软组织漂移对电磁导航经颊颅底穿刺影响的动物实验研究

目的：测试颊部软组织漂移对电磁导航经颊颅底穿刺精度的影响,从而推断电磁导航辅助半月神经节射频温控热凝术、颅底肿瘤穿吸活检或深部脓肿切排等的可行性。方法：3名初学者分别对3只6月龄山羊的双侧眶下裂进行盲穿和电磁导航辅助穿刺各5次,CT扫描测量穿刺针尖与眶下裂中心点的距离,采用SAS6.12统计软件的t检验和方差分析进行统计学比较。结果：3名实验者盲穿均未进入眶下裂,针尖与眶下裂中心点的平均间距右侧为15 mm,左侧为14.3 mm;电磁导航辅助穿刺时,测量颊部软组织中针尖与预设路径的平均偏差为4.3 mm/6.2,°终点均进入眶下裂,针尖与眶下裂中心点的平均间距右侧为2.7 mm,左侧为2.8 mm;盲穿与导航辅助存在统计学差异（P值范围于0.0008与0.0239之间）。结论：由于终点为骨性孔隙结构,穿刺中途的软组织漂移不影响电磁导航系统的穿刺精度,因此电磁导航可用于半月神经节射频温控热凝术、颅底肿瘤穿吸活检或深部脓肿切排等的精确穿刺。     

CT/MRI图像整合建立半月神经节射频手术的导航界面

目的:建立CT/MRI配准和融合基础上的卵圆孔与半月神经节共存的手术界面,实现半月神经节与穿刺针关系的可视化。方法:将10例三叉神经痛患者的增强3d Fiesta序列的MRI数据和头颅CT数据导入surgView-RFT电磁导航系统,增强3d Fiesta上分割出半月神经节图像,单独保存。头颅增强3dFiesta和CT以鼻根点、双侧髁突外侧嵴点3点进行线性配准,在CT/MRI融合基础上二次融合半月神经节图像,建立卵圆孔与半月神经节共存的手术界面。结果:10例患者的20侧半月神经节均在增强3d Fiesta上被分割成像。经图像融合后卵圆孔与半月神经节的位置关系如下:冠状位、矢状位上半月神经节不位于卵圆孔开口区的为2/20,半月神经节位于卵圆孔开口区的为18/20。结论:CT/MRI整体配准和融合基础上的卵圆孔与半月神经节共存的导航手术界面,可以排除非靶组织的干扰,使靶点和穿刺针的关系更加简单明了,便于应用者识别,同时为实现分支选择性射频温控热凝术奠定基础。     

导航辅助山羊下颌体牵张成骨术的实验研究

目的：应用立体定向导航外科手术系统初步建立山羊单侧下颌骨牵张成骨术的研究方法,分析导航辅助牵张成骨术的精度。方法：选用成年山羊3只。局麻下在上颌骨植入5颗定位钉,用蜡片记录咬合关系后行颌间固定,将螺旋CT扫描数据导入AccuNavi1.0软件,进行三维测量与虚拟手术。全麻下,应用TBNavis-CMFS导航系统行下颌骨单侧体部牵张成骨术,牵引到位后,行CT扫描并同法进行测量,并应用Surgicase5.0软件测量牵引长轴间交角,与模拟手术结果进行比较。结果：山羊口内上颌前部定位钉出现松动,口外上颌两侧定位钉稳固。平均牵引长度为10.12mm（9.88-10.34mm）。三维测量分析显示,术后与术前模拟结果各指标间无显著性差异（P〉0.05）,牵引长轴交角均值为5.49°（4.70°～6.84°）。结论：选择口外入路的上颌骨区域植入钛钉作为山羊颌骨导航手术的配准方法精确性好。导航辅助山羊下颌骨牵张成骨术,可准确地将手术规划转移到实际手术中。     

X线下2种穿刺方法射频热凝治疗上颌神经痛的疗效分析

目的研究X线下经皮穿刺卵圆孔和圆孔射频治疗上颌神经痛临床疗效对比。方法对2008—2015年收治住院的69例单纯上颌神经痛患者随机分为2组。A组:33例,穿刺卵圆孔,患者采用Hartel前入路法,根据射频针尖至耳-床线的垂直距离确定入颅深度后,行射频热凝。B组:36例,穿刺圆孔,采用弯针穿刺进入翼腭窝,局部注射2%利多卡因1 m L,X线定位圆孔穿刺方向,再穿入圆孔,X线下定位确定进入圆孔后行射频治疗。结果所有患者均顺利完成手术,穿刺针均准确位于圆孔内和卵圆孔内,治疗后疼痛即刻缓解,无严重并发症发生,眶下区及上腭均有感觉迟钝。所有患者随访6个月~2年,两组3天有效率、术后复发率差异比较无统计学意义(P>0.05)。两组在非患支神经损伤的发生率差异显著(P<0.05)。手术时间A组平均48.79 min,B组平均50.32 min;术中疼痛评分A组平均7.48分,B组平均2.92分;术中患者满意度评分A组平均2.64分,B组平均5.36分。两组在手术时间无统计学差异,在术中疼痛评分及患者满意度评分具有统计学差异。结论经翼腭窝穿刺圆孔治疗上颌神经疼痛具有一定的优势,值得推广。     

牙支持3D导板辅助穿刺卵圆孔射频热凝治疗三叉神经痛的疗效分析

目的:探讨牙支持式3D打印导板辅助穿刺卵圆孔射频热凝治疗三叉神经痛术中术后的疗效分析.方法:对2019年1月～2021年5月收治的三叉神经痛患者40人,根据患者需要随机分成2组:A组(对照组),常规按照Hartel前入路法穿刺卵圆孔,进入卵圆孔后,耳-床线定位确定入颅深度后行射频治疗.B组(导板组),采用3D导板,给患者戴上导板固定后,完成穿刺,耳-床线定位确定入颅深度后行射频治疗.分析2组的术前疼痛评分(VAS)术后即刻及术后1月疼痛消失的有效率,手术时间,穿刺次数,并发症,穿刺的偏移程度.结果:与对照组A组比较在术后即刻有效率、术后1月随访有效率比较无统计学差异(P>0.05).在穿刺次数、穿刺偏移率、手术时间、并发症两组间比较有统计学差异(P<0.05).导板与牙齿紧密贴合率100％.结论:3D打印导板应用于穿刺卵圆孔具有明显的优势,可以减少患者创伤,减少X线辐射,减少穿刺偏移,术后疗效肯定,值得广泛应用.     

计算机导航技术在颌骨骨纤维异常增殖症手术中的应用

目的:探讨计算机导航技术在颌骨骨纤维异常增殖症手术中的应用价值.方法:纳入14例颌面部骨纤维异常增殖症患者,先将患者的术前CT数据导入计算机导航系统中,根据颌骨镜像原理进行术前设计及三维手术模拟,确定骨切除位置及范围.术中,根据病变部位及手术范围可将参考架置于患者前额或是下颌骨颏部.完成注册与配准,使手术视野和导航显示屏上的虚拟图像完全匹配.结果:面部的解剖结构与三维重建模型完全吻合,术中顺利完成实时导航.手术器械可实现空间定位,能够明确其与手术区域解剖结构的位置关系,手术具有高度的精确性与安全性.术后疗效的评估是通过术前计划和术后CT重建影像相融合得到的,1～3年的随访中没有发现并发症.结论:计算机导航系统在提高颌面部骨纤维异常增殖症的安全性与准确性方面具有较好的应用价值.     

三维CT引导下经卵圆孔穿刺射频治疗三叉神经痛

目的:探讨三维CT引导下经卵圆孔穿刺射频治疗三叉神经痛的临床疗效。方法:随机选取我院2013—2015年收治的三叉神经痛患者38例,行三维CT引导卵圆孔穿刺射频术治疗,对其临床疗效和术后并发症进行分析,并进行6个月的随访。结果:38例患者行三维CT引导卵圆孔穿刺射频治疗三叉神经痛手术均成功。术后第1天有效率达78.95%,12例患者完全缓解,有1例未缓解。术后1个月与术后6个月的有效率分别为94.74%和97.37%,二者之间差异不具有统计学意义(P>0.05),且均显著高于术后第1天和第7天,差异均具有统计学意义(P<0.05)。结论:三维CT引导下经卵圆孔穿刺射频治疗三叉神经痛可提高穿刺成功率,减少并发症,选择性毁损痛觉纤维有助于提高患者生活质量,值得临床推广使用。     

基于快速原型技术的导航辅助下颌骨内置式牵张成骨术的实验研究

目的：应用自主研发的导航手术系统,在快速原型技术制作的三维头颅模型上进行内置式下颌骨牵张成骨术的实验研究,通过三维定点测量,分析该导航手术的精度。方法：对1例单侧下颌骨发育不足的患者行螺旋CT扫描后,采用快速原型技术制作5个相同的头模,按导航配准原则植入定位钉后再行CT扫描。应用AccuNavi 1.0软件对三维图像进行测量,并与游标卡尺实体测量的相应指标进行头模制作精度检测。然后进行下颌骨三维测量分析与虚拟单侧内置式下颌支牵张成骨术,将制定的手术规划通过实时TBNavis-CMFS导航系统在三维头模上实施,牵引到位后,行CT扫描图像重建,应用AccuNavi1.0软件与Surgicase5.0软件进行三维测量与牵引长轴间成角测量,采用SPSS13.0软件包对结果进行配对t检验。结果：快速原型制作的三维头模与AccuNavi1.0软件重建的三维图像间各测量指标无统计学差异（P〉0.05）。模型手术平均牵引长度12.40mm（11.79～12.68mm）,模拟手术与导航模型术后牵引长轴间成角均值为4.67°（2.01°～6.49°）。导航术后各项指标中,除CoL-CoR（P=0.037）、CoL-GoL（P=0.017）与模拟手术值间有显著性差异外,其余指标间均无显著性差异（P〉0.05）。结论：应用快速原型技术制作的三维头颅模型与AccuNavi1.0软件的三维重建图像精度相仿。通过TBNavis-CMFS导航系统平台,建立了导航辅助下颌骨牵引成骨术的实验方法,准确地将手术规划转移到模型手术中。     

光学导航技术在口腔颌面深部间隙异物取出术中的应用

目的:探讨光学导航技术应用于口腔颌面深部异物留置取出术的适应条件和临床价值。方法:对5例口腔颌面部外伤后异物留置于深部间隙的患者在导航辅助下行异物取出术,术前进行三维CT和数字减影血管造影检查,对异物进行空间定位,并将CT的Dicom数据导入STN导航系统中,用于术前手术规划和术中导航。术中观察导航系统的实时性和精确性,评价导航技术对口腔颌面部深部间隙异物取出的有效性。结果:在光学导航技术辅助下,5例留置的异物均能通过微创入路顺利定位和取出,术中未发现神经、血管损伤,术后亦未发现感染、呼吸困难等并发症。术后随访3～12个月,患者主诉症状均缓解,功能和面型取得了满意的效果。结论:光学导航技术在口腔颌面深部间隙异物取出术中的应用,尤其在解剖位置复杂和危险的区域,可以提高手术的精确性、微创性和安全性。     

计算机辅助导航外科在颞下颌关节成形术中的应用

目的:评价计算机辅助导航(CANS)技术在颞下颌关节成形术中的应用价值.方法:4例单侧颞下颌关节骨性强直患者,定位钉植入后行面部CT扫描.在CANS上行术前设计及三维手术模拟,确定骨切除位置及范围,计算机辅助导航下行颞下颌关节成形术.术后CT复查.并与术前设计比较.结果:患者解剖结构与面部三维重建模型完全吻合,术中实现实时导航.手术器械实现空间定位,术者能够明确其与解剖结构的位置关系,精确度高,系统误差小于1mm.术后CT检查示切除范围与术前设计完全一致,手术刨伤小,无并发症.结论:计算机辅助导航颞下颌关节成形术是一种较为安全、有效的治疗颞下颌关节强直的方法.     

Tissue reaction to Endométhasone sealer in root canal fillings short of or beyond the apical foramen

Objective

This study evaluated the response of periapical tissues to the endodontic sealer Endométhasone in root canal fillings short of or beyond the apical foramen.

Material and Methods

Twenty root canals of premolars and incisors of 2 mongrel dogs were used. After coronal access and pulp extirpation, the canals were instrumented up to a size 55 K-file and the apical cemental barrier was penetrated with a size 15 K-file to obtain a main apical foramen, which was widened to a size 25 K-file. The canals were irrigated with saline at each change of file. The root canals were obturated either short of or beyond the apical foramen by the lateral condensation of gutta-percha and Endométhasone, originating 2 experimental groups: G1: Endométhasone/short of the apical foramen; G2: Endométhasone/beyond the apical foramen. The animals were killed by anesthetic overdose 90 days after endodontic treatment. The individual roots were obtained and serial histological sections were prepared for histomorphological analysis (H&E and Brown & Brenn techniques) under light microscopy. The following parameters were examined: closure of the apical foramen of the main root canal and apical opening of accessory canals, apical cementum resorption, intensity of the inflammatory infiltrate, presence of giant cells and thickness and organization of the apical periodontal ligament. Each parameter was scored 1 to 4, 1 being the best result and 4 the worst. Data were analyzed statistically by the Wilcoxon nonparametric tests (p=0.05).

Results

Comparing the 2 groups, the best result (p<0.05) was obtained with root canal filling with Endométhasone short of the apical foramen but a chronic inflammatory infiltrate was present in all specimens.

Conclusions

Limiting the filling material to the root canal space apically is important to determine the best treatment outcome when Endométhasone is used as sealer.     

不同镍钛旋转器械平解剖性根尖孔长度预备根管后根尖孔表面形态变化的研究

目的:研究不同镍钛旋转器械在平解剖性根尖孔长度时预备根管后根尖孔表面形态的变化。方法:选取因牙周病拔除的离体牙40颗,随机分为两组并在扫描电子显微镜下拍摄术前片,记录根尖孔表面形态;分别采用K3锉、TF锉在工作长度下(平解剖性根尖孔长度)预备根管,扫描电子显微镜下观察并记录预备后根尖孔表面形态的变化:记录根尖孔的偏移、根尖孔周围牙骨质缺损及根尖孔周围表面的裂纹。结果:K3组、TF组根管预备后均存在根尖孔的偏移、牙骨质的缺损及根尖孔周围表面的裂纹,其中根尖孔的偏移的样本数目、根尖孔周围牙骨质缺损样本数目两组之间存在统计学差异(P<0.05),根尖孔周围表面裂纹样本数两组之间无统计学差异。结论:K3、TF两种镍钛旋转器械在平解剖性根尖孔长度下预备根管时由于超根尖止点预备,均可导致根尖孔偏移,根尖孔周围的牙骨质缺损及根尖孔表面裂纹线产生,与K3锉相比,TF锉在减少根尖孔偏移及根尖孔周围牙骨质缺损方面更具优越性。     

Evaluation of bone thickness around the mental foramen for potential fixation of a bone‐borne functional appliance: a computer tomography scan study

Aim: A mandible bone‐borne Herbst appliance (MBBHA) would avoid the proclination of the lower incisors that occurs with any teeth‐borne functional appliance. But mapping of the bone characteristics at potential fixation areas around the mental foramen has not been carried out so far. The aim of this computer tomographic (CT) study was to evaluate bone thickness at specific positions around the mental foramen. Material and methods: CT scans of 60 randomly chosen adult Hong Kong Chinese subjects (mean age 28±6.3 years) were used to measure the bi‐cortical bone thickness in the mandible in the mental foramen area. The thickness of buccal and lingual cortical and cancellous bone was assessed at the following locations: 10 mm (A10 mm) and 5 mm (A5 mm) anterior, 10 mm (P10 mm) and 5 mm (P5 mm) posterior, and 5 mm (Inf5 mm) below the mental foramen. Results: The amount of buccal cortical bone thickness ranged between 1.89 mm, 10 mm anterior of the mental foramen, and 2.16 mm, 10 mm posterior to its location. At the A10 mm level, cortical thickness showed a marginal statistically significant difference between A5 and A10 mm. The total amount of bone thickness ranged from 10.19 to 12.06 mm. Conclusion: At the locations studied around the mental foramen, a mean bicortical bone thickness of 10–12 mm was measured. No large variation in the thickness was found between bicortical bone thicknesses in the measured locations around the mental foramen. Thorough evaluation on a case‐by‐case basis is advisable. To cite this article:
Al‐Kalaly AA, Wong RWK, Cheung LK, Purkayastha SK, Schätzle M, Rabie ABM. Evaluation of bone thickness around the mental foramen for potential fixation of a bone‐borne functional appliance: a computer tomography scan study.
Clin. Oral Impl. Res. 21 , 2010; 1288–1293.
doi: 10.1111/j.1600‐0501.2010.01947.x     

Age changes in location of mandibular foramen

In order to understand the changes in location of the mandibular foramen with age in children, lateral cephalometric radiographs from 112 child and adult patients, including both males and females, were randomly selected according to age. The subjects were divided into 6 age-groups; 3, 5, 7, 9, 11 and adult. Certain lines and points were traced on the radiographs used. The location of the mandibular foramen was identified by two persons. The perpendicular distance from the center of the mandibular foramen to the occlusal plane and the location of the mandibular foramen relative to the ramus height (Ar-Kk), as well as to the ramus width (a-p), were measured. The mandibular foramen was located 4.12 mm below the occlusal plane at the age of 3. It subsequently moved upward with age. By the age of 9, it had reached approximately the same level as the occlusal plane. The foramen continued to move upward to 4.16 mm above the occlusal plane in the adult group. The height percentage averages ranged from the lower 1/3 of the ramus height in the 3 year-old group to the middle of the ramus height in adults. The depth percentage averages ranged from 67.8% in 3 year-old children to 61.7% in adults. For greater accuracy in anesthetic procedures, dentists should relate the locational changes in the mandibular foramen with age when performing block anesthesia for the inferior alveolar nerve.     

镍钛器械在3种不同运动模式下预备根管后根尖孔表面形态变化

目的:研究3种不同运动模式下镍钛器械在平解剖性根尖孔长度时预备根管后根尖孔表面形态变化。方法:收集新鲜拔除的离体牙60颗,随机分为3组,用扫描电子显微镜拍摄术前片,记录根尖孔表面形态,然后分别采用Twist File Adaptive(TFA)、WaveOne、ProTaper(机用)3种镍钛锉在平解剖性根尖孔的工作长度下进行根管预备,然后在扫描电子显微镜下拍摄术后片,记录根尖孔周围牙骨质的缺损、根尖孔偏移、根尖孔周围表面的裂纹。结果:实验组均出现根尖孔周围牙骨质的缺损、根尖孔偏移、根尖孔周围表面的裂纹。3种镍钛器械根管预备后发生根尖孔偏移、根尖孔周围表面裂纹概率的差异有统计学意义(P＜0.05),3种镍钛器械根管预备后发生根尖孔周围牙骨质缺损概率的差异无统计学意义。结论:TFA和WaveOne在进行预备根管后相比ProTaper可降低根尖孔偏移的发生率,TFA比ProTaper和WaveOne在进行预备根管后产生根尖孔周围表面的裂纹少,降低了根折的风险。     

Ex vivo evaluation of the ability of four different electronic apex locators to determine the working length in teeth with various foramen diameters

BACKGROUND: The aim of this ex vivo study was to evaluate the accuracy of four electronic apex locators (EALs) to determine the working length in teeth with various foramen diameters. Our previous study revealed that electronically measured canal length was influenced by the root canal diameter. It is not known whether foramen size would interfere with the reading accuracy of an EAL. METHODS: A total of 36 extracted human lower single rooted premolar teeth were divided into four groups of nine teeth each. In groups A, B and C, the root canals were instrumented using #10-80, #10-100 and #10-120 K-files, and the tip of size #80, #100 and #120 K-files were permitted to pass through the apical foramen to a length of 1mm, respectively. In group D, the teeth were instrumented using #10-140 K-files and the tip of #140 K-file was permitted to pass through the apical foramen to a length of 5 mm. Thus, the average apical foramen diameters in groups A, B, C and D were approximately 0.82 mm, 1.02 mm, 1.22mm and 1.5 mm, respectively. The teeth were then mounted in 1% agar and four EALs were used: Root ZX, Foramatron D10, Apex NRG and Apit 7. For electronic measurement, sizes #10 and #80, #10 and #100, #10 and #120, and #10 and #140 K-files were used for groups A, B, C and D, respectively. During electronic measurement the canals were flushed with 6% sodium hypochlorite solution. RESULTS: Three-way ANOVA and Bonferroni test showed that EAL, file size and foramen size all had a significant influence on the measurement error (P<0.0001), with all the interactions between these three factors being significant (P<0.0001). CONCLUSIONS: The four EALs were unreliable to determine the working length of teeth with a wide apical foramen, when using a small size file. The Root ZX and Foramatron D10 showed significantly better scores than the other two EALs and may be more reliable to determine the working length of teeth with a wide apical foramen, if a tight-fit file is used.     

Apical extrusion of debris by manual and mechanical instrumentation

The aim of the present study was to assess the presence of apically extruded debris and evaluate the influence of canal curvature on the amount of debris produced by manual and mechanical techniques. Forty single-rooted mature teeth with 15 to 30 degree of root canal curvature were selected. The presence of only one foramen was confirmed using a magnifying lens. A size 15 K-file was placed up to the apical foramen to determine the patency. Working length was determined with the same instrument, 1 mm short of the foramen. According to the employed technique, the groups were labeled as follows: Group 1 - Manual instrumentation with Mor-flex files; Group 2 - Mechanical instrumentation with Cursor and Mor-flex files; Group 3 - Manual instrumentation with Flexi-cut files; Group 4 - Mechanical instrumentation with Cursor and Flexi-cut files. During instrumentation, the root canals were irrigated with 20 mL. Debris extruded through the apical foramen was collected using the Myers and Montgomery technique. The values (in mg) were: Group 1: 0.422 +/- 0.683; Group 2: 0.688 +/- 0.795; Group 3: 0.409 +/- 0.323; Group 4: 0.810 +/- 0.708. Data were analyzed statistically by ANOVA at 5% significance level. There was no statistically significant difference among the groups (p<0.05). No statistically significant differences were found between slight and moderate curvatures in terms of the amount of extruded debris (p>0.05).     

Shaping ability of ProTaper NEXT,ProTaper Universal and iRace files in simulated S‐shaped canals

The aim of this study was to determine the shaping ability of three nickel‐titanium endodontic file systems by comparing three parameters: canal deviation, apical foramen position and instrumentation time. A glide path was established in 30 simulated S‐shaped canal blocks that were randomly assigned into three groups (n = 10): ProTaper Universal, ProTaper NEXT and iRace. Each group was instrumented per its manufacturer's directions. Pre‐ and postoperative images were superimposed to determine any canal deviation or change in apical foramen position. The instrumentation times were recorded. The iRace system resulted in the least mean canal deviation. The apical foramen position was least shifted by the iRace system. The iRace system also required the least instrumentation time. The iRace system demonstrated the most favourable shaping ability in all three parameters.     

Clinical evaluation of the voltage gradient method for root canal measurement

The voltage gradient method for root canal measurement was evaluated in vivo and in vitro. For the evaluation in vivo, 25 single root teeth, were employed. The working length was measured by bipolor or monopolor electrode. After measurement, the electrode was fixed on the tooth, and the tooth was extracted. Radiograph was taken from 12 directions perpendicular to longer axis of tooth, and the relation between anatomical foramen, physiological foramen and the attained position of electrode tip was assessed. In the evaluation in vitro, 7 extracted teeth were used, for which the positions of anatomical foramen and physiological foramen had been determined in advance from radiograph, in order to determine the influence of the root canal irrigants and medicaments. The electrode was fixed on electronic calipers and direct reading of the movement. Root canal irrigants and medicaments were injected into root canal, and the measurements were evaluated. The results were as follows: (1) In the cases of 22 teeth measured by monopolar electrode in vivo, the electrode tip was within 0.5mm from physiological foramen except one tooth. (2) In the cases of 3 teeth measured by monopolar electrode in vivo, the electrode tip was within 0.4mm from anatomical foramen. (3) In the cases, where electrolyte solution was filled in root canal and measurement was made by bipolar in the evaluation in vitro, the results of measurement were stable, and the electrode tip tended to be slightly closer to coronal direction from physiological foramen. (4) In the cases where non-electrolyte solution was filled in root canal and measurement was made by bipolar electrode in the evaluation in vitro, the results of measurement were not stable, and the electrode tip tended to be closer to the apex from physiological foramen. (5) In the case of the evaluation in vitro, where electrolyte solution was filled in root canal and measurement was made by monopolar electrode, the electrode tip tended to be a little closer to the front than the anatomical foramen. (6) In the evaluation in vitro, where non-electrolyte solution was filled in root canal and measurement was made by monopolar, the measurement was not achievable. (7) 10% NaOCl solution was found to be very useful as electrolyte solution filled in root canal to search physiological foramen by this measurement method. The above results suggest that the voltage gradient method for root canal measurement is highly reliable because root canal morphology at the apex can be directly in identified.