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Reproducibility of Natural Head Position assessed with stereophotogrammetry
Abstract
Objective:
The aim of this study was to assess the stability of Natural Head Position (NHP) over time using the 3dMDface System.
Setting and sample population:
This was an experimental study. Three-dimensional facial images of 40 students were captured on two different occasions, with an interval of at least two weeks.
Materials and methods:
The images were taken using a stereophotogrammetric device (3dMD, Atlanta, Georgia). The mirror positioned NHP was obtained in a standing position and then replicated in a sitting position for capturing. The self - balanced NHP was taken in a sitting position. Rapidform 3D software was used for position angle calculations. The angle changes between the positions were calculated for rotations around the x-, y- and z- axes.
Results:
The differences between NHP in the self-balanced and mirror positions recorded on the first and second occasions were 2.43 and 1.75 degrees, respectively, around the x-axis. The average changes in NHP around the x-axis between the self-balanced and mirror balanced positions exceeded 3 degrees at the two-week interval. The differences were smaller for the rotations around the y- and z- axes. Some subjects consistently tended to hold their heads in a more extended position when self-balanced, while others did this when mirror balanced. There was no difference in the reproducibility of NHP between men and women.
Conclusion:
The reproducibility of NHP for consecutive stereophotogrammetric captures is generally acceptable. The reproducibility of NHP using the mirror position was slightly better compared with NHP in the sitting self-balanced position.
... NHP refers to the head's balanced position in a relaxed state, with the eyes looking straight forward and focusing on a point at eye level; the visual axis is parallel to the horizontal plane. The research conducted by Jakobsone et al. (2020) demonstrated that the mirror-guided position is steady and reproducible (Jakobsone et al., 2020). ...
... NHP refers to the head's balanced position in a relaxed state, with the eyes looking straight forward and focusing on a point at eye level; the visual axis is parallel to the horizontal plane. The research conducted by Jakobsone et al. (2020) demonstrated that the mirror-guided position is steady and reproducible (Jakobsone et al., 2020). ...
Background
Head posture deviation is seen in 52.5 % of children aged 6–15 years. Studies have shown that poor posture habits can impair muscle function during craniofacial growth and development. A muscle imbalance causes abnormal positioning of dental and skeletal structures, a condition that exerts negative impacts, such as changes in facial morphology.
Objective
To determine through photometric analysis the relationship between craniovertebral angle as a function of head posture and glabella-subnasale-pogonion (G-Sn-Pg) angle as a function of facial profile in 10–12-year-old children, and the results will help to avoid facial development issues.
Methods
Thirty-three subjects met the inclusion criteria. Their craniovertebral angles and facial profiles were measured using lateral photometry and ImageJ. The craniovertebral angle was determined by connecting the tragus and C7 with a horizontal line, whereas the facial profile angle was determined by connecting the glabella, subnasale, and pogonion. The relationship between the craniovertebral and G-Sn-Pg angle values was analyzed using the Pearson correlation test.
Results
A significant relationship was observed between the craniovertebral angle and the G-Sn- Pg angle (p < 0.05), although such a relationship was weak (r = 0.373).
Conclusion
A more forward head posture is associated with a more convex facial profile, and this relationship is useful for the early prevention and treatment.
... The volunteers's head were scanned in two different positions in order to determine the most reproducible method, first in the Jakobsone et al. 15 determined natural head position (Fig. 1) and second by fixating the head in a head frame designed for this purpose (Fig. 2). Fixation was achieved by placing earbuds, that were attached www.nature.com/scientificreports/ to the device by bars, in both of the participant's ears. ...
... Before scanning, the 3D-scanner was warmed up according to the recommendations of the manufacturer to achieve maximum accuracy. During the first scan (T1), to achieve a natural head position and habitual occlusion, the volunteers had to stand upright and were asked to swallow and keep their molars softly in occlusion, while looking at themselves (into their own eyes) in the mirror with their habitual facial expression 15 . The volunteers were then placed in the fixation device for the second scan (T2), while continuously looking with a habitual facial expression at a fixed point on the wall (at eye height). ...
The reproducibility of scanning in the periorbital region with 3D technology to enable objective evaluations of surgical treatment in the periorbital region was assessed. Facial 3D-scans of 15 volunteers were captured at different time points with a handheld Artec Space Spider structured light scanner. Two scans were made with a one minute interval and repeated after 1 year; for both a natural head position and with the head in a fixation-device. On assessing the area between the eyelashes and eyebrows, the medians of the average deviations between the various cross-sections of the one minute interval 3D-scans ranged from 0.17 to 0.21 mm at baseline, and from 0.10 to 0.11 mm when the minute-interval scanning was repeated one year later. The systematic differences when scanning in a natural head position and fixated position were comparable. The reproducibility of the 3D processing was excellent (intraclass correlation coefficient > 0.9). The repeated scanning deviations (baseline versus one year data) were well within the accepted clinical threshold of 1 mm. Scanning with a hand-held 3D-scanning device (Artec Space Spider) is a promising tool to assess changes in the periorbital region following surgical treatment since the median deviations are well below the clinically accepted 1 mm measuring error, for both the natural head and fixated positions.
... Each participant in the study was instructed to sit upright and adopt a natural head position (NHP) [49]. They were asked to keep their eyes wide open and maintain minimal facial expression and maximum intercuspation position (MIP). ...
Objectives
To evaluate the validity and reliability of smartphone-generated three-dimensional (3D) facial images for routine evaluation of the oronasal region of patients with cleft by comparing their accuracy to that of direct anthropometry (DA) and 3dMD.
Materials and methods
Eighteen soft-tissue facial landmarks were manually labelled on each of the 17 (9 males and 8 females; mean age 23.3 ± 5.4 years) cleft lip and palate (CLP) patients’ faces. Two surface imaging systems, 3dMDface and Bellus3D FaceApp, were used to perform two imaging operations on each labelled face. Subsequently, 32 inter-landmark facial measurements were directly measured on the labelled faces and digitally measured on the 3D facial images. Statistical comparisons were made between smartphone-generated 3D facial images (SGI), DA, and 3dMD measurements.
Results
The SGI measurements were slightly higher than those from DA and 3dMD, but the mean differences between inter-landmark measurements were not statistically significant across all three methods. In terms of clinical acceptability, 16% and 59% of measures showed differences of ≤ 3 mm or ≤ 5º, with good agreement between DA and SGI and 3dMD and SGI, respectively. A small systematic bias of ± 0.2 mm was observed generally among the three methods. Additionally, the mean absolute difference between the DA and SGI methods was the highest for linear measurements (1.31 ± 0.34 mm) and angular measurements (4.11 ± 0.76º).
Conclusions
SGI displayed fair trueness compared to DA and 3dMD. It exhibited high accuracy in the orolabial area and specific central and flat areas within the oronasal region. Notwithstanding this, it has limited clinical applicability for assessing the entire oronasal region of patients with CLP. From a clinical application perspective, SGI should accurately encompass the entire oronasal region for optimal clinical use.
Clinical relevance
SGI can be considered for macroscopic oronasal analysis or for patient education where accuracy within 3 mm and 5º may not be critical.
... angular, and area measurements, 10 making this method accurate and reliable for most clinical and research applications. 17 The participants were instructed to sit upright in a chair with their heads positioned in a natural position, 18 and their eyes focused on a stationary point while relaxing their facial muscles and touching their lips lightly. To avoid interference, disposable caps were used to cover the hair, and metallic objects, such as earrings and piercings, were removed to prevent reflections from flash light. ...
This cross-sectional observational study aimed to evaluate and compare facial metrics in women aged 20–65 years using a three-dimensional (3D) stereophotogrammetry system and to establish standardized values for facial metric variations in different age subgroups. This study included 84 Caucasian women divided into two groups based on their age: group 1 (G1) included women aged 20–40 years and group 2 (G2) included women aged 41–65 years. Twenty-one morphometric points on the face were identified, and the facial images were captured using a 3D stereophotogrammetry system, Twenty-three linear measures and 12 angular measures were evaluated, revealing statistically significant differences in 11 linear and 5 angular measures between the groups. In the G2 group, nasal and mouth width, lip philtrum height, Tragus-Nasion and Tragus-Pronasale lengths were increased, along with increased nasofrontal angle, decreased palpebral fissure inclination, and lip vermilion angles. However, palpebral fissure width and height, binocular width, and lip vermilion height were reduced. The aging process in women causes substantial changes in facial features, particularly in the middle and lower thirds of the face. Conversely, no major changes were observed in the upper third of the face. Our study findings provide potential insights for clinicians in developing facial rejuvenation procedures as well as for forensic purposes and surgical planning. The standardized facial metrics values in different age subgroups can guide clinicians in determining appropriate treatment plans for patients seeking facial rejuvenation.
... Another important factor to consider in the acquisition of the photograph is the position of the patient since, as reported by Riml and colleagues, it influences facial measurements. 15 From this point of view, Peng and Cooke 16 indicated as a stable and reproducible position the natural position of the head, which has also been studied and evaluated in 2D and 3D photography by Jakobsone et al 17 and in radiographic studies by Hsung et al, 18 maintaining the good results of stability and reproducibility. For this reason, the photographs were taken maintaining the natural position of the head to subsequently orient the photographs with the bipupillary plane and the Frankfurt plane parallel to the base of the image. ...
Background
Artificial intelligence (AI) has been a contribution in recent years to the development of new tools for dental, surgical, and esthetic treatment. In the case of image diagnosis, AI allows automated analysis of some facial parameters. The aim of this study was to evaluate the precision and reproducibility of these IA analyses compared with a human operator.
Methods
Thirty subjects were selected, and frontal and profile photographs were taken of each. The photographs were previously calibrated and then analyzed by a human operator and an AI for vertical, horizontal, symmetry parameters, and facial profile angles.
Results
Statistically significant differences were found in at least 1 vertical, horizontal, symmetry, and facial profile measurement.
Conclusions
The 2D facial analysis performed on photographs using AI is an interesting and constantly evolving tool. However, there are still many differences with the analysis performed by the human operator, so it should be used carefully. Further studies using metric measurements should be performed to contrast the values obtained by human operators and AI and to analyze the accuracy of point selection in facial soft tissues.
... Previous studies have shown the high degree of reproducibility of this position in photogrammetry, cephalometry, and tomography, and it has been preserved over time. [43][44][45][46] However, complementary examinations used in maxillofacial surgery and orthodontics, such as CBCT, are regularly performed considering the use of positioners, which use the Frankfort horizontal plane as a reference. Xia and colleagues (2011) and Hsung and colleagues (2021) evaluated the reproducibility of the Natural Head Position acquisition of tomographic images and observed a high degree of reproducibility, making it an ideal position to be used throughout the diagnostic process. ...
Objective: Orthognathic surgery is a viable and reproducible treatment for facial deformities. Despite the precision of the skeletal planning of surgical procedures, there is little in- formation about the relations between hard and soft tissues in three-dimensional (3D) analysis, resulting in unpredictable soft tissue outcomes. Three-dimensional photography is a viable tool for soft tissue analysis because it is easy to use, has wide availability, low cost, and is harmless. This review aims to es- tablish parameters for acquiring consistent and reproducible 3D facial images.
Methods: A scoping review was conducted across PubMed, SCOPUS, Scientific Electronic Library Online (SciELO), and Web of Science databases, adhering to “Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews” guidelines. Articles presenting 3D facial photographs in the diagnostic phase were considered.
Results: A total of 79 articles were identified, of which 29 were selected for analysis.
Conclusion: The predominant use of automated systems like 3dMD and VECTRA M3 was noted. User positioning has highest agreement among authors. Noteworthy aspects include the importance of proper lighting, facial expression, and dental positioning, with observed discrepancies and inconsistencies among authors. Finally, the authors proposed a 3D image ac- quisition protocol based on this research findings.
... NHP, which TVL and GALL are based on, is the balance and physiological position of head when viewing an object at eye level [12] and represents the anatomic pattern of the craniofacial complex [23]. Nevertheless, natural head postures are difficult to define correctly in clinical use, due to variable intraindividual reproducibility over time and practical constraints such as equipment and staff training [12,24]. Besides, G point, used by Andrews to evaluate the position of incisors, has high individual variability [25] and is too far away from the dentition and overly influenced by the head position. ...
Objectives:
This study was designed to determine the optimal anterior-posterior (AP) position of upper incisors through Anterior Nasal Spine (ANS) point.
Materials and methods:
Lateral cephalometric radiographic images of 690 patients were collected and divided into a derivation group and a validation group, and the former were subdivided into a proper AP position (PAP) group and an improper AP position (iPAP) group. The distance from facia-axis (FA) point of upper incisors to the line perpendicular to Frankfort horizontal (FH) plane through ANS (FA-ANS) was measured, and the relationship between FA-ANS and several cephalometric indices were studied through Pearson correlation analysis. Receiver operating characteristic (ROC) curves for different clinical indices were analyzed to evaluate the diagnostic efficiency of optimal AP position of upper incisors.
Results:
The average value of FA-ANS in PAP group was 0.57±1.99, which was significantly different from FA-ANS in iPAP group. Cephalometric indices such as U1-NA, U1-SN, AB-NPo, UL-TVL, Wits, and ANB were found to be correlated with FA-ANS. The receiver operating characteristic (ROC) curves represented a greater diagnostic efficiency of FA-ANS compared with other clinical indices.
Conclusions:
ANS point, as a stable skeletal landmark, could be used to access an optimal AP position of upper incisors, providing aids to clinical diagnosis and treatment goal determination for clinical practice.
Clinical relevance:
A new index FA-ANS, together with other traditional indices, could help determine the optimal position of upper incisors and provide a personalized therapeutic plan.
... However, the study designs are either arbitrary with fiducial markers or based on dry skull models 5,15,16 . Although lately different methods for head orientation in 3D space have been proposed, they have either been focused on 3D facial scans or based on high-resolution medical CT images 4,[17][18][19][20] . ...
Low dose and accessibility have increased the application of cone beam computed tomography (CBCT). Often serial images are captured for patients to diagnose and plan treatment in the craniofacial region. However, CBCT images are highly variable and lack harmonious reproduction, especially in the head’s orientation. Though user-defined orientation methods have been suggested, the reproducibility remains controversial. Here, we propose a landmark-free reorientation methodology based on principal component analysis (PCA) for harmonious orientation of serially captured CBCTs. We analyzed three serial CBCT scans collected for 29 individuals who underwent orthognathic surgery. We first defined a region of interest with the proposed protocol by combining 2D rendering and 3D convex hull method, and identified an intermediary arrangement point. PCA identified the y-axis (anterioposterior) followed by the secondary x-axis (transverse). Finally, by defining the perpendicular z-axis, a new global orientation was assigned. The goodness of alignment (Hausdorff distance) showed a marked improvement (> 50%). Furthermore, we clustered cases based on clinical asymmetry and validated that the protocol was unaffected by the severity of the skeletal deformity. Therefore, it could be suggested that integrating the proposed algorithm as the preliminary step in CBCT evaluation will address a fundamental step towards harmonizing the craniofacial imaging records.
... All studies were evaluated for eligibility based on the following PICO model: (P) the patients diagnosed with malocclusion without a history of orthodontic treatment were included; (I) not applicable; (C) the group of Class I malocclusion (subjects with a normal sagittal jaw relationship) was applied as the control to assess the relationship of cranio-cervical posture with Class II and III malocclusion; (O) Outcome measures consisted of craniovertical angles, cervicohorizontal angles, craniocervical angles and cervical curvature obtained by cephalometric analysis. In addition, all postural variables were measured in natural head position (NHP) to reduce the influence of intracranial reference planes like Sella Nasion (SN) and Frankfort Horizontal (FH) planes, which was adopted worldwide because of its good stability and reproducibility [30][31][32][33]. Observational studies including cross-sectional studies, cohort studies, and case-control studies were screened out for evaluation. ...
Background
The association of head and cervical posture with malocclusion has been studied for many years. Despite extensively encouraging researches, no conclusive evidence has been reached for clinical application.
Objective
To identify the question “Does head and cervical posture correlate to malocclusion?”, a systematic review and meta-analysis based on the available studies were carried out (PROSPERO registration number: CRD42022319742).
Methods
A search of PubMed, Embase, Cochrane Library, and the grey literature was performed without language restrictions. The study screening, data extraction, risk-of-bias evaluation and methodological quality assessment were performed by two independent investigators. When a disagreement arose, a third author was consulted.
Results
6 original cross-sectional studies involving 505 participants were included, which were of moderate methodological quality. NL/VER in Class Ⅱ group and NL/CVT in Class Ⅲ group showed significant differences compared to Class Ⅰ group, but no significant differences were observed in most of the variables like NSL/VER, OPT/CVT, OPT/HOR, CVT/HOR, NSL/OPT, NSL/CVT, NL/OPT in Class Ⅱ and Ⅲ groups.
Conclusions
The results suggested that the current research evidence is not sound enough to prove the association of head and cervical posture with sagittal malocclusion. Better controlled design and a larger sample size are required for clarifying this question in future study.
... To determine the natural head position, all participants were asked to position their heads at the greatest comfort (self-balanced position) and look toward a distant spot at the wall. 22 An SCP device, Bellus Face Camera Pro (Bellus 3D, Inc., Campbell, Calif), was positioned on top of the computer monitor, and the participants were prompted to turn their heads to capture facial features and compile a 3D image. The final set of 3D images was obtained with the MCP device 3dMD Trio (3dMD LLC, Atlanta, Ga). ...
Objectives
To assess the precision and accuracy of single-camera photogrammetry (SCP) and multicamera photogrammetry (MCP) compared with direct anthropometry (DA).
Materials and Methods
A total of 30 participants were recruited, and 17 soft tissue landmarks were identified and used to complete a total of 16 measurements. Using SCP and MCP, two three-dimensional (3D) images were acquired from each participant. All 3D measurements and direct measurements were measured twice by the same operator to assess intraexaminer repeatability. Intraclass coefficients (ICCs) were used to evaluate intraexaminer repeatability and interexaminer agreement of the methods. Nonparametric bootstrap analyses were used to compare the means of the measurements among the three methods.
Results
All three methods showed excellent intraexaminer repeatability (ICCs > 0.90), except interpupillary distance (ICC = 0.86) measured by SCP. Both SCP and MCP showed excellent interexaminer agreement (ICCs > 0.90), except interpupillary distance (ICC = 0.79), left gonion-pogonion (ICC = 0.74), and columella-subnasale-labrale superior angle (ICC = 0.86) measured by SCP. Overall, there was good agreement between methods, except for columella-subnasale-labrale superior angle (ICC = 0.40) between SCP and MCP.
Conclusions
Both SCP and MCP techniques were found to be reliable and valid options for 3D facial imaging. SCP produced slightly larger mean values for several measurements, but the differences were within a clinically acceptable range. Because of the larger margin of errors, measurements including the gonial area and subnasale should be assessed with caution.
... 8 The self-guided position is when a person looks at themselves in a mirror. 8 Different studies indicate that the mirror-guided head position is the most stable and reproducible 9,10 ; however, it is rarely adopted in everyday life. It is thus preferable, in order to more accurately simulate the head position in a natural environment, to analyse the self-balanced head position that is more frequently adopted. ...
Aim
The purpose of this study was to evaluate the variation in natural head position (NHP) over five minutes using an inertial measurement unit (IMU).
Material and methods
Fifteen healthy young volunteers were asked to sit on a chair and keep their head in the self-balanced position for five minutes. A mirror was then revealed in front of them, and they were asked to look at their eyes for 20 seconds. This procedure was undertaken on two separate occasions with a one-week interval. This was compared to an instantaneous measurement of head position at a specific time point corresponding to the 15th second of the recording.
Results
During the five minutes of recording, the participants tended to elevate their head progressively by a mean of 1.5°, which is then corrected by looking at oneself in the mirror. Most participants tended to rotate their head to the left and continued that progressive rotation despite looking in the mirror. The roll axis had no systematic changes observed between the self-balanced position and the mirror-guided position and was the most reproducible axis. Moderate to good correlations were found comparing both sessions for each axis.
Conclusion
The comparison between the five-minute analysis and the instantaneous measurement showed a systematic difference on the pitch axis but no differences for the yaw and roll. These results suggest that the variation in NHP during a period of five minutes is generally specific to each participant with a head elevation and rotation to the left in most cases.
Several new systems for three-dimensional (3D) surface imaging of the face have become available to assess changes following orthognathic or facial surgery. Before they can be implemented in practice, their reliability and validity must be established. Our aim, therefore, was to study the intra- and inter-system reliability and validity of 3dMD (stereophotogrammetry), Artec Eva and Artec Space Spider (both structured light scanners). Intra- and inter-system reliability, expressed in root mean square distance, was determined by scanning a mannequin’s head and the faces of healthy volunteers multiple times. Validity was determined by comparing the linear measurements of the scans with the known distances of a 3D printed model. Post-processing errors were also calculated. Intra-system reliability after scanning the mannequin’s head was best with the Artec Space Spider (0.04 mm Spider; 0.07 mm 3dMD; 0.08 mm Eva). The least difference in inter-system reliability after scanning the mannequin’s head was between the Artec Space Spider and Artec Eva. The best intra-system reliability after scanning human subjects was with the Artec Space Spider (0.15 mm Spider; 0.20 mm Eva; 0.23 mm 3dMD). The least difference in inter-system reliability after scanning human subjects was between the Artec Eva and Artec Space Spider. The most accurate linear measurement validity occurred with the Artec Space Spider. The post-processing error was 0.01 mm for all the systems. The Artec Space Spider is the most reliable and valid scanning system.
Introduction
Several new systems of three-dimensional (3D) surface imaging of the face have become available to assess changes following orthognathic or facial surgery. Before they can be implemented into practice their reliability and validity must be established. Our aim was therefore to study 3dMD (stereophotogrammetry), Artec Eva and Artec Space Spider (both structured light scanners) regarding intra- and inter-system reliability and validity.
Material and Methods
Intra- and inter-system reliability expressed in root mean square (RMS) distance was determined by scanning multiple times a mannequin’s head and faces of healthy volunteers. Validity was determined by comparing linear measurements of scans with known distances of a 3D printed model. Post-processing errors were calculated.
Results
Intra-system reliability of mannequin’s head was best for the Artec Space Spider (0.04 mm Spider; 0.07 mm 3dMD; 0.08 mm Eva;). Inter-system reliability of the mannequin’s head showed least differences between Artec Space Spider and Artec Eva. Intra-system reliability of human subjects was best for the Artec Space Spider (0.15 mm Spider; 0.20 mm Eva; 0.23 mm 3dMD). Inter-system reliability of human subjects showed least differences between Artec Eva and Artec Space Spider. Validity of linear measurements was most accurate in the Artec Space Spider. Post-processing error was 0.01mm for all systems.
Conclusion
The Artec Space Spider was the most reliable and valid scanning system.
Low dose and accessibility have increased the application of cone beam computed tomography (CBCT). Often serial images are captured for patients to diagnose and plan treatment in the craniofacial region. However, CBCT images are highly variable and lack harmonious reproduction, especially in the head's orientation. Though user-defined orientation methods have been suggested, the reproducibility remains controversial. Here, we propose a landmark-free reorientation methodology based on principal component analysis (PCA) for harmonious orientation of serially captured CBCTs. We analyzed three serial CBCT scans collected for 29 individuals who underwent orthognathic surgery. We first defined a region of interest with the proposed protocol by combining 2D rendering and 3D convex hull method, and identified an intermediary arrangement point. PCA identified the y-axis (anterioposterior) followed by the secondary x-axis (transverse). Finally, by defining the perpendicular z-axis, a new global orientation was assigned. The goodness of alignment (Hausdorff distance) showed a marked improvement (> 50%). Furthermore, we clustered cases based on clinical asymmetry and validated that the protocol was unaffected by the severity of the skeletal deformity. Therefore, it could be suggested that integrating the proposed algorithm as the preliminary step in CBCT evaluation will address a fundamental step towards harmonizing the craniofacial imaging records.
Purpose
A facial reference frame is a 3-dimensional Cartesian coordinate system that includes 3 perpendicular planes: midsagittal, axial and coronal. The order in which one defines the planes matters. The purposes of this study were to determine: 1) what sequence (axial-midsagittal-coronal versus midsagittal-axial-coronal) produced more appropriate reference frames, and 2) whether orbital or auricular dystopia influenced the outcomes.
Materials and Methods
This was an ambispective cross-sectional study. Fifty-four subjects with facial asymmetry were included. The facial reference frames of each subject (outcome variable) were constructed using 2 methods (independent variable): axial-plane-first and midsagittal plane-first. Two board-certified orthodontists together blindly evaluated the results using a 3-point categorical scale based on their careful inspection and expert intuition. The covariant for stratification was the existence of orbital or auricular dystopia. Finally, Wilcoxon signed rank tests were performed.
Results
The facial reference frames defined by the midsagittal plane-first method was statistically significantly different from ones defined by the axial-plane-first method (P=0.001). Using midsagittal plane-first method, the reference frames were more appropriately defined in 22 (40.7%) subjects, equivalent in 26 (48.1%) and less appropriately defined in 6 (11.1%). After stratified by orbital or auricular dystopia, the results also showed that the reference frame computed using midsagittal plane-first method was statistically significantly more appropriate in both subject groups regardless of the existence of orbital or auricular dystopia (27 with orbital or auricular dystopia and 27 without, both P<0.05).
Conclusion
The midsagittal plane-first sequence improves the facial reference frames compared with the traditional axial-plane-first approach. However, regardless of the sequence used, clinicians need to judge the correctness of the reference frame prior to diagnosis or surgical planning.
Objectives::
To determine the relationship between traditional cephalometric measurements and corresponding nonradiographic three-dimensional (3D) photogrammetry measurements.
Materials and methods::
This was a cross-sectional study of 20 orthodontic patients (10 male and 10 female) who received lateral cephalometric radiographs and 3D dentofacial photogrammetric records with each subject serving as his or her own control for a total sample size of 40 images (20 per method). A 3D analysis that resembled a traditional cephalometric analysis was established using the eyes and natural head orientation as substitutes for the cranial base. Pearson correlation coefficients and multivariable linear regression plots were calculated to evaluate the relationship between the photogrammetry measurements and the cephalometric measurements.
Results::
The ANB angle, mandibular plane angle, lower anterior face height, upper incisor angle to SN, upper incisor angle to NA, and all measurements of lower incisor position and inclination had strong positive Pearson correlation coefficients with the corresponding 3D photogrammetry measurements ( P < .004). Statistically significant regression plots demonstrated that cephalometric relationships between the jaws and incisor orientation can be predicted from corresponding 3D photogrammetry measurements.
Conclusions::
3D photogrammetry measurements relating the jaws to each other and incisor orientation has a strong positive correlation with corresponding traditional cephalometric measurements and can serve as cephalometric predictors. Capturing the eyes using 3D photogrammetry can obviate the need to expose the cranial base and allow limiting the radiographic field to the area of interest.
Objective
To correlate traditional Steiner's skeletal and dental measurements to similar measurements that use the eyes and natural head position as references instead of the cranial base.
Setting and Sample
One hundred and fifty‐two lateral cephalometric radiographs (66 female, and 86 male) from the Harvard Forsyth twin sample were included in the study based on record availability.
Material and Methods
This was an observational study in which all cephalometric radiographs were traced and analyzed using Steiner's cephalometric analysis. Each cephalogram was then altered to perform a similar analysis that uses the maximum convexity of the cornea together with natural head position as references instead of the cranial base. A Pearson product‐moment correlation coefficient was measured to determine the correlation between the conventional Steiner analysis measurements and the novel measurements relying on the eyes and natural head position.
Results
Steiner's cephalometric measurements of the jaws to each other, the divergency, and the orientation of the incisors had a strong positive correlation with their counterparts that relied on true horizontal and/or the eyes (p < 0.001).
Conclusion
The eyes and true horizontal can be used as alternatives to the cranial base when diagnosing the relationship between the jaws, and the position and orientation of the teeth. Since the eyes and natural head position are identifiable without ionizing radiation, future research should focus on the use of radiographic exposures limited to the upper and lower jaws for orthodontic diagnosis and outcome assessment.
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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.
The aim of this study was to compare facial 3D analysis to DNA testing in twin zygosity determinations. Facial 3D images of 106 pairs of young adult Lithuanian twins were taken with a stereophotogrammetric device (3dMD, Atlanta, Georgia) and zygosity was determined according to similarity of facial form. Statistical pattern recognition methodology was used for classification. The results showed that in 75% to 90% of the cases, zygosity determinations were similar to DNA-based results. There were 81 different classification scenarios, including 3 groups, 3 features, 3 different scaling methods, and 3 threshold levels. It appeared that coincidence with 0.5 mm tolerance is the most suitable feature for classification. Also, leaving out scaling improves results in most cases. Scaling was expected to equalize the magnitude of differences and therefore lead to better recognition performance. Still, better classification features and a more effective scaling method or classification in different facial areas could further improve the results. In most of the cases, male pair zygosity recognition was at a higher level compared with females. Erroneously classified twin pairs appear to be obvious outliers in the sample. In particular, faces of young dizygotic (DZ) twins may be so similar that it is very hard to define a feature that would help classify the pair as DZ. Correspondingly, monozygotic (MZ) twins may have faces with quite different shapes. Such anomalous twin pairs are interesting exceptions, but they form a considerable portion in both zygosity groups.
To determine the reliability of obtaining two-dimensional cephalometric measurements using two virtual head orientations from cone-beam computed tomography (CBCT) models.
CBCT scans of 12 patients (6 class II and 6 class III) were randomly selected from a pool of 159 patients. An orthodontist, a dental radiologist, and a third-year dental student independently oriented CBCT three-dimensional (3D) renderings in either visual natural head position (simulated NHP) or 3D intracranial reference planes (3D IRP). Each observer created and digitized four CBCT-generated lateral cephalograms per patient, two using simulated NHP and two using 3D IRP at intervals of at least 3 days. Mixed-effects analysis of variance was used to calculate intraclass correlation coefficients (ICCs) and to test the difference between the orientations for each measure.
ICC indicated good reliability both within each head orientation and between orientations. Of the 50 measurements, the reliability coefficients were > or =0.9 for 45 measurements obtained with 3D IRP orientation and 36 measurements with simulated NHP. The difference in mean values of the two orientations exceeded 2 mm or 2 degrees for 14 (28%) of the measurements.
The reliability of both virtual head orientations was acceptable, although the percentage of measurements with ICC >0.9 was greater for 3D IRP. This may reflect the ease of using the guide planes to position the head in the 3D IRP during the simulation process.
Purpose:
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.
Methods:
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.
Results:
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.
Conclusion:
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.
The Symposium held in Pisa, July 1971, was designed for complete coverage of one main subject, namely the basic aspects of central vestibular mechanisms. The present volume contains the papers delivered at the Symposium. The book is subdivided into chapers dealing with the relations between the vestibular nuclei and the receptor organs, the spinal cord, the cerebellum, the brain stem and the cerebral cortex. Present knowledge of these subjects is reviewed, the latest developments in anatomy and physiology are given and areas for continued exploration are discussed. The wealth of detailed information available today gives a striking illustration of the extreme complexity in the structural and functional organization of the vestibular system. In general the results of research on structure and function are in complete agreement, even concerning rather specific problems. The material discussed will be of interest to clinical otologists and neurologists, and will be indespensible for workers in neural sciences interested in the vestibular system and its relations to other spheres of the nervous system.
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.
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.
We describe an alternative workup protocol for virtual surgical planning of orthognathic surgery using an intraoral fiducial marker, clinical photography, and the digital transfer of occlusal data. We also discuss our initial experience using this protocol in a series of patients.
A retrospective cohort study was performed of consecutive patients who had undergone combined maxillary and mandibular osteotomies for the correction of dentofacial deformities at 1 center. These patients underwent treatment planning using the modified virtual surgical planning protocol described in the present report. The primary outcome evaluated was the accuracy of the method, which was determined through superimposition of the surgical plan to the postoperative cone-beam computed tomography (CBCT) scan. The secondary outcomes included the accuracy of the natural head position readings and the adequacy of the CBCT scanned stone models for the fabrication of occlusal splints.
The population included 25 patients. The root mean standard deviation (RMSD) from the preoperative plan to the postoperative scan at the maxillary cephalometric points was 1.2, 1.4, and 2.1 mm in the axial, sagittal, and coronal planes, respectively. The RMSD of the superimposed plan to the postoperative scan at the 3 mandibular cephalometric points was 1.2, 0.8, and 0.7 mm in the axial, sagittal, and coronal planes, respectively. The average variance from the axial, sagittal, and coronal planes for the natural head position was 0.05, 2.22, and 0.69 mm, respectively. All splints fabricated from the CBCT occlusal data fit the stone models and were used intraoperatively. In the subset of patients whose models were both digitally transferred and laser scanned, the superimposition of the laser scan data to the CBCT scanned data was found to have a maximum variation of 0.2 mm at the occlusal level.
The use of an intraoral fiducial marker changed the workflow for the data collection needed for virtual surgical planning of the correction of dentofacial deformities, while still obtaining accurate results. Because the device does not cause lip distortion, the possibility of virtually predicting a more expectant postoperative lip position exists without the need for additional scans. Furthermore, this work flow allows the transfer of data to be isolated to digital media.
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.
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.
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.
We developed a modified laser level technique to record the natural position of the head in all three planes of space. This is a simple method for use with three-dimensional images and may be valuable in routine craniofacial assessment.
In a sample of orthodontic patients (27 boys and 25 girls, 10 to 14 years old), natural head position (NHP) was photographically recorded. A vertical axis was recorded on the photographs with a plumb line and transferred to the lateral head radiographs of the patients. Three cephalometric reference lines (sella-nasion, basion-nasion, and porion-orbitale) were compared with regard to their inclination to the horizontal plane. These angles showed standard deviations of between 4.5 degrees and 5.6 degrees. Reproducibility of NHP, assessed as the error of a single observation, was close to 2 degrees. These findings, in combination with the fact that the NHP represents a realistic appearance of patients, support its use as a basis for cephalometric analysis of dentofacial anomalies. A strong correlation was found between the inclinations of the three cephalometric reference lines to the horizontal plane. The close anatomic relationship between these lines, in combination with the small random movements of the head around NHP, were believed to explain the covariation.
This paper sets out to evaluate the variability and reproducibility of frontal head position in healthy young adults. Two posteroanterior skull radiographs of 22 dental students and 2 frontal photographs of these and 24 other students, taken at a 1-week interval, were analyzed with regard to head position and cervical spine inclination. Head position varied in the range of +/- 5 degrees with regard to the vertical. The cervical spine was more often inclined to the right than to the left. The reproducibility of the head position with regard to the craniovertical angle was 1.15 degrees and that of the craniocervical and cervicohorizontal angles 0.93 degrees and 1.45 degrees, respectively. Any deviation in the frontal head position tended to be spontaneously corrected on looking in a mirror. It is concluded that the frontal head position is slightly more accurately reproducible than the sagittal head position. The use of a mirror in front of the patient when recording the frontal natural head position is not to be recommended.
Current clinical interest in natural head posture (NHP) derives from studies correlating NHP to craniofacial morphology, future growth trends, and to respiratory needs. It has also been argued that NHP is the logical reference and orientation position for craniofacial analysis and the publication of illustrations. The individual or group is presented as they naturally appear in life. Hence, lateral cephalometric radiographs recorded routinely in NHP would be more meaningful for the clinician. Underpinning all these potential clinical benefits is the incompletely answered question of the clinical reproducibility of NHP. In this study a natural head posture, the orthoposition, was defined and standardized for clinical use. The effects of ear posts, an external source of eye reference (a wall mirror), sex and time were evaluated in relation to the reproducibility of recording lateral cephalometric radiographs in this natural head posture. The sample comprised 217 randomly selected 12-year-old Chinese children in Hong Kong. Boys looked up more when changing from the self-balance position to the mirror eye reference position (mean change 2 degrees, P less than or equal to 0.001). No other significant male-versus-female differences were detected. NHP reproducibility was better with a mirror (with mirror, method error = 1.9 degrees, without mirror, method error = 2.7 degrees). No significant differences in reproducibility were detected between NHP recordings taken with and without ear posts. However, without ear posts the radiographs tended to be of poor quality. The reproducibility of same-day repeat radiographs recorded with ear posts and with a mirror (after 4 to 10 minutes and 1 to 2 hours) was 1.9 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)
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 purpose of this study was to investigate longitudinally, by cephalometric means, alterations in craniocervical morphology and hyoid bone position in adult males and females, in three different age groups at 10-year intervals, and to compare the changes between the two genders. The material consisted of three series of cephalograms of 26 males and 24 females with approximately a 10-year interval between each series. Alterations with increasing age in males and females included: 1 An increase in anterior and posterior facial height in both genders, a reduction in mandibular prognathism, and an increase in the mandibular plane angle in females only. 2 The hyoid bone assumed a more inferior position in relation to different skeletal structures for both sexes. 3 Head posture alterations were similar for the male and female group over time. The overall significant inter-sex changes over a 20-year period were a reduction in mandibular prognathism, an increase in the mandibular plane angle in females, and a more inferior position of the hyoid bone in males.
The aim of this study was to investigate head posture and hyoid bone position using cephalometric radiographs of adults.
The material consisted of 76 cephalometric films (38 each male/female) taken at the natural head posture. The individuals were over 18 years of age, had parents of Turkish origin, an acceptable face structure, ideal dental occlusion, and an ANB angle of 1-5 degrees; the dentitions were complete except the third molars and there were no visual, hearing, breathing or swallowing disorders. In addition, the subjects had not undergone orthodontic treatment or orthognathic surgery, had no burns, injuries, or scars in the head and neck regions. In order to determine the natural head position, the subjects were asked to stand in a relaxed manner (the self-balance position), and this position was transferred to the cephalostat by means of a fluid level device. The differences among sexes were investigated by means of Student's t-test, carried out using SPSS (Windows 7.5).
It was found that there were no sex variations in head position. The linear measurements regarding the position of hyoid bone showed statistically significant differences with respect to sex. However, hyoid bone position was higher and more posterior in females, while natural head position was not affected by sex.
Background:
There has been a growing interest in three-dimensional (3D) surface imaging devices over the last few years.
Methods:
This comprehensive review discusses the various emerging technologies in this field of 3D imaging and applies the use of technology to oral and maxillofacial imaging.
Results:
The paper shows that there is increased awareness and application of technology to the field.
Conclusion:
3D surface acquisition technology is improving at a rapid pace and has a place in oral and maxillofacial surgery.