Surgical cephalometrics: applications and developments

Chin Dysmorphology in the Primary Rhinoplasty Population: Prevalence, Objective Analysis, and Implications

BACKGROUND

Chin flaws are far more common than recognized. Denial of genioplasty by parents or adult patients can present a surgical planning enigma, especially in patients with microgenia and chin deviation. This study aims to investigate the frequency of chin imperfections on patients seeking rhinoplasty, review the conundrum they generate, and offer management suggestions based on over 40 years of the senior author's experience.

METHODS

This review included 108 consecutive patients presenting for primary rhinoplasty. Demographics, soft tissue cephalometrics, and surgical details were obtained. Exclusion criteria included prior orthognathic or isolated chin surgery, mandiblular trauma, or congenital craniofacial deformities.

RESULTS

Of the 108 patients, 92 (85.2%) were female. Mean age was 30.8 years (SD±13, range 14-72). Ninety-seven (89.8%) patients exhibited some degree of objective chin dysmorphology. Fifteen (13.9%) had Class I deformities (macrogenia), 63 (58.3%) Class II (microgenia), and 14 (12.9%) Class III (combined macro and microgenia in the horizontal or vertical vectors). Forty-one (38%) patients had Class IV deformities (asymmetry). While all patients were offered the opportunity to correct chin flaws, only 11 (10.1%) underwent such procedures. Five (4.6%) patients had simultaneous osseous genioplasty (mean advancement 7.8mm, range 5-9mm); 7 (6.5%) received fat grafting to the chin (mean volume 4.4cc, range 1-9cc).

CONCLUSIONS

A considerable proportion of primary rhinoplasty patients possess quantifiable chin dysmorphology on circumspect examination, high-resolution photographs and cephalometric analysis. Only a small number agree to surgical interventions that pursue full facial harmony. Potential reasons for these findings, patient aversion, and mitigation strategies will be discussed.

LEVEL OF EVIDENCE III

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Reproducibility of Computerized Cephalometric Analysis Software Compared with Conventional Manual Tracing for Analyzing Skeletal Stability After Orthognathic Surgery

Objective

This study aimed to compare the difference between analyzing skeletal stability after orthognathic surgery by lateral cephalogram measurement created from Dolphin software (version 11.95) compared with the manual technique.

Methods

Twenty-eight patients who underwent mandibular setback surgery (BSSRO) were randomly selected between 2015 and 2021. Serial lateral cephalograms were analyzed at four different time sets postoperatively, and a total of 112 cephalometric radiographs were obtained. Horizontal measurement (BX), vertical measurement (BY), and 3 angular measurements (SNB, ANB, and Gonial angle) were analyzed by manual tracing and Dolphin software by 2 examiners. The intraclass correlation coefficient determined the intra-rater reliability. Parameter differences between timelines were observed for skeletal stability, and mean values between methods were compared using the Student's t-test.

Results

Both examiners were generally consistent in the repeated measurements (ICCs of the manual method ranged from 0.926 to 0.994, and the digital method ranged from 0.719 to 0.956). All variables represented skeletal stability at T0-T1, T0-T2, and T0-T3 showed no statistically significant differences between methods except ANB (T0-T1; p value = 0.009).

Conclusions

Computerized cephalometric analysis software is relatively reproducible for assessing skeletal changes after orthognathic surgery and can be used routinely in follow-up.

Managing Predicted Post-Orthognathic Surgical Defects Using Combined Digital Software: A Case Report

For facial abnormalities, recent developments in virtual surgical planning (VSP) and the virtual design of surgical splints are accessible. Software companies have worked closely with surgical teams for accurate outcomes, but they are only as reliable as the data provided to them. The current case's aim was to show a fully digitized workflow using a combination of three digital software to correct predicted post-upward sliding genioplasty defects. To reach our goal, we presented a 28-year-old man with long-face syndrome for orthodontic treatment. Before orthognathic surgery, a clinical and paraclinical examination was performed. For a virtual surgical plan, we used the dedicated surgical planning software NemoFab (Nemotec, Madrid, Spain) and Autodesk MeshMixer (Autodesk Inc., San Rafael, CA, USA). To create the design of the digital guides, DentalCAD 3.0 Galway (exocad GmbH, Darmstadt, Germany) and Autodesk MeshMixer (Autodesk Inc., San Rafael, CA, USA) were used. The patient had undergone bilateral sagittal split osteotomy in addition to Le Fort 1 osteotomy and genioplasty, followed by mandible base recontouring ostectomy. Stable fixation was used for each osteotomy. Based on our case, the current orthognathic surgery planning software was not able to perform all the necessary operations autonomously; therefore, future updates are eagerly awaited.

Structure-Aware Long Short-Term Memory Network for 3D Cephalometric Landmark Detection

Detecting 3D landmarks on cone-beam computed tomography (CBCT) is crucial to assessing and quantifying the anatomical abnormalities in 3D cephalometric analysis. However, the current methods are time-consuming and suffer from large biases in landmark localization, leading to unreliable diagnosis results. In this work, we propose a novel Structure-Aware Long Short-Term Memory framework (SA-LSTM) for efficient and accurate 3D landmark detection. To reduce the computational burden, SA-LSTM is designed in two stages. It first locates the coarse landmarks via heatmap regression on a down-sampled CBCT volume and then progressively refines landmarks by attentive offset regression using multi-resolution cropped patches. To boost accuracy, SA-LSTM captures global-local dependence among the cropping patches via self-attention. Specifically, a novel graph attention module implicitly encodes the landmark's global structure to rationalize the predicted position. Moreover, a novel attention-gated module recursively filters irrelevant local features and maintains high-confident local predictions for aggregating the final result. Experiments conducted on an in-house dataset and a public dataset show that our method outperforms state-of-the-art methods, achieving 1.64 mm and 2.37 mm average errors, respectively. Furthermore, our method is very efficient, taking only 0.5 seconds for inferring the whole CBCT volume of resolution 768×768×576 .

The Expanding Role of Geometric Morphometrics in Craniofacial Surgery

INTRODUCTION

Geometric morphometrics (GM) is an advanced landmark-based quantitative method used to study biological shape and form. Historically, GM has been limited to non-biomedical fields such as comparative biology; however, this technique confers advantages over traditional cephalometric methods, warranting a review of current applications of GM to human craniofacial disorders.

METHODS

The RISmed package was used to extract metadata associated with PubMed publications referencing GM analysis techniques in craniofacial and reconstructive surgery. PubMed search terms included "geometric AND morphometric AND craniofacial;" and "geometric AND morphometric AND reconstructive surgery." Duplicate search results were eliminated.

RESULTS

Search yielded 139 studies between 2005 and 2020, of which 27 met inclusion criteria. Human craniofacial studies constituted 2% of all queried GM studies. Among these, cleft lip and palate were the most commonly studied craniofacial conditions (7 studies, 26%), followed by sagittal craniosynostosis (4 studies, 15%). Seventeen studies (63%) used GM to assess skeletal structures, seven studies (26%) examined both skeletal and soft tissues, and three studies (11%) analyzed soft tissues only. Eleven studies (40.1%) employed a GM approach to evaluate postoperative changes in craniofacial morphology. Two studies (7%) systematically compared GM analysis with conventional shape measurements.

CONCLUSION

The ability to study shape while controlling for variability in structure size and imaging technique make GM a promising tool for understanding growth patterns in complex craniofacial diseases. Furthermore, GM overcomes many limitations of traditional cephalometric techniques, and hence may claim an expanded role in the study of human craniofacial disorders in clinical and research settings.

Measuring Differential Volume Using the Subtraction Tool for Three-Dimensional Breast Volumetry: A Proof of Concept Study

Background. Three-dimensional (3D) photography provides a promising means of breast volumetry. Sources of error using a single-captured surface to calculate breast volume include inaccurate designation of breast boundaries and prediction of the invisible chest wall generated by computer software. An alternative approach is to measure differential volume using subtraction of 2 captured surfaces. Objectives. To explore 3D breast volumetry using the subtraction of superimposed images to calculate differential volume. To assess optimal patient positioning for accurate volumetric assessment. Methods. Known volumes of breast enhancers simulated volumetric changes to the breast (n = 12). 3D photographs were taken (3dMDtorso) with the subject positioned upright at 90° and posteriorly inclined at 30°. Patient position, breathing, distance and camera calibration were standardised. Volumetric analysis was performed using 3dMDvultus software. Results. A statistically significant difference was found between actual volume and measured volumes with subjects positioned at 90° (P < .05). No statistical difference was found at 30° (P = .078), but subsequent Bland–Altman analysis showed evidence of proportional bias (P < .05). There was good correlation between measured and actual volumes in both positions (r = .77 and r = .85, respectively). Univariate analyses showed breast enhancer volumes of 195 mL and 295 mL to incur bias. The coefficient of variation was 5.76% for single observer analysis. Conclusion. Positioning the subject at a 30° posterior incline provides more accurate results from better exposure of the inferior breast. The subtraction tool is a novel method of measuring differential volume. Future studies should explore methodology for application into the clinical setting.

Outcome of facial contour asymmetry after conventional two-dimensional versus computer-assisted three-dimensional planning in cleft orthognathic surgery

Computer-assisted 3D planning has overcome the limitations of conventional 2D planning-guided orthognathic surgery (OGS), but difference for facial contour asymmetry outcome has not been verified to date. This comparative study assessed the facial contour asymmetry outcome of consecutive patients with unilateral cleft lip and palate who underwent 2D planning (n = 37)- or 3D simulation (n = 38)-guided OGS treatment for correction of maxillary hypoplasia and skeletal Class III malocclusion between 2010 and 2018. Normal age-, gender-, and ethnicity-matched individuals (n = 60) were enrolled for comparative analyses. 2D (n = 60, with 30 images for each group) and 3D (n = 43, with 18 and 25 images for 2D planning and 3D simulation groups, respectively) photogrammetric-based facial contour asymmetry-related measurements were collected from patients and normal individuals. The facial asymmetry was further verified by using subjective perception of a panel composed of 6 blinded raters. On average, the facial contour asymmetry was significantly (all p < 0.05) reduced after 3D virtual surgery planning for all tested parameters, with no significant differences between post-OGS 3D simulation-related values and normal individuals. No significant differences were observed for pre- and post-OGS values in conventional 2D planning-based treatment, with significant (all p < 0.05) differences for all normal individuals-related comparisons. This study suggests that 3D planning presents superior facial contour asymmetry outcome than 2D planning.

Accuracy in orthognathic surgery─comparison of preoperative plan and postoperative outcome using computer-assisted two-dimensional cephalometry by the Onyx Ceph® system

PURPOSE

This retrospective study analyzes deviations between preoperative planning and postoperative outcome in orthognathic surgery using 2D Onyx Ceph^®-cephalometric analyzing and planning system.

MATERIALS AND METHODS

A total of 100 patients with a mean age 25.1 of years were included in this study. In 33 patients a bilateral sagittal split osteotomy and in seven patients a Le Fort I osteotomy was performed. A total of 60 patients were treated by a bimaxillary approach. Onyx Ceph^® was used as cephalometric planning software (Onyx Ceph^®), followed by mock operations. Postoperative cephalograms were obtained after 3.3 days and compared to preoperative planning cephalograms for sagittal (SNA, SNB, ANB) and vertical (ArGoMe, ML-NSL, NL-NSL) angle measurements. Real and absolute mean deviation were documented.

RESULTS

Absolute mean deviation (degrees) between postoperative and planned jaw movement was lower for the sagittal parameters SNA (0.58), SNB (1.15) and ANB (1.05) compared to the vertical parameters NL-NSL (1.47), ML-NSL (1.96) and ArGoMe (3.20). SNA, SNB and ANB showed constant deviations independent from the extent of jaw movement. With regard to the vertical parameters ML-NSL, ArGoMe and NL-NSL the extent of the postoperative rotational jaw movement was not as much as planned, particularly for vertical shifts of more than 4°.

CONCLUSION

By using the 2D Onyx Ceph^® cephalometric software for orthognathic surgery, the deviations between planned and actual movements are within an acceptable and predictable range. Planning of extensive vertical alterations may result in greater deviations after surgery.

Three-dimensional canine displacement patterns in response to translation and controlled tipping retraction strategies

OBJECTIVE

To validate whether applying a well-defined initial three-dimensional (3D) load can create consistently expected tooth movement in patients.

MATERIALS AND METHODS

Twenty-one patients who needed bilateral canine retraction to close extraction space were selected for this split-mouth clinical trial. After initial alignment and leveling, two canines in each patient were randomly assigned to receive either translation (TR) or controlled tipping (CT) load. The load was delivered by segmental T-loops designed to give specific initial moment/force ratios to the canines in each treatment interval (TI), verified with an orthodontic force tester. Maxillary dental casts were made before canine retraction and after each TI. The casts were digitized with a 3D laser scanner. The digital models were superimposed on the palatal rugae region. The 3D canine displacements and the displacement patterns in terms of TR, CT, and torque were calculated for each TI.

RESULTS

The method can reliably detect a TR displacement greater than 0.3 mm and a rotation greater than 1.5°. Ninety-two TIs had displacements that were greater than 0.3 mm and were used for further analysis. Most displacements were oriented within ±45° from the distal direction. The displacement pattern in terms of TR or CT was not uniquely controlled by the initial moment/force ratio.

CONCLUSIONS

The initial load system is not the only key factor controlling tooth movement. Using a segmental T-loop with a well-controlled load system, large variations in canine displacement can be expected clinically.

Computer-Assisted Orthognathic Surgery for Patients with Cleft Lip/Palate: From Traditional Planning to Three-Dimensional Surgical Simulation

BACKGROUND

Although conventional two-dimensional (2D) methods for orthognathic surgery planning are still popular, the use of three-dimensional (3D) simulation is steadily increasing. In facial asymmetry cases such as in cleft lip/palate patients, the additional information can dramatically improve planning accuracy and outcome. The purpose of this study is to investigate which parameters are changed most frequently in transferring a traditional 2D plan to 3D simulation, and what planning parameters can be better adjusted by this method.

PATIENTS AND METHODS

This prospective study enrolled 30 consecutive patients with cleft lip and/or cleft palate (mean age 18.6±2.9 years, range 15 to 32 years). All patients received two-jaw single-splint orthognathic surgery. 2D orthodontic surgery plans were transferred into a 3D setting. Severe bony collisions in the ramus area after 2D plan transfer were noted. The position of the maxillo-mandibular complex was evaluated and eventually adjusted. Position changes of roll, midline, pitch, yaw, genioplasty and their frequency within the patient group were recorded as an alternation of the initial 2D plan. Patients were divided in groups of no change from the original 2D plan and changes in one, two, three and four of the aforementioned parameters as well as subgroups of unilateral, bilateral cleft lip/palate and isolated cleft palate cases. Postoperative OQLQ scores were obtained for 20 patients who finished orthodontic treatment.

RESULTS

83.3% of 2D plans were modified, mostly concerning yaw (63.3%) and midline (36.7%) adjustments. Yaw adjustments had the highest mean values in total and in all subgroups. Severe bony collisions as a result of 2D planning were seen in 46.7% of patients. Possible asymmetry was regularly foreseen and corrected in the 3D simulation.

CONCLUSION

Based on our findings, 3D simulation renders important information for accurate planning in complex cleft lip/palate cases involving facial asymmetry that is regularly missed in conventional 2D planning.

Prenatal Assessment of the Antero-Posterior Jaw Relationship in Human Fetuses: From Anatomical to Ultrasound Cephalometric Analysis

Objectives

We wished to develop an ultrasound cephalometric analysis, particularly of the antero-posterior jaw relationship, to increase the accuracy of prenatal diagnosis of retrognathism during the routine midterm test.

Methods

Anatomical cephalometric analysis was performed in 18 formalin-fixed human fetuses (between 16 and 39 gestational weeks), and ultrasound cephalometry was prospectively carried out in 52 pregnant women (21 to 25 gestational weeks). The same landmarks were used in the anatomical and ultrasound median sagittal planes for comparison. Four cephalometric angles were measured relative to the anterior cranial base: alveolar projection of the maxilla and the mandible, chin projection, and facial angle. The antero-posterior jaw discrepancy was calculated.

Results

The projection of the maxilla was similar in the two cephalometric analyses (IC [–3.39, 0.23]), whereas the values of the projection of the mandible were lower in the ultrasound sample. The slope of the regression line of the antero-posterior jaw discrepancy on fetuses' age did not show significant differences (IC [–0.05, 1.54]) between anatomical and ultrasound cephalometry, although a difference of 3.23° ± 0.78° (IC [1.69, 4.77]) was observed. Despite this variability, the projections of mandible and chin were well determined by the projection of the maxilla both in the anatomical and ultrasound sample.

Conclusions

Cephalometric analysis by prenatal sonography can be performed to study the antero-posterior jaw relationship. We think that this procedure could be useful to improve prenatal diagnosis of retrognathism in high-risk pregnancies. Further studies should address the reproducibility and accuracy of such analysis.

A new method for improved standardisation in three-dimensional computed tomography cephalometry

Interest for three-dimensional computed tomography cephalometry has risen over the last two decades. Current methods commonly rely on the examiner to manually point-pick the landmarks and/or orientate the skull. In this study, a new approach is presented, in which landmarks are calculated after selection of the landmark region on a triangular model and in which the skull is automatically orientated in a standardised way. Two examiners each performed five analyses on three skull models. Landmark reproducibility was tested by calculating the standard deviation for each observer and the difference between the mean values of both observers. The variation can be limited to 0.1 mm for most landmarks. However, some landmarks perform less well and require further investigation. With the proposed reference system, a symmetrical orientation of the skulls is obtained. The presented methods contribute to standardisation in cephalometry and could therefore allow improved comparison of patient data.

CT measurement of the frontal sinus - gender differences and implications for frontal cranioplasty

OBJECTIVE

To describe frontal sinus anatomy and explore gender variations that may have significance for cranioplasty and sinus surgery.

METHODS

150 subjects who underwent maxillofacial computed tomography (CT) between 1/1/2008 and 6/11/2008 were enrolled. Frontal sinus dimensions and forehead measurements were taken at midline and at 10, 20, and 30 mm to the left and right of midline using sagittal, coronal, and axial images. The data was analyzed for significant differences between measurements made at the selected points in the frontal sinus, for left to right variations, and for gender variations.

RESULTS

Mean anterior table thickness ranged from 2.6 to 4.1 mm and was thinnest at 10 mm left and right of midline (2.9 and 2.6 mm). Mean anteroposterior depth of the frontal sinus ranged from 8.0 to 9.3 mm and did not vary significantly at any distance from midline. Frontal sinus height was greatest at midline (mean=24.5 mm) and progressively lessened at lateral distances. Mean total width at the level of the supraorbital ridge was 52.2 mm. For all measurements, no significant left to right variation was noted. Comparing the sexes, males were found to have greater dimensions in most frontal sinus measurements, though these differences were only found to be significant at or close to midline. The male forehead was marked by more acute nasofrontal angle (119.9° versus 133.5°) and a steeper posterior forehead inclination (-7.2° versus -3.5°). The glabella was wider in males (44.4 versus 33.9 mm) and more frequently protruded beyond the ideal forehead slope line (51% versus 30%).

CONCLUSIONS

Using CT imaging, forehead and frontal sinus dimensions have been described. Generally, males had larger overall frontal sinus dimensions, and this was most pronounced in the medial area of the supraorbital ridge known as the glabella.

Precision of cephalometric landmark identification: cone-beam computed tomography vs conventional cephalometric views

INTRODUCTION

In this study, we compared the precision of landmark identification using displays of multi-planar cone-beam computed tomographic (CBCT) volumes and conventional lateral cephalograms (Ceph).

METHODS

Twenty presurgical orthodontic patients were radiographed with conventional Ceph and CBCT techniques. Five observers plotted 24 landmarks using computer displays of multi-planer reconstruction (MPR) CBCT and Ceph views during separate sessions. Absolute differences between each observer's plot and the mean of all observers were averaged as 1 measure of variability (ODM). The absolute difference of each observer from any other observer was averaged as a second measure of variability (DEO). ANOVA and paired t tests were used to analyze variability differences.

RESULTS

Radiographic modality and landmark were significant at P <0.0001 for DEO and ODM calculations. DEO calculations of observer variability were consistently greater than ODM. The overall correlation of 1920 paired ODM and DEO measurements was excellent at 0.972. All bilateral landmarks had increased precision when identified in the MPR views. Mediolateral variability was statistically greater than anteroposterior or caudal-cranial variability for 5 landmarks in the MPR views.

CONCLUSIONS

The MPR displays of CBCT volume images provide generally more precise identification of traditional cephalometric landmarks. More precise location of condylion, gonion, and orbitale overcomes the problem of superimposition of these bilateral landmarks seen in Ceph. Greater variability of certain landmarks in the mediolateral direction is probably related to inadequate definition of the landmarks in the third dimension.