Comparison of the Planned Versus Actual Jaw Movement Using Splint-Based Virtual Surgical Planning: How Close Are We at Achieving the Planned Outcomes?

Accuracy of maxillary repositioning surgery in teaching hospitals using conventional model surgery

PURPOSE

The aim of this study was to assess the accuracy of maxillary repositioning surgery in teaching hospitals using conventional model surgery.

MATERIALS AND METHODS

A total of 73 patients undergoing single-piece LeFort I osteotomies in the maxilla and bilateral sagittal split osteotomies in the mandible were included in the study. Preoperative and immediate postoperative cone-beam CT were compared in computer software (Dolphin3D©). Maxillary landmarks relative to the vertical and horizontal reference lines were evaluated. The difference between the planned and achieved maxillary positions was measured. Distance error in millimeters and achievement ratio (achieved displacement/planned displacement*100) were calculated for different maxillary movements.

RESULTS

Midline correction and advancement were the most accurate movements with an overall mean distance error of 0.53 mm and 0.63 mm respectively while posterior impaction and setback were the least accurate movements with 1.38 mm and 1.76 mm mean discrepancies, respectively. A significant difference was observed only in setback movement regarding the discrepancy value (P < .05). Although setback and down-graft movements tended to under-correction, all other movements were overcorrected. As the magnitude of maxillary movements increases, the accuracy decreases. In severe displacements (≥ 8 mm), the accuracy declines significantly (P < .05).

CONCLUSION

Classic cast surgery and manually fabricated intermediate splints in teaching hospitals yield accurate and acceptable results in the majority of cases (84.6%). The accuracy of maxillary repositioning decreases as the magnitude of displacement increases.

Evaluation of a Fully Digital, In-House Virtual Surgical Planning Workflow for Bimaxillary Orthognathic Surgery

BACKGROUND

The advantages of virtual surgical planning (VSP) for orthognathic surgery are clear. Previous studies have evaluated in-house VSP; however, few fully digital, in-house protocols for orthognathic surgery have been studied.

PURPOSE

The purpose of this study was to evaluate the difference between the virtual surgical plan and actual surgical outcome for orthognathic surgery using a fully digital, in-house VSP workflow.

STUDY DESIGN, SETTING, SAMPLE

This is a prospective cohort study from September 2020 to November 2022 of patients at the Victoria General Hospital in Halifax, NS, Canada who underwent bimaxillary orthognathic surgery. Patients were excluded if they had previously undergone orthognathic surgery or were diagnosed with a craniofacial syndrome.

MAIN OUTCOME VARIABLES

The primary outcome variables were the mean 3-dimensional (3D) (Euclidean) distance error, as well as mean error and mean absolute error in the transverse (x axis), vertical (y axis), and anterior-posterior (z axis) dimensions.

COVARIATES

Covariates included age, sex, and surgical sequence (mandible-first or maxilla-first).

ANALYSES

The primary outcome was tested using Z and t critical value confidence intervals. The P value was set at .05. The 3D distance error for mandible-first and maxilla-first groups was compared using a 2-sample t-test as well as analysis of variance.

RESULTS

The study sample included 52 subjects (24 males and 28 females) with a mean age of 27.7 (± 12.1) years. Forty three subjects underwent mandible-first surgery and 9 maxilla-first surgery. The mean absolute distance error was largest in the anterior-posterior dimension for all landmarks (except posterior nasal spine, left condyle, and gonion) and exceeded the threshold for clinical acceptability (2 mm) in 16 of 23 landmarks. Additionally, mean distance error in the anterior-posterior dimension was negative for all landmarks, indicating deficient movement in that direction. The effect of surgical sequence on 3D distance error was not statistically significant (P = .37).

CONCLUSION AND RELEVANCE

In general, the largest contributor to mean 3D distance error was deficient movement in the anterior-posterior direction. Otherwise, mean absolute distance error in the vertical and transverse dimensions was clinically acceptable (< 2 mm). These findings were felt to be valuable for treatment planning purposes when using a fully digital, in-house VSP workflow.

Enhancing skeletal stability and Class III correction through active orthodontist engagement in virtual surgical planning: A voxel-based 3-dimensional analysis

INTRODUCTION

Skeletal stability after bimaxillary surgical correction of Class III malocclusion was investigated through a qualitative and quantitative analysis of the maxilla and the distal and proximal mandibular segments using a 3-dimensional voxel-based superimposition among virtual surgical predictions performed by the orthodontist in close communication with the maxillofacial surgeon and 12-18 months postoperative outcomes.

METHODS

A comprehensive secondary data analysis was conducted on deidentified preoperative (1 month before surgery [T1]) and 12-18 months postoperative (midterm [T2]) cone-beam computed tomography scans, along with virtual surgical planning (VSP) data obtained by Dolphin Imaging software. The sample for the study consisted of 17 patients (mean age, 24.8 ± 3.5 years). Using 3D Slicer software, automated tools based on deep-learning approaches were used for cone-beam computed tomography orientation, registration, bone segmentation, and landmark identification. Colormaps were generated for qualitative analysis, whereas linear and angular differences between the planned (T1-VSP) and observed (T1-T2) outcomes were calculated for quantitative assessments. Statistical analysis was conducted with a significance level of α = 0.05.

RESULTS

The midterm surgical outcomes revealed a slight but significantly less maxillary advancement compared with the planned position (mean difference, 1.84 ± 1.50 mm; P = 0.004). The repositioning of the mandibular distal segment was stable, with insignificant differences in linear (T1-VSP, 1.01 ± 3.66 mm; T1-T2, 0.32 ± 4.17 mm) and angular (T1-VSP, 1.53° ± 1.60°; T1-T2, 1.54° ± 1.50°) displacements (P >0.05). The proximal segments exhibited lateral displacement within 1.5° for both the mandibular right and left ramus at T1-VSP and T1-T2 (P >0.05).

CONCLUSIONS

The analysis of fully digital planned and surgically repositioned maxilla and mandible revealed excellent precision. In the midterm surgical outcomes of maxillary advancement, a minor deviation from the planned anterior movement was observed.

Predictability of the virtual surgical plan for orthognathic surgery with the mandible surgery first sequence

The aim of this study was to compare the virtually planned position to the postoperative position of the maxilla, having performed the maxilla-first sequence or mandible-first sequence orthognathic surgery. An audit of 64 patients who underwent bimaxillary surgery between 2017 and 2020 was performed. Thirty patients had maxilla-first surgery and 34 had mandible-first surgery. The planned and post-surgical positions were analyzed using specific skeletal landmarks. Differences were calculated and the two-sample t-test was used to compare the groups. Measured differences between the planned and postoperative results differed significantly between the mandible-first and maxillary-first surgery groups (P < 0.001). The maxillary central incisors were under-advanced in the anterior-posterior direction in both groups. Most data points showed deviation from the surgical plan ≤ 2 mm and ≤ 4°. Secondarily, maxillary under-advancement in the mandible-first cohort was evaluated; these patients were subdivided into rigid and non-rigid fixation groups. The non-rigid fixation group showed less accuracy compared to the rigid fixation group, which was statistically significant (P = 0.014). The findings of this study demonstrate that virtual surgical planning can be less accurate in predicting the maxillary incisor position when performing mandible-first surgery, but this inaccuracy is within the acceptable range and can be mitigated by rigid fixation of the mandible.

PSI-Guided Mandible-First Orthognathic Surgery: Maxillo-Mandibular Position Accuracy and Vertical Dimension Adjustability

In orthognathic surgery, patient-specific osteosynthesis implants (PSIs) represent a novel approach for the reproduction of the virtual surgical planning on the patient. The aim of this study is to analyse the quality of maxillo-mandibular positioning using a hybrid mandible-first mandibular-PSI-guided procedure on twenty-two patients while the upper maxilla was fixed using manually bent stock titanium miniplates. The virtual surgical plan was used to design PSIs and positioning guides, which were then 3D printed using biocompatible materials. A Cone Beam Computed Tomography (CBCT) scan was performed one month after surgery and postoperative facial skeletal models were segmented for comparison against the surgical plan. A three-dimensional cephalometric analysis was carried out on both planned and obtained anatomies. A Spearman correlation matrix was computed on the calculated discrepancies in order to achieve a more comprehensive description of maxillo-mandibular displacement. Intraoperatively, all PSIs were successfully applied. The procedure was found to be accurate in planned maxillo-mandibular positioning reproduction, while maintaining a degree of flexibility to allow for aesthetics-based verticality correction in a pitch range between −5.31 and +1.79 mm. Such a correction did not significantly affect the achievement of planned frontal symmetry.

What Do We Know Beyond Reliability in Voxel-Based Registration? Validation of the Accuracy of Regional Voxel-Based Registration (R-VBR) Techniques for Orthognathic Surgery Analysis

PURPOSE

Despite having excellent reproducibility, the accuracy of regional voxel-based registration (R-VBR) techniques used for postoperative orthognathic surgical analysis has not been validated. The purpose of this study was to validate the accuracy of R-VBR.

METHODS

Preoperative (T0) and postoperative (T1) cone beam computed tomography (CBCT) of consecutive patients treated at a single center with nonsegmental LeFort I and bilateral sagittal split osteotomy were included. T1 CBCTs were oriented to match that of the standardized T0, and thus were assigned a known rotational transformation matrix in pitch/roll/yaw (P/R/Y), to create T1'. A copy of T1 (cT1) was made and was superimposed to T1' using R-VBR for 4 regions of interest (ROI): maxilla, distal mandible, right proximal mandible, and left proximal mandible, to create cT1'. The transformation matrix for each of the ROI was compared to those of T1' using paired t test and Bland-Altman analysis.

RESULTS

Twenty-eight eligible subjects' CBCTs were analyzed. Mean difference between T1' and cT1' ranged from -0.08 to 0.14° (maximum 0.73°), with no statistically significant differences (P = 0.216 to 1). Mean absolute difference ranged from 0.13 to 0.31° (maximum 0.73°). Bland-Altman analysis showed good agreement between T1' and cT1', indicating excellent accuracy.

CONCLUSIONS

R-VBR using the maxilla, distal mandible, and the bilateral proximal mandibular segments as ROI has excellent accuracy in terms of rotational measurements.

A Complete Digital Workflow for Planning, Simulation, and Evaluation in Orthognathic Surgery

The purpose of this study was to develop a complete digital workflow for planning, simulation, and evaluation for orthognathic surgery based on 3D digital natural head position reproduction, a cloud-based collaboration platform, and 3D landmark-based evaluation. We included 24 patients who underwent bimaxillary orthognathic surgery. Surgeons and engineers could share the massive image data immediately and conveniently and collaborate closely in surgical planning and simulation using a cloud-based platform. The digital surgical splint could be optimized for a specific patient before or after the physical fabrication of 3D printing splints through close collaboration. The surgical accuracy was evaluated comprehensively via the translational (linear) and rotational (angular) discrepancies between identical 3D landmarks on the simulation and postoperative computed tomography (CT) models. The means of the absolute linear discrepancy at eight tooth landmarks were 0.61 ± 0.55, 0.86 ± 0.68, and 1.00 ± 0.79 mm in left–right, advance–setback, and impaction–elongation directions, respectively, and 1.67 mm in the root mean square direction. The linear discrepancy in the left–right direction was significantly different from the other two directions as shown by analysis of variance (ANOVA, p < 0.05). The means of the absolute angular discrepancies were 1.43 ± 1.06°, 0.50 ± 0.31°, and 0.58 ± 0.41° in the pitch, roll, and yaw orientations, respectively. The angular discrepancy in the pitch orientation was significantly different from the other two orientations (ANOVA, p < 0.05). The complete digital workflow that we developed for orthognathic patients provides efficient and streamlined procedures for orthognathic surgery and shows high surgical accuracy with efficient image data sharing and close collaboration.

Virtual Analysis of Segmental Bimaxillary Surgery: A Validation Study

PURPOSE

Three-dimensional (3D) assessment of orthognathic surgery is often time consuming, relies on manual re-identification of anatomical landmarks or is limited to non-segmental osteotomies. The purpose of the present study was to propose and validate an automated approach for 3D assessment of the accuracy and postoperative outcome of segmental bimaxillary surgery.

METHODS

A semi-automatic approach was developed and validated for virtual surgical analysis (VSA) of segmental bimaxillary surgery using a pair of pre- and postoperative (2 weeks) cone-beam computerized tomography (CBCT) scans. The output of the VSA, the accuracy of the surgical outcome, was calculated as 3D translational and rotational differences between the planned and postoperative movements of the individual bone segments. To evaluate the reliability of the proposed VSA, intra-class correlation coefficients (ICC) were calculated at a 95% confidence interval on measurements of 2 observers. The VSA was deemed reliable if the ICC was excellent (> 0.80) and the absolute difference of the repeated intra- and inter-observer translational and rotational measurements were significantly lower (p < 0.05) than a hypothesized clinical relevant threshold of 1 voxel (0.45 mm) and 1 degree, respectively.

RESULTS

A total of 10 subjects (6 male; 4 women; mean age 24.4 years) with skeletal class 2 and 3, who underwent segmental bimaxillary surgery, 3-piece Le Fort I, bilateral sagittal split osteotomy and genioplasty, were recruited. The intra- and inter-observer reliability was excellent, ICC range [0.96 - 1.00]. The range of the mean absolute difference of the repeated intra- and inter-observer translational and rotational measurements were [0.07 mm (0.05) - 0.20 mm (0.19)] and [0.11˚ (0.08) - 0.63˚ (0.42)], respectively. This was significantly lower than the hypothesized clinical relevant thresholds (P < .001).

CONCLUSION

The validation showed that the VSA has excellent reliability for quantitative assessment of the postoperative outcome and accuracy of segmental bimaxillary surgery.

Three dimensional assessment of segmented Le Fort I osteotomy planning and follow-up: A validation study

OBJECTIVES

The planning accuracy and stability during follow-up of segmented Le Fort I osteotomy, often evaluated using 2D cephalometry and dental cast analysis, is controversial. The aim of this study is to develop and validate a 3D semi-automatic, voxel-based registration assessment protocol to evaluate planning accuracy and stability of segmented Le Fort I osteotomy with individualization of the maxillary segments.

METHODS

Preoperative, immediate postoperative and six months postoperative CBCT images were used to evaluate accuracy and stability of the individual segments in 20 patients (13 female; 7 male) who underwent segmented Le Fort I osteotomy. Three translational (left/right, intrusion/extrusion, anterior/posterior) and three rotational (pitch, roll, yaw) dimensions were calculated for each maxillary segment by means of a user-friendly module. Inter- and intra-observer Inter Class Coefficient (ICC) and mean absolute difference (MAD) were calculated.

RESULTS

The inter- and intra-observer reliability ICC varied between 0.93 and 0.99 for the translational and rotational accuracy and stability assessments, indicating excellent reliability. The MAD ranged between 0.21 mm and 0.32 mm for the translational error and between 0.6° and 0.9° for the rotational dimension.

CONCLUSIONS

The 3D assessment protocol for accuracy of segmented Le Fort I planning and short-term follow-up, proved to have high reliability with only a small margin of error.

CLINICAL SIGNIFICANCE

The proposed 3D assessment protocol allows future in-depth analysis of segmented Le Fort I osteotomy and might implicate future improvement where necessary.

Three-dimensional surgical accuracy between virtually planned and actual surgical movements of the maxilla in two-jaw orthognathic surgery

Objective

To investigate the three-dimensional (3D) surgical accuracy between virtually planned and actual surgical movements (SM) of the maxilla in two-jaw orthognathic surgery.

Methods

The sample consisted of 15 skeletal Class III patients who underwent two-jaw orthognathic surgery performed by a single surgeon using a virtual surgical simulation (VSS) software. The 3D cone-beam computed tomography (CBCT) images were obtained before (T0) and after surgery (T1). After merging the dental cast image onto the T0 CBCT image, VSS was performed. SM were classified into midline correction (anterior and posterior), advancement, setback, anterior elongation, and impaction (total and posterior). The landmarks were the midpoint between the central incisors, the mesiobuccal cusp tip (MBCT) of both first molars, and the midpoint of the two MBCTs. The amount and direction of SM by VSS and actual surgery were measured using 3D coordinates of the landmarks. Discrepancies less than 1 mm between VSS and T1 landmarks indicated a precise outcome. The surgical achievement percentage (SAP, [amount of movement in actual surgery/amount of movement in VSS] × 100) (%) and precision percentage (PP, [number of patients with precise outcome/number of total patients] × 100) (%) were compared among SM types using Fisher’s exact and Kruskal–Wallis tests.

Results

Overall mean discrepancy between VSS and actual surgery, SAP, and PP were 0.13 mm, 89.9%, and 68.3%, respectively. There was no significant difference in the SAP and PP values among the seven SM types (all p > 0.05).

Conclusions

VSS could be considered as an effective tool for increasing surgical accuracy.