Reliability of three-dimensional anterior cranial base superimposition methods for assessment of overall hard tissue changes: A systematic review

Long-term evaluation of soft-tissue changes after miniscrew-assisted and conventional rapid palatal expansion using voxel-based superimposition of cone-beam computed tomography scans

INTRODUCTION

This study aimed to evaluate the soft-tissue changes in the long-term after miniscrew-assisted rapid palatal expansion (MARPE) and conventional rapid palatal expansion (RPE) appliances compared with a matched control group using voxel-based superimposition of cone-beam computed tomography (CBCT) scans.

METHODS

A total of 180 CBCTs for 60 patients at 3-time points were evaluated: pretreatment (T1), postexpansion (T2), and posttreatment (T3) for 3 groups: (1) MARPE, (2) RPE, and (3) controls (time-period T1 to T3: MARPE, 2 years 8 months; RPE, 2 years 9 months; control, 2 years 7 months). The voxel-based superimposition technique was used to superimpose the CBCT scans, after which the soft-tissue surfaces were extracted from the superimposed T1-CBCT, T2-CBCT, and T3-CBCT scans. Nine landmarks were identified on the CBCT scans: nasion, A-point, pogonion, right and left alar base, right and left zygoma, and right and left gonion. The coordinates of the 9 parameters were obtained in the x-axis, y-axis, and z-axis for the CBCT scans and subjected to statistical analyses. The changes in the soft-tissue surfaces were also evaluated by color-coded maps for short-term (T2) and long-term (T3) changes. The mean changes from T1 to T2 and T1 to T3 were tested against no change within the groups by paired t test, and the mean changes among the 3 groups were compared with analysis of variance F test with Tukey's Honest significant difference used for adjusting P values for multiple testing.

RESULTS

In the short term, both MARPE and RPE led to a significant downward movement of pogonion, left gonion, and lateral movement of the right and left alar base compared with controls at T2 (P <0.05). In addition, MARPE led to a significant downward movement of right gonion than controls at T2 (P <0.05). Moreover, RPE led to a significant downward and forward movement of A-point and downward movement of the right and left alar base than controls at T2 (P <0.05). However, in the long-term, there were no significant differences in the soft-tissue changes among the MARPE, RPE, and control groups.

CONCLUSIONS

MARPE and RPE do not lead to significant soft-tissue changes in the long term when compared with controls.

Novel Anterior Cranial Base Area for Voxel-Based Superimposition of Craniofacial CBCTs

A standard method to assess changes in craniofacial morphology over time is through the superimposition of serial patient images. This study evaluated the reliability of a novel anterior cranial base reference area, principally including stable midline structures (EMACB) after an early age, and compared it to the total anterior cranial base (TACB) and an area including only midline structures (MACB). Fifteen pairs of pre-existing serial CBCT images acquired from growing patients were superimposed with all techniques by applying a best-fit registration algorithm of corresponding voxel intensities (Dolphin 3D software). The research outcomes were the reproducibility of each technique and the agreement between them in skeletal change detection, as well as their validity. The TACB and EMACB methods were valid, since the superimposed midline ACB structures consistently showed adequate overlap. They also presented perfect overall reproducibility (median error < 0.01 mm) and agreement (median difference < 0.01 mm). MACB showed reduced validity, higher errors, and a moderate agreement to the TACB. Thus, the EMACB method performed efficiently and mainly included the stable midline ACB structures during growth. Based on the technical, anatomical, and biological principles applied when superimposing serial 3D data to assess craniofacial changes, we recommend the EMACB method as the method of choice to fulfil this purpose.

Stability of fiducial cephalometric landmarks of growing Class II malocclusion patients: a three-dimensional retrospective study

OBJECTIVES

To evaluate three-dimensionally (3D) the stability of Nasion (Na), Sella (S), Basion (Ba), Porion (Po), and Orbitale (Or) in different age groups of growing Class II malocclusion patients and, additionally, to assess rotational changes of the S-Na and Ba-Na lines and the Frankfurt Horizontal Plane (FHP).

MATERIALS AND METHODS

Cone-beam computed tomography studies of 67 Class II division 1 malocclusion patients, acquired at baseline (T0) and 1 year later (T1), were retrospectively assessed. Anterior cranial fossa was used for volumetric superimposition. Subjects were grouped according to their age at T0: group 1 (G1) (8-10 years), G2 (11-13 years), and G3 (14-17 years). Quantitative assessments of the 3D linear displacements (Euclidean distance) in the position of Na, S, Ba, Po, and Or were performed. Displacement in the X, Y, and Z projections and the rotation of S-Na, Na-Ba, and FHP were also quantified.

RESULTS

All cephalometric landmarks showed 3D displacement (P = .001) in the three age groups. Orbitale remained stable in the vertical and sagittal dimension from 8 to 17 years (P > .05). S-Na, Na-Ba, and the FHP showed statistically significant angular rotation (P < .05) in younger patients (G1), while in older individuals (G2 and G3) they were stable (P > .05).

CONCLUSIONS

Na, S, Ba, and Po showed vertical and sagittal positional changes relative to the anterior cranial fossa during the growth of Class II individuals. After age 11, S-Na, Na-Ba, and FHP did not show rotation and, thus, are valid parameters for angular cephalometric analysis in Class II growing patients.

Three-dimensional assessment of facial asymmetry in Class III subjects. Part 1: a retrospective study evaluating postsurgical outcomes

OBJECTIVE

The present study aimed to determine the site and severity of maxillomandibular asymmetry before and after orthognathic surgery in asymmetric patients.

MATERIALS AND METHODS

Presurgery and postsurgery cone beam computed tomography (CBCT) data of 21 facial asymmetry patients (7 males and 14 females, mean age: 23.0 ± 3.36 years) with soft tissue chin deviation ≥ 3 mm who had undergone bimaxillary surgery were evaluated. Seven midline and twenty bilateral hard tissue landmarks were identified for the evaluation of facial asymmetry and outcomes were assessed against age- and gender-matched control subjects.

RESULTS

In the asymmetry group, bilateral landmarks exhibited significant deviation in the mandible and midface regions. Before surgery, asymmetry was more severe at the mandibular midline and sites close to it, in the asymmetry group. Bimaxillary surgery proved to be highly effective, with a significant correction of the menton to a clinically normal value (2.90 mm, p < 0.001). After surgery, significant residual asymmetry was observed at the mental foramen (p = 0.001) in the R-L direction. Moreover, significant asymmetry persisted at the sigmoid notch (p = 0.001) in the S-I direction.

CONCLUSIONS

Mandibular midline landmarks and chin peripheral regions contribute significantly to overall facial asymmetry characteristics. Despite significant correction after bimaxillary surgery, asymmetry persisted at several sites, thereby requiring secondary correction. Comprehensive 3D presurgical planning is central for asymmetry correction in a single surgery.

CLINICAL RELEVANCE

The present study specifies the location of residual asymmetry sites and advocates the correction of those sites during initial surgery.

Computed tomography imaging superimposition protocols to assess outcomes in orthognathic surgery: a systematic review with comprehensive recommendations

OBJECTIVES

A systematic review was performed to analyze the current evidence on three-dimensional (3D) computed tomography (CT) superimposition protocols used to assess dentomaxillofacial changes after orthognathic and orthofacial surgery. Accuracy, reproducibility, and efficiency were evaluated.

METHODS

The search was divided into Main Search (PubMed, EMBASE, Cochrane Library, LILACS, and SciELO), Grey Literature search (Google Scholar and Open Grey), and Manual search. Thirteen studies were included. Of these, 10 reported data on accuracy, 10 on reproducibility and five on efficiency. Seven proposed or evaluated methods of voxel-based superimposition, three focused on the surface-based technique, one compared surface- and voxel-based superimposition protocols, one used the maximum mutual information algorithm, and one described a landmark-based superimposition method. Cone-beam computed tomography (CBCT) was the most common imaging technique, being used in 10 studies.

RESULTS

The accuracy of most methods was high, showing mean differences smaller than voxels' dimensions, ranging between 0.05 and 1.76 mm for translational accuracy, and 0.10-1.09° for rotational accuracy. The overall reproducibility was considered good as demonstrated by the small mean error (range: 0.01-0.26 mm) and high correlation coefficients (range: 0.53-1.00). Timing to complete virtual superimposition techniques ranged between a few seconds up to 40 min.

CONCLUSIONS

Voxel-based superimposition protocols presented the highest accuracy and reproducibility. Moreover, superimposition protocols that used automated processes and involved only one software were the most efficient.

Comparison of surface- and voxel-based registration on the mandibular ramus for long-term three-dimensional assessment of condylar remodelling following orthognathic surgery

OBJECTIVES

The purpose of the present study was to validate and compare the accuracy and reliability of surface- and voxel-based registration on the mandibular rami for long-term three-dimensional (3D) evaluation of condylar remodelling following Orthognathic Surgery.

METHODS

The mandible was 3D reconstructed from a pair of superimposed pre- and postoperative (two years) cone-beam computerized tomography scans and divided into the condyle, and 21 ramal regions. The accuracy of surface- and voxel-based registration was measured by the absolute mean surface distance of each region after alignment of the pre- and postoperative rami. To evaluate the reliability, mean absolute differences and intra class correlation coefficients (ICC) were calculated at a 95% confidence interval on volumetric and surface distance measurements of two observers. Paired t-tests were applied to statistically evaluate whether the accuracy and reliability of surface- and voxel-based registration were significantly different (p < 0.05).

RESULTS

A total of twenty subjects (sixteen female; four male; mean age 27.6 years) with class II malocclusion and maxillomandibular retrognathia, who underwent bimaxillary surgery, were included. Surface-based registration was more accurate and reliable than voxel-based registration on the mandibular ramus two years post-surgery (p < 0.05). The inter observer reliability of using surface-based registration was excellent, ICC range [0.82-1.00]. For voxel-based registration, the inter observer reliability ranged from poor to excellent [0.00-0.98]. The measurement error introduced by applying surface-based registration for assessment of condylar remodelling was considered clinical irrelevant (1.83% and 0.18 mm), while the measurement error introduced by voxel-based registration was considered clinical relevant (5.44% and 0.52 mm).

CONCLUSIONS

Surface-based registration was proven more accurate and reliable compared to voxel-based registration on the mandibular ramus for long-term 3D assessment of condylar remodelling following Orthognathic Surgery. However, importantly, the performance difference may be caused by an inappropriate reference structure, proposed in the literature, and applied in this study.

Reliability of Different Anterior Cranial Base Reference Areas for Voxel-Based Superimposition

The study aimed to evaluate the reliability and reproducibility and compare the outcomes of two 3D voxel-based superimposition techniques for craniofacial CBCT images, using anterior cranial base areas of different extent as references. Fifteen preexisting pairs of serial CBCTs (initial age: 11.7 ± 0.6 years; interval: 1.7 ± 0.4 years) were superimposed on total anterior cranial base (TACB) or middle anterior cranial base (MACB) structures through the Dolphin 3D software. The overlap of the reference structures was assessed visually to indicate reliability. All superimpositions were repeated by the same investigator. Outcomes were compared to assess the agreement between the two methods. Reliability was perfect for the TACB and moderate for the MACB method (p = 0.044). Both areas showed good overall reproducibility, though in individual cases there were notable differences for MACB superimpositions, ranging from −1.84 to 1.64 mm (TACB range: −0.48 to 0.31 mm). The overall agreement in the detected T0/T1 changes was also good, though it was significantly reduced for individual measurements (median < 0.01 mm, IQR: 0.46 mm, range: −2.81 to 0.73 mm). In conclusion, the voxel-based superimposition on TACB was more reliable and showed higher reproducibility than the superimposition on MACB. Thus, the extended anterior cranial base area is recommended for the assessment of craniofacial changes.

Intra-individual variation of upper airway measurements based on computed tomography

The aims of this study were (1) to quantify the intra-individual variation in the upper airway measurements on supine computed tomography (CT) scans at two different time points; and (2) to identify the most stable parameters of the upper airway measurements over time. Ten subjects with paired CT datasets (3-6 months interval) were studied, using computer software to segment and measure the upper airway. The minimum cross-sectional area of the total airway and all its segments (velopharynx, oropharynx, tongue base, and epiglottis) generally had the largest variation, while the length of the total airway had the lowest variation. Sphericity was the only parameter that was stable over time (relative difference <15%), both in the total airway and each subregion. There was considerable intra-individual variation in CT measurements of the upper airway, with the same patient instruction protocol for image acquisitions. The length of the total airway, and the sphericity of the total upper airway and each segment were stable over time. Hence, such intra-individual variation should be taken into account when interpreting and comparing upper airway evaluation parameters on CT in order to quantify treatment results or disease progress.

Evaluation of the accuracy of virtual planning in bimaxillary orthognathic surgery: Systematic review

The purpose of this research was to evaluate the accuracy of virtual planning in bimaxillary orthognathic surgery in bone by comparing the mean linear and angular measurements of the surgical plan with the actual surgical result. Electronic databases, MEDLINE via PubMed, Web of Science, SCOPUS, the Cochrane Library, grey literature, and the American clinical trials registry (www.ClinicalTrials.gov), were accessed as search engines. The studies consisted of publications on the assessment of accuracy in virtual planning in bimaxillary orthognathic surgery between 2010 and 2020. After application of the eligibility criteria, 26 articles were included, and their quality was evaluated using the methodological index for non-randomised studies (MINORS) tool and Cohen's kappa statistic in the MedCalc program (MedCalc Software Ltd). Evidence obtained by comparing the planning and surgical results, both in the maxilla and mandible, showed that there is great accuracy in virtual planning in bimaxillary orthognathic surgery.

Voxel-based superimposition of serial craniofacial cone-beam computed tomographies for facial soft tissue assessment: Reproducibility and segmentation effects

INTRODUCTION

The aim of this investigation was to evaluate the reproducibility of a voxel-based 3-dimensional superimposition method and the effect of segmentation error on determining soft tissue surface changes.

METHODS

A total of 15 pairs of serial cone-beam computed tomography images (interval: 1.69 ± 0.37 years) from growing subjects (initial age: 11.75 ± 0.59 years) were selected from an existing digital database. Each pair was superimposed on the anterior cranial base, in 3 dimensions with Dolphin 3D software (version 2.1.6079.17633; Dolphin Imaging & Management Solutions, Chatsworth, Calif). The reproducibility of superimposition outcomes and surface segmentation were tested with intra- and interoperator comparisons.

RESULTS

Median differences in inter- and intrarater measurements at various areas presented a range of 0.08-0.21 mm. In few instances, the differences were larger than 0.5 mm. In areas where T0-T1 changes were increased, the error did not appear to increase. However, the method error increased the farther the measurement area was from the superimposition reference structure. For individual images, the median soft tissue segmentation error ranged from 0.05 to 0.06 at various areas and in no subject exceeded 0.13 mm.

CONCLUSIONS

The presented voxel-based superimposition method was efficient and well reproducible. The segmentation process was a minimal source of error; however, there were a few cases in which the total error was more than 0.5 mm and could be considered clinically significant. Therefore, this method can be used clinically to assess 3-dimensional soft tissue changes during orthodontic treatment in growing patients.

Two decades of research on CBCT imaging in DMFR - an appraisal of scientific evidence

OBJECTIVE

This article aims to appraise how scientific evidence related to CBCT has changed over the years, based on levels of evidence and diagnostic efficacy.

METHODS

A general search strategy was used in different databases (Pubmed, Embase, and Web of Science) to identify systematic reviews (SRs) on CBCT until November of 2020. The SRs included were divided according to different specialties of dentistry. A critical review of the articles was made, describing the level of evidence and efficacy.

RESULTS

In total, 75 articles were selected. There was an increase in the number of SRs on CBCT from 2014 onwards, as 83% of the SRs on this topic were published after 2013, and 72% between 2016 and to date. Twenty SRs (27%) performed meta-analysis. Only 28% of the SRs provided a detailed description of CBCT protocols. According to SR evidence, almost all specialties of dentistry have advanced concomitantly with the introduction of CBCT. The majority of SRs were related to clinical applications (level 2 of efficacy), followed by technical parameters (level 1 of efficacy). Only some CBCT models were mentioned in the SRs selected.

CONCLUSION

Over the course of 20 years, SRs related to CBCT applications for a broad range of dental specialties have been published, with the vast majority of studies at levels 1 and 2 of diagnostic efficacy. Not all CBCT models available on the market have been scientifically validated. At all times, one should remain cautious as such not to simply extrapolate in vitro results to the clinical setting. Also, considering the wide variety of CBCT devices and protocols, reported results should not be overstated or generalized, as outcomes often refer to specific CBCT devices and protocols.

A comparison of 2- and 3-dimensional mandibular superimposition techniques against Björk's structural superimposition method

INTRODUCTION

The purpose of this research was to compare mandibular growth rotation relative to the cranial base in different vertical facial patterns on the basis of multiple 2-dimensional (2D) and 3-dimensional (3D) superimposition methods.

METHODS

Cone-beam computed tomography (CBCT) images taken at a mean interval of 54.8 ± 16.8 months were assessed from a sample of 70 growing patients. Three mandibular superimposition methods were compared against Björk's structural method: (1) a 2D landmark method (2D-M1), (2) a voxel-based 3D method based on a previously reported method (3D-M1), and (3) a voxel-based 3D method incorporating symphyseal structures as references (3D-M2). After superimposition, the relative change in cranial base lines as depicted in sagittal views were measured for true mandibular rotation. Agreement between methods was assessed with Lin's concordance correlation coefficient, Bland-Altman's limits of agreement, and the Bradley-Blackwood test.

RESULTS

Lin's concordance correlation coefficients ranged between 0.924 for the 2D-M1 method, 0.695 for the 3D-M1 method, and 0.965 for the 3D-M2 method. Bland-Altman limits of agreement were wide for all but the 3D-M2 method. Finally, the Bradley-Blackwood test of equality of means and variances was significant in all except the 3D-M2 method.

CONCLUSIONS

For time intervals between CBCT volume acquisitions >3 years, the use of the 2D-M1 and 3D-M1 methods is not recommended. There was a high concordance between the 3D-M2 method and Björk's structural method when assessing mandibular growth rotation using relative changes in cranial base lines. The high concordance was displayed across all vertical facial types and for all time differences between first and second CBCT data acquisitions.

Three dimensional movement analysis of maxillary impacted canine using TADs: a pilot study

BACKGROUND

The aim of the present study was to compare two different anchorage systems efficiency to disinclude impacted maxillary canines using as evaluation tool superimposed Cone Beam Computed Tomography (CBCTs).

METHODS

The study has been conducted with two parallel groups with an allocation ratio of 1:1. Group test received treatment using as anchorage a miniscrew, control group was treated using an anchorage unit a trans palatal arch (TPA). Both groups received a calibrated traction force of 50 g. CBCT before treatment and 3 months after traction were superimposed and canine tip and root movement were evaluated in mm/month ratio.

RESULTS

No differences were observed between groups for apex displacement, tip displacement and observation timespan. Twenty-two patients (12 female, 10 male, mean age:13.4 years) undergoing orthodontic treatment for impacted maxillary canines were recruited for this study. No differences were observed between groups for apex displacement, tip displacement and observation timespan.

CONCLUSIONS

The present pilot study provided no evidence that indirect anchorage on miniscrews could make canine disimpaction faster than anchorage on a TPA. An apex root movement of 0.4-0.8 mm per month was found, while average canine tip movement ranged between 1.08 mm and 1.96 mm per month. No miniscrews failures were observed.

TRIAL REGISTRATION

The study reports the preliminary results of the randomized clinical trial registered at www.register.clinicaltrials.gov (registration number: NCT01717417 ).

Accuracy and reliability of maxillary digital model (MDM) superimposition in evaluating teeth movement in adults compared with CBCT maxillary superimposition

Superimposition of 3D maxillary digital dental models of different time points based on palatal vault region has been used to evaluate tooth movement during orthodontic treatment. This study evaluated the accuracy and reliability of 3D maxillary digital model (MDM) superimposition in adults by comparing it with CBCT maxillary superimposition. In CBCT maxillary superimposition, voxel-based superimposition was firstly conducted, and MDMs were matched with corresponding CBCT models (CBCT-MDM superimposition). MDM superimposition (palatal vault regional superimposition) were performed on another pair of pre- and posttreatment MDMs. The position and orientation of upper first molars (U6s) and upper central incisors (U1s) on the posttreatment MDMs were compared to assess the accuracy of the MDM superimposition methods. The reliability was validated in both MDM superimposition and CBCT maxillary superimposition. In terms of accuracy, the average linear deviations in U6 and U1 positions were less than ± 0.3 mm, the average angular deviations of U6s and U1s were less than ± 0.2°, both have no significant difference from zero. The ICCs for MDM superimposition ranged from 0.85 to 0.99. The ICCs for CBCT-MDM superimposition were larger than 0.99 in all items. MDM superimposition was an efficient, accurate and reliable method for evaluating teeth movement in adults, although its reliability is slightly lower than CBCT maxillary superimposition.

Voxel-based superimposition of Cone Beam CT scans for orthodontic and craniofacial follow-up: Overview and clinical implementation

INTRODUCTION

The increasing use of three-dimensional (3D) imaging in orthodontics has led to the development of 3D superimposition techniques. These techniques use stable anatomic structures as references in order to compare Cone Beam CT (CBCT) scans of the same subject at different time-points. Three methods have been described in the literature: landmark-based, surface-based and voxel-based 3D superimpositions.

OBJECTIVE

This article focuses on the voxel-based approach, which is the most described and the only one that can be fully automatized. The aim of this paper is to offer clinicians a practical tutorial on craniofacial voxel-based 3D superimposition.

MATERIAL AND METHODS

We provide an updated overview of the available implementation methods, describing their methodology, validations, main steps, advantages and drawbacks. The historical open-source method is the most widespread for research purposes, but takes around three hours to achieve for an experienced operator. Several commercially-available software perform superimpositions in a few minutes.

RESULTS

We used two of the available methods to conduct the superimposition process with three representative clinical cases in order to illustrate the different types of results that can be obtained.

CONCLUSIONS

Commercially-available software provide user-friendly and fully automatized superimposition methods, allowing clinicians to perform it easily and helping to reduce human error in image analysis. Still, quantitative evaluation of the results remains the main challenge of this technique.

Assessment of methods used for 3-dimensional superimposition of craniofacial skeletal structures: a systematic review

Background

So far, several techniques have been recommended for the assessment of craniofacial changes through skeletal tissue superimposition, but the evidence that supports them remains unexplored. The purpose of the present study is to assess the available literature on skeletal-tissue superimpositions of serial craniofacial CT or CBCT images used to detect morphological changes.

Materials and Methods

Medline (via Pubmed), EMBASE, Google Scholar, Cochrane Library, Open Grey and Grey Literature Report were searched (last search: 17.11.2019) using specific terms that fulfilled the requirements of each database in the context of the study aim. Hand searches were also performed. The outcomes of interest were the accuracy, precision, or agreement between skeletal-tissue superimposition techniques to assess changes in the morphology of craniofacial structures. Studies of any design with sample size ≥3 were assessed by two authors independently. The study protocol was registered in PROSPERO (ID: CRD42019143356).

Results

Out of 832 studies, fifteen met the eligibility criteria. From the 15 included studies, 12 have shown high total risk of bias, one low risk of bias, and two studies have shown unclear risk of bias. Thirteen out of the 15 studies showed high applicability concerns, two unclear and no study had low applicability concerns. There was high heterogeneity among studies regarding the type of participants, sample size, growth status, machines, acquisition parameters, superimposition techniques, assessment techniques and outcomes measured. Fourteen of them were performed on Cone Beam Computed Tomography (CBCT) and one on Computed Tomography (CT) derived 3D models. Most of the studies (eleven) used voxel-based registration, one landmark-based registration and three studies compared different registration techniques, which include the surface-based registration. Concerning the area of interest, nine studies focused on the anterior cranial base and certain facial structures, four on maxillary structures and four on mandibular structures. Non-growing participants were included in six studies, growing in eight, whereas one study had both.

Conclusion

Most of the available studies had methodological shortcomings and high applicability concerns. At the moment, certain voxel-based and surface-based superimpositions seem to work properly and to be superior to landmark-based superimposition. However, further research in the field is required to develop and properly validate these techniques on different samples, through high quality studies with low applicability concerns.

The effect of threshold level on bone segmentation of cranial base structures from CT and CBCT images

The use of a single grey intensity threshold is one of the most straightforward and widely used methods to segment cranial base surface models from a 3D radiographic volume. In this study we used thirty Cone Beam Computer Tomography (CBCT) scans from three different machines and ten CT scans of growing individuals to test the effect of thresholding on the subsequently produced anterior cranial base surface models. From each scan, six surface models were generated using a range of voxel intensity thresholds. The models were then superimposed on a manually selected reference surface model, using an iterative closest point algorithm. Multivariate tests showed significant effects of the machine type, threshold value, and superimposition on the spatial position and the form of the created models. For both, CT and CBCT machines, the distance between the models, as well as the variation within each threshold category, was consistently increasing with the magnitude of difference between thresholds. The present findings highlight the importance of accurate anterior cranial base segmentation for reliable assessment of craniofacial morphology through surface superimposition or similar methods that utilize this anatomical structure as reference.

The use of three-dimensional model construction of virtual technology in orthopedic treatment

Objective

The objective of this study is to explore the construction of a digital three-dimensional model of virtual technology that plays an auxiliary role in orthopedic treatment.

Methods

Three fracture patients were selected, with no abnormality was observed in bone examination, no musculoskeletal disease in the past; and spiral CT scan of the spine and pelvis, upper limbs, and lower limbs was performed. The virtual technology was used to build a digital 3D model, mainly using the editing software Mimics10.0 software. In addition, the virtual three-dimensional model was verified by virtual surgery, data storage security, work efficiency of the model, model validity, three-dimensional characteristics of the model, the interaction mode of the model, and the data accuracy of the model were studied.

Results

The digital 3D model was successfully established by Mimics10.0 software. The data fitting efficiency was very high. The data storage security of the 3D model was greatly improved compared with the 2D model, and the work efficiency was improved by at least 50%. There was also a significant change in the accuracy and interaction of data acquisition. Therefore, the detection of digital 3D model work through virtual surgery simulation fully demonstrated the positive auxiliary role of 3D model in orthopedic treatment.

Conclusion

The digital 3D model based on Mimics10.0 software is efficient and accurate in obtaining data. It is very effective for subsequent adjuvant therapy in the field of orthopedics, reducing the probability of misdiagnosis by doctors, saving time and improving efficiency, reducing patient's physical pain and unnecessary economic expenses.

3D superimposition of craniofacial imaging-The utility of multicentre collaborations

Clinical applications of 3D image registration and superimposition have contributed to better understanding growth changes and clinical outcomes. The use of 3D dental and craniofacial imaging in dentistry requires validate image analysis methods for improved diagnosis, treatment planning, navigation and assessment of treatment response. Volumetric 3D images, such as cone-beam computed tomography, can now be superimposed by voxels, surfaces or landmarks. Regardless of the image modality or the software tools, the concepts of regions or points of reference affect all quantitative of qualitative assessments. This study reviews current state of the art in 3D image analysis including 3D superimpositions relative to the cranial base and different regional superimpositions, the development of open source and commercial tools for 3D analysis, how this technology has increased clinical research collaborations from centres all around the globe, some insight on how to incorporate artificial intelligence for big data analysis and progress towards personalized orthodontics.

Voxel-based superimposition of serial craniofacial CBCTs: Reliability, reproducibility and segmentation effect on hard-tissue outcomes

OBJECTIVES

To test the reliability and reproducibility of a fast and user-friendly voxel-based 3D superimposition method and the effect of bone segmentation on its outcomes.

SETTING AND SAMPLE POPULATION

This prospective methodological study assessed 15 pairs of pre-existing serial CBCT images (interval: 1.69 ± 0.37 years) obtained from growing patients (initial age: 11.75 ± 0.59 years).

MATERIALS AND METHODS

Volumes were superimposed on the anterior cranial base using Dolphin 3D software. Reliability was assessed visually, by inspecting the overlap of the superimposition reference structures. Reproducibility was tested with intra- and inter-operator comparisons of superimposition outcomes.

RESULTS

The method presented good reliability in all cases. The median differences between intra- and inter-operator comparisons at various tested areas ranged from 0.06 to 0.16 mm and from 0.15 to 0.24 mm, respectively. In few individual cases, differences exceeded 0.5 mm. There was no evidence that the error increased upon increase in the magnitude of the detected T0-T1 changes. However, the superimposition error increased when the distance between the measurement area and the superimposition reference also increased. For a single image, the median error of bone surface segmentation ranged in different areas between 0.05 and 0.12 mm, with few exceptions where it slightly exceeded 0.25 mm.

CONCLUSIONS

The tested voxel-based superimposition method presented good efficiency, cranial base matching and reproducibility in a growing patient sample. Segmentation error was considered minimal. The total error reached clinically relevant levels in very few cases. Thus, this technique is considered appropriate for clinical use, when 3D assessment of craniofacial changes is required.

Automated identification of cephalometric landmarks: Part 2- Might it be better than human?

OBJECTIVES

To compare detection patterns of 80 cephalometric landmarks identified by an automated identification system (AI) based on a recently proposed deep-learning method, the You-Only-Look-Once version 3 (YOLOv3), with those identified by human examiners.

MATERIALS AND METHODS

The YOLOv3 algorithm was implemented with custom modifications and trained on 1028 cephalograms. A total of 80 landmarks comprising two vertical reference points and 46 hard tissue and 32 soft tissue landmarks were identified. On the 283 test images, the same 80 landmarks were identified by AI and human examiners twice. Statistical analyses were conducted to detect whether any significant differences between AI and human examiners existed. Influence of image factors on those differences was also investigated.

RESULTS

Upon repeated trials, AI always detected identical positions on each landmark, while the human intraexaminer variability of repeated manual detections demonstrated a detection error of 0.97 ± 1.03 mm. The mean detection error between AI and human was 1.46 ± 2.97 mm. The mean difference between human examiners was 1.50 ± 1.48 mm. In general, comparisons in the detection errors between AI and human examiners were less than 0.9 mm, which did not seem to be clinically significant.

CONCLUSIONS

AI showed as accurate an identification of cephalometric landmarks as did human examiners. AI might be a viable option for repeatedly identifying multiple cephalometric landmarks.

Predicting soft tissue changes after orthognathic surgery: The sparse partial least squares method

OBJECTIVES

To develop a prediction algorithm for soft tissue changes after orthognathic surgery that would result in accurate predictions (1) regardless of types or complexity of operations and (2) with a minimum number of input variables.

MATERIALS AND METHODS

The subjects consisted of 318 patients who had undergone the surgical correction of Class II or Class III malocclusions. Two multivariate methods-the partial least squares (PLS) and the sparse partial least squares (SPLS) methods-were used to construct prediction equations. While the PLS prediction model included 232 input variables, the SPLS method included a reduced number of variables generated by a handicapping algorithm via the sparsity control. The accuracy between the PLS and SPLS models was compared.

RESULTS

There were no significant differences in prediction accuracy depending on surgical movements, the sex of the subjects, or additional surgeries. The predictive performance with a reduced set of 34 input variables chosen using the SPLS method was statistically indistinguishable from the full set of variables with the original PLS prediction model.

CONCLUSIONS

The prediction method proposed in the present study was accurate for a wide range of orthognathic surgeries. A reduced set of input variables could be selected through the SPLS method while simultaneously maintaining a prediction level that was as accurate as that of the original PLS prediction model.