A New Method to Orient 3-Dimensional Computed Tomography Models to the Natural Head Position: A Clinical Feasibility Study

doi:10.1016/j.joms.2010.10.034

Journal of Oral and Maxillofacial Surgery

Volume 69, Issue 3, March 2011, Pages 584-591

https://doi.org/10.1016/j.joms.2010.10.034 Get rights and content

Purpose

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

Patients and Methods

Fifteen patients with craniomaxillofacial deformities were included in the study. Each patient's NHP is recorded 3 times. The first NHP was recorded with a laser scanning method without the presence of the digital orientation device. The second NHP was recorded with the digital orientation 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 facial model, resulting in 3 different orientations for each patient: the orientation generated via the laser scanning method without the presence of the digital orientation sensor and facebow (orientation 1), the orientation generated by use of the laser scanning method with the presence of the digital orientation sensor 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 2 and 3, respectively. Statistical analyses are performed.

Results

The results show that in each pair, the difference (Δ) between the 2 measurements is not statistically significantly different from 0°. In addition, in the first pair, the Bland-Altman lower and upper limits of the Δ between the 2 measurements are within 1.5° in pitch and within a subdegree in roll and yaw. In the second pair, the limits of the Δ in all 3 dimensions are within 0.5°.

Conclusion

Our technique can accurately record NHP in 3 dimensions and precisely transfer it to a 3D model. In addition, the extra weight of the digital orientation sensor and facebow has minimal influence on the self-balanced NHP establishment.

Section snippets

Patients

A total of 15 consecutive patients with craniomaxillofacial deformities seen at our institution between July 2006 and July 2008 were included in the study. Patient inclusion criteria were as follows: 1) patients who were scheduled to undergo double-jaw orthognathic surgery to treat dentofacial deformities including hemifacial microsomia, 2) patients who were scheduled to undergo a CT scan as part of their treatment, and 3) patients who agreed to participate in the study. Patients with abnormal

To Determine Whether the Extra Weight of the Recording Device Influenced NHP

ANOVA for repeated measures showed that the Δ of the measurements recorded with and without the presence of the digital orientation sensor and the facebow were not statistically significantly different from 0° (F_1,14 = 0.12, P = .74). There was also no statistically significant difference in the Δ among the 4 dimensions (pitch, roll, yaw, and constructed fourth dimension) (F_3,42 = 0.23, P = .87). In addition, the intraclass correlation coefficients between the 2 measurements were 0.997 (95%

Discussion

The most common method to orient a 3D CT model in the NHP is to first visualize the 3D model on the computer and then to orient it to a balanced position based on the clinician's best perception or digitized landmarks.²⁵ This method may approximate the NHP if the craniofacial structures are perfectly symmetrical. However, when the upper face and skull base have significant asymmetries, this method is questionable. Another possible method is to simply record the NHP during CT scanning. However,

Acknowledgments

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

References (27)

C.F. Moorrees
Natural head position—A revival
Am J Orthod Dentofacial Orthop
(1994)
K.J. Showfety et al.
A simple method for taking natural-head-position cephalograms
Am J Orthod
(1983)
S. Usumez et al.
Inclinometer method for recording and transferring natural head position in cephalometrics
Am J Orthod Dentofacial Orthop
(2001)
S. Usumez et al.
Reproducibility of natural head position measured with an inclinometer
Am J Orthod Dentofacial Orthop
(2003)
P.S. Vig et al.
Experimental manipulation of head posture
Am J Orthod
(1980)
G.W. Arnett et al.
Facial planning for orthodontists and oral surgeons
Am J Orthod Dentofacial Orthop
(2004)
J. Gateno et al.
Clinical feasibility of computer-aided surgical simulation (CASS) in the treatment of complex cranio-maxillofacial deformities
J Oral Maxillofac Surg
(2007)
J.J. Xia et al.
New clinical protocol to evaluate craniomaxillofacial deformity and plan surgical correction
J Oral Maxillofac Surg
(2009)
F. Lundstrom et al.
Natural head position as a basis for cephalometric analysis
Am J Orthod Dentofacial Orthop
(1992)
M. Soncul et al.
The reproducibility of the head position for a laser scan using a novel morphometric analysis for orthognathic surgery
Int J Oral Maxillofac Surg
(2000)

J.J. Xia et al.

Three-dimensional computer-aided surgical simulation for maxillofacial surgery

Atlas Oral Maxillofac Surg Clin North Am

(2005)

C.F. Moorrees et al.

Natural head position, a basic consideration in the interpretation of cephalometric radiographs

Am J Phys Anthropol

(1958)

J.F. Cleall et al.

Head posture and its relationship to deglutition

Angle Orthod

(1966)

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Variation between natural head orientation and Frankfort horizontal planes in orthognathic surgery patients: 187 consecutive cases
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The purpose of this study was to assess the relationship between the Frankfort horizontal (FH) and natural head orientation (NHO), their correlation between patients’ malocclusion, and the impact of counterclockwise rotation (CCW) on the FH-NHO angle variation after orthognathic surgery. An evaluation of 187 consecutive patients was performed at the Maxillofacial Institute (Teknon Medical Center, Barcelona). FH-NHO° was measured pre- and postoperatively at 1 and 12 months, after three-dimensional (3D) superimposition using a software (Dolphin®). Patients were classified as follows: 3.2%, 48.7% and 48.1%, class I, II and III, respectively. Baseline FH-NHO° was significantly positive for patients with dentofacial deformities (2.73° ± 4.19 (2.12–3.33°, P < 0.001). The impact of orthognathic surgery in FH-NHO° was greater in class II when compared with class III patients, with a variation of 2.04° ± 4.79 (P < 0.001) and −1.20° ± 3.03 (P < 0.001), respectively. FH-NHO° increased when CCW rotational movements were performed (P = 0.006). The results of this study suggest that pre- and postoperative NHO differs from FH in orthognathic patients. The angle between FH and NHO is significantly larger in class III than in class II patients at baseline, which converges after orthognathic surgery when CCW rotation is performed. Therefore, NHO should be used as the real horizontal plane when planning for orthognathic surgery.
Accuracy of maxillary repositioning surgery using CAD/CAM customized surgical guides and fixation plates
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The advent of three-dimensional imaging and computer-aided surgical simulation (CASS) have brought about a paradigm shift in surgical planning. The aim of this study was to assess the accuracy of maxillary repositioning surgery using computer-aided design and manufacturing (CAD/CAM) customized titanium surgical guides and fixation plates. Thirty consecutive adult patients, 13 male and 17 female, with a mean age of 29.2 years and 25.5 years, respectively, requiring Le Fort I maxillary osteotomy, with or without simultaneous mandibular surgery, were evaluated retrospectively. All orthognathic surgeries were performed by one experienced surgeon. The pre-surgical and post-surgical volumetric imaging were superimposed to assess the linear and angular differences between the planned and actual positions of the maxilla following surgery. With the use of the CAD/CAM titanium surgical guides and fixation plates, all surgical movements were within 2 mm and 4° of the planned movements, which is considered clinically insignificant. The overall root mean square error between the planned and actual surgical movements was 0.38 mm in the transverse dimension, 0.64 mm in the anteroposterior dimension, and 0.55 mm in the vertical dimension. In regard to the centroid of the maxilla, the absolute angular difference of the maxillary centroid was 1.06° in pitch, 0.47° in roll, and 0.49° in yaw. Maxillary repositioning surgery can be performed with high accuracy using CAD/CAM titanium surgical guides and fixation plates.
A comparative study of the accuracy between two computer-aided surgical simulation methods in virtual surgical planning
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The aim of this retrospective and observational study was to compare the accuracy of two different virtual surgical planning (VSP) protocols, namely, the CASS method and the modified CASS method.
The patients underwent bimaxillary orthognathic surgery, planned using either the CASS method or the modified CASS method. Linear and angular discrepancies between the VSP outcome and postoperative outcome for both groups were compared for maxilla, mandible, and chin segments. Aside from the comparison between both groups, additional criteria were used to determine the accuracy of the protocol based on a linear and angular difference between planned and actual outcomes of less than 2 mm and 4°, respectively. The intergroup comparisons were performed by one-way ANOVA, with the level of significance set at 5%.
A total of 21 patients, of both genders, were assigned into group I (n = 11), planned with the CASS method, and group II (n = 10), planned with the modified CASS method. Both the CASS and modified CASS methods presented similar accuracy with regard to linear differences for the maxilla, mandible, and chin segments, except for ΔX for the mandibular segment, where the modified CASS method showed slightly better accuracy. However, there was a statistically significant difference with regard to angular differences in the chin segment, with the CASS method shown to be the more accurate. Aside from Δpitch for the chin segment, no linear or angular differences exceeded 2 mm or 4°.
Although statistically significant differences were found with regard to angular measurements in the chin segment, the accuracy of the modified CASS method for virtual planning can be considered as clinically equivalent, with a performance comparable to that of the CASS method.
Both the Observer's Expertise and the Subject's Facial Symmetry Can Affect Anatomical Position of the Head
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It is easier to judge facial deformity when the patient's head is in anatomic position. The purposes of this study were to determine 1) whether a group of expert observers would agree more than a group of nonexperts on what is the correct anatomic position of the head, 2) whether there would be more variation in the alignment of an asymmetrical face compared with a symmetrical one, and 3) whether the alignments of experts would be more repeatable than those of nonexperts.
Thirty-one orthodontists (experts) and 31 dental students (nonexperts) were recruited for this mixed-model study. They were shown randomly oriented 3-dimensional head photographs of an adult with a symmetrical face and an adolescent with an asymmetrical face. In viewing software, the observers oriented the images into anatomic position. They repeated the orientations 4 weeks later. Data were analyzed using a generalized linear model and Bland-Altman plots. The primary predictor variables were experience and symmetry status. The outcome variable was the anatomic position of the head. The other variables of interest included time and orientation direction.
There was a statistically significant difference between measurements completed by experts and nonexperts (F_1,60 = 14.83; P < .01). The interaction between expertise and symmetrical status showed a statistically significant difference between symmetrical and asymmetrical faces in the expert and nonexpert groups (F_1,60 = 9.93; P = .003). The interaction between expertise and time showed a statistically significant difference in measurement over time in the expert and nonexpert groups (F_1,60 = 4.66; P = .03).
The study shows that experts can set a head into anatomic position better than nonexperts. In addition, facial asymmetry has a profound effect on the ability of an observer to align a head in the correct anatomic position. Moreover, observer-guided alignment is not reproducible.
Accuracy of 3D reproduction of natural head position using three different manual reorientation methods compared to 3D software
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Citation Excerpt :
After using a laser scanner to acquire the surface geometry of patient's face in the NHP, a 3D CT model can be reoriented according to the soft tissues surface model (Xia et al., 2009). These laser scanning techniques are very accurate, but are impractical for routine clinical practice because the equipment is very expensive and bulky (Xia et al., 2011a). Another method is to use a digital gyroscope attached to an individualized bite jig (Schatz et al., 2010; Xia et al., 2011a, 2011b).
The aim of this study was to analyze the positional differences of three-dimensional (3D) natural head positions (NHPs) reproduced by three different manual reorientation methods without special software by the Pose from Orthography and Scaling with ITerations (POSIT) method.
Five ceramic markers were attached to each of 12 patients’ faces, and frontal and lateral photographs in the NHP and 3D computed tomography (CT) were taken. The 3D surface model was reoriented for the NHP reproduction by four different methods: the POSIT method (standard method), the location of the markers (A), the soft tissue landmarks (B) on the photographs, and manual correction without photographs (C). On each 3D surface model, the location of the skull was evaluated three-dimensionally.
Differences between reproduced NHPs in each of the four different methods were statistically significant (p < 0.0001). Compared to the POSIT method, the accuracy of the other reproducing methods was lower. The A and B methods showed a similar accuracy to each other, while the C method presented the most inaccurate NHP.
If 3D NHP reproduction using special software is impossible, reproducing NHP with photographs may be used as an alternative method, but its application should be clinically limited.

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: This manuscript was submitted in partial fulfillment of the requirements 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 Clinical Research Center (UCRC) (UT-Houston Medical School) grant M01 RR002558 (National Institutes of Health).

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A paradigm shift in orthognathic surgery: A special series part IIA New Method to Orient 3-Dimensional Computed Tomography Models to the Natural Head Position: A Clinical Feasibility Study

Purpose

Patients and Methods

Results

Conclusion

Section snippets

Patients

To Determine Whether the Extra Weight of the Recording Device Influenced NHP

Discussion

Acknowledgments

Am J Orthod Dentofacial Orthop

Am J Orthod

Am J Orthod Dentofacial Orthop

Am J Orthod Dentofacial Orthop

Am J Orthod

Am J Orthod Dentofacial Orthop

J Oral Maxillofac Surg

J Oral Maxillofac Surg

Am J Orthod Dentofacial Orthop

Int J Oral Maxillofac Surg

Atlas Oral Maxillofac Surg Clin North Am

Natural head position, a basic consideration in the interpretation of cephalometric radiographs

Am J Phys Anthropol

Head posture and its relationship to deglutition

Angle Orthod

A paradigm shift in orthognathic surgery: A special series part II
A New Method to Orient 3-Dimensional Computed Tomography Models to the Natural Head Position: A Clinical Feasibility Study