Korean J Orthod 2023; 53(2): 77-88 https://doi.org/10.4041/kjod22.120
First Published Date March 25, 2023, Publication Date March 25, 2023
Copyright © The Korean Association of Orthodontists.
Hangmiao Lyua , Li Xub, Huimin Maa, Jianxia Houb, Xiaoxia Wangc, Yong Wangd, Yijiao Zhaod, Weiran Lia
, Xiaotong Lia
aDepartment of Orthodontics, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
bDepartment of Periodontology, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
cDepartment of Oral and Maxillofacial Surgery, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
dCenter of Digital Dentistry, Peking University School and Hospital of Stomatology; National Engineering Laboratory for Digital and Material Technology of Stomatology; Research Center of Engineering and Technology for Digital Dentistry of Ministry of Health; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
Correspondence to:Weiran Li.
Professor, Department of Orthodontics, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, No. 22 Zhongguancun Nandajie, HaiDian District, Beijing 100081, China.
Tel +86-010-82195381 e-mail weiranli@bjmu.edu.cn
Correspondence to: Xiaotong Li.
Associate Professor, Department of Orthodontics, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, No. 22 Zhongguancun Nandajie, HaiDian District, Beijing 100081, China.
Tel +86-010-82195739 e-mail xiaotonglee@hotmail.com
How to cite this article: Lyu H, Xu L, Ma H, Hou J, Wang X, Wang Y, Zhao Y, Li W, Li X. Accuracy of three-dimensional periodontal ligament models generated using cone-beam computed tomography at different resolutions for the assessment of periodontal bone loss. Korean J Orthod 2023;53(2):77-88. https://doi.org/10.4041/kjod22.120
Objective: To develop a method for generating three-dimensional (3D) digital models of the periodontal ligament (PDL) using 3D cone-beam computed tomography (CBCT) reconstruction and to evaluate the accuracy and agreement of the 3D PDL models in the measurement of periodontal bone loss. Methods: CBCT data collected from four patients with skeletal Class III malocclusion prior to periodontal surgery were reconstructed at three voxel sizes (0.2 mm, 0.25 mm, and 0.3 mm), and 3D tooth and alveolar bone models were generated to obtain digital PDL models for the maxillary and mandibular anterior teeth. Linear measurements of the alveolar bone crest obtained during periodontal surgery were compared with the digital measurements for assessment of the accuracy of the digital models. The agreement and reliability of the digital PDL models were analyzed using intra- and interexaminer correlation coefficients and Bland–Altman plots. Results: Digital models of the maxillary and mandibular anterior teeth, PDL, and alveolar bone of the four patients were successfully established. Relative to the intraoperative measurements, linear measurements obtained from the 3D digital models were accurate, and there were no significant differences among different voxel sizes at different sites. High diagnostic coincidence rates were found for the maxillary anterior teeth. The digital models showed high intra- and interexaminer agreement. Conclusions: Digital PDL models generated by 3D CBCT reconstruction can provide accurate and useful information regarding the alveolar crest morphology and facilitate reproducible measurements. This could assist clinicians in the evaluation of periodontal prognosis and establishment of an appropriate orthodontic treatment plan.
Keywords: Digital models, Three-dimensional reconstruction, Cone-beam computed tomography
The periodontal ligament (PDL) is an aligned fibrous network anchored firmly to the cementum covering the tooth root on one side and the alveolar bone of the jaw on the other side,1,2 and it can be represented by the root surface area (RSA) below the alveolar bone crest. The area of contact between tooth roots and the surrounding bone plays an important role in orthodontic and periodontal treatment. It has been proposed that the PDL and alveolar bone are functional units that undergo robust remodeling during orthodontic tooth movement.3 Moreover, the PDL area plays an important role in tooth anchorage,4 and morphological changes in the PDL reflect the vertical bone level (VBL).5 Quantification of the PDL area can help assess the severity of periodontal disease and the prognosis of orthodontic treatment.
Measurement of the alveolar bone thickness and VBL in the sagittal plane of cone-beam computed tomography (CBCT) images is a well-established method.6-8 Past studies have focused primarily on measurement of the height and thickness of the alveolar bone on the labial and lingual sides of the incisors in the sagittal plane. Evaluation of two-dimensional (2D) measurements without consideration of the three-dimensional (3D) PDL area may not adequately indicate the severity of periodontal lesions. Moreover, 2D linear measurements describe VBL in a one-dimensional manner without taking changes in the root shape into account, thus underestimating the true amount of periodontal loss.9-11
In other previous studies,9,12 microcomputed tomography (micro-CT) data were used to measure the RSA on reconstructed digital models of extracted teeth. However, the micro-CT technique cannot be used for
Researchers have also used CBCT to reconstruct the root surface to detect apical root resorption cavities14 and measure the RSA as an important marker for determination of the periodontal treatment plan and prognosis. However, RSA measurements do not take alveolar bone conditions into account; in recent years, the PDL surface area, or the RSA below the alveolar bone crest, has been studied as a marker of periodontal health, and researchers have artificially simulated the PDL area using digital models of teeth.5,9,10,12,17 Nevertheless, to our knowledge, this is the first study to obtain
In the present study, instead of artificially simulating the alveolar bone crest
Forty-eight anterior teeth from four patients (two female and two male) with skeletal Class III malocclusion requiring surgical orthodontic treatment and augmented corticotomy (AC) were evaluated in this study at Peking University School and Hospital of Stomatology from May 2021 to October 2021. All patients signed informed consent forms. The study was approved by the Biomedical Ethics Committee of the Peking University School and Hospital of Stomatology (approval number: PKUSSIRB-201839156) and registered on the Clinical Trials Register as ChiCTR1900021778 (Chinese Clinical Trials Registry Platform of the World Health Organization).
The inclusion criteria were as follows: 1) age > 18 years for male patients and > 16 years for female patients;18,19 2) A point–nasion–B point (ANB) angle of < 0° and overjet of < 0 mm; 3) no more than two sites with a probing depth of ≥ 5 mm in the entire oral cavity, bleeding on probing score of ≤ 20%, and plaque score of ≤ 30%; and 4) labial alveolar bone thickness of < 1 mm around the maxillary and mandibular central incisors, as measured by CBCT. The mean alveolar bone thickness at the root apex of the maxillary and mandibular central incisors was 0.81 ± 0.17 mm and 0.4 ± 0.15 mm, respectively. Patients with poor oral hygiene or uncontrolled periodontal disease were excluded.
All orthodontic treatments were performed by a single orthodontist using a straight-wire fixed appliance (0.022" slot size, MBT prescription). For the maxillary anterior teeth, the arch-wire sequence involved 0.014-, 0.016-, 0.018-, and 0.018 × 0.025-inch nickel-titanium wires before periodontal surgery. For the mandibular anterior teeth, periodontal surgery was performed after bracket bonding without any arch wire in place. Two weeks after periodontal surgery, aligning and leveling were initiated with 0.014-inch nickel-titanium wires.
Prior to periodontal surgery, CBCT images were acquired with the NewTom VG device (Aperio Services, Verona, Italy) in the regular scan mode (field of view [FOV], 10 × 10 cm; voltage, 110 kV; current, 3.00 mA; and exposure, 1.8 seconds). The CBCT images were reconstructed using different voxel sizes (0.20, 0.25, and 0.30 mm). To reduce scatter at the occlusal plane, patients were instructed to bite on cotton rolls. Within 24 hours of CBCT image acquisition, the patients underwent intraoral scanning.
Digital Imaging and Communication in Medicine (DICOM) files were imported into Mimics 19.0 software (Materialise, Leuven, Belgium). In Mimics, 3D digital models of the anterior teeth and bone
The digital models were exported in stereolithographic (STL) format and imported into Geomagic software (Geomagic, Cary, NC, USA). For more realistic digitalization of the metal brackets bonded to the teeth, a digital model derived from the intraoral scan was superimposed over the 3D model generated from the CBCT datasets (Figure 2).
In Geomagic software, the vertical distance between the CEJ and alveolar bone crest parallel to the long axis of the anatomic crown was defined as the VBL. The long axis of the anatomic crown was determined by connecting the lowest point of the labial CEJ curve and the midpoint of the mesial and distal incisal angles. The five selected measurement sites on the digital models were the mesiolabial (VBL_MLa), mesiobracket (VBL_MB), midlabial (VBL_La), distobracket (VBL_DB), and distolabial (VBL_DLa) sites. The La point was chosen at the midlabial site on the surface. Proximal points on the surface, i.e., the MLa and DLa points, were located at the corner of each tooth. The vertical distance between the marginal bone crest and the gingival boundary of the metal bracket was defined as the bone-bracket distance (BBD). The three selected measurement points were the mesiobracket (BBD_MB), midlabial (BBD_La), and distobracket (BBD_DB) points. Detailed information about the measurement procedure is shown in Figure 3. Measurements were made to the nearest 0.01 mm using a linear measurement tool in a quiet and dark room.
All AC procedures were performed by a single periodontist using surgical loupes. The AC procedure was performed as follows.21 A crevicular incision was made from the canine on one side to the canine on the other side, and a full thickness flap on the labial side was elevated. The distance parallel to the long axis of the anatomic crown between the CEJ and alveolar bone crest was measured at five sites, in addition to the distance between the alveolar bone crest and gingival boundary at the mesial and distal metal bracket sites (Figure 4). All measurements were made to the nearest 1 mm by the same experienced periodontist who performed the AC procedure using a manual periodontal probe (UNC-15, graded in millimetres; HU-Friedy, Chicago, IL, USA) placed parallel to the long axis of the tooth. The intraoperative measurements were considered the “reference standard.”
To segment the PDL in the digital model, we identified the alveolar bone crest in the digital model and drew points on the teeth in the model (Figure 5A and 5B). A curve was generated by connecting the points marked on the model surface using the creation method in Geomagic (Figure 5B). The created boundary curve represented the alveolar bone crest (Figure 5C). The teeth were then separated along the curve into two parts (Figure 5D), with preservation of the PDL (Figure 5E), and the PDL area in the digital model was calculated (Figure 5F).
Statistical analyses were performed using SPSS 20.0 (IBM Corp., Armonk, NY, USA). All linear measurements for the digital models were obtained twice at an interval of 2 weeks by the same investigator, and the average of these two measurements was used for statistical analysis. The systematic intraexaminer error was determined using a paired
Descriptive statistics for differences between the intraoperative and digital measurements were separately computed. In addition, the 95% confidence interval (CI) was calculated, and diagnostic coincidence rates were calculated using an introduced variable measurement difference to evaluate the accuracy of site-based image assessment relative to the clinical measurement.
If the measurement difference ranged from −1 to +1 mm (including −1 and +1 mm), the measurement obtained from the 3D digital image was considered consistent with the intraoperative measurement; otherwise, the measurements were considered inconsistent. Thereafter, the corresponding diagnostic coincidence rates were calculated. To examine the agreement between the digital models obtained by different examiners, 24 randomly chosen teeth were assessed in a blinded manner by two authors with 4–8 years of experience in dental and periodontal imaging. The error was evaluated by measuring the surface area of the PDL in the models. The systematic interexaminer agreement was calculated using the ICC, and the Bland–Altman method was applied to identify the limits of agreement.
For both the maxillary and mandibular anterior teeth, there were no significant differences in digital measurements at different sites among different voxel sizes (
Table 1 . Comparison of intraoperative measurements and digital linear measurements at different sites with different voxel sizes
Measurements | Digital | Intraoperative | Multiple comparison | |||
---|---|---|---|---|---|---|
0.2 mm | 0.25 mm | 0.3 mm | ||||
Maxillary anterior teeth | ||||||
VBL_MLa (mm) | 1.08 ± 0.50 | 1.06 ± 0.44 | 1.01 ± 0.47 | 1.00 ± 0.74 | 0.22 | - |
VBL_MB (mm) | 1.58 ± 0.53 | 1.49 ± 0.72 | 1.39 ± 0.54 | 1.46 ± 0.66 | 0.74 | - |
VBL_La (mm) | 1.98 ± 0.57 | 2.04 ± 0.74 | 1.93 ± 0.69 | 1.79 ± 0.72 | 0.63 | - |
VBL_DB (mm) | 1.68 ± 0.47 | 1.52 ± 0.59 | 1.51 ± 0.54 | 1.60 ± 0.63 | 0.71 | - |
VBL_DLa (mm) | 1.41 ± 0.63 | 1.16 ± 0.75 | 1.01 ± 0.55 | 1.35 ± 0.76 | 0.15 | - |
BBD_MB (mm) | 7.47 ± 1.08 | 7.27 ± 1.07 | 7.32 ± 0.99 | 7.33 ± 1.11 | 0.92 | - |
BBD_La (mm) | 8.09 ± 0.91 | 7.86 ± 1.03 | 7.81 ± 1.04 | 7.96 ± 1.21 | 0.81 | - |
BBD_DB (mm) | 7.77 ± 0.97 | 7.32 ± 0.95 | 7.36 ± 0.98 | 7.63 ± 0.94 | 0.32 | - |
Mandibular anterior teeth | ||||||
VBL_MLa (mm) | 1.56 ± 0.60 | 1.30 ± 0.45 | 1.55 ± 0.57 | 2.13 ± 0.76 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_MB (mm) | 2.54 ± 0.86 | 2.37 ± 0.79 | 2.48 ± 0.84 | 3.31 ± 0.70 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_La (mm) | 3.87 ± 1.72 | 3.69 ± 1.40 | 3.65 ± 1.56 | 4.52 ± 1.05 | 0.15 | - |
VBL_DB (mm) | 2.75 ± 0.86 | 2.47 ± 1.16 | 2.39 ± 0.62 | 3.44 ± 0.97 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_DLa (mm) | 1.50 ± 0.58 | 1.27 ± 0.46 | 1.51 ± 0.54 | 2.25 ± 0.81 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
BBD_MB (mm) | 8.16 ± 1.56 | 8.01 ± 1.54 | 7.94 ± 1.50 | 7.92 ± 1.59 | 0.95 | - |
BBD_La (mm) | 9.36 ± 2.23 | 9.42 ± 2.00 | 9.24 ± 2.20 | 9.35 ± 1.60 | 0.99 | - |
BBD_DB (mm) | 8.09 ± 1.52 | 8.01 ± 1.84 | 7.78 ± 1.40 | 7.98 ± 1.77 | 0.92 | - |
Values are presented as mean ± standard deviation.
One-way ANOVA with Duncan’s multiple comparison test was performed for comparisons between intraoperative and digital linear measurements.
VBL, vertical bone level; BBD, bone–bracket distance; MLa, mesiolabial; MB, mesiobracket; La, midlabial; DB, distobracket; DLa, distolabial.
**
The maxillary anterior teeth showed no significant differences between the digital and intraoperative VBL measurements (
A statistically significant ICC was found for the correlation between all digital and intraoperative measurements (
Table 2 . Intraclass correlation coefficient (ICC) analysis of intraoperative and digital linear measurements obtained with different voxel sizes
Measurements | 0.2 mm | 0.25 mm | 0.3 mm | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
ICC | 95% CI | ICC | 95% CI | ICC | 95% CI | |||||||
Lower bound Upper bound | Lower bound | Upper bound | Lower bound | Upper bound | ||||||||
Maxillary anterior teeth | VBL | 0.793** | 0.715 | 0.851 | 0.684** | 0.576 | 0.769 | 0.646** | 0.528 | 0.739 | ||
BBD | 0.887** | 0.825 | 0.928 | 0.850** | 0.771 | 0.904 | 0.908** | 0.857 | 0.942 | |||
Mandibular anterior teeth | VBL | 0.726** | 0.629 | 0.801 | 0.769** | 0.684 | 0.833 | 0.689** | 0.582 | 0.772 | ||
BBD | 0.839** | 0.754 | 0.896 | 0.872** | 0.803 | 0.918 | 0.842** | 0.758 | 0.898 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval.
**
The mean differences and descriptive statistics for the measurements are shown in Tables 3 and 4. The mean differences (and 95% CIs) between the digital and intraoperative measurements for the maxillary anterior teeth were approximately 0; this confirmed no significant differences. Statistically significant mean differences were found in the VBL measurements for the mandibular anterior teeth, regardless of the voxel size (
Table 3 . Descriptive statistics, diagnostic coincidence rates, limits of agreement, and 95% CIs for differences in linear measurements obtained with different voxel sizes for the maxillary anterior teeth
Measurement difference | Mean difference (mm) | Median (mm) | SD (mm) | Range (mm) | Diagnostic coincidence rates (%) | Limits of agreement (mm) | 95% CI (mm) |
---|---|---|---|---|---|---|---|
VBL (n = 120) | |||||||
0.2 mm | −0.07 | −0.10 | 0.43 | 2.28 | 96.66 | −0.92–0.78 | −0.15–0.00 |
0.25 mm | −0.01 | −0.01 | 0.58 | 2.72 | 92.50 | −1.15–1.12 | −0.11–0.09 |
0.3 mm | 0.07 | 0.09 | 0.58 | 2.61 | 90.00 | −1.06–1.21 | −0.03–0.17 |
BBD (n = 72) | |||||||
0.2 mm | −0.09 | 0.01 | 0.51 | 2.60 | 90.27 | −1.08–0.91 | −0.21–0.03 |
0.25 mm | 0.11 | 0.11 | 0.59 | 3.34 | 94.44 | −1.04–1.26 | −0.03–0.25 |
0.3 mm | 0.09 | 0.02 | 0.47 | 2.59 | 97.22 | −0.82–1.00 | −0.02–0.19 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval; SD, standard deviation.
Table 4 . Descriptive statistics, diagnostic coincidence rates, limits of agreement, and 95% CIs for differences in linear measurements obtained with different voxel sizes for the mandibular anterior teeth
Measurement difference | Mean difference (mm) | Median (mm) | SD (mm) | Range (mm) | Diagnostic coincidence rates (%) | Limits of agreement (mm) | 95% CI (mm) |
---|---|---|---|---|---|---|---|
VBL (n = 120) | |||||||
0.2 mm | 0.68 | 0.71 | 0.95 | 5.82 | 63.33 | −1.17–2.54 | 0.51–0.85 |
0.25 mm | 0.91 | 0.88 | 0.85 | 5.92 | 56.66 | −0.76–2.58 | 0.75–1.06 |
0.3 mm | 0.82 | 0.81 | 0.95 | 6.58 | 56.66 | −1.05–2.68 | 0.64–0.98 |
BBD (n = 72) | |||||||
0.2 mm | −0.04 | −0.10 | 0.98 | 5.03 | 66.67 | −1.96–1.88 | −0.26–0.19 |
0.25 mm | 0.11 | 0.20 | 0.89 | 5.13 | 77.78 | −1.65–1.86 | −0.10–0.31 |
0.3 mm | 0.17 | 0.08 | 0.98 | 6.23 | 70.83 | −1.76–2.10 | −0 06–0.40 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval; SD, standard deviation.
The diagnostic coincidence rates for the VBL and BBD values for the maxillary anterior teeth were ≥ 90%. For the mandibular anterior teeth, the diagnostic coincidence rates ranged from 56.66% to 63.33% for the VBL and from 66.67% to 77.78% for the BBD (Tables 3 and 4).
For validation of the different measurements, the differences between the digital and intraoperative measurements were plotted against the average, as recommended in Bland–Altman analysis. The limits of agreement were defined as ± 1.96 × standard deviation and are shown in Figure 6. The limits of agreement for the maxillary anterior teeth showed discrepancies of approximately 2 mm in the measurements. However, high variability was observed in the mandibular measurements, as indicated by the large 95% limits of agreement range of approximately 3.5 mm.
High intraexaminer agreement was observed for the linear measurements of the digital model. The results showed no significant systematic intraexaminer error (
Differences in PDL area measurements between examiners were also analyzed, and the results showed high interexaminer agreement (ICC, 0.947; 95% CI, 0.871–0.979). Moreover, the Bland–Altman analysis showed good consistency between the two examiners in the process of PDL segmentation in the model. The mean bias for the PDL area (mm2) was 2.57, with limits of agreement ranging from −17.89 to 23.03 (Figure 7), indicating good consistency between the two examiners in the process of PDL segmentation.
Digital models of the PDL of the maxillary and mandibular anterior teeth of the four patients were successfully established. A representative case is shown in Figure 8.
Detection and monitoring of alveolar bone loss are important because they provide a hard-tissue index for the presence of periodontal disease and the effects of preventative and corrective therapies for periodontal disease.22,23 In the present study, we introduced an accurate and reproducible method to obtain alveolar bone crest-based digital PDL models using 3D CBCT reconstruction.
The present study suggests that 3D CBCT reconstruction provides relatively accurate information regarding the alveolar bone around the anterior teeth. There were no significant differences among measurements obtained using CBCT voxel resolutions of 0.20, 0.25, and 0.30 mm; this indicates that the method is highly valuable for clinical application. Previous studies have shown that discernment of the PDL space requires CBCT data with a resolution capable of detecting structures less than 0.2 mm in size.22,24 However, data with higher resolution may require higher levels of radiation, which would increase the radiation exposure of patients.25 The present study shows that CBCT with a voxel size of 0.30 mm and relatively little radiation is sufficient to represent the morphology of the alveolar crest, relative to the gold standard. Furthermore, the position of the alveolar crest can be determined, which helps in identification of the coronal margin of the PDL.
Many previous studies have focused on factors influencing the accuracy of CBCT datasets for 3D reconstruction-based measurements26-28 or linear measurements of the alveolar bone, such as the alveolar bone level in the sagittal plane.25,29-31 Some studies have shown that a smaller voxel size is associated with better spatial resolution,26,27 while others have concluded that there is no significant difference between high-resolution and low-resolution CBCT protocols.28,29 A lower resolution also results in higher levels of image noise and influences the accuracy of alveolar bone measurements.30,32 This may explain the divergence in conclusions to some extent. Moreover, various exposure parameters in CBCT may influence the image quality, such as the FOV and presence of metallic restorations.33,34 In the present study, the FOV, voltage, and other conditions were controlled to investigate the effects of the voxel size. In addition, all patients had metal brackets because CBCT was performed during orthodontic treatment, which is a common clinical situation. Although CBCT can provide an accurate 3D view of the tooth roots and alveolar bone, dense intraoral metal brackets can severely compromise the image quality of crowns.35 Therefore, in this study, intraoral optical scans were used to obtain profiles of anterior tooth crowns and surrounding soft tissue in the STL format, thus eliminating the impact of metal artefacts on the crown morphology.
Previous studies have reported that accurate 3D models of entire dentition could be generated with an intraoral scan superimposed over the CBCT images during orthodontic treatment with brackets.36-38 In the present study, the orthodontic brackets were chosen as reference marks for evaluation of the alveolar bone crest. Our results showed that the digital VBL measurements for the mandibular anterior teeth were significantly smaller than the intraoperative VBL measurements, while there were no significant differences in the BBD at any site between the two methods. This indicates that the main source of deviation in the VBL measurements was selection of the CEJ point. The position of the CEJ around the mandibular anterior teeth on the 3D model tends to be gingivally oriented. Previously, Wang et al.39 found that reconstruction of the crown and root still showed a clear CEJ boundary and a smooth area on the surface. The present study, however, indicated that the CEJ may not be an accurate or reproducible anatomical landmark for mandibular anterior teeth using a 3D model. This finding agrees with Kuralt et al.,40 who found that CEJ point selection was the main source of variability in measurements obtained from an intraoral optical scan-derived model. The inaccurate positioning of the CEJ and the difficulty in its identification in the present study may be attributed to the flatter morphology of the mandibular anterior teeth on the labial side and wear of the CEJ.41 Furthermore, in the reconstruction of mandibular anterior tooth models using CBCT datasets, the maximum inaccuracy was mainly found at the cervical margins.42 Therefore, when the CEJ is used as an anatomical landmark for examining the periodontal health status of the mandibular anterior teeth using a 3D model, the possibility of underestimation of the alveolar bone loss severity should be considered.
Because the gold standard in this study was periodontal probe measurements, precision to ±1 mm with a manual periodontal probe was acceptable. The results showed a high diagnostic coincidence rate (> 90%) for the maxilla and a relatively low for the mandible. The Bland–Altman method showed that the limits of agreement were −1 mm to +1 mm for the maxillary anterior teeth; this finding was generally consistent with the results of a previous study.29 However, the broader limits of agreement and the wider span of differences in digital measurements for the mandibular anterior teeth indicate that the mandibular models are less reliable. This could be attributed to the thinner anterior alveolar bone and more vertical bone loss in skeletal Class III patients than in those with Class I patients with normal occlusion,7 as well as the difficulty in obtaining accurate measurements of the boundary of thin alveolar bone using CBCT, even with a 0.125-mm-voxel protocol.29
The present study presents a feasible and noninvasive method for obtaining
Despite the limitations described above, the present study introduced an accurate and consistent method for obtaining PDL measurements from a reconstructed 3D model, which has important implications for clinical treatment. The 3D morphology of the PDL is a significant prognostic indicator in patients with periodontal disease or those undergoing orthodontic therapy, particularly those with previous periodontal bone loss.
The present study introduced a method for obtaining PDL measurements from 3D reconstructions of
None.
Conceptualization: WL. Data curation: HL, XW. Formal analysis: HM. Funding acquisition: XL. Methodology: YW, YZ. Project administration: XL, XW. Visualization: LX, JH. Writing–original draft: HL. Writing–review & editing: XL.
No potential conflict of interest relevant to this article was reported.
This study was supported by the National Program for Multidisciplinary Cooperative Treatment on Major Diseases (PKUSSNMP-201902).
Korean J Orthod 2023; 53(2): 77-88 https://doi.org/10.4041/kjod22.120
First Published Date March 25, 2023, Publication Date March 25, 2023
Copyright © The Korean Association of Orthodontists.
Hangmiao Lyua , Li Xub, Huimin Maa, Jianxia Houb, Xiaoxia Wangc, Yong Wangd, Yijiao Zhaod, Weiran Lia
, Xiaotong Lia
aDepartment of Orthodontics, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
bDepartment of Periodontology, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
cDepartment of Oral and Maxillofacial Surgery, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
dCenter of Digital Dentistry, Peking University School and Hospital of Stomatology; National Engineering Laboratory for Digital and Material Technology of Stomatology; Research Center of Engineering and Technology for Digital Dentistry of Ministry of Health; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, Beijing, China
Correspondence to:Weiran Li.
Professor, Department of Orthodontics, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, No. 22 Zhongguancun Nandajie, HaiDian District, Beijing 100081, China.
Tel +86-010-82195381 e-mail weiranli@bjmu.edu.cn
Correspondence to: Xiaotong Li.
Associate Professor, Department of Orthodontics, National Engineering Laboratory for Digital and Material Technology of Stomatology; Beijing Key Laboratory of Digital Stomatology, Peking University School and Hospital of Stomatology, No. 22 Zhongguancun Nandajie, HaiDian District, Beijing 100081, China.
Tel +86-010-82195739 e-mail xiaotonglee@hotmail.com
How to cite this article: Lyu H, Xu L, Ma H, Hou J, Wang X, Wang Y, Zhao Y, Li W, Li X. Accuracy of three-dimensional periodontal ligament models generated using cone-beam computed tomography at different resolutions for the assessment of periodontal bone loss. Korean J Orthod 2023;53(2):77-88. https://doi.org/10.4041/kjod22.120
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Objective: To develop a method for generating three-dimensional (3D) digital models of the periodontal ligament (PDL) using 3D cone-beam computed tomography (CBCT) reconstruction and to evaluate the accuracy and agreement of the 3D PDL models in the measurement of periodontal bone loss. Methods: CBCT data collected from four patients with skeletal Class III malocclusion prior to periodontal surgery were reconstructed at three voxel sizes (0.2 mm, 0.25 mm, and 0.3 mm), and 3D tooth and alveolar bone models were generated to obtain digital PDL models for the maxillary and mandibular anterior teeth. Linear measurements of the alveolar bone crest obtained during periodontal surgery were compared with the digital measurements for assessment of the accuracy of the digital models. The agreement and reliability of the digital PDL models were analyzed using intra- and interexaminer correlation coefficients and Bland–Altman plots. Results: Digital models of the maxillary and mandibular anterior teeth, PDL, and alveolar bone of the four patients were successfully established. Relative to the intraoperative measurements, linear measurements obtained from the 3D digital models were accurate, and there were no significant differences among different voxel sizes at different sites. High diagnostic coincidence rates were found for the maxillary anterior teeth. The digital models showed high intra- and interexaminer agreement. Conclusions: Digital PDL models generated by 3D CBCT reconstruction can provide accurate and useful information regarding the alveolar crest morphology and facilitate reproducible measurements. This could assist clinicians in the evaluation of periodontal prognosis and establishment of an appropriate orthodontic treatment plan.
Keywords: Digital models, Three-dimensional reconstruction, Cone-beam computed tomography
The periodontal ligament (PDL) is an aligned fibrous network anchored firmly to the cementum covering the tooth root on one side and the alveolar bone of the jaw on the other side,1,2 and it can be represented by the root surface area (RSA) below the alveolar bone crest. The area of contact between tooth roots and the surrounding bone plays an important role in orthodontic and periodontal treatment. It has been proposed that the PDL and alveolar bone are functional units that undergo robust remodeling during orthodontic tooth movement.3 Moreover, the PDL area plays an important role in tooth anchorage,4 and morphological changes in the PDL reflect the vertical bone level (VBL).5 Quantification of the PDL area can help assess the severity of periodontal disease and the prognosis of orthodontic treatment.
Measurement of the alveolar bone thickness and VBL in the sagittal plane of cone-beam computed tomography (CBCT) images is a well-established method.6-8 Past studies have focused primarily on measurement of the height and thickness of the alveolar bone on the labial and lingual sides of the incisors in the sagittal plane. Evaluation of two-dimensional (2D) measurements without consideration of the three-dimensional (3D) PDL area may not adequately indicate the severity of periodontal lesions. Moreover, 2D linear measurements describe VBL in a one-dimensional manner without taking changes in the root shape into account, thus underestimating the true amount of periodontal loss.9-11
In other previous studies,9,12 microcomputed tomography (micro-CT) data were used to measure the RSA on reconstructed digital models of extracted teeth. However, the micro-CT technique cannot be used for
Researchers have also used CBCT to reconstruct the root surface to detect apical root resorption cavities14 and measure the RSA as an important marker for determination of the periodontal treatment plan and prognosis. However, RSA measurements do not take alveolar bone conditions into account; in recent years, the PDL surface area, or the RSA below the alveolar bone crest, has been studied as a marker of periodontal health, and researchers have artificially simulated the PDL area using digital models of teeth.5,9,10,12,17 Nevertheless, to our knowledge, this is the first study to obtain
In the present study, instead of artificially simulating the alveolar bone crest
Forty-eight anterior teeth from four patients (two female and two male) with skeletal Class III malocclusion requiring surgical orthodontic treatment and augmented corticotomy (AC) were evaluated in this study at Peking University School and Hospital of Stomatology from May 2021 to October 2021. All patients signed informed consent forms. The study was approved by the Biomedical Ethics Committee of the Peking University School and Hospital of Stomatology (approval number: PKUSSIRB-201839156) and registered on the Clinical Trials Register as ChiCTR1900021778 (Chinese Clinical Trials Registry Platform of the World Health Organization).
The inclusion criteria were as follows: 1) age > 18 years for male patients and > 16 years for female patients;18,19 2) A point–nasion–B point (ANB) angle of < 0° and overjet of < 0 mm; 3) no more than two sites with a probing depth of ≥ 5 mm in the entire oral cavity, bleeding on probing score of ≤ 20%, and plaque score of ≤ 30%; and 4) labial alveolar bone thickness of < 1 mm around the maxillary and mandibular central incisors, as measured by CBCT. The mean alveolar bone thickness at the root apex of the maxillary and mandibular central incisors was 0.81 ± 0.17 mm and 0.4 ± 0.15 mm, respectively. Patients with poor oral hygiene or uncontrolled periodontal disease were excluded.
All orthodontic treatments were performed by a single orthodontist using a straight-wire fixed appliance (0.022" slot size, MBT prescription). For the maxillary anterior teeth, the arch-wire sequence involved 0.014-, 0.016-, 0.018-, and 0.018 × 0.025-inch nickel-titanium wires before periodontal surgery. For the mandibular anterior teeth, periodontal surgery was performed after bracket bonding without any arch wire in place. Two weeks after periodontal surgery, aligning and leveling were initiated with 0.014-inch nickel-titanium wires.
Prior to periodontal surgery, CBCT images were acquired with the NewTom VG device (Aperio Services, Verona, Italy) in the regular scan mode (field of view [FOV], 10 × 10 cm; voltage, 110 kV; current, 3.00 mA; and exposure, 1.8 seconds). The CBCT images were reconstructed using different voxel sizes (0.20, 0.25, and 0.30 mm). To reduce scatter at the occlusal plane, patients were instructed to bite on cotton rolls. Within 24 hours of CBCT image acquisition, the patients underwent intraoral scanning.
Digital Imaging and Communication in Medicine (DICOM) files were imported into Mimics 19.0 software (Materialise, Leuven, Belgium). In Mimics, 3D digital models of the anterior teeth and bone
The digital models were exported in stereolithographic (STL) format and imported into Geomagic software (Geomagic, Cary, NC, USA). For more realistic digitalization of the metal brackets bonded to the teeth, a digital model derived from the intraoral scan was superimposed over the 3D model generated from the CBCT datasets (Figure 2).
In Geomagic software, the vertical distance between the CEJ and alveolar bone crest parallel to the long axis of the anatomic crown was defined as the VBL. The long axis of the anatomic crown was determined by connecting the lowest point of the labial CEJ curve and the midpoint of the mesial and distal incisal angles. The five selected measurement sites on the digital models were the mesiolabial (VBL_MLa), mesiobracket (VBL_MB), midlabial (VBL_La), distobracket (VBL_DB), and distolabial (VBL_DLa) sites. The La point was chosen at the midlabial site on the surface. Proximal points on the surface, i.e., the MLa and DLa points, were located at the corner of each tooth. The vertical distance between the marginal bone crest and the gingival boundary of the metal bracket was defined as the bone-bracket distance (BBD). The three selected measurement points were the mesiobracket (BBD_MB), midlabial (BBD_La), and distobracket (BBD_DB) points. Detailed information about the measurement procedure is shown in Figure 3. Measurements were made to the nearest 0.01 mm using a linear measurement tool in a quiet and dark room.
All AC procedures were performed by a single periodontist using surgical loupes. The AC procedure was performed as follows.21 A crevicular incision was made from the canine on one side to the canine on the other side, and a full thickness flap on the labial side was elevated. The distance parallel to the long axis of the anatomic crown between the CEJ and alveolar bone crest was measured at five sites, in addition to the distance between the alveolar bone crest and gingival boundary at the mesial and distal metal bracket sites (Figure 4). All measurements were made to the nearest 1 mm by the same experienced periodontist who performed the AC procedure using a manual periodontal probe (UNC-15, graded in millimetres; HU-Friedy, Chicago, IL, USA) placed parallel to the long axis of the tooth. The intraoperative measurements were considered the “reference standard.”
To segment the PDL in the digital model, we identified the alveolar bone crest in the digital model and drew points on the teeth in the model (Figure 5A and 5B). A curve was generated by connecting the points marked on the model surface using the creation method in Geomagic (Figure 5B). The created boundary curve represented the alveolar bone crest (Figure 5C). The teeth were then separated along the curve into two parts (Figure 5D), with preservation of the PDL (Figure 5E), and the PDL area in the digital model was calculated (Figure 5F).
Statistical analyses were performed using SPSS 20.0 (IBM Corp., Armonk, NY, USA). All linear measurements for the digital models were obtained twice at an interval of 2 weeks by the same investigator, and the average of these two measurements was used for statistical analysis. The systematic intraexaminer error was determined using a paired
Descriptive statistics for differences between the intraoperative and digital measurements were separately computed. In addition, the 95% confidence interval (CI) was calculated, and diagnostic coincidence rates were calculated using an introduced variable measurement difference to evaluate the accuracy of site-based image assessment relative to the clinical measurement.
If the measurement difference ranged from −1 to +1 mm (including −1 and +1 mm), the measurement obtained from the 3D digital image was considered consistent with the intraoperative measurement; otherwise, the measurements were considered inconsistent. Thereafter, the corresponding diagnostic coincidence rates were calculated. To examine the agreement between the digital models obtained by different examiners, 24 randomly chosen teeth were assessed in a blinded manner by two authors with 4–8 years of experience in dental and periodontal imaging. The error was evaluated by measuring the surface area of the PDL in the models. The systematic interexaminer agreement was calculated using the ICC, and the Bland–Altman method was applied to identify the limits of agreement.
For both the maxillary and mandibular anterior teeth, there were no significant differences in digital measurements at different sites among different voxel sizes (
Table 1 . Comparison of intraoperative measurements and digital linear measurements at different sites with different voxel sizes.
Measurements | Digital | Intraoperative | Multiple comparison | |||
---|---|---|---|---|---|---|
0.2 mm | 0.25 mm | 0.3 mm | ||||
Maxillary anterior teeth | ||||||
VBL_MLa (mm) | 1.08 ± 0.50 | 1.06 ± 0.44 | 1.01 ± 0.47 | 1.00 ± 0.74 | 0.22 | - |
VBL_MB (mm) | 1.58 ± 0.53 | 1.49 ± 0.72 | 1.39 ± 0.54 | 1.46 ± 0.66 | 0.74 | - |
VBL_La (mm) | 1.98 ± 0.57 | 2.04 ± 0.74 | 1.93 ± 0.69 | 1.79 ± 0.72 | 0.63 | - |
VBL_DB (mm) | 1.68 ± 0.47 | 1.52 ± 0.59 | 1.51 ± 0.54 | 1.60 ± 0.63 | 0.71 | - |
VBL_DLa (mm) | 1.41 ± 0.63 | 1.16 ± 0.75 | 1.01 ± 0.55 | 1.35 ± 0.76 | 0.15 | - |
BBD_MB (mm) | 7.47 ± 1.08 | 7.27 ± 1.07 | 7.32 ± 0.99 | 7.33 ± 1.11 | 0.92 | - |
BBD_La (mm) | 8.09 ± 0.91 | 7.86 ± 1.03 | 7.81 ± 1.04 | 7.96 ± 1.21 | 0.81 | - |
BBD_DB (mm) | 7.77 ± 0.97 | 7.32 ± 0.95 | 7.36 ± 0.98 | 7.63 ± 0.94 | 0.32 | - |
Mandibular anterior teeth | ||||||
VBL_MLa (mm) | 1.56 ± 0.60 | 1.30 ± 0.45 | 1.55 ± 0.57 | 2.13 ± 0.76 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_MB (mm) | 2.54 ± 0.86 | 2.37 ± 0.79 | 2.48 ± 0.84 | 3.31 ± 0.70 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_La (mm) | 3.87 ± 1.72 | 3.69 ± 1.40 | 3.65 ± 1.56 | 4.52 ± 1.05 | 0.15 | - |
VBL_DB (mm) | 2.75 ± 0.86 | 2.47 ± 1.16 | 2.39 ± 0.62 | 3.44 ± 0.97 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_DLa (mm) | 1.50 ± 0.58 | 1.27 ± 0.46 | 1.51 ± 0.54 | 2.25 ± 0.81 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
BBD_MB (mm) | 8.16 ± 1.56 | 8.01 ± 1.54 | 7.94 ± 1.50 | 7.92 ± 1.59 | 0.95 | - |
BBD_La (mm) | 9.36 ± 2.23 | 9.42 ± 2.00 | 9.24 ± 2.20 | 9.35 ± 1.60 | 0.99 | - |
BBD_DB (mm) | 8.09 ± 1.52 | 8.01 ± 1.84 | 7.78 ± 1.40 | 7.98 ± 1.77 | 0.92 | - |
Values are presented as mean ± standard deviation..
One-way ANOVA with Duncan’s multiple comparison test was performed for comparisons between intraoperative and digital linear measurements..
VBL, vertical bone level; BBD, bone–bracket distance; MLa, mesiolabial; MB, mesiobracket; La, midlabial; DB, distobracket; DLa, distolabial..
**
The maxillary anterior teeth showed no significant differences between the digital and intraoperative VBL measurements (
A statistically significant ICC was found for the correlation between all digital and intraoperative measurements (
Table 2 . Intraclass correlation coefficient (ICC) analysis of intraoperative and digital linear measurements obtained with different voxel sizes.
Measurements | 0.2 mm | 0.25 mm | 0.3 mm | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
ICC | 95% CI | ICC | 95% CI | ICC | 95% CI | |||||||
Lower bound Upper bound | Lower bound | Upper bound | Lower bound | Upper bound | ||||||||
Maxillary anterior teeth | VBL | 0.793** | 0.715 | 0.851 | 0.684** | 0.576 | 0.769 | 0.646** | 0.528 | 0.739 | ||
BBD | 0.887** | 0.825 | 0.928 | 0.850** | 0.771 | 0.904 | 0.908** | 0.857 | 0.942 | |||
Mandibular anterior teeth | VBL | 0.726** | 0.629 | 0.801 | 0.769** | 0.684 | 0.833 | 0.689** | 0.582 | 0.772 | ||
BBD | 0.839** | 0.754 | 0.896 | 0.872** | 0.803 | 0.918 | 0.842** | 0.758 | 0.898 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval..
**
The mean differences and descriptive statistics for the measurements are shown in Tables 3 and 4. The mean differences (and 95% CIs) between the digital and intraoperative measurements for the maxillary anterior teeth were approximately 0; this confirmed no significant differences. Statistically significant mean differences were found in the VBL measurements for the mandibular anterior teeth, regardless of the voxel size (
Table 3 . Descriptive statistics, diagnostic coincidence rates, limits of agreement, and 95% CIs for differences in linear measurements obtained with different voxel sizes for the maxillary anterior teeth.
Measurement difference | Mean difference (mm) | Median (mm) | SD (mm) | Range (mm) | Diagnostic coincidence rates (%) | Limits of agreement (mm) | 95% CI (mm) |
---|---|---|---|---|---|---|---|
VBL (n = 120) | |||||||
0.2 mm | −0.07 | −0.10 | 0.43 | 2.28 | 96.66 | −0.92–0.78 | −0.15–0.00 |
0.25 mm | −0.01 | −0.01 | 0.58 | 2.72 | 92.50 | −1.15–1.12 | −0.11–0.09 |
0.3 mm | 0.07 | 0.09 | 0.58 | 2.61 | 90.00 | −1.06–1.21 | −0.03–0.17 |
BBD (n = 72) | |||||||
0.2 mm | −0.09 | 0.01 | 0.51 | 2.60 | 90.27 | −1.08–0.91 | −0.21–0.03 |
0.25 mm | 0.11 | 0.11 | 0.59 | 3.34 | 94.44 | −1.04–1.26 | −0.03–0.25 |
0.3 mm | 0.09 | 0.02 | 0.47 | 2.59 | 97.22 | −0.82–1.00 | −0.02–0.19 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval; SD, standard deviation..
Table 4 . Descriptive statistics, diagnostic coincidence rates, limits of agreement, and 95% CIs for differences in linear measurements obtained with different voxel sizes for the mandibular anterior teeth.
Measurement difference | Mean difference (mm) | Median (mm) | SD (mm) | Range (mm) | Diagnostic coincidence rates (%) | Limits of agreement (mm) | 95% CI (mm) |
---|---|---|---|---|---|---|---|
VBL (n = 120) | |||||||
0.2 mm | 0.68 | 0.71 | 0.95 | 5.82 | 63.33 | −1.17–2.54 | 0.51–0.85 |
0.25 mm | 0.91 | 0.88 | 0.85 | 5.92 | 56.66 | −0.76–2.58 | 0.75–1.06 |
0.3 mm | 0.82 | 0.81 | 0.95 | 6.58 | 56.66 | −1.05–2.68 | 0.64–0.98 |
BBD (n = 72) | |||||||
0.2 mm | −0.04 | −0.10 | 0.98 | 5.03 | 66.67 | −1.96–1.88 | −0.26–0.19 |
0.25 mm | 0.11 | 0.20 | 0.89 | 5.13 | 77.78 | −1.65–1.86 | −0.10–0.31 |
0.3 mm | 0.17 | 0.08 | 0.98 | 6.23 | 70.83 | −1.76–2.10 | −0 06–0.40 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval; SD, standard deviation..
The diagnostic coincidence rates for the VBL and BBD values for the maxillary anterior teeth were ≥ 90%. For the mandibular anterior teeth, the diagnostic coincidence rates ranged from 56.66% to 63.33% for the VBL and from 66.67% to 77.78% for the BBD (Tables 3 and 4).
For validation of the different measurements, the differences between the digital and intraoperative measurements were plotted against the average, as recommended in Bland–Altman analysis. The limits of agreement were defined as ± 1.96 × standard deviation and are shown in Figure 6. The limits of agreement for the maxillary anterior teeth showed discrepancies of approximately 2 mm in the measurements. However, high variability was observed in the mandibular measurements, as indicated by the large 95% limits of agreement range of approximately 3.5 mm.
High intraexaminer agreement was observed for the linear measurements of the digital model. The results showed no significant systematic intraexaminer error (
Differences in PDL area measurements between examiners were also analyzed, and the results showed high interexaminer agreement (ICC, 0.947; 95% CI, 0.871–0.979). Moreover, the Bland–Altman analysis showed good consistency between the two examiners in the process of PDL segmentation in the model. The mean bias for the PDL area (mm2) was 2.57, with limits of agreement ranging from −17.89 to 23.03 (Figure 7), indicating good consistency between the two examiners in the process of PDL segmentation.
Digital models of the PDL of the maxillary and mandibular anterior teeth of the four patients were successfully established. A representative case is shown in Figure 8.
Detection and monitoring of alveolar bone loss are important because they provide a hard-tissue index for the presence of periodontal disease and the effects of preventative and corrective therapies for periodontal disease.22,23 In the present study, we introduced an accurate and reproducible method to obtain alveolar bone crest-based digital PDL models using 3D CBCT reconstruction.
The present study suggests that 3D CBCT reconstruction provides relatively accurate information regarding the alveolar bone around the anterior teeth. There were no significant differences among measurements obtained using CBCT voxel resolutions of 0.20, 0.25, and 0.30 mm; this indicates that the method is highly valuable for clinical application. Previous studies have shown that discernment of the PDL space requires CBCT data with a resolution capable of detecting structures less than 0.2 mm in size.22,24 However, data with higher resolution may require higher levels of radiation, which would increase the radiation exposure of patients.25 The present study shows that CBCT with a voxel size of 0.30 mm and relatively little radiation is sufficient to represent the morphology of the alveolar crest, relative to the gold standard. Furthermore, the position of the alveolar crest can be determined, which helps in identification of the coronal margin of the PDL.
Many previous studies have focused on factors influencing the accuracy of CBCT datasets for 3D reconstruction-based measurements26-28 or linear measurements of the alveolar bone, such as the alveolar bone level in the sagittal plane.25,29-31 Some studies have shown that a smaller voxel size is associated with better spatial resolution,26,27 while others have concluded that there is no significant difference between high-resolution and low-resolution CBCT protocols.28,29 A lower resolution also results in higher levels of image noise and influences the accuracy of alveolar bone measurements.30,32 This may explain the divergence in conclusions to some extent. Moreover, various exposure parameters in CBCT may influence the image quality, such as the FOV and presence of metallic restorations.33,34 In the present study, the FOV, voltage, and other conditions were controlled to investigate the effects of the voxel size. In addition, all patients had metal brackets because CBCT was performed during orthodontic treatment, which is a common clinical situation. Although CBCT can provide an accurate 3D view of the tooth roots and alveolar bone, dense intraoral metal brackets can severely compromise the image quality of crowns.35 Therefore, in this study, intraoral optical scans were used to obtain profiles of anterior tooth crowns and surrounding soft tissue in the STL format, thus eliminating the impact of metal artefacts on the crown morphology.
Previous studies have reported that accurate 3D models of entire dentition could be generated with an intraoral scan superimposed over the CBCT images during orthodontic treatment with brackets.36-38 In the present study, the orthodontic brackets were chosen as reference marks for evaluation of the alveolar bone crest. Our results showed that the digital VBL measurements for the mandibular anterior teeth were significantly smaller than the intraoperative VBL measurements, while there were no significant differences in the BBD at any site between the two methods. This indicates that the main source of deviation in the VBL measurements was selection of the CEJ point. The position of the CEJ around the mandibular anterior teeth on the 3D model tends to be gingivally oriented. Previously, Wang et al.39 found that reconstruction of the crown and root still showed a clear CEJ boundary and a smooth area on the surface. The present study, however, indicated that the CEJ may not be an accurate or reproducible anatomical landmark for mandibular anterior teeth using a 3D model. This finding agrees with Kuralt et al.,40 who found that CEJ point selection was the main source of variability in measurements obtained from an intraoral optical scan-derived model. The inaccurate positioning of the CEJ and the difficulty in its identification in the present study may be attributed to the flatter morphology of the mandibular anterior teeth on the labial side and wear of the CEJ.41 Furthermore, in the reconstruction of mandibular anterior tooth models using CBCT datasets, the maximum inaccuracy was mainly found at the cervical margins.42 Therefore, when the CEJ is used as an anatomical landmark for examining the periodontal health status of the mandibular anterior teeth using a 3D model, the possibility of underestimation of the alveolar bone loss severity should be considered.
Because the gold standard in this study was periodontal probe measurements, precision to ±1 mm with a manual periodontal probe was acceptable. The results showed a high diagnostic coincidence rate (> 90%) for the maxilla and a relatively low for the mandible. The Bland–Altman method showed that the limits of agreement were −1 mm to +1 mm for the maxillary anterior teeth; this finding was generally consistent with the results of a previous study.29 However, the broader limits of agreement and the wider span of differences in digital measurements for the mandibular anterior teeth indicate that the mandibular models are less reliable. This could be attributed to the thinner anterior alveolar bone and more vertical bone loss in skeletal Class III patients than in those with Class I patients with normal occlusion,7 as well as the difficulty in obtaining accurate measurements of the boundary of thin alveolar bone using CBCT, even with a 0.125-mm-voxel protocol.29
The present study presents a feasible and noninvasive method for obtaining
Despite the limitations described above, the present study introduced an accurate and consistent method for obtaining PDL measurements from a reconstructed 3D model, which has important implications for clinical treatment. The 3D morphology of the PDL is a significant prognostic indicator in patients with periodontal disease or those undergoing orthodontic therapy, particularly those with previous periodontal bone loss.
The present study introduced a method for obtaining PDL measurements from 3D reconstructions of
None.
Conceptualization: WL. Data curation: HL, XW. Formal analysis: HM. Funding acquisition: XL. Methodology: YW, YZ. Project administration: XL, XW. Visualization: LX, JH. Writing–original draft: HL. Writing–review & editing: XL.
No potential conflict of interest relevant to this article was reported.
This study was supported by the National Program for Multidisciplinary Cooperative Treatment on Major Diseases (PKUSSNMP-201902).
Table 1 . Comparison of intraoperative measurements and digital linear measurements at different sites with different voxel sizes.
Measurements | Digital | Intraoperative | Multiple comparison | |||
---|---|---|---|---|---|---|
0.2 mm | 0.25 mm | 0.3 mm | ||||
Maxillary anterior teeth | ||||||
VBL_MLa (mm) | 1.08 ± 0.50 | 1.06 ± 0.44 | 1.01 ± 0.47 | 1.00 ± 0.74 | 0.22 | - |
VBL_MB (mm) | 1.58 ± 0.53 | 1.49 ± 0.72 | 1.39 ± 0.54 | 1.46 ± 0.66 | 0.74 | - |
VBL_La (mm) | 1.98 ± 0.57 | 2.04 ± 0.74 | 1.93 ± 0.69 | 1.79 ± 0.72 | 0.63 | - |
VBL_DB (mm) | 1.68 ± 0.47 | 1.52 ± 0.59 | 1.51 ± 0.54 | 1.60 ± 0.63 | 0.71 | - |
VBL_DLa (mm) | 1.41 ± 0.63 | 1.16 ± 0.75 | 1.01 ± 0.55 | 1.35 ± 0.76 | 0.15 | - |
BBD_MB (mm) | 7.47 ± 1.08 | 7.27 ± 1.07 | 7.32 ± 0.99 | 7.33 ± 1.11 | 0.92 | - |
BBD_La (mm) | 8.09 ± 0.91 | 7.86 ± 1.03 | 7.81 ± 1.04 | 7.96 ± 1.21 | 0.81 | - |
BBD_DB (mm) | 7.77 ± 0.97 | 7.32 ± 0.95 | 7.36 ± 0.98 | 7.63 ± 0.94 | 0.32 | - |
Mandibular anterior teeth | ||||||
VBL_MLa (mm) | 1.56 ± 0.60 | 1.30 ± 0.45 | 1.55 ± 0.57 | 2.13 ± 0.76 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_MB (mm) | 2.54 ± 0.86 | 2.37 ± 0.79 | 2.48 ± 0.84 | 3.31 ± 0.70 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_La (mm) | 3.87 ± 1.72 | 3.69 ± 1.40 | 3.65 ± 1.56 | 4.52 ± 1.05 | 0.15 | - |
VBL_DB (mm) | 2.75 ± 0.86 | 2.47 ± 1.16 | 2.39 ± 0.62 | 3.44 ± 0.97 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
VBL_DLa (mm) | 1.50 ± 0.58 | 1.27 ± 0.46 | 1.51 ± 0.54 | 2.25 ± 0.81 | 0.000** | Intra > (0.2 mm, 0.25 mm, 0.3 mm) |
BBD_MB (mm) | 8.16 ± 1.56 | 8.01 ± 1.54 | 7.94 ± 1.50 | 7.92 ± 1.59 | 0.95 | - |
BBD_La (mm) | 9.36 ± 2.23 | 9.42 ± 2.00 | 9.24 ± 2.20 | 9.35 ± 1.60 | 0.99 | - |
BBD_DB (mm) | 8.09 ± 1.52 | 8.01 ± 1.84 | 7.78 ± 1.40 | 7.98 ± 1.77 | 0.92 | - |
Values are presented as mean ± standard deviation..
One-way ANOVA with Duncan’s multiple comparison test was performed for comparisons between intraoperative and digital linear measurements..
VBL, vertical bone level; BBD, bone–bracket distance; MLa, mesiolabial; MB, mesiobracket; La, midlabial; DB, distobracket; DLa, distolabial..
**
Table 2 . Intraclass correlation coefficient (ICC) analysis of intraoperative and digital linear measurements obtained with different voxel sizes.
Measurements | 0.2 mm | 0.25 mm | 0.3 mm | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
ICC | 95% CI | ICC | 95% CI | ICC | 95% CI | |||||||
Lower bound Upper bound | Lower bound | Upper bound | Lower bound | Upper bound | ||||||||
Maxillary anterior teeth | VBL | 0.793** | 0.715 | 0.851 | 0.684** | 0.576 | 0.769 | 0.646** | 0.528 | 0.739 | ||
BBD | 0.887** | 0.825 | 0.928 | 0.850** | 0.771 | 0.904 | 0.908** | 0.857 | 0.942 | |||
Mandibular anterior teeth | VBL | 0.726** | 0.629 | 0.801 | 0.769** | 0.684 | 0.833 | 0.689** | 0.582 | 0.772 | ||
BBD | 0.839** | 0.754 | 0.896 | 0.872** | 0.803 | 0.918 | 0.842** | 0.758 | 0.898 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval..
**
Table 3 . Descriptive statistics, diagnostic coincidence rates, limits of agreement, and 95% CIs for differences in linear measurements obtained with different voxel sizes for the maxillary anterior teeth.
Measurement difference | Mean difference (mm) | Median (mm) | SD (mm) | Range (mm) | Diagnostic coincidence rates (%) | Limits of agreement (mm) | 95% CI (mm) |
---|---|---|---|---|---|---|---|
VBL (n = 120) | |||||||
0.2 mm | −0.07 | −0.10 | 0.43 | 2.28 | 96.66 | −0.92–0.78 | −0.15–0.00 |
0.25 mm | −0.01 | −0.01 | 0.58 | 2.72 | 92.50 | −1.15–1.12 | −0.11–0.09 |
0.3 mm | 0.07 | 0.09 | 0.58 | 2.61 | 90.00 | −1.06–1.21 | −0.03–0.17 |
BBD (n = 72) | |||||||
0.2 mm | −0.09 | 0.01 | 0.51 | 2.60 | 90.27 | −1.08–0.91 | −0.21–0.03 |
0.25 mm | 0.11 | 0.11 | 0.59 | 3.34 | 94.44 | −1.04–1.26 | −0.03–0.25 |
0.3 mm | 0.09 | 0.02 | 0.47 | 2.59 | 97.22 | −0.82–1.00 | −0.02–0.19 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval; SD, standard deviation..
Table 4 . Descriptive statistics, diagnostic coincidence rates, limits of agreement, and 95% CIs for differences in linear measurements obtained with different voxel sizes for the mandibular anterior teeth.
Measurement difference | Mean difference (mm) | Median (mm) | SD (mm) | Range (mm) | Diagnostic coincidence rates (%) | Limits of agreement (mm) | 95% CI (mm) |
---|---|---|---|---|---|---|---|
VBL (n = 120) | |||||||
0.2 mm | 0.68 | 0.71 | 0.95 | 5.82 | 63.33 | −1.17–2.54 | 0.51–0.85 |
0.25 mm | 0.91 | 0.88 | 0.85 | 5.92 | 56.66 | −0.76–2.58 | 0.75–1.06 |
0.3 mm | 0.82 | 0.81 | 0.95 | 6.58 | 56.66 | −1.05–2.68 | 0.64–0.98 |
BBD (n = 72) | |||||||
0.2 mm | −0.04 | −0.10 | 0.98 | 5.03 | 66.67 | −1.96–1.88 | −0.26–0.19 |
0.25 mm | 0.11 | 0.20 | 0.89 | 5.13 | 77.78 | −1.65–1.86 | −0.10–0.31 |
0.3 mm | 0.17 | 0.08 | 0.98 | 6.23 | 70.83 | −1.76–2.10 | −0 06–0.40 |
VBL, vertical bone level; BBD, bone–bracket distance; CI, confidence interval; SD, standard deviation..