The accuracy of three-dimensional prediction planning for the surgical correction of facial deformities using Maxilim

The motivation for orthognathic surgery is to improve facial appearance and quality of life. This study aimed to validate a three-dimensional (3D) orthognathic planning programme (Maxilim) for predicting soft tissue changes following Le Fort I advancements. Cone beam computed tomography (CBCT) scans were taken before surgery (T₁) and at 6–12 months after surgery (T₂) for 13 patients. For each patient the 3D hard tissue changes between T₁ and T₂ were determined by CBCT superimposition on the cranial vault. Using Maxilim, each patient's skeletal movements were used to generate a 3D soft tissue prediction. The actual soft tissue mesh at T₂ was compared to the predicted mesh. The face was divided into areas: nose, right and left nares, right and left paranasal regions, upper and lower lip, and chin. The absolute distance between meshes for each region was calculated. A one-sample t-test showed the distances between the meshes for all of the areas were within 3 mm (P < 0.05), except for the upper lip which was greater than 3 mm (P = 0.577). Using Maxilim, 3D soft tissue predictions for Le Fort I advancements were clinically satisfactory in the regions assessed, but associated with marked errors around the region of the upper lip.     

Volumetric CBCT analysis of the palatine process of the anterior maxilla: a potential source for bone grafts

The aim of this research was to use cone-beam computerized tomography (CBCT) to analyze the available bone volume in the palatine process of the maxilla (PPM), which is a potential source of bone grafts. 20 CBCT scans were evaluated. From the most caudal axial slice of the PPM, the bony surface was calculated cranially up to the nasal floor. The predetermined thickness of each slice was 0.9 mm. A 2 mm safety margin was established considering the incisive canal and teeth 14–24. A ±0.1 mm error deviation was established for all calculations. By connecting these points and those defined at the posterior bone boundary, a surface was obtained. A three-dimensional (3D) image of the delimited zone was constructed and analyzed using 3D imaging software. The study comprised 6 women and 14 men (mean age 39.4 ± 11.5 years). Calculated bone volume averaged 2.41 ± 0.785 cm³. The palatine process of the maxilla contains a considerable bone volume (2.41 ± 0.785 cm³). This area should be regarded as a potential donor site for the regeneration of maxillary atrophic bones. Further investigation is required before these findings lead to routine clinical application.     

Accuracy of analytic model planning in bimaxillary surgery

The purpose of this study was to assess our method of analytic model planning in achieving a planned maxillary advancement for the correction of a dentofacial deformity. A consecutive series of 20 patients who underwent bimaxillary orthognathic surgery, at a minimum, were included in the study group. For each study subject, consistent analytic model planning with splint fabrication was used to establish the desired horizontal repositioning of the maxilla. Using preoperative and 5-week postoperative lateral cephalometric radiographs, an analysis was designed to assess the difference between the planned and actual advancement of the maxilla. The average difference between the planned and actual 5-week postsurgical advancement of the maxilla was 0.6 mm (range 0.2–1.0, P > 0.05). There was a strong correlation between the two data sets (R = 0.96). The results of the study indicate that the described method of analytic model planning is reliable (within 1 mm) in achieving the planned level of maxillary advancement in bimaxillary orthognathic procedures.     

The virtual human face: Superimposing the simultaneously captured 3D photorealistic skin surface of the face on the untextured skin image of the CBCT scan

The aim of this study was to evaluate the impact of simultaneous capture of the three-dimensional (3D) surface of the face and cone beam computed tomography (CBCT) scan of the skull on the accuracy of their registration and superimposition. 3D facial images were acquired in 14 patients using the Di3d (Dimensional Imaging, UK) imaging system and i-CAT CBCT scanner. One stereophotogrammetry image was captured at the same time as the CBCT and another 1 h later. The two stereophotographs were individually superimposed over the CBCT using VRmesh. Seven patches were isolated on the final merged surfaces. For the whole face and each individual patch: maximum and minimum range of deviation between surfaces; absolute average distance between surfaces; and standard deviation for the 90th percentile of the distance errors were calculated. The superimposition errors of the whole face for both captures revealed statistically significant differences (P = 0.00081). The absolute average distances in both separate and simultaneous captures were 0.47 and 0.27 mm, respectively. The level of superimposition accuracy in patches from separate captures was 0.3–0.9 mm, while that of simultaneous captures was 0.4 mm. Simultaneous capture of Di3d and CBCT images significantly improved the accuracy of superimposition of these image modalities.     

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.     

Is there a difference between the thicknesses of the rami in mandibular asymmetry?

The purpose of this retrospective study was to investigate whether the thicknesses of the two rami differ in patients with mandibular asymmetry. Preoperative cone beam computed tomography scans of 78 patients with mandibular asymmetry were assessed for ramus thickness, mandibular length, and mandibular shift. The results showed that the ramus was thinner on the longer side than on the shorter side in 85.9% of the patients. On average, the longer side of the mandible was 2.74 mm longer (range 0.07–9.90 mm, standard deviation 1.92 mm) and 0.55 mm thinner (range ?0.61 to 2.02 mm, standard deviation 0.59 mm) than the shorter side (both P < 0.001). This study indicates a trend in the discrepancy in ramus thickness between the longer and shorter side of about 8% of the mean thickness of the ramus. Regression analysis showed that for every 1-mm increase in the length of the mandible, the thickness of the superior aspect of the ramus was reduced by 0.041 mm (P = 0.009) and the anterior aspect by 0.125 mm (P = 0.001). Age and sex did not have a significant influence on the thickness of the mandible. It is concluded that the longer side of the mandible tends to be thinner at the ramus than the shorter side in patients with mandibular asymmetry. The implication of this finding could be important in relation to the sagittal split ramus osteotomy.     

Accuracy of mandible-independent maxillary repositioning using pre-bent locking plates: a pilot study

The double splint method is considered the gold standard for maxillary repositioning, but the procedure is lengthy and prone to error. Recent splintless methods have shown high repositioning accuracy; however, high costs and technical demands make them inaccessible to many patients. Therefore, a new cost-effective method of mandible-independent maxillary repositioning using pre-bent locking plates is proposed. Plates are bent on maxillary models in the planned position prior to surgery. The locations of the plate holes are replicated during surgery using osteotomy guides made from thermoplastic resin sheets. Pre-bent plates are subsequently fitted onto the maxilla, and plate holes are properly set to reposition the maxilla. The purpose of this study was to evaluate the accuracy of this method for maxillary repositioning and the reproducibility of the plate holes. Fifteen orthognathic surgery patients were evaluated retrospectively by superimposing preoperative simulations over their postoperative computed tomography models. The median deviations in maxillary repositioning and plate hole positioning between the preoperative plan and postoperative results were 0.43 mm (range 0–1.55 mm) and 0.33 mm (range 0–1.86 mm), respectively. There was no significant correlation between these deviations, suggesting that the method presented here allows highly accurate and reliable mandible-independent maxillary repositioning.     

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.     

Accuracy of implant position when placed using static computer-assisted implant surgical guides manufactured with two different optical scanning techniques: a randomized clinical trial

Data from cone beam computed tomography (CBCT) and optical scans (intraoral or model scanner) are required for computer-assisted implant surgery (CAIS). This study compared the accuracy of implant position when placed with CAIS guides produced by intraoral and extraoral (model) scanning. Forty-seven patients received 60 single implants by means of CAIS. Each implant was randomly assigned to either the intraoral group (n = 30) (Trios Scanner, 3Shape) or extraoral group (n = 30), in which stereolithographic surgical guides were manufactured after conventional impression and extraoral scanning of the stone model (D900L Lab Scanner, 3Shape). CBCT and surface scan data were imported into coDiagnostiX software for virtual implant position planning and surgical guide design. Postoperative CBCT scans were obtained. Software was used to compare the deviation between the planned and final positions. Average deviation for the intraoral vs. model scan groups was 2.42° ± 1.47° vs. 3.23° ± 2.09° for implant angle, 0.87 ± 0.49 mm vs. 1.01 ± 0.56 mm for implant platform, and 1.10 ± 0.53 mm vs. 1.38 ± 0.68 mm for implant apex; there was no statistically significant difference between the groups (P > 0.05). CAIS conducted with stereolithographic guides manufactured by means of intraoral or extraoral scans appears to result in equal accuracy of implant positioning.     

Splintless surgery using patient-specific osteosynthesis in Le Fort I osteotomies: a randomized controlled multi-centre trial

The accuracy of orthognathic surgery has improved with three-dimensional virtual planning. The translation of the planning to the surgical result is reported to vary by >2 mm. The aim of this randomized controlled multi-centre trial was to determine whether the use of splintless patient-specific osteosynthesis can improve the accuracy of maxillary translation. Patients requiring a Le Fort I osteotomy were included in the trial. The intervention group was treated using patient-specific osteosynthesis and the control group with conventional osteosynthesis and splint-based positioning. Fifty-eight patients completed the study protocol, 27 in the patient-specific osteosynthesis group and 31 in the control group. The per protocol median anteroposterior deviation was found to be 1.05 mm (interquartile range (IQR) 0.45–2.72 mm) in the patient-specific osteosynthesis group and 1.74 mm (IQR 1.02–3.02 mm) in the control group. The cranial–caudal deviation was 0.87 mm (IQR 0.49–1.44 mm) and 0.98 mm (IQR 0.28–2.10 mm), respectively, whereas the left–right translation deviation was 0.46 mm (IQR 0.19–0.96 mm) in the patient-specific osteosynthesis group and 1.07 mm (IQR 0.62–1.55 mm) in the control group. The splintless patient-specific osteosynthesis method improves the accuracy of maxillary translations in orthognathic surgery and is clinically relevant for planned anteroposterior translations of more than 3.70 mm.     

Comparison of the accuracy of maxillary position between conventional model surgery and virtual surgical planning

The aim of this study was to determine whether virtual surgical planning (VSP) is an accurate method for positioning the maxilla when compared to conventional articulator model surgery (CMS), through the superimposition of computed tomography (CT) images. This retrospective study included the records of 30 adult patients submitted to bimaxillary orthognathic surgery. Two groups were created according to the treatment planning performed: CMS and VSP. The treatment planning protocol was the same for all patients. Pre- and postoperative CT images were superimposed and the linear distances between upper jaw reference points were measured. Measurements were then compared to the treatment planning, and the difference in accuracy between CMS and VSP was determined using the t-test for independent samples. The success criterion adopted was a mean linear difference of <2 mm. The mean linear difference between planned and obtained movements for CMS was 1.27 ± 1.05 mm, and for VSP was 1.20 ± 1.08 mm. With CMS, 80% of overlapping reference points had a difference of <2 mm, while for VSP this value was 83.6%. There was no statistically significant difference between the two techniques regarding accuracy (P > 0.05).     

Nasolabial soft tissue effects of segmented and non-segmented Le Fort I osteotomy using a modified alar cinch technique—a cone beam computed tomography evaluation

The aim of this study was to verify soft tissues changes and the effect of a minimally invasive surgical technique in the nasolabial region after segmented and non-segmented Le Fort I osteotomy, using cone beam computed tomography (CBCT) evaluation of three-dimensional (3D) volume surfaces. Two groups were evaluated: group 1, bimaxillary surgery with maxillary segmentation (n = 40); group 2, bimaxillary surgery without maxillary segmentation (n = 40). In both groups, a specific alar cinching technique was used to control nasal base broadening. CBCT evaluation was performed at three different treatment time points: T0, 1 month before surgery; T1, 1 month after surgery; T2, 1 year after surgery. The results showed statistically significant differences in the nasolabial area (P < 0.001). For group 1, the mean change in alar base width (Al_inf–Al_inf) was 1.31 ± 1.40 mm at T1 and 0.93 ± 1.77 mm at T2; for group 2 these values were 1.12 ± 2.01 mm at T1 and 0.54 ± 1.54 mm at T2. For group 1, the mean changes in inter-alar width (Al–Al) were 1.68 ± 1.46 mm at T1 and 1.49 ± 1.33 mm at T2; for group 2, they were 2.22 ± 1.93 mm at T1 and 1.34 ± 1.79 mm at T2. The alar cinch technique proposed here appears to be effective in controlling nasolabial soft tissue widening.     

Accuracy of virtual planned surgery versus conventional free-hand surgery for reconstruction of the mandible with osteocutaneous free flaps

Virtual surgical planning (VSP) promises higher accuracy, efficiency, and superior patient outcomes, helping normalize outcomes from surgeons of different experience levels. A systematic review was conducted in agreement with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The objective was to evaluate the accuracy and secondarily efficiency of VSP compared with free-hand surgery, for mandibular reconstruction with free flaps. Six studies met inclusion criteria and had quantitative data suitable for meta-analysis. Intercondylar distance and gonion angle were used to assess accuracy, evaluated by mean change from preoperative VSP and postoperative imaging. The mean weighted difference in VSP intercondylar distance was 2.0 mm, compared with 3.9 mm for free hand (P = 0.101) and mean change in gonion angle for VSP was 3.6°, compared with 7.7° for free hand (P < 0.05). Efficiency assessed by mean ischemia time, was 73.8 min and 109.9 min, for VSP and free hand, respectively (P = 0.203), and by total operative time, which was 391.8 min and 457.6 min in the VSP and free hand, respectively (P = 0.340). VSP is consistently proven to be more accurate and efficient than traditional free-hand surgery; however, a standardized method for accuracy and efficiency measurements is still missing, causing heterogeneity among the scientific reports.     

Digital replacement of the distorted dentition acquired by cone beam computed tomography (CBCT): a pilot study

During cone beam computed tomography (CBCT) scanning, intra-oral metallic objects may produce streak artefacts, which impair the occlusal surface of the teeth. This study aimed to determine the accuracy of replacement of the CBCT dentition with a more accurate dentition and to determine the clinical feasibility of the method. Impressions of the teeth of six cadaveric skulls with unrestored dentitions were taken and acrylic base plates constructed incorporating radiopaque registration markers. Each appliance was fitted to the skull and a CBCT performed. Impressions were taken of the dentition with the devices in situ and dental models were produced. These were CBCT-scanned and the images of the skulls and models imported into computer-aided design/computer-aided manufacturing (CAD/CAM) software and aligned on the registration markers. The occlusal surfaces of each dentition were then replaced with the occlusal image of the corresponding model. The absolute mean distance between the registration markers in the skulls and the dental models was 0.09 ± 0.02 mm, and for the dentition was 0.24 ± 0.09 mm. When the method was applied to patients, the distance between markers was 0.12 ± 0.04 mm for the maxilla and 0.16 ± 0.02 mm for the mandible. It is possible to replace the inaccurate dentition on a CBCT scan using this method and to create a composite skull which is clinically acceptable.     

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.     

Inlay–onlay grafting for three-dimensional reconstruction of the posterior atrophic maxilla with mandibular bone

This prospective study describes and evaluates a surgical approach for 3D reconstruction of the posterior maxilla with autogenous mandibular bone in 16 patients (mean age 51 years). Bone blocks were harvested from the mandible and used as lateral or vertical block grafts (onlay); they were also partially milled and used for sinus elevation (inlay). In 4 cases, anorganic bovine bone was added at the periphery of the blocks. 4 months after grafting, implants were placed in a second operation and loaded after 12 weeks. Lateral and vertical augmentations were measured immediately after grafting and at re-entry for implant placement. Mean lateral augmentation performed was 5.5 mm, reduced to 4.3 mm (p < 0.01) after 4 months’ healing. Mean vertical augmentation was 3.2 mm, reduced to 2.1 mm (p < 0.01) after healing. The amounts of lateral and vertical graft resorption were similar (1.2 mm vs. 1.1 mm) but were different when compared with the original graft (22% vs. 34%). 49 implants were placed 4 months after grafting. Implant parameters were evaluated after 32–48 months follow up and demonstrated 100% survival rates. The use of mandibular bone grafts for 3D augmentation of the posterior maxilla has shown good results and minor complications.     

Pharyngeal airway space changes after maxillomandibular advancement: a five-year retrospective study

The aim of this study was to compare the alterations in three regions of the airway—nasopharynx, oropharynx, and hypopharynx—in relation to the area of the midsagittal plane, volume, and minimal axial area after maxillomandibular advancement (MMA) surgery. Thirty patients who had undergone MMA surgery were evaluated at four time points: preoperative (T0), immediately postoperative (T1), 1 year postoperative (T2), and ≥5 years postoperative (T3). All measurements were performed using computed tomography, analyzed in Dolphin Imaging 11.0 Premium 3D software. The area in the midsagittal plane presented a mean increase of 22.0% between T0 and T3 (P < 0.001), with the highest increase in the oropharynx (24.1%, P < 0.001). The total volumetric increase at T3 was 16.7% (P < 0.001), with the highest increase in the nasopharynx (15.7%; P < 0.001). The lowest minimal axial area was found for the oropharynx at all time points, and the highest increase in minimal axial area was found for the nasopharynx (114.9%; P < 0.001). MMA surgery showed the highest increase in upper posterior airway between T0 and T1, and this was followed by a progressive reduction until T3, but with a statistically significant increase at T3 compared with T0 in all cases.     

Soft and hard tissue changes in skeletal Class III patients treated with double-jaw orthognathic surgery—maxillary advancement and mandibular setback

The soft tissues of the facial profile may change after skeletal movement in orthognathic surgery. The aim of this study was to evaluate and compare the differences and correlation between hard and soft tissues after double-jaw surgery in skeletal Class III subjects. Radiographs from the following time points were assessed using Dolphin Imaging software: preoperative (T0), 2–4 months postoperative (T1), and 6–12 months postoperative (T2). Eleven hard and soft tissue points of the facial profile were evaluated. The Student's t-test was used to assess the significance of differences between the time intervals; Pearson's correlation coefficient was used to assess the significance of correlation existing between these points; significance was set at P < 0.05. In the sample of 58 subjects, the correlation between hard and soft tissues in the mandible was greater than in the maxilla. Similarly, the correlations only between hard tissues and only between soft tissues presented a greater correlation in the mandible. The results are similar to those found in studies on single-jaw surgery for both the maxilla and the mandible. The influence of movements in hard tissues was restricted to the soft tissues of the same jaw, although there were exceptions.     

Influence of TiO2 nanoparticles on the optical properties of resin composites

ObjectivesTo determine the influence of titanium dioxide (TiO₂) nanoparticle addition on the opalescence, color, translucency and fluorescence of experimental resin composites.MethodsA light curing resin matrix was made by mixing 60 wt.% Bis-GMA and 40 wt.% TEGDMA. Silane coated glass filler (mean particle size: 1.55 μm) was added in the ratio of 50 wt.% of the resin composites. A fluorescent whitening agent was also added (0.05 wt.%). TiO₂ nanoparticles (<40 nm) were added with the concentrations of 0, 0.1, 0.25 and 0.5 wt.%. Reflected and transmitted colors of 1 and 2 mm thick specimens were measured relative to the illuminant D65 with reflection spectrophotometers. Opalescence parameter (OP), color difference (ΔE*_ab), translucency parameter (TP), fluorescence parameter (FL), and fluorescence and opalescence spectra were calculated.ResultsFor the 1 mm thick specimens measured with 3 mm × 8 mm rectangular aperture, when the concentration of TiO₂ increased from 0% to 0.5%, OP increased from 2.4 to 18.0, TP decreased from 35.4 to 13.1, and fluorescence spectra remained unchanged. Color difference between these specimens was in the range of 3.4–6.6 ΔE*_ab units. OP values were significantly influenced by the thickness of the specimens and the configuration of the spectrophotometers (p < 0.05).SignificanceAddition of TiO₂ nanoparticles significantly increased the opalescence of resin composites while leaving the fluorescence spectra unchanged; however, it significantly decreased the translucency and also changed the color (p < 0.05). Resin composites with 0.1–0.25% TiO₂ nanoparticle would simulate the opalescence of human enamel.     

Airway changes and prevalence of obstructive sleep apnoea after bimaxillary orthognathic surgery with large mandibular setback

This study used three-dimensional computed tomography and polysomnography to evaluate the effect of a large mandibular setback on the postoperative pharyngeal airway space and obstructive sleep apnoea (OSA). Twelve patients who underwent bimaxillary surgery for a mandibular setback movement of >9 mm were included in this study. Changes in the pharyngeal airway space and polysomnography parameters based on the surgical movements were analyzed. The median mandibular setback movement was 11.08 mm. The total pharyngeal, oropharyngeal, and hypopharyngeal volumes, and the retroglossal cross-sectional area were significantly decreased postoperatively (P = 0.006; P = 0.005; P = 0.012; P = 0.005, respectively). The apnoea–hypopnoea index (AHI) increased significantly after surgery (P = 0.021). There were significant positive correlations between the preoperative inferiorly located hyoid bone and both AHI and respiratory disturbance index (RDI) postoperative (P = 0.008 and P = 0.027) and between the postoperative inferiorly dislocated retropalatal level and both AHI and RDI postoperative (P = 0.002 and P = 0.014). Four patients (33.3%) developed new onset OSA postoperatively. Large mandibular setback movements significantly reduced the pharyngeal airway space in the setting of bimaxillary surgery (P = 0.006).