Danger zone in mandibular molars before instrumentation: an in vitro study

The aim of this work was to measure the danger zone in mandibular molars, relating to strip perforations that might affect the mesial root during canal instrumentation. One hundred mesial roots were sectioned 2mm below the furcation and the distal concavities were measured with a microscope from the border of the canals to the outer dentin of the root. The average thickness of the danger zone of the mesial roots was 0.789 +/- 0.182mm. No significant statistical differences were observed comparing the danger zone of mesiobuccal and mesiolingual canals.     

The impact of post space preparation with Gates-Glidden drills on residual dentin thickness in distal roots of mandibular molars

BACKGROUND: Posts frequently are used to retain buildups. The authors examined the effects of post space preparation with Gates-Glidden drills on residual dentin thickness in distal roots of mandibular molars. METHODS: The authors embedded 26 root-treated mandibular molars in endodontic cubes and sectioned them perpendicularly to their long axis at 1.8-millimeter intervals. They placed Gates-Glidden drills nos. 3, 4, 5 and 6 sequentially to 5 mm short of working length in the distal canals. After using each drill size, the authors measured the dentin thickness from light microscopic images of the tooth slices. RESULTS: The authors analyzed data to detect changes resulting from canal instrumentation. They performed statistical analysis by partitioning the variability in a nested analysis of variance. Strip perforations occurred with a no. 4 Gates-Glidden drill 7.3 percent of the time and more frequently with larger drills. After endodontic treatment alone, the canal wall on the furcal side was less than 1 mm thick 82 percent of the time and less than 0.5 mm thick 17.5 percent of the time. CONCLUSIONS: Dentin thickness correlates inversely to post space diameter. A no. 4 Gates-Glidden drill caused strip perforations in 7.3 percent of the canals studied, and therefore the authors recommend that Gates-Glidden drills larger than a no. 3 not be used in these roots. After endodontic treatment, the furcation-side dentin thickness was less than 1 mm in 82 percent of the teeth. CLINICAL IMPLICATIONS: Post space preparation in mandibular molars carries significant risk of perforation. Post space in such teeth should be limited to the endodontically prepared canal.     

The risk of furcal perforation in mandibular molars using Gates-Glidden drills with anticurvature pressure

OBJECTIVE: The aim of this study was to determine whether using Gates-Glidden (GG) drills and anticurvature pressure in curved mesial root canals of mandibular molars could remove more dentin from the mesial canal wall and remove less dentin from the distal canal wall at a level 2 mm below the furcation. STUDY DESIGN: In 5 groups of mesial roots with an average curvature of 32-34 degrees, 103 canals were prepared using a size #2 or #3 GG drill in the coronal third (straight portion of the canal only) or coronal half (straight portion and part of the curved portion), with or without applying anticurvature pressure. Using a modification of the Bramante muffle mold the cross-section of the mesial root at 2 mm below bifurcation was photographed twice, before and after the use of GG; the photos were then scanned as tagged image files. The thickness of the mesial and distal canal walls wer measured using an image analysis program. The reduction of the wall thickness after the use of GG was calculated. RESULTS: Before enlargement, the average and minimal thickness of the distal wall was 0.92 and 0.43 mm respectively, thinner than that of the mesial wall (1.50 and 0.87 mm, correspondingly). After the use of GG, the reduction of the mesial wall was similar to the reduction of the distal wall (P > .05 for all groups). In 4 groups the maximal reduction of the distal wall was > or =0.72 mm. CONCLUSIONS: After using GG drills and anticurvature pressure, dentin was uniformly removed regardless of the size of the GG and the depth of placement of GG. Flaring with GG drills in mandibular molars may result in perforations; application of anticurvature pressure did not reduce the risk.     

Comparison of the effects of TripleGates and Gates-Glidden burs on cervical dentin thickness and root canal area by using cone beam computed tomography

The search for new instruments to promote an appropriate cervical preparation has led to the development of new rotary instruments such as TripleGates. However, to the best of the authors'' knowledge, there is no study evaluating TripleGates effect on the “risk zone” of mandibular molars.

Objectives

: The aim of this study was to evaluate the effects of a crown-down sequence of Gates-Glidden and TripleGates burs on the remaining cervical dentin thickness and the total amount of dentin removed from the root canals during the instrumentation by using cone beam computed tomography. The number of separated instruments was also evaluated.

Material and Methods

: Mesial roots of 40 mandibular first molars were divided into 2 equal groups: crown-down sequence of Gates-Glidden (#3, #2, #1) and TripleGates burs. Cervical dentin thickness and canal area were measured before and after instrumentation by using cone beam computed tomography and image analysis software. Student’s t-test was used to determine significant differences at p<0.05.

Results

: No significant differences (p>0.05) were observed between the instruments, regarding the root canal area and dentin wall thickness.

Conclusion

: Both tested instruments used for cervical preparation were safe to be used in the mesial root canal of mandibular molars.     

The Impact of TruNatomy and ProTaper Gold Instruments on the Preservation of the Periradicular Dentin and on the Enlargement of the Apical Canal of Mandibular Molars

IntroductionThis study aimed to evaluate the preservation of periradicular dentin and the enlargement of the apical canal of mandibular molars with TruNatomy (Dentsply Sirona, Ballaigues, Switzerland) and ProTaper Gold (Dentsply Sirona) instruments.MethodsTwenty mandibular molars were scanned in a micro–computed tomographic device, anatomically paired, and distributed into 2 groups (n = 10). In the ProTaper Gold group, mesial and distal canals were prepared up to F2 (25/.08v) and F3 (30/.09v) instruments, whereas in the TruNatomy group, mesial and distal canals were enlarged up to the prime (26/.04v) and medium (36/.03v) instruments, respectively. After a new scan, the surface area, volume, unprepared areas, transportation, percentage of dentin removal, and dentin thickness parameters were calculated. Data were compared between groups using the Mann-Whitney test, the Student t test, and the nonmetric multidimensional scaling test with alpha set at 5%.ResultsNo difference was found between groups regarding unprepared canal areas and the reduction of dentin thickness (P > .05). Transportation was lower than 0.1 mm in all groups, and statistical differences were observed only at the apical third of the mesiobuccal canal with lower values in the TruNatomy group. ProTaper Gold removed more dentin than TruNatomy at the coronal level of mesial roots (1.8% and 1.0%, respectively) (P < .05).ConclusionsTruNatomy and ProTaper Gold were efficient for performing canal preparation in mandibular molars. The tested systems were similar in terms of untouched canal walls and remaining dentin thickness and slightly different in the apical transportation of mesial canals and the percentage of dentin removal at the coronal third but without clinically significant errors.     

Remaining dentin thickness in the apical 4 mm following four cleaning and shaping techniques

The aim of this study was to determine the remaining dentin thickness (RDT) in the apical 4 mm following four cleaning and shaping techniques. Sixty human adult extracted mandibular incisors and 60 mesial buccal canals of mandibular molars were assigned to five groups of 12 teeth for each tooth type: Step-down stainless steel hand instrumentation, Lightspeed, Profile GT and 0.4 taper, K3 "g pack," control group. After instrumentation the teeth were sectioned at 0.5, 1.5, 2.5, and 3.5 mm short of working length (WL) and evaluated for the minimum RDT at each level. ANOVA of RDT showed significant differences among levels and techniques. For incisors, no technique yielded greater RDT than the other techniques (p < 0.0001). For molars, K3 had greater RDT than the other techniques (p = 0.0006) at the 1.5, 2.5, and 3.5 mm levels. While there were significant statistical differences in RDT among techniques at different levels, further study would be required to determine any significant clinical difference in RDT.     

Apical anatomy in mesial and mesiobuccal roots of permanent first molars

The purpose of this in vitro study was to investigate the canal configuration types, and the prevalence and location of anatomical variations in the mesiobuccal (MB) and mesial roots of permanent maxillary and mandibular first molars after instrumentation. The number and the type of canals were determined before instrumentation using conventional methods. All root canals from the 47 MB roots and 42 mesial roots were then instrumented to size #30 with ProFile .04 taper rotary instruments in a crown-down method and then filled with a single gutta-percha cone and sealer. Transverse 1 mm-thick cross-sections at 2, 3, 4, and 5 mm from the apex were obtained, stained and examined using a stereomicroscope. The canal configuration types and the prevalence and location of isthmi and accessory canals in roots with two canals were evaluated. The prevalence of two canals was 80.8% in the maxillary MB roots and 95.2% in the mandibular mesial roots. There were six types of canal configurations in the instrumented root apices. The prevalence of anatomical variations was highest at the apical 4 mm level, and was more frequent in mandibular first molars, and in roots with Weine type III canal. chi test showed that the prevalence of the anatomical variations was statistically higher in the maxillary MB roots with Weine type III canals than in those with Weine type II canals (p < 0.05). Different canal configurations were often found at different levels in the same root. The results indicate that anatomical variations persist following instrumentation of roots with two canals in first molars. These anatomical variations should be considered during surgical or nonsurgical endodontic procedures of the permanent first molars.     

Effects of Gates-Glidden, LA Axxess and orifice shaper burs on the cervical dentin thickness and root canal area of mandibular molars

This study evaluated the increase of the instrumented area and dentin thickness in the mesial and distal aspects of mesial canals of mandibular molars after the use of Gates Glidden (GG), LA Axxess (LA) and Orifice Shaper (OS) instruments. A total of 53 canals from 27 mandibular molars were embedded in resin and divided into 3 groups. The roots were sectioned 3 mm below the cementoenamel junction and the images were captured before and after instrumentation. The increase of the instrumented area in terms of percentages and the remaining dentin thickness, in mm, at the mesial and furcal aspects were calculated using the Image tools software. Data were analyzed using the Kruskal-Wallis and Dunn's test. The significance level was set at 5%. All instruments promoted cervical flaring with different amounts of dentin removal at the mesial and distal aspects of the root canals. Statistically significant difference (p<0.05) was found between LA and all other instruments after using the first instrument. Regarding dentin thickness, no significant difference (p>0.05) was found between the mesial and distal walls in all groups. It may be concluded that LA 35.06 and GG 3 burs produced the thinnest dentin walls, and thus their use in mesial canals of mandibular molars should be done with caution.     

Evaluation of the risk of a stripping perforation with Gates-Glidden drills: serial versus crown-down sequences

The aim of this study was to evaluate the remaining dentine/cementum thickness using Gates-Glidden burs in serial and crown-down sequences and to observe which of the two sequences is the safest for preparing mesial roots of molars. Thirty-six left and right human mandibular first molars were selected. Standard access cavities were made and initially explored with Flexofiles sizes 10 and 15 until the tip was visible at the apex. The teeth were embedded in a muffle specially developed for this study using a PVC tube with two parallel metal rods in its lid. Each tooth-block was sectioned 3 mm apically to the furcation using a low-speed saw with a diamond disc. The tooth-block was examined under a microscope and an initial image was captured by a digital video system with 8 X and 12 X magnifications. Finally, the tooth-blocks were reassembled in the muffle so that the canals could be instrumented. After instrumentation the area of each mesial canal as well as the smallest distance to the root furcation were measured again. The mesio-buccal canals (crown-down order) and the mesio-lingual canals (serial sequence) presented an average area of 0.46 +/- 0.16 mm(2) and 0.88 +/- 0.27 mm(2) (P < 0.01), respectively. The mean values of the smallest distance to the furcation for the mesio-buccal and mesio-lingual canals were 0.66 +/- 0.19 mm and 0.39 +/- 0.13 mm (P < 0.01), respectively. The remaining dentine/cementum thickness using Gates-Glidden burs was greater in the crown-down sequence than in the serial sequence.     

Effect of sonic versus ultrasonic instrumentation on canal preparation

The instrumentation time, and the resulting root canal angulation change and shape after using ultrasonic, sonic, and hand instrumentation techniques were studied in the mesial canals of 55 extracted human mandibular first and second molars. After instrumentation, the roots were sectioned horizontally in the apical, middle, and coronal thirds and evaluated for shape, mesial and distal canal widths, and canal diameter. MM3000 and hand were significantly faster than the other techniques (p less than 0.005). MM3000 resulted in less angulation change than the Enac (p less than 0.005). Hand instrumentation was judged to have given the best shape (p less than 0.01).     

Comparative Assessment of the Effects of Gates-Glidden,Largo, LA-Axxess,and New Brazilian Drill CPdrill on Coronal Pre-enlargement: Cone-beam Computed Tomographic Analysis

Introduction

The removal of dentin interferences from the cervical third of root canals is essential for their correct cleaning and shaping and to facilitate access of endodontic instruments to the critical apical region. In mandibular molars, the concavity observed in the furcation area reduces dentin thickness, making this region more susceptible to perforation. The present ex vivo study used cone-beam computed tomographic imaging to compare 3 rotary burs with a new rotary bur recently launched in Brazil (ie, CPdrill; Helse Industry and Commerce Ltda, Santa Rosa, São Paulo, Brazil) regarding the amount of dentin removal from the distal wall of the mesial root of mandibular first molars.

Methods

A total of 40 root canals were selected and randomly divided into 4 groups for cervical preparation: Gates-Glidden burs #2 and #3 (Dentsply Maillefer, Ballaigues, Switzerland), Largo burs #1 and #2 (Dentsply Maillefer), LA-Axxess burs #1 and #2 (SybronEndo, Glendora, CA), and CPdrill burs (1-size only). Dentin thickness in the distal wall of mesial canals at 2 mm from the furcation was measured using I-CATvision software before and after cervical preparation.

Results

There was no statistically significant difference between groups regarding residual dentin thickness after instrumentation with the drills (P = .684).

Conclusions

It was concluded that CPdrill is safe for use in cervical preparation of the mesial root of mandibular first molars because it did not promote excessive dentin removal on distal walls.     

Influence of cervical preflaring on determination of apical file size in mandibular molars: SEM analysis

This study investigated the influence of cervical preflaring with different rotary instruments on determination of the initial apical file (IAF) in mesiobuccal roots of mandibular molars. Fifty human mandibular molars whose mesial roots presented two clearly separated apical foramens (mesiobuccal and mesiolingual) were used. After standard access opening and removal of pulp tissue, the working length (WL) was determined at 1 mm short of the root apex. Five groups (n=10) were formed at random, according to the type of instrument used for cervical preflaring. In group 1, the size of the IAF was determined without preflaring of the cervical and middle root canal thirds. In groups 2 to 5, preflaring was performed with Gates-Glidden drills, ProTaper instruments, EndoFlare instruments and LA Axxes burs, respectively. Canals were sized manually with K-files, starting with size 08 K-files, inserted passively up to the WL. File sizes were increased until a binding sensation was felt at the WL and the size of the file was recorded. The instrument corresponding to the IAF was fixed into the canal at the WL with methylcyanoacrylate. The teeth were then sectioned transversally 1 mm short of the apex, with the IAF in position. Cross-sections of the WL region were examined under scanning electron microscopy and the discrepancies between canal diameter and the diameter of IAF were calculated using the tool "rule" (FEG) of the microscope's proprietary software. The measurements (microm) were analyzed statistically by Kruskal-Wallis and Dunn's tests at 5% significance level. There were statistically significant differences among the groups (p<0.05). The non-flared group had the greatest discrepancy (125.30 +/- 51.54) and differed significantly from all flared groups (p<0.05). Cervical preflaring with LA Axxess burs produced the least discrepancies (55.10 +/- 48.31), followed by EndoFlare instruments (68.20 +/- 42.44), Gattes Glidden drills (68.90 +/- 42.46) and ProTaper files (77.40 +/- 73.19). However, no significant differences (p>0.05) were found among the rotary instruments. In conclusion, cervical preflaring improved IAF fitting to the canals at the WL in mesiobuccal roots of maxillary first molars. The rotary instruments evaluated in this study did not differ from each other regarding the discrepancies produced between the IAF size and canal diameter at the WL.     

The Effect of Larger Apical Preparations in the Danger Zone of Lower Molars Prepared Using the Mtwo and Reciproc Systems

Introduction

The aim of this study was to evaluate the effects of large apical preparations in the danger zones of the mesial root canals of mandibular molars instrumented with the Mtwo and Reciproc systems (VDW, Munich, Germany) until reaching apical diameters of 0.25 and 0.40 mm.

Methods

Twelve mandibular molars, the mesial roots of which presented distinct foramens and similar anatomies, were selected using micro–computed tomographic scanning. Mtwo and Reciproc instruments were used to shape the mesiobuccal or mesiolingual canals. The mesial canals were scanned before and after the use of 0.25- and 0.40-mm Mtwo and Reciproc instruments. The analyzed parameters included the root canal volume and remaining dentin thickness at 5 different levels. The obtained data were subjected to paired analysis of variance and Tukey or Friedman and Dunn tests for intragroup analysis and the Mann-Whitney U test for comparison between the mesial and distal walls.

Results

There were no significant differences between the mesial and distal dentin thickness for the points analyzed with both instrumentation techniques (P > .05). The volumetric analysis revealed a significant difference (P < .05) among the initial volume and after the use of the 0.25- and 0.40-mm instruments for both systems. The use of the 0.40-mm instrument increased the root canal volume in comparison to the 0.25-mm instrument (P < .05).

Conclusions

Both systems performed similarly for the preparation of curved root canals with separate apical foramens. The increase of the root canal preparation with the 0.40-mm instrument significantly increased the root canal volume at the apical third without significantly reducing the dentin thickness in the danger zone for both instrument systems.     

Comparison of the Canal Master endodontic instrument and K-type files for enlargement of curved root canals

Twenty mandibular molars with 40 mesial curved root canals were instrumented with a circumferential technique using K files and the Canal Master instrumentation technique by junior dental students whose only endodontic experience had been completion of a preclinical endodontic course. Preoperative and postoperative radiographs were taken facially and mesially with instruments in place. The canals were evaluated radiographically for transportation 1 mm and 4 mm from the apex. The mesial roots were cross-sectioned at the same level. The sections were evaluated for roundness of the canal preparation. It was concluded that the Canal Master instrumentation technique transported the root canal less and produced rounder preparations than the K file circumferential technique. There appears to be a greater tendency for breakage with the Canal Master.     

Dentine removal in the coronal portion of root canals following two preparation techniques

AIM: To measure the root canal area and the reduction of the mesial and buccal/lingual wall thickness at the level of the coronal interference in mesial roots of mandibular molars after instrumentation with a crown-down or a simultaneous root canal preparation technique. METHODOLOGY: Twenty mesial roots of first mandibular molars with a moderate root canal curvature were embedded in resin and sectioned horizontally at the level of the coronal interference, using a modification of the Bramante technique. After scanning and processing, the sections were reassembled. One root canal of each root was prepared using ProTaper instruments, while Mtwo instruments were used in the other root canal of the same mesial root. After scanning and processing, the data obtained were analysed for two parameters: changes in root canal area after instrumentation (Delta A) and reduction of the mesial and buccal/lingual wall thickness (Delta T). The data were subjected to Student's t-tests for statistical analysis at a significance level of P < 0.05. RESULTS: No statistically significant differences were found between the two groups with respect to the changes in the areas (Delta A) at the level considered (P = 0.410). No statistically significant differences were noticed between the two groups for dentine thickness (Delta T) of both the mesial wall (P = 0.077) and the buccal or lingual wall (P = 0.171). CONCLUSIONS: There was no difference between the ProTaper and Mtwo groups for the amount of dentine removed.     

下颌第二磨牙C形根管的特点和临床治疗

目的探讨下颌第二磨牙C形根管的发生率、临床诊断和治疗方法。方法通过对152例下颌第二磨牙拍摄术前X线片和术中根管探查,按照Melton标准诊断C形根管;采用机用镍钛器械Hero642进行根管预备,次氯酸钠超声冲洗,热牙胶垂直加压技术充填根管。记录C形根管的发生率及临床特点,根据治疗前、中、后的X线片评价根管预备和充填的效果。结果下颌第二磨牙C形根管的发生率为32.2%,79.6%的C形根管患牙X线片表现为锥形融合牙根,20.4%表现为近、远中独立牙根;所有患牙均无根管内并发症发生,治疗效果好。结论下颌第二磨牙C形根管主要存在于融合牙根,根管探查结合X线片可诊断C形根管;机用镍钛器械预备根管、次氯酸钠超声冲洗和垂直加压技术充填根管可获得良好的治疗效果。     

下颌第一磨牙近中根管的根管口分型和临床疗效分析

目的探讨下颌第一磨牙近中根管的根管口形态特点和临床治疗方法。方法选取71颗临床进行根管治疗的下颌第一磨牙．在手术显微镜下观察并记录近中根管的根管口形态．分类计数;采用Protaper机用镍钛器械及超声器械进行根管预备,常规针式冲洗合并超声荡洗．热牙胶垂直加压充填技术充填根管;根据治疗前后临床检查及x线片评价根管预备和充填的效果。结果所有样本中单根管口出现率为2．82％（2例）、双根管口为91．55％（65例）、三根管口为5．63％（4例）。其中双根管口之间有峡区的为38例（53．52％）、无峡区的为27例（38．03％）。所有患牙根管治疗后均无根管内并发症发生．术后1年根管治疗成功率为92．9％。结论下颌第一磨牙根管形态复杂,手术显微镜有助于根管形态的探查．机用镍钛器械合并超声技术预备根管．超声冲洗和热牙胶垂直加压技术充填根管可获得良好的治疗效果。     

Digitization, analysis and processing of dental images during root canal preparation with Quantec Series 2000 instruments

AIM: The aim of this study was to determine the shaping ability of Quantec Series 2000 nickel-titanium instruments in the mesio-buccal roots of maxillary first molars and the mesial roots of mandibular first molars. METHODOLOGY: A total of 20 canals were prepared with Quantec instruments, adopting the technique recommended by the manufacturer. Each canal was sectioned horizontally into four and the canal in each portion photographed before and after preparation. The images obtained were digitized and the increase in canal surface for each quadrant of the four sections was evaluated, along with the variation in centre of mass after instrumentation. RESULTS: Mechanical instrumentation of the canals generated mean centre of mass displacements that did not vary between sections, except for the mid-apical section, which showed significant mesial displacement, i.e. toward the side opposite the furcation. Thus, overall, the widening of the canal was symmetrical. CONCLUSIONS: Under the conditions of the study, the Quantec Series 2000 rotary system was simple and safe to use, and created good three-dimensional mechanical preparation of natural canals.     

A preliminary in vitro study of the incidence and position of the root canal isthmus in maxillary and mandibular first molars

AIM: To investigate in vitro the incidence and position of the root canal isthmus in extracted mesiobuccal roots of maxillary and mesial roots of mandibular first molars. METHODOLOGY: Fifty maxillary and 50 mandibular molars were included in the study. The mesiobuccal roots of maxillary molars and the mesial roots of mandibular molars were sectioned from their crowns in the furcation region and embedded in clear resin. Transverse serial 1-mm-thick sections from the apical 6 mm were prepared. The apical side of each section was stained with India ink and observed through a light microscope. The sample images were saved to disk using a digital camera and the root canals in terms of the number present and the incidence and classification of isthmuses. RESULTS: In the mesiobuccal root of the maxillary first molars, 70% had one canal, whereas 29.5% had two canals. In the mesial root of mandibular molars, 41% had one canal, whereas 59% had two canals. In some sections, more than two canals were found close to the apical foramen. The isthmus incidence was greatest 3-5 mm from the apex. In teeth having two canals, a complete or partial isthmus was frequently observed in the sections between 3 and 4 mm from the apex. Of the isthmuses present, 22% were complete and 37% partial in mandibular molars and 17.3% were complete and 11.7% partial in maxillary molars. CONCLUSIONS: The incidence of isthmus in the mesiobuccal root of the maxillary first molars and in the mesial root of the mandibular first molars was high, particularly in sections 3-5 mm from the apex. Cleaning the isthmus is a major challenge during root canal treatment.     

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.