Measurement errors in 3D cephalometrics: about the buccal cranio-facial analysis

The development of three-dimensional radiological techniques generating low levels of radiation, like computed tomography and positron emission tomography with cone beam, has made it possible for orthodontists to utilize three dimensional cephalometry for certain complex clinical cases instead of conventional two dimensional imagery. Nevertheless, these new techniques rely on the identification of the most dependable anatomic landmarks. Fifteen randomly selected orthodontists were asked to identify on a computed tomography film 33 points that were chosen for a buccal cranio-facial analysis because they have been traditionally recognized for their reproducibility. The results confirmed the high reliability level of the reference point vestibion that is related to the semi-circular canals. They showed, in the same way that conventional 2D cephalometry does, that each landmark presents a cloud and dispersion characteristic and that the most reliable landmarks are based on easily identifiable anatomic structures like foramens and osseous points.     

Consistency and precision of landmark identification in three-dimensional cone beam computed tomography scans

The purpose of this study was to quantify the consistency and precision of locating three-dimensional (3D) anatomic landmarks. The hypotheses tested are that these landmarks have characteristic and variable error patterns associated with their type and location. The consistency and precision of nine orthodontists identifying 32 landmarks of 19 patients were quantified. The cone beam computed tomography (CBCT) data were acquired using a Hitachi CB MercuRay system. Prior to the study, all examiners were calibrated with respect to the definitions of the landmarks and on the use of the software program (Dolphin) for identifying the landmarks. In addition, a reference guide was provided that had the definitions and sample images of the landmarks. Data were collected in spreadsheets as x, y, and z co-ordinates and statistically analysed to determine the mean and standard deviation (SD). The mean location for a given landmark on a given patient served as the reference point. The mean of the distances from the reference point was used as the consistency, while the SD of this mean was used as a measure of precision. The error in the x, y, and z planes was calculated in order to determine the specific characteristics of each landmark. The consistency in landmark location and precision did not differ significantly among the nine examiners. Sella turcica was the most consistently (0.50 mm) and most precisely (0.23 mm) identified anatomic landmark. The most inconsistent landmark was porion-right (2.72 mm) and the most imprecise landmark was orbitale-right (1.81 mm). Due to the lack of even distribution of the errors, careful use of these landmarks for analysis purposes is needed.     

A study of the height of intact alveolar bone on panoramic radiographs of adult patients

This study describes a method of estimating alveolar bone height on panoramic radiographs by using constant anatomic landmarks as reference points and calculating ratios of given distances between certain of these landmarks in dentate patients with no radiographic evidence of horizontal bone loss. Measurements were performed on four different types of panoramic radiographs. Results determined for the maxillae and mandible were constant between the different types of panoramic films. Because of differences in the measurements obtained on the right and left sides on Panorex films that have been trimmed and spliced to remove anatomic overlap in the midline areas, this type of projection may not be suitable for analysis of the maxillary alveolar bone as described in this study. The use of the mental foramen as a constant anatomic landmark for analysis of mandibular alveolar bone on panoramic radiographs may not be feasible since it appears that it may not be possible to consistently determine the exact location of the foramen. The results of the present study suggest a difference of as much as 25% among patients in the same ratio in the maxillae and as much as 12% in the same ratio in the mandible. Therefore, the results may not be of significant value as "baseline" data to estimate alveolar bone loss at a given time after tooth loss. However, this method could prove valuable in serial studies where alveolar bone height for a single patient is compared at different times before and after tooth loss.     

The evaluation of high-speed screen/film combinations in cephalometric radiography

Cephalometric radiographs of a tissue equivalent plastic encased dry skull, each made with eight different screen/film combinations, were compared for usefulness in making orthodontic analyses. The eight screen/film combinations chosen ranged in relative speed from 80 to 600. Only one grid cassette was used, and it was a Par speed screen/film combination. Ten orthodontists identified 13 selected anatomic landmarks and rated the adequacy of their radiographic images. The density of each cephalometric radiograph was analyzed for each anatomic landmark. The results showed a difference in density readings for the various landmarks visualized. The optical density preferences of the 13 anatomic landmarks ranged between 0.87 and 2.09. The study leads to the conclusion that cephalometric radiographs can be taken with screen/film combinations that provide maximum useful information with a minimum dose level to the patient.     

Digital cephalometrics

There are different methods to produce digital head films and all have advantages and disadvantages. With a digital head film and a computer programme for digital cephalometry an analysis can be performed easily. All existing computer programmes for digital cephalometry use reference values to compare with the patient's values. However, the magnification factors of the two data sets, which are compared, must be known and correction to the same magnification must be possible within the programme. Furthermore, the reference values should be age, gender, and population related. Many commercially available programmes do not fulfil these criteria. A well-designed programme for digital cephalometry should have the possibility to calculate age and gender-related reference values based on values of the target population. Furthermore it should have the possibility to analyse several longitudinal head films at the same time and to present the data graphically. A national survey among Dutch orthodontists by the end of 2000 demonstrated that 35% of Dutch orthodontists used digital cephalometry in their office. The most commonly used analysis was the Steiner-Tweed analysis, which was performed by nearly 60% of the orthodontists.     

Maxillary superimposition: a comparison of three methods for cephalometric evaluation of growth and treatment change

Two anatomic methods are statistically compared with the implant method for superimposing serial head films in 18 subjects with metallic implants. Findings showed that the "best fit" method--that is, superimposition along the palatal plane registered at ANS--traditionally used by orthodontists, significantly underestimates the eruption of the teeth by 30% to 50%. The "structural method," which is based on the use of stable structures in the maxilla, showed no significant differences in vertical displacement of selected landmarks in comparison with the implant method.     

Reproducibility of soft tissue landmarks on three-dimensional facial scans

This study evaluated the reproducibility of 24 soft tissue landmarks on six three-dimensional (3D) facial scans. The scans were taken on a DSP400 facial scanner and were viewed using a customized software program. Intraoperator data were obtained by one researcher placing the 24 landmarks on all six scans a total of 30 times. Thirty different orthodontists of varying experience were then asked to place all 24 landmarks on each of the six facial scans in order to establish interoperator reproducibility. The standard deviations (SDs) from the mean were calculated from the data for each individual landmark in the x-, y-, and z-axes. For the intraoperator data, 12 of the 24 landmarks were found to be reproducible to within a 1 mm SD for each plane of space. The interoperator data showed lower reproducibility with just two landmarks showing less than a 1 mm SD in all three planes of space. Familiarity with 3D facial scans and associated software programs is important in improving reproducibility. In addition, the landmarks investigated in this study included those not often used. It is suggested that landmarks showing poor reproducibility for both inter- and intraoperator data should be avoided, if at all possible, or at least used with caution.     

The establishment of the photo management system for orthodontics and its clinical application

It is necessary for orthodontists to collect and analyze the patients' photographic data. By conventional methods, these photo data were commonly saved on film, which were frail and often resulted in data loss. Furthermore, it is not convenient for the orthodontists to consult and study these data during clinical research. A critical problem thus arises in managing these photo data scientifically. The computer technique and picture processing method were employed in the present study to establish the Photo Management System for Orthodontics (PMSO), which makes the administration of patients' photo data more scientific, convenient, and effective than before. This system is characterized as follows: (1) Clinical orthodontists designed and programmed the system, which is "close to clinical reality and serves the clinic". Orthodontists can easily use it without any training course. (2) The images can be imported from many devices, such as digital cameras, scanners, and electronic data storage media such as floppy disks. (3) Even two groups of photos (four images) could be displayed in the same window for comparison and study. This function allows orthodontists to easily observe the differences in the same patient's photos at different stages, which is important to obtain comprehensive knowledge of the patient. (4) The network technique makes it possible for the photos to be shared. The orthodontists can get the patients' photos through the network without going to the radiology department or the imaging room. (5) It is helpful for orthodontic research since the photos can be exported easily in different ways. (6) This is shared software; orthodontists can use it for free.     

Reliability of cranial base measurements on lateral skull radiographs

Authors – Arponen H, Elf H, Evälahti M, Waltimo‐Sirén J Objective – To explore the reliability of identification of anatomic landmarks on lateral skull radiographs of young unaffected individuals that has conventionally been used to diagnose pathologic relationships in the craniovertebral junction. Material and Methods – From the Helsinki longitudinal growth study, 20 randomly selected lateral radiographs were analyzed and re‐analyzed by two examiners. Both located seven cephalometric landmarks based on which five measurements were calculated. The differences of results were compared. With similar method three radiographs were analysed by 11 examiners and results were compared. Results – Some anatomic landmarks were easier to locate than others on lateral skull radiographs leading to differences in measurements based on them. We found the magnitude of the difference to be dependent on the landmark serving as reference. Inter‐ and intra‐examiner errors were of similar magnitude, although intra‐examiner error declined in the repeated landmark identification. Variation in a single landmark location had in general little effect on the measurement value. Conclusion – Variations in landmark location lead to differences in numeric evaluation of the anatomic relationships in the skull base area. These differences were, however, shown to have little clinical significance. Hence, the documented methods are applicable for screening of basilar pathology.     

The mesh diagram for analysis of facial growth

Facial growth of twins by means of proportionate analysis of changes in the location of landmarks within a rectilinear coordinate system (mesh diagram) has been conducted, utilizing cephalometric data on 148 males and 128 females, observed annually from 8 to 16 years of age. Findings show relative consistence of the facial configuration during this 8 year time period, which includes the adolescent growth spurt. The median face in each sex shows little change in the location of soft and hard tissue landmarks, except for slight advancement of the chin as well as dorsal and caudad movement of Gonion. Nonetheless, individual variations in landmark location after 8 years of growth among the subjects studied signal the hazards of prediction within the precise framework that orthodontists seek.     

Repeated measures analysis of geometrically constructed and directly determined cephalometric points

Cephalometric landmarks were directly determined visually from bony anatomy on lateral cephalometric radiographs and compared with geometrically constructed cephalometric landmarks for repeated measures reliability of identification. Three groups of four orthodontists, grouped by level of experience, identified 18 landmarks on each of four cephalometric radiographs. This measurement procedure was repeated four times in 1-week intervals. The variability, main associations and interactions among the variables of tracer experience, quality of radiograph traced, and the anatomic landmarks traced were assessed by means of the repeated measures analysis of variance and follow-up Tukey HSD test. The coefficient of variation was used to compare the relative variability of replicate identification of the 18 cephalometric landmarks. Rank order and statistically significant groupings by variability are listed. The level of observer experience and quality of radiograph were statistically unrelated to landmark variability on replicate examination. The geometrically constructed landmarks tested were not statistically different from the reliability of the directly determined bony-based landmarks. This finding would lend support to the techniques of geometric construction used in the Ricketts cephalometric analysis.     

Dental arch analysis system

The purpose of our research is to describe a computerized method, which enables orthodontists and researchers to analyze variation of dental arch form and dimension. The analysis system is composed of two independent parts: the database, where the images of scanned dental casts are stored, and the software. The operator uses the software to identify some landmarks on dental cast images. Corresponding distances are calculated (interincisive, intercanine and intermolar widths and the curve axis). Then the software algorithms calculate and draw the curves passing trough the selected landmarks (conics, catenary, cubic spline and polynomial curves). In the chosen curves the arch length is measured. The dental cast data, recorded at different times of the subject's life or in different steps of orthodontic treatment, are compared in order to evaluate the change in dimension (arch length and width) and form (shape). The statistical analysis of the data evaluates the variation in form and in dimension separately. The shape change is defined by Euclidean Distance Matrix Analysis (EDMA) and Bootstrap analysis. The computerized method allows orthodontists and researches to evaluate the variation in dimension and form of the dental arch in un-treated subjects and-or orthodontic patients over time. After the analysis of a large sample of patients or subjects, information concerning changes in dental arch dimension and form can be added to previous studies of other authors, distinguishing variation during and after orthodontic treatment, during growth or aging.     

Application and comparison of techniques for three-dimensional analysis of craniofacial anomalies

Traditionally, cephalometric analysis has been limited to data determined from two-dimensional (2-D) cephalograms. With imaging facilities such as CT and biplanar radiography now available, the natural extension has been towards the use of three-dimensional (3-D) coordinate positions of landmarks for comparative purposes. While these data have been potentially available for several years, the accurate and reproducible extraction of anatomic landmarks suitable for comparative purposes has been limited. This paper presents results of the application of traditional comparative techniques to well determined 3-D coordinate data acquired from biplanar radiography and CT for a patient with Treacher Collins syndrome and further provides a comparison with the technique of strain analysis, often referred to as finite element analysis, which has been applied recently to craniofacial data. Comparisons of distances and angles between landmarks, landmark coordinate positions, and strains of the patient relative to experimental reference standards reveal that the essential skeletal features of Treacher Collins syndrome have been identified and quantified by the analysis techniques. Further, a measure of the significance of the deviations has been determined by comparisons with the experimental reference standards.     

Prevention and treatment after age 10 with the edgewise technique

The success of therapy for Class II malocclusions depends on the choice orthodontists make on when to intervene. Usually they begin a two-stage treatment, first orthopedic, then orthodontic, in the mixed dentition. If they want to their non-extraction therapy to coincide with and benefit from growth, they need to diagnose the malocclusion as early as possible. Treatment of Class II malocclusions works best when it is undertaken before the second molars erupt. By correcting the malrelationship between the jaws with an orthopedic appliance, they facilitate the second, full-banded stage of treatment.     

Landmark identification in computerized posteroanterior cephalometrics

A lack of cognition regarding the reliability of landmark identification in posteroanterior cephalometrics keeps the extracted data questionable. The present study was designed to analyze this problem for the purpose of providing certain insights. An interactive computer graphic package was developed. This package was called EA-PAX (Error Analysis of Postero-Anterior cephalometric X-ray films). A random sample of 40 clear posteroanterior cephalometric head plates was studied. The reliability of landmark identification was established. The skeletal landmarks seemed more reliable than the dental landmarks. The variation in the direction and magnitude of the error was determined for each landmark. Most landmarks had their own characteristic noncircular envelope of error. It is not the philosophy of the present authors to tell the orthodontists what to use. Rather, the philosophy is to be aware of the amount and direction of variation for a particular landmark. Taking this into consideration will enable the orthodontists to look on their cephalometric numbers with a mental awareness of the possible variations. Several clinical and research studies are suggested in the article.     

Indications and limitations of intraoperative navigation in maxillofacial surgery.

PURPOSE: Although primarily developed for neurosurgical application, intraoperative navigation has gained acceptance even in maxillofacial surgery with an increasing field of indications. We want to demonstrate our clinical experiences, focusing on the indications and limitations of intraoperative navigation. MATERIALS AND METHODS: In our department, the navigation system VectorVision (BrainLAB, Heimstetten, Germany) is used. The accuracy of this referencing method, consisting of a cortical fixed reference system and surface scanning, was checked by anatomic landmarks. Surgical treatment of 20 patients was performed with the help of the navigation system. RESULTS: The VectorVision system proved to be a useful supplement during the surgical exploration of complex anatomic regions. However, resolution of imaging data sets, errors of image fusion, and discrepancies during referencing increased the inaccuracy before surgery. The main problem was the topographic changes caused by surgery, resulting in discrepancies between the preoperative image data and the surgical site. In one case suffering from a meningioma extending to the neck, topography was changed by surgery making navigation inaccurate. CONCLUSION: Generally, a promising field for intraoperative navigation systems were small surgical approaches allowing only limited exposure. From our point of view, additional promising indications include vast tumors or recurrent tumors because of altered anatomy with lost landmarks during surgery. The same was the case of patients suffering from plexiform neurofibroma caused by neurofibromatosis type I. Further, intraoperative navigation was helpful to determine the position of foreign bodies during imaging, making the intraoperative location easier.     

Cephalometric analysis with digital storage phosphor images: extreme low-exposure images with and without postprocessing noise reduction.

This study evaluated extreme exposure reduction in cephalography with monitor-displayed DICOM (Digital Imaging and Communication in Medicine, Rosslyn, Va) images. The purposes were to investigate to what extent exposure can be reduced without losing diagnostic information for tracing analysis, whether postprocessing noise reduction could benefit localization of anatomic landmarks in extreme low-exposure images, and the quality of the images. Three images (optimal, extreme low exposure, and noise-reduced extreme low exposure) were obtained from 24 volunteers. Three orthodontists traced 18 landmarks and subjectively judged the quality of the images. Sixteen of the landmarks were well identified on the extreme low-exposure images when they were compared with the optimal images. Apex inferius and apex superius were not well identified. The evaluation of image quality on a visual analogue scale showed that the optimal images were given the highest scores, extreme low-exposure images with postprocessing noise reduction the second highest scores, and extreme low-exposure images the lowest scores. Monitor-based tracing analysis on storage phosphor cephalographic images with a 94% exposure reduction, compared with conventional exposure, can be performed with only 2 of 18 landmarks not well identified. The landmarks were better identified on the low-exposure images with standard postprocessing than on the images with post-processing noise reduction, although the subjective evaluation of the image quality indicated the opposite.     

The delivery of orthodontic care in New Zealand. Part I: Analysis of a census of orthodontists.

A two-part study was undertaken to determine the supply of orthodontic services in New Zealand. Part I focuses on services supplied by specialist orthodontists. A companion paper will describe the amount and characteristics of orthodontic services supplied by dentists. All orthodontists in New Zealand in 1999 were surveyed to provide information on practice location and days practiced in 1996 (the year of the last population Census), and the amount and type of orthodontic treatment carried out in the year 1 July 1998 to 30 June 1999. The response rate was 78.9 percent. Data from 1996 were used to establish and quantify the location and distribution of orthodontists in New Zealand, and their spatial relationship to 12-year-olds and 10- to 14-year-olds using Geographic Information Systems. The information from 1998-1999 was used to determine the amount and variety of services provided by orthodontists and the makeup of their patient base. Nearly two-thirds of orthodontists had a branch practice. Over 50 percent of the 10- to 14-year-old population resided within 5 km of an orthodontist, and nearly three-quarters within 10 km. Disparities between regions existed in the supply of specialist orthodontic services. The catchment areas of main urban areas had more than three times the supply of orthodontists to 12-year-olds than did the secondary and minor urban areas combined. The mean average active patient load was 371, and the mean number of full upper and lower fixed appliances placed was 130.3 during the year of the study. Nearly half of all patients had been referred from dentists, approximately one-quarter were self-referred, and a quarter had been referred by dental therapists. Adults comprised 12.1 percent of the patient load of orthodontists; 60 percent were female.     

In Process Citation

Traditionally, the orthodontists evaluate the modifications made by the general growth of the face by superimposing "as well as possible" (best fit) the serial head-films of beginning and end of treatment on easily locatable anatomical points of the cranial base. Many authors showed that this evaluation method of the development of the facial skeleton is vague and thus generator of considerable errors of appreciation. The process of superimposition of profile head-films on stable structures of the former base of cranium rests primarily on the observation made by De Coster in 1952 on "the immutability of the basi-cranial line", confirmed histologically by Melsen in 1971. In 1972, the longitudinal studies undertaken by Bj?rk and Skieller using metal implants on more than 200 cases highlighted the stability of certain anatomical structures within the maxilla and the mandible. The "Structural Method" of general and local superimpositions, thus developed starting from these discoveries, brought a new vision of the different facial growth patterns and allowed a greater comprehension of the effectiveness of the orthodontic techniques.