Three-dimensional computed tomography cephalometric craniofacial analysis: experimental validation in vitro

The development of three-dimensional (3D) cephalometric analysis is essential for the computer-assisted planning of orthognathic surgery. The aim of this study was to transform and adapt Delaire's two-dimensional cephalometric analysis into the third dimension; this transposition was then validated. The comparative advantage of using 3D computed tomography (CT) surface renderings over profile X-rays was analysed. Comparison was made of inter- and intra-observer reproducibility of the cephalometric measurements done on profile X-rays and on 3D CT surface renderings on the same 26 dry skulls. The accuracy was also tested of the measurements done on 3D CT surface renderings (ACRO 3D) in relation to those directly taken on dry skulls with the help of a 3D measuring instrument. Inter- and intra-observer reproducibility proved significantly superior (p<0.0001) following the 3D CT method. There were no significant differences in the accuracy of measurements between the ACRO 3D software and the 3D measuring instrument. The ACRO 3D software was confirmed as being a reliable tool for developing 3D CT cephalometric analyses. Further research may entail clinical validation of the 3D CT craniofacial cephalometric method of analysis.     

A comparison between 2D and 3D cephalometry on CBCT scans of human skulls

The purpose of this study was to evaluate whether measurements on conventional cephalometric radiographs are comparable with 3D measurements on 3D models of human skulls, derived from cone beam CT (CBCT) data. A CBCT scan and a conventional cephalometric radiograph were made of 40 dry skulls. Standard cephalometric software was used to identify landmarks on both the 2D images and the 3D models. The same operator identified 17 landmarks on the cephalometric radiographs and on the 3D models. All images and 3D models were traced five times with a time-interval of 1 week and the mean value of repeated measurements was used for further statistical analysis. Distances and angles were calculated. Intra-observer reliability was good for all measurements. The reproducibility of the measurements on the conventional cephalometric radiographs was higher compared with the reproducibility of measurements on the 3D models. For a few measurements a clinically relevant difference between measurements on conventional cephalometric radiographs and 3D models was found. Measurements on conventional cephalometric radiographs can differ significantly from measurements on 3D models of the same skull. The authors recommend that 3D tracings for longitudinal research are not used in cases were there are only 2D records from the past.     

A three-dimensional comparison of a morphometric and conventional cephalometric midsagittal planes for craniofacial asymmetry

Morphometric methods are used in biology to study object symmetry in living organisms and to determine the true plane of symmetry. The aim of this study was to determine if there are clinical differences between three-dimensional (3D) cephalometric midsagittal planes used to describe craniofacial asymmetry and a true symmetry plane derived from a morphometric method based on visible facial features. The sample consisted of 14 dry skulls (9 symmetric and 5 asymmetric) with metallic markers which were imaged with cone-beam computed tomography. An error study and statistical analysis were performed to validate the morphometric method. The morphometric and conventional cephalometric planes were constructed and compared. The 3D cephalometric planes constructed as perpendiculars to the Frankfort horizontal plane resembled the morphometric plane the most in both the symmetric and asymmetric groups with mean differences of less than 1.00 mm for most variables. However, the standard deviations were often large and clinically significant for these variables. There were clinically relevant differences (>1.00 mm) between the different 3D cephalometric midsagittal planes and the true plane of symmetry determined by the visible facial features. The difference between 3D cephalometric midsagittal planes and the true plane of symmetry determined by the visible facial features were clinically relevant. Care has to be taken using cephalometric midsagittal planes for diagnosis and treatment planning of craniofacial asymmetry as they might differ from the true plane of symmetry as determined by morphometrics.     

A comparison between two-dimensional and three-dimensional cephalometry on frontal radiographs and on cone beam computed tomography scans of human skulls

The aim of this study was to evaluate whether measurements performed on conventional frontal radiographs are comparable to measurements performed on three-dimensional (3D) models of human skulls derived from cone beam computed tomography (CBCT) scans and if the latter can be used in longitudinal studies. Cone beam computed tomography scans and conventional frontal cephalometric radiographs were made of 40 dry human skulls. From the CBCT scan a 3D model was constructed. Standard cephalometric software was used to identify landmarks and to calculate ratios and angles. The same operator identified 10 landmarks on both types of cephalometric radiographs, and on all images, five times with a time interval of 1 wk. Intra-observer reliability was acceptable for all measurements. There was a statistically significant and clinically relevant difference between measurements performed on conventional frontal radiographs and on 3D CBCT-derived models of the same skull. There was a clinically relevant difference between angular measurements performed on conventional frontal cephalometric radiographs, compared with measurements performed on 3D models constructed from CBCT scans. We therefore recommend that 3D models should not be used for longitudinal research in cases where there are only two-dimensional (2D) records from the past.     

Comparison of CT scanograms and cephalometric radiographs in craniofacial imaging

Objective– To compare measurements from human skulls and their images from cephalometric radiographs (CR) and computed tomography (CT) scanograms, in order to gauge the potential clinical use of the latter. Design– Based on specific inclusion criteria, including stable centric occlusion, 13 adult skulls were selected from a larger collection. The mandible was taped to the maxilla after securing the occlusion of teeth and condylar seating in the glenoid fossa. Lateral and posteroanterior cephalographs and CT `scout views' were taken of each skull by standardized methods. Landmarks were identified on skulls and images. Outcome Measures– Linear measurements were made on all three records; angular measurements only on CR and CT images. Intraclass correlation coefficients (r) were calculated to assess similarity among records. Paired t‐tests were used to compare differences between mean measurements. Results– No statistically significant differences were noted between mean angular values on CR and CT views (P > 0.05). The highest correlations were observed for several vertical midline distances between CT and direct skull measures: 0.82 < r < 0.995–greatest for nasion–menton. For sagittal distances, the highest correlation was between the direct measure of condylion–pogonion and its CR image (r=0.73). Correlations between CR and skull transverse measures were higher (0.46 < r < 0.80) than the corresponding skull vs. CT measures (0.06 < r < 0.38). CT and CR images are 2D slices and projections, respectively, of 3D structures. Vertical CT and skull measures correspond because the CT projection reflects a 1 : 1 ratio in the midsagittal plane; CT projected lateral images are smaller than the skull measures. The CR image reflects a distortion (～8%) that brings Co–Pg closer to its anatomic distance, inadvertently contributing to better clinical planning, particularly in orthognathic surgery. The pattern of distortion of PA images was in opposite directions for CR and CT views. Conclusions– Cephalograms and CT scanograms are close in depicting angular relations of structures, but they differ in the accuracy of imaging linear measurements, because the location and size of an object within the imaged 3D structure varies with both records. Logistic and economic considerations favor the use of cephalographs.     

Linear accuracy and reliability of cone beam CT derived 3-dimensional images constructed using an orthodontic volumetric rendering program

OBJECTIVE: To compare accuracy of linear measurements made on cone beam computed tomographic (CBCT) derived 3-dimensional (3D) surface rendered volumetric images to direct measurements made on human skulls. MATERIALS AND METHODS: Twenty orthodontic linear measurements between anatomical landmarks on 23 human skulls were measured by observers using a digital caliper. The skulls were imaged with CBCT and Dolphin 3D (version 2.3) software used to generate 3D volumetric reconstructions (3DCBCT). The linear measurements between landmarks were computed by a single observer three times and compared to anatomic dimensions using Student's t-test (P < or = .05). The intraclass correlation coefficient (ICC) and absolute linear and percentage error were calculated. RESULTS: The ICC for 3DCBCT (0.975 +/- 0.016) was significantly less than for skull (0.996 +/- 0.007) measurements. Mean percentage measurement error for 3DCBCT (2.31% +/- 2.11%) was significantly higher than replicate skull measurements (0.63% +/- 0.51%). Statistical differences between 3DCBCT means and true dimensions were found for all of the midsagittal measurements except Na-A and six of the 12 bilateral measurements. The mean percentage difference between the mean skull and 3D-based linear measurements was -1.13% (SD +/- 1.47%). Ninety percent of mean differences were less than 2 mm, and 95% confidence intervals were all less than 2 mm except for Ba-ANS (3.32 mm) and Pog-Go(left) (2.42 mm). CONCLUSIONS: While many linear measurements between cephalometric landmarks on 3D volumetric surface renderings obtained using Dolphin 3D software generated from CBCT datasets may be statistically significantly different from anatomic dimensions, most can be considered to be sufficiently clinically accurate for craniofacial analyses.     

Application of cone beam CT 3D images to cephalometric analysis

Orthodontic diagnosis is currently based primarily on two-dimensional (2D) measurements. The development of maxillofacial cone beam X-ray computed tomography (CBCT) has promoted the use of three-dimensional (3D) measurements for orthodontic diagnosis. This technology is also expected to generate new analytic methods aiming at establishing optimal occlusion according to the individual's maxillary shape and function. However, during the transitional stage from 2D to 3D measurements, it is necessary to relate 3D data to existing data analysis methods (e.g., lateral cephalogram) for the assessment of skeletal and dental relationship. Our objectives were to develop a new cephalometric analysis method based on 3D data obtained by CBCT from four aspects: (1) measurement of magnification of cephalogram, (2) assessment of the dimensional accuracy of CBCT images, (3) development of a method of cephalometric analysis using CBCT images and (4) comparison of cephalometric analytical values obtained from CBCT images with those obtained from existing cephalograms. The results demonstrated that our analytical method facilitated cephalometric analysis of CBCT images and therefore allowed direct comparison of CBCT images with existing cephalograms. Cephalometric analysis using CBCT images resulted in a smaller range of inter-operator measurement variability than that using conventional cephalograms.     

The reproducibility of cephalometric landmarks: an experimental study on skulls

Few previous cephalometric studies have used dry skulls in order to eliminate the effects of the facial soft tissues. The aim of this study were to quantify the intra-examiner reproducibility of the commonly used cephalometric landmarks, angles and distances, using dry skulls and to compare these errors with previous error data obtained from normal cephalograms of living patients. Thirty skulls were mounted in a purpose-designed holder and repeat cephalograms of each skull were recorded and digitised. All measurements were made relative to an X-Y coordinate reference grid. Scattergrams were produced to show the characteristic distribution of the intra-examiner reproducibility errors for the landmarks, and the reproducibility of the angles and distances were tabulated. This data was compared with a related study that included the soft tissue profile. The standard deviations of the skeletal and dental angles and distances were greater in the presence of the soft tissues. These differences were up to four times larger for measurements including the location of Nasion (e.g. SNA, SNB and SNPg), which was the landmark location most affected by the presence of soft tissues, and for the distance: Incisal tip of Lower Incisor to Pogonion. Anterior Nasal Spine, in the horizontal plane, was also greatly affected by the presence of the soft tissues. By using dry skulls, the errors observed in this study may serve as standards for the rational interpretation of clinical cephalometric values.     

A comparison of frontal radiographs obtained from cone beam CT scans and conventional frontal radiographs of human skulls

This study evaluated whether measurements on conventional frontal radiographs are comparable with measurements on cone beam computed tomography (CBCT)-constructed frontal cephalometric radiographs taken from dry human skulls. CBCT scans and conventional frontal cephalometric radiographs were made of 40 dry skulls. With I-Cat Vision^® software, a cephalometric radiograph was constructed from the CBCT scan. Standard cephalometric software was used to identify landmarks and calculate ratios and angles. The same operator identified 10 landmarks on both types of cephalometric radiographs on all Images 5 times with a time-interval of 1 week. Intra-observer reliability was acceptable for all measurements. The reproducibility of the measurements on the frontal radiographs obtained from the CBCT scans was higher than those on conventional frontal radiographs. There is a statistically significant and clinically relevant difference between measurements on conventional and constructed frontal radiographs. There is a clinically relevant difference between angular measurements performed on conventional frontal cephalometric radiographs, compared with measurements on frontal cephalometric radiographs constructed from CBCT scans, owing to different positioning of patients in both devices. Positioning of the patient in the CBCT device appears to be an important factor in cases where a 2D projection of the 3D scan is made.     

The use of a new 3D splint and double CT scan procedure to obtain an accurate anatomic virtual augmented model of the skull

Three-dimensional (3D) virtual planning of orthognathic surgery requires detailed visualization of the interocclusal relationship. The purpose of this study was to introduce the modification of the double computed tomography (CT) scan procedure using a newly designed 3D splint in order to obtain a detailed anatomic 3D virtual augmented model of the skull. A total of 10 dry adult human cadaver skulls were used to evaluate the accuracy of the automatic rigid registration method for fusion of both CT datasets (Maxilim, version 1.3.0). The overall mean registration error was 0.1355+/-0.0323 mm (range 0.0760-0.1782 mm). Analysis of variance showed a registration method error of 0.0564 mm (P < 0.001; 95% confidence interval = 0.0491-0.0622). The combination of the newly designed 3D splint with the double CT scan procedure allowed accurate registration and the set-up of an accurate anatomic 3D virtual augmented model of the skull with detailed dental surface.     

Craniofacial skeletal measurements based on computed tomography: Part I. Accuracy and reproducibility.

Computed tomography (CT) is a useful modality for the management of craniofacial anomalies. A study was undertaken to assess whether CT measurements of the upper craniofacial skeleton accurately represent the bony region imaged. Measurements taken directly from five dry skulls (approximate ages: adults, over 18 years; child, 4 years; infant, 6 months) were compared to those from axial CT scans of these skulls. Excellent agreement was found between the direct (dry skull) and indirect (CT) measurements. The effect of head tilt on the accuracy of these measurements was investigated. The error was within clinically acceptable limits (less than 5 percent) if the angle was no more than +/- 4 degrees from baseline (0 degrees). Objective standardized information gained from CT should complement the subjective clinical data usually collected for the treatment of craniofacial deformities.     

蒙古族正常成年人颅颌面硬组织的三维CT测量研究

目的研究蒙古族正常成年人颅颌面硬组织的三维头影测量正常值,为正颌外科提供临床诊断、治疗计划及手术方案制定的数字依据。方法对48名符合正常标准的三代蒙古族后裔成年人进行颅颌面螺旋CT薄层扫描,用三维软件重建颅颌面硬组织三维图像,在屏幕上定点测量37项线距和19项角度。结果获得了蒙古族正常成年人颅颌面硬组织双螺旋CT三维头影测量正常值。结论①蒙古族正常成年人颅颌面硬组织的差异主要体现在骨骼大小上,而在骨骼轮廓和比例关系上差异较小,蒙古族女性的下颌开张度大于男性,而男性较女性面部前凸。②蒙古族正常成年人颅颌面硬组织结构左右也存在着一定程度的属于正常形态变异的不对称现象。③蒙古族正常成年人颅颌面硬组织形态具有明显的性别差异及种族特点,在正颌外科的临床诊断、治疗计划、手术方案的制定及术后面形预测应参考蒙古族自身的正常值。     

Assessment of three-dimensional X-ray images: reconstruction from conventional tomograms, compact computerized tomography images, and multislice helical computerized tomography images

Three-dimensional X-ray images (3D images) were used for imaging diagnosis in the oral and maxillofacial region. These images could be fundamentally reconstructed from various tomograms, though clinical 3D images were mainly reconstructed from computerized tomography (CT) images. In this investigation, 3D images were reconstructed from conventional tomograms with a panoramic unit, compact CT images, and multislice helical CT images, and the usefulness of each system was subjectively assessed for dental implant treatment. Three hemilateral dried human mandibles were used and were examined by linear tomography with a panoramic unit, compact CT, and multislice helical CT, and 3D images were reconstructed by using the rendering software for each system. The 3D images were visually evaluated on a 5-point scale covering the alveolar ridge, buccal and lingual bone surface, mental foramen, and tooth sockets. As a result, 3D images reconstructed from conventional tomograms with the panoramic unit were assessed as fair to unsure, compact CT 3D images were assessed as unsure to good, and multislice helical CT 3D images were assessed as good to excellent. It was concluded that compact CT 3D images and multislice helical CT 3D images were useful in dental implant treatment.     

A method for three-projection infant cephalometry.

OBJECTIVE: To assess morphology and growth in infants and children with craniofacial anomalies based on comprehensive digitization of radiographic films in three, mutually orthogonal projections. METHOD: The method consists of (1) acquisition of radiographic films in a highly standardized three-projection (lateral, frontal, and axial) cephalometer, (2) marking and digitization of a total of 279 anatomical landmarks in the three projections, and (3) computation and presentation (tabular and graphical) of 356 linear and angular variables describing the craniofacial morphology, including soft tissue. Computation of statistical entities describing a patient, a group of patients, the differences between patients or groups of patients was carried out. Error assessment of the method involved investigation of error distribution among a number of error sources. Duplicate digitization of radiographic films from 30 randomly selected patients, and from 10 dry skulls, was carried out to determine the errors contributed by the procedure of landmark digitization and the distribution of error among landmarks and variables, as well as between projections. RESULTS: The average error due to landmark digitization, s(i), determined by duplicate digitization and calculated by use of Dahlberg's formula was 0.8 mm for linear variables and 1.6 degrees for angular variables. CONCLUSION: This method of infant cephalometry has been shown to be highly accurate and reproducible, and it adds significant new potential for, e.g., asymmetry detection, population comparison, and growth measurements compared to other cephalometric techniques due to its standardized acquisition and digitization protocol, inclusion of an axial projection, and the large number of well-defined landmarks and variables involved.     

A comparison between computerized tomography, magnetic resonance imaging, and laser scanning for capturing 3-dimensional data from a natural ear to aid rehabilitation

PURPOSE: To compare dimensional measurements on computer images generated from data captured digitally by 3 different methods to those obtained directly from natural ears and ear casts, so as to determine the optimal method of creating a computer-generated ear image. MATERIALS AND METHODS: Magnetic resonance imaging (MRI) was used to obtain 3-dimensional (3D) data images of the normal ears of 14 subjects. Computerized tomography (CT) and laser scanning (LS) were used to obtain 3D data images from stone casts of the same ears. Dimensional measurements were recorded on 2 occasions between anthropometric landmarks on the subjects' natural ears, casts of the ears, and reconstructed ear images obtained by CT, MRI, and LS. The intraclass correlation coefficients and coefficients of repeatability were calculated. The means of the 2 measurements for each of the dimensions were analyzed using 2-way analysis of variance to determine whether there were differences between the methods of data collection. RESULTS: The intraclass correlation coefficients indicated that dimensions could be reliably measured on the natural ears, casts, and CT, MRI, and LS images. The coefficients of repeatability were all of a small magnitude in relation to the overall dimensions studied. No statistical differences existed between the various sources of data (P = .866) (i.e., direct, cast, CT, MRI, and LS). CONCLUSION: The 3 methods of imaging have generally resulted in dimensional measurements on the reconstructed images that are similar to those of the original source. These are considered appropriate for manufacturing 3D models that can be used to fabricate a prosthesis. However, other factors may also be important, such as shape, contour, and internal form, and these require further investigation.     

The use of 3 different imaging methods for the localization of the mandibular canal in dental implant planning

PURPOSE: The purpose of this study was to investigate the efficiency of panoramic radiography, conventional (cross-sectional) tomography, and computerized tomography for location of the mandibular canal before implant placement in the posterior region of the mandible. MATERIALS AND METHODS: Edentulous mandibles from 6 dry adult human skulls were used in this study. Four measurements (D1, D2, D3, D4) were made of 12 areas, one on each side of each mandible. Panoramic radiographs, conventional tomograms, and computerized tomograms were obtained. On each image, measurements were made for localization of the mandibular canal by one researcher. All measurements were repeated 3 times within a period of 3 weeks. Upon completion of imaging, the mandibles were surgically sectioned to provide direct measurements. The measurements obtained from the images were compared with direct measurements. Pearson correlation coefficients were calculated to detect statistical correlations between repeated measurements. The Dunnett t test was performed for statistical comparison of measurements from images and direct measurements. RESULTS: Pearson correlation coefficients showed strong linear correlation for all measurements (P < .01). No statistically significant difference was observed between direct measurement and D1, D2, or D4 (P < .05), but a statistically significant difference for D3 (buccolingual width 5 mm under mandibular crest; Dunnett t test; P > .05) between measurements was obtained from the images and direct measurements. CONCLUSION: The measurements obtained from computerized tomographic images were more consistent with direct measurements than the measurements obtained from panoramic radiographic images or conventional tomographic images.     

The use of a computer to measure linear and angular variables for an assessment of symmetry of the base of the skull

The use of a computer is described to make linear and angular measurements of the base of the skull. A group of 19 adult skulls from mediaeval Poland were chosen for this study. The cephalometric analysis defined 11 linear and 9 angular morphological variables. An assessment of method error due to point location by the cursor was made by duplicate determination, and an assessment of symmetry was carried out by comparing angular values derived from basion (ba) for right and left sides of the maxillary dental arch, zygomatic arch and cranial base. The results demonstrate that skull measurements could be recorded with a small method error of 0.2 mm for linear, and 0.2 degrees for angular recordings. Mean values for the 21 variables in the sample were recorded and statistically tested for point placement accuracy using measures of skewness and kurtosis to detect gross distribution errors.     

Improved Lateral Cephalometric Superimposition Using an Automated Image Fitting Technique

Objective:To test the feasibility of automated lateral cephalometric radiograph (LCR) superimposition using an image fitting algorithm.Materials and Methods:Using radiopaque markers, we identified seven cephalometric landmarks on three dry skulls, took digital LCRs on each in several rotated positions, and used a custom software program (XRay3D) to automatically superimpose each rotated image on the initial image using an anterior cranial base reference. We measured superimposition error at each landmark and adjusted image brightness levels to simulate potential fitting error due to exposure variation.Results:The greatest mean error for 24 image rotation trials of less than 10° was less than 0.5 mm. Rotations of 10° or more were not reliably superimposed. Errors of 0.2–1.6 mm occurred for ±10% brightness but increased exponentially with further brightness alteration.Conclusion:Automated superimposition of LCRs, using this fitting technique, has great potential when rotation is less than 10° and brightness variation is less than 10%.     

Validity and reliability of alveolar bone level measurements made on dry skulls

The validity of the radiographic alveolar bone level measurements in relation to direct measurements, and the reliability of both the direct and the radiographic measurements were estimated on dry skulls. The CEJ-AC distances in the proximal areas of teeth in 6 dry skulls were assessed directly, on periapical radiographic films taken with the Eggen film holder only and on films taken with the film holder and a rubber impression material. The validity of the bone level measurements made on films taken by the 2 radiographic techniques was evaluated by comparing each of these 2 with the direct measurements by means of the paired t-test. The reliability of the measurements made by each of the 3 methods was estimated by means of the test-retest, the paired t-test and the direct error estimation methods. It was found that both radiographic methods significantly underestimated the proximal bone level (p less than 0.001). There were no significant differences between the test-retest scoring of the bone level in any of the 3 methods. However, the measurements made by both radiographic techniques showed better correlations, and smaller error due to the measurement technique than the direct measurements. When repeated radiographic exposures were made, the exposure technique in method C produced no error, while the estimated error variance in method B was 0.07. It was concluded that the validity and the reliability of both radiographic methods were satisfactory and that the observed underestimation has little impact on longitudinal studies monitoring the alveolar bone level changes.     

Impact of the number of registration points for replacement of three-dimensional computed tomography images in dental areas using three-dimensional light-scanned images of dental models

Objectives

The aim of this study was to investigate the accuracy and reliability of registration methods for replacing dental areas of three-dimensional (3D) computed tomography (CT) images with 3D light-scanned dental images using tooth cusp tips and the occlusal surface. The number of registration points was investigated for its impact on the tooth cusp tip-based method.

Methods

Computed tomography image data on ten skull models and light-scanned data from dental cast models of the skulls were registered with imaging registration software. The marker-free registration using tooth cusp tips involved five protocols identifying 3–14 points as registration references. The control registration protocol consisted of a surface-matching method that used the occlusal surface. Errors were measured between the reference data and the registered images at the mesial, distal, buccal, and lingual tooth surfaces.

Results

For image registration using dental cusp tips, the mean error ranged from 0.164 mm for seven points to 0.198 mm for 14 points. The error did not decrease with an increase in the number of registration points from three to 14. The use of dental cusp tips resulted in no significant error with respect to the number of registration points. Image registration using the occlusal surface yielded a mean error of 0.116 mm. Significant differences between the errors were observed in comparisons of the dental cusp tip and occlusal surface registrations.

Conclusions

When positioning scanned dental images onto CT images, surface-based image registration using the occlusal surface gives less error than reference point-based image registration with dental cusp tips. We found no significant difference in the error with an increase in the number of registration points from three to 14.