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CAM–engineered surgical template based on a facebow for orthognathic surgery: an experiment with a rapid prototyping maxillary model
Accepted Manuscript Precision of a CAD/CAM-engineered surgical template based on a facebow for orthognathic surgery: an experiment with a rapid prototyping maxillary model Jae-Won Lee, DDS, MS, Se-Ho Lim, DDS, Moon-Key Kim, DDS, PhD, Sang-Hoon Kang, DDS PhD PII:
S2212-4403(15)01086-X
DOI:
10.1016/j.oooo.2015.07.007
Reference:
OOOO 1250
To appear in:
Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology
Received Date: 13 January 2015 Revised Date:
21 April 2015
Accepted Date: 13 July 2015
Please cite this article as: Lee J-W, Lim S-H, Kim M-K, Kang S-H, Precision of a CAD/CAM-engineered surgical template based on a facebow for orthognathic surgery: an experiment with a rapid prototyping maxillary model, Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology (2015), doi: 10.1016/ j.oooo.2015.07.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Precision of a CAD/CAM-engineered surgical template based on a facebow for orthognathic surgery: an experiment with a rapid prototyping
Jae-Won Lee, DDS, MS,a
Se-Ho Lim, DDS,a
Moon-Key Kim, DDS, PhD,a,b Sang-Hoon
a
Department of Oral and Maxillofacial Surgery, National Health Insurance Service Ilsan
Hospital, Goyang, Republic of Korea
Department of Oral and Maxillofacial Surgery, College of Dentistry, Yonsei University,
Seoul, Republic of Korea
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b
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Kang, DDS PhD,a,b,
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maxillary model
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Corresponding author:
Sang-Hoon Kang DDS, PhD
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Faculty, Department of Oral and Maxillofacial Surgery, National Health Insurance Service Ilsan Hospital, 100 Ilsan-ro, Ilsan-donggu, Goyang, Gyeonggi-do, 410-719, Republic of Korea
Clinical assistant professor, Department of Oral and Maxillofacial Surgery, College of Dentistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea E-mail address : [email protected] Tel.: +82-31-900-0267; Fax: +82-31-900-0343
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CONFLICT OF INTEREST STATEMENT
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The authors declare no conflicts of interest in this study.
ACKNOWLEDGEMENT
Research
Foundation
of
Korea
funded
by
the
Ministry
of
Education
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(2013R1A1A2009251)
(NRF)
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This research was supported by Basic Science Research Program through the National
- Word count for the abstract : 199
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- Complete manuscript word count: 4547 (body text:4213 and figure legends:334)
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- Number of references: 14 - Number of figures: 5
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- Number of tables: 7
- No supplementary elements
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ACCEPTED MANUSCRIPT Precision of a CAD/CAM-engineered surgical template based on a facebow for
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orthognathic surgery: an experiment with a rapid prototyping maxillary model
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ABSTRACT Objective. We examined the precision of a CAD/CAM-engineered, manufactured, facebowbased surgical guide template (facebow wafer) by comparing it with a bite splint-type
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orthognathic CAD/CAM-engineered surgical guide template (bite wafer). Study Design. We used 24 rapid prototyping (RP) models of the craniofacial skeleton with maxillary deformities. Twelve RP models each were used for the facebow wafer group and
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the bite wafer group (experimental group). Experimental maxillary orthognathic surgery was performed on the RP models of both groups. Errors were evaluated through comparisons with
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surgical simulations. We measured the minimum distances from three planes of reference to determine the vertical, lateral, and anteroposterior errors at specific measurement points. The measured errors were compared between experimental groups using a t-test. Results. There were significant intergroup differences in the lateral error when we compared
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the absolute values of the 3D linear distance, as well as vertical, lateral, and anteroposterior errors between experimental groups. The bite wafer method exhibited little lateral error overall, and little error in the anterior tooth region. The facebow wafer method exhibited very
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little vertical error in the posterior molar region. Conclusions. The clinical precision of the facebow wafer method did not significantly
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exceed that of the bite wafer method.
Keywords: CAD/CAM; Computer aided surgery; Facebow; Orthognathic surgery; Surgical guide template
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INTRODUCTION Three-dimensional (3D) imaging acquired with computed tomography (CT) has recently become universally recognized as an important tool in the diagnosis and evaluation
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of dentocraniofacial deformity and in orthognathic surgical simulations.1 In orthognathic surgeries, 3D images can be utilized to perform surgical simulations before the actual
operation. The 3D images can also be used to manufacture appropriate orthognathic surgical
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devices with 3D printers.2
When the surgical treatment plan is accurately represented with a preoperative
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virtual simulation, it indicates the exact dimensions needed for a surgical template (wafer). Then, an appropriate surgical template can be designed and manufactured with computeraided design (CAD) and a 3D printer.2,3 However, even state-of-the-art surgical devices— particularly the widely-used splints—are vulnerable to error. There may be a number of
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causes for errors, including a change in the positioning of the jaws; reproducibility of the reference point; and problems with vertical dimensions. To reduce these potential errors, surgical methods can be designed in various forms for a range of purposes. One device that is
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used determines the location of the mandibular condyle; in other cases, a surgical navigation
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method is used that augments surgical precision by matching the surgical reference point in the actual patient in the operating room to the corresponding reference point in a 3D surgical simulation.4 Various surgical devices have been developed to connect intact anatomical structures other than the upper and lower jaws, which are displaced during surgery.2,3,5,6 Recent studies have reported new methods with waferless systems, including navigation systems and skull-related repositioning systems.4,7,8 Facebow-using methods have also been described that can minimize error regarding the location of the maxilla.9 Traditionally, facebows have been used to mount dental cast
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ACCEPTED MANUSCRIPT models on articulators or to preoperatively identify a location relative to the cranial region. Facebows have not been considered an effective method for use during surgery because they are characterized by poor reproducibility and instability, and they are difficult to anchor
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extraorally. Nevertheless, a facebow may be useful in surgery, when it is able to achieve location stability within a certain range, and when it is possible to manufacture an appropriate surgical template that can be anchored onto the facebow plate during the operation. This
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method retains the primary advantages of 3D imaging technology. Moreover, facebow data can apply patient-specific location data from the cranial region and maintain the vertical
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dimensions without depending on the positioning of the mandible.
The aim of the present study was to develop a new method for guiding the placement of the maxilla using a facebow. The surgical templates were designed with CAD. Preoperative 3D surgical simulations were performed using facebow data in order to
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manufacture the templates using 3D printers. Then, we examined the precision of the manufactured facebow-based surgical template (facebow wafer) by comparing it with the bite splint-type orthognathic surgical template (bite wafer) manufactured using stereolithography
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(STL) data.
MATERIALS AND METHODS
Rapid prototyping model of craniofacial skeleton and 3D surgical simulation This study was performed with a rapid prototyping (RP) model of the craniofacial skeleton based on CT data acquired from a plastic skull model (A20 classic human skull model, 3B Scientific, Hamburg, Germany). The DICOM file of the CT data was imported into Mimics, version 14.0 software (Materialise, Leuven, Belgium). Then, the data was 6
ACCEPTED MANUSCRIPT restructured to create a 3D image (Figure 1, A). The model of the maxilla and mandible was adjusted to represent different maxillary deformities. The variant maxillary deformity models were created with three translational movements—lateral, vertical, and horizontal—all
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displaced by 3 mm, and three rotational movements about the joint—roll, yaw, and pitch (Figure 1, B). Twelve variant maxillary deformity models were created (six translated
deformity models and six rotated deformity models), and the data were then extracted to an
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STL file. We manufactured one pair of each maxilla-deformed model with a 3D printer
(ProJet 360, 3D Systems, Inc, Rock Hill, SC), for a total of 24 RP models (Figure 1, C).
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Thus, we used 12 RP models for the facebow wafer group and 12 for the bite wafer group. Each RP model was used in a simulation of a surgery that would treat the displaced maxilla. The simulation was conducted in Mimics software. In the surgical simulation, the maxilla was displaced in a symmetrical skeleton, as it would be displaced in an actual clinical
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simulation protocol.
Facebow wafer group: orthognathic surgical template based on the facebow
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The facebow (Artex®, Amann Girrbach AG, Koblach, Austria) was used in the facebow wafer group. Two STL surgical templates were designed prior to the surgery. The
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first surgical template (facebow positioning guide) was used to set the facebow. The template was designed to determine the location of the bite plate of the facebow based on the position of the maxilla in the preoperative condition (Figure 2, A). The second surgical template (maxillary surgical guide) was designed to position the maxilla during surgery, as informed by the surgical simulation based on the position of the postoperative maxilla and the preset position of the bite plate on the facebow (Figure 2, B). The simulation data for the designs of these two surgical templates (facebow positioning guide and maxillary surgical guide) were extracted into STL file formats. The STL data were then used to manufacture the two 7
ACCEPTED MANUSCRIPT orthognathic surgical templates using a 3D printer (ProJet 3500 HDMax 3D Printer). The facebow was positioned using the first surgical template, and then maxillary surgery was performed on the RP models using the second surgical template. Briefly, we
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used one first surgical template (facebow positioning guide) that set the axis of the facebow and determined the location of the facebow bite plate in the RP experimental model (Figure 2, C). Then, the second surgical template (maxillary surgical guide) was mounted in a preset
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fixed bite plate connected to the facebow. A Le Fort I osteotomy was performed on the
maxilla, starting from the lateral nasal aperture area and extending to the posterior maxilla,
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with a fissure bur and an industrial-grade thread saw. Then, the maxilla was moved to the position indicated by the second surgical template mounted onto the facebow (Figure 2, D). The maxilla was secured with the second surgical template mounted onto the facebow using cyanoacrylate adhesive. After this experimental maxillary orthognathic surgery was
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complete, we performed maxillary fixation with utility wax.
Bite wafer group: orthognathic surgical template based on the mandible
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For the bite wafer group, the design of the orthognathic surgical template was based on the postoperative maxillary position after an orthognathic surgical simulation (Fig. 3, A,
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B). Using the boolean function in Mimics, the surgical template was designed from the tooth region of the operative maxilla and the current mandible. The surgical template was guided by the mandible. The simulated design data for the surgical template were extracted into the STL file format, which was then used to manufacture the surgical template with a 3D printer (ProJet 3500 HDMax 3D Printer, 3D Systems, Inc., Rock Hill, SC). The manufactured orthognathic surgical template was used to perform surgery on the maxilla in the RP model; maxillary surgery was based on the mandible location (Fig. 3, C, D). After positioning the 3D-printed surgical template, we performed an osteotomy on the 8
ACCEPTED MANUSCRIPT maxilla with reference to the vertical distance from the nasion to the anterior teeth, as measured in the surgical simulation. As with the experimental group, the maxillary cut was performed with a fissure bur and an industrial-grade thread saw, and it extended from the
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lateral nasal aperture to the posterior maxilla. The maxilla and mandible were secured to the bite wafer by intermaxillary fixation using stainless steel wire. Then, the fixed
maxillomandibular complex with the bite wafer was manipulated while the condyle head was
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kept in contact with the glenoid fossa. Condylar contact with the glenoid fossa was
maintained manually during the experimental maxillary orthognathic surgery. After the
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experimental maxillary surgery, maxillary fixation was accomplished using utility wax.
Error measurements and analysis of results with the surgical templates We performed CT scans on the 12 RP models in the facebow and bite wafer groups
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after they underwent maxillary orthognathic surgery. All scans were performed under the same conditions. The CT data was overlapped with the simulation data from the orthognathic surgery based on the preoperative plan, and we compared the actual results with the
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simulation data (Figure 4).
To overlap the surgical simulation data with actual experimental data, we used the
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same settings to acquire CT images of the RP models before and after orthognathic maxilla surgery. We transformed these images into 3D structures using Mimics software, and then extracted the data into an STL file format. We also extracted the data resulting from the surgical simulation into an STL file format. Using XOV2 software (INUS Technology, Seoul, Republic of Korea), we set the non-operated cranial region as the reference region for registering the images. With this regional reference, the STL data from the experimental surgery were overlapped with the data from the simulation results. Then, we used Mimics software to import the overlapped data into SimPlant software version 14.0 (Materialise 9
ACCEPTED MANUSCRIPT Dental, Leuven, Belgium). We measured the vertical, lateral, anteroposterior, and 3D minimum distance differences between the simulation results and the actual experimental surgery results.
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The measurements were made using the SimPlant program; three reference planes were set in the cranial region of each dataset (Figure 5). Then, we measured the distance from corresponding points on the operated maxilla and the surgical simulation to the reference
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planes, and evaluated the difference between those distances. The first reference plane was the Frankfort (FH) plane, which was established with three points: a center-point between the
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bilateral orbitale (infraorbital margin), and two points on the porions of the external auditory canal regions, one on each side. The second reference plane was the mid-sagittal plane, which was perpendicular to the FH plane and extended through the nasion and the internal occipital crest. The third reference plane was the coronal plane, which extended through the nasion and
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was perpendicular to both the FH plane and the mid-sagittal plane. We measured the minimum distances from each of these three planes in order to determine the vertical, lateral, and anteroposterior errors of the measured points.
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We selected four measurement points on each side of the maxilla (Figure 5): the first point was on the central incisor corner (Is; Figure 5), the second was in the first molar
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mesiobuccal cusp region (Ms; Figure 5), the third was in the maxillary tuberosity region (MxTb), and the fourth was in the lateral nasal aperture region (LNA). One examiner marked the measurement points and ensured that the locations were identical in the surgical simulation and the actual experimental image. We evaluated the differences (errors) between the surgical result and the simulation at each of these measurement points. At each point, we measured the vertical, lateral, and anteroposterior distances from the preset vertical FH plane, mid-sagittal plane, and coronal plane. A positive vertical error indicated that the postexperimental region was placed inferiorly (downward) with respect to the cranial region, 10
ACCEPTED MANUSCRIPT compared with the simulation. A positive lateral error indicated that the post-experimental region was placed leftward with respect to the cranial region, compared with the simulation. A positive anteroposterior error indicated that the post-experimentally measured region was
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placed anteriorly with respect to the cranial region, compared with the simulation. Finally, the 3D minimum distance was measured between corresponding measurement points on the experimental model and the simulation. Total error was defined as the mean error of the
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combined four measurement points. We also evaluated absolute values of differences (errors) between the surgical result and the simulation at each of these measurement points and
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planes.
Using a t-test, the measured results (errors) were compared between groups that received maxillary orthognathic surgery with either the facebow wafer group or the bite wafer group. P < .05 was considered statistically significant. The intra-operator error was
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RESULTS
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determined by comparing 12 repetitive selections of a single point.
We compared the results of orthognathic surgery on the maxilla performed using two
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different methods. One method utilized a surgical facebow wafer that was combined with a facebow for maxillary positioning; the second method utilized an bite wafer. The total errors in the 3D minimum distances were 1.21±0.63 mm (mean±SD) for
surgery with a bite wafer and 1.22±0.62 mm for surgery with a facebow wafer (Table I). The two surgical methods did not differ significantly (P = .942). Comparison of the measurements for each of the four preset points—Is, Ms, MxTb, and LNA—also did not reveal any significant differences between the bite wafer and facebow wafer groups.
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ACCEPTED MANUSCRIPT The total errors in the absolute values of vertical distances were 0.69±0.59 mm (mean±SD) with the bite wafer, and 0.61±0.48 mm with the facebow wafer (Table II), which did not represent a significant difference between the surgical groups (P = .295). A
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comparison of the mean absolute values of differences in vertical distance at each measured point demonstrated that the bite wafer group (0.49 ± 0.40) had a smaller error than the
facebow wafer group (0.80 ± 0.50) in the LNA (P = .023). On the other hand, the facebow
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wafer group (0.44 ± 0.43) had a smaller error than the bite wafer group (0.81 ± 0.51) in the Ms (P = .010), which indicated a smaller error in the posterior maxillary region.
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The total errors in the absolute values of lateral distances were 0.35±0.29 mm (mean±SD) for the bite wafer and 0.54±0.47 mm for the facebow wafer (Table III), which represented a significant difference between the surgical groups (P = .001). The bite wafer method had a smaller lateral error than the facebow wafer method. Comparison of all the
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measured regions revealed that the bite wafer method produced smaller errors than the facebow wafer method. Regarding the Is, the error was 0.42±0.32 mm with the bite wafer and 0.79±0.59 mm with the facebow wafer, which indicated a significant difference between
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groups (P = .010).
The total errors in the absolute values of anteroposterior distances were 0.73±0.55
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mm (mean±SD) with the bite wafer and 0.65±0.56 mm with the facebow wafer (Table IV). The two surgical methods did not differ significantly (P = .305). A comparison of the differences measured at each preset point showed that none of the four measurement points differed significantly between groups; thus, the anteroposterior positions were similar for the bite wafer and facebow wafer methods. The total errors in the vertical distances were 0.47±0.77 mm (mean±SD) with the bite wafer and 0.00±0.78 mm with the facebow wafer (Table V), which represented a significant difference between the surgical groups (P < .001). The bite wafer method had a large vertical 12
ACCEPTED MANUSCRIPT error with a positive mean value, which indicated an inferior deviation of the maxilla. Moreover, the facebow wafer group had negative mean values in the Is and Ms regions; this revealed a superior (upward) deviation.
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The total errors in the lateral distances were 0.08±0.45 mm (mean±SD) for the bite wafer and –0.34±0.64 mm for the facebow wafer (Table VI), which represented a significant difference between the surgical groups (P < .001). The bite wafer method had a smaller
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lateral error than the facebow wafer method. Moreover, the negative mean value observed with the facebow wafer method revealed a rightward deviation pattern.
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The total errors in the anteroposterior distances were –0.00±0.92 mm (mean±SD) with the bite wafer and 0.25±0.82 mm with the facebow wafer (Table VII). However, the two surgical methods did not differ significantly (P = .058). The bite wafer produced a positive shift in both tooth regions, which indicated an anterior position compared with the
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preoperative surgical simulation. The facebow wafer produced mean negative values in all four measured regions, which indicated a posterior deviation compared with the preoperative
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DISCUSSION
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surgical simulation.
Recent attention has focused on surgical simulations and device manufacturing
methods that utilize CAD and computer-aided manufacturing (CAM) technology. The objective of this study was to compare two methods for performing maxillary orthognathic surgery. One method combined a facebow and a CAD/CAM surgical template to guide maxillary positioning (facebow wafer group). The other method used only a CAD/CAM surgical template based on the mandible to guide maxillary positioning (bite wafer group). We examined the precision of each method for orthognathic surgery by comparing 13
ACCEPTED MANUSCRIPT experimental results with the results of a simulation. A comparison of the absolute value of distance difference with the simulation results revealed significant between-group differences in the lateral error. The bite wafer method
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exhibited little lateral error, as well as little error in the anterior tooth region. The facebow wafer method exhibited very little vertical error in the posterior molar region.
During the current preclinical experiment, the clinical utility of the facebow wafer did
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not significantly exceed that of the bite wafer. For real clinical procedures, we recommend that using a posterior vertical measurement reference in addition to the anterior vertical
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measurement might reduce the posterior error observed regarding the bite wafer method. When we compared the 3D minimum distance errors at each of the four measured points, we observed no significant between-group differences; the mean error ranged from 1.0 mm to 1.4 mm. When we compared the other distances, the two methods exhibited
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similar vertical errors (mean absolute values: bite wafer method: 0.69; facebow wafer method: 0.61). The facebow wafer group exhibited smaller vertical errors regarding the Ms, which indicated a smaller vertical error in the posterior molar region of the maxilla.
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Meanwhile, the bite wafer group exhibited smaller errors than the facebow wafer group regarding the LNA, which suggested a smaller error in the anterior region of the maxilla. The
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mean absolute value of vertical error in the bite wafer group ranged from 0.4 mm to 0.8 mm. This error was thought to be caused by the fact that the operation was performed based on the vertical distance from the nasion to the anterior tooth. Furthermore, the facebow method might have exhibited less posterior molar region error than the bite wafer method because in the latter method posterior errors can occur with rotation of the mandible. The total error of the absolute value of lateral distance difference was 0.35 mm with the bite wafer, which was smaller than the facebow wafer method error of 0.54 mm. The mean absolute value of lateral error in the bite wafer group was less than 0.42 mm in all 14
ACCEPTED MANUSCRIPT regions. In comparison, the mean absolute value of lateral error in the facebow wafer group exceeded 0.41 mm in all regions. Thus, the bite wafer method appeared to be less prone to lateral error than the facebow wafer method. In the directional evaluation, the facebow wafer
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method exhibited negative errors in the Is, Ms, and LNA, indicating a rightward deviation pattern. These errors were thought to be due to the unilateral location of facebow structures, including the bite plate and the facebow flank burs, which may induce a deviation in the
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maxilla.
The anteroposterior error in the bite wafer group did not differ significantly from that
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the facebow wafer group. The anteroposterior mean errors of absolute value in the bite wafer group and facebow wafer group were approximately 0.7 mm and 0.6 mm, respectively. Anteroposterior errors in the facebow wafer group ranged from -0.1 to -0.5 mm, with a negative mean value, which indicated a posterior deviation pattern. This was thought to
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originate from the natural pull of gravity on the facebow, which displaces it towards the posterior, even when it is fixed on the face. The bite wafer group had a positive mean value in the incisal and molar tooth regions, which indicated an anterior deviation in the lower
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maxilla; however, it had a negative mean value in the LNA and MxTb, which indicated a posterior deviation in the upper maxilla. This pattern, in which the upper bone of the maxilla
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deviated to the posterior and the lower maxillary tooth region deviated to the anterior, may have been caused by a rotation of the mandible. The bite wafer method displayed little lateral error, but a relatively large vertical
error. These deviations might be attributed to the orthognathic surgical template based on the mandible. Mandibular rotation could have asserted heavy influence on the vertical error, with relatively little influence on the lateral movement. Therefore, a measurement in the vertical dimension can be used as a reference for the bite wafer method. The present study used the distance from the nasion to the anterior tooth region as a reference.10 As shown in this study, 15
ACCEPTED MANUSCRIPT there can be a smaller anterior vertical error at LNA in the bite wafer method than in the facebow wafer method when the surgery is performed with reference to the vertical anterior dimension to position the anterior maxillary region. However, other outcomes are also
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possible, depending on the method used to determine the vertical dimension. In this study, the facebow wafer method had a smaller posterior vertical error than the bite wafer method. However, a different result may have been achieved with the bite wafer method if, for
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example, the vertical reference had been based on the posterior maxillary region. The bite wafer method had a positive mean vertical dimension value, which revealed that the
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postoperative maxilla exhibited an inferior (downward) deviation pattern compared with the surgical simulation. The mean errors were approximately 0.2 mm at the Is and LNA points, approximately 0.6 mm in the Ms, and approximately 0.7 mm in the MxTb. Thus, the measuring regions that are selected for the vertical dimension reference are important when
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determining the vertical error of the bite wafer method. For the facebow wafer method, the mean errors were -0.5 mm and 0.7 mm in the Is and the LNA, respectively, and -0.2 mm and 0.06 mm in the Ms and the MxTb, respectively. Thus, the facebow wafer method exhibited
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greater precision than the bite method regarding vertical location in posterior maxillary
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Sun et al. performed a clinical study on patients using an orthognathic surgical template manufactured from a 3D printer, and compared the results to a surgical simulation. They reported that the mean vertical, lateral, and anteroposterior errors in the anterior maxillary region were 0.57 mm, 0.35 mm, and 0.5 mm, respectively.11 In addition, in the present study the total absolute errors for the vertical, lateral, and anteroposterior dimensions were 0.69 mm, 0.35 mm, and 0.73 mm, respectively. Both studies used surgical guide templates manufactured by a 3D printer, the surgical simulation method, and the surgical wafer based on the mandible. 16
ACCEPTED MANUSCRIPT A clinical study by Zinser et al. employed a 3D printed orthognathic surgical guide template based on the uncut maxillary region, and compared the results to a surgical simulation. They reported that the mean vertical, lateral, and anteroposterior errors, compared
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with the anterior maxillary region, were 0.23 mm, 0.04 mm, and 0.09 mm, respectively.2 Compared with the posterior maxillary region, the vertical, lateral, and anteroposterior errors were 0.15 mm, 0.04 mm, and 0.1 mm, respectively. The surgical template design used by
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Zinser et al. was not based on the mandible or facebow, and they used the cranial maxilla for template fixation. Other recent studies have also reported the use of orthognathic surgical
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templates fixed to the upper cranial maxillary regions.2,3,6
This study had some limitations. First, we utilized RP models. Although an actual human jaw with a maxillofacial deformity might be credited with greater reliability, such materials are in limited supply. Second, the facebow runs the risk of error owing to the
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instability of its location in the cranial region and the connection between the bite plate and the facebow. Furthermore, the process of connecting the surgical template to the bite plate may introduce errors in the surgical template and in location reproducibility. In particular,
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this study was vulnerable to additional errors in the bite wafer because the CT data for the tooth region were not supplemented with cast optical scan data. Moreover, an RP model lacks
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the temporomandibular joint and external ear canal, which results in a gap that allows mandibular movement and facebow instability in actual clinical cases. Clinically, rigid fixation of a facebow-type device requires an invasive procedure, such as screw fixation on the craniofacial skeleton. Non-invasive fixation methods may result in mobility during the surgical procedure because the soft tissue is weakly supported. Additionally, we did not use metal plates, which are employed in actual clinical cases to prevent maxillary movement during the fixation process. Recently, CAD/CAM technology has been widely used to create preoperative virtual 17
ACCEPTED MANUSCRIPT simulations and to manufacture surgical templates with 3D printers.12,13 In some cases, orthognathic surgical templates are fixed onto the superior maxillary region or zygomatic region. In addition, augmented reality images, including navigation methods, are taking root
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as imaging technology advances.4,7,8,14
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CONCLUSION
In conclusion, this study evaluated the precision of a CAD/CAM-engineered surgical
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template combined with a facebow compared with a CAD/CAM-engineered wafer based on the mandible. We observed no significant between-group differences in the 3D minimum distance error or in the vertical or anteroposterior errors. The bite wafer method exhibited little lateral error, and a small error in the anterior region. The facebow wafer method
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exhibited little vertical error in the posterior region. We determined that using a posterior vertical measurement reference might reduce the posterior error observed in the bite wafer method. The clinical utility of the facebow wafer did not significantly exceed that of the bite
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wafer.
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Sadiq Z, Collyer J, Sneddon K, Walsh S. Orthognathic treatment of asymmetry: two cases of "waferless" stereotactic maxillary positioning. Br J Oral Maxillofac Surg 2012;50(2):e27-9.
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Zinser MJ, Mischkowski RA, Dreiseidler T, Thamm OC, Rothamel D, Zoller JE. Computer-assisted orthognathic surgery: waferless maxillary positioning, versatility,
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ACCEPTED MANUSCRIPT and accuracy of an image-guided visualisation display. Br J Oral Maxillofac Surg 2013;51(8):827-33. 9.
Zizelmann C, Hammer B, Gellrich NC, Schwestka-Polly R, Rana M, Bucher P. An
Maxillofac Surg 2012;70(8):1944-50. 10.
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evaluation of face-bow transfer for the planning of orthognathic surgery. J Oral
Bouchard C, Landry PE. Precision of maxillary repositioning during orthognathic
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surgery: a prospective study. Int J Oral Maxillofac Surg 2013;42(5):592-6.
Sun Y, Luebbers HT, Agbaje JO, Schepers S, Vrielinck L, Lambrichts I, et al.
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Accuracy of upper jaw positioning with intermediate splint fabrication after virtual planning in bimaxillary orthognathic surgery. J Craniofac Surg 2013;24(6):1871-6. 12.
Wang G, Li J, Khadka A, Hsu Y, Li W, Hu J. CAD/CAM and rapid prototyped titanium for reconstruction of ramus defect and condylar fracture caused by
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mandibular reduction. Oral Surg Oral Med Oral Pathol Oral Radiol 2012;113(3):356-
Kokuryo S, Habu M, Miyamoto I, Uehara M, Kodama M, Iwanaga K, et al.
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Predictability and accuracy of maxillary repositioning during bimaxillary surgery using a three-dimensional positioning technique. Oral Surg Oral Med Oral Pathol Oral
14.
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Radiol 2014;118(2):187-93. Zinser MJ, Sailer HF, Ritter L, Braumann B, Maegele M, Zoller JE. A paradigm shift in orthognathic surgery? A comparison of navigation, computer-aided designed/computer-aided manufactured splints, and "classic" intermaxillary splints to surgical transfer of virtual orthognathic planning. J Oral Maxillofac Surg 2013;71(12):2151 e1-21.
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ACCEPTED MANUSCRIPT Figure Legends Fig. 1. Experimental models. A, A 3D image of a plastic skull model. B, A 3D reconstructed image of a maxillary deformity model with maxillary transitional and rotational movements
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(e.g., 3 mm left transition model). C, A rapid prototype model of a maxillary deformity with maxillary transitional and rotational movements (e.g., 3 mm left transition model).
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Fig. 2. Orthognathic surgery with the 3D-printed surgical template, based on the facebow. A, The design of a facebow positioning guide (first surgical template), which set the axis of the
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facebow and determined the location of the facebow bite plate in the experimental model. B, The design of a maxillary surgical guide (second surgical template) connected to a facebow for maxillary repositioning. C, Setting the axis of a facebow with a facebow positioning guide (first surgical template) in the rapid prototype (RP) experimental model. D, Maxillary
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orthognathic surgery in the RP model utilizing a maxillary surgical guide (second surgical template) mounted in a preset fixed bite plate connected to a facebow.
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Fig. 3. Orthognathic surgery with the 3D-printed surgical template, based on the mandible. A, A 3D-reconstructed image of the maxillary deformity model. B, The design of a bite splint-
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type orthognathic surgical template, based on the mandible, for maxillary repositioning. C, A rapid prototype (RP) model of a maxillary deformity for experimental surgery. D, Maxillary orthognathic surgery in the RP model utilizing a bite splint-type orthognathic surgical template based on the mandible.
Fig. 4. Outcomes of surgical simulation (grey) compared with experimental postoperative results (pink). Data was overlapped using surface-based image registration; the reference area was the cranial region (yellow mesh). 21
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Fig. 5. Three reference planes for measuring the differences in distance between the simulation and the postoperative experimental results. The four measuring points shown were
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placed symmetrically on both sides of the skull. For example, on the left side, the measurement points are labeled as follows: #21, Left incisor tip; #26MBC, Left first molar mesiobuccal cusp; Lt-Nasal Aperture, Left lateral nasal aperture; Lt-Mx tuberosity, Left
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maxillary tuberosity.
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Tables Table I. Differences in 3D minimum distance for different surgical template types (mm) Measuring pointa
Facebow wafer
p-value
Is (n=24)
1.18 ± 0.60
1.42 ± 0.64
.199
Ms (n=24)
1.27 ± 0.58
1.01 ± 0.67
.167
MxTb (n=24)
1.26 ± 0.81
1.11 ± 0.52
.460
LNA (n=24)
1.14 ± 0.52
1.34 ± 0.58
.232
Total (n=96)
1.21 ± 0.63
1.22 ± 0.62
.942
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Note: Values represent the mean ± standard deviation of the difference between measurements made with the indicated surgical template (wafer) and those made during the
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preoperative simulation (i.e., template-simulation).
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.64 ± 0.44
0.59 ± 0.44
.702
Ms (n=24)
0.81 ± 0.51
0.44 ± 0.43
.010
MxTb (n=24)
0.83 ± 0.85
0.61 ± 0.51
LNA (n=24)
0.49 ± 0.40
0.80 ± 0.50
Total (n=96)
0.69 ± 0.59
0.61 ± 0.48
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Bite wafer
.282 .023 .295
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measurements made with the indicated surgical template (wafer) and those made during the
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preoperative simulation (i.e., template-simulation).
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.42 ± 0.32
0.79 ± 0.59
.010
Ms (n=24)
0.31 ± 0.26
0.43 ± 0.35
.193
MxTb (n=24)
0.29 ± 0.23
0.41 ± 0.35
LNA (n=24)
0.38 ± 0.32
0.55 ± 0.49
Total (n=96)
0.35 ± 0.29
0.54 ± 0.47
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Bite wafer
.178 .163 .001
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measurements made with the indicated surgical template (wafer) and those made during the
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preoperative simulation (i.e., template-simulation).
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.68 ± 0.66
0.67 ± 0.68
.986
Ms (n=24)
0.76 ± 0.52
0.67 ± 0.58
.577
MxTb (n=24)
0.72 ± 0.44
0.61 ± 0.47
.402
LNA (n=24)
0.78 ± 0.59
0.65 ± 0.51
.440
Total (n=96)
0.73 ± 0.55
0.65 ± 0.56
.305
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Bite wafer
Note: Values represent the mean ± standard deviation of the difference between
preoperative simulation (i.e., template-simulation).
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measurements made with the indicated surgical template (wafer) and those made during the
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Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.25 ± 0.74
-0.50 ± 0.54
<0.001
Ms (n=24)
0.66 ± 0.71
-0.25 ± 0.57
<0.001
MxTb (n=24)
0.76 ± 0.91
0.06 ± 0.80
LNA (n=24)
0.22 ± 0.59
0.72 ± 0.62
Total (n=96)
0.47 ± 0.77
0.00 ± 0.78
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Bite wafer
.007
.008
<0.001
Note: Values represent the mean ± standard deviation of the difference between
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measurements made with the indicated surgical template (wafer) and those made during the preoperative simulation (i.e., template-simulation). Positive values indicate an inferior deviation of the maxilla.
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region.
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.04 ± 0.53
-0.68 ± 0.72
<0.001
Ms (n=24)
0.09 ± 0.40
-0.27 ± 0.49
.007
MxTb (n=24)
0.07 ± 0.37
0.01 ± 0.55
LNA (n=24)
0.10 ± 0.49
-0.44 ± 0.60
Total (n=96)
0.08 ± 0.45
-0.34 ± 0.64
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Bite wafer
.664
.001
<0.001
Note: Values represent the mean ± standard deviation of the difference between
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measurements made with the indicated surgical template (wafer) and those made during the preoperative simulation (i.e., template-simulation). Positive values indicate a left lateral deviation of the maxilla.
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region.
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.20 ± 0.93
-0.18 ± 0.95
.169
Ms (n=24)
0.39 ± 0.84
-0.11 ± 0.89
.045
MxTb (n=24)
-0.04 ± 0.86
-0.18 ± 0.76
.551
LNA (n=24)
-0.59 ± 0.79
-0.51 ± 0.66
.719
Total (n=96)
-0.00 ± 0.92
-0.25 ± 0.82
.058
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Bite wafer
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measurements made with the indicated surgical template (wafer) and those made during the preoperative simulation (i.e., template-simulation). Positive values indicate an anterior
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deviation of the maxilla.
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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ACCEPTED MANUSCRIPT Clinical relevance Controlled preclinical experimentation proved that the clinical utility of the facebow wafer did not significantly exceed that of the bite wafer. Using a posterior vertical measurement
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reference might reduce the posterior error observed in the bite wafer method.
S2212-4403(15)01086-X
DOI:
10.1016/j.oooo.2015.07.007
Reference:
OOOO 1250
To appear in:
Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology
Received Date: 13 January 2015 Revised Date:
21 April 2015
Accepted Date: 13 July 2015
Please cite this article as: Lee J-W, Lim S-H, Kim M-K, Kang S-H, Precision of a CAD/CAM-engineered surgical template based on a facebow for orthognathic surgery: an experiment with a rapid prototyping maxillary model, Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology (2015), doi: 10.1016/ j.oooo.2015.07.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Precision of a CAD/CAM-engineered surgical template based on a facebow for orthognathic surgery: an experiment with a rapid prototyping
Jae-Won Lee, DDS, MS,a
Se-Ho Lim, DDS,a
Moon-Key Kim, DDS, PhD,a,b Sang-Hoon
a
Department of Oral and Maxillofacial Surgery, National Health Insurance Service Ilsan
Hospital, Goyang, Republic of Korea
Department of Oral and Maxillofacial Surgery, College of Dentistry, Yonsei University,
Seoul, Republic of Korea
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b
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Kang, DDS PhD,a,b,
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maxillary model
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Corresponding author:
Sang-Hoon Kang DDS, PhD
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Faculty, Department of Oral and Maxillofacial Surgery, National Health Insurance Service Ilsan Hospital, 100 Ilsan-ro, Ilsan-donggu, Goyang, Gyeonggi-do, 410-719, Republic of Korea
Clinical assistant professor, Department of Oral and Maxillofacial Surgery, College of Dentistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea E-mail address : [email protected] Tel.: +82-31-900-0267; Fax: +82-31-900-0343
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CONFLICT OF INTEREST STATEMENT
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The authors declare no conflicts of interest in this study.
ACKNOWLEDGEMENT
Research
Foundation
of
Korea
funded
by
the
Ministry
of
Education
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(2013R1A1A2009251)
(NRF)
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This research was supported by Basic Science Research Program through the National
- Word count for the abstract : 199
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- Complete manuscript word count: 4547 (body text:4213 and figure legends:334)
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- Number of references: 14 - Number of figures: 5
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- Number of tables: 7
- No supplementary elements
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ACCEPTED MANUSCRIPT Precision of a CAD/CAM-engineered surgical template based on a facebow for
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orthognathic surgery: an experiment with a rapid prototyping maxillary model
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ABSTRACT Objective. We examined the precision of a CAD/CAM-engineered, manufactured, facebowbased surgical guide template (facebow wafer) by comparing it with a bite splint-type
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orthognathic CAD/CAM-engineered surgical guide template (bite wafer). Study Design. We used 24 rapid prototyping (RP) models of the craniofacial skeleton with maxillary deformities. Twelve RP models each were used for the facebow wafer group and
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the bite wafer group (experimental group). Experimental maxillary orthognathic surgery was performed on the RP models of both groups. Errors were evaluated through comparisons with
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surgical simulations. We measured the minimum distances from three planes of reference to determine the vertical, lateral, and anteroposterior errors at specific measurement points. The measured errors were compared between experimental groups using a t-test. Results. There were significant intergroup differences in the lateral error when we compared
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the absolute values of the 3D linear distance, as well as vertical, lateral, and anteroposterior errors between experimental groups. The bite wafer method exhibited little lateral error overall, and little error in the anterior tooth region. The facebow wafer method exhibited very
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little vertical error in the posterior molar region. Conclusions. The clinical precision of the facebow wafer method did not significantly
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exceed that of the bite wafer method.
Keywords: CAD/CAM; Computer aided surgery; Facebow; Orthognathic surgery; Surgical guide template
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INTRODUCTION Three-dimensional (3D) imaging acquired with computed tomography (CT) has recently become universally recognized as an important tool in the diagnosis and evaluation
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of dentocraniofacial deformity and in orthognathic surgical simulations.1 In orthognathic surgeries, 3D images can be utilized to perform surgical simulations before the actual
operation. The 3D images can also be used to manufacture appropriate orthognathic surgical
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devices with 3D printers.2
When the surgical treatment plan is accurately represented with a preoperative
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virtual simulation, it indicates the exact dimensions needed for a surgical template (wafer). Then, an appropriate surgical template can be designed and manufactured with computeraided design (CAD) and a 3D printer.2,3 However, even state-of-the-art surgical devices— particularly the widely-used splints—are vulnerable to error. There may be a number of
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causes for errors, including a change in the positioning of the jaws; reproducibility of the reference point; and problems with vertical dimensions. To reduce these potential errors, surgical methods can be designed in various forms for a range of purposes. One device that is
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used determines the location of the mandibular condyle; in other cases, a surgical navigation
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method is used that augments surgical precision by matching the surgical reference point in the actual patient in the operating room to the corresponding reference point in a 3D surgical simulation.4 Various surgical devices have been developed to connect intact anatomical structures other than the upper and lower jaws, which are displaced during surgery.2,3,5,6 Recent studies have reported new methods with waferless systems, including navigation systems and skull-related repositioning systems.4,7,8 Facebow-using methods have also been described that can minimize error regarding the location of the maxilla.9 Traditionally, facebows have been used to mount dental cast
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extraorally. Nevertheless, a facebow may be useful in surgery, when it is able to achieve location stability within a certain range, and when it is possible to manufacture an appropriate surgical template that can be anchored onto the facebow plate during the operation. This
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method retains the primary advantages of 3D imaging technology. Moreover, facebow data can apply patient-specific location data from the cranial region and maintain the vertical
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dimensions without depending on the positioning of the mandible.
The aim of the present study was to develop a new method for guiding the placement of the maxilla using a facebow. The surgical templates were designed with CAD. Preoperative 3D surgical simulations were performed using facebow data in order to
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manufacture the templates using 3D printers. Then, we examined the precision of the manufactured facebow-based surgical template (facebow wafer) by comparing it with the bite splint-type orthognathic surgical template (bite wafer) manufactured using stereolithography
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(STL) data.
MATERIALS AND METHODS
Rapid prototyping model of craniofacial skeleton and 3D surgical simulation This study was performed with a rapid prototyping (RP) model of the craniofacial skeleton based on CT data acquired from a plastic skull model (A20 classic human skull model, 3B Scientific, Hamburg, Germany). The DICOM file of the CT data was imported into Mimics, version 14.0 software (Materialise, Leuven, Belgium). Then, the data was 6
ACCEPTED MANUSCRIPT restructured to create a 3D image (Figure 1, A). The model of the maxilla and mandible was adjusted to represent different maxillary deformities. The variant maxillary deformity models were created with three translational movements—lateral, vertical, and horizontal—all
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displaced by 3 mm, and three rotational movements about the joint—roll, yaw, and pitch (Figure 1, B). Twelve variant maxillary deformity models were created (six translated
deformity models and six rotated deformity models), and the data were then extracted to an
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STL file. We manufactured one pair of each maxilla-deformed model with a 3D printer
(ProJet 360, 3D Systems, Inc, Rock Hill, SC), for a total of 24 RP models (Figure 1, C).
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Thus, we used 12 RP models for the facebow wafer group and 12 for the bite wafer group. Each RP model was used in a simulation of a surgery that would treat the displaced maxilla. The simulation was conducted in Mimics software. In the surgical simulation, the maxilla was displaced in a symmetrical skeleton, as it would be displaced in an actual clinical
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simulation protocol.
Facebow wafer group: orthognathic surgical template based on the facebow
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The facebow (Artex®, Amann Girrbach AG, Koblach, Austria) was used in the facebow wafer group. Two STL surgical templates were designed prior to the surgery. The
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first surgical template (facebow positioning guide) was used to set the facebow. The template was designed to determine the location of the bite plate of the facebow based on the position of the maxilla in the preoperative condition (Figure 2, A). The second surgical template (maxillary surgical guide) was designed to position the maxilla during surgery, as informed by the surgical simulation based on the position of the postoperative maxilla and the preset position of the bite plate on the facebow (Figure 2, B). The simulation data for the designs of these two surgical templates (facebow positioning guide and maxillary surgical guide) were extracted into STL file formats. The STL data were then used to manufacture the two 7
ACCEPTED MANUSCRIPT orthognathic surgical templates using a 3D printer (ProJet 3500 HDMax 3D Printer). The facebow was positioned using the first surgical template, and then maxillary surgery was performed on the RP models using the second surgical template. Briefly, we
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used one first surgical template (facebow positioning guide) that set the axis of the facebow and determined the location of the facebow bite plate in the RP experimental model (Figure 2, C). Then, the second surgical template (maxillary surgical guide) was mounted in a preset
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fixed bite plate connected to the facebow. A Le Fort I osteotomy was performed on the
maxilla, starting from the lateral nasal aperture area and extending to the posterior maxilla,
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with a fissure bur and an industrial-grade thread saw. Then, the maxilla was moved to the position indicated by the second surgical template mounted onto the facebow (Figure 2, D). The maxilla was secured with the second surgical template mounted onto the facebow using cyanoacrylate adhesive. After this experimental maxillary orthognathic surgery was
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complete, we performed maxillary fixation with utility wax.
Bite wafer group: orthognathic surgical template based on the mandible
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For the bite wafer group, the design of the orthognathic surgical template was based on the postoperative maxillary position after an orthognathic surgical simulation (Fig. 3, A,
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B). Using the boolean function in Mimics, the surgical template was designed from the tooth region of the operative maxilla and the current mandible. The surgical template was guided by the mandible. The simulated design data for the surgical template were extracted into the STL file format, which was then used to manufacture the surgical template with a 3D printer (ProJet 3500 HDMax 3D Printer, 3D Systems, Inc., Rock Hill, SC). The manufactured orthognathic surgical template was used to perform surgery on the maxilla in the RP model; maxillary surgery was based on the mandible location (Fig. 3, C, D). After positioning the 3D-printed surgical template, we performed an osteotomy on the 8
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lateral nasal aperture to the posterior maxilla. The maxilla and mandible were secured to the bite wafer by intermaxillary fixation using stainless steel wire. Then, the fixed
maxillomandibular complex with the bite wafer was manipulated while the condyle head was
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kept in contact with the glenoid fossa. Condylar contact with the glenoid fossa was
maintained manually during the experimental maxillary orthognathic surgery. After the
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experimental maxillary surgery, maxillary fixation was accomplished using utility wax.
Error measurements and analysis of results with the surgical templates We performed CT scans on the 12 RP models in the facebow and bite wafer groups
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after they underwent maxillary orthognathic surgery. All scans were performed under the same conditions. The CT data was overlapped with the simulation data from the orthognathic surgery based on the preoperative plan, and we compared the actual results with the
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simulation data (Figure 4).
To overlap the surgical simulation data with actual experimental data, we used the
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same settings to acquire CT images of the RP models before and after orthognathic maxilla surgery. We transformed these images into 3D structures using Mimics software, and then extracted the data into an STL file format. We also extracted the data resulting from the surgical simulation into an STL file format. Using XOV2 software (INUS Technology, Seoul, Republic of Korea), we set the non-operated cranial region as the reference region for registering the images. With this regional reference, the STL data from the experimental surgery were overlapped with the data from the simulation results. Then, we used Mimics software to import the overlapped data into SimPlant software version 14.0 (Materialise 9
ACCEPTED MANUSCRIPT Dental, Leuven, Belgium). We measured the vertical, lateral, anteroposterior, and 3D minimum distance differences between the simulation results and the actual experimental surgery results.
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The measurements were made using the SimPlant program; three reference planes were set in the cranial region of each dataset (Figure 5). Then, we measured the distance from corresponding points on the operated maxilla and the surgical simulation to the reference
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planes, and evaluated the difference between those distances. The first reference plane was the Frankfort (FH) plane, which was established with three points: a center-point between the
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bilateral orbitale (infraorbital margin), and two points on the porions of the external auditory canal regions, one on each side. The second reference plane was the mid-sagittal plane, which was perpendicular to the FH plane and extended through the nasion and the internal occipital crest. The third reference plane was the coronal plane, which extended through the nasion and
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was perpendicular to both the FH plane and the mid-sagittal plane. We measured the minimum distances from each of these three planes in order to determine the vertical, lateral, and anteroposterior errors of the measured points.
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We selected four measurement points on each side of the maxilla (Figure 5): the first point was on the central incisor corner (Is; Figure 5), the second was in the first molar
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mesiobuccal cusp region (Ms; Figure 5), the third was in the maxillary tuberosity region (MxTb), and the fourth was in the lateral nasal aperture region (LNA). One examiner marked the measurement points and ensured that the locations were identical in the surgical simulation and the actual experimental image. We evaluated the differences (errors) between the surgical result and the simulation at each of these measurement points. At each point, we measured the vertical, lateral, and anteroposterior distances from the preset vertical FH plane, mid-sagittal plane, and coronal plane. A positive vertical error indicated that the postexperimental region was placed inferiorly (downward) with respect to the cranial region, 10
ACCEPTED MANUSCRIPT compared with the simulation. A positive lateral error indicated that the post-experimental region was placed leftward with respect to the cranial region, compared with the simulation. A positive anteroposterior error indicated that the post-experimentally measured region was
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placed anteriorly with respect to the cranial region, compared with the simulation. Finally, the 3D minimum distance was measured between corresponding measurement points on the experimental model and the simulation. Total error was defined as the mean error of the
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combined four measurement points. We also evaluated absolute values of differences (errors) between the surgical result and the simulation at each of these measurement points and
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planes.
Using a t-test, the measured results (errors) were compared between groups that received maxillary orthognathic surgery with either the facebow wafer group or the bite wafer group. P < .05 was considered statistically significant. The intra-operator error was
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RESULTS
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determined by comparing 12 repetitive selections of a single point.
We compared the results of orthognathic surgery on the maxilla performed using two
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different methods. One method utilized a surgical facebow wafer that was combined with a facebow for maxillary positioning; the second method utilized an bite wafer. The total errors in the 3D minimum distances were 1.21±0.63 mm (mean±SD) for
surgery with a bite wafer and 1.22±0.62 mm for surgery with a facebow wafer (Table I). The two surgical methods did not differ significantly (P = .942). Comparison of the measurements for each of the four preset points—Is, Ms, MxTb, and LNA—also did not reveal any significant differences between the bite wafer and facebow wafer groups.
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ACCEPTED MANUSCRIPT The total errors in the absolute values of vertical distances were 0.69±0.59 mm (mean±SD) with the bite wafer, and 0.61±0.48 mm with the facebow wafer (Table II), which did not represent a significant difference between the surgical groups (P = .295). A
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comparison of the mean absolute values of differences in vertical distance at each measured point demonstrated that the bite wafer group (0.49 ± 0.40) had a smaller error than the
facebow wafer group (0.80 ± 0.50) in the LNA (P = .023). On the other hand, the facebow
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wafer group (0.44 ± 0.43) had a smaller error than the bite wafer group (0.81 ± 0.51) in the Ms (P = .010), which indicated a smaller error in the posterior maxillary region.
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The total errors in the absolute values of lateral distances were 0.35±0.29 mm (mean±SD) for the bite wafer and 0.54±0.47 mm for the facebow wafer (Table III), which represented a significant difference between the surgical groups (P = .001). The bite wafer method had a smaller lateral error than the facebow wafer method. Comparison of all the
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measured regions revealed that the bite wafer method produced smaller errors than the facebow wafer method. Regarding the Is, the error was 0.42±0.32 mm with the bite wafer and 0.79±0.59 mm with the facebow wafer, which indicated a significant difference between
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groups (P = .010).
The total errors in the absolute values of anteroposterior distances were 0.73±0.55
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mm (mean±SD) with the bite wafer and 0.65±0.56 mm with the facebow wafer (Table IV). The two surgical methods did not differ significantly (P = .305). A comparison of the differences measured at each preset point showed that none of the four measurement points differed significantly between groups; thus, the anteroposterior positions were similar for the bite wafer and facebow wafer methods. The total errors in the vertical distances were 0.47±0.77 mm (mean±SD) with the bite wafer and 0.00±0.78 mm with the facebow wafer (Table V), which represented a significant difference between the surgical groups (P < .001). The bite wafer method had a large vertical 12
ACCEPTED MANUSCRIPT error with a positive mean value, which indicated an inferior deviation of the maxilla. Moreover, the facebow wafer group had negative mean values in the Is and Ms regions; this revealed a superior (upward) deviation.
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The total errors in the lateral distances were 0.08±0.45 mm (mean±SD) for the bite wafer and –0.34±0.64 mm for the facebow wafer (Table VI), which represented a significant difference between the surgical groups (P < .001). The bite wafer method had a smaller
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lateral error than the facebow wafer method. Moreover, the negative mean value observed with the facebow wafer method revealed a rightward deviation pattern.
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The total errors in the anteroposterior distances were –0.00±0.92 mm (mean±SD) with the bite wafer and 0.25±0.82 mm with the facebow wafer (Table VII). However, the two surgical methods did not differ significantly (P = .058). The bite wafer produced a positive shift in both tooth regions, which indicated an anterior position compared with the
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preoperative surgical simulation. The facebow wafer produced mean negative values in all four measured regions, which indicated a posterior deviation compared with the preoperative
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DISCUSSION
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surgical simulation.
Recent attention has focused on surgical simulations and device manufacturing
methods that utilize CAD and computer-aided manufacturing (CAM) technology. The objective of this study was to compare two methods for performing maxillary orthognathic surgery. One method combined a facebow and a CAD/CAM surgical template to guide maxillary positioning (facebow wafer group). The other method used only a CAD/CAM surgical template based on the mandible to guide maxillary positioning (bite wafer group). We examined the precision of each method for orthognathic surgery by comparing 13
ACCEPTED MANUSCRIPT experimental results with the results of a simulation. A comparison of the absolute value of distance difference with the simulation results revealed significant between-group differences in the lateral error. The bite wafer method
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exhibited little lateral error, as well as little error in the anterior tooth region. The facebow wafer method exhibited very little vertical error in the posterior molar region.
During the current preclinical experiment, the clinical utility of the facebow wafer did
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not significantly exceed that of the bite wafer. For real clinical procedures, we recommend that using a posterior vertical measurement reference in addition to the anterior vertical
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measurement might reduce the posterior error observed regarding the bite wafer method. When we compared the 3D minimum distance errors at each of the four measured points, we observed no significant between-group differences; the mean error ranged from 1.0 mm to 1.4 mm. When we compared the other distances, the two methods exhibited
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similar vertical errors (mean absolute values: bite wafer method: 0.69; facebow wafer method: 0.61). The facebow wafer group exhibited smaller vertical errors regarding the Ms, which indicated a smaller vertical error in the posterior molar region of the maxilla.
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Meanwhile, the bite wafer group exhibited smaller errors than the facebow wafer group regarding the LNA, which suggested a smaller error in the anterior region of the maxilla. The
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mean absolute value of vertical error in the bite wafer group ranged from 0.4 mm to 0.8 mm. This error was thought to be caused by the fact that the operation was performed based on the vertical distance from the nasion to the anterior tooth. Furthermore, the facebow method might have exhibited less posterior molar region error than the bite wafer method because in the latter method posterior errors can occur with rotation of the mandible. The total error of the absolute value of lateral distance difference was 0.35 mm with the bite wafer, which was smaller than the facebow wafer method error of 0.54 mm. The mean absolute value of lateral error in the bite wafer group was less than 0.42 mm in all 14
ACCEPTED MANUSCRIPT regions. In comparison, the mean absolute value of lateral error in the facebow wafer group exceeded 0.41 mm in all regions. Thus, the bite wafer method appeared to be less prone to lateral error than the facebow wafer method. In the directional evaluation, the facebow wafer
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method exhibited negative errors in the Is, Ms, and LNA, indicating a rightward deviation pattern. These errors were thought to be due to the unilateral location of facebow structures, including the bite plate and the facebow flank burs, which may induce a deviation in the
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maxilla.
The anteroposterior error in the bite wafer group did not differ significantly from that
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the facebow wafer group. The anteroposterior mean errors of absolute value in the bite wafer group and facebow wafer group were approximately 0.7 mm and 0.6 mm, respectively. Anteroposterior errors in the facebow wafer group ranged from -0.1 to -0.5 mm, with a negative mean value, which indicated a posterior deviation pattern. This was thought to
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originate from the natural pull of gravity on the facebow, which displaces it towards the posterior, even when it is fixed on the face. The bite wafer group had a positive mean value in the incisal and molar tooth regions, which indicated an anterior deviation in the lower
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maxilla; however, it had a negative mean value in the LNA and MxTb, which indicated a posterior deviation in the upper maxilla. This pattern, in which the upper bone of the maxilla
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deviated to the posterior and the lower maxillary tooth region deviated to the anterior, may have been caused by a rotation of the mandible. The bite wafer method displayed little lateral error, but a relatively large vertical
error. These deviations might be attributed to the orthognathic surgical template based on the mandible. Mandibular rotation could have asserted heavy influence on the vertical error, with relatively little influence on the lateral movement. Therefore, a measurement in the vertical dimension can be used as a reference for the bite wafer method. The present study used the distance from the nasion to the anterior tooth region as a reference.10 As shown in this study, 15
ACCEPTED MANUSCRIPT there can be a smaller anterior vertical error at LNA in the bite wafer method than in the facebow wafer method when the surgery is performed with reference to the vertical anterior dimension to position the anterior maxillary region. However, other outcomes are also
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possible, depending on the method used to determine the vertical dimension. In this study, the facebow wafer method had a smaller posterior vertical error than the bite wafer method. However, a different result may have been achieved with the bite wafer method if, for
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example, the vertical reference had been based on the posterior maxillary region. The bite wafer method had a positive mean vertical dimension value, which revealed that the
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postoperative maxilla exhibited an inferior (downward) deviation pattern compared with the surgical simulation. The mean errors were approximately 0.2 mm at the Is and LNA points, approximately 0.6 mm in the Ms, and approximately 0.7 mm in the MxTb. Thus, the measuring regions that are selected for the vertical dimension reference are important when
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determining the vertical error of the bite wafer method. For the facebow wafer method, the mean errors were -0.5 mm and 0.7 mm in the Is and the LNA, respectively, and -0.2 mm and 0.06 mm in the Ms and the MxTb, respectively. Thus, the facebow wafer method exhibited
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greater precision than the bite method regarding vertical location in posterior maxillary
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Sun et al. performed a clinical study on patients using an orthognathic surgical template manufactured from a 3D printer, and compared the results to a surgical simulation. They reported that the mean vertical, lateral, and anteroposterior errors in the anterior maxillary region were 0.57 mm, 0.35 mm, and 0.5 mm, respectively.11 In addition, in the present study the total absolute errors for the vertical, lateral, and anteroposterior dimensions were 0.69 mm, 0.35 mm, and 0.73 mm, respectively. Both studies used surgical guide templates manufactured by a 3D printer, the surgical simulation method, and the surgical wafer based on the mandible. 16
ACCEPTED MANUSCRIPT A clinical study by Zinser et al. employed a 3D printed orthognathic surgical guide template based on the uncut maxillary region, and compared the results to a surgical simulation. They reported that the mean vertical, lateral, and anteroposterior errors, compared
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with the anterior maxillary region, were 0.23 mm, 0.04 mm, and 0.09 mm, respectively.2 Compared with the posterior maxillary region, the vertical, lateral, and anteroposterior errors were 0.15 mm, 0.04 mm, and 0.1 mm, respectively. The surgical template design used by
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Zinser et al. was not based on the mandible or facebow, and they used the cranial maxilla for template fixation. Other recent studies have also reported the use of orthognathic surgical
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templates fixed to the upper cranial maxillary regions.2,3,6
This study had some limitations. First, we utilized RP models. Although an actual human jaw with a maxillofacial deformity might be credited with greater reliability, such materials are in limited supply. Second, the facebow runs the risk of error owing to the
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instability of its location in the cranial region and the connection between the bite plate and the facebow. Furthermore, the process of connecting the surgical template to the bite plate may introduce errors in the surgical template and in location reproducibility. In particular,
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this study was vulnerable to additional errors in the bite wafer because the CT data for the tooth region were not supplemented with cast optical scan data. Moreover, an RP model lacks
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the temporomandibular joint and external ear canal, which results in a gap that allows mandibular movement and facebow instability in actual clinical cases. Clinically, rigid fixation of a facebow-type device requires an invasive procedure, such as screw fixation on the craniofacial skeleton. Non-invasive fixation methods may result in mobility during the surgical procedure because the soft tissue is weakly supported. Additionally, we did not use metal plates, which are employed in actual clinical cases to prevent maxillary movement during the fixation process. Recently, CAD/CAM technology has been widely used to create preoperative virtual 17
ACCEPTED MANUSCRIPT simulations and to manufacture surgical templates with 3D printers.12,13 In some cases, orthognathic surgical templates are fixed onto the superior maxillary region or zygomatic region. In addition, augmented reality images, including navigation methods, are taking root
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as imaging technology advances.4,7,8,14
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CONCLUSION
In conclusion, this study evaluated the precision of a CAD/CAM-engineered surgical
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template combined with a facebow compared with a CAD/CAM-engineered wafer based on the mandible. We observed no significant between-group differences in the 3D minimum distance error or in the vertical or anteroposterior errors. The bite wafer method exhibited little lateral error, and a small error in the anterior region. The facebow wafer method
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exhibited little vertical error in the posterior region. We determined that using a posterior vertical measurement reference might reduce the posterior error observed in the bite wafer method. The clinical utility of the facebow wafer did not significantly exceed that of the bite
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References 1.
Eggers G, Senoo H, Kane G, Muhling J. The accuracy of image guided surgery based
Oral Radiol Endod 2009;107(3):e41-8. 2.
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on cone beam computer tomography image data. Oral Surg Oral Med Oral Pathol
Zinser MJ, Mischkowski RA, Sailer HF, Zoller JE. Computer-assisted orthognathic surgery: feasibility study using multiple CAD/CAM surgical splints. Oral Surg Oral
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Med Oral Pathol Oral Radiol 2012;113(5):673-87.
Kang SH, Kim MK, Kim BC, Lee SH. Orthognathic Y-splint: a CAD/CAM-
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engineered maxillary repositioning wafer assembly. Br J Oral Maxillofac Surg 2014;52(7):667-9. 4.
Li B, Zhang L, Sun H, Shen SG, Wang X. A new method of surgical navigation for orthognathic surgery: optical tracking guided free-hand repositioning of the
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maxillomandibular complex. J Craniofac Surg 2014;25(2):406-11. Polley JW, Figueroa AA. Orthognathic positioning system: intraoperative system to transfer virtual surgical plan to operating field during orthognathic surgery. J Oral
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Maxillofac Surg 2013;71(5):911-20.
Li B, Zhang L, Sun H, Yuan J, Shen SG, Wang X. A novel method of computer aided
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orthognathic surgery using individual CAD/CAM templates: a combination of osteotomy and repositioning guides. Br J Oral Maxillofac Surg 2013;51(8):e239-44.
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Sadiq Z, Collyer J, Sneddon K, Walsh S. Orthognathic treatment of asymmetry: two cases of "waferless" stereotactic maxillary positioning. Br J Oral Maxillofac Surg 2012;50(2):e27-9.
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Zinser MJ, Mischkowski RA, Dreiseidler T, Thamm OC, Rothamel D, Zoller JE. Computer-assisted orthognathic surgery: waferless maxillary positioning, versatility,
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ACCEPTED MANUSCRIPT and accuracy of an image-guided visualisation display. Br J Oral Maxillofac Surg 2013;51(8):827-33. 9.
Zizelmann C, Hammer B, Gellrich NC, Schwestka-Polly R, Rana M, Bucher P. An
Maxillofac Surg 2012;70(8):1944-50. 10.
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evaluation of face-bow transfer for the planning of orthognathic surgery. J Oral
Bouchard C, Landry PE. Precision of maxillary repositioning during orthognathic
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surgery: a prospective study. Int J Oral Maxillofac Surg 2013;42(5):592-6.
Sun Y, Luebbers HT, Agbaje JO, Schepers S, Vrielinck L, Lambrichts I, et al.
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Accuracy of upper jaw positioning with intermediate splint fabrication after virtual planning in bimaxillary orthognathic surgery. J Craniofac Surg 2013;24(6):1871-6. 12.
Wang G, Li J, Khadka A, Hsu Y, Li W, Hu J. CAD/CAM and rapid prototyped titanium for reconstruction of ramus defect and condylar fracture caused by
61. 13.
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mandibular reduction. Oral Surg Oral Med Oral Pathol Oral Radiol 2012;113(3):356-
Kokuryo S, Habu M, Miyamoto I, Uehara M, Kodama M, Iwanaga K, et al.
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Predictability and accuracy of maxillary repositioning during bimaxillary surgery using a three-dimensional positioning technique. Oral Surg Oral Med Oral Pathol Oral
14.
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Radiol 2014;118(2):187-93. Zinser MJ, Sailer HF, Ritter L, Braumann B, Maegele M, Zoller JE. A paradigm shift in orthognathic surgery? A comparison of navigation, computer-aided designed/computer-aided manufactured splints, and "classic" intermaxillary splints to surgical transfer of virtual orthognathic planning. J Oral Maxillofac Surg 2013;71(12):2151 e1-21.
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ACCEPTED MANUSCRIPT Figure Legends Fig. 1. Experimental models. A, A 3D image of a plastic skull model. B, A 3D reconstructed image of a maxillary deformity model with maxillary transitional and rotational movements
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(e.g., 3 mm left transition model). C, A rapid prototype model of a maxillary deformity with maxillary transitional and rotational movements (e.g., 3 mm left transition model).
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Fig. 2. Orthognathic surgery with the 3D-printed surgical template, based on the facebow. A, The design of a facebow positioning guide (first surgical template), which set the axis of the
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facebow and determined the location of the facebow bite plate in the experimental model. B, The design of a maxillary surgical guide (second surgical template) connected to a facebow for maxillary repositioning. C, Setting the axis of a facebow with a facebow positioning guide (first surgical template) in the rapid prototype (RP) experimental model. D, Maxillary
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orthognathic surgery in the RP model utilizing a maxillary surgical guide (second surgical template) mounted in a preset fixed bite plate connected to a facebow.
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Fig. 3. Orthognathic surgery with the 3D-printed surgical template, based on the mandible. A, A 3D-reconstructed image of the maxillary deformity model. B, The design of a bite splint-
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type orthognathic surgical template, based on the mandible, for maxillary repositioning. C, A rapid prototype (RP) model of a maxillary deformity for experimental surgery. D, Maxillary orthognathic surgery in the RP model utilizing a bite splint-type orthognathic surgical template based on the mandible.
Fig. 4. Outcomes of surgical simulation (grey) compared with experimental postoperative results (pink). Data was overlapped using surface-based image registration; the reference area was the cranial region (yellow mesh). 21
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Fig. 5. Three reference planes for measuring the differences in distance between the simulation and the postoperative experimental results. The four measuring points shown were
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placed symmetrically on both sides of the skull. For example, on the left side, the measurement points are labeled as follows: #21, Left incisor tip; #26MBC, Left first molar mesiobuccal cusp; Lt-Nasal Aperture, Left lateral nasal aperture; Lt-Mx tuberosity, Left
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maxillary tuberosity.
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Tables Table I. Differences in 3D minimum distance for different surgical template types (mm) Measuring pointa
Facebow wafer
p-value
Is (n=24)
1.18 ± 0.60
1.42 ± 0.64
.199
Ms (n=24)
1.27 ± 0.58
1.01 ± 0.67
.167
MxTb (n=24)
1.26 ± 0.81
1.11 ± 0.52
.460
LNA (n=24)
1.14 ± 0.52
1.34 ± 0.58
.232
Total (n=96)
1.21 ± 0.63
1.22 ± 0.62
.942
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Bite wafer
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Note: Values represent the mean ± standard deviation of the difference between measurements made with the indicated surgical template (wafer) and those made during the
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preoperative simulation (i.e., template-simulation).
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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*P < .05
ACCEPTED MANUSCRIPT Table II. Absolute values of differences in vertical distance for different surgical template types (mm) Measuring pointa
Facebow wafer
p-value
Is (n=24)
0.64 ± 0.44
0.59 ± 0.44
.702
Ms (n=24)
0.81 ± 0.51
0.44 ± 0.43
.010
MxTb (n=24)
0.83 ± 0.85
0.61 ± 0.51
LNA (n=24)
0.49 ± 0.40
0.80 ± 0.50
Total (n=96)
0.69 ± 0.59
0.61 ± 0.48
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Bite wafer
.282 .023 .295
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Note: Values represent the mean ± standard deviation of the difference between
measurements made with the indicated surgical template (wafer) and those made during the
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preoperative simulation (i.e., template-simulation).
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.42 ± 0.32
0.79 ± 0.59
.010
Ms (n=24)
0.31 ± 0.26
0.43 ± 0.35
.193
MxTb (n=24)
0.29 ± 0.23
0.41 ± 0.35
LNA (n=24)
0.38 ± 0.32
0.55 ± 0.49
Total (n=96)
0.35 ± 0.29
0.54 ± 0.47
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Bite wafer
.178 .163 .001
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Note: Values represent the mean ± standard deviation of the difference between
measurements made with the indicated surgical template (wafer) and those made during the
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preoperative simulation (i.e., template-simulation).
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.68 ± 0.66
0.67 ± 0.68
.986
Ms (n=24)
0.76 ± 0.52
0.67 ± 0.58
.577
MxTb (n=24)
0.72 ± 0.44
0.61 ± 0.47
.402
LNA (n=24)
0.78 ± 0.59
0.65 ± 0.51
.440
Total (n=96)
0.73 ± 0.55
0.65 ± 0.56
.305
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Bite wafer
Note: Values represent the mean ± standard deviation of the difference between
preoperative simulation (i.e., template-simulation).
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measurements made with the indicated surgical template (wafer) and those made during the
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Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.25 ± 0.74
-0.50 ± 0.54
<0.001
Ms (n=24)
0.66 ± 0.71
-0.25 ± 0.57
<0.001
MxTb (n=24)
0.76 ± 0.91
0.06 ± 0.80
LNA (n=24)
0.22 ± 0.59
0.72 ± 0.62
Total (n=96)
0.47 ± 0.77
0.00 ± 0.78
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Bite wafer
.007
.008
<0.001
Note: Values represent the mean ± standard deviation of the difference between
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measurements made with the indicated surgical template (wafer) and those made during the preoperative simulation (i.e., template-simulation). Positive values indicate an inferior deviation of the maxilla.
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region.
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.04 ± 0.53
-0.68 ± 0.72
<0.001
Ms (n=24)
0.09 ± 0.40
-0.27 ± 0.49
.007
MxTb (n=24)
0.07 ± 0.37
0.01 ± 0.55
LNA (n=24)
0.10 ± 0.49
-0.44 ± 0.60
Total (n=96)
0.08 ± 0.45
-0.34 ± 0.64
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Bite wafer
.664
.001
<0.001
Note: Values represent the mean ± standard deviation of the difference between
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measurements made with the indicated surgical template (wafer) and those made during the preoperative simulation (i.e., template-simulation). Positive values indicate a left lateral deviation of the maxilla.
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region.
Each point was measured once on each side of the maxilla, on 12 models for each group.
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Facebow wafer
p-value
Is (n=24)
0.20 ± 0.93
-0.18 ± 0.95
.169
Ms (n=24)
0.39 ± 0.84
-0.11 ± 0.89
.045
MxTb (n=24)
-0.04 ± 0.86
-0.18 ± 0.76
.551
LNA (n=24)
-0.59 ± 0.79
-0.51 ± 0.66
.719
Total (n=96)
-0.00 ± 0.92
-0.25 ± 0.82
.058
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Bite wafer
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Note: Values represent the mean ± standard deviation of the difference between
measurements made with the indicated surgical template (wafer) and those made during the preoperative simulation (i.e., template-simulation). Positive values indicate an anterior
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deviation of the maxilla.
Abbreviation: Is, central incisor corner; Ms, first molar mesiobuccal cusp region; MxTb, maxillary tuberosity region; LNA, lateral nasal aperture region. a
Each point was measured once on each side of the maxilla, on 12 models for each group.
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ACCEPTED MANUSCRIPT Clinical relevance Controlled preclinical experimentation proved that the clinical utility of the facebow wafer did not significantly exceed that of the bite wafer. Using a posterior vertical measurement
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reference might reduce the posterior error observed in the bite wafer method.