Novel method of constructing a stable reference frame for 3-dimensional cephalometric analysis

Establishment of the mid-sagittal reference plane for three-dimensional assessment of facial asymmetry: a systematic review : Establishment of the mid-sagittal reference plane: a systematic review

OBJECTIVE

To systematically review the literature for mid-sagittal plane establishment approaches to identify the most effective method for constructing the mid-sagittal plane for the evaluation of facial asymmetry.

MATERIALS AND METHODS

Six electronic databases (PubMed, Medline (via Ovid), EMBASE (via Ovid), Cochrane Library, Web of Science, and Scopus) and grey literature were searched for the studies that computed the mid-sagittal reference plane three-dimensionally, using a combination of MeSH terms and keywords. The methodological quality and the level of evidence for the included studies were analyzed using QUADAS-2 and GRADE, respectively.

RESULTS

The preliminary search yielded 6746 records, of which 42 articles that met the predefined inclusion criteria were included in the final analysis. All the included articles reported the construction of the mid-sagittal reference plane (MSP) using varied methods. The risk of bias and concerns regarding the applicability of the included studies were judged to be 'low'. The level of evidence was determined to be 'low' for the effectiveness of the technique and 'moderate' for the ease of clinical applicability.

CONCLUSION

Despite methodological heterogeneity, this review substantiates the comparable efficacy of cephalometric and morphometric MSP construction methods. A fully automated morphometric MSP holds promise as a viable option for routine clinical use. Nevertheless, future prospective studies with an emphasis on the impact, accuracy, and clinical applicability of MSP construction techniques in cases of facial asymmetry are required.

CLINICAL RELEVANCE

The present review will assist clinicians in selecting the most suitable method for MSP construction, leading to improved treatment planning and ultimately more favorable treatment outcomes.

The accuracy and reliability of different midsagittal planes in the symmetry assessment using cone-beam computed tomography

Symmetry is an essential component of esthetic assessment. Accurate assessment of facial symmetry is critical to the treatment plan of orthognathic surgery and orthodontic treatment. However, there is no internationally accepted midsagittal plane (MSP) for orthodontists and orthognathic surgeons. The purpose of this study was to explore a clinically friendly MSP, which is more accurate and reliable than what is commonly used in symmetry assessment. Forty patients with symmetric craniofacial structures were analyzed on cone-beam computed tomography (CBCT) scans. The CBCT data were exported to the Simplant Pro software to build four reference planes that were constructed by nasion (N), basion (Ba), sella (S), odontoid (Dent), or incisive foramen (IF). A total of 31 landmarks were located to determine which reference plane is the most optimal MSP by comparing the asymmetry index (AI). The mean value of AI showed a significant difference (p < 0.05) among four reference planes. Also, the mean value of AI for all landmarks showed that Plane 2 (consisting of N, Ba, and IF) and Plane 4 (consisting of N, IF, and Dent) were more accurate and stable. In conclusion, the MSP consisting of N, Dent, and IF shows more accuracy and reliability than the other planes. Further, it is more clinically friendly because of its significant advantage in landmarking.

Anterior cerebral falx plane in MR images to estimate the craniofacial midline

Multiple methods have been proposed for evaluating the symmetry of facial contour by utilizing the median sagittal plane of the skull as a reference and measuring the maxillofacial region. To replace the manual mark point analysis method, we used the anterior cerebral falx plane in MRI images as an indicator of the craniofacial midline. The MRI examination data of 30 individuals were analyzed with a MeVisLab workstation. Two independent examiners performed 15 anthropometric measurements (4 angular, 11 linear) and compared the MRI-based anterior cerebral falx plane with the manual mark point analysis of the craniofacial midline estimation. All measurements were repeated after 3 weeks. Statistical analyses included the repeatability and reproducibility of the 2 methods based on intra-observer and inter-observer correlation coefficients (ICCs), respectively. Precision was estimated by intergroup comparison of the coefficient of variation. The anterior falx plane derived from the MRI data resulted in an intra-observer ICC of 0.869 ± 0.065 (range 0.733-0.936) and inter-observer ICC of 0.876 ± 0.0417 (0.798-0.932) for all measurements, showing significant correlations with the ICC values obtained by the mark point method (p < 0.05). The coefficient of variation showed that the precisions of the 2 methods were statistically comparable. We conclude that, for MRI-based craniofacial midline estimation, measurements made using the anterior cerebral falx plane are as precise, repeatable, and reproducible as those using the manual mark point analysis method. It has a high potential for application in radiation-free 3-dimensional craniofacial analysis.

Sex estimation of Malaysian sub-adults using craniometrics: A computed tomography study

Sex estimation is crucial in biological profiling of skeletal human remains. Methods used for sex estimation in adults are less effective for sub-adults due to varied cranium patterns during the growth period. Hence, this study aimed to develop a sex estimation model for Malaysian sub-adults using craniometric measurements obtained through multi-slice computed tomography (MSCT). A total of 521 cranial MSCT dataset of sub-adult Malaysians (279 males, 242 females; 0-20 years old) were collected. Mimics software version 21.0 (Materialise, Leuven, Belgium) was used to construct three-dimensional (3D) models. A plane-to-plane (PTP) protocol was utilised to measure 14 selected craniometric parameters. Discriminant function analysis (DFA) and binary logistic regression (BLR) were used to statistically analyze the data. In this study, low level of sexual dimorphism was observed in cranium below 6 years old. The level was then increased with age. For sample validation data, the accuracy of DFA and BLR in estimating sex improved with age from 61.6% to 90.3%. All age groups except 0-2 and 3-6 showed high accuracy percentage (≥75%) when tested using DFA and BLR. DFA and BLR can be utilised to estimate sex for Malaysian sub-adult using MSCT craniometric measurements. However, BLR showed higher accuracy than DFA in sex estimation of sub-adults.

A three-dimensional investigation of mandibular deviation in patients with mandibular prognathism

BACKGROUND

Craniofacial disharmony in cases of jaw deformity associated with abnormal lateral deviation of the jaw mostly involves both the maxilla and mandible. However, it has been still difficult to capture the jaw deviation aspect in a 3-dimensional and quantitative techniques. In this study, we focused on 3-dimensional mandibular morphology and position of the condylar head in relation to the base of the skull in patients with mandibular prognathism, one of the most common jaw deformities. We used cluster analysis to quantify and classify deviation and clarified its characteristics. We also investigated the degree of correlation between those findings and menton (Me) deviation measured on frontal cephalograms, which is a conventional indicator of jaw deformity.

RESULTS

Findings obtained from 100 patients (35 men, 65 women) were classified into the following three groups based on mandibular morphology and condylar position relative to the skull base. Then, reclassification using these parameters enabled classification of cluster analysis findings into seven groups based on abnormal jaw deviation characteristics. Comparison among these seven groups showed that the classification criteria were ramus height, mandibular body length, distance from the gonion to the apex of the coronoid process, and the lateral and vertical positions of the mandible. Weak correlation was also found between Me deviation on frontal cephalograms and each of the above parameters measured on 3D images.

CONCLUSIONS

Focusing on mandibular morphology and condylar position relative to the skull base in patients with mandibular prognathism, we used cluster analysis to quantify and classify jaw deviation. The present results showed that the 3D characteristics of the mandible based on mandibular morphology and condylar position relative to the skull base can be classified into seven groups. Further, we clarified that Me deviation on frontal cephalograms, which has been used to date, is inadequate for capturing jaw deviation characteristics.

Cranial reconstruction evaluation - comparison of European statistical shape model performance on Chinese dataset

Purpose

Morphological variability of the skull is an important consideration for cranioplasty and implant design. Differences in morphology of the skull based on the ethnicity are known. In a previous study we could show the accuracy and benefits of virtual reconstructions based on a statistical shape model (SSM) for neurocranial defects. As the SSM is trained on European data, the question arises how well this model fares when dealing with patients with a different ethnic background. In this study we aim to evaluate the accuracy and applicability of our proposed method when deploying a cranial SSM generated from European data to estimate missing parts of the neurocranium in a Chinese population.

Methods

We used the same data and methods as in our previous study and compared the outcomes when applied to Chinese individuals. A large unilateral defect on the right side and a bilateral defect were created. The outer surface of the cranial table was reconstructed from CT scans, meshed with triangular elements, and registered to a template. Principal component analysis together with Thin Plate Spines (TPS) deformation was applied to quantify modes of variation. The mesh to mesh distances between the original defects´ surfaces and the reconstructed surface were computed.

Results

Comparing the Chinese test group with the European control group, regarding the entire defect the analysis shows no significant difference for unilateral defects (test vs. control group/0.46 mm ± vs. 0.44 mm). Reconstruction of bilateral defects exhibited only in slightly higher prediction errors than those of unilateral defects (0.49 mm ± vs. 0.45 mm).

Conclusion

The proposed method shows a high accuracy that seems to be ethnical independent - with low error margins for virtual skull reconstruction and implant design.

Clinical relevance: Metallic objects may severely impact image quality in several CBCT devices.

•

Statistical shape modelling enables automatic skull reconstruction for computer assisted surgery

•

Despite a Caucasian database, the statistical shape model can provide accurate results for other ethnic groups.

•

The results facilitate the development of reconstruction algorithms, as the data basis can be kept smaller

Using the anterior cranial base to provide a reliable reference plane for patients with or without facial asymmetry

INTRODUCTION

This study aimed to investigate the midsagittal reference plane (MSP) reliability derived from the 3-dimensional characteristics of patients with or without facial asymmetry in the anterior cranial base (ACB).

METHODS

We divided the cone-beam computed tomography (CBCT) images of 60 adult patients into maxillofacial symmetry and asymmetry groups. The ACB models were 3-dimensionally constructed, and then symmetrical characteristics were evaluated with surface asymmetry for each group. The reliability of the MSP derived from the symmetry of the anterior cranial base (MSPACB) was assessed in comparison with the true craniofacial symmetry plane determined using the morphometric method.

RESULTS

The ACB was symmetrical, as demonstrated by slight surface asymmetry. The MSPACB was reliable for maxillofacial asymmetrical analysis as the intraobserver and interobserver measurements using the MSPACB were of excellent agreement, and there was no significant difference between MSPACB and morphometric method in asymmetrical measurements in both groups. The MSPACB remained stable (maximum deviation <0.32 mm) when cranial landmark identification errors (1 mm and 4 mm) were simulated.

CONCLUSIONS

MSPACB is reliable for patients with or without facial asymmetry in maxillofacial asymmetry analysis, which is beneficial to patients with severe midfacial asymmetry or trauma when conventional landmarks are displaced or disappear. When using MSPACB for patients with cranial malformations or those whose ACBs differ from normal dimensions, caution should be taken.

Reliability of cone beam CT for morphometry of nasolabial soft tissue in patients with skeletal class III malocclusion: A qualitative and quantitative analysis

OBJECTIVE

To assess reliability of cone-beam CT (CBCT) for nasolabial soft tissue measurements in patients with skeletal class III malocclusion based on 3-dimensional (3D) facial scanner results.

METHODS

CBCT and 3D facial scan images of 20 orthognathic patients are used in this study. Eleven soft tissue landmarks and 15 linear and angular measurements are identified and performed. For qualitative evaluation, Shapiro-Wilk test and Bland-Altman plots are applied to analyze the equivalence of the measurements derived from these two kinds of images. To quantify specific deviation of CBCT measurements from facial scanner, the latter is set as a benchmark, and mean absolute difference (MAD) and relative error magnitude (REM) for each variable are also calculated.

RESULTS

Statistically significant differences are observed in regions of nasal base and lower lip vermilion between two methods. MAD value for all length measurements are less than 2 mm and for angular variables < 8°. The average MAD and REM for length measurements are 0.94 mm and 5.64%, and for angular measurements are 2.27° and 3.78%, respectively.

CONCLUSIONS

The soft tissue results measured by CBCT show relatively good reliability and can be used for 3D measurement of soft tissue in the nasolabial region clinically.

Midsagittal Plane First: Building a Strong Facial Reference Frame for Computer-Aided Surgical Simulation

PURPOSE

A facial reference frame is a 3-dimensional Cartesian coordinate system that includes 3 perpendicular planes: midsagittal, axial, and coronal. The order in which one defines the planes matters. The purposes of this study are to determine the following: 1) what sequence (axial-midsagittal-coronal vs midsagittal-axial-coronal) produced more appropriate reference frames and 2) whether orbital or auricular dystopia influenced the outcomes.

METHODS

This study is an ambispective cross-sectional study. Fifty-four subjects with facial asymmetry were included. The facial reference frames of each subject (outcome variable) were constructed using 2 methods (independent variable): axial plane first and midsagittal plane first. Two board-certified orthodontists together blindly evaluated the results using a 3-point categorical scale based on their careful inspection and expert intuition. The covariant for stratification was the existence of orbital or auricular dystopia. Finally, Wilcoxon signed rank tests were performed.

RESULTS

The facial reference frames defined by the midsagittal plane first method was statistically significantly different from ones defined by the axial plane first method (P = .001). Using the midsagittal plane first method, the reference frames were more appropriately defined in 22 (40.7%) subjects, equivalent in 26 (48.1%) and less appropriately defined in 6 (11.1%). After stratified by orbital or auricular dystopia, the results also showed that the reference frame computed using midsagittal plane first method was statistically significantly more appropriate in both subject groups regardless of the existence of orbital or auricular dystopia (27 with orbital or auricular dystopia and 27 without, both P < .05).

CONCLUSIONS

The midsagittal plane first sequence improves the facial reference frames compared with the traditional axial plane first approach. However, regardless of the sequence used, clinicians need to judge the correctness of the reference frame before diagnosis or surgical planning.

Three-Dimensional Analysis of the Skull Base of Individuals With Cleft Lip and Palate

AIMS

Identify variations of skull base measurements in individuals with dentofacial deformities associated or not with cleft lip and palate and compare the results with individuals without dentofacial deformities.

METHODS AND RESULTS

The individuals were categorized into three different groups: dentofacial deformity without cleft malformation, dentofacial deformity associated with cleft lip and palate, and without facial deformity. The inclusion criteria were individuals over 18 years of age, without any intervention involving facial bones or structures of interest for the study and field of view encompassing from the glabella to the hyoid bone. Poor quality CT scans or lack of adequate medical records were considered exclusion criteria. In the analysis by computerized tomography using the Dolphin Imaging Software, the length determined by the Ba-S and S-N lines was evaluated, as well as the Ba-S-N angle formed by landmarks.

RESULTS

The length of S-N was not statistically different between the groups, the Ba-S length and the Ba-S-N angle demonstrated statistical difference.

CONCLUSION

There was statistically significant difference in the morphometry of the (Ba-S) between groups (FS) and (C). This suggests that the standard values for cephalometric analyzes involving these structures, especially to determine the treatment planning, should be used with caution.

Construction and validity of a midsagittal plane based on the symmetry of a 3-dimensional model of the relevant cranial base

INTRODUCTION

The midsagittal plane (MSP) is the foundation for 3-dimensional (3D) cephalometric analyses. This article aimed to provide a protocol to construct a reliable and accurate MSP for 3D cephalometric craniofacial analysis.

METHODS

Cone-beam computed tomography data of 16 adult patients without obvious bilateral asymmetry were collected. The model of the anterior cranial base and sphenoid bone was constructed, and the candidate MSP was determined on the basis of the symmetry of this model. Intraclass correlation coefficients were used to assess intra- and interexaminer reliability of the candidate MSP. To investigate the accuracy of this candidate MSP, we constructed a true plane of symmetry of craniomaxillofacial structure and a control plane on the basis of 3 cranial midline points. We then compared these with the candidate MSP.

RESULTS

This candidate MSP resembled the true plane of symmetry with all the mean absolute errors <1 mm, and all the absolute errors for the candidate MSP were significantly smaller than the control plane (P ≤0.002). The relative intra- and interexaminer reliability for this candidate MSP was almost perfect (intraclass correlation coefficients >0.9).

CONCLUSIONS

The candidate MSP constructed using this method was thought to be reliable and accurate for 3D cephalometric analysis in patients without obvious cranial asymmetry.