Refined intraoperative repositioning of the osteotomized maxilla in relation to the skull and TMJ

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.

The use of virtual surgical planning and navigation in the treatment of orbital trauma

Virtual surgical planning (VSP) has recently been introduced in craniomaxillofacial surgery with the goal of improving efficiency and precision for complex surgical operations. Among many indications, VSP can also be applied for the treatment of congenital and acquired craniofacial defects, including orbital fractures. VSP permits the surgeon to visualize the complex anatomy of craniofacial region, showing the relationship between bone and neurovascular structures. It can be used to design and print using three-dimensional (3D) printing technology and customized surgical models. Additionally, intraoperative navigation may be useful as an aid in performing the surgery. Navigation is useful for both the surgical dissection as well as to confirm the placement of the implant. Navigation has been found to be especially useful for orbit and sinus surgery. The present paper reports a case describing the use of VSP and computerized navigation for the reconstruction of a large orbital floor defect with a custom implant.

The accuracy of two-dimensional planning for routine orthognathic surgery

Two-dimensional cephalometric planning software should be helpful for prediction of hard tissue outcome after bilateral sagittal split ramus osteotomy (BSSRO) or bimaxillary osteotomy, but transferring two-dimensional data to three-dimensions (including mock operation and surgery) may result in errors. The objective of this retrospective study was to analyze deviations between predicted results and postoperative outcome using cephalometric analyses, and to evaluate this procedure for daily use. Fifty-four subjects (mean (SD) age 26 (8) years) had a BSSRO (n=21) alone or in combination with Le Fort I osteotomy (n=33). Predictions were made for each case by cephalometric planning software and mock operations done with study models. Postoperative cephalograms were obtained after 14 days and compared with predicted cephalograms for sagittal (SNA, SNB, ANB,) and vertical (ArMeGo, ML-NSL, NL-NSL) measurements. Mean (SD) differences for all measurements varied between 1.3 degrees (1.1 degrees) and 2.2 degrees (1.6 degrees) for BSSRO; and between 1.1 degrees (1.3 degrees) and 2.2 degrees (1.6 degrees) for bimaxillary osteotomy. There were no significant differences between measurements or operations, indicating that the predictions were accurate. A difference of up to 8.5 degrees could be measured in a single case. Cephalometric prediction therefore remains an accurate tool for planning, particularly maxillary rearrangement in the vertical and sagittal dimension for routine operations. If greater shifts in the transversal dimension are necessary, exact planning should be adapted with three-dimensional planning devices to avoid significant differences.

Accuracy of maxillary positioning in bimaxillary surgery

The aim of the study was to investigate the accuracy of a modified pin system for the vertical control of maxillary repositioning in bimaxillary osteotomies. The preoperative cephalograms of 239 consecutive patients who were to have bimaxillary osteotomies were superimposed on the postoperative films. Planned and observed vertical and horizontal movements of the upper incisor were analysed statistically. The mean deviations of -0.07 mm (95% confidence intervals (CIs) -0.17 to 0.04 mm) for the vertical movement and 0.12 mm (95% CI -0.06 to 0.30 mm) for the horizontal movement did not differ significantly from zero. Comparison of the two variances between intrusion and extrusion of the maxilla did not differ significantly either (p=0.51). These results suggest that the modified pin system for vertical control combined with interocclusal splints provides accurate vertical positioning of the anterior maxilla in orthognathic surgery.

Computer-Assisted Condyle Positioning in Orthognathic Surgery

PURPOSE

Le Fort I repositioning osteotomy can affect the position of the temporomandibular joints (TMJs). During the operation, the surgeon does not have direct visual control of the TMJ. In this study, the TMJ movements in patients undergoing a Le Fort I repositioning osteotomy were recorded intraoperatively using the Surgical Segment Navigator (SSN) computer-assisted navigation system.

PATIENTS AND METHODS

Unintended TMJ positions resulting from conventional repositioning of the maxillary segment were recorded. The TMJ positions in these patients were then corrected in relation to the skull base, using information obtained from the SSN. The position of the condyle was then redetermined. The accuracy of conventional and SSN-guided segment adjustments were compared in terms of their influence on TMJ position in the same group of patients.

RESULTS

The median spacial malposition of the condyles without navigation was 2.4 mm. Corrective "SSN positioning" on the same patients reduced this to 0.7 mm.

CONCLUSIONS

SSN allows accurate intraoperative navigation of the TMJ.

Prediction Accuracy of Computer-Assisted Surgical Visual Treatment Objectives as Compared With Conventional Visual Treatment Objectives

PURPOSE

This present study used the conventional visualized treatment objectives (VTOs) as a tool to evaluate the predictive value of the Dolphin computer-assisted VTOs.

MATERIALS AND METHODS

Presurgical cephalometric tracing predictions generated by oral and maxillofacial surgeons and the Dolphin Imaging software were compared with the postsurgical outcome as seen on lateral cephalometric tracings. Sixteen measurements of the predicted and actual postsurgical hard tissue landmarks were compared statistically.

RESULTS

A paired Student's t test showed that 7 measurements had statistically significant differences for the conventional VTOs (facial angle, P < .0001; AOC, P < .0001; SNB, P = .003; ANB, P = .004; U1-NA-degrees, P = .01; U1-NA-mm, P = .02; and N perp Pog, P < .0001), while 9 measurements were statistically significant ( P = <.0001) for Dolphin (facial angle, P = .0001; AOC, P = .005; SNB, P = .001; ANB, I = .04; U1-NA-degrees, P = .003; PogNB, P = .04; U1-NA-mm, P = .002; N perp Pog, P = .0001; UFH, P = .03; and LFH, P = .03).

CONCLUSION

From these data, it appears that both VTOs demonstrated good predictive comparative outcome and are equally precise.

Comparison of the predicted surgical results following virtual planning with those actually achieved following bimaxillary operation of dysgnathia

AIM

To simulate the surgery of dysgnathia, several forms of computer software allowing two-dimensional 'virtual' planning are frequently used. However, in many cases it is not possible to transfer the virtual plan accurately to the surgical site. It is the purpose of this study to find the errors likely to occur when transferring the data.

METHODS

In 22 bimaxillary osteotomies for dysgnathia, the results of preoperative planning were compared with the surgical outcomes. The programme WinCeph 4.19 (Compudent) was used for cephalometric analyses and simulation of the operations.

RESULTS

Six major skeletal parameters were evaluated when comparing both the planned and the actual outcome, and the following results were recorded: Delta-SNA 1.53 degrees (+/-1.20), Delta-SNB 1.67 degrees (+/-1.29), Delta-ANB 1.62 degrees (+/-1.47), Delta-NL-NSL 3.9 degrees (+/-2.30), Delta-ML-NSL 3.6 degrees (+/-3.7) and Delta-ArGoMe 6.1 degrees (+/-4.6).

CONCLUSION

It was anticipated that the most important differences between planned and surgical outcomes were found to be in the vertical changes. Planning and data transfer was comparatively accurate with regard to sagittal data. Apart from several mechanical methods for data transfer, systems using navigation are therefore being discussed and used increasingly. They ensure accurate data transfer to the surgical site.

Indications to the use of condylar repositioning devices in the surgical treatment of dental-skeletal class III

PURPOSE

The aim of this report was to compare the clinical and radiographic findings observed at the 12-month follow-up in 2 groups of 15 patients who underwent Le Fort I and bilateral sagittal split osteotomy for the correction of dental-skeletal Class III. In the first group, the condylar positioning devices were used, whereas in the second group, an alternative method was used for the intraoperative assessment of mandibular repositioning.

MATERIALS AND METHODS

All of the patients of our study in the immediate presurgical period were without temporomandibular joint disorders and with a normal anatomic relationship between condyle and fossae. The condyle position and morphology were examined at the 12-month follow-up through cephalometric measurements and the postsurgical findings in both groups were compared with those observed in the presurgical period.

RESULTS

In all of the 30 patients in our study, no relapse or postsurgical temporomandibular joint disturbance was observed at the 12-month follow-up. Variations in condyle position of more than 2 mm or 2 degrees were not observed in the 15 patients treated with condylar positioning devices. Changes in condyle position between 2 and 4 mm and 2 degrees and 4 degrees were observed in 6 of the 15 patients treated without the devices.

CONCLUSIONS

The use of condylar positioning devices can be avoided in patients with dental-skeletal Class III without presurgical temporomandibular dysfunction. The manual positioning of the mandibular condyle is easier, but it requires the utmost care and an experienced operator.

Reproducibility of maxillary positioning in Le Fort I osteotomy: a 3-dimensional evaluation

PURPOSE

In the present study, we evaluated the difference between the model surgery movement and the actual surgical movement in the horizontal (X), vertical (Y), and transverse (Z) directions using the same reference coordinates.

PATIENTS AND METHODS

Twelve patients (6 male and 6 female, mean age of 24.3 years) who underwent Le Fort I osteotomy and sagittal split ramus osteotomy were included in the study. The maxillary position was controlled by an intermediate splint and face-bow/bite-fork combination system. A coordinate transformation system with transition matrices was developed, which enabled objective comparison between the planned surgical change of the maxilla on the articulator and the actual surgical change assessed by the 3-dimensional cephalogram.

RESULTS

The absolute mean difference was 2.2 mm. The difference between the model surgery and the surgical result ranged from -7.7 mm to 6.6 mm. The surgical result differed from the planned surgical movement by more than 2 mm in more than 45% of the measured coordinate values.

CONCLUSION

Although all of the patients were satisfied with their postsurgical appearance and occlusion, the result shows that further development is required in the maxillary positioning system.

A radiographic analysis of computer prediction in conjunction with orthognathic surgery

This retrospective study analysed the accuracy and reliability of predictions generated in patients treated with orthognathic surgery by comparing Quick Ceph Image software (Quick Ceph Image Pro version 3.0) predictions with post-surgical lateral cephalographs. Pre- and post-surgical lateral cephalographs of 28 adult patients (12 males and 16 females) were scanned into the computer and 28 landmarks were identified and digitized. Digitization error was assessed from repeated digitization. Fourteen measurements of the predicted and actual postsurgical hard tissue landmarks were compared using Student's t-test. Results showed a good correlation between repeated digitization for all measurements. Student's t-test indicated that 10 of the 14 measurements showed no statistically significant differences. Only the ANB (P=0.008), FMA (P=0.001), SN-Mxl (P=0.03) and Wit's (P=0.0001) showed statistically significant differences between the predicted and actual measurements. However only the Wit's showed clinical significant differences between the two measurements. Caution still must remain as the surgeon may not achieve his planned position in an individual patient. In some cultures there may also be medico-legal implications of these predictions.

Surgical accuracy in Le Fort I maxillary osteotomies

The surgical outcome of planned movements of Le Fort I osteotomies is dependent on the surgeon's ability to achieve such movements intraoperatively. Our aim was to assess the surgical accuracy achieved for 30 consecutive patients undergoing Le Fort I osteotomies treated by one maxillofacial surgeon and his team.

METHOD

Intraoperative control of the mobilized maxilla vertically was achieved by a combination of a nasion screw as the external reference point and bony marks above and below the osteotomy cuts intraorally. Movements horizontally and transversely were controlled with occlusal wafers. The surgical accuracy of maxillary movements vertically and horizontally (anteroposteriorly) were assessed by standard lateral cephalometric tracings of radiographs taken within two weeks prior to operation and 48 hours afterwards. Audit targets were arbitrarily set to be satisfactory when the difference between planned movements and actual movements as measured on the cephalometric tracings were 2 mm or less.

RESULTS

The mean (SD) difference from planned vertical movements of the anterior maxilla was 0.37 mm (SD 0.64) and horizontal movements 0.85 mm (SD 0.91). Ninety-seven percent (29/30) of anterior maxillary movements in the vertical dimension, 90% (27/30) of anterior maxillary movements in the horizontal dimension and 87% (26/30) of movements in both dimensions had a difference of 2 mm or less. These results were comparable with the reported 'gold standard'.

CONCLUSION

Good surgical accuracy in positioning the mobilized maxilla in Le Fort I osteotomies can be achieved with the use of external and internal reference points.

Stability of simultaneous maxillary and mandibular osteotomy for treatment of class III malocclusion: an analysis of three-dimensional cephalograms

PURPOSE

The current investigation was undertaken to study the three-dimensional (3-D) stability of simultaneous maxillary advancement and mandibular setback using rigid fixation. The study also aimed to analyse the factors involved in postsurgical relapse by evaluation of changes in various parameters.

PATIENTS

Twenty-five cases were evaluated of simultaneous Le Fort I maxillary advancement and mandibular setback using rigid fixation.

METHODS

Preoperative, immediate and 6-month postoperative skeletal and dental changes were analysed using 3-D cephalograms obtained from biplanar stereoradiography. Maxillary fixation screws were used as landmarks to evaluate postoperative stability.

RESULTS

The mean maxillary advancement was 3.7 mm. Relapse in the sagittal, vertical, and transverse planes was not detectable in the maxilla (p > 0.05). However, for an average mandibular setback of 5.7 mm, mean mandibular relapse was 1.1 mm or 19.3% anteriorly (p < 0.05). Surgical or postsurgical skeletal changes in the maxilla had no detectable influence on mandibular relapse (p > 0.05). Vertical alterations of the facial skeleton achieved surgically predicted the mandibular relapse (R2 = 0.27, p < 0.05).

CONCLUSION

Maxillary advancement and vertical changes of +/- 2 mm did not influence the postoperative stability of the mandible. Relapse of the mandible seems to be influenced mainly by the amount and direction of the surgical alteration of mandibular position.

Computerized cephalometric evaluation of orthognathic surgical precision and stability in relation to maxillary superior repositioning combined with mandibular advancement or setback

PURPOSE

A computerized, cephalometric, orthognathic surgical program (TIOPS) was applied in orthognathic surgical simulation, treatment planning, and postoperatively to assess precision and stability of bimaxillary orthognathic surgery.

PATIENTS AND METHODS

Forty consecutive patients with dentofacial deformities requiring bimaxillary orthognathic surgery with maxillary superior repositioning combined with mandibular advancement or setback were included. All patients were managed with rigid internal fixation (RIF) of the maxilla and mandible and without maxillomandibular fixation (MMF). Preoperative cephalograms were analyzed and treatment plans produced by computerized surgical simulation. Planned, 5-week postoperative and 1-year postoperative maxillary and mandibular cephalometric-positions were compared.

RESULTS

In the mandibular advancement group, the anterior maxilla was placed too far superiorly, with an inaccuracy of 0.4 mm. The posterior maxilla and the anterior mandible were placed in the planned positions. The lower posterior part of the mandibular ramus was placed too far anteriorly, with an inaccuracy of 2.0 mm. However, the mandibular condyles were accurately placed. In the setback group, the anterior maxilla was placed too far superiorly and posteriorly, with a vertical and sagittal inaccuracy of 1.0 mm and 0.7 mm, respectively. The posterior part of the maxilla was placed in a posterior position with an inaccuracy of 1.9 mm. The anterior mandible was placed too far anteriorly with an inaccuracy of 0.9 mm. The lower posterior part of the mandibular ramus was placed in a posterior position with an inaccuracy of 0.9 mm. However, the mandibular condyles were accurately placed. The statistical analysis of the 1-year stability data showed that the maxilla had moved 0.3 mm posteriorly in the advancement group and the lower incisors had moved 0.8 mm superiorly. No other significant positional maxillary or mandibular changes were found. In the setback group, the maxilla had moved 0.5 mm posteriorly, the anterior mandible 0.5 mm anteriorly, and the lower incisors 0.7 mm superiorly. No significant positional changes were seen in the mandibular ramus.

CONCLUSION

The TIOPS computerized, cephalometric, orthognathic program is useful in orthognathic surgical simulation, planning, and prediction, and in postoperative evaluation of surgical precision and stability. The simulated treatment plan can be transferred to model surgery and finally to the orthognathic surgical procedures. The results show that this technique yields acceptable postoperative precision and stability.

Two-step repositioning of the maxilla in bimaxillary orthognathic surgery

A two-step repositioning system in bimaxillary osteotomies, a combination of a modified face-bow transfer and the use of an occlusal plane indicator is described. With this system, the risks involved in depending solely on reproduction of the model-constructed position can be avoided.

Maintenance of the preoperative condyle position in orthognathic surgery

A bimaxillary osteotomy for mandibular prognathism and maxillary retrognathia was performed on 30 patients with an Angle Class III malocclusion. The Luhr condylar positioning device was used intraoperatively to reproduce the condylar position. Pre- and postoperative condylar positions were compared by recording joint movements with axiography. Steps, jags and jumps as symptoms of pathological joint function could not be identified. Only in one case could a pathological shortening of the joint track length be measured. This suggests that the Luhr device is effective in securing condyle position and therefore temporomandibular joint (TMJ) function. Pre- and postoperative axiography is an adequate method of controlling these results and a helpful supplement to the armentarium of orthognathic surgery.

An investigation into the accuracy and validity of three points used in the assessment of autorotation in orthognathic surgery

OBJECTIVE

To assess the accuracy and validity of three points used in the cephalometric assessment of autorotation in orthognathic surgery.

DESIGN

A retrospective study of 15 cases of maxillary surgery.

SETTING

A postgraduate dental hospital in London.

SUBJECT

Fifteen well-documented cases of maxillary surgery with mandibular autorotation, treated by a single surgical, team were examined. Cephalometric surgical predictions were prepared, using the planned surgical movements, incorporating three different points advocated as centres of mandibular autorotation, for each case. These predictions were compared with the results achieved at surgery.

MAIN OUTCOME MEASURES

The discrepancy between the predictions and the surgical result in each case was measured and subjected to statistical analysis. The method error was assessed and considered with the measured discrepancy.

RESULTS

Individual variation was seen, both between the individual landmarks and the individual cases studied. The discrepancies measured were broadly similar for each of the centres of autorotation. Statistical analysis failed to show any significant differences between the points studied.

CONCLUSION

All 3 points of autorotation examined will approximate mandibular autorotation following maxillary surgery and all can be considered equally valid.

Precision of orthognathic surgery. A computerized cephalometric analysis of 27 patients

The precision of orthognathic surgery was evaluated in 27 patients. Rigid internal skeletal fixation was used without intermaxillary fixation. A computerized cephalometric program package (TIOPS) was utilized in the preoperative analysis, surgical planning, and postoperative examination. The mean positional difference of the cephalometric landmarks between planned and observed outcome ranged from -0.4 to 0.7 mm. Only one reference point (pm) differed statistically significantly from the plan (P = 0.02). All other mean differences in point location were of a magnitude that was not statistically different from zero (P > 0.05). It was concluded that no systematic sources of error could be demonstrated. However, the range of random variation in the individual cases left room for considerable improvement.

Control of vertical dimension during maxillary orthognathic surgery. A clinical trial comparing internal and external fixed reference points

The accuracy of vertical control during maxillary orthognathic surgery was assessed in 45 patients, comparing the use of traditional internal measurements across the osteotomy lines (15 subjects) with measurements between the incisor teeth and an external reference point consisting of a bone screw placed at nasion (two groups of 15 subjects each). Although use of a fixed external reference point can significantly decrease positioning error (p < 0.001), considerable care is required during application of rigid fixation to maintain the correct vertical dimension.

Computerized cephalometric orthognathic surgical simulation, prediction and postoperative evaluation of precision

A new computerized, cephalometric, orthognathic surgical program (TIOPS) has been evaluated in surgical simulation, prediction and postoperative assessment of precision. Records of 10 consecutive patients admitted for orthognathic surgical treatment were analysed and prediction plans produced by computerized surgical simulation. Predicted and postoperative positions of maxilla and mandible were compared with linear and angular measurements. No statistically significant differences between predicted and postoperative positions could be demonstrated (p greater than 0.05).

Three-dimensional craniofacial surgery: transfer from a three-dimensional model (Endoplan) to clinical surgery: a new technique (Graz)

A new technique of individual, three-dimensional (3-D) planning and transferring this to craniofacial operations is reported. The combination of an individual model of the skull of the patient with a transfer device enables planning of real 3-D surgery. The surgical technique is demonstrated in a case with an asymmetrical midface and mandible after ankylosis of the TMJ in childhood.

The significance of an erroneous recording of the centre of mandibular rotation in orthognathic surgery

The effect of post-operative jaw position of an error in locating the true centre of mandibular rotation was evaluated using a computer-simulation model and a mock surgery model. The centre of the condyle serves as a reference point in surgical procedures involving the maxilla. The purpose of this study was to describe the amount of malpositioning of the jaws at surgery due to a discrepancy between a simulated true centre of rotation and the centre of the condyle. The results showed, that a 20 mm error in location of the true centre of rotation could result in a 3 mm horizontal malpositioning of the maxilla.