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Development of a Technique for Recording and Transferring Natural Head Position in 3 Dimensions
Abstract
The purpose of this study was to develop and test a new technique for recording natural head position (NHP) in 3 dimensions and transferring it into a three-dimensional computed tomography (CT) model. In this technique, a digital gyroscope was first attached to a human head using a bite-jig and a face-bow with a set of built-in fiducial markers. The relationship between the gyroscope and fiducial markers was predetermined and kept constant. The orientation (pitch, roll, and yaw) of the head was then recorded by this gyroscope. In next step, the head was CT scanned with the bite-jig and the face-bow in place, and three-dimensional CT models of the head and fiducial markers were generated. The head model was coupled with a predetermined three-dimensional model of the gyroscope assembly via fiducial markers. The three-dimensional head model was reoriented to the recorded orientation by applying the recorded pitch, roll, and yaw to the gyroscope model. Finally, the accuracy of the technique was tested on a human dry skull. The results showed that the NHP was successfully recorded and transferred to the three-dimensional CT model. The orientations between the dry skull and its three-dimensional computer model were absolutely correlated. The difference (the lack of agreement) was within a range of -1.1 to 1.1 degrees, indicating no clinical significance. The authors concluded that our technique could accurately and repeatedly record NHP three-dimensionally and transfer it to a three-dimensional CT head model.
... Therefore, a general CT image does not reflect the patient's NHP in clinical practice [9]. To overcome this limitation of CT imaging for the diagnosis and treatment of orthognathic patients, several studies have been conducted to record 3D NHPs [1,[9][10][11][12][13][14]. ...
... In one method, the authors recorded the 3D NHP using an orientation or gyroscope sensor mounted on a personalized bite jig [1,10,11]; however, the weight of the sensor caused distortions in the shape of the lips [9,12]. Since the position of the upper lip significantly affects predictions regarding soft tissue changes during 3D surgical simulations, the shape of the lips should not be deformed in computer-assisted orthognathic surgery [8][9][10][11]. ...
... In one method, the authors recorded the 3D NHP using an orientation or gyroscope sensor mounted on a personalized bite jig [1,10,11]; however, the weight of the sensor caused distortions in the shape of the lips [9,12]. Since the position of the upper lip significantly affects predictions regarding soft tissue changes during 3D surgical simulations, the shape of the lips should not be deformed in computer-assisted orthognathic surgery [8][9][10][11]. In another method, the CT model was rotated to the 3D NHP using the position of the radiopaque stickers attached to the horizontal and vertical laser lines on the face to avoid changing the shape of the lips [12]. In another method, the 3D NHP of the CT model was reproduced by a pose from orthography and scaling with iterations (POSIT) algorithm using a common 2D digital camera and ceramic markers [9]. ...
This paper developed a new method to easily record and automatically reproduce the 3D natural head position (NHP) of patients using a portable 3D scanner based on immediate calibration. We first optically scanned the patient’s face using a portable 3D scanner, and the scanned model was easily aligned with the global horizon based on an immediate calibration procedure using a developed calibration plate. The 3D patient NHP Computed Tomography(CT) model was reproduced automatically by performing registration between the CT model and the optically scanned model in the NHP using a modified coherent point drift (CPD) algorithm. In a phantom experiment, we evaluated the developed method’s accuracy using the error between the true and the calculated orientations in roll, pitch, and yaw directions. The mean difference was −0.05 ± 0.13°, 0.08 ± 0.22°, and −0.05 ± 0.18° in the roll, pitch, and yaw directions, respectively. The measured roll, pitch, and yaw directions were not significantly different from the true directions (p > 0.05). The calibration procedure for aligning the scanner coordinate system was easy enough for an inexperienced user to operate, and the 3D NHP CT model could be reproduced automatically. The developed method could be used for diagnosing and treating orthognathic patients with facial asymmetry accurately and conveniently in dental clinics.
... the patient to look into horizontal infinity 12 , and the mirror position asks the patient to look into his or her own eyes in a mirror 3,22 . The estimated position is generally thought to be that wherein the head position can be reproduced with less variation when corrections are made by the doctor 2 . ...
... This method is more accurate when the craniofacial structures are symmetrical than when the patient has severe facial asymmetries. Recently, several newly developed methods for recording NHP in three dimensions have been introduced, including a digital gyroscope that can record NHP in three dimensions 12,25 . For this method, an electronic device is mounted on a bite jig, and the patient holds the device by biting the bite jig until the 3D photographs are taken with the patient in a NHP. ...
... The NHP orientation data are automatically recorded and transferred to the virtual imaging software for 3D CT model reconstruction. However, there is potential for error because the patient is holding a heavy instrument for a long period of time 12 . The 3dMDface imaging system was used to record sitting NHP 3,26,27 . ...
Objectives:
The concept of natural head position (NHP) was first introduced by Broca in 1862, and was described as a person's stable physiologic position "when a man is standing and his visual axis is horizontal." NHP has been used routinely for clinical examination; however, a patient's head position is random during cone-beam computed tomography (CBCT) acquisition. To solve this problem, we developed an accelerometer to record patients' NHP and reproduce them for CBCT images. In this study, we also tested the accuracy and reproducibility of our accelerometer.
Materials and methods:
A total of 15 subjects participated in this study. We invented an accelerometer that measured acceleration on three axes and that could record roll and pitch calculations. Recorded roll and pitch data for each NHP were applied to a reoriented virtual image using three-dimensional (3D) imaging software. The data between the 3D models and the clinical photos were statistically analyzed side by side. Paired t-tests were used to statistically analyze the measurements.
Results:
The average difference in the angles between the clinical photograph and the 3D model was 0.04° for roll and 0.29° for pitch. The paired ttests for the roll data (P=0.781) and the pitch data (P=0.169) showed no significant difference between the clinical photographs and the 3D model (P>0.05).
Conclusion:
By overcoming the limitations of previous NHP-recording techniques, our new method can accurately record patient NHP in a time-efficient manner. Our method can also accurately transfer the NHP to a 3D virtual model.
... As a result, our team has developed a clinical protocol using a CASS method for planning orthognathic surgery [3,20]. It includes a detailed protocol on generating an accurate composite skull model by registering digital dental models into computed tomography (CT) models [21], correctly developing a unique global reference frame for the head models [22][23][24][25][26], performing true 3D cephalometric analysis (in opposite to so-called "3D" analysis that is directly expanded from its 2D counterpart) [24][25][26], logically simulating surgical movement [20], and designing surgical splints [20,27]. Our CASS protocol has proven to be imperative in producing a more accurate and effective treatment plan [16,28,29]. ...
... In the Registration/NHP module, a composite skull model is constructed to accurately render skeleton, dentition, and facial soft tissues [21]. In addition, the global reference frame for surgical planning is established, i.e., placing all the models in a unique 3D coordinate system [22,23,25,26,31]. In the 3D Cephalometric Analysis module, our innovative 3D cephalometry [24,25], which solves many problems associated with current 2D and purported 3D cephalometry, is incorporated for the first time. ...
... By establishing NHP, the digital environment directly reflects the clinical environment, as if the surgeon is actually examining the patient. NHP can be recorded using a digital orientation sensor [22,23,31], a self-leveling laser [16,34], or the standardized photograph method [3] during the patient's clinical examination. The clinically recorded NHP, in pitch, roll, yaw, is then applied to the original data space, mapping the entire original 2D and 3D datasets into the patient's NHP. ...
Orthognathic surgery is a surgical procedure to correct jaw deformities. It requires extensive presurgical planning. We developed a novel computer-aided surgical simulation (CASS) system, the AnatomicAligner, for doctors planning the entire orthognathic surgical procedure in computer following our streamlined clinical protocol. The computerized plan can be transferred to the patient at the time of surgery using digitally designed surgical splints. The system includes six modules: image segmentation and three-dimensional (3D) model reconstruction; registration and reorientation of the models to neutral head posture (NHP) space, 3D cephalometric analysis, virtual osteotomy, surgical simulation, and surgical splint designing. The system has been validated using the 5 sets of patient’s datasets. The AnatomicAligner system will be soon available freely to the broader clinical and research communities.
... 1 Two methods are described to determine NHP in the clinic. The first method asks the patient to look into horizontal infinity, 2 and second method asks the patient to look into his or her own eyes in a mirror. 3,4 Physiologically, head position is controlled by vestibulo-ocular and vestibulospinal reflexes, as well as by inner ear otolithic gravitational responses that provide interactions among eye position, head position, and muscles. ...
... Since NHP provides a coordinate reference system for taking measurements and therefore has vital importance for diagnosis, surgical design, postoperative outcome evaluation, and developmental tracking in patients with dentomaxillofacial deformities, it has gained the interest of many experts. 2,12,13 Previous studies have mainly focused on how to record NHP 2 dimensionally. [14][15][16][17][18] Now, with the development of computer-assisted surgical design, many authors are using new methods for recording 3-dimensional (3D) NHP and integrating it into a computer-assisted surgical design protocol. ...
... As a consequence, the entire procedure, including the computed tomography (CT) scan, must be repeated at each follow-up visit, with an unacceptable increase in radiation exposure. 2,19 Other disadvantages of the gyroscopic procedure include (1) the requirement for specialized software and equipment such as a bite-jid, facebow, and acrylic materials; and (2) the total weight of the gyroscope that might affect head orientation because the weight is in front of the center of gravity. 2 Weber 4 first reported the method of recording NHP using a stereophotographic system. In that study, the true vertical and horizontal laser lines were projected for orientation and then were marked on the patient's face with ink dots. ...
As computer-assisted surgical design becomes increasingly popular in maxillofacial surgery, recording patients' natural head position (NHP) and reproducing it in the virtual environment are vital for preoperative design and postoperative evaluation. Our objective was to test the repeatability and accuracy of recording NHP using a multicamera system and a laser level.
A laser level was used to project a horizontal reference line on a physical model, and a 3-dimensional image was obtained using a multicamera system. In surgical simulation software, the recorded NHP was reproduced in the virtual head position by registering the coordinate axes with the horizontal reference on both the frontal and lateral views. The repeatability and accuracy of the method were assessed using a gyroscopic procedure as the gold standard.
The interclass correlation coefficients for pitch and roll were 0.982 (0.966, 0.991) and 0.995 (0.992, 0.998), respectively, indicating a high degree of repeatability. Regarding accuracy, the lack of agreement in orientation between the new method and the gold standard was within the ranges for pitch (-0.69°, 1.71°) and for roll (-0.92°, 1.20°); these have no clinical significance.
This method of recording and reproducing NHP with a multicamera system and a laser level is repeatable, accurate, and clinically feasible.
Copyright © 2015 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.
... In the Registration/NHP module, a composite skull model is constructed to accurately render skeleton, dentition, and facial soft tissues [21]. In addition, the global reference frame for surgical planning is established, i.e., placing all the models in a unique 3D coordinate system [22,23,25,26,31]. In the 3D Cephalometric Analysis module, our innovative 3D cephalometry [24,25], which solves many problems associated with current 2D and purported 3D cephalometry, is incorporated for the first time. ...
... By establishing NHP, the digital environment directly reflects the clinical environment, as if the surgeon is actually examining the patient. NHP can be recorded using a digital orientation sensor [22,23,31], a self-leveling laser [16,34], or the standardized photograph method [3] during the patient's clinical examination. The clinically recorded NHP, in pitch, roll, yaw, is then applied to the original data space, mapping the entire original 2D and 3D datasets into the patient's NHP. ...
Purpose:
There are many proven problems associated with traditional surgical planning methods for orthognathic surgery. To address these problems, we developed a computer-aided surgical simulation (CASS) system, the AnatomicAligner, to plan orthognathic surgery following our streamlined clinical protocol.
Methods:
The system includes six modules: image segmentation and three-dimensional (3D) reconstruction, registration and reorientation of models to neutral head posture, 3D cephalometric analysis, virtual osteotomy, surgical simulation, and surgical splint generation. The accuracy of the system was validated in a stepwise fashion: first to evaluate the accuracy of AnatomicAligner using 30 sets of patient data, then to evaluate the fitting of splints generated by AnatomicAligner using 10 sets of patient data. The industrial gold standard system, Mimics, was used as the reference.
Result:
When comparing the results of segmentation, virtual osteotomy and transformation achieved with AnatomicAligner to the ones achieved with Mimics, the absolute deviation between the two systems was clinically insignificant. The average surface deviation between the two models after 3D model reconstruction in AnatomicAligner and Mimics was 0.3 mm with a standard deviation (SD) of 0.03 mm. All the average surface deviations between the two models after virtual osteotomy and transformations were smaller than 0.01 mm with a SD of 0.01 mm. In addition, the fitting of splints generated by AnatomicAligner was at least as good as the ones generated by Mimics.
Conclusion:
We successfully developed a CASS system, the AnatomicAligner, for planning orthognathic surgery following the streamlined planning protocol. The system has been proven accurate. AnatomicAligner will soon be available freely to the boarder clinical and research communities.
... Another solution for building a sagittal plane for patients with asymmetric heads is to use the natural head posture (NHP). 6,8 Unfortunately, the NHP method is inconsistent for two reasons. First, some patients have difficulty aligning their heads in the NHP. ...
... Until now, we have done this by using the NHP. 6,8 The principle behind its use is that the primal frame of reference of the head can be derived from the NHP. When humans stand erect, looking straight forward, the cardinal directions of their faces (anterior, posterior, superior, inferior, right, and left) are orthogonal to gravity. ...
To assess facial form, one has to determine the size, position, orientation, shape, and symmetry of the different facial units. Many of these assessments require a frame of reference. The customary coordinate system used for these assessments is the 'standard anatomical frame of reference', a three-dimensional Cartesian system made by three planes: the sagittal, the axial, and the coronal. Constructing the sagittal plane seems simple, but because of universal facial asymmetry, it is complicated. Depending on the method one selects, one can build hundreds of different planes, never knowing which one is correct. This conundrum can be solved by estimating the sagittal plane a patient would have had if his or her face had developed symmetrically. We call this the 'primal sagittal plane'. To estimate this plane we have developed a mathematical algorithm called LAGER (Landmark Geometric Routine). In this paper, we explain the concept of the primal sagittal plane and present the structure of the LAGER algorithm.
... In this protocol, a three-dimensional (3D) composite skull model of a patient is generated to accurately represent the CMF skeleton, the dentition, and the facial soft tissue [2][3][4][5] . In addition, an anatomical reference frame is created for the 3D composite skull model [6][7][8] . Virtual osteotomies are then performed and orthognathic surgery is simulated 1,3,[9][10][11] . ...
... To record the NHP, the authors use an electronic orientation sensor (3DM; MicroStrain Inc., Williston, VA, USA). The sensor is first attached to the previously fabricated bite-jig ( Fig. 4A, B) [6][7][8] . The jig is then placed between the patient's teeth. ...
The success of craniomaxillofacial (CMF) surgery depends not only on the surgical techniques, but also on an accurate surgical plan. The adoption of computer-aided surgical simulation (CASS) has created a paradigm shift in surgical planning. However, planning an orthognathic operation using CASS differs fundamentally from planning using traditional methods. With this in mind, the Surgical Planning Laboratory of Houston Methodist Research Institute has developed a CASS protocol designed specifically for orthognathic surgery. The purpose of this article is to present an algorithm using virtual tools for planning a double-jaw orthognathic operation. This paper will serve as an operation manual for surgeons wanting to incorporate CASS into their clinical practice.
... The NHP method 4,8,9 can solve the problems associated with the anatomical landmark method. This posture is unaltered by most facial deformities and can readily be used to create a reference frame. ...
... The third method of orienting a head to NHP is to reorient a CT/CBCT model to NHP using a digital orientation sensor 4,8,9 . The orientation sensor is attached to a bite-jig. ...
Three-dimensional (3D) cephalometry is not as simple as just adding a ‘third’ dimension to a traditional two-dimensional cephalometric analysis. There are more complex issues in 3D analysis. These include how reference frames are created, how size, position, orientation and shape are measured, and how symmetry is assessed. The main purpose of this article is to present the geometric principles of 3D cephalometry. In addition, the Gateno–Xia cephalometric analysis is presented; this is the first 3D cephalometric analysis to observe these principles.
... Traditional approaches to obtaining NHP involve capturing physical references and the patients' images at the same time. Methods include placing markers on subjects' face [19,20]; holding orientation sensors with bite-jig [21,22]; wearing eyeglasses mounted with inclinometers [23]; or hold spirit level equipped face bow [24] etc. The best accuracy achieved was ±1.1° [ 21,22]. ...
... Methods include placing markers on subjects' face [19,20]; holding orientation sensors with bite-jig [21,22]; wearing eyeglasses mounted with inclinometers [23]; or hold spirit level equipped face bow [24] etc. The best accuracy achieved was ±1.1° [ 21,22]. In using SP device, the proposed method captures physical references and patients' images in separate scans [11]. ...
The aim of this study was to develop an automatic orientation calibration and reproduction method for recording the natural head position (NHP) in stereo-photogrammetry (SP). A board was used as the physical reference carrier for true verticals and NHP alignment mirror orientation. Orientation axes were detected and saved from the digital mesh model of the board. They were used for correcting the pitch, roll and yaw angles of the subsequent captures of patients’ facial surfaces, which were obtained without any markings or sensors attached onto the patient. We tested the proposed method on two commercial active (3dMD) and passive (DI3D) SP devices. The reliability of the pitch, roll and yaw for the board placement were within ±0.039904°, ±0.081623°, and ±0.062320°; where standard deviations were 0.020234°, 0.045645° and 0.027211° respectively. Conclusion: Orientation-calibrated stereo-photogrammetry is the most accurate method (angulation deviation within ±0.1°) reported for complete NHP recording with insignificant clinical error.
... Nevertheless, application of this approach is limited in some demanding situations, such as facial scoliosis and hemifacial microsomia in which the existing facial imbalance complicates the identification of planes. Alternatively, the recording can be performed using 1) laser-assisted surface marking during CT image acquisition, [7][8][9] 2) direct recording of the NHP using orientation sensors 10,11 (integrated triaxial accelerometers and magnetometers) from which the readings are applied to reorient the CT virtual model, 3) inclinometers, 12 and 4) a facebow equipped with a spirit level. 13 Currently, stereophotogrammetry (SP) machines are readily available for the assessment of dentofacial deformity. ...
... Traditional approaches to obtaining an NHP require the placement of markers on a patient's face, 7-9 using orientation sensors with a bite jig, 10,11 wearing eyeglasses mounted with inclinometers, 12 or holding a facebow equipped with a spirit level. 13 When using markers, 7-9 the procedure of putting marks on a patient's face could introduce reproducibility and variability problems. ...
The purpose of this study was to develop a technique to record physical references and orient digital mesh models to natural head position (NHP) using stereo-photogrammetry (SP). The first step was to record the digital mesh model of a hanging reference board placed at the capturing position of the SP machine. The board was aligned to the true vertical using a plumb bob. It was also aligned with laser plane parallel to the hanging mirror which was located at the center of the machine. Parameter derived from the digital mesh model of the board was then used to adjust the roll, pitch and yaw of the subsequent captures of subjects. This information was valid until the next machine calibration. The board placement was repeatable with standard deviation of less than 0.1 degrees for both pitch and yaw; 0.15 degrees for roll angles.
... [15][16][17][18] Images obtained by traditional (fanbeam) CT and CBCT scanners can be used to create 3D models of the craniofacial skeleton, the teeth and the soft-tissues. [19][20][21][22][23][24] By placing these models into the neutral head posture (NHP) [25][26][27][28][29] , we can now convert them into "3D cephalograms" in the same way as a lateral head film is consider to be cephalogram if taken at a fixed distance from the subject with the subject's head in a cephalostat. ...
... The NHP is the position of the head where the head in neither flexed nor extended, neither rotated nor tilted. A most convenient way of capturing the NHP is by using a digital orientation device 26,[40][41][42] as described by the authors in an accompanying article in this journal. 28 ...
Two basic problems have been associated with traditional 2-dimensional cephalometry. First, many important parameters cannot be measured on plain cephalograms; and second, most 2-dimensional cephalometric measurements are distorted in the presence of facial asymmetry. Three-dimensional cephalometry, which has been facilitated by the introduction of cone-beam computed tomography, can solve these problems. However, before this can be realized, fundamental problems must be solved. These include the unreliability of internal reference systems and some 3-dimensional measurements, and the lack of tools to assess and measure the symmetry. In the present report, we present a new 3-dimensional cephalometric analysis that uses different geometric approaches to solve these fundamental problems. The present analysis allows the accurate measurement of the size, shape, position, and orientation of the different facial units and incorporates a novel method to measure asymmetry.
... Although recording the NHP using a laser scanner was very accurate, this method is impractical for routine clinical practices because it is very bulky and expensive (62). In their study, Schatz et al. (64) used a guiding sen-sor attached to the patient's teeth through a bite block to reproduce the NHP; although the guiding sensor method is inexpensive relative to the laser scanning method, it requires the construction of a bite block, and this severely alters the states of the upper and lower lips while capturing the CBCT image. Other authors such as Tiam et al. (65) and Weber et al. (66) reliably replicated NHP by conforming to a self-balanced head position when acquiring photographic and 3D images of the study subjects. ...
... There was not sufficient consideration on a method to reduce the occurrence of abnormal results or to ensure the safe use of the model in clinical practice. The abnormal outcomes have also inspired us to further optimize the whole process of automatic landmarks detection, including aligning the head position [17][18][19], standardizing the process of CT imaging, addressing abnormal data and evaluating the applicability of the model to different patients. Furthermore, in the field of landmarks detection, incorporating the dependency between landmarks into model training is proved to be effective [7,20]. ...
Background
Accurate cephalometric analysis plays a vital role in the diagnosis and subsequent surgical planning in orthognathic and orthodontics treatment. However, manual digitization of anatomical landmarks in computed tomography (CT) is subject to limitations such as low accuracy, poor repeatability and excessive time consumption. Furthermore, the detection of landmarks has more difficulties on individuals with dentomaxillofacial deformities than normal individuals. Therefore, this study aims to develop a deep learning model to automatically detect landmarks in CT images of patients with dentomaxillofacial deformities.
Methods
Craniomaxillofacial (CMF) CT data of 80 patients with dentomaxillofacial deformities were collected for model development. 77 anatomical landmarks digitized by experienced CMF surgeons in each CT image were set as the ground truth. 3D UX-Net, the cutting-edge medical image segmentation network, was adopted as the backbone of model architecture. Moreover, a new region division pattern for CMF structures was designed as a training strategy to optimize the utilization of computational resources and image resolution. To evaluate the performance of this model, several experiments were conducted to make comparison between the model and manual digitization approach.
Results
The training set and the validation set included 58 and 22 samples respectively. The developed model can accurately detect 77 landmarks on bone, soft tissue and teeth with a mean error of 1.81 ± 0.89 mm. Removal of region division before training significantly increased the error of prediction (2.34 ± 1.01 mm). In terms of manual digitization, the inter-observer and intra-observer variations were 1.27 ± 0.70 mm and 1.01 ± 0.74 mm respectively. In all divided regions except Teeth Region (TR), our model demonstrated equivalent performance to experienced CMF surgeons in landmarks detection (p > 0.05).
Conclusions
The developed model demonstrated excellent performance in detecting craniomaxillofacial landmarks when considering manual digitization work of expertise as benchmark. It is also verified that the region division pattern designed in this study remarkably improved the detection accuracy.
... 9,13,21 NHP can be recorded by using photographic, radiographic, or 3-dimensional (3D) imaging techniques 13 including stereophotogrammetry, 22,23 laser scanning, 24 facial radiopaque markings combined with cone beam computed tomography, 25,26 and the digital gyroscope. 27,28 Furthermore, a facial reference system has been described to standardize the NHP and photographic recording for the purpose of treatment planning. 29 When using computer-aided design (CAD) software programs, 2-dimensional (2D) photographs and 3D facial scans can be used to incorporate the patient's vertical and horizontal facial references and integrate them into the virtual patient. ...
A virtual patient is obtained by aligning a patient’s digital information, including facial and intraoral digital scans with or without hard tissue information from a cone beam computed tomography scan. However, while computer-aided design programs facilitate virtual patient integration, they do not provide a way to relate the horizon orientation with the patient’s horizontal and vertical facial references. The present technique describes a way of relating the horizon orientation plane to the natural head position of the patient. An additively manufactured natural head position reference device was used to transfer the horizon orientation plane to the 3-dimensional virtual patient.
... Finally, the patient is scanned in the CBCT, and the volume is oriented in the software following the markers. The final method involves a digital sensor and an occlusal jig [36]. Measurements of the yaw, roll and pitch are recorded with the patient in NHP, and the patient is CBCT -scanned with the jig in place. ...
Objectives
: Since cone beam computed tomography (CBCT) became available, research in the field of computer assisted orthognathic surgery (CAOS) is constantly on the rising. It is the purpose of the present paper to describe the use of the available digital technology in the workflow of CAOS and to provide insight on the advantages and limitations which arise from the use of both hardware and software.
Study selection, data and sources
: Randomised controlled trials, systematic reviews, prospective and retrospective clinical studies, case series and reports were consulted with search terms having been entered into PubMed, Google Scholar and the Cochrane database.
Results
: There is evidence that supports the use of CAOS, which is based on the lack of time-consuming preparatory steps, more accurate treatment planning and overall, better surgical results. On the contrary, there is also evidence of increased need for training and greater financial cost.
Conclusions
: The workflow of CAOS involves the acquisition of data which are manipulated to provide the virtual patient, the treatment planning with the appropriate software and the actual preparations for surgery. In case of a non-dynamically guided procedure, it includes the 3d printing of surgical wafers, osteotomy guides and templates. Even though the native environment for any given surgical treatment planning is the 3 dimensions of space, several hurdles seem to impede the universal acceptance of CAOS amongst clinicians.
Clinical Significance
: CAOS is a much desired yet sparsely employed practice for the correction of congenital, developmental or acquired pathologies in the dentomaxillofacial region. This paper addresses the small details in CAOS workflow towards an effective practice and describes the advantages and limitations of the software and hardware currently in use.
... Also, there was no statistically significant influence of observer experience or asymmetry of cases, which highlights the broad applicability and clinical significance of this method. 16 The orientation method hereby presented was not validated for prospective purposes such as computer assisted surgical planning, however it does seem to be theoretically suitable for such as long as the orientation matches the clinical facial analyses and surgical movements obey the upper central incisor midpoint to be the fulcrum to any given movement of the jaws. 5 While no automatically computed method for craniofacial orientation is available, if such were to even exist, the use of skull landmarks could overcome such difficulties without the need for any additional hardware or cost. ...
Inadequate craniofacial orientation of computed tomography scans can have significant implications in all three planes of space. The purpose of this study is to present the reproducibility of a three-dimensional skeletal-based method of craniofacial orientation for virtual surgical planning. The craniofacial orientation protocol was defined by landmarks commonly used for cephalometry and required identification of Basion, Nasion, right Porion and right Orbitale and navigation in all computed tomography views (i.e. coronal, sagittal and axial) for correction of the yaw, roll, and pitch. Reproducibility of the method was assessed using eight computed tomography scans that were randomly selected and de-identified. The observer group consisted of six oral and maxillofacial surgeons with varying levels of experience (resident or faculty) who performed craniofacial orientation according to the proposed method. Results were expected to be below two degrees of variation, considering overall accuracy as well as the influence of academic level of the observers and symmetry of the evaluated anatomy as independent variables. Overall accuracy for all cases and in yaw, roll and pitch were always below 2 degrees of variation, without influence of level of experience and symmetry. Inter-observer assessment was categorized as excellent in all instances, while intra-observer evaluation demonstrated consistency in the orientation of all axes. The proposed craniofacial orientation protocol presented in this study is easy to learn, applicable to computer-aided surgical planning and can be performed by the non-technical clinician, resulting in excellent reproducibility and consistency.
... Consiste en un giroscopio digital que está unido a una plantilla de mordida, se pide al paciente que muerda la plantilla, se coloque en (NPH) y el giroscopio digital registra la orientación de los eje axial, coronal y sagital, con estos datos se orienta la tomografía a la NHP del paciente. 21 Estos métodos están basados en la hipótesis de que la NHP es una postura reproducible, es decir que no importa quién solicite al paciente que adopte esa postura y no importa cuántas veces en diferentes momentos se le solicite, siempre será la misma postura. Pero en la literatura hay estudios que reportan que hay un margen de error de 2 o en el eje axial, lo cual en cefalometría bidimensional no representa un error clínicamente significativo, pero no hay estudios sobre la reproducibilidad con respecto a los ejes coronal y sagital. ...
... Even computerized analysis of occlusal contacts can function as an indicator of occlusal plane [52]. Furthermore, the natural head position can be transferred to a virtual articulator by applying a gyroscope [53]. ...
Objective: The purpose of the present review was to demonstrate the utility of articulator systems and link instrumentation in determining the occlusal plane. The impact of the natural head position and anatomical landmarks on the occlusal plane location has been reported in the literature. Properly chosen instrumentation and management methods eliminate errors in determining the occlusal plane.
Methods: The PubMed and the Dentistry & Oral Sciences Source (through EbscoHost) databases were searched for ways to minimize the occurrence of errors when registering and determining the occlusal plane location, with or without the use of face-bows. A hand search and citation mining supplemented the results.
Results: Overall, 11 original approaches to occlusal plane determination were identified.
Discussion: Identified methods of occlusal plane transfer are based on real or virtual solutions. Owing to the large variety of devices, additional comparative studies are needed.
... To improve the accuracy of the anatomical plane determination, our medical collaborators have used a method of recording head orientation, i.e. natural head position (NHP), using digital orientation sensors [12,17]. The 3D CT model was reoriented using the recorded NHP as the world frame of the reference. ...
It is difficult to estimate the midsagittal plane of human subjects with craniomaxillofacial (CMF) deformities. We have developed a LAndmark GEometric Routine (LAGER), which automatically estimates a midsagittal plane for such subjects. The LAGER algorithm was based on the assumption that the optimal midsagittal plane of a patient with a deformity is the premorbid midsagittal plane of the patient (i.e. hypothetically normal without deformity). The LAGER algorithm consists of three steps. The first step quantifies the asymmetry of the landmarks using a Euclidean distance matrix analysis and ranks the landmarks according to their degree of asymmetry. The second step uses a recursive algorithm to drop outlier landmarks. The third step inputs the remaining landmarks into an optimization algorithm to determine an optimal midsaggital plane. We validate LAGER on 20 synthetic models mimicking the skulls of real patients with CMF deformities. The results indicated that all the LAGER algorithm-generated midsagittal planes met clinical criteria. Thus it can be used clinically to determine the midsagittal plane for patients with CMF deformities.
... The images obtained by traditional (fan-beam) computed tomography and cone-beam computed tomography scanners can be used to create 3D models of the craniofacial skeleton, teeth, and soft tissues [1,14,[21][22][23][24]. By placing these models into the neutral head posture, [25][26][27][28][29] we can now convert them into -3D cephalograms‖ similar to how a lateral head film is considered a cephalogram if taken at a fixed distance from the subject with the subject's head in a cephalostat. The goal of our new 3D cephalometric analysis was to maintain all the positive aspects of conventional 2D analysis and to address its negative aspects. ...
... Then, one must mark down the soft tissue fiducial on the skin right above the bony point of the orbitale, which is very cumbersome in clinical practice. In addition, THL is not identical to the FHP, making it difficult to detect FHP accurately even by expansive methods such as laser, CT, and MRI [11,[18][19][20][21][22][23][24]. Therefore, the conventional method for identifying true horizontal or vertical lines to match those of a face has certain problems. ...
Due to the lack of internationally standardized, objective, and scientific photographic standardization methods, differences in photographic documents have gravely affected the truth of surgical outcomes by visual misperception or illusion, thus hindering the development of plastic surgery clinically and scholastically. Here I suggest a simple method for standardization of facial photographs. The method consists of an imaginary transverse line (tentatively the "PSA line") rather than the Frankfort horizontal plane and uses a white background with black grids and standard RGB with CMYK circles. This simplified method of photographic standardization would help our professional society to make international standards on facial photographic documentation to maintain scholastic ethics, conscience, and morals.
No level assigned:
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... 44 Natural head position recording device: this uses a small and inexpensive device that consists of a digital orientation sensor attached to the patient by a bite jig and a facebow, which is capable of digitally recording natural head position in three dimensions and transferring it precisely to a 3-dimensional model. 44,51 Although the orientation sensor method is inexpensive compared with the laser scanner, it requires the construction of a patient-specific bite jig, and severely displaces the upper and lower lips during the CT imaging. Because the position of the upper lip is the most important landmark for predicting soft tissue in the simulation of 3-dimensional surgery, an undeformed resting lip position is essential in computer-assisted orthognathic surgery. ...
Both the correct position of the patient's head and a standard system for the acquisition of images are essential for objective evaluation of the facial profile and the skull, and for longitudinal superimposition. The natural position of the head was introduced into orthodontics in the late 1950s, and is used as a postural basis for craniocervical and craniofacial morphological analysis. It can also have a role in the planning of the surgical correction of craniomaxillofacial deformities. The relatively recent transition in orthodontics from 2-dimensional to 3-dimensional imaging, and from analogue to digital technology, has renewed attention in finding a versatile method for the establishment of an accurate and reliable head position during the acquisition of serial records. In this review we discuss definition, clinical applications, and procedures to establish the natural head position and their reproducibility. We also consider methods to reproduce and record the position in two and three planes.
... Advances such as 3D photography and gyroscopic natural head position systems can also be a valuable tool for assessing the facial midline of a patient, but ultimately the best determination of the facial midline comes from a detailed clinical evaluation. 18 ...
Orthognathic surgery can eliminate severe esthetic and functional deformities and be a life-changing event for a patient. An orthodontist's role in orthognathic surgery can be divided into several phases: the initial evaluation, presurgical orthodontics, surgical planning, and postsurgical orthodontics. At each of these phases, collaboration between the orthodontist and the surgeon is critical. The ability of an orthodontist and a surgeon to coordinate their efforts during this time is what will lead to a successful outcome.
... 5,11,13,20 In addition, the patient's neutral head posture (NHP) is recorded and transferred to the three-dimensional (3D) models. [21][22][23] Furthermore, the user performs virtual osteotomies and simulates orthognathic surgery. 2,5,19,24,25 Finally, surgical splints and templates are generated in the computer, fabricated by a rapid prototyping machine, and used during surgery to accurately position the bony segments. ...
Purpose:
The purpose of this prospective multicenter study was to assess the accuracy of a computer-aided surgical simulation (CASS) protocol for orthognathic surgery.
Materials and methods:
The accuracy of the CASS protocol was assessed by comparing planned outcomes with postoperative outcomes of 65 consecutive patients enrolled from 3 centers. Computer-generated surgical splints were used for all patients. For the genioplasty, 1 center used computer-generated chin templates to reposition the chin segment only for patients with asymmetry. Standard intraoperative measurements were used without the chin templates for the remaining patients. The primary outcome measurements were the linear and angular differences for the maxilla, mandible, and chin when the planned and postoperative models were registered at the cranium. The secondary outcome measurements were the maxillary dental midline difference between the planned and postoperative positions and the linear and angular differences of the chin segment between the groups with and without the use of the template. The latter were measured when the planned and postoperative models were registered at the mandibular body. Statistical analyses were performed, and the accuracy was reported using root mean square deviation (RMSD) and the Bland-Altman method for assessing measurement agreement.
Results:
In the primary outcome measurements, there was no statistically significant difference among the 3 centers for the maxilla and mandible. The largest RMSDs were 1.0 mm and 1.5° for the maxilla and 1.1 mm and 1.8° for the mandible. For the chin, there was a statistically significant difference between the groups with and without the use of the chin template. The chin template group showed excellent accuracy, with the largest positional RMSD of 1.0 mm and the largest orientation RMSD of 2.2°. However, larger variances were observed in the group not using the chin template. This was significant in the anteroposterior and superoinferior directions and the in pitch and yaw orientations. In the secondary outcome measurements, the RMSD of the maxillary dental midline positions was 0.9 mm. When registered at the body of the mandible, the linear and angular differences of the chin segment between the groups with and without the use of the chin template were consistent with the results found in the primary outcome measurements.
Conclusions:
Using this computer-aided surgical simulation protocol, the computerized plan can be transferred accurately and consistently to the patient to position the maxilla and mandible at the time of surgery. The computer-generated chin template provides greater accuracy in repositioning the chin segment than the intraoperative measurements.
Objective:
To design a virtual operation of joint replacement for surgical drills using a haptic device, SenSable_FreeForm_Modelling (SFM), to enhance surgeons' efficiency and enable "Virtual tutorial without reality" for interns.
Method:
A patient with hip joint osteoarthritis is randomly selected to perform Total Hip Replacement (THR). The hip images were input into Mimics in the format of *.dicom after CT scan and then exported to SFM using the stereolithographic (*.stl) format. A surgical toolkit can be created virtually with Computer Aided Design software such as Pro-E or Ghost SDK and a visual drill scenario of THR directed by a force-respondent stick, namely Phantom.
Result:
3D models of the hip joint were rebuilt illustrating clearly that the geometrical shapes of the surgical equipment created are similar to real instruments, and the THR operation is emulated distinctly in novelty.
Conclusion:
In obedience to an ancient maxim, so called 'genuine knowledge originated from practice', this simulative operation offers hands-on experience for students in the orthopaedics field with remarkable effects, contributing not only teaching cases for medical courses but also a planning basis for physical surgery.
Introduction
Research in Orthodontics and Oral Surgery has been relying on three-dimensional (3D) models to evaluate treatment results with displacement color map techniques, even though it has important limitations.
Objectives
This study proposed a method of tracking translational movements of 3D objects to evaluate displacements in surfaces with no shape modification.
Methods
Cone Beam Computed Tomography (CBCT) data of ten patients were imported to the Dolphin software. A hypothetical virtual surgical plan (randomly defined) was developed in the software and afterwards verified using the proposed method. All the procedures were carried out by two evaluators, in two different time-points, with a 15-day interval. ITK-Snap software was used to generate high quality STL models. Centroid points were automatically generated and their coordinates were compared to confirm if they represented the known displacements simulated. The paired t-test and the Bland-Altman plots were used, as well as the intraclass correlation coefficient.
Results
Interexaminers and intra-examiner tests showed excellent reliability of the method, with mean displacement measurement error values under 0.1mm. The paired t-test did not show any statistically significant differences.
Conclusion
The method showed excellent reliability to track the simulated translational displacements of bone segments.
Keywords:
Orthognathic surgery; Orthodontics; Imaging, three-dimensional
The definitive reconstruction of associated maxillomandibular deformities in craniofacial microsomia may have different connotations. For instance, if a growing number of patients receive a costochondral graft to reconstruct a temporomandibular joint, and that is able to adequately position the maxillomandibular complex, all the patients may need further orthodontic treatment. In that case, the growing number of patients received a definitive treatment. Most of the times, however, this will not be the case, and the affected side will still need surgical treatment after skeletal maturity. This chapter focuses on the important aspect to be evaluated during clinical examination, treatment planning, and the techniques available to treat a craniofacial microsomia patient that has reached skeletal maturity.
Cone Beam Computed Tomography (CBCT) is about more information which allowed clinicians to see the patient as what they really are, three-dimensional (3D) structures. A 3D image allows the individual to evaluate valuable information, not possible with traditional 2D imaging, and this may significantly impact the type of treatment plan and potentially the results. The additional information is also useful when assessing changes and evaluating results, so outcome assessments also can be more comprehensive. The purpose of this chapter is to describe how clinicians can use all three-dimensional tools like virtual planning, airway assessment, and 3D superimpositions for a more comprehensive diagnosis and illustrate techniques that go beyond the regular diagnosis to provide further information for the treatment planning and outcome assessment of the orthodontic patient.
RESUMEN
Diversos estudios han tratado de correlacionar los signos y síntomas, los desórdenes musculares y los trastornos en la articulación temporomandibular; sin embargo, aún no existe un método estándar debido a la sensibilidad y especificidad del diagnóstico clínico y la diversidad de los estudios auxiliares del diagnóstico. Los criterios de diagnóstico internacionales en la investigación de los trastornos temporomandibulares (CDI/TTM) recopilan datos de la historia clínica y el examen físico utilizando cuestionarios, formularios y planillas y la electromiografía (EMG), que es un estudio que permite evaluar la función motora de los músculos masticatorios. El propósito del presente artículo es conocer la importancia del estudio de la electromiografía en pacientes con trastornos temporomandibulares.
PALABRAS CLAVE
Electromiografía, trastornos temporomandibulares, disfunción de la articulación temporomandibular, músculos masticatorios, criterios de diagnóstico.
AimTo describe different modalities to record and transfer natural head position (NHP) to 3D facial imaging by using the virtual surgical planning software in three facial asymmetry patients.Case ReportsThree patients with facial asymmetries (A, B, and C) were evaluated by means of dental and facial analysis, photographs, cone-beam computed tomography (CBCT) and digitized dental arches. Before starting the VSP workflow with Dolphin Imaging, NHP was recorded by three modalities and transferred to three-dimensional (3D) facial images as follows: (a) facial photographs taken with digital camera and the estimated NHP was transferred to 3D images by comparing lines and planes from both images; (b) cross-line level laser was used to place radiopaque markers on the face skin for recording the estimated NHP, which was transferred to 3D images by alignment of planes and markers in the software; and (c) photographs of the face were processed to generate facial surface mesh by using the Agisoft PhotoScan software, which maintained the same position of the estimated NHP in 3D for aligning the images of the soft tissue with the facial surface mesh by using superimposition. All the three patients underwent bi-maxillary orthognathic surgery.Conclusion
There are different modalities using simple and available technologies in the clinical routine, but whose reproducibility, reliability and validation could not be assessed nor compared to each other. There was no trend for better predictability, feasibility and efficiency because the postoperative outcomes were adequate regarding the patients’ satisfaction and facial symmetry.
Purpose:
Computer-aided surgical simulation (CASS) is an evolving technology which has significantly affected surgical correction of dentofacial deformities, a key step of which is orientation of the virtual skull model to allow for analysis and treatment planning. Explored in this study is the coplanarity of a 3-dimensional Frankfort horizontal plane (3D FHP).
Materials and methods:
The 122 17.0 cm field-of-view cone-beam computed-tomogram (CBCT) scans were oriented to a 3D FHP using right porion, right orbitale, and left orbitale. The distance between the 3D FHP and left porion was then measured. The 18 CBCT scans were found to have external fiducial markers which were used for orientation into natural head position (NHP). The distance between left porion and a true horizontal plan coincidental with the right porion was measured. Concordance reliability measures were calculated to compare NHP to 3D FHP.
Results:
The average distance of left porion to 3D FHP was found to be -0.107 mm (SD = 1.148), and the average distance from the coincidental left porion in NHP was found to be 0.846 mm (SD = 2.611). Concordance reliability calculations shows little consistency between the 2 methods of orientation (P = 0.838).
Conclusions:
The data shows coincidence between left porion and 3D FHP. Orientation of the virtual skull model according to 3D FHP offers a quick and easy method for this important step in CASS. Further study is needed for evaluation of this method in vivo.
This chapter covers evaluation and treatment planning for patients needing orthognathic surgery. Evaluation and treatment planning are two processes that are part of the approach used to care for patients. This approach has four sequential processes: evaluation, assessment, treatment planning, and treatment (Fig. 39.1). Evaluation is a structured process used to appraise patients; it begins with the patient encounter and ends with an assessment. It has three steps: history, physical examination, and evaluation of diagnostic test. Treatment planning is a process used to determine the details of treatment. It begins after the assessment and ends before the treatment.
Purpose:
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.
Materials and methods:
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.
Results:
There was a statistically significant difference between measurements completed by experts and nonexperts (F1,60 = 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 (F1,60 = 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 (F1,60 = 4.66; P = .03).
Conclusions:
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.
Digital technologies are impacting reconstructive surgery like never before. The convergence of volumetric medical imaging, powerful software tools, and 3D printing is enabling personalized surgery. The craniomaxillofacial (CMF) specialty has always been an early adopter for volumetric medical imaging and 3D technologies, primarily driven by the need for functional and aesthetic outcomes, and dealing with the face, a very cosmetically and emotionally sensitive area. Reconstructive surgery of the CMF skeleton require precision, and this precision can be further refined by the use of digital technologies, both for the planning and the guidance of the procedure.
The purposes of this study were to determine: (1) whether an observer’s perception of the correct anatomical alignment of the head changes with time, and (2) whether different observers agree on the correct anatomical alignment. To determine whether the perception of the correct anatomical alignment changes with time (intra-observer comparison), a group of 30 observers were asked to orient, into anatomical alignment, the three-dimensional (3D) head photograph of a normal man, on two separate occasions. To determine whether different observers agree on the correct anatomical alignment (inter-observer comparison), the observed orientations were compared. The results of intra-observer comparisons showed substantial variability between the first and second anatomical alignments. Bland–Altman coefficients of repeatability for pitch, yaw, and roll, were 6.9°, 4.4°, and 2.4°, respectively. The results of inter-observer comparisons showed that the agreement for roll was good (sample variance 0.4, standard deviation (SD) 0.7°), the agreement for yaw was moderate (sample variance 2.0, SD 1.4°), and the agreement for pitch was poor (sample variance 15.5, SD 3.9°). In conclusion, the perception of correct anatomical alignment changes considerably with time. Different observers disagree on the correct anatomical alignment. Agreement among multiple observers was bad for pitch, moderate for yaw, and good for roll.
Purpose:
Three-dimensional (3D) images are taken with positioning devices to ensure a patient's stability, which, however, place the patient's head into a random orientation. Reorientation of images to the natural head position (NHP) is necessary for appropriate assessment of dentofacial deformities before any surgical planning. The aim of this study was to review the literature systematically to identify and evaluate the various modalities available to record the NHP in 3 dimensions and to compare their accuracy.
Materials and methods:
A systematic literature search of the PubMed, Cochrane Library and Embase databases, with no limitations on publication time or language, was performed in July 2015. The search and evaluations of articles were performed in 4 rounds. The methodologies, accuracies, advantages, and limitations of various modalities to record NHP were examined.
Results:
Eight articles were included in the final review. Six modalities to record NHP were identified, namely 1) stereophotogrammetry, 2) facial markings along laser lines, 3) clinical photographs and the pose from orthography and scaling with iterations (POSIT) algorithm, 4) digital orientation sensing, 5) handheld 3D camera measuring system, and 6) laser scanning. Digital orientation sensing had good accuracy, with mean angular differences from the reference within 1° (0.07 ± 0.49° and 0.12 ± 0.54°, respectively). Laser scanning was shown to be comparable to digital orientation sensing. The method involving clinical photographs and the POSIT algorithm was reported to have good accuracy, with mean angular differences for pitch, roll, and yaw within 1° (-0.17 ± 0.50°). Stereophotogrammetry was reported to have the highest reliability, with mean angular deviations in pitch, roll, and yaw for active and passive stereophotogrammetric devices within 0.1° (0.004771 ± 0.045645° and 0.007572 ± 0.079088°, respectively).
Conclusions:
This systematic review showed that recording the NHP in 3 dimensions with a digital orientation sensor has good accuracy. Laser scanning was found to have comparable accuracy to digital orientation sensing, but routine clinical use was limited by its high cost and low portability. Stereophotogrammetry and the method using a single clinical photograph and the POSIT algorithm were potential alternatives. Nevertheless, clinical trials are needed to verify their applications in patients. Preferably, digital orientation sensor should be used as a reference for comparison with new proposed methods of recording the NHP in future research.
Introduction:
The aims of this study were to evaluate how head orientation interferes with the amounts of directional change in 3-dimensional (3D) space and to propose a method to obtain a common coordinate system using 3D surface models.
Methods:
Three-dimensional volumetric label maps were built for pretreatment (T1) and posttreatment (T2) from cone-beam computed tomography images of 30 growing subjects. Seven landmarks were labeled in all T1 and T2 volumetric label maps. Registrations of T1 and T2 images relative to the cranial base were performed, and 3D surface models were generated. All T1 surface models were moved by orienting the Frankfort horizontal, midsagittal, and transporionic planes to match the axial, sagittal, and coronal planes, respectively, at a common coordinate system in the Slicer software (open-source, version 4.3.1; http://www.slicer.org). The matrix generated for each T1 model was applied to each corresponding registered T2 surface model, obtaining a common head orientation. The 3D differences between the T1 and registered T2 models, and the amounts of directional change in each plane of the 3D space, were quantified for before and after head orientation. Two assessments were performed: (1) at 1 time point (mandibular width and length), and (2) for longitudinal changes (maxillary and mandibular differences). The differences between measurements before and after head orientation were quantified. Statistical analysis was performed by evaluating the means and standard deviations with paired t tests (mandibular width and length) and Wilcoxon tests (longitudinal changes). For 16 subjects, 2 observers working independently performed the head orientations twice with a 1-week interval between them. Intraclass correlation coefficients and the Bland-Altman method tested intraobserver and interobserver agreements of the x, y, and z coordinates for 7 landmarks.
Results:
The 3D differences were not affected by the head orientation. The amounts of directional change in each plane of 3D space at 1 time point were strongly influenced by head orientation. The longitudinal changes in each plane of 3D space showed differences smaller than 0.5 mm. Excellent intraobserver and interobserver repeatability and reproducibility (>99%) were observed.
Conclusions:
The amount of directional change in each plane of 3D space is strongly influenced by head orientation. The proposed method of head orientation to obtain a common 3D coordinate system is reproducible.
In this study, we evaluated the reproducibility of natural head position for pitch and roll acquired using 3 methods.
The participants were 30 Chinese adults (ages, 23-28 years) who had normal occlusion with no history of orthodontic therapy, maxillofacial trauma, or surgery. The natural head position was acquired using the self-balanced, mirror, and estimated positions, which were performed in duplicate and repeated after 1 week. Three-dimensional photographs were recorded with a horizontal laser line projected onto the face. The laser lines were observed by registering the repeated 3-dimensional photographs. The roll and pitch of the head orientation were measured with a digital ruler. Reproducibility was calculated using Dahlberg's formula and the Bland-Altman method.
The reproducibility values calculated with Dahlberg's formula were 1.51°, 1.2°, and 0.99° for pitch, and 0.78°, 0.76°, and 0.41° for roll in the self-balanced, mirror, and estimated positions, respectively.
The 3 methods are reproducible for both pitch and roll, and the estimated position showed the best reproducibility among these methods. This indicates that the estimated position could be used for acquiring the reference plane in preoperative planning for orthognathic surgery.
Copyright © 2015 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.
To fulfill the requirements of computer-aided orthognathic surgery, the authors developed a method of recording head positions in pitch and roll and tested its accuracy and reliability.
A laser level was used to project a horizontal laser line onto a volunteer's face. A 3-dimensional (3D) photograph of the volunteer was taken to capture the laser line using the 3dMDface System, so the head positions could be recorded. To test the accuracy and reliability of this method, 35 head positions were recorded and compared with the positions recorded by the gyroscope method (Pn for pitch and Rn for roll). A cone-beam computed tomographic (CBCT) scan was taken, during which the head position was recorded by the gyroscope (P0 and R0). CBCT data were imported into ProPlan CMF 1.3 software and a virtual head was created. To reproduce each recorded head position, each 3D photograph was superimposed onto the virtual head through surface registration, and the virtual head was rotated to make the laser line parallel to the coordinate axes in the lateral and frontal views; the rotation angles were recorded, respectively, as Pn' and Rn'. Under ideal conditions, Pn' should equal Pn - P0 and Rn' should equal Rn - R0. The accuracy was evaluated using the Bland-Altman method. Reliability was tested by intraclass correlation coefficient (ICC) analysis.
The 95% limits of agreement between the rotation angles recorded by the present method (Pn', Rn') and the gyroscope method (Pn - P0, Rn - R0) were -0.598° to 1.589° for pitch and -1.156° to 1.674° for roll; such a difference was generally accepted as being accurate. The ICCs were 0.996 (0.992, 0.998) for pitch and 0.998 (0.997, 0.999) for roll.
The 3dMDface System and laser level method of recording head positions was accurate and reliable.
Copyright © 2015 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.
We developed a new method to record and reproduce the three-dimensional natural head position (NHP) from a single photograph of a patient’s face using a pose from orthography and scaling with iterations (POSIT) algorithm. We attached 4-mm spherical ceramic markers to the patient’s face as feature points. A frontal photograph of the patient’s NHP was taken using an ordinary digital camera parallel to the global horizon. Computed tomography (CT) was then performed on the patient with the markers. The ceramic marker positions were determined in the 2D image and corresponded to points in the 3D model. The 3D rotation matrix determined using the feature points via the POSIT method was applied to the CT model to reproduce the NHP. A skull phantom was used to evaluate the accuracy and reproducibility of the developed method. The degree difference (°) between the true and POSIT orientations in the roll, pitch, and yaw directions was quantified as the error. The mean accuracy was -0.04±0.15°, -0.17±0.50°, and -0.02±0.37° in the roll, pitch, and yaw directions, respectively. The method developed was highly reproducible during intra-observer and inter-observer variation analyses. The accuracy of the method was clinically acceptable, and the procedure was time- and cost-effective. This method is accurate and inexpensive; additionally, it does not affect the patient’s lip position, and we expect it to be routinely used during orthognathic surgery.
Traditional cephalograms are X-ray films, which provide either frontal or lateral overlapped perspective medical imaging. Although computed tomography imaging provides more information in 3-dimensional anatomy, the landmarks for cephalometry are located in space which does not carry normal standards in 3-D cephalometry. The CT natural imaging method is different from X-ray in that they respectively use orthogonal and perspective projections. Thus, we cannot apply the statistical normal values gathered from traditional 2D cephometry to 3D cephalometry. This study makes use of calibrated synthesized cephalograms from computed tomography to construct a cephalometry bridge between 2-D and 3-D. In this thesis, we first review the imaging model of a specific X-ray machine (Asahi OrthoStage AUTO IIIN) by a camera calibration method. We then construct a reference system for a virtual head, and synthesize calibrated X-ray cephalograms using the volume rendering algorithm. System accuracy for the synthesis X-ray cephalograms is verified through an interactive corresponding landmark system between 2-D and 3-D. An experimental clinician was invited to manually place 17 landmarks on the X-rays and their corresponding, shuffled in random order. The systematic error, average error, and standard deviation of landmark positions are 0.15 mm, 0.97 mm, and 0.45 mm, respectively. The interactive system bridges the transformation from orthogonal 3-D to perspective 2-D cephalometry.
Although natural head position has proven to be reliable in the sagittal plane, with an increasing interest in 3-dimensional craniofacial analysis, a determination of its reproducibility in the coronal and axial planes is essential. This study was designed to evaluate the reproducibility of natural head position over time in the sagittal, coronal, and axial planes of space with 3-dimensional imaging.
Three-dimensional photographs were taken of 28 adult volunteers (ages, 18-40 years) in natural head position at 5 times: baseline, 4 hours, 8 hours, 24 hours, and 1 week. Using the true vertical and horizontal laser lines projected in an iCAT cone-beam computed tomography machine (Imaging Sciences International, Hatfield, Pa) for orientation, we recorded references for natural head position on the patient's face with semipermanent markers. By using a 3-dimensional camera system, photographs were taken at each time point to capture the orientation of the reference points. By superimposing each of the 5 photographs on stable anatomic surfaces, changes in the position of the markers were recorded and assessed for parallelism by using 3dMDvultus (3dMD, Atlanta, Ga) and software (Dolphin Imaging & Management Solutions, Chatsworth, Calif).
No statistically significant differences were observed between the 5 time points in any of the 3 planes of space. However, a statistically significant difference was observed between the mean angular deviations of 3 reference planes, with a hierarchy of natural head position reproducibility established as coronal > axial > sagittal.
Within the parameters of this study, natural head position was found to be reproducible in the sagittal, coronal, and axial planes of space. The coronal plane had the least variation over time, followed by the axial and sagittal planes.
Virtual surgical planning is an excellent teaching instrument, allowing 3D analysis of the clinical problem and visualization of idealized digital osteotomies and manipulations. The preoperative virtual plan is transferred to patients in 1 of 3 ways depending on the clinical problem. Orthognathic surgery is facilitated by the use of intermediate and final occlusal splints. These splints are designed based the virtual reconstruction of the idealized image of the patients' craniofacial skeleton after correcting for pitch, roll, and yaw. Computer-aided surgery, with the range of techniques discussed in this article, may add safety and predictability to the complete range of oral and maxillofacial surgical procedures and has the potential to replace analytical model surgery as the treatment planning technique of choice in bimaxillary orthognathic surgery.
The success of cranio-maxillofacial (CMF) surgery depends not only on surgical techniques, but also upon an accurate surgical plan. Unfortunately, traditional planning methods are often inadequate for planning complex cranio-maxillofacial deformities. To this end, we developed 3D computer-aided surgical simulation (CASS) technique. Using our CASS method, we are able to treat patients with significant asymmetries in a single operation which in the past was usually completed in two stages. The purpose of this article is to introduce our CASS method in evaluating craniofacial deformities and planning surgical correction. In addition, we discuss the problems associated with the traditional surgical planning methods. Finally, we discuss the strength and pitfalls of using three-dimensional measurements to evaluate craniofacial deformity.
To review the past year's literature regarding current computer-assisted reconstruction techniques and their outcomes.
Current computer-assisted craniofacial reconstruction research is focused on data acquisition, planning, surgical and assessment phases. The major areas of interest among researchers include cosmetic surgery; cleft and craniofacial surgery; traumatic reconstruction, head and neck tumor reconstruction; and orthognathic surgery and distraction osteogenesis. Recent advances in the fields include facial analysis and planning in rhinoplasty, facial surface and bone graft volume analysis in cleft surgery, computer-guided tumor ablation and osteocutaneous reconstruction in tumor surgery, and preoperative planning and surgical assistance in orthognathic and distraction osteogenesis surgery.
Research in computer-aided craniofacial surgery is progressing at a rapid rate. Rather than just the latest innovation, sound research studies are proving computer assistance to be invaluable in producing superior outcomes, especially in the fields of head and neck surgery, orthognathic surgery, and craniomaxillofacial trauma surgery. Further outcome studies and cost-benefit analyses are still needed to show the superiority of these methods to contemporary techniques.
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.
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.
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°.
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.
The importance of clinical examination for treatment planning of CMF deformitiesAs we discussed above, with this new technology we are able to create 3D models of the face that incorporate accurate renditions of the teeth, the skeleton and the soft tissues. Moreover, these models can be accurately oriented to the natural head position, an important pre-requisite for accurate planning. From this, one may infer that the value of the physical examination in the clinical decision making process will become irrelevant. In our experience, this is far from the truth. Although, these models can capture the anatomy with great detail, they are static and only present the status of the tissues at the time of image capture. Therefore, the physical examination still provides us with extremely valuable dynamic information that cannot be obtained from any other source. To illustrate this issue, we will discuss examples of pitfalls that can be encounter by relaying only on the static images.The first example is a patient with significant mandibular laterognathia (lateral chin deviation) (Fig 14a). On assessing the alignment of the maxillary dental midline we have discovered that in some of these patients the relationship of the maxillary dental midline to the upper lip varies depending on the mediolateral position of the chin. During the physical examination, we first measure the transverse alignment of the maxillary dental midline to the middle of the upper lip while the patient is in centric relationship. In this position, the maxillary dental midline seems to be deviated opposite to the chin deviation (Fig 14b). We then measure the same alignment after we have asked the patient to move his chin to the midline simulating correction of the mandibular asymmetry. In this position, the maxillary dental midline is no longer deviated (Fig 14c). What is happening here is that the lateral displacement of the mandible is producing a deformation of the upper lip by dragging it to the side of the chin deviation. When the chin is moved to the midline, the upper lip regains its normal shape. The pitfall here is that if this dynamic deformation is not taken into account, the surgeon will “correct” a maxillary dental midline deviation that is not real. Obviously, this will create and unwanted outcome. Therefore, we recommend that the decision of correcting a maxillary midline deviation should be based on physical examination, rather than the study images.Fig 14The maxillary dental midline deviation changes depending on different mandibular position.Another possible pitfall on the static images relates to the assessment of the amount of maxillary incisal show. Experienced clinicians know that the amount of incisal show may vary with the patient's position. It tends to decrease when the patient changes position from supine, to sitting, and to standing (Fig 15a). If the CT scan is done on a medical scanner, it is done with the patient in the supine position. In this scenario, the amount of incisal show may seem excessive, when it is not (Fig 15b). If the scan is done of a cone-beam scanner it is usually done with the patient sitting or standing. In these scenarios, the amount of incisal shown more closely resembles the actual amount.Fig 15The amount of maxillary incisal show may vary with the patient's position.One more issue regarding the measurement of the incisal show is the uncertainty of the functional state of the lips during image acquisition. Ideally, they should be in repose. However, the functional state of the lips is questionable unless the surgeon is present during the scanning. Strained lips will produce an inaccurate determination of incisal show. Therefore, it is best to determine this parameter clinically during the physical exam rather than relying of the computer images. During the physical exam, this parameter should be measured with the patient standing in front of the surgeon. The decision on how much to change the amount of incisal show should not be based solely on the amount of show at rest. Other important issues should also be taking into account. They include the amount of gingival show during smiling, the presence of delayed passive eruption, or the presence of attrition. Finally, clinical measurements of the occlusal cant, degree of dystopia, and ear position also serve to verify that the composite skull model is correctly oriented in the 3D coordinate system.
In clinical measurement comparison of a new measurement technique with an established one is often needed to see whether they agree sufficiently for the new to replace the old. Such investigations are often analysed inappropriately, notably by using correlation coefficients. The use of correlation is misleading. An alternative approach, based on graphical techniques and simple calculations, is described, together with the relation between this analysis and the assessment of repeatability.
Cranial posture and its possible relationship to the morphology of the skull has been studied in some detail, as have the relationships between cranial posture and such functions as respiration and jaw movements. To date, cranial posture has been assessed mainly with techniques that give static interpretations of the angular relationships between intracranial and extracranial reference lines. The present project was undertaken to develop a system of instruments capable of the continuous measurement and recording of cranial posture for extended periods of time. A number of aspects of this system were tested. The results indicate that the experimental array of instruments measures head posture accurately over a defined range of cranial movement. This new technique should make it possible to measure cranial posture in a more dynamic and physiologic manner.
No Abstract Available. From the Orthodontic Department of the University of Manitoba and the Winnipeg Children's Hospital, Winnipeg, Manitoba. This investigation was supported by Grant MA-1681 from the Medical Research Council, National Research, Ottawa, Canada.
The natural head position in standing subjects was studied on cephalometric profile radiographs of 120 Danish male students aged 22-30 years. Two head positions were recorded, one determined by the subjects own feeling of a natural head balance (the self balance position) and the other by the subject looking straight into a mirror (the mirror position). The reproducibility of the two head positions was assessed. The reference points were recorded by the D-Mac Pencilfollower on punched cards, and a computerized technique was developed for transfer of reference points between the two series of films. It was found that in the mirror position the head was kept higher than in the self balance position. The variability in inclination of the craniofacial and cervical reference lines to the true vertical and to each other in the two head positions was reported. Analysis of the pattern of associations within the craniocervical complex was suggested to clarify the relationship between head balance and facial morphology.
Standing natural head position is a reproducible, physiologically determined aspect of function. Recent studies have demonstrated associations between this aspect of function and the form of the skeletodental features, in both growing and nongrowing persons. A simple method has been devised which obviates the need for multiple radiographs to determine the clinical reliability of the method. The device, its construction, and method of use are described.
A three-part study was designed in order to test the applicability of the fluid-level method for registration of natural head position. In the first part the fluid-level method was utilized to make two repeated cephalometric radiographs of 33 young adults. The reproducibility of the craniovertical, craniocervical and cervicohorizontal relationships was comparable with previous results with the mirror method. In the second part, the fluid-level method was compared with the mirror method when used by two radiographers for repeated radiographs in 40 subjects. The reproducibility of the craniocervical and cervicohorizontal angles was less accurate with both methods and the only difference between them was a slightly better reproducibility of the craniovertical angle with the fluid-level method for one of the radiographers. In the third part, it was shown that using the fluid level, a patient can be transferred from a standing to a sitting position in the cephalostat without any systematic change in craniovertical, craniocervical or cervicohorizontal relationships.
The purposes of this study were (1) to construct a device to record natural head position and transfer it to the cephalostat, (2) to assess its clinical use, and (3) to evaluate the reproducibility of lateral cephalograms taken with the device. The device, incorporated into a pair of eyeglass frames, included 2 tilt sensors to measure pitch and roll of the head. The natural head positions of 20 subjects were established 10 times by self balance and mirror position, recorded with the device, and reproduced in the cephalostat by using the average of these 10 measurements. Three lateral cephalograms were obtained in this manner at 30-minute intervals. The first 2 films were made with the subject wearing the device to assess the reproducibility of the recorded position in the cephalostat by the inclinometer. During exposure of the third film, the device was not worn, and this film was used to determine the stability of the established position when the inclinometer was removed. The results revealed method errors of 0.6 degrees (SD, 0.9) between the first 2 sets of radiographs with a correlation coefficient of 0.985. Method errors between the first and third and the second and third sets were 0.6 degrees (SD, 0.8) and 0.7 degrees (SD, 1), respectively, with correlation coefficients of 0.989 and 0.982. The reproducibility of the method was high, and the system was clinically practical for both recording and transferring natural head position in cephalometrics. This technique should make it possible to measure and reproduce head position accurately. Minimizing the size of the device, making it radiolucent, and integrating it into the radiographic device will make it more versatile and decrease error.
Sagittal (pitch) and transversal (roll) natural head position (NHP) was measured once in 20 subjects, 18 to 24 years of age, with an inclinometer; the measurements were repeated 2 years later. The method error (reproducibility) after 2 years was 1.1 degrees for sagittal and transversal measurements. The mean change in NHP measurement was -0.3 degrees for both measurements, and the variance was 1.21 degrees (= 1.1(2)).