Accuracy of in vitro mandibular volumetric measurements from CBCT of different voxel sizes with different segmentation threshold settings

Influence of exposure protocol, voxel size, and artifact removal algorithm on the trueness of segmentation utilizing an artificial-intelligence-based system

PURPOSE

To evaluate the effects of exposure protocol, voxel sizes, and artifact removal algorithms on the trueness of segmentation in various mandible regions using an artificial intelligence (AI)-based system.

MATERIALS AND METHODS

Eleven dry human mandibles were scanned using a cone beam computed tomography (CBCT) scanner under differing exposure protocols (standard and ultra-low), voxel sizes (0.15 mm, 0.3 mm, and 0.45 mm), and with or without artifact removal algorithm. The resulting datasets were segmented using an AI-based system, exported as 3D models, and compared to reference files derived from a white-light laboratory scanner. Deviation measurement was performed using a computer-aided design (CAD) program and recorded as root mean square (RMS). The RMS values were used as a representation of the trueness of the AI-segmented 3D models. A 4-way ANOVA was used to assess the impact of voxel size, exposure protocol, artifact removal algorithm, and location on RMS values (α = 0.05).

RESULTS

Significant effects were found with voxel size (p < 0.001) and location (p < 0.001), but not with exposure protocol (p = 0.259) or artifact removal algorithm (p = 0.752). Standard exposure groups had significantly lower RMS values than the ultra-low exposure groups in the mandible body with 0.3 mm (p = 0.014) or 0.45 mm (p < 0.001) voxel sizes, the symphysis with a 0.45 mm voxel size (p = 0.011), and the whole mandible with a 0.45 mm voxel size (p = 0.001). Exposure protocol did not affect RMS values at teeth and alveolar bone (p = 0.544), mandible angles (p = 0.380), condyles (p = 0.114), and coronoids (p = 0.806) locations.

CONCLUSION

This study informs optimal exposure protocol and voxel size choices in CBCT imaging for true AI-based automatic segmentation with minimal radiation. The artifact removal algorithm did not influence the trueness of AI segmentation. When using an ultra-low exposure protocol to minimize patient radiation exposure in AI segmentations, a voxel size of 0.15 mm is recommended, while a voxel size of 0.45 mm should be avoided.

Influence of Kennedy class and number of implants on the accuracy of dynamic implant navigation: An in vitro study using an X-ray free evaluation methodology

OBJECTIVES

The aim of this in vitro study was to evaluate the accuracy of fully guided dynamic implant navigation surgery in Kennedy I, II, and III class dental arch defects with two different implant designs, using an X-ray free evaluation method.

METHODS

Polyurethane resin maxillary models simulated posterior edentulous defects. Four cone beam computed tomography (CBCT) scans and four intraoral (IOS) scans were obtained for each model and a digital wax-up with the correct implant positions was made. The accuracy of implant positions was evaluated using an IOS-based X-ray-free method (3Shape). Four deviation characteristics were evaluated: insertion point, depth deviation, horizontal and angle deviation.

RESULTS

The insertion point deviation measures ranged from 0.19 mm to 1.71 mm. Depth (s) and (u) deviations ranged from -1.47 mm to 0.74 mm and from 0.02 mm to 1.47 mm, respectively. Horizontal deviation ranged from 0.09 mm to 1.37 mm.

CONCLUSIONS

There is a tendency of a decreasing insertion point deviation for an increasing number and distribution area of the teeth (increasing Kennedy class number). Kennedy class II and distal implant position had the most influence for the higher deviations.

CLINICAL SIGNIFICANCE

Dynamic implant guidance provides accurate spacing, angulation, depth and position of the implants. It is important to understand how the number of missing teeth and implant design could influence the accuracy of dynamic implant navigation. Thus, it is important to evaluate factors influencing the accuracy of dynamic systems by using a X-ray-free post-operative method and to overcome the limitations of providing multiple CBCT scans.

Effects of the cone-beam computed tomography protocol on the accuracy and image quality of root surface area measurements: An in vitro study

Purpose

The objective of this study was to evaluate and compare the accuracy and image quality of root surface area (RSA) measurements obtained with various cone-beam computed tomography (CBCT) protocols, relative to the gold standard of micro-computed tomography (CT), in an in vitro setting.

Materials and Methods

Four dry human skulls were scanned using 8 different protocols, with voxel sizes of 0.15 mm, 0.3 mm, and 0.4 mm. Three-dimensional models of the selected teeth were constructed using CBCT and micro-CT protocols, and the RSA was automatically measured by the image-processing software. The absolute difference in the percentage of the RSA (%ΔRSA) was calculated and compared across the 8 CBCT protocols using repeated-measures analysis of variance. Finally, image quality scores of the RSA measurements were computed and reported in terms of percent distribution.

Results

No significant differences were observed in the %ΔRSA across the 8 protocols (P>0.05). The deviation in %ΔRSA ranged from 1.51% to 4.30%, with an increase corresponding to voxel size. As the voxel size increased, the image quality deteriorated. This decline in quality was particularly noticeable at the apical level of the root, where the distribution of poorer scores was most concentrated.

Conclusion

Relative to CBCT protocols with voxel sizes of 0.15 mm and 0.3 mm, the protocols with a voxel size of 0.4 mm demonstrated inferior image quality at the apical levels. In spite of this, no significant discrepancies were observed in RSA measurements across the different CBCT protocols.

Reliability and reproducibility of CBCT assessment of mandibular changes before and after treatment for Class III growing patients - an easy and quick way for evaluation

The objective of this study was to evaluate intraobserver reliability and inter-observer reproducibility of a 3-dimensional (3D) assessment method for mandibular changes of growing patients after orthodontic treatment for Class III malocclusion.Methods Cone-beam computed tomography (CBCT) scans were performed before and after orthodontic treatment for 27 patients. During the scan, the patient was positioned such that his/her mandibular plane was parallel to floor. Three observers independently worked on the DICOM data, reconstructed the pre- and post-treatment 3D models in software, selected the stable anatomical structures (basal bone area from the lingual surface of the symphysis to the distal aspect of the first molars) to guide the automated superimposition process. Then, each observer registered 14 anatomical landmarks on the virtual models, for three times after suitable interval, to generate 3 sets of coordinates; the mean was taken as the coordinates for that particular landmark. The intraobserver reliability and inter-observer reproducibility of the method were analyzed.Results The ICCs was > 0.90 for 25 (92.6%) of the intraobserver assessments. The precision of the measurement method was < 0.3 mm in 24 (88.9%) cases. The interobserver reproducibility errors were < 0.3 mm in 21 of the 27 cases.Conclusions The intraobserver reliability and inter-observer reproducibility of 3D assessment of mandibular changes using the virtual models were excellent.

Accuracy of digital duplication scanning methods for complete dentures

PURPOSE

To compare the accuracy of four digital scanning methods in duplicating a complete denture.

MATERIAL AND METHODS

Four scanning methods were used: cone beam computed tomography (CBCT), Straumann desktop scanner (DS), Trios intraoral scanner (TIO), and Virtuo Vivo intraoral scanner (VVIO). Each method was used to duplicate all the surfaces of a printed complete denture. The denture was scanned 10 times in each group. The trueness (in root mean square, RMS) and precision (in standard deviation, SD) were calculated by comparing the combined dentition, denture extension, and intaglio surfaces with the reference file. One-way analysis of variance and F-tests were used to test statistical differences (α = 0.05).

RESULTS

For the scanning accuracy of the whole denture, CBCT showed the highest RMS (0.249 ± 0.020 mm) and lowest trueness than DS (0.124 ± 0.014 mm p < 0.001), TIO (0.131 ± 0.006 mm p < 0.001), and VVIO (0.227 ± 0.020 mm p = 0.017), while DS and TIO showed smaller RMS than VVIO (p < 0.001). For the trueness of dentition, denture extension, and intaglio surfaces, CBCT also showed the highest mean RMS and lowest trueness among all groups (p < 0.001). DS and TIO had smaller mean RMS and higher trueness among all groups in all surfaces (p < 0.001, except VVIO in intaglio surface, p > 0.05). TIO had significantly lower within-group variability of RMS and highest precision compared to DS (p = 0.013), CBCT (p = 0.001), and VVIO (p < 0.001) in the combined surface. For dentition and denture extension surfaces, TIO showed similar within-group variability of RMS with the DS group (p > 0.05) and lower than CBCT and VVIO (p < 0.001).

CONCLUSION

The 7 Series desktop scanner and Trios 4 intraoral scanner can duplicate dentures in higher trueness than CBCT and the Virtuo Vivo intraoral scanner. The Trios 4 intraoral scanner was more precise in the combined surfaces than other scanning methods, while the 7 Series desktop scanner and Trios 4 intraoral scanner were more precise in the denture extension surface.

Three-dimensional evaluation of a virtual setup considering the roots and alveolar bone in molar distalization cases

We aimed to evaluate root parallelism and the dehiscence or fenestrations of virtual teeth setup using roots isolated from cone beam computed tomography (CBCT) images. Sixteen patients undergoing non-extraction orthodontic treatment with molar distalization were selected. Composite teeth were created by merging CBCT-isolated roots with intraoral scan-derived crowns. Three setups were performed sequentially: crown setup considering only the crowns, root setup-1 considering root alignment, and root setup-2 considering the roots and surrounding alveolar bone. We evaluated the parallelism and exposure of the roots and compared the American Board of Orthodontics Objective Grading System (ABO-OGS) scores using three-dimensionally printed models among the setups. The mean angulation differences between adjacent teeth in root setups-1 and -2 were significantly smaller than in the crown setup, except for some posterior teeth (p < 0.05). The amount of root exposure was significantly smaller in root setup-2 compared to crown setup and root setup-1 except when the mean exposure was less than 0.6 mm (p < 0.05). There was no significant difference in ABO-OGS scores among the setups. Thus, virtual setup considering the roots and alveolar bone can improve root parallelism and reduce the risk of root exposure without compromising occlusion quality.

The impact of teeth and dental restorations on gray value distribution in cone-beam computer tomography: a pilot study

PURPOSE

To investigate the influence of teeth and dental restorations on the facial skeleton's gray value distributions in cone-beam computed tomography (CBCT).

METHODS

Gray value selection for the upper and lower jaw segmentation was performed in 40 patients. In total, CBCT data of 20 maxillae and 20 mandibles, ten partial edentulous and ten fully edentulous in each jaw, respectively, were evaluated using two different gray value selection procedures: manual lower threshold selection and automated lower threshold selection. Two sample t tests, linear regression models, linear mixed models, and Pearson's correlation coefficients were computed to evaluate the influence of teeth, dental restorations, and threshold selection procedures on gray value distributions.

RESULTS

Manual threshold selection resulted in significantly different gray values in the fully and partially edentulous mandible. (p = 0.015, difference 123). In automated threshold selection, only tendencies to different gray values in fully edentulous compared to partially edentulous jaws were observed (difference: 58-75). Significantly different gray values were evaluated for threshold selection approaches, independent of the dental situation of the analyzed jaw. No significant correlation between the number of teeth and gray values was assessed, but a trend towards higher gray values in patients with more teeth was noted.

CONCLUSIONS

Standard gray values derived from CT imaging do not apply for threshold-based bone segmentation in CBCT. Teeth influence gray values and segmentation results. Inaccurate bone segmentation may result in ill-fitting surgical guides produced on CBCT data and misinterpreting bone density, which is crucial for selecting surgical protocols. Created with BioRender.com.

Effect of the Segmentation Threshold on Computed Tomography-Based Reconstruction of Skull Bones with Reference Optical Three-Dimensional Scanning

BACKGROUND

A variety of applications related to neurosurgical procedures, education, and training require accurate reconstruction of the involved structures from the medical images such as computed tomography (CT). This study evaluates the quality of CT-based reconstruction of dry skull bones for advanced neurosurgical applications. The accuracy and precision of these models were examined with reference optical scanning.

METHODS

Three consecutive CT and optical scans of different skull bones were acquired and used to develop three-dimensional models. The accuracy of three-dimensional models was examined by manual inspection of the defined anatomical landmarks of the skull. Reproducibility was examined by deviation analysis of the models developed from repeated CT and optical scans.

RESULTS

Precision was excellent in both the techniques with less than 0.1 mm deviation error. On the interscan evaluation of the CT versus optical scan model, deviations of more than 0.1 mm were observed in 16 out of 21 instances. CT reconstruction using standard segmentation algorithms results in missing bone portions while using the default bone segmentation threshold. The segmentation threshold was varied to construct missing bone regions, and its effect on the iso-surface generation was evaluated. The threshold variation led to increased mean deviations of surfaces up to 0.6 mm.

CONCLUSIONS

The study reveals that bone structure, complexity, and segmentation threshold lead to CT reconstruction variability. The trade-off between the desirable model and accepted mean deviation should be considered as per traits of the desired application.

Influence of Voxel Size on CBCT Images for Dental Implants Planning

Objective  This study was developed to evaluate the influence of voxel size on bone measurements for implant planning.

Materials and Methods  The research was performed by using edentulous synthetic human mandibles with different levels of bone resorption. For each mandible, height and bone thickness were measured with a digital caliper. The PaX-i3d device was used to acquire the volumes of the five mandibles, with 50kVp, 4 mA, and a voxel size of 0.08 mm. After the acquisition, the images were reconstructed in the software CS three-dimensional Imaging, with four different sizes of voxels: 0.1, 0.2, 0.3, and 0.4 mm. All volumes were analyzed by a single evaluator who performed measurements to obtain bone height and thickness, using the reference points that were considered in obtaining the gold standard. The data were analyzed by ANOVA with a significance level of 5%.

Results  There was no significant difference in the measurements obtained with different voxel sizes, both for bone height measurements and bone thickness. There was no statistically significant difference in measurements in thickness in comparison to the gold standard.

Conclusion  When necessary, to measure height and bone thickness, it is possible to recommend voxel images of larger size (0.40 mm) without compromising the quality of the patient's clinical planning.

A 3D mirroring and colormap asymmetry study of Class II subdivision patients

INTRODUCTION

Patients with Class II subdivision malocclusion present skeletal and dental asymmetries. The purpose of this study is to assess those asymmetries by 3D mirroring and colormap quantification.

METHODS

This study analyzed 50 initial CBCTs divided into two groups: Class I (control group) and Class II subdivision (study group) malocclusion patients. CBCTs were oriented and full skull was segmented generating a 3D model. The right side of the 3D models was mirrored, using a midsagittal plane as reference, resulting in a perfectly symmetric skull based on two right sides. Original and mirrored models were superimposed on the unchanged right half, and differences were quantified using a colormap. Eight regions of interest were assessed: gonion, mandibular front, maxillary front, zygomatic process, maxillary and mandibular canine and molar areas.

RESULTS

Statistically significant differences using the Mann-Whitney test were found in six of the eight evaluated areas when comparing the control to the study group. The maxillary skeletal areas did not show any difference between the groups.

CONCLUSIONS

Patients with Class II subdivision malocclusion show true skeletal and dental asymmetries when comparing right and left sides. The maxilla showed no significant skeletal asymmetry, but the maxillary teeth were positioned more mesially on the Class II side. The maxillary canine on the Class II side was also more bucally positioned. The mandible showed significant asymmetries with both skeletal and dental areas in the Class II side more distally and bucally positioned.

Effects of Exposure Parameters and Voxel Size for Cone-Beam Computed Tomography on the Image Matching Accuracy with an Optical Dental Scan Image: An In Vitro Study

This study is aimed at assessing the effects of exposure parameters and voxel size for cone-beam computed tomography (CBCT) on the image matching accuracy with an optical dental scan image. CBCT and optical scan images of a dry human mandible were obtained. Different CBCT settings were used: tube voltage, 60, 80, and 100 kVp; tube current, 6 and 8 mA; and voxel size, 100, 200, and 300 μm. Image matching between the CBCT and optical scan images was performed using implant planning software by dental professionals (n = 18). The image matching accuracy in each combination of CBCT settings was evaluated by assessing the linear discrepancy between the three-dimensionally reconstructed radiological image and the registered optical scan image using an image analysis software program. The Kruskal-Wallis test and a post hoc Mann–Whitney U test with Bonferroni correction were used to compare the accuracy of image registration between the groups (α = 0.05). Overall, the image matching accuracy was not significantly different between tube voltage and current settings; however, significantly higher image registration errors were found at the combination of 100 kVp tube voltage/8 mA tube current (F = 8.44, P < 0.001). Changes in voxel sizes did not significantly interfere with the image registration results. No interaction was found among voltage, current, and voxel size in terms of image registration accuracy (F = 2.022, P = 0.091). Different exposure parameter settings in tube voltage and tube current did not significantly influence the image matching accuracy between CBCT and optical dental scan images; however, a high radiation dose could be inappropriate. The image matching accuracy was not significantly affected by changing the voxel sizes of CBCT.

Effect of multiple injections of botulinum toxin into painful masticatory muscles on bone density in the temporomandibular complex

Background

Adverse effects of masticatory muscle injections of Botulinum Toxin (Btx) have been noted in animal and, less dramatically, human studies.

Objective

Among women treated in multiple community‐based private practices, to compare TMJ bone density and mandibular condylar volume between patients with myofascial TMJD receiving multiple masticatory muscle Btx treatments and similarly diagnosed women not receiving such treatment.

Methods

Cohorts consisted of women whose treatment charts indicated a diagnosis of myofascial TMJD: 35 received at least 2 Btx treatment cycles; 44 received none. Bone density at pre‐specified regions of interest (ROI) was defined by grey scale values from Cone Beam CT, adjusting for a fixed density phantom included in each scan. Mean bone density and mandibular condyle volume were compared between groups. Dose‐response effects were tested within the Btx‐exposed group.

Results

The mean density of primary and secondary ROIs was similar between exposure groups, as was condylar volume. Among Btx‐exposed women, increasing dose of Btx to the temporalis muscle was inversely proportional to the density of the trabecular area of the mandible body. Many Btx‐exposed women received smaller doses of Btx to the masseter muscles than in most TMJD Btx clinical trials.

Conclusion

Masticatory muscle injections of Btx failed to produce clinically significant TMJ bone‐related changes. Should Btx receive regulatory approval for treatment of myofascial TMJD, a phase IV study is recommended to evaluate potential adverse effects of Btx on bone and muscle when administered at higher doses and/or for more treatment cycles.

Evaluation of Imaging Software Accuracy for 3-Dimensional Analysis of the Mandibular Condyle. A Comparative Study Using a Surface-to-Surface Matching Technique

The aim of this study was to assess the accuracy of 3D rendering of the mandibular condylar region obtained from different semi-automatic segmentation methodology. A total of 10 Cone beam computed tomography (CBCT) were selected to perform semi-automatic segmentation of the condyles by using three free-source software (Invesalius, version 3.0.0, Centro de Tecnologia da Informação Renato Archer, Campinas, SP, Brazil; ITK-Snap, version2.2.0; Slicer 3D, version 4.10.2) and one commercially available software Dolphin 3D (Dolphin Imaging, version 11.0, Chatsworth, CA, USA). The same models were also manually segmented (Mimics, version 17.01, Materialise, Leuven, Belgium) and set as ground truth. The accuracy of semi-automatic segmentation was evaluated by (1) comparing the volume of each semi-automatic 3D rendered condylar model with that obtained with manual segmentation, (2) deviation analysis of each 3D rendered mandibular models with those obtained from manual segmentation. No significant differences were found in the volumetric dimensions of the condylar models among the tested software (p > 0.05). However, the color-coded map showed underestimation of the condylar models obtained with ITK-Snap and Slicer 3D, and overestimation with Dolphin 3D and Invesalius. Excellent reliability was found for both intra-observer and inter-observer readings. Despite the excellent reliability, the present findings suggest that data of condylar morphology obtained with semi-automatic segmentation should be taken with caution when an accurate definition of condylar boundaries is required.

Artificial intelligence in fixed implant prosthodontics: a retrospective study of 106 implant-supported monolithic zirconia crowns inserted in the posterior jaws of 90 patients

Background

Artificial intelligence (AI) is a branch of computer science concerned with building smart software or machines capable of performing tasks that typically require human intelligence. We present a protocol for the use of AI to fabricate implant-supported monolithic zirconia crowns (MZCs) cemented on customized hybrid abutments.

Methods

The study protocol consisted of: (1) intraoral scan of the implant position; (2) design of the individual abutment and temporary crown using computer-aided design (CAD) software; (3) milling of the zirconia abutment and the temporary polymethyl-methacrylate (PMMA) crown, with extraoral cementation of the zirconia abutment on the relative titanium bonding base, to generate an individual hybrid abutment; (4) clinical application of the hybrid abutment and the temporary PMMA crown; (5) intraoral scan of the hybrid abutment; (6) CAD of the final crown with automated margin line design using AI; (7) milling, sintering and characterisation of the final MZC; and (8) clinical application of the MZC. The outcome variables were mathematical (quality of the fabrication of the individual zirconia abutment) and clinical, such as (1) quality of the marginal adaptation, (2) of interproximal contact points and (3) of occlusal contacts, (4) chromatic integration, (5) survival and (6) success of MZCs. A careful statistical analysis was performed.

Results

90 patients (35 males, 55 females; mean age 53.3 ± 13.7 years) restored with 106 implant-supported MZCs were included in the study. The follow-up varied from 6 months to 3 years. The quality of the fabrication of individual hybrid abutments revealed a mean deviation of 44 μm (± 6.3) between the original CAD design of the zirconia abutment, and the mesh of the zirconia abutment captured intraorally at the end of the provisionalization. At the delivery of the MZCs, the marginal adaptation, quality of interproximal and occlusal contacts, and aesthetic integration were excellent. The three-year cumulative survival and success of the MZCs were 99.0% and 91.3%, respectively.

Conclusions

AI seems to represent a reliable tool for the restoration of single implants with MZCs cemented on customised hybrid abutments via a full digital workflow. Further studies are needed to confirm these positive results.