Accuracy of model surgery: evaluation of an old technique and introduction of a new one.

This article evaluates the ability of 4th-year residents to accurately perform maxillary model surgical repositioning in the conventional manner. Using a special model surgery--measuring platform, measurements of the maxillary dental casts were recorded before and after model surgery was performed by residents in 20 bimaxillary cases. The model surgery was performed in the usual manner described in several texts, using reference lines scored on the casts and measurements made to the incisal pin and upper member of the articulator. Analysis of the differences between the planned movements and the postsurgical position of the maxillary model surgery casts showed statistically significant errors in maxillary repositioning for all measures. This indicates that the manner in which model surgery was performed by the residents, as reported in the literature, was inaccurate. A new technique and instrument for more accurately recording measurements and repositioning the maxillary cast is introduced.     

Accuracy of virtual surgical planning in bimaxillary orthognathic surgery with mandible first sequence: A retrospective study

The aim of this study was to verify treatment accuracy using virtual surgical planning (VSP) with a mandible-first sequence and strict surgical protocol to determine what surgical and methodological factors might influence outcomes.VSP transfer accuracy was evaluated retrospectively through a modified method involving voxel-based superimposition in patients who had undergone bimaxillary surgery with a mandible-first sequence to correct dentoskeletal deformities. Data analysis showed that the movements planned and those executed were substantially equivalent (p < 0.01), with the exception of mandibular and maxillary sagittal movements that were 0.72 ± 0.90 mm and 1.41 ± 1.04 mm smaller, respectively, than planned.This study showed that a mandible-first sequence is accurate for transferring virtual surgical planning intraoperatively. There are several factors involved in the proper transfer of virtual planning beyond the software, such as surgical technique and sequencing. Inaccurate sagittal movements and maxillary repositioning seem to depend mainly on surgical factors.     

The accuracy of maxillary positioning using digital model planning and 3D printed wafers in bimaxillary orthognathic surgery

Objective: Orthognathic wafers may be made using digital model movements and CAD-CAM technology. This paper analysed the accuracy of maxillary movements using this new process.

Design: Retrospective study of pre and post-operative cephalograms.

Participants: Thirty consecutive orthognathic patients undergoing bimaxillary osteotomies in a UK hospital.

Methods: Jaw movements were planned using cephalometric and Orthoanalyzer? software. The resultant intermediate and final wafer occlusal relationships were used for wafer fabrication by 3D printing of the inter-occlusal space. Pre- and post-operative lateral cephalograms were compared in terms of maxillary antero-posterior and vertical movements. Statistical analyses including the paired t-test, two-sample t-test and Fisher’s exact test.

Results: Wide individual variation was observed between the planned and actual movements. Thirteen cases (43%) had a 2 mm discrepancy in at least one variable. Statistically significant differences between the planned and actual maxillary vertical movements were observed for the molar (U6y: p < 0.0001) and anterior maxillary (Ay: p < 0.01) differences. Analysis of a subgroup with primarily impaction movements demonstrated a statistically significant bias towards excessive maxillary advancement (U1x: p < 0.01) and incisor impaction (U1y: p < 0.01) in this group.

Conclusions: This new digital surgical wafer technique achieves a similar level of accuracy to the conventional facebow and model surgery process.     

Accuracy of maxillary repositioning in two-jaw surgery with conventional articulator model surgery versus virtual model surgery

The purpose of this study was to compare the accuracy of maxillary repositioning using the recently introduced computerized virtual model surgery (VMS) with conventional articulator model surgery (AMS). Forty-two patients who had undergone bimaxillary surgery were investigated retrospectively in this study. The patients were divided into two groups: conventional AMS (n = 23) and VMS (n = 19) for intermediate splint fabrication in maxillary positioning. Planned surgical movements and actual postsurgical changes of the lateral and frontal cephalometric measurements were compared. Although variations from the planned surgical movements were relatively small, both methods had statistically significant errors in some of the linear measurements. Both groups had a similar range of errors. The overall absolute mean discrepancy between the planned and actual surgical movements for the linear measurements was 1.17 mm (0–3.6 mm) in AMS and 0.95 mm (0–3.2 mm) in VMS. Of the total measurements, measurements reflecting a surgical discrepancy of more than 2 mm or 2° comprised 12.0% of the cases in AMS and 7.9% in VMS. The surgical accuracy of maxillary positioning with VMS was comparable to conventional AMS. Because VMS has the definitive advantage of eliminating the complex laboratory step and shortening the laboratory time, this can be accepted as an alternative to AMS.     

How accurate is digital-assisted Le Fort I maxillary osteotomy? A three-dimensional perspective

The aim of this study was to evaluate the surgical accuracy of Le Fort I surgery compared to the three-dimensional (3D) virtual planning. Fifty-five patients (29 males, 26 females; age range 15–58 years) with skeletal class III malocclusion, who underwent bimaxillary surgery were included. A validated 3D accuracy assessment tool was utilized to assess the surgical accuracy of the maxillary positioning. For translational movements, the least amount of error was associated with mediolateral translation, whereas the surgical accuracy for anteroposterior and superoinferior translation showed a tendency towards a more posterior and inferior positioning of the maxilla compared to the planning. For rotational movements, the highest discrepancy was observed for pitch. Linear regression showed increased inaccuracy with increasing advancement for anteroposterior, superoinferior and pitch movements. To conclude, 3D virtual planning of maxilla was generally accurate when compared to achieved outcome for skeletal class III patients undergoing bimaxillary surgery.     

Wafer as an adjunct to plating patient-specific implants for the multi-segment maxilla: a useful tool

Virtual surgical planning for orthognathic surgery using patient-specific implants (PSI) is usually waferless nowadays. However, without an occlusal wafer, difficulties arise in controlling the accuracy of multi-segment maxillary osteotomies, especially for expansion and rotational movements of each segment. It is technically challenging intraoperatively to manipulate multiple segments to fit into the PSI, as the relatively small bone segments need to be secured into the PSI while simultaneously achieving individual segment movements in all planes and with potential bony interferences with each other. Therefore, the use of a maxillary tooth-supported surgical guide is proposed and described. When the guide is inserted before the PSI, it overcomes difficulties in handling multiple maxillary segments and facilitates achieving maximal positional precision of each individual bone segment. The guide enables multiple smaller segments to behave as one unit with the designated occlusion whilst visualizing bony interferences before PSI plating is commenced. Adding a tooth-borne surgical guide in the form of a wafer and a customized arch bar is a cost-effective method to enhance accuracy in virtually planned multi-segment maxillary surgery. Further investigations are required to validate the accuracy and advantages of using wafers and PSI in multi-segment maxillary and mandibular orthognathic surgeries.     

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.     

Does a learning curve exist for accuracy in three-dimensional planning for maxillary positioning in bimaxillary orthognathic surgery?

The purpose of this study was to investigate the influence of time, and experience, on the accuracy of maxillary repositioning in bimaxillary orthognathic surgery performed using virtual surgical planning (VSP). Patients who had undergone bimaxillary orthognathic surgery were reviewed. Maxillary position on pre- and postoperative computed tomography scans was compared. The patients were divided into groups according to the year in which VSP was performed and surgery completed. Linear distances between upper jaw reference landmarks were measured in all three planes of space to determine accuracy between the preoperative VSP and the surgical outcome at various time points. One hundred subjects met the eligibility criteria for assessment and were allocated to groups: 2013 (n = 10), 2014 (n = 17), 2015 (n = 39), 2016 (n = 20), and 2017 (n = 14). Overall, the results demonstrated improved precision in maxillary position over the years, with more accurate results in patients who underwent surgery in 2015, 2016, and 2017. Mean linear differences between planned and obtained results demonstrated more accurate results in the horizontal direction, followed by transverse and vertical directions. An overall average difference within 1 mm was observed for 51.3% of the measurements included in the sample group. Time, and surgeon experience, can influence the accuracy of maxillary positioning in bimaxillary orthognathic surgery.     

Predictability of maxillary repositioning during bimaxillary surgery: accuracy of a new technique

The purpose of this retrospective study was to evaluate the predictability of maxillary repositioning following Le Fort I osteotomy during bimaxillary surgery using a new technique with splints to reposition the maxilla in the three planes of space. In order to assess the accuracy of horizontal and vertical maxillary movements of the maxilla, 32 consecutive patients who underwent bimaxillary surgery had their predictive tracings and model surgery measures compared to postoperative cephalograms taken 1 week after surgery. There was a strong positive correlation between model surgery and postoperative result: 53% of horizontal movements and 41% of vertical movements showed less than 0.2 mm variation. When predictive tracings were compared to postoperative results 44% of horizontal and 50% of vertical movements showed less than 0.2 mm variation. There was no significant difference (P>0.05) between the planned and actual maxillary positions in the sample evaluated. This technique for maxillary repositioning during two-jaw surgery proved to be effective and predictable, with strong agreement between predictive tracings, model surgery and postoperative results.     

Improving accuracy of the intermediate splint in substantial intermaxillary sagittal discrepancies using an extra anterior anchorage point: technical note

Background To describe a technical feature that increases the stability of the intermediate splint in patients where bimaxillary surgery with great maxillary/mandibular advancements are planned. Material and Methods Prospective evaluation of the intermediate splint dental vertical penetration in patients undergoing bimaxillary surgery where great sagittal discrepancy occur in the anterior sector between the upper and lower jaws when the intermediate splint is placed by adding an extra intermaxillary fixation (IMF) screw (2x9 mm) placed between the central incisors of the maxilla and fixed to the most anterior aspect of the intermediate splint following the direction of the sagittal maxillo-mandibular discrepancy from January to September 2018. Results The postoperative evaluation comparing the accuracy of conventional fixation versus fixation with an extra anterior anchorage point through photographic assessment and intraoral digital scanner demonstrated better dental penetration, and therefore improved intermediate splint precision with the latter in all cases Conclusions Our results suggest that this is a simple and safe technique that can be easily reproduced and optimizes the outcomes by increasing the accuracy of translation of the planned surgical movements to the operating room. Key words:Orthognathic surgery, intermediate splint, accuracy, intermaxillary fixation, bone screw.     

Reliability of bimaxillary surgical planning with the 3-D orthognathic surgery simulator

Functional and esthetic dysgnathia surgery requires accurate planning and precise surgical technique. Programs that simulate such surgery have thus become increasingly important. These are useless, however, when there is no technique for reproduction of surgical planning in the patient. This can be mediated by a surgical model. The present study investigates the accuracy resulting from use of the 3-D orthognathic surgery simulator (3-D OSS) in reproducing planned patient treatment. Eighteen patients with Angle Class III malocclusions who required bimaxillary surgery were evaluated. Planning criteria depended on the orthognathically intended occlusion and the jaw position simulated in the dentofacial planner, which predicted a harmonious profile. Model planning was carried out in the 3-D OSS. The accuracy of surgical reproduction was determined by cephalometric comparison of the postoperative cephalograms and computer simulation images. There were horizontal repositioning errors of 0.61 +/- 0.45 mm to 0.78 +/- 0.52 mm at the maxillary reference points (posterior nasal spine, anterior nasal spine, point A, and incision superius). Analysis of the positioning precision attained vertically was of the same order of magnitude, with values between 0.57 +/- 0.46 mm and 0.85 +/- 0.71 mm. Less precision was achieved in the mandible. The mean horizontal variation observed at incision inferius (0.91 +/- 0.51 mm) was still within the range of values for the maxilla, but an increase in the error to 1.61 +/- 0.79 mm was registered caudally to menton. The attained position of the maxilla did not vary significantly from the planned position (P < or = 0.05). Use of the orthognathic surgery simulator allowed precise implementation of the planned surgery. The model planning proved to be very helpful in preparing difficult bimaxillary operations.     

The validity of a computer-assisted simulation system for orthognathic surgery (CASSOS) for planning the surgical correction of class III skeletal deformities: single-jaw versus bimaxillary surgery

The aim of this study was to assess the accuracy of the two-dimensional profile prediction produced by the computer-assisted simulation system for orthognathic surgery (CASSOS), for the correction of class III facial deformities. Correction was by maxillary advancement (n=17) or bimaxillary surgery (n=16). The mean age was 24 years (range 18-42). The surgical and dental movements obtained from the postoperative cephalogram were used to produce a CASSOS profile prediction, which was compared with the soft-tissue profile. The prediction was superimposed onto the postoperative radiograph, and a coordinate system was used to measure linear differences. For the maxillary advancement group there were statistical differences for three horizontal landmarks: superior labial sulcus (p=0.017), labrale superious (p=0.038) and labiomental fold (p=0.014). In the bimaxillary group only the landmark vertical labrale superious (p=0.002) showed a statistical difference. Generally, CASSOS produced useful profile predictions for maxillary advancement surgery or bimaxillary surgery for Class III patients, although there was considerable individual variation. The main areas of inaccuracy were the lips. The major difference between the two types of surgery was that most of the errors in the maxillary surgery group were in the horizontal direction, whilst for the bimaxillary surgery the errors were mainly in the vertical direction.     

Use of articulators in the United Kingdom by consultant orthodontists in planning orthognathic surgery

This questionnaire survey aimed to investigate articulator use in orthognathic surgical planning by consultant specialists in the United Kingdom (UK). A total of 205 questionnaires was sent to all consultant orthodontists in the UK. One hundred thirty questionnaires were completed, representing a 63.4% response rate. Consultants had been in their post for a median of 10.5 years (range 0 to 30 years) with a mean of 11.3 (SD 8.4) surgical cases per year. When asked which cases had been planned on a semiadjustable articulator, two thirds of consultants (67.7%) planned maxillary single-jaw procedures, 45.4% planned mandibular single-jaw procedures, and 77.7% planned bimaxillary procedures. While 98.5% of consultants reported access to at least one type of articulator, 14.6% of maxillary single-jaw and 5.4% of bimaxillary surgery was not planned on any articulator. Twice as many consultants who had been in their post fewer than 11 years had been trained on a semiadjustable articulator, compared to those who had more than 11 years of experience. Semiadjustable articulators were the most popular for planning orthognathic surgery. Consultants with less than 11 years of experience completed more surgical cases each year and were more likely to have been trained on a semiadjustable articulator than consultants with more than 11 years of experience. However, no link exists between the age of the consultant and the type of articulator selected for planning; this suggests that more mature consultants have received further training on contemporary articulator systems since receiving their accreditation.     

The role of anterior segmental osteotomies in orthognathic surgery for protrusive faces in a Southeast Asian population: 10-year retrospective data of 51 patients treated in a single centre

Bimaxillary protrusion is a dentofacial deformity common in the East Asian population. It is often difficult to decide between orthodontic and surgical retraction to treat patients with bimaxillary protrusion, especially if surgery to correct skeletal base discrepancies is also required. The objective of this study was to investigate the treatment outcomes of surgical versus orthodontic retraction in patients with bimaxillary protrusion undergoing orthognathic surgery. A retrospective cohort study was conducted, where the medical records and radiographs of 51 patients with bimaxillary protrusion who had an anterior segmental osteotomy concomitant with orthognathic surgery were examined. Patients who had bimaxillary anterior segmental osteotomies were more likely to achieve an inter-incisal angle of 135 ± 5° at the end of treatment, when compared to patients who had orthodontic retraction (P < 0.01). The total treatment duration of patients who had bimaxillary anterior segmental osteotomies was significantly shorter as compared to that of the patients who only had these osteotomies in the maxilla (P < 0.001) or mandible (P = 0.012). Complications and permanent long-term sequelae following anterior segmental osteotomies were uncommon. It is concluded that bimaxillary anterior segmental osteotomies are a viable alternative for patients with concomitant bimaxillary protrusion and skeletal base discrepancies. This allows for a significantly shorter treatment time and greater correction of inter-incisal angles, without a significant increase in complications.     

Quantification of the inaccuracy of conventional articulator model surgery in Le Fort 1 osteotomy: evaluation of 30 patients controlled by the Orthopilot® navigation system

Occlusal splints are commonly used to position the maxilla during traditional orthognathic surgery. We aimed to quantify the inaccuracy of the maxillary positioning (in three dimensions) in traditional model surgery with the Orthopilot^® navigation system. Thirty Le Fort I osteotomies were made using a standard technique. The position of the maxilla was recorded by the navigation system and defined by three values of translation and three of rotation. The recorded data were compared with the planned data. The accuracy of positioning was classified in distinct classes with three major criteria (conformity, non-conformity, and failure) according to the discrepancy. The positioning of the maxilla was in conformity with operative planning in 3/30 of our Le Fort I osteotomies (95% CI 2% to 27%) and in failure in 22/30 (95% CI 54% to 88%). The dispersion of the discrepancy was more important in the sagittal plane, particularly for the sagittal rotation and for the back-front translation, which reflected greater inaccuracy in this plan. The frontal orientation of the maxilla was better controlled. The risk of maxillary malposition was proportional to the planned maxillary advancement.     

Three-dimensional surgical planning for maxillary and midface distraction osteogenesis

Computerized surgical planning protocols for distraction osteogenesis are still in their rudimentary phase. The authors have developed a system to plan distraction osteogenesis in craniofacial and maxillofacial surgery that uses three-dimensional computed tomography scans and computer simulation in a virtual reality environment. This involves the creation of a three-dimensional bone model of the craniofacial skeleton, which incorporates virtual globes. Virtual osteotomies are performed on the bone model and the movements of the bone segments are simulated. The program generates a recipe for the linear and the angular changes necessary to achieve the desired outcome. The purpose of this article is to present this surgical planning process and discuss its use in maxillary and midface distraction.     

Accuracy of maxillary repositioning surgery using CAD/CAM customized surgical guides and fixation plates

The advent of three-dimensional imaging and computer-aided surgical simulation (CASS) have brought about a paradigm shift in surgical planning. The aim of this study was to assess the accuracy of maxillary repositioning surgery using computer-aided design and manufacturing (CAD/CAM) customized titanium surgical guides and fixation plates. Thirty consecutive adult patients, 13 male and 17 female, with a mean age of 29.2 years and 25.5 years, respectively, requiring Le Fort I maxillary osteotomy, with or without simultaneous mandibular surgery, were evaluated retrospectively. All orthognathic surgeries were performed by one experienced surgeon. The pre-surgical and post-surgical volumetric imaging were superimposed to assess the linear and angular differences between the planned and actual positions of the maxilla following surgery. With the use of the CAD/CAM titanium surgical guides and fixation plates, all surgical movements were within 2 mm and 4° of the planned movements, which is considered clinically insignificant. The overall root mean square error between the planned and actual surgical movements was 0.38 mm in the transverse dimension, 0.64 mm in the anteroposterior dimension, and 0.55 mm in the vertical dimension. In regard to the centroid of the maxilla, the absolute angular difference of the maxillary centroid was 1.06° in pitch, 0.47° in roll, and 0.49° in yaw. Maxillary repositioning surgery can be performed with high accuracy using CAD/CAM titanium surgical guides and fixation plates.     

Model surgery for orthognathic planning

A modification of a popular North American model surgery technique is described, with a brief comparison with the key-spacer planning system of Lockwood. This technique enables bimaxillary movements to be planned with greater accuracy than with the Lockwood system.     

Accuracy of Le Fort I osteotomy in bimaxillary splint-based orthognathic surgery: focus on posterior maxillary movements

This retrospective study was performed to verify the accuracy of horizontal and vertical repositioning of the maxilla in bimaxillary osteotomy with a focus on posterior vertical displacement. Data from 39 orthognathic patients undergoing bimaxillary surgery including a one-piece Le Fort I osteotomy with pitch rotation and advancement at the University Hospitals of Leuven (Belgium), between January 2015 and April 2016, were included in the study. Preoperative and 1-week postoperative lateral cephalograms were digitized and imported into cephalometric software. Horizontal and vertical measurements of dental landmarks were used to assess the accuracy of maxillary repositioning, and errors were reported in terms of the mean and absolute mean. The horizontal advancements were randomly under- and over-corrected an average of 1.4 mm ± 1.2 mm. Vertical repositioning of the anterior maxilla followed the planning. A tendency for under-correction was found for posterior vertical intrusion of the maxilla. The same tendency towards under-correction of posterior maxillary inferior repositioning was detected when planned movements were greater than 3 mm. For all studied groups, no significant difference was found between the planning and the results achieved, validating the use of intermediate splints.     

Reaching the vertical versus horizontal target position in multi-segmental Le Fort I osteotomy is more difficult,but yields comparably stable results to one-segment osteotomy

This retrospective cohort study evaluated the postoperative outcomes of preoperatively planned positional changes for Le Fort I osteotomy in 77 patients (average age 26.6 years). Movement relapse and planning accuracy were evaluated by lateral cephalometric analysis, with an average follow-up of 257 days. In one-segment osteotomy cases, 73% of the horizontal movements were positioned within 2 mm of the surgical plan. With posterior–inferior repositioning of the maxilla, results fell within 2 mm of the prescribed plan in 60% of cases. Maxillary advancement and superior repositioning proved more stable than inferior maxillary repositioning. Relapse did not differ between three-piece and one-piece osteotomies for any movements; however, in three-piece cases, only half of the positional changes on average stayed within 2 mm of the prescribed surgical plan. Relapse did not vary with bone grafting among the groups. To summarize, in most Le Fort I osteotomy cases, the surgical plan is achieved within 2 mm, with posterior extrusion of the maxilla showing the greatest deviation both in reaching the target and maintaining the result achieved. Although maxillary segmentation makes the surgical plan more difficult to achieve, the results are at least as stable as those of one-piece osteotomies.