Three-Dimensional Analysis of Root Anatomy and Root Canal Curvature in Mandibular Incisors Using Micro-Computed Tomography with Novel Software
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applied sciences Article Three-Dimensional Analysis of Root Anatomy and Root Canal Curvature in Mandibular Incisors Using Micro-Computed Tomography with Novel Software 1, 2, 3 4 5 JongKi Lee y, Shin-Hoon Lee y, Jong-Rak Hong , Kee-Yeon Kum , Soram Oh , Adel Saeed Al-Ghamdi 6, Fawzi Ali Al-Ghamdi 7, Ayman Omar Mandorah 8, Ji-Hyun Jang 5,9 and Seok Woo Chang 5,9,* 1 Private Practice, Changwon 51495, Korea; [email protected] 2 Eunpyeong Appletree Dental Clinic, 19, Jingwan 2-ro, Eunpyeong-gu, Seoul 03306, Korea; [email protected] 3 Department of Oral and Maxillofacial Surgery, Gaon Dental Hospital, 129, Dongseo-daero, Seobuk-gu, Cheonan-si, Choongcheongnam-do 31109, Korea; [email protected] 4 Department of Conservative Dentistry, Dental Research Institute, National Dental Care Centre for Persons with Special Needs, Seoul National University Dental Hospital, Seoul National University School of Dentistry, Seoul 03080, Korea; [email protected] 5 Department of Conservative Dentistry, Kyung Hee University Dental Hospital, 23 Kyungheedaero, Dongdaemun-gu, Seoul 02447, Korea; [email protected] (S.O.); [email protected] (J.-H.J.) 6 King Abdulaziz Hospital, Jeddah 22421, Saudi Arabia; [email protected] 7 Director of Dental Services, Ministry of Health, P.O.Box 109196, Jeddah 21351, Saudi Arabia; [email protected] 8 Department of Endodontics, Restorative and Dental Materials, Faculty of Dentistry, Taif University, Taif 26571, Saudi Arabia; [email protected] 9 Department of Conservative Dentistry, Kyung Hee University School of Dentistry, 23 Kyungheedaero, Dongdaemun-gu, Seoul 02447, Korea * Correspondence: [email protected] Contributed equally to this study as first authors. y Received: 22 May 2020; Accepted: 24 June 2020; Published: 26 June 2020 Abstract: Root canal treatment of mandibular incisor is difficult because of the narrow pulp space and apical curvature. The aim of this study was to measure the anatomical indicators of the mandibular incisors in Koreans using micro-computed tomography (MCT) with novel software (Kappa 2). The MCT-scanned data from 27 mandibular incisors were reconstructed and analyzed. For each canal, 3-dimensional (3D) surface models were re-sliced at 0.1 mm intervals perpendicular to the central axis of the root canal. Root canal width, dentine thickness, and direction and degree of root canal curvatures were measured automatically on each slice. Measurements were analyzed statistically with Bhapkar test, Friedman test, and Wilcoxon signed rank test. Labial and lingual dentine thicknesses were significantly larger than mesial and distal thicknesses (p < 0.001). The thinnest dentine was mainly located on the mesio-lingual side of the canals in the apical third. The mean narrowest and widest canal width in the apical sixth were 0.22 mm and 0.40 mm, respectively. The canal curvature abruptly increased in the apical 0.5-mm portion. MCT with novel software provided useful anatomical information for root canal instrumentation. Keywords: apical curvature; canal width; dentin thickness; mandibular incisor; micro-computed tomography Appl. Sci. 2020, 10, 4385; doi:10.3390/app10124385 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 4385 2 of 11 1. IntroductionAppl. Sci. 2020, 10, 4385 2 of 11 1.For Introduction successful endodontic treatment, an understanding of the complex root canal anatomy as well as surrounding root dentine architecture is essential. Although the mandibular incisors usually For successful endodontic treatment, an understanding of the complex root canal anatomy as have a single canal (72% (Leoni et al., 2014) [1], 91.1% and 82.5% (Liu et al., 2014) [2]), they pose the well as surrounding root dentine architecture is essential. Although the mandibular incisors usually greatesthave dia singlefficulty canal in access (72% (Leoni preparation et al., 2014) owing [1], to91.1% the and narrowness 82.5% (Liu of et the al., crown 2014) [2]), and they pulp pose space the in the mesio-distalgreatest difficulty direction in access [3]. Furthermore, preparation owing mandibular to the narrowness incisors often of the have crown mesial and pulp and space distal in curvesthe in theirmesio-distal apical third direction [3], which [3]. makesFurtherm theore, root mandibular canal preparation incisors often in this have area mesial even and more distal di fficurvescult. in theirIn terms apical of third root [3], canal which preparation, makes the root the canal root preparation canal width, in dentinthis area thickness even more around difficult. the root canal, and 3-dimensionalIn terms of root (3D) canal direction preparatio andn, the degree root canal of the width, root dentin canal thickness curvature around are relevant. the root canal, However, previousand 3-dimensional studies on the (3D) root direction canal anatomy and degree of the of mandibularthe root canal incisors curvature were are mainly relevant. focused However, on the root canalprevious type, the studies number on the of rootroot canals,canal anatomy and the of shape the mandibular of root canals incisors [1,2 ].were These mainly factors focused provide on the valuable root canal type, the number of root canals, and the shape of root canals [1,2]. These factors provide information on the root canal anatomy itself. However, more clinically relevant information for root valuable information on the root canal anatomy itself. However, more clinically relevant information canalfor preparation root canal preparation is the narrowest is the narrowest and the and widest the widest root root canal canal width, width, the the dentin dentin thickness, thickness, and and the directionthe direction and degree and ofdegree the root of the canal root curvature. canal curv Thereature. have There been have no been previous no previous studies investigatingstudies the 3Dinvestigating direction the or degree3D direction of root or degree canal curvature of root canal of curvature human mandibular of human mandibular incisors. incisors. Micro-computedMicro-computed tomographytomography (MCT) (MCT) with with math mathematicalematical modeling modeling is an accurate is an and accurate non- and non-destructivedestructive tool tool for forstudying studying root rootcanal canalanatomy anatomy [4]; it provides [4]; it provides detailed information detailed information on root canal on root canaldimensions, dimensions, dentin dentin thickness, thickness, and anddirection direction and anddegree degree of the of root the canal root canalcurvature. curvature. Additionally, Additionally, imageimage analysis analysis software software is essential is essential to analyzeto analyze the the information information obtained obtained via via MCT. MCT. Our Our previous previous studies usedstudies custom-made used custom-made Kappa 2 software, Kappa 2 software, which produced which produced detailed detailed 3D measurements 3D measurements of various of various aspects of aspects of canal anatomic parameters [5–7]. This method used slices of images perpendicular to the canal anatomic parameters [5–7]. This method used slices of images perpendicular to the central axis of central axis of the root canal (Figure 1A), not the long axis of the tooth, which can reduce distortions the rootof measurements canal (Figure in1 A),areas not where the longa curvature axis of is the a pr tooth,esent (Figure which can1B). reduceOur previous distortions studies of measuring measurements in areasthe 3D where root canal a curvature anatomy is of a presentthe lateral (Figure incisor1 B).[8],Our maxillary previous first studiesmolar [5,9], measuring and mandibular the 3D rootfirst canal anatomymolar of[6] the confirmed lateral incisor the validity [8], maxillary of this firstcustom-made molar [5 ,9image], and analyzing mandibular software first molar (Kappa [6 ]2) confirmed in the validitycoordination of this with custom-made MCT. image analyzing software (Kappa 2) in coordination with MCT. Figure 1. Slice of reconstructed image. (A) When sliced perpendicular to the long axis of the root canal, no distortions are produced. (B) When sliced perpendicular to the long axis of the tooth, distortions are Figure 1. Slice of reconstructed image. (A) When sliced perpendicular to the long axis of the root canal, produced in the images of the root canal and surrounding dentin. no distortions are produced. (B) When sliced perpendicular to the long axis of the tooth, distortions are produced in the images of the root canal and surrounding dentin. The aim of this study was to determine the minimum and maximum root canal widths, dentin thickness, and 3D direction and degree of the root canal curvature in extracted human mandibular incisors. Appl. Sci. 2020, 10, 4385 3 of 11 The aim of this study was to determine the minimum and maximum root canal widths, dentin thickness, and 3D direction and degree of the root canal curvature in extracted human mandibular Appl. Sci. 2020, 10, 4385 3 of 11 incisors. 2. Materials2. Materials and and Methods Methods ThisThis study study was was approved approved by bythe the institutional institutional review review board board of ofSamsung Samsung Medical Medical Center, Center, Seoul, Seoul, KoreaKorea (SMC (SMC 2014-08-088). 2014-08-088). One-canalled One-canalled human human mandibular mandibular incisors incisors (n (=n 27)= 27) with with mature mature apices apices and and intactintact crowns crowns without without caries caries or orprevious previous root root canal canal treatment treatment were were collected. collected. To To get get rid rid of ofthe the