A PARADIGM SHIFT IN ORTHOGNATHIC SURGERY: A SPECIAL SERIES PART II

J Oral Maxillofac Surg69:584-591, 2011

A New Method to Orient 3-DimensionalComputed Tomography Models to the

Natural Head Position: A ClinicalFeasibility Study

James J. Xia, MD, PhD, MS,* J. Kevin McGrory, DDS, MS,†

Jaime Gateno, DDS, MD,‡ John F. Teichgraeber, MD,§

Brian C. Dawson, BS,� Kathleen A. Kennedy, MD, MPH,¶

Robert E. Lasky, PhD,# Jeryl D. English, DDS, MS,**

Chung H. Kau, BSD, MScD, MBA, PhD,††

and Kathleen R. McGrory, DDS, MS‡‡

Purpose: The purpose of this study was to evaluate the clinical feasibility of a new method to orient3-dimensional (3D) computed tomography models to the natural head position (NHP). This method usesa small and inexpensive digital orientation device to record NHP in 3 dimensions. This device consistsof a digital orientation sensor attached to the patient via a facebow and an individualized bite jig. Thestudy was designed to answer 2 questions: 1) whether the weight of the new device can negativelyinfluence the NHP and 2) whether the new method is as accurate as the gold standard.

*Director of Surgical Planning Laboratory, Department of Oral

and Maxillofacial Surgery, The Methodist Hospital Research Insti-

tute, Houston, TX; Associate Professor of Surgery (Oral and Maxil-

lofacial Surgery), Weill Medical College, Cornell University, New

York, NY; and Associate Professor, Departments of Pediatric Sur-

gery and Orthodontics, The University of Texas Health Science

Center at Houston, Houston, TX.

†Currently, Private Practice, Houston, TX; Formerly, Resident

and MS Student, Department of Orthodontics, The University of

Texas Health Science Center at Houston, Houston, TX.

‡Chairman, Department of Oral and Maxillofacial Surgery, The

Methodist Hospital, Houston, TX; Professor of Clinical Surgery

(Oral and Maxillofacial Surgery), Weill Medical College, Cornell

University, New York, NY; and Associate Professor, Department of

Pediatric Surgery, The University of Texas Health Science Center at

Houston, Houston, TX.

§Professor and Chief, Division of Pediatric Plastic Surgery, De-

partment of Pediatric Surgery, The University of Texas Health

Science Center at Houston, Houston, TX.

�Computer System Analyst, Howard Hughes Medical Institute,

Baylor College of Medicine, Houston, TX.

¶Professor of Pediatrics, Division of Neonatal-Perinatal Medicine,

Department of Pediatrics, and Director of Master of Science in

Clinical Research Degree Program, Medical School, The University

of Texas Health Science Center at Houston, Houston, TX.

#Professor, Departments of Pediatrics and Obstetrics and Gynecol-

ogy, and Director, Design and Analysis Support Services, The Univer-

sity of Texas Health Science Center at Houston, Houston, TX.

**Chairman, Professor and Graduate Program Director, Depart-

ment of Orthodontics, The University of Texas Health Science

Center at Houston, Houston, TX.

††Currently, Chair and Professor of Orthodontics, University of

Alabama at Birmingham, Birmingham, AL; Formerly, Associate Pro-

fessor in Orthodontics and Director, Facial Imaging Facility, Depart-

ment of Orthodontics, The University of Texas Health Science

Center at Houston, Houston, TX.

‡‡Clinical Director, Department of Orthodontics, The University

of Texas Health Science Center at Houston, Houston, TX.

This manuscript was submitted in partial fulfillment of the re-

quirements of the Degree of Master of Science at The University of

Texas Health Science Center at Houston (J.K.M.).

This work was partially supported by National Institutes of

Health/National Institute of Dental and Craniofacial Research

grants 1R41DE016171 and 2R42DE016171 and University Clini-

cal Research Center (UCRC) (UT-Houston Medical School) grant

M01 RR002558 (National Institutes of Health).

Address correspondence and reprint requests to Dr Xia: 6560

Fannin St, Ste 1228, Houston, TX 77030; e-mail: jxia@tmhs.org

© 2011 American Association of Oral and Maxillofacial Surgeons

0278-2391/11/6903-0003$36.00/0

doi:10.1016/j.joms.2010.10.034

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Patients and Methods: Fifteen patients with craniomaxillofacial deformities were included in thestudy. Each patient’s NHP is recorded 3 times. The first NHP was recorded with a laser scanning methodwithout the presence of the digital orientation device. The second NHP was recorded with the digitalorientation device. Simultaneously, the third NHP was also recorded with the laser scanning method.Each recorded NHP measurement was then transferred to the patient’s 3D computed tomography facialmodel, resulting in 3 different orientations for each patient: the orientation generated via the laserscanning method without the presence of the digital orientation sensor and facebow (orientation 1), theorientation generated by use of the laser scanning method with the presence of the digital orientationsensor and facebow (orientation 2), and the orientation generated with the digital orientation device(orientation 3). Comparisons are then made between orientations 1 and 2 and between orientations 2and 3, respectively. Statistical analyses are performed.

Results: The results show that in each pair, the difference (�) between the 2 measurements is notstatistically significantly different from 0°. In addition, in the first pair, the Bland-Altman lower and upperlimits of the � between the 2 measurements are within 1.5° in pitch and within a subdegree in roll andyaw. In the second pair, the limits of the � in all 3 dimensions are within 0.5°.

Conclusion: Our technique can accurately record NHP in 3 dimensions and precisely transfer it to a 3Dmodel. In addition, the extra weight of the digital orientation sensor and facebow has minimal influence onthe self-balanced NHP establishment.© 2011 American Association of Oral and Maxillofacial Surgeons

J Oral Maxillofac Surg 69:584-591, 2011

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he natural head position (NHP) is the natural physio-ogic position of the head when a relaxed subject lookst an infinite horizon.1,2 An accurately recorded NHP isital for clinicians in the diagnosis and treatment ofatients with craniomaxillofacial deformities. This is es-ecially true for patients with significant facial asymme-ries. Without the head oriented in the NHP, the quan-ification of their deformities is often inaccurate.

As a result of recent advances in computer technol-gy, 3-dimensional (3D) computed tomography (CT)

s now routinely used in clinical practice. However,ecause the orientation of the patient’s head is ran-om during the CT acquisition, most 3D CT scans areot oriented to the NHP. Unfortunately, traditionalethods for recording NHP are limited to 2-dimen-

ional cephalograms3-8 and are not appropriate for 3DT models. Because of this problem, clinicians have

o place the 3D CT models in the NHP using 3Dntracranial reference planes9 or their best percep-tion.9,10

In the past our group has used laser surface scansto orient 3D CT models in the NHP. We have foundthis technique to be very accurate,11,12 but it ismpractical for routine clinical practice. Thesecans are acquired with a calibrated laser scanner,hich is very expensive and bulky. To solve thisroblem, we have developed a new method torient a 3D CT model to the NHP. This method usessmall and inexpensive device to record NHP in 3imensions. The device consists of a digital orien-ation sensor attached to the patient via a bite jignd a facebow. The results from our previous in

itro accuracy studies have shown that our new d

ethod is highly accurate.13-16 However, the accu-acy of this technique in patients has not yet beenstablished. Moreover, although the total weight ofhe digital orientation sensor and the facebow isnly 95 g, the question of whether the weight ofhe new device can negatively influence the NHPas also not been answered. Therefore we con-ucted this study to answer these questions.

Patients and Methods

PATIENTS

A total of 15 consecutive patients with craniomax-illofacial deformities seen at our institution betweenJuly 2006 and July 2008 were included in the study.Patient inclusion criteria were as follows: 1) patientswho were scheduled to undergo double-jaw orthog-nathic surgery to treat dentofacial deformities includ-ing hemifacial microsomia, 2) patients who werescheduled to undergo a CT scan as part of theirtreatment, and 3) patients who agreed to participatein the study. Patients with abnormal head postures(eg, torticollis) were excluded because their self-bal-anced NHP is unreliable. The study was approved bythe institutional review board, and informed consentwas obtained before the patients’ enrollment.

The patient sample size was calculated based onthe study of Lundstrom and Lundstrom,17 whichhowed that the reproducibility of NHP is close to 2°.y use of the equivalence (simulation) for 2 correlatedeans method, the sample size was estimated with a

orrelation of 0.50 achieving 90% statistical power to

etect equivalence when the margin of equivalence

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586 A NEW METHOD OF RECORDING NHP

between our new technique and the laser surfacescan method (gold standard) ranged from �2.0 to 2.0and the actual mean difference was 0.0. The calcula-tion yielded 13 pairs. With a 10% increase,18 15 pairswere used in this study. The PASS statistical package(NCSS, Kaysville, UT) was used for this calculation.

LASER SCANNING METHOD TO ORIENT 3D CTINTO NHP

Because of its proven accuracy,19,20 the laser scan-ing method can be considered the gold standard. Itses a calibrated laser surface scanner (Cyberware030 Head & Face Color Scanner; Cyberware, Mon-erey, CA) to capture both the 3D geometry and thebsolute orientation of the human face.19,20 The pa-ient sits on a calibrated chair positioned at the centerf the laser scanner (Fig 1A). He or she is asked tostablish his or her NHP. The laser scanner thenaptures the surface geometry of the face and itsbsolute orientation, resulting in a 3D facial image inhe NHP (Fig 1B). By use of a 3DS software package3D Studio Max; Autodesk, San Rafael, CA), the re-orded NHP is transferred to the 3D CT facial modely registering it to the laser-scanned facial image (FigC-F).

NEW NHP RECORDING METHOD TO ORIENT 3D CTINTO NHP

The new method tested in this study uses a noveldevice to record the NHP in 3 dimensions. The re-cording is then used to reorient the 3D CT scan in theNHP following a specific protocol. The new NHP re-cording device has 3 parts: a digital orientation sensor, afacebow, and a bite jig. The main component is thedigital orientation sensor (3DM; MicroStrain, Williston,VT) (Fig 2A). The sensor is capable of digitally record-

FIGURE 1. Laser scanning method. A, The patient sits on a calibratmage in the NHP is captured by the laser scanner. C, A 3D CT fahe recorded NHP is transferred to the 3D CT facial model by registn the NHP. F, Resultant 3D CT bone model in the NHP.

ia et al. A New Method of Recording NHP. J Oral Maxillofac Su

ing pitch, roll, and yaw. It is coupled to the inferior

aspect of the plastic facebow through a detachableconnection. The specially designed facebow (MedicalModeling, Golden, CO) (Fig 2B) contains an array offiducial markers (Fig 2C) that are compatible with CTand laser surface scanners. These fiducial markers areused to register individual 3D images. The inner as-pect of the facebow contains a second detachableconnector that links it to a bite jig. The bite jig con-sists of a stock frame and an individualized rigid biteregistration.

In the first step of the new method, an individualizedbite registration is obtained in centric relationship. Thebite registration is taken with self-curing, rigid, dimen-sionally stable material, for example, DuraLay (Reliance

ir that is positioned at the center of the laser scanner. B, A 3D faciald bone (underneath the soft tissue) model of the patient’s head. D,to the 3D facial image in the NHP. E, Resultant 3D CT facial model

1.

FIGURE 2. NHP recording device assembly. A, Digital orientationsensor. B, Facebow. C, Built-in fiducial markers. D, Individualizedbite jig.

Xia et al. A New Method of Recording NHP. J Oral Maxillofac Surg

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Dental Mfg Co, Worth, IL) or LuxaBite (Chemisch-Pharmazeutische Fabrik GmbH, Berlin, Germany). Thematerial is placed on a stock frame, and the impressionsare taken on the occlusal surfaces of the upper andlower teeth (Fig 2D).13-16 In the second step, the wholedevice is assembled and placed in the mouth (Fig 3A).The patient is then placed in the NHP, and the pitch,roll, and yaw readings of the orientation device arerecorded (Fig 3B). In the third step, the orientationsensor is detached from the device, and CT scanning ofthe patient is performed with the bite jig and facebow inplace. In the fourth step, the CT data are segmented,creating 3D CT models of the skeleton (including teeth),the skin surface, and the fiducial markers (Fig 3C). In thefifth step, a computer model of our new device assem-bly, composed of the facebow and the orientation sen-sor, is imported into the computer (Fig 3D). To avoidconfusion, we will refer to this assembly as thecomputer-aided design (CAD) model. In the sixth step,the fiducial markers of the CAD model are registered tothe fiducial markers of the 3D CT model (Fig 3E). Thistask is done automatically by the interactive closest-point algorithm.21 Once this is done, the 3D CT modelsnd the CAD model are linked together, so any move-ent of the CAD model will produce the same move-ent in the 3D CT models. In the last step, the recordeditch, roll, and yaw are applied to the center of the CADodel’s orientation sensor, bringing the 3D CT model to

he NHP (Fig 3F). Finally, the CAD model is hidden and3D CT is displayed in the NHP (Fig 3G).

STUDY DESIGN

The study was designed to answer 2 questions: 1)hether the extra weight of the new device influenced

FIGURE 3. Digital orientation sensor method. A, Patient at self-balaorientation sensor. C, Patient’s 3D CT model of head and fiducial mCAD model of the digital orientation sensor is registered and “gluedpitch, roll, and yaw to center of registered CAD model of orientatmodel of the orientation sensor and fiducial markers are hidden.

Xia et al. A New Method of Recording NHP. J Oral Maxillofac Su

he NHP and 2) whether our method was as accurate as

he gold standard. Each patient’s NHP was recorded 3imes. The NHP was established by asking the patientso self-balance their head to a position of comfort afterexing and extending the head. This was done with theatient sitting upright, looking at eye-level straight at alank wall 2 m away. During this process, the examinersid not give any specific instructions that could poten-ially influence this position. The first NHP was recordedy the laser scanning method without the new NHPecording device in place (Fig 4). After the patient hadested for at least 15 minutes, the new NHP recordingevice was placed. The second and third NHPs wereecorded simultaneously with both the laser scannernd the new NHP recording device (Fig 5).

HP. B, Pitch, roll, and yaw of head orientation recorded by digital. D, Predetermined CAD model of digital orientation sensor. E, Thee 3D CT model via the fiducial markers. F, Application of recordedsor. G, The 3D CT model at the NHP is generated after the CAD

1.

FIGURE 4. The first NHP is recorded by use of the laser scanningmethod when the digital orientation sensor, bite jig, and faceboware not attached to the patient.

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Once the head orientation was recorded, the ori-entation sensor was detached from the facebow. A CTscan of the patient’s head was performed only withthe bite jig and facebow in place. The CT was com-pleted by use of the following scanning parameters:slice thickness of 1.25 mm and field of view of 22 cm.Finally, 3D CT models of the patient’s facial skin,skeleton, and fiducial markers were generated. Threecopies of these models were made, and the three

FIGURE 6. A 3D CT facial model is registered to the 3D facialimage with the presence of the digital orientation sensor andfacebow.

Xia et al. A New Method of Recording NHP. J Oral Maxillofac Surg

FIGURE 5. The second and third NHPs are simultaneously re-corded with the digital orientation sensor and facebow attached tothe patient.

Xia et al. A New Method of Recording NHP. J Oral Maxillofac Surg2011.

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recorded NHPs were transferred to each of the 3D CTmodel copies (Fig 6). The same 3DS software packagewas used for this purpose.

DATA ANALYSIS

After all the 3D CT facial models were oriented tothe NHP, the pitch, roll, and yaw of each 3D CT facialmodel was automatically calculated and recorded bythe 3DS software (Fig 7). For each patient, 3 sets oforientations of the 3D facial model were obtained: theorientation generated by use of the laser scanningmethod without the new NHP recording device (ori-entation 1), the orientation generated by use of thelaser scanning method with the presence of the newNHP recording device (orientation 2), and the orien-tation generated with only the new NHP recordingdevice (orientation 3).

The clinical feasibility of the NHP recordingmethod was evaluated by 2 separate tests (Fig 8). Thefirst test was done to determine whether the extraweight of the digital orientation sensor and facebowinfluenced the patient’s NHP (Fig 8). This was doneby comparing orientation 1 (control group) with ori-entation 2 (experimental group). The second test wasdone to determine whether the digital orientationdevice was equal to the current gold standard (Fig 8).This was done by comparing orientation 2 (controlgroup) with orientation 3 (experimental group). Foreach comparison, the data were paired in pitch, roll,and yaw, respectively. The difference (�) betweeneach pair was calculated and tabulated. The resultant3 tables were then screened, and the largest � in each

atient, either in pitch, roll, or yaw, was selected toonstruct a fourth dimension. This fourth dimensionepresented a hypothetical largest � between the 2

FIGURE 7. The pitch, roll, and yaw of each 3D CT facial modelare automatically calculated.

Xia et al. A New Method of Recording NHP. J Oral Maxillofac Surg2011.

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The data were initially screened, and the normaldistribution assumption could not be rejected. Analy-sis of variance (ANOVA) for repeated measures wascomputed to test whether the � between the 2 mea-surements was statistically apart from “0,” the hypo-thetical ideal number of the � between 2 measure-ments. The response variable was the �. The withinfactors were the 2 recordings and the 4 dimensions(pitch, roll, yaw, and constructed fourth dimension).We used the NCSS statistics software package (NCSS,Kaysville, UT) for this computation. In addition, a2-way mixed-effects model (absolute agreement defi-nition) for intraclass correlation coefficient was com-puted to determine the absolute agreement betweenthe measurements in each pair. We used the SPSSsoftware package (SPSS, Chicago, IL) for this compu-tation. Finally, the methods of Bland and Altman22

were used to assess the agreement between the 2measurements. Microsoft Excel (Microsoft, Redmond,WA) was used for this computation. On the basis ofpublished studies on reproducibility of establishingNHP, a difference of less than 2° was considered to benot clinically significant.17,23,24

Results

TO DETERMINE WHETHER THE EXTRA WEIGHT OFTHE RECORDING DEVICE INFLUENCED NHP

ANOVA for repeated measures showed that the �of the measurements recorded with and without thepresence of the digital orientation sensor and thefacebow were not statistically significantly differentfrom 0° (F1,14 � 0.12, P � .74). There was also no

FIGURE 8. Flow

ia et al. A New Method of Recording NHP. J Oral Maxillofac Su

statistically significant difference in the � among the 4 (

dimensions (pitch, roll, yaw, and constructed fourthdimension) (F3,42 � 0.23, P � .87). In addition, thentraclass correlation coefficients between the 2 mea-urements were 0.997 (95% confidence interval [CI],.986-0.999) in pitch, 0.996 (95% CI, 0.978-0.999) inoll, and 0.987 (95% CI, 0.935-0.997) in yaw. For theonstructed fourth dimension of the hypotheticalargest discrepancy between the 2 measurements, theoefficient was 0.996 (95% CI, 0.982-0.999). All theargest � values came from the pitch measurementsxcept 1 from the yaw. They indicated that the headrientations generated in the presence and absence ofhe digital orientation sensor and facebow were abso-utely in agreement. Finally, by use of the Bland-ltman methods for assessing measurement agree-ent, all the lower and upper limits of the � between

he 2 measurements were within 1.4° (Table 1).

TO DETERMINE WHETHER THE NEW METHOD WASEQUAL TO THE LASER SCANNING METHOD

ANOVA for repeated measures showed that the �of the measurements recorded by the digital orienta-tion sensor and the laser scanner methods was notstatistically significantly different from 0° (F1,14 �0.00, P � .98). There was also no statistically signifi-cant difference in the � among the 4 dimensions(pitch, roll, yaw, and constructed fourth dimension)(F3,42 � 0.23, P � .88). In addition, the intraclassorrelation coefficients were 1.000 (95% CI, 0.999-.000) in pitch, 0.998 (95% CI, 0.994-0.999) in roll,nd 0.997 (95% CI, 0.992-0.999) in yaw. For the con-tructed fourth dimension of the hypothetical largest, the intraclass correlation coefficient was 0.999

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constructed table were equally distributed among thepitch, roll, and yaw measurements. They indicatedthat the head orientations generated by the 2 record-ing methods were absolutely in agreement. Finally, byuse of the Bland-Altman methods for assessing mea-surement agreement, all the lower and upper limits ofthe � between the 2 recording methods were within.5° (Table 2).

Discussion

The most common method to orient a 3D CT modelin the NHP is to first visualize the 3D model on thecomputer and then to orient it to a balanced positionbased on the clinician’s best perception or digitizedlandmarks.25 This method may approximate the NHPf the craniofacial structures are perfectly symmetri-al. However, when the upper face and skull baseave significant asymmetries, this method is question-ble. Another possible method is to simply record theHP during CT scanning. However, this method is

lso questionable. If a medical spiral CT scanner issed, the patient is scanned in the supine position.herefore it is impossible to place the patient’s head

n the NHP during the CT scanning. If a cone beamomputed tomography (CBCT) scanner is used, theatient is in a sitting or standing position. Because thehortest scanning time is 5 seconds,26 a chin rest isequired to stabilize the patient’s head to ensure theuality of the CBCT images. Although it is possible to

Table 2. DIFFERENCE OF HEAD ORIENTATION GENERAT

Mean SDLower Limi

(95

Pitch �0.01 0.109 �0.225 (�0oll �0.01 0.18 �0.362 (�0aw �0.014 0.191 �0.389 (�0ourth dimension 0.033 0.211 �0.380 (�0

Table 1. INFLUENCE OF EXTRA WEIGHT OF DIGITAL ORNHP ESTABLISHMENT

Mean SDLower Limi

(95

itch �0.017 0.642 �1.275 (�oll �0.022 0.189 �0.393 (�aw 0.014 0.379 �0.729 (�ourth dimension �0.104 0.668 �1.412 (�

Xia et al. A New Method of Recording NHP. J Oral Maxillofac Su

Xia et al. A New Method of Recording NHP. J Oral Maxillofac Surg 201

osition the patient’s head in the NHP without thehin rest, the already-less-than-ideal quality of theBCT images may be even more compromised be-ause of the head motion. It is our opinion that aatient’s reference head orientation should be re-orded directly on the patient, either at a self-bal-nced NHP or at a doctor-manipulated head orienta-ion. Clearly, there is a need for a technique thatecords the patient’s NHP and accurately transfers ito a 3D model.

Our Surgical Planning Laboratory has developed aew method to record the patient’s NHP and transfer

t to the 3D CT model. Our method uses a small andnexpensive digital orientation sensor to record NHPn 3 dimensions. This sensor is attached to the patientia a facebow and an individualized bite jig. Theesults of this study confirm that the extra weight ofhe digital orientation sensor and facebow has mini-al influence on the self-balanced NHP. The mean

ifferences in the measurements recorded with andithout the presence of the digital orientation sensor

nd the facebow are within a subdegree in all 3imensions and the constructed fourth dimension.he Bland-Altman measurement agreement assess-ent show that the lower and upper limits are withinsubdegree in roll and yaw, but they are within 1.3°

n pitch and 1.4° in the fourth dimension (mainlyontributed from the pitch) after the facebow andigital orientation sensor are attached. This may beecause the weight of this device is located at the

2 METHODS

ifference Upper Limit ofDifference (95% CI)

Precision ofEstimated MeanDifferences of

Agreement

o 0.214) 0.204 (0.194 to 0.214) �0.016 to 0.004o 0.344) 0.341 (0.323 to 0.360) �0.021 to 0.000o 0.362) 0.361 (0.334 to 0.389) �0.030 to 0.002o 0.334) 0.447 (0.400 to 0.493) 0.007 to 0.060

TION SENSOR AND FACEBOW ON

ifference Upper Limit ofDifference (95% CI)

Precision ofEstimated MeanDifferences of

Agreement

to 1.245) 1.241 (1.211 to 1.271) �0.035 to 0.000to 0.355) 0.348 (0.311 to 0.386) �0.044 to 0.001to 0.703) 0.758 (0.732 to 0.783) 0.000 to 0.029to 1.233) 1.205 (1.026 to 1.383) �0.207 to 0.000

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front of the face. However, we believe this deviationdoes not have clinical significance because the vari-ability in NHP establishment is 2°.17,23,24

The results of this study also prove that the newmethod is highly accurate. The mean differences inthe measurements recorded with our method and thecurrent gold standard are within a subdegree in all 3dimensions, as well as the constructed fourth dimen-sion. The accuracy is also verified by the Bland-Altmanmethods for assessing measurement agreement. Thelargest lower and upper limit of the mean differenceis within a subdegree, with a very tight 95% CI,indicating that the measurements are highly reliable.

An additional benefit of our new technique is that itallows the detachment of the digital orientation sen-sor from the patient during CT scanning, thus pre-venting artifacts from the circuit boards. Another ben-efit is that it is CBCT compatible. The field of view inthe CBCT scanner is much smaller than that in theregular medical spiral CT scanner. If the orientationsensor is attached to the facebow during the CBCTscan, the effective field of view for scanning thepatient’s head is significantly reduced, thus makingCBCT useless. We have solved this problem by usinga set of fiducial markers as the points of reference toregister the CAD model of the digital orientation sen-sor to the patient’s 3D CT model. A final benefit of ourtechnique is that the bite jig and facebow used forrecording NHP are designed for multiple purposes,that is, creating a composite skull model for computer-aided surgical simulation.11,12,27

Acknowledgments

The authors thank Brendan Hi Lee, MD, PhD, Professor of Mo-lecular and Human Genetics, Howard Hughes Medical Institute,Baylor College of Medicine, Houston, TX, for providing the Cyber-ware laser scanner.

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