Selection of a horizontal reference plane in 3D evaluation: Identifying facial asymmetry and occlusal cant in orthognathic surgery planning

Diagnosing Maxillary Occlusal Cant with Average 3-Dimensional Skeletofacial Model Template

BACKGROUND

Diagnosing maxillary occlusal cant involves varied methods, yet classification remains incomplete. This includes determining whether the cant results from equal faults on both sides or whether one side exhibits overdevelopment and the other underdevelops. This study introduces an innovative average 3-dimensional skull template for classifying maxillary occlusal cant instances.

METHODS

Sixty adult patients were divided into 2 groups: 30 with a mesoprosopic facial type and 30 with a leptoprosopic facial type. Using 7 pairs of anatomical landmarks (nasion, orbitale [left (l), right (r)], lateral orbitale [L, R], and zygion [L, R]), the average skull models were aligned and superimposed onto the patients' skull models. Image resizing facilitated optimal registration area fitting. Vertical distances from the maxillary first molar mesial buccal cusp tip to the Frankfort horizontal plane were measured to analyze occlusal cant, classified into 3 classes: overdevelopment (class A), underdevelopment (class B), and equal fault on both sides (class C).

RESULTS

In the mesoprosopic group, class B was most common (40%), followed by class A (27%) and class C (33%). In the leptoprosopic facial type group, class B remained prevalent (50%), followed by class A (43%) and class C (7%). Statistical analysis revealed a significant association between facial types and the 3 classes.

CONCLUSIONS

Contrary to expectations, equal fault patterns were not predominant; instead, underdevelopment of the maxilla constituted the majority of occlusal cant cases. Using average 3-dimensional skeletofacial models as templates emerges as an effective tool and alternative for diagnosing instances of maxillary occlusal cant.

Naso-alveolar Asymmetry in Unilateral Cleft Lip and Palate Patients-CT Analysis of the Paranasal Region

Secondary deformities to the midfacial area in adolescence and adulthood are common sequelae after primary cleft lip and palate repair and lead to significant functional, aesthetic and psychosocial challenges. Treatment for patients with normal occlusion or treated malocclusion and remaining midfacial hypoplasia includes autologous and alloplastic augmentation of the maxilla. Because of the great variation of deformities, accurate evaluation is essential for appropriate treatment planning. To provide insights in the altered midfacial anatomy in cleft patients, a retrospective computed tomography morphologic analysis of the anterior projection of the maxilla in the paranasal region, soft tissue thickness, and relation of soft tissue to bony landmarks was performed in adolescent, unilateral, non-syndromic complete cleft and palate patients. The anterior projection of the maxilla was very variable with the cleft side bone surface being more anterior relative to the non-cleft side in some patients. Soft tissue thickness was not significantly different between cleft and non-cleft side. The lateral distance from the most anterior point of the maxilla to subalare was significantly smaller on the cleft side as compared with the non-cleft side. The authors' study demonstrates that in cleft lip and palate patients midfacial anatomy with regards to maxilla projection at the pyriform aperture is very variable making accurate evaluation of the bone morphology and an individualized treatment plan a prerequisite for successful correction of nasomaxillary deformities.

Iliac crest towards alveolar processes or mandibular inferior margin in mandibular reconstruction with a vascularized iliac bone flap: which is better?

OBJECTIVE

The study aims to compare differences among iliac bone flaps with different iliac crest orientations for the repair of mandibular defects with an aim to analyze their advantages, disadvantages, and effects.

MATERIAL AND METHODS

Clinical data and computed tomography scans of all patients who underwent iliac bone flap repair of the mandible in Peking University School and Hospital of Stomatology from January 2016 to April 2021 were collected. Patients were divided into the iliac crest towards alveolar process (Group A) and the iliac crest towards mandibular inferior margin (Group B). Software was used to measure corresponding indicators. The results obtained for the groups were statistically analyzed.

RESULTS

The study included 78 patients (25 and 53 in groups A and B, respectively). The symmetry of the LC-type defect was better in group A (p < 0.05). The all-bone width of the alveolar process side in group A was greater than 6 mm; in 15 cases of group B, the width was less than 6 mm (p < 0.05). The intermaxillary distance of two sites were higher in group B (p < 0.05). The bone cortical thickness was significantly thicker in group A (p < 0.05).

CONCLUSION

One year after the mandibular body defect was reconstructed with a vascularized iliac bone flap, the iliac crest towards alveolar process group showed better bone symmetry, width, intermaxillary distance, and cortical thickness to meet the planting requirements.

CLINICAL RELEVANCE

The use of an iliac crest towards alveolar process may be a better approach for mandible reconstruction.

Maxillary Sinus Volume in Patients with Canted Occlusal Plane: A Cone‐Beam Computed Tomography Study

OBJECTIVES

To compare the maxillary sinus volume between both sides in adult patients with upper occlusal canting (>2 mm cant) and a control group (≤2 mm cant) using cone-beam computed tomography scans.

MATERIALS AND METHODS

This retrospective study included a total of 84 scans (42 scans per group) according to predetermined selection criteria. OnDemand 3-D™ software was used for volumetric and linear measurements of the maxillary sinus. Maxillary occlusal canting was determined at the level of the maxillary first molars. It was defined as the vertical difference between right and left sides relative to the Frankfort horizontal plane. Non-parametric tests were applied.

RESULTS

The median difference in the maxillary sinus volume between the sides was statistically significant between the control and cant groups (P < 0.001). Also, the median difference in the maxillary sinus craniocaudal height and apex sinus distance between the sides was statistically significant between the control and cant groups (P < 0.05 and P < 0.001, respectively).

CONCLUSION

In adult patients, maxillary occlusal canting of more than 2 mm was associated with asymmetric maxillary sinus volumes. In the cant group, maxillary first molars on the canted-down side were in close proximity to the sinus floor, which suggests a limited leeway for molar intrusion.

[Diagnostic and treatment alternatives for the correction of facial asymmetries: a literature review]

Facial symmetry refers to a complete coincidence of each facial component on the sagittal plane, while asymmetry refers to the bilateral difference between these components. The presence of perfect bilateral symmetry is almost never present in human, so it is more common for individuals to predominate facial asymmetry. However, this condition can result from functional and esthetic problems. This research seeks to determine the alternatives, diagnosis and ideal treatment plan for the correction of each type of facial asymmetry through orthognathic surgery. For this purpose, a review of articles published between 2015 to date was carried out. Selecting those that were focused on describing or evaluating facial and dentofacial symmetry and asymmetry, type of diagnosis or treatment plan, including clinical cases. The Google search engine, SciELO and databases of medical interest, such as PubMed, PMC and Medigraphic were used. According to the research and treatments carried out during the last few years in the dental clinic, it has been proven that orthognathic treatment accompanied by previous planning is the best option for the management of skeletal facial asymmetries.

Outcome of full digital workflow for orthognathic surgery planning in the treatment of asymmetric skeletal class III deformity

BACKGROUND/PURPOSE

Studies have reported the advantages of digital imaging-assisted orthognathic surgery planning, but there is scarce information about a full digital planning modality. This study evaluated the 3D cephalometric-based and patient-reported outcomes of a full digital workflow for orthognathic surgery planning in the treatment of asymmetric maxillomandibular disharmony.

METHODS

A postoperative 3D image dataset of 30 Taiwanese Chinese patients with asymmetric skeletal Class III deformities who underwent full digital planning for two-jaw surgery were retrieved from the authors' database. The 3D cephalometric data (dental, skeletal, and soft tissue evaluations) were compared to the ethnicity-matched 3D cephalometric normative values. Patient-reported outcome measure tools regarding postoperative overall appearance and satisfaction with facial areas (ranging from 0 to 100 and 0 to 10, respectively) were administered. The number of needed or requested revisionary surgery was collected.

RESULTS

No difference (all p > 0.05) was observed between the orthognathic-surgery-treated patients and the normative value for most of the tested 3D cephalometric parameters, with the exception (p < 0.05) of three mandible and occlusal-plane-related parameters. Both patient-reported outcome measure tools showed that patients' satisfaction with their postoperative appearance was high for overall face (89.7 ± 4.5) and specific facial regions (nose, 7.1 ± 1.3; lip, 8.3 ± 1.6; upper gum, 8.5 ± 1.2; cheek, 8.8 ± 1.1; chin, 9.2 ± 1.2; and teeth, 9.3 ± 0.8), with no need for revisionary surgery.

CONCLUSION

The patients treated with a full 3D digital planning-assisted two-jaw surgery had a similar 3D dental relation, facial convexity, and symmetry compared to healthy ethnicity-matched individuals, and they reported higher satisfaction levels with their postoperative facial appearance results.

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 Cephalometric Landmarking and Frankfort Horizontal Plane Construction: Reproducibility of Conventional and Novel Landmarks

In some dentofacial deformity patients, especially patients undergoing surgical orthodontic treatments, Computed Tomography (CT) scans are useful to assess complex asymmetry or to plan orthognathic surgery. This assessment would be made easier for orthodontists and surgeons with a three-dimensional (3D) cephalometric analysis, which would require the localization of landmarks and the construction of reference planes. The objectives of this study were to assess manual landmarking repeatability and reproducibility (R&R) of a set of 3D landmarks and to evaluate R&R of vertical cephalometric measurements using two Frankfort Horizontal (FH) planes as references for horizontal 3D imaging reorientation. Thirty-three landmarks, divided into “conventional”, “foraminal” and “dental”, were manually located twice by three experienced operators on 20 randomly-selected CT scans of orthognathic surgery patients. R&R confidence intervals (CI) of each landmark in the -x, -y and -z directions were computed according to the ISO 5725 standard. These landmarks were then used to construct 2 FH planes: a conventional FH plane (orbitale left, porion right and left) and a newly proposed FH plane (midinternal acoustic foramen, orbitale right and left). R&R of vertical cephalometric measurements were computed using these 2 FH planes as horizontal references for CT reorientation. Landmarks showing a 95% CI of repeatability and/or reproducibility > 2 mm were found exclusively in the “conventional” landmarks group. Vertical measurements showed excellent R&R (95% CI < 1 mm) with either FH plane as horizontal reference. However, the 2 FH planes were not found to be parallel (absolute angular difference of 2.41°, SD 1.27°). Overall, “dental” and “foraminal” landmarks were more reliable than the “conventional” landmarks. Despite the poor reliability of the landmarks orbitale and porion, the construction of the conventional FH plane provided a reliable horizontal reference for 3D craniofacial CT scan reorientation.

Subcutaneous Face and Neck lift: A Traditional Method With Definite Effects Among Asians

BACKGROUND

The mainstream facelifts in Western countries always involve the superficial fascia/superficial musculoaponeurotic system treatment. Meanwhile, subcutaneous face and neck lifts are widely applied among Asians.

OBJECTIVES

The authors sought to evaluate outcomes of subcutaneous face and neck lift, including patient-reported and 3-dimensional (3D) measurement outcomes, and report on details of surgical procedures.

METHODS

Patients who received a subcutaneous face and neck lift from January 2017 to June 2019 were asked to complete FACE-Q scales, and facial information was collected by the Vectra 3D imaging system preoperatively and postoperatively. Volume changes in midface and possible displacement of facial landmarks were measured. The range of dissection and the amount of skin removed were recorded intraoperatively.

RESULTS

In total, 119 patients (median age, 46 years, interquartile range, 40-53 years) received a subcutaneous face and neck lift. Among them, 88 patients completed pre- and postoperative FACE-Q scales. Patients' satisfaction with facial subunits improved and wrinkles were significantly relieved (P < 0.001). Nineteen patients (38 midface sides) completed 3D image data collection. Postoperatively, zygomatic volume increased, and nasolabial and lateral cheek volumes decreased (volume change of 2.2 ± 1.3 mL). Mouth, nose, and eye displacements were negligible postoperatively. The widths of skin removed at the middle temporal, front of the sideburns, upper helix, earlobe, and retro-auricular were 13.8 ± 1.9 mm, 19.6 ± 3.1 mm, 27.6 ± 3.9 mm, 16.4 ± 3.9 mm, and 32.2 ± 4.0 mm, respectively.

CONCLUSIONS

The authors' subcutaneous face and neck lift was effective in relieving nasolabial sagging, improving wrinkles, and achieving facial rejuvenation.

LEVEL OF EVIDENCE: 4

Cheek soft tissue prediction in cleft orthognathic surgery: A 3D computer-assisted investigation with comparative analysis

BACKGROUND

The Le Fort I maxillary advancement and rotational movement have been adopted to treat patients with cleft-related skeletal Class III pattern and anteromedial cheek soft tissue deficiency, but cleft-specific cheek soft tissue prediction data are insufficient. This 3D imaging-based study addressed the issue.

METHODS

3D craniofacial soft tissue and bone models were created from 32 consecutive patients who received computer-aided two-jaw orthognathic surgery for the correction of cleft-related Class III deformity and cheek soft tissue deficiency. Using superimposed 3D models, the cheek volumetric change, the cheek sagittal movement, and the 3D cheek mass position were calculated. 3D data from orthognathic surgery-treated patients with no cleft (noncleft cohort) and individuals with no facial deformity (3D norm value) were retrieved for comparative analysis.

RESULTS

Surgical maxillary advancement (p < 0.001) but not maxillary clockwise rotation (p > 0.05) had a significant impact on the cheek soft tissue change, with prediction models showing that maxillary advancement elucidated 77 and 79% of this change on the cleft and noncleft sides, respectively. Cleft cohort (0.46±0.12) had a significantly (p < 0.001) smaller cheek soft-to-hard tissue ratio than that of the noncleft cohort (0.73±0.13). Cleft maxillary advancements >4 mm resulted in a 3D cheek mass position (2.1±1.1 mm) similar (p > 0.05) to the 3D norm value (2.2±1.2 mm), but different (p = 0.037) from the noncleft cohort (2.38±0.7 mm).

CONCLUSION

This study showed that maxillary advancement but not the maxillary rotation affects the cheek soft tissue change, and the predictive values and comparative data could assist the orthodontist-surgeon interaction during preoperative planning and patient counseling.

Effect of Le Fort I Maxillary Repositioning on Three-Dimensional Nasal Tip Rotation: A Comparative Study with Implication for the Asian Nose

BACKGROUND

Le Fort I maxillary repositioning influences nasal morphology. In Asian cultures, upward nasal tip rotation with increased nostril exposure is considered aesthetically unpleasant and can have psychosocial consequences. This three-dimensional imaging-based study evaluated the effect of different Le Fort I maxillary movements on nasal tip rotation.

METHODS

Consecutive patients who underwent two-jaw orthognathic surgery (n = 107) were enrolled. To achieve a standard head orientation, preoperative and 1-week and 12-month postoperative cone-beam computed tomography-derived three-dimensional craniofacial models were superimposed. Tip rotation angle was calculated according to the Frankfort horizontal plane for all three-dimensional digital models. The final tip rotation angle change was defined as 12-month postoperative value minus preoperative value. Translational maxillary movement types (advancement versus setback and intrusion versus extrusion), postoperative maxillary segment locations (anterosuperior, anteroinferior, posterosuperior, or posteroinferior), and actual linear maxillary changes were noted.

RESULTS

Advancement (1.79 ± 5.20 degrees) and intrusion (2.23 ± 4.96 degrees) movements demonstrated significantly larger final tip rotation angle changes than setback (-0.88 ± 5.15 degrees) and extrusion (0.09 ± 5.44 degrees) movements (all p < 0.05). Postoperative anterosuperior location (2.95 ± 4.52 degrees) of the maxillary segment demonstrated a significantly larger final tip rotation angle change than anteroinferior (0.48 ± 5.65 degrees), posterosuperior (-1.08 ± 4.77 degrees), and posteroinferior (-0.64 ± 5.80 degrees) locations (all p < 0.05). Translational maxillary movement and actual linear maxillary change were not correlated with final tip rotation angle change.

CONCLUSION

Effects of Le Fort I maxillary repositioning on nasal tip rotation depend on movement types and maxillary segment location.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Cephalometry without complex dedicated postprocessing in an oriented magnetic resonance imaging dataset: a pilot study

OBJECTIVES

Magnetic resonance imaging (MRI) enables a 3D-volume-imaging without ionizing radiation. Therefore, it was the aim of this study to present a post-processing-free method for cephalometric analysis of a MRI-dataset and to examine whether there is a significant difference between cephalometric analysis of conventional 2D cephalograms and MRI scans.

METHODS

One MRI scan each was performed on three cadaver heads using a 3T-MR-scanner. Cephalometric analysis was conducted directly on the 3D dataset. All reference points were projected onto a virtual sagittal plane that was perpendicular to the Frankfort horizontal plane. Double-sided points were averaged. Cephalometric angles were measured from the projected points. Results were compared with cephalometric measurements on conventional lateral cephalometric radiographs (LCRs). The cephalometric analysis was performed by five raters.

RESULTS

390-angle measurements were obtained. The inter-rater reliability was high [intraclass correlation coefficients (ICCs) ≥ 0.74 for all angles]. Differences between the measurements on the cephalograms and MRI scans ranged between -0.91° (-1.88°, 0.07°) and 0.97° (-0.63°, 2.57°) on average and were equivalent with respect to a margin of [-2°, 2°] in all angles except L1-Me-Tgo (Bonferroni-Holm-corrected P < 0.05 in all angles except L1-Me-Tgo). The best match was found for the SNA angle.

CONCLUSION

The clinical comparability of the MRI- and LCR-based cephalometry could be stated. Using MRI in orthodontics would reduce radiation exposure and the risk of stochastic radiation damage, which is of importance especially in younger patients.

Type of maxillary segment mobilization affects three-dimensional nasal morphology

BACKGROUND

Surgical mobilization of the maxillary segment affects nasal morphology. This study assessed the impact of the type of maxillary mobilization on the three-dimensional (3D) nasal morphometry.

METHODS

Pre- and postsurgery cone beam computed tomography-derived facial image datasets of consecutive patients who underwent two-jaw orthognathic surgery were reviewed. Using preoperative 3D facial models as the positional reference of the skeletal framework, 12-month postoperative 3D facial models were classified into four types of maxillary mobilizations (advancement [n = 83], setback [n = 24], intrusion [n = 55], and extrusion [n = 52]) and four types of final maxillary positions (anterosuperior [n = 44], anteroinferior [n = 39], posterosuperior [n = 11], and posteroinferior [n = 13]). Six 3D soft tissue nasal morphometric parameters were measured, with excellent intra- and interexaminer reliability scores (ICC>0.897) for all the measurements. The 3D nasal change for each nasal parameter was computed as the difference between postoperative and preoperative measurement values.

RESULTS

The intrusion maxillary mobilization resulted in a significantly (all p<0.05) larger 3D nasal change in terms of alar width, alar base width, and nostril angle parameters, and a smaller change in terms of the nasal tip height parameter than the extrusion maxillary mobilization; however, no significant (all p>0.05) difference was observed between advancement and setback maxillary mobilizations. The anterosuperior and posterosuperior maxillary positions had a significantly (all p<0.05) larger 3D nasal change in terms of the alar base width and nostril angle than the anteroinferior and posteroinferior maxillary positions.

CONCLUSION

The type of maxillary mobilization affects the 3D nasal morphometry.

Three-Dimensional Computer-Assisted Orthognathic Surgery: Traditional Hybrid Versus Full Digital Planning Models

PURPOSE

Three-dimensional (3D) computer-aided planning has truly revolutionized orthognathic surgery (OGS) treatment, but no study has compared the traditional hybrid and full 3D digital planning models. This study compared these virtual planning models in the treatment of asymmetric maxillomandibular disharmony.

METHODS

Young adult patients with an asymmetric skeletal class III deformity who underwent 3D computer-aided 2-jaw OGS using hybrid (alginate dental impression, 2D cephalometric tracings, manual-guided stone model surgery, occlusion setup, and splint fabrication; n = 30) or full digital (laser-scanned dentition, 3D cephalometric tracings, virtual-based occlusion setup and surgery, and computer-generated surgical splint; n = 30) planning models were consecutively recruited. Preoperative and postoperative 3D cephalometric analyses (dental relation, skeletal assessments based on sagittal and frontal views, and soft tissue evaluations) were adopted for intragroup and intergroup comparisons. Postoperative patient-perceived satisfaction with facial appearance was also recorded.

RESULTS

Both hybrid and full digital planning groups had significant (all P < 0.05) improvements after surgery with respect to facial convexity, incisor overjet, and frontal symmetry parameters. The full 3D digital planning-based OGS treatment had similar (all P > 0.05) 3D cephalometric-derived outcomes (preoperative, postoperative, and treatment-induced change data) and patient-perceived outcomes compared with the traditional hybrid 3D planning method.

CONCLUSIONS

For the decision-making process in selecting the planning model, multidisciplinary teams could consider additional parameters such as patient comfort, storage needs, convenience for data reuse, overall planning time, availability, and costs.

Landmark annotation and mandibular lateral deviation analysis of posteroanterior cephalograms using a convolutional neural network

Background/purpose

Facial asymmetry is relatively common in the general population. Here, we propose a fully automated annotation system that supports analysis of mandibular deviation and detection of facial asymmetry in posteroanterior (PA) cephalograms by means of a deep learning-based convolutional neural network (CNN) algorithm.

Materials and methods

In this retrospective study, 400 PA cephalograms were collected from the medical records of patients aged 4 years 2 months-80 years 3 months (mean age, 17 years 10 months; 255 female patients and 145 male patients). A deep CNN with two optimizers and a random forest algorithm were trained using 320 PA cephalograms; in these images, four PA landmarks were independently identified and manually annotated by two orthodontists.

Results

The CNN algorithms had a high coefficient of determination (R ² ), compared with the random forest algorithm (CNN-stochastic gradient descent, R ²  = 0.715; CNN-Adam, R ²  = 0.700; random forest, R ²  = 0.486). Analysis of the best and worst performances of the algorithms for each landmark demonstrated that the right latero-orbital landmark was most difficult to detect accurately by using the CNN. Based on the annotated landmarks, reference lines were defined using an algorithm coded in Python. The CNN and random forest algorithms exhibited similar accuracy for the distance between the menton and vertical reference line.

Conclusion

Our findings imply that the proposed deep CNN algorithm for detection of facial asymmetry may enable prompt assessment and reduce the effort involved in orthodontic diagnosis.

Effects of Changes in the Frankfort Horizontal Plane Definition on the Three-Dimensional Cephalometric Evaluation of Symmetry

The plane formed by the intersection of bilateral porions (PoR and PoL) and left orbitale (OrL) is conventionally defined as the Frankfort horizontal (FH) plane. We aim to test the influence of the FH plane definition on a 3D cephalometric assessment. We selected 38 adult patients (20 males, 18 females; average age: 22.87 ± 5.17 years) without any gross asymmetry from retrospective records and traced and analyzed their cone-beam computed tomographic images. The findings were categorized into the following four groups: FH1: conventional; FH2: PoR, PoL, right orbitale (OrR); FH3: OrR, OrL, PoL; FH4: OrR, OrL, PoR. The average menton (Me) deviation from the MSP was statistically significant for the FH1 group (0.56 ± 0.27 mm; p < 0.001), compared to the FH3 (1.37 ± 1.23 mm) and FH4 (1.33 ± 1.16 mm) groups. The spatial orientation level (SOL) of the FH plane showed a marked difference (p < 0.05) between the FH2 (0.602° ± 0.503°) and FH4 (0.944° ± 0.778°) groups. The SOL of the MSP was comparatively small (p < 0.001) for FH2 (0.015° ± 0.023°) in comparison to both FH 3 (0.644° ± 0.546°) and FH 4 (0.627° ± 0.516°). Therefore, the FH plane definition can significantly influence the interpretation of cephalometric findings. Future studies should focus on standardization to improve the reliability and reproducibility of 3D cephalometry.

Quantifying the Severity of Metopic Craniosynostosis: A Pilot Study Application of Machine Learning in Craniofacial Surgery

The standard for diagnosing metopic craniosynostosis (CS) utilizes computed tomography (CT) imaging and physical exam, but there is no standardized method for determining disease severity. Previous studies using interfrontal angles have evaluated differences in specific skull landmarks; however, these measurements are difficult to readily ascertain in clinical practice and fail to assess the complete skull contour. This pilot project employs machine learning algorithms to combine statistical shape information with expert ratings to generate a novel objective method of measuring the severity of metopic CS.Expert ratings of normal and metopic skull CT images were collected. Skull-shape analysis was conducted using ShapeWorks software. Machine-learning was used to combine the expert ratings with our shape analysis model to predict the severity of metopic CS using CT images. Our model was then compared to the gold standard using interfrontal angles.Seventeen metopic skull CT images of patients 5 to 15 months old were assigned a severity by 18 craniofacial surgeons, and 65 nonaffected controls were included with a 0 severity. Our model accurately correlated the level of skull deformity with severity (P < 0.10) and predicted the severity of metopic CS more often than models using interfrontal angles (χ = 5.46, P = 0.019).This is the first study that combines shape information with expert ratings to generate an objective measure of severity for metopic CS. This method may help clinicians easily quantify the severity and perform robust longitudinal assessments of the condition.

Digital Occlusion Setup Is Quantitatively Comparable With the Conventional Dental Model Approach: Characteristics and Guidelines for Orthognathic Surgery in Patients With Unilateral Cleft Lip and Palate

BACKGROUND

The evolving 3-dimensional computer-based technology revolutionized the field of orthognathic surgery (OGS). Digital occlusion setup for OGS may provide advantages in the planning comparing with the conventional approach based on the manual setup using dental casts, but we are not aware of any study focusing on digital occlusion setup for cleft OGS. The purposes of this study were to compare the conventional and digital occlusion setup approaches and to propose a protocol for digital occlusion setup in unilateral cleft OGS.

METHODS

Thirty consecutive patients with unilateral cleft lip/palate who underwent orthodontic treatment by a single orthodontist and 2-jaw OGS by a single surgeon using 3-dimensional surgical simulation were adopted for analysis. Quantitative data were collected from the dental cast occlusion setup approach (conventional group). A multidisciplinary team combined this quantitative data and established a protocol for digital occlusion setup in cleft OGS. Digital occlusions were set according to this protocol using the images of the 30 patients, and quantitative data were collected accordingly (digital group). The results of 2 groups were compared. All information was reviewed to refine the protocol and define the final guidelines.

RESULTS

There were no significant differences (all P > 0.05) for all parameters, except midline discrepancy (conventional group > digital group, P < 0.001). The root-mean-square deviation (0.46 ± 0.26 mm) indicated acceptable relationship between the conventional and digital groups. A 6-step protocol for digital occlusion setup in cleft OGS was established: dental midline, overjet/overbite, yaw rotation, pitch rotation, roll rotation, and overall facial skeletal appearance.

CONCLUSIONS

This study shows that digital occlusion setup is quantitatively comparable with the conventional dental model approach and contributes for cleft OGS by establishing a protocol for surgical occlusion setup using digital approach.

Three-dimensional evaluation of the correlation between lip canting and craniofacial planes

Objective

This study aimed to analyze the correlation of horizontal and sagittal planes used in two-dimensional diagnosis with lip canting by using threedimensional (3D) analysis.

Methods

Fifty-two patients (25 men, 27 women; average age: 24 years) undergoing treatment for dentofacial deformity were enrolled. Computed tomography images were acquired, and digital imaging and communication in medicine files were reconstructed into a 3D virtual model wherein horizontal and sagittal craniofacial planes were measured. Subsequently, the correlations of lip canting with these horizontal and sagittal planes were investigated.

Results

The mandibular symmetry plane, the occlusal plane, Camper's plane, the mandibular plane, Broadbent's plane, and the nasal axis plane were correlated with the amount of lip canting (Pearson's correlation coefficients: 0.761, 0.648, 0.556, 0.526, 0.438, and 0.406, respectively). Planes associated with the lower part of the face showed the strongest correlations; the strength of the correlations decreased in the midfacial and cranial regions. None of the planes showed statistically significant differences between patients with clinical lip canting (> 3°) and those without prominent lip canting.

Conclusions

The findings of this study suggest that lip canting is strongly correlated with the mandibular symmetry plane, which includes menton deviation. This finding may have clinical implications with regard to the treatment of patients requiring correction of lip canting. Further studies are necessary for evaluating changes in lip canting after orthognathic surgery.

Towards an early 3D-diagnosis of craniofacial asymmetry by computing the accurate midplane: A PCA-based method

BACKGROUND AND OBJECTIVE

Craniofacial asymmetry is a common growth disorder often caused by unilateral chewing. Although an early orthodontic treatment would avoid surgical procedures later in life, the uncertainty of defining the accurate sagittal midplane potentially leads to misdiagnosis and therefore inaccurate orthodontic treatment plans. This novel study aims to 3D-diagnose craniofacial complex malformations in children with unilateral crossbite (UXB) considering a midplane which compensates the asymmetric morphology.

METHODS

The sagittal midplane of 20 children, fifteen of whom exhibited UXB, was computed by a PCA-based method which compensates the asymmetry mirroring the 3D models obtained from cone-beam computed tomography data. Once determined, one side of the data was mirrored using the computed midplane to visualize the malformations on the hard and soft tissues by 3D-computing the distances between both halves. Additionally, 31 skull's landmarks were manually placed in each model to study the principal variation modes and the significant differences in the group of subjects with and without UXB through PCA and Mann-Whitney U test analyses respectively.

RESULTS

Morphological 3D-analysis showed pronounced deformities and aesthetic implications for patients with severe asymmetry (jaw deviation > 0.8 mm) in whole craniofacial system, while initial signs of asymmetry were found indistinctly in the mandible or maxilla. We detected significant (p < 0.05) malformations for example in mandibular ramus length (0.0086), maxillary palate width (0.0481) and condylar head width (0.0408). Craniofacial malformations increased the landmarks' variability in the group of patients with UXB over the control group requiring 8 variation modes more to define 99% of the sample' variability.

CONCLUSIONS

Our findings demonstrated the viability of early diagnosis of craniofacial asymmetry through computing the accurate sagittal midplane which compensates the individual's asymmetrical morphology. Furthermore, this study provides important computational insights into the determination of craniofacial deformities which are caused by UXB, following some empirical findings of previous clinical studies. Hence, this computational approach can be useful for the development of new software in craniofacial surgery or for its use in biomedical research and clinical practice.

Quantitative evaluation of symmetry after navigation-guided surgical recontouring of zygomatic fibrous dysplasia: a comparative study

Zygomatic fibrous dysplasia is a slowly progressive disorder of bone, which commonly causes facial asymmetry. Precise surgical recontouring can effectively improve facial aesthetics. The aim of this study was to quantitatively evaluate the effectiveness of surgical navigation guidance in correcting zygomatic asymmetry. The study included 26 patients with unilateral zygomatic fibrous dysplasia who underwent bony recontouring. They were divided into two groups according to the use of intraoperative surgical navigation (navigation group and conventional group; n=13 in each group). Clinical outcomes were evaluated using three-dimensional computed tomography. Six pairs of landmarks were identified, and the coordinates were used to calculate asymmetry indices. The curvature of protruding regions in the surgical area was measured to determine facial skeletal symmetry in three dimensions. The results were compared between the groups. All patients recovered uneventfully and their facial symmetry and aesthetics improved. For three of the six pairs of landmarks, symmetry was better in the navigation group than in the conventional group (all P≤ 0.02). The postoperative curvature ratios were better (more symmetrical) in the navigation group (P= 0.01). Surgical navigation enhances postoperative facial symmetry. However, the clinical significance of this enhancement when compared to conventional non-navigation surgery needs further investigation.

Primary Rhinoplasty Does Not Interfere with Nasal Growth: A Long-Term Three-Dimensional Morphometric Outcome Study in Patients with Unilateral Cleft

BACKGROUND

Primary rhinoplasty has not been universally adopted because the potential for nasal growth impairment remains an unsolved issue in cleft care. This study's purpose was to assess the long-term effects of primary rhinoplasty performed by a single surgeon in a cohort of patients with a unilateral cleft lip nose deformity.

METHODS

Three-dimensional nasal morphometric measurements (linear, angular, proportional, surface area, and volume) were collected from consecutive patients (cleft group, n = 52; mean age, 19 ± 1 year) who had undergone primary rhinoplasty with the use of the Noordhoff approach between 1995 and 2002 and reached skeletal maturity. Normal age-, sex-, and ethnicity-matched subjects (control group, n = 52) were identified for comparative analyses.

RESULTS

No significant differences (all p > 0.05) were observed for most measures, including nasal height, alar width, nasal dorsum angle, columellar angle, columellar-labial angle, nasal tip/height ratio, nasal index, alar width/intercanthal distance ratio, nasal surface area, and nasal volume. The cleft group displayed significantly (all p < 0.05) lower nasal bridge length and nasal tip projection, and greater nasal protrusion, tip/midline deviation, nasal tip angle, nasal tip protrusion width index, and alar width/mouth ratio values than the control group.

CONCLUSIONS

Primary rhinoplasty does not interfere with nasal growth as measured by three-dimensional photogrammetric analysis. Further imaging studies are required for the assessment of development in other anatomical nasal structures.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

The Drilling Guiding Templates and Pre-Bent Titanium Plates Improves the Operation Accuracy of Orthognathic Surgery With Computer-Aided Design and Computer-Aided Manufacturing Occlusal Splints for Patients With Facial Asymmetry

Facial asymmetry is a common maxillofacial deformity which requires surgery to recover the 3-dimensional relationship of bones. The computer-aided design and computer-aided manufacturing (CAD/CAM) has been developed and applied to improve orthognathic analysis and surgery design. How to accurately realize the preoperative design of orthognathic surgery with CAD/CAM occlusal splints during operation remains a big problem. In this study, 24 consecutive patients with facial asymmetry were recruited and assigned to 2 groups. For Group A, CAD/CAM was applied to designing and producing not only the occlusal splints, but also the drilling guiding templates and pre-bent titanium plates, and for Group B CAD/CAM was applied for occlusal splints only. Postoperative clinical examinations, symmetry evaluation through 3D cephalometric analysis, accuracy comparison using color distance maps and quantitative accuracy analysis were performed. Symmetry evaluation showed that patients of both groups achieved improved facial symmetry after surgery. The color distance maps and quantitative accuracy analysis together demonstrated significantly less difference found between virtual simulated surgery and postoperative CT scan data in Group A than in Group B. In conclusion, by navigation with the drilling guiding templates and pre-bent titanium plates, the facial symmetry for patients with facial asymmetry was successfully restored after orthognathic surgery, same as applying CAD/CAM occlusal splints only. However, the drilling guiding templates and pre-bent titanium plates would provide a more accurate performance according to preoperative simulation, especially for proximal mandibular segments.

The outcome of skeletofacial reconstruction with mandibular rotation for management of asymmetric skeletal class III deformity: A three-dimensional computer-assisted investigation

The mandibular proximal ramus segments should be moved and rotated during orthognathic surgery-based skeletofacial reconstruction for the correction of challenging patients with facial asymmetry and malocclusion, but quantitative data regarding this rotation were not sufficient to date. This 3D computer-assisted study measured the proximal ramus segment rotation after 3D simulation-guided two-jaw surgery in patients with facial asymmetric deformity and class III malocclusion (n = 31). Using 3D mandible models and a reliable proximal ramus segment-related plane, angular changes in pitch, roll and yaw directions were measured before and one month after surgery. Significant rotational changes (p < 0.01) were observed in the left and right sides and overall proximal ramus segments after surgery, with absolute differences of 4.1 ± 3.0 (range -7.8 to 6.9), 2.8 ± 2.3 (-8.8 to 5.0), and 2.7 ± 2.4 (-6.6 to 9.9) degrees in pitch, roll, and yaw rotations, respectively. Numbness and mouth opening limiting occurred within the first 6 months after surgery but the patients had an unremarkable long-term postoperative course, with no revisionary surgery required. This study contributes to the multidisciplinary-related literature by revealing that proximal ramus segment rotation and rigid fixation with no postoperative intermaxillary immobilization was practicable in skeletofacial surgery for the successful treatment of asymmetric deformity and class III malocclusion.

Two-year observation of the occlusal vertical dimension after bite raising via cone-beam computerized tomography: A preliminary study

Variation of the occlusal vertical dimension (OVD) has been discussed empirically for decades, but it has not been thoroughly explored with experimental data. In the present study, cone-beam computerized tomography (CBCT) of six selected patients was conducted to evaluate the bones of the lower facial structures. The anterior lower facial heights (ALFHs), alveolar process heights (APHs), vertical facial pattern (VFP), occluding dentition height (ODH) and condyle space (CS), which were evaluated by three-dimensional (3D) and two-dimensional (2D) lateral cephalometry derived from CBCT, were compared before and two years after the OVD increased full mouth rehabilitation. Consistent significant increases in ALFHs and the VFP indicated the OVD increase, while a significant decrease in the ΔODH indicated compressed dentition. In addition, 55 of the 56 sites (98.21%) of APH measurement illustrated no significant difference before and after treatment. The findings indicated that the increased OVD did not relapse to baseline and was sufficiently tolerated, with mostly constant APHs and an altered ODH after two years of observation in the six patients.

Three-dimensional region-based study on the relationship between soft and hard tissue changes after orthognathic surgery in patients with prognathism

Both deep understanding and reliable prediction of postoperative soft tissue changes are crucial for planning orthognathic surgery. Instead of estimating soft tissue responses by measuring individual landmark changes, this study aimed to investigate the relationship (ratio) between soft and hard tissue movements in different facial regions through three-dimensional cone-beam computed tomography (CBCT). Preoperative and postoperative CBCT images were superimposed using the surface registration method on the basis of the cranial base, and 10 facial regions of interest were defined. Region-based volumetric subtractions between the preoperative and postoperative segments were performed. The volumetric differences and surface of each region were used to estimate the average movement. Correlation and regression analyses were performed to examine the relationships between the corresponding soft and hard tissue movements. An overall pattern of facial soft tissue movement was observed in patients with prognathism who underwent orthognathic surgery. The experiment results have shown that mean ratios for the average soft-to-hard tissue movements in the facial regions varied, which may not exactly be similar to the published reports because of the population biocharacteristics and study methods, but the trend is in agreement with the previous studies. Additionally, the prediction capability of the regression model was significantly high, ranging from 0.786 to 0.857, in upper lip, upper vermilion, and chin regions, thus demonstrating that the skin outline changes in these critical regions could be reliably predicted from the underlying bone movements. These results could likely be applied in future soft tissue simulation in orthognathic surgery.

Hemimandibular Hyperplasia Correction by Simultaneous Orthognathic Surgery and Condylectomy Under Digital Guidance

PURPOSE

Orthognathic surgery with simultaneous condylectomy under digital guidance has been proved to be a feasible method to treat hemimandibular hyperplasia (HH). The objective of this study was to evaluate the effects and precision of correction of HH by use of this method.

PATIENTS AND METHODS

This was a case-series study. Fourteen patients with HH who had undergone simultaneous bimaxillary orthognathic surgery and condylectomy from January 2016 to April 2017 were included in this study. Presurgical virtual treatment planning was performed, transferred to the operation room, and realized with the assistance of surgical navigation and 3-dimensionally printed occlusion splints. Postoperative computed tomography data were used to analyze improvement in facial symmetry and verify the accuracy of the surgical procedure.

RESULTS

All patients exhibited satisfactory clinical effects; facial asymmetry was corrected as expected. Postoperative validation showed that the presurgical planning had been achieved more precisely on the unaffected side than on the affected side. Moreover, bilateral mandibular proximal segments showed a tendency for outward rotation compared with the presurgical planning model. Furthermore, when we assessed facial symmetry compared with the presurgical model, deviation of all midline landmarks was less than 2 mm, occlusal-plane inclination was less than 1 mm, and the asymmetry index of paired landmarks was remarkably decreased after surgery (P < .01).

CONCLUSIONS

Orthognathic surgery with simultaneous condylectomy under digital guidance is a realistic and precise method for treatment of HH. Surgical results can be validated during surgery by virtual navigation. However, movement of each bone segment cannot be accurately controlled as planned before surgery.