportation. Results were subjected to statistical analysis using two‐way analysis of variance (anova ). Results No significant differences were found in degree of apical transportation at different levels of the root canal (P > 0.05) nor in loss of WL between groups (P > 0.05). Conclusion In this laboratory study, maintaining apical patency did not influence canal transportation in the apical 4 mm.     

A comparison of the shaping characteristics of two nickel-titanium endodontic hand instruments

AIM: The purpose of this study was to compare the shaping characteristics of Ni-Ti K-files and Ni-Ti S-files manipulated by hand. METHODOLOGY: A total of 60 extracted human roots were embedded in resin blocks. The embedded roots were divided into three groups: (i) roots with straight; (ii) apically curved; and (iii) continuously curved canals. Each of the three groups was randomly divided into two subgroups; one subgroup in each group was prepared with Ni-Ti K-files and the other with Ni-Ti S-files. The files were used with a step-back technique and enlarged so that the master apical file was size 30, and the canals were stepped back to size 40. The performance of the files was assessed by the superimposition of projected radiographs taken in bucco-lingual and mesio-distal directions before and after the preparation. The results were analysed statistically using analysis of covariance and Duncan's multiple range test. RESULTS: Although canal preparation using Ni-Ti K-files was quicker, there were no statistically significant differences between file types. The Ni-Ti S-file removed significantly more material at the most coronal level (P < 0.05). There were minor differences between instruments at the apical level. Only in the proximal view of apically curved canals prepared with Ni-Ti S-files was significantly more dentine removed from the outer aspect of the curvature (P < 0.05). At the middle level (wide danger zone) the Ni-Ti S-files removed more dentine from the inner aspect of the curvature in those roots with apically curved canals. CONCLUSIONS: Under the conditions of this study, preparation with Ni-Ti K-files produced more appropriate shapes in roots with apically curved canals than Ni-Ti S-files.     

A comparison of spreader penetration depth and load required during lateral condensation in teeth prepared using various root canal preparation techniques

AIM: To compare the influence of various root canal preparation techniques on spreader penetration depth and load required during lateral condensation with gutta-percha and sealer. METHODOLOGY: Eighty extracted human teeth with single and straight canals were used. Twenty teeth were instrumented using one of four root canal preparation techniques. The four preparation techniques were: step-back technique without Gates-Glidden drills, step-back technique with Gates-Glidden drills, crown-down pressureless technique and hybrid technique (step-down/step-back). After root canal preparation had been completed a simulated periodontal ligament was fabricated from a uniform layer of silicone impression material. The roots were then mounted in an acrylic resin to simulate the physical condition found in tooth socket. A standardized stainless steel hand spreader of the same size as the master apical file was mounted in an Instron testing machine and lateral compaction with gutta-percha and sealer was performed. The load value was recorded from the Instron testing machine. The spreader penetration depths were measured with an endodontic ruler. The data obtained were analysed statistically using anova and Student's t-tests. RESULTS: No significant difference in initial spreader load needed to condense the master cone was found amongst the four canal preparation techniques (P > 0.05). The step-back technique with Gates-Glidden drills and the hybrid technique demonstrated the least difference between the initial spreader penetration and the working length (mean 1.925 and 2.25 mm, respectively). The step-back technique without Gates-Glidden drills and the crown-down pressureless technique had the greatest difference between initial spreader penetration and the working length (mean 4.425 and 4.75 mm, respectively). CONCLUSION: The flare created by canal preparation affected spreader penetration depth, but had no effect on the spreader load.     

In vitro comparison of root canal preparation with step-back technique and GT rotary file--a nickel-titanium engine driven rotary instrument system

The aim of the authors' study was to compare the remaining root canal wall thickness and the preparation time of root canals, prepared either with step-back technique, or with GT Rotary File, an engine driven nickel-titanium rotary instrument system. Twenty extracted molars were decoronated. Teeth were divided in two groups. In Group 1 root canals were prepared with step-back technique. In Group 2 GT Rotary File System was utilized. Preoperative vestibulo-oral X-ray pictures were taken from all teeth with radiovisiograph (RVG). The final preparations at the mesiobuccal canals (MB) were performed with size #30 and palatinal/distal canals with size #40 instruments. Postoperative RVG pictures were taken ensuring the preoperative positioning. The working time was measured in seconds during each preparation. The authors also assessed the remaining root canal wall thickness at 3, 6 and 9 mm from the radiological apex, comparing the width of the canal walls of the vestibulo-oral projections on pre- and postoperative RVG pictures both mesially and buccally. The ratios of the residual and preoperative root canal wall thickness were calculated and compared. The largest difference was found at the MB canals of the coronal and middle third level of the root, measured on the distal canal wall. The ratio of the remaining dentin wall thickness at the coronal and the middle level in the case of step-back preparation was 0.605 and 0.754, and 0.824 and 0.895 in the cases of GT files respectively. The preparation time needed for GT Rotary File System was altogether 68.7% (MB) and 52.5% (D/P canals) of corresponding step-back preparation times. The use of GT Rotary File with comparison of standard step-back method resulted in a shortened preparation time and excessive damage of the coronal part of the root canal could be avoided.     

Residual dentin thickness in mesial roots of mandibular molars prepared with Lightspeed rotary instruments and Gates-Glidden reamers

OBJECTIVE: We sought to measure the residual dentin thickness (RDT) in the mesial roots of mandibular molars after instrumentation with Lightspeed and Gates-Glidden rotary instruments.Study design Thirty extracted, untreated human mesial roots of mandibular molars were separated from the distal roots and embedded in clear polyester resin. The roots were cut horizontally at 1, 4, and 7 mm short of the anatomic apex. The diameter of each mesiobuccal canal was measured by using a stereo measuring microscope at each level in the buccolingual and mesiodistal directions. The dentin thickness was measured in each level in the mesial, distal, buccal, and lingual directions. Sections were reassembled with a muffle. The canals were enlarged to the working length with Lightspeed rotary instruments, of which the average size used was a No. 50 file. The coronal third was flared with No. 2 Gates-Glidden reamers. Slices were separated again, and the RDT and canal diameters were measured. RESULTS: The minimal measured RDT after instrumentation at the 1-, 4-, and 7-mm levels was 0.70 +/- 0.28 mm, 1.04 +/- 0.18 mm, and 1.09 +/- 0.19 mm, respectively. The average diameter of the canals after instrumentation at the 1-, 4-, and 7-mm levels was 0.50 +/- 0.04 mm, 0.52 +/- 0.05 mm, and 0.74 +/- 0.08 mm, respectively. The canal diameter did not exceed one third of the root diameter at all levels. CONCLUSIONS: Root canal preparation of mandibular mesial roots with Lightspeed instruments to No. 50 in the apical third and Gates-Glidden reamers to No. 2 in the coronal third does not significantly decrease the RDT.