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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 33  |  Issue : 2  |  Page : 141-145

Comparison of the CBCT, CT, 3D printing, and CAD-CAM Milling options for the most accurate root form duplication required for the root analogue implant (RAI) protocol


Department of Prosthodontics and Implant Dentistry, Saveetha Dental College, Chennai, Tamil Nadu, India

Date of Submission25-Nov-2020
Date of Decision31-Mar-2021
Date of Acceptance21-Apr-2021
Date of Web Publication22-Jun-2021

Correspondence Address:
Dr. Saloni Kachhara
Department of Prosthodontics and Implant Dentistry, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences, 162, Poonamallee High Road, Chennai - 600 077, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jiaomr.jiaomr_244_20

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   Abstract 


Background: A computerized tomography (CT) scan or a cone beam computerized tomography (CBCT) imaging techniques can be used for tooth segmentation and acquisition of a three-dimensional (3D) reconstruction using CADCAM milling and 3D printing methods. Aim: This experimental study was done to assess the accuracy of CBCT, CT, CAD-CAM milling, and 3D printing for acquiring the most accurate duplication for root analog implant (RAI). Materials and Methods: The study was an ex-vivo feasibility study comparing CBCT, CT, CAD-CAM milling, and 3D printing methods for acquiring the most accurate duplication for root analog implant (RAI). Informed consent was obtained from patients for the study purpose for recording CT and CBCT scans and to utilize the extracted teeth for research purpose. The teeth were segmented from the DICOM files of CBCT and CT scans of the patients and Standard Tessellation Language files (STL) were obtained for individual teeth. The STL files of the individual teeth obtained were printed and milled in polymethylmethacrylate material (PMMA). The study thus consisted of 5 groups—Natural teeth as control, CBCT milled group, CT milled group, CBCT printed group and CT printed group of 16 samples each. Morphological differences in the three dimensions namely apico-coronal, bucco-lingual, and mesio-distal between the natural tooth and the 3D replicas were assessed using the one-way ANOVA test using the statistical software. Results: There was no statistically significant difference among the dimensions between the CBCT, CT, CAD-CAM milling, and 3D printing groups with respect to the most accurate duplication for root analog implant (p > 0.05). Conclusion: Within the limitations of this study, the CBCT segmentation and the Milling technique produce the least distortion for fabricating the root analog implant.

Keywords: 3D printing, CBCT, CT, milling, root analog implant


How to cite this article:
Kachhara S, Nallaswamy D, Ganapathy D, Ariga P. Comparison of the CBCT, CT, 3D printing, and CAD-CAM Milling options for the most accurate root form duplication required for the root analogue implant (RAI) protocol. J Indian Acad Oral Med Radiol 2021;33:141-5

How to cite this URL:
Kachhara S, Nallaswamy D, Ganapathy D, Ariga P. Comparison of the CBCT, CT, 3D printing, and CAD-CAM Milling options for the most accurate root form duplication required for the root analogue implant (RAI) protocol. J Indian Acad Oral Med Radiol [serial online] 2021 [cited 2021 Jul 29];33:141-5. Available from: https://www.jiaomr.in/text.asp?2021/33/2/141/319069




   Introduction Top


Recently, immediate dental implant placement protocol has been introduced that allows immediate placement after extraction but only in highly selected cases.[1] There are many benefits of immediate implant placement like reduction in the treatment time, cost, and a number of surgical interventions for the patient along with avoidance of alveolar bone resorption and soft tissue regression due to early functional loading.[2] However, immediate conventional implants are incongruent with the extraction socket and demand the use of a barrier membrane and/or bone augmentation.[3] Implant success depends on a satisfactory fit between the implant and the host bed.[4] This leads us to the idea of custom-made root analog implant (RAI), a precise root form duplication of the tooth to be extracted and placed into the socket.[5],[6] RAI adapts to the extraction socket instead of bone adapting to a conventional standardized implant in turn reducing trauma to the bone and soft-tissue.


   Materials and Methods Top


This study was done to assess the accuracy of CBCT, CT, CAD-CAM milling, and 3D printing for acquiring the most accurate duplication for root analog implant (RAI) and to compare the morphological differences between the teeth models manufactured by 3D printers with those fabricated by CNC milling machines.

Study design

This study was an ex-vivo feasibility study comparing CBCT, CT, CAD-CAM milling, and 3D printing for acquiring the most accurate duplication for root analog implant (RAI). The control group consisted of the natural teeth obtained from the orthodontic extractions of the patients from the dental college, India. A pilot study was done with 10 samples and based on results and standard deviation the sample size was re-estimated to be 80. The sample size per group was 16 and each patient underwent extraction of 4 teeth, 4 healthy patients were selected and ethical concerns made to undergo Cone Beam Computed Tomography (CBCT) (Sirona Orthophos®) and Computed Tomography (CT) (Phillips®) scans before extraction. The study consisted of 5 groups in all and 16 samples per group calculated with the help of GPower (3.0.10) software at 80% power [Table 1]. The data obtained from the DICOM files of CBCT and CT scans were processed. The STL files of individual teeth were milled and printed and all the five groups were compared for morphological dimensions. Informed written consent was obtained from the patients for willingness to undergo CT and CBCT scans and to use their extracted teeth as per the guidelines by the Helsinki Declaration, 1954. The study was approved by the Scientific Review Board of the University, vide letter number [Ref No. SRB/SDMDS08/19/PROSTH/01] dated 28.08.2019.
Table 1: Table showing the distribution of study groups CBCTM, CBCTP, CTM, CTP, and Control (Natural teeth) groups along with the sample size

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Inclusion criteria

  1. Patients aged between 18 and 25 undergoing orthodontic extractions.
  2. Healthy teeth with complete morphology.


Exclusion criteria

  1. Diseased tooth with caries, periodontitis, fracture, regressive alterations.
  2. Root stumps.
  3. Grossly carious tooth.


Data processing

The teeth to be extracted were segmented from the DICOM files of CBCT and CT scans and Standard Tessellation Language files (STL) were obtained for individual teeth. The software Materialise Mimics® (Materialise Interactive Medical Image Control System) was used to obtain the files. It is an image processing software for 3D design and modeling, developed by Materialise NV®, a Belgian company. It calculates surface 3D models from stacked image data such as CT and CBCT, through image segmentation. The Region of Interest (ROI), selected in the segmentation process is converted to a 3D surface model using an adapted marching cubes algorithm that takes the partial volume effect into account, leading to very accurate 3D models.

Model processing

The STL files of the individual teeth obtained from CBCT and CT scans were printed and milled in polymethylmethacrylate material (PMMA). The subtractive milling procedure was done using the CNC milling machine (CORiTEC 350i, Germany) [Figure 1] and PMMA blank (Huge Dent; 98*25 mm), Computer Numerical Control (CNC) is the automated control of machining tools and 3D printers by means of a computer. A CNC machine processes a piece of material (metal, plastic, wood, ceramic, or composite) to meet specifications by following a coded programmed instruction and without a manual operator directly controlling the machining operation. The additive 3D printing was completed using the SprintRay printer (Pro 3D printer, China) and the model resin (Sprint Ray). Sixteen teeth samples were fabricated in each of the four groups.
Figure 1: CNC Milling machine CORiTEC 350i depicting the samples milled using PMMA blank

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Morphological measurements

Measurements were made manually using the digital Vernier caliper (Kolylong carbon fiber LCD). These were done in three directions namely apico-coronal, mesio-distal, and bucco-lingual up to 2 decimals in millimeters [Figure 2]. The buccal cusp tip and apical root tip were marked for apico-coronal direction while for mesio-distal and bucco-lingual directions, the point lying on the perpendicular bisector of CEJ of the four surfaces were marked on all the five samples before making the measurements. The distance between these points were measured for morphological measurements.
Figure 2: Figure showing morphological measurements using digital vernier caliper

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Manual measurements using digital vernier calipers

Measurements were done manually using a digital caliper (0.01 mm accuracy) which gave values up to two decimals in millimeters.[7] Human error could happen for identifying the pointers used for measurements, so morphological landmarks were used for fixing the points.[8],[9] Two operators did the measurements and the average values were considered for the analysis to improve the internal validity of the study. Another factor affecting the dimension is the placement of sprues before milling or printing the tooth. Extra care was taken to place the sprues away from the measuring points.

Statistical analysis

Data were analyzed using the statistical software package IBM SPSS (Version 23.0, IBM Corporation, Armonk, NY, USA) Statistical package for social sciences (SPSS). Morphological differences in the three dimensions namely apico-coronal, buccolingual and mesio-distal between the natural tooth and the 3D replicas were assessed using the one-way ANOVA test, where the significance level was set at 0.05. Post hoc Bonferroni multiple comparison tests were used to compare the individual groups, comparing the milled and the printed models as well as the CBCT and CT groups.


   Results Top


The dimensional measurements were recorded in three planes namely the apico-coronal, mesio-distal, and bucco-lingual for each sample. In the apico-coronal dimension, the lengths of milled as well as printed models were less compared to that of the natural teeth. In the mesio-distal dimension, the lengths were more compared to the natural teeth whereas in bucco-lingual dimension the lengths were almost similar.

There was no statistically significant difference among the dimensions between the groups (p > 0.05) [Table 2]. However, it was observed that in the apico-coronal dimension, CBCTM group was closest to the natural group followed by CBCTP, CTP, and CTM being the last. But there was a decrease in the length in all the groups [Figure 3].
Table 2: Dimensions of tooth models obtained by the experimental interventions

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Figure 3: Figure showing bar graph depicting the mean length of each group in apico-coronal dimension with all groups being lesser than the natural tooth

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In the mesio-distal dimension, CBCTP group was closest to the natural tooth followed by CTP, CTM, and CBCTM [Figure 4]. In the bucco-lingual dimension, CBCTM was closest to the natural group followed by CBCTP, CTP, and CTM [Figure 5].
Figure 4: Figure showing bar graph depicting the mean length of each group in mesio-distal dimension with all groups being more than the natural tooth

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Figure 5: Figure showing bar graph depicting mean length of each group in bucco-lingual dimension with CTM group being more while all others lesser than the natural tooth

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   Discussion Top


In this study, that deployed the use of CT, CBCT, printing, and milling for the fabrication of root analog implant, it appears that the use of CBCT and milling provided the most accurate reproduction of the natural extracted tooth but this finding was not statistically significant (ANOVA, Bonferroni, P < 0.05). These results are in accordance with the previous studies which concluded that CBCT could be used as a tool for the segmentation of teeth.[10],[11],[12]

Though results have been encouraging and similar for all the five groups, we need to discuss the following confounding factors like the variations in manual measurements, placement of sprues before fabrication, quality of resin used for printing and milling, armamentarium used for printing and milling, CBCT and CT image quality related to the patient positioning, volume reconstruction, machine settings, type of system used and the DICOM export, segmentation protocols for DICOM file processing and various environmental factors like temperature and humidity of the room while operator carried out the measurements.

CBCT and CT image quality

Image quality differs according to different CBCT and CT machines used.[10],[13] In the present study, all patients undertook scans using the same machine, so the adversities caused due to different quality of machines were avoided. The factors like patient positioning did not confound as the protocols for taking the scan were followed[14] and the same operator was selected to take the scan. The voxel size of the scanner also affects the 3D reconstruction quality of the image.[11],[15] The voxel size of the CBCT machine used in the study was 400 microns, better image quality can be obtained by other machines.

Segmentation protocol

Various softwares are available which can help to segment an individual structure from the DICOM file but their accuracy to reproduce the exact replica has not been studied.[16] In this study, the software Materialise Mimics® (Materialise Interactive Medical Image Control System) was used to obtain the files of the individual teeth which were supposed to be extracted.[17] This software has been used for medical purposes to study the volume of calculi.[18] The obtained STL file was then given for milling and printing.

Armamentarium for printing and milling

In this study, no statistically significant difference was found in the dimensional accuracy between the printed, milled, and natural teeth. This was opposed to the results obtained by Yau et al., 2016[19] which concluded that the 5-axis milling machine is more accurate compared to the 3D printing (0.01–0.02 mm accuracy levels). Another study concluded that printing is better than milling.[20] These differences can be explained as different milling and printing machines were used in these studies and also shows that more studies need to be done in this field. Even though there was no statistically significant difference between printed and milled models, the dimensions of milled teeth were closer to that of natural teeth (difference of 0.17 mm and 0.32 mm for milled and printed model respectively, ANOVA, Bonferroni test, P < 0.05). This difference could also be explained as the different resins were used for printing and milling. Pre-sintered blank was used in milling while the non-sintered model resin was used for printing which underwent curing shrinkage after printing.[21],[22]

Environmental factors

Various environmental factors like the temperature of the room and humidity in the room could affect the resin models. There are no immediate effects but long-term effects allow extrapolation of accelerated aging of the resin.[23] In this study, the samples received after printing and milling were immediately measured at room temperature in a room where humidity was maintained. The samples were later stored in airtight containers.

Limitation and future prospects

Comparing only the linear measurements within the groups was a limitation for the study. Volumetric analysis and superimposition of the STL files could have been added.[24] Also, different machines for printing and milling as well as scanners for taking the computed tomography of the patient could have been compared. Determining the accuracy may not have drastic effect on the overall implant success rate. Cost-effectiveness of the overall technique is a concern. Ready availability of the 3D printing module and software could be another limitation for this process.

This study helped to establish that the exact tooth replica can be obtained with the help of pre-surgical CBCT, tooth segmentation from the DICOM file, and milling of the STL file. A clinical trial could be conducted wherein the above conclusion can be used to fabricate the zirconia root analog implant.


   Conclusion Top


Though there was no significant difference between the morphological dimensions amongst the natural tooth and 3D replicas, the CBCTM group was found to be closest to the natural group. This study concluded that the closest replica of the natural tooth could be obtained with the help of pre-extraction CBCT of the patient, tooth segmentation from the DICOM file of CBCT, and milling of the STL file using a 5-axis CNC milling machine. This method can be followed to fabricate a root analog implant.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Chambers D, Bohay R, Kaci L, Barnett R, Battista J. The effective dose of different scanning protocols using the Sirona GALILEOS® comfort CBCT scanner. Dentomaxillofac Radiol 2015;44:20140287.  Back to cited text no. 14
    
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Yau HT, Yang TJ, Lin YK. Comparison of 3-D Printing and 5-axis milling for the production of dental e-models from intra-oral scanning. Comput Aided Des Appl 2016;13:32–8.  Back to cited text no. 19
    
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Jeong Y-G, Lee W-S, Lee K-B. Accuracy evaluation of dental models manufactured by CAD/CAM milling method and 3D printing method. J Adv Prosthodont 2018;10:245–51.  Back to cited text no. 20
    
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24.
Khalil W, EzEldeen M, Van De Casteele E, Shaheen E, Sun Y, Shahbazian M, et al. Validation of cone beam computed tomography–based tooth printing using different three-dimensional printing technologies. Oral Surg Oral Med Oral Pathol Oral Radiol 2016;121:307–15.  Back to cited text no. 24
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2]



 

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