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Validity and Reliability of External Apical Root Resorption (EARR) Measurements: A 3D Cone Beam Computed Tomography (CBCT) Study

The purpose of this study was to evaluate the validity and reliability of external apical root resorption (EARR) measurements on commercial and open source software. The data sources were CBCT high volumetric data acquisition from the Malay ethnic group who are undergoing orthodontic treatment in School of Dental Sciences, Universiti Sains Malaysia. A total of 16 CBCT radiograph with 512 variables were measured using the Planmeca Romexis TM Software 2.3.1.R (Helsinki, Finland) and 3D Slicer v. 4.8.1 (open-source software, http://www.slicer.org). Two examiners (A and B) carried out all the measurements of the selected radiographs using the two softwares. Intra class correlation (ICC) coefficient test was applied to check the validity and reliability of EARR measurements. The validity of the 3D EARR measurements from both examiners A and B showed strong correlations. Moreover, ICC co-efficient values of inter examiner A and B were all in the range of strong correlation for EARR measurements in which reliability coefficient values were comparable with the measurements using Planmeca Romexis and 3D Slicer, respectively. All ICC coefficient values were positively correlated. Linear measurements of EARR using 3D CBCT in both commercial and open source software and are valid and reliable.


INTRODUCTION
Successful orthodontic treatment requires detailed investigative evidence and comprehensive analysis. Assessing the root resorption is an essential part of orthodontic investigations as in some cases it may compromise the result of successful treatment (Nowrin et al. 2018). Different types of root resorption can be assessed precisely in different kind of radiographs. Orthopantamogram (OPG) and lateral cephalogram are widely used as a diagnostic radiograph in terms of orthodontic treatment. However, panaromic radiographs has disadvantages of its artefact especially in anterior root region. Moreover, detecting root resorption through the lateral cephalogram is limited due to the super-impositioning of the teeth (Leach et al. 2001;Md Mashfique & Mohammad Khursheed 2017). To restrain these drawbacks, cone beam computed tomography (CBCT) is the best option to assess root length (Lund et al. 2010;Yu et al. 2013). In late 1990's CBCT has been introduced to dentistry and its low radiation doses, affordability and high spatial resolution has directed to its acceptance in orthodontics (Arai et al. 1999;Mozzo et al. 1998;Palomo et al. 2006). CBCT radiographs are distortion free and its reproducible images of single root has the advantages of clear landmarks at different magnifications and accurate cross-sectional images (Lund et al. 2010;Roscoe et al. 2015).
Assessment of root resorption on CBCT radiograph has been performed in different studies (Leach et al. 2001;Lund et al. 2010;Mohandesan et al. 2007). However, all the assessments performed in the aforementioned studies were proprietary or belongs to the commercial software package thus can only be used after purchasing the software with huge budgets. Commercial software is usually limited for few users and specific gadget. In addition, nowadays, different open source software is easily accessible without using any budget of purchasing to perform the desire measurements for the benefit of patients or research purposes. To the best of our knowledge, no studies has been performed to evaluate the root length area using an open source software which is find in webpages with free of charge.
Therefore, the purpose of this study was to evaluate the validity and reliability of external apical root resorption (EARR) measurements on both commercial and open source software named Planmeca Romexis TM Software 2.3.1.R and 3D slicer v. 4.8.1, respectively.

MATERIALS AND METHODS
Eight patients (seven females and one male, ages from 18 to 22 years) were selected for this study. All the patients were receiving orthodontic treatment with premolar extraction. The CBCT images of the patients were obtained before and after leveling-alignment stage (average 7 months) of orthodontic treatment. All CBCT images were acquired using the following specifications: 90 kVp, 320 μm voxel resolution, 12 mA. Orthodontic treatment was conducted by the same orthodontist with fixed appliances bonded until 2nd molars. All patients were reviewed with 4 weeks' intervals. Sequences of wires were as followed: 0.014 NiTi, 0.016 NiTi, 0.018 NiTi, 0.017× 0.025 NiTi and 0.019×0.025 NiTi size of arch wire on a 0.022-inch slot until the leveling-alignment stage of treatment. Ethical approval was obtained from the Human Research and Ethics Committee (HREC), Universiti Sains Malaysia USM/ JEPeM/15020074.

MEASUREMENT PROCEDURE
CBCT was used to assess all anterior and molars teeth of 8 patients using the crown and root height in 16 radiographs. With the help of DICOM export, 3D images were constructed in acquisition softwares Planmeca Romexis TM Software 2.3.1.R (Helsinki, Finland) and 3D Slicer v. 4.8.1 (open-source software, http://www.slicer.org). All the teeth except premolars (due to extraction) and 3rd molars were measured. To measure the tooth length, all the teeth were divided in crown and root portion. Cemento enamel junction (CEJ) was taken as a guideline to divide the teeth (Figure 1). A correction factor (CF) was calculated for crown length as crown length should be unchanged over the observation period. The following formula was used to determine the EARR from the CBCT images: EARR= R 1 -(R 2 ×CF); CF= C 1 /C 2 where R 1 is the initial root length; R 2 is the root length after leveling alignment stage; C 1 is the initial crown length; C 2 is the crown length after leveling alignment stage; and CF is the correction factor.
Two investigators (A and B) carried out all the EARR measurement in both Romexis (Figures 2 & 3) and 3D  (Figures 4 & 5). Interrater agreement is considered as excellent if the value of ICC is 0.75-1, good if ICC is 0.60-0.74, fair if ICC is 0.40-0.59, and poor if ICC is less than 0.40 (Cicchetti 1994).

STATISTICAL ANALYSIS
All the statistical analyses were performed using SPSS version 22.0 (Chicago, USA). Measurements of validity and reliability were statistically assessed using intra class correlation coefficient (ICC). The validity of 3D measurements was analyzed with ICC between 3D slicer values and Romexis value. ICC was performed to examine inter-examiner measurement reliability.

RESULTS
Tables 1 and 2 show the validity of 3D EARR measurements from intra examiners A and B which exhibited the values of coefficient were in range of strong correlation. Moreover, for inter examiner A and B, ICC co-efficient values also showed an excellent correlation for EARR measurements for both Planmeca Romexis and 3D Slicer software (Tables  2 & 4).    (Castro et al. 2012;Lund et al. 2010;Yu et al. 2013 (Luu et al. 2014) can yield adequate surface reconstruction, voxel-based registration and/or positioning adequate landmark, however these are not open source software. Furthermore, modification is difficult, do not offer flexibility for customization, and most importantly pre and post measurement of the same patients in different facial morphology or 3D correspondence problems were not addressed properly (Schilling et al. 2013

CONCLUSION
Linear measurements of EARR using 3D CBCT in both commercial and open source software are valid and reliable. Open source 3D Slicer software is a valid tool to be used for measurements of EARR, besides it can also be used for various clinical orthodontic procedure (for instance, root resorption, bone density, tooth movement, tooth size analysis, arch length discrepancies, mixed dentition analysis study) even if any commercial software are not available for research.