Oral and Maxillofacial Surgery https://doi.org/10.1007/s10006-018-0693-y
ORIGINAL ARTICLE
Accuracy of two-dimensional pharyngeal airway space prediction for bimaxillary orthognathic surgery Amanda Lury Yamashita 1 & Lilian Cristina Vessoni Iwaki 1 & Gustavo Nascimento de Souza Pinto 2 & Bárbara Aline Gerke 1 & Mariliani Chicarelli 1 & Liogi Iwaki Filho 1 Received: 5 December 2017 / Accepted: 27 March 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract Purpose The aim of this retrospective study was to evaluate the accuracy of two-dimensional (2D) virtual surgical planning (VSP) of pharyngeal airway space (PAS) in patients submitted to bimaxillary orthognathic surgery. Methods This study was conducted with lateral cephalograms acquired through cone-beam computed tomography records of 33 patients, divided into group 1—patients submitted to maxillary advancement and mandibular setback (n = 17) and group 2— patients submitted to maxillomandibular advancement (n = 16). Records were taken 1 to 2 months prior to surgery, which was used to perform the 2D VSP (Tp), and 6 to 8 months after surgery (T1). In Dolphin Imaging software, the anteroposterior size of the PAS was calculated at the level of four craniometric points: A, occlusal plane (Mx), B, and pogonion (Pog). Two previously calibrated examiners performed these measurements. Statistical analyses were conducted using Kendall and t tests at a 5% level of significance. Results There was a concordance between the two examiners at all points and times. In group 1, points A and B have statistically significant differences between the PAS measurements performed in Tp and T1, while in group 2, none of the PAS points showed statistically significant differences when comparing Tp to T1. Conclusions 2D computer-based cephalometric prediction in Dolphin Imaging software offers a good orientation to professionals during the surgical procedure of bimaxillary surgeries since its use is considered clinically relevant in daily practice. Keywords Orthognathic surgery . Virtual surgical planning . Pharynx . Mandibular advancement
Introduction Dentomaxillofacial deformities compromise the masticatory function and the facial profile of patients and lead to alterations of the pharyngeal airway space (PAS) [1]. In patients submitted to orthognathic surgery, the accurate treatment planning is crucial for more favorable esthetic and occlusal results [2]. So, the possibility of visualization of orthognathic surgery treatment is very important for these patients [3]. Virtual surgical planning (VSP) describes different types of surgical * Amanda Lury Yamashita
[email protected] 1
Dentistry Department, State University of Maringá, Av. Mandacaru, 1550, Maringá, Paraná 87080-000, Brazil
2
Department of Oral Diagnosis, Area of Oral Radiology, Piracicaba Dental School, University of Campinas, Av. Limeira, 901, Piracicaba, Sao Paulo 13414-018, Brazil
planning and execution, using various softwares. It also offers a new alternative to analyze the relationship between the dental arch and facial bones in a virtual model [4] This virtual model of the maxillofacial skeleton makes the patient’s structures closer to reality [4, 5], providing analysis of facial deformities, asymmetries, and tooth position, which may not be detected in a clinical exam [6]. Besides that, with VSP, the surgeon is able to perform Bvirtual surgeries^ and create a prediction of surgical outcomes [3, 7]. Studies evaluating the changes in the pharyngeal airway space (PAS), due to orthognathic surgery, are rapidly emerging in the literature, since the PAS dimensions interfere in the patient’s quality of life [8]. Before the advent of cone-beam computed tomography (CBCT), a two-dimensional (2D) technique from cephalometric radiography and photographs was used to assess the PAS. In daily practice, cephalometric prediction of orthognathic treatment outcome is usually a part of the routine of diagnostic and treatment planning by orthodontists and maxillofacial surgeons [3]. This method can be done
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manually, but it has been replaced by computerized cephalometric systems to analyze and predict the postoperative outcomes of orthognathic surgery [3]. Softwares performing VSP have increased the clinician’s ability to rapidly evaluate different estimates of postoperative profile with the possible surgical techniques [9]. Dolphin Imaging software (Dolphin Imaging & Management Solutions®, Chatsworth, CA, USA) is considered one of the main software systems for VSP [3, 4]. This software utilizes a landmark-based morphing algorithm, which has been validated using lateral cephalometric radiographs and 2D photographs [10]. Furthermore, previous studies reported that this software is reliable in PAS measurements, presenting few errors [11, 12]. According to Stokbro et al. [4], further studies are needed to validate the accuracy and reproducibility of VSP. Thus, the aim of this study was to evaluate the accuracy of 2D VSP of the PAS in patients submitted to bimaxillary surgery, through differences between 2D computer-based cephalometric prediction and postoperative surgical outcome of the PAS.
Materials and methods This retrospective study was conducted in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki), and was approved by the Permanent Ethics Committee for Experiments Involving Humans of the State University of Maringá (UEM), Brazil. (Protocol number 49185715.3.0000.0104). The sample of this study consisted of 33 patients of both genders, submitted to bimaxillary orthognathic surgery, between 2014 and 2015. The inclusion criteria in this study were patients diagnosed with Angle class II and class III skeletal deformities and > 18 years, since the growth of dentofacial structures and PAS were finalized [13]. The exclusion criteria were patients with craniofacial syndromes (lip and palate clefts) or with a history of previous surgeries in the head and neck region [14–16]. These patients were divided into two groups according to the type of orthognathic surgery: group 1—patients submitted to maxillary advancement and mandibular setback (n = 17) and group 2—patients submitted to maxillomandibular advancement (n = 16). Mandibular setback and advancement were achieved with bilateral sagittal split osteotomy and the use of functionally stable fixation, while Le Fort I osteotomy was used for maxillary advancement [8]. A single experienced oral and maxillofacial surgeon performed all the virtual surgical planning and supervised all the surgeries, conducted by a team of surgeons at the residency program in buccomaxillofacial surgery and traumatology (UEM). In order to reduce radiation exposure, 2D radiographs (panoramic radiograph, frontal and lateral cephalograms) used in
Fig. 1 Craniometric analysis in the software Dolphin Imaging & Management®, illustrating the PAS measurements at points A, Mx, B, and Pog. a Preoperative. b 2D VSP. c Postoperative
this study were reconstructed from CBCT scans, which were stored in the database of the radiology and imaging area of UEM [17]. CBCTs were obtained with i-CAT® Next Generation (Imaging Sciences International, Hatfield, PA, EUA). Volumes were reconstructed with 0.300 mm of isometric voxel size, FOV (Field of View) of 17 X 23 cm, tube tension of 120 kVp, and tube current of 3–8 mA. The same dental radiology and imaging professional specialist conducted these CBCTs. Selected records were performed at two periods: preoperatively—1 to 2 months before surgery, which was used to perform the 2D VSP (Tp) and postoperatively— 6 to 8 months after surgery (T1), guaranteeing that structures of the stomatognathic system have already adhered to their new bone conformation, moreover, to complete reduction of the edema resulting from the surgery, ensuring that this would
Oral Maxillofac Surg Table 1 Intra-examiner analysis in both groups and times, using the Kendall test
Examiner 1
Examiner 2
Group 1
Group 2
Group 1
Group 2
Tp e T1
Tp e T1
Tp e T1
Tp e T1
T
p value
T
p value
T
p value
T
p value
A
0.8893
< 0.05
0.8930
< 0.05
0.6985
< 0.05
0.8533
< 0.05
Mx B
0.9000 0.8933
< 0.05 < 0.05
0.9375 0.8335
< 0.05 < 0.05
0.5917 0.8439
< 0.05 < 0.05
0.7930 0.8230
< 0.05 < 0.05
Pog
0.7645
< 0.05
0.8152
< 0.05
0.8448
< 0.05
0.9067
< 0.05
*p < 0.05
surgery with software proficiency and experience in surgical planning. Craniometric tracings were performed in the sagittal reconstructions at Tp and T1 by two duly calibrated examiners, who were trained and calibrated by a Dolphin Imaging Company representative. Calibration was performed with the use of 10 randomly chosen images. Moreover, neither examiner was involved in the presurgical planning process or the virtual surgeries for these patients. The planned and achieved outcomes were evaluated by a numerical comparison of four craniometric points, adopting the Arnett/Gunson FAB Surgery analysis: (1) point A— deepest point of the maxillary curvature between the anterior and the cervical spines of the alveolar bone, representing the anterior segment of the maxilla; (2) point Mx—the occlusal plane, a line that cuts off the intercrossing of the first molars in occlusion and touches the incisal edge of the lower incisor; (3) point B—point located in the largest concavity of the anterior portion of the mental symphysis, representing the anterior segment of the mandible; (4) point Pog—most anterior point of the mental symphysis. After the craniometric delimitation, the software automatically calculated the anteroposterior size of the PAS at the level of the four soft tissue points (A, Mx, B, and Pog) (Fig. 1). To avoid that the evaluators would be fatigued, the image measurements were conducted over a period of 10 days. All statistical tests were performed with the program R version 3.2.1 for Windows (R-project for statistical computing),
not interfere with the measures of the PAS [7, 13, 16]. During acquisition, patients were instructed to remain seated on a chair and adopt a natural head position by looking at their own eyes in a mirror at the opposite wall [15, 18, 19]. No support for the chin and head was used during image acquisition, as these could be confused with the soft tissues in the region, and negatively affect VSP [19]. They also were instructed to keep their tongues and lips at rest [15, 19, 20], breath lightly, and avoid swallowing [16, 19, 20]. 2D cephalometric analysis and prediction tracing were performed in Dolphin Imaging software version 11.9 in DICOM (Digital Imaging and Communications in Medicine) extension. To transfer the acquired images to the virtual environment, spatial orientation was performed so that the axial plane was repositioned coincident with the Frankfurt Horizontal Plane (FHP) and the midsagittal plane, coincident with the midline perpendicular to the FHP and passing through the craniometric of the point nasion [8, 14, 19]. This virtual orientation achieved the correct rotation of the patient’s head, in which the bilateral structures were coincident [8, 14, 18, 19]. For the execution of VSP, lateral cephalogram was traced using standard cephalometric landmarks, and the facial photographies of the patients [17, 21] were superimposed onto the traced cephalogram, in order to create more realistic images. This superimposition is performed through a ruler (mm or DPI) that is provided by Dolphin Imaging software. All VSP was performed by a single specialist in oral and maxillofacial Table 2 Inter-examiner analysis in both groups and times, using the Kendall test
Group 1
Group 2
Tp
A Mx B Pog *p < 0.05
T1
Tp
T1
T
p value
T
p value
T
p value
T
p value
0.8266 0.9169 0.8347 0.8516
< 0.05 < 0.05 < 0.05 < 0.05
0.8838 0.7823 0.8634 0.9138
< 0.05 < 0.05 < 0.05 < 0.05
0.8789 0.7589 0.7788 0.9143
< 0.05 < 0.05 < 0.05 < 0.05
0.8859 0.8299 0.8618 0.9396
< 0.05 < 0.05 < 0.05 < 0.05
Oral Maxillofac Surg Table 3 Mean, standard deviation (SD) and p value of the craniometric points of the PAS in group 1 using the t test Tp Mean ± SD
T1 Mean ± SD
p value
A
20.11 ± 3.30
17.00 ± 2.26
0.003*
Mx B
13.88 ± 3.46 10.94 ± 3.52
14.17 ± 2.72 13.47 ± 3.33
0.785 0.039*
Pog
13.35 ± 5.83
14.11 ± 4.49
0.672
*p < 0.05; SD standard deviation
which has free access and no cost. The Kendall test was applied to verify intra-examiner and inter-examiner agreement. In order to verify the normality of data distribution, the Shapiro-Wilk test was used. Based on the outcome of this test, the t test was used to ascertain the equivalence of the 2D VSP with the T1 measurements of PAS. All hypothesis tests considered a significance of 5% (p < 0.05).
Results Among the 33 patients selected, 17 underwent maxillary advancement and mandibular setback (group 1) and 16 were submitted to the maxillomandibular advancement (group 2), being 8 male and 25 female were selected. The mean age of patients in group 1 was 19.0 ± 8.46 years and in group 2 was 28.0 ± 10.41 years. According the Kendall test, both obtained a good level of significance at Tp and T1, showing intraclass and interclass agreement at the four points (A, Mx, B, and Pog) (Tables 1 and 2). Considering that there was agreement between the two examiners at all points and at both times, the average of the examiners’ values for each point was calculated. In group 1, the t test showed that the points A and B had statistically significant differences between the measurements of PAS performed in Tp and T1 (Table 3). However, in group 2, none of the evaluated points had statistically significant differences. Thus, all points of PAS in Tp were similar in T1 (Table 4). Table 4 Mean, standard deviation (SD) and p value of the craniometric points of the PAS in group 2 using t test
A Mx B Pog
Tp Mean ± SD
T1 Mean ± SD
p value
16.81 ± 6.87 11.31 ± 3.28 13.43 ± 3.61 16.81 ± 5.17
18.62 ± 5.13 12.56 ± 3.48 11.93 ± 2.99 13.37 ± 4.74
0.405 0.304 0.211 0.060
*p < 0.05; SD standard deviation
Discussion The aim of this study was to evaluate the accuracy of 2D VSP of PAS in patients submitted to two different types of orthognathic surgery. Our study showed that the PAS measurements in 2D VSP were accurate at Mx and Pog points in group 1 (Table 3). However, in group 2, there was no statistical difference in the PAS measurements between the 2D VSP and the postoperative surgical outcome (Table 4). The success of orthognathic surgery is intimately related to the technical aspects of the operation and the formulation of a detailed surgical planning [2, 4, 7], being reproducible in the surgical procedure [22]. Previous studies reported that it is acceptable the difference of maximum 2 mm in measurements between VSP and the actual surgical outcome [4, 5]. Less than 2 mm is clinically insignificant in conventional lateral cephalometric analysis [4, 23]. In our study, five of the eight analyzed points did not exceed this difference, suggesting that 2D VSP of PAS could be a viable clinical tool with a good predictive value for surgical treatment of patients with dentomaxillofacial deformities. VSP also promotes autonomy for orthodontists and maxillofacial surgeons to simulate different techniques in order to obtain the best treatment for the patient [3, 7]. This can be an excellent communication tool between orthodontists, maxillofacial surgeons, and patients, increasing their understanding and acceptance regarding the recommended treatment [3, 4, 24]. Previous studies reported that 2D cephalometric analysis and prediction allow evaluation of skeletal and dental movements [3]. 2D computer-based cephalometric prediction was used in our study, because it is still a widely used method by professionals to evaluate the PAS alterations after orthognathic surgery [3, 7, 25, 26]. Moreover, 2D planning is considered a standard method to evaluate and predict outcomes in orthognathic surgery [21, 27]. Orthognathic surgery planning can be done manually or virtually. Manual methods are more time-consuming, while virtual ones facilitate and enable better visualization of surgery results [3, 21]. Currently, there are several software systems that perform VSP [3]. They allow orthodontists and maxillofacial surgeons to quickly manipulate the digital representations of hard and soft tissue profile traces and, consequently, modify patient’s profile (preoperative) to obtain a treatment simulation. Dolphin Imaging software was used in this study, because it can simulate changes in anteroposterior and vertical dimensions [28]. Kusnoto [29] reported that in this software, cephalometric norms based on population group, age, gender, and the soft tissue response to the hard tissue changes can be adjusted accordingly. Dolphin Imaging software dynamically recalculate the analysis and indicate the surgical moves that can be easily translated to model surgery [29]. The speed and accuracy of the analysis and manipulation give the operator the option of simulating a variety of surgical procedures, and
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the ability to choose the outcome based on morphologic criteria [29]. Therefore, this software uses a morphing algorithm [10, 21, 29], in which a group of image pixels that were constrained/surrounded by control vector lines are transformed based on how far the control point was moved [29]. This software is still used in several studies, which analyzed the PAS measurements [1, 8, 11], with few errors [11, 12]. A limitation of this study was the heterogeneity of the sample, not being possible to quantify the magnitude of surgical maxillomandibular movements. Therefore, it is suggested to carry out studies with larger samples divided according to the magnitude of surgical movement. Another limitation was the lack of studies evaluating the accuracy of 2D computer-based cephalometric prediction of PAS. This may have occurred due to the increase of methods that use 3D techniques, mainly through CBCTs. Despite the new 3D technologies, there is still no reliable technique for predicting orthognathic surgery [3]. In addition, further studies are still needed to clarify the accuracy of orthognathic surgery planning.
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Conclusions Based on the results obtained in this study, it may be concluded that the differences between 2D VSP and actual outcomes in PAS measurements were less pronounced in patients submitted to maxillomandibular advancement than maxillary advancement and mandibular setback, since all the points of PAS showed accurate in patients submitted to maxillomandibular advancement. Thus, 2D computer-based cephalometric prediction in Dolphin Imaging software offers a good orientation for professionals during the surgical procedure, and its use is considered clinically relevant in daily practice.
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Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest.
15.
Ethical approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
16.
Informed consent For this type of study (retrospective study) formal consent is not required.
17.
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