Regional Superimposition Research Articles

Precision and accuracy of suggested maxillary and mandibular landmarks with cone-beam computed tomography for regional superimpositions: An in vitro study.

Our objective was to identify and evaluate the accuracy and precision (intrarater and interrater reliabilities) of various anatomic landmarks for use in 3-dimensional maxillary and mandibular regional superimpositions. We used cone-beam computed tomography reconstructions of 10 human dried skulls to locate 10 landmarks in the maxilla and the mandible. Precision and accuracy were assessed with intrarater and interrater readings. Three examiners located these landmarks in the cone-beam computed tomography images 3 times with readings scheduled at 1-week intervals. Three-dimensional coordinates were determined (x, y, and z coordinates), and the intraclass correlation coefficient was computed to determine intrarater and interrater reliabilities, as well as the mean error difference and confidence intervals for each measurement. Bilateral mental foramina, bilateral infraorbital foramina, anterior nasal spine, incisive canal, and nasion showed the highest precision and accuracy in both intrarater and interrater reliabilities. Subspinale and bilateral lingulae had the lowest precision and accuracy in both intrarater and interrater reliabilities. When choosing the most accurate and precise landmarks for 3-dimensional cephalometric analysis or plane-derived maxillary and mandibular superimpositions, bilateral mental and infraorbital foramina, landmarks in the anterior region of the maxilla, and nasion appeared to be the best options of the analyzed landmarks. Caution is needed when using subspinale and bilateral lingulae because of their higher mean errors in location.

Three-dimensional cephalometric superimposition of the nasomaxillary complex

Two-dimensional maxillary superimposition techniques have been routinely used in clinical practice, but a 3-dimensional plane has yet to be introduced and validated. The purposes of this study were to propose a new plane for regional superimposition of the maxillary complex and then to validate it through clinical data. Pretreatment and posttreatment palatal expansion records were used. The magnitudes of the transverse expansion at the levels of the first premolars and the first molars were assessed using the proposed superimposition plane and then were compared with the gold standard plaster model measurements. Descriptive statistics and agreement testing were performed to compare the methods. When comparing the superimposition and plaster measurement methods, the mean errors for intermolar and interpremolar distances were 0.57 and 0.59mm, respectively. Both the intraclass correlation coefficient and the Bland-Altman plot demonstrated high agreement between the 2 methods (intraclass correlation coefficient greater than 0.9). The proposed maxillary superimposition plane yields clinically suitable results when compared with the gold standard technique, with a mean error of less than 0.6mm for typical intra-arch measurements. This new landmark-derived maxillary plane for superimposition is a promising tool for evaluating maxillary dentoalveolar changes after treatment.

Class II malocclusion: The aftermath of a “perfect storm”

To characterize the relative contribution of skeletal growth and tooth movement to occlusal development. Longitudinal cephalograms were obtained for 39 untreated subjects between 5 and 16 years of age. The sample was divided into three terminal-plane groups: mesial step, flush terminal plane, and distal step. Based on their final occlusion, the flush group (24 of the 39 patients) was sub-divided into three sub-groups: Class I, end-to-end, and Class II. Regional superimposition was used to measure yearly increments of skeletal and dental change. The mesial- and distal-step groups tended to maintain their initial Class I or Class II molar relationships. In the three flush-terminal-plane sub-groups, occlusal progression could be explained by neither an early nor a late mesial shift, both of which featured more upper molar movement than lower. Instead, the groups differed in terms of the timing of the mandibular excess and mesial movement of the upper molars. Mandibular excess and mesial movement of the maxillary molars seems to be the most significant determinants of occlusal development in flush-terminal-plane subjects. The present data argue that the strategy of holding lower leeway space and distalizing the upper molars is a rational early-treatment strategy.

Evaluation of effects of activator treatment on mandibular growth by analyzing components of condylar growth and mandibular rotation

PurposeThe objective of this study is to clarify the effects of activator treatment on mandibular growth in relation to condylar growth and total rotation of the mandible, and to investigate the relationships between the treatment responses and pretreatment facial morphology. Materials and methodsThirty Japanese girls with Class II division 1 malocclusion treated with activator were examined. Mean age at the start of treatment was 9.6±1.6 years. Mean treatment duration was 19±4 months. Lateral cephalograms obtained before and after treatment were used to analyze skeletal changes during treatment. Regional superimposition analysis was performed to evaluate activator effects by decomposing the mandibular growth into condylar growth and mandibular total rotation. ResultsThe changes in intermaxillary relationships were significantly correlated with vertical condylar growth and mandibular total rotation (P<0.05 and P<0.01). The changes in the forward displacement of the mandible were significantly correlated with sagittal condylar growth and mandibular total rotation (P<0.05 and P<0.01). Vertical condylar growth and mandibular total rotation were significantly correlated with pretreatment mandibular morphology (P<0.05 and P<0.01). ConclusionBoth the sagittal condylar growth and counterclockwise mandibular total rotation attributed to activator treatment contribute to forward displacement of the mandible. The activator effects are expected greater in patients with flat mandibular plane, small gonial angle, backwardly inclined mandibular ramus and long posterior facial height.

Stable region for maxillary dental cast superimposition in adults, studied with the aid of stable miniscrews

To identify a stable and reproducible reference region to superimpose serial maxillary dental models in adult extraction cases. Fifteen adult volunteers were enrolled. To reduce protrusion, bilateral maxillary first premolars were extracted in all volunteers. Each volunteer received six miniscrews, including two loaded miniscrews used to retract anterior teeth and four unloaded miniscrews. Impressions for maxillary models were taken at T1 (1 week after miniscrew placement) and T2 (17 months later). Dental models were created and then scanned using a laser scanner. Stability of the miniscrews was evaluated, and dental models were registered using stationary miniscrews. The palatal region, where deviation was within 0.5 mm in all subjects, was determined to be the stable region. Reproducibility of the new palatal region for 3D digital model superimposition was evaluated. Deviation of the medial 2/3 of the palatal region between the third rugae and the line in contact with the distal surface of the bilateral maxillary first molars was within 0.5 mm. Tooth movement of 15 subjects was measured to evaluate the validity of the new 3D superimposition method. Displacements were 8.18 ± 2.94 mm (central incisor) and 2.25 ± 0.73 mm (first molar) measured by miniscrew superimposition, while values of 7.81 ± 2.53 mm (central incisor) and 2.29 ± 1.03 mm (first molar) were measured using the 3D palatal vault regional superimposition method; no significant difference was observed. The medial 2/3 of the third rugae and the regional palatal vault dorsal to it is a stable region to register 3D digital models for evaluation of orthodontic tooth movement in adult patients.

Comparison of Hand-Traced and Computer-Based Cephalometric Superimpositions

To determine the ability to produce comparable superimpositions using hand tracing and digital methods (Dolphin v10). In addition, if the two methods were comparable, we wanted to determine if a difference existed between the best-fit cranial base superimposition and S-N superimpositions using the digital method. Sixty-four initial (T(1)) and final (T(2)) cephalometric film radiographs were obtained. Cranial base and regional superimpositions were completed independently for each pair of radiographs by either hand tracing and digital methods. To quantitatively evaluate the differences between the two methods, the hand and digital superimpositions were digitized to obtain x-y coordinates of routine cephalometric landmarks at T(2). Linear distance between multiple corresponding (hand and digital) T(2) cephalometric landmark locations (e.g., A point) were measured and defined as the T(2) landmark distance (T(2) LD). Additionally, 61 patient records were used to compare the digital method for best-fit cranial base superimpositions versus S-N superimpositions. A Friedman test was applied to examine for differences. The upper 95% confidence limit for the mean of the T(2) LD for hand and digital superimposition methods was <1 mm for all landmarks except maxillary incisor tip and apex. The upper 95% confidence interval for best-fit vs S-N was >1 mm for most landmarks. This study validates the use of superimpositions produced by Dolphin Imaging version 10 and is a necessary step forward toward widespread acceptance of digital superimpositions.

Comparison of hand-traced and computerized cephalograms: Landmark identification, measurement, and superimposition accuracy

The purposes of this study were (1) to investigate the variations of landmark identification between film and digital cephalometric tracings, (2) to compare the ability of Quick Ceph 2000 (Quick Ceph Systems, Inc, San Diego, Calif) to measure the linear and angular measurements with the hand-traced method, and (3) to compare Quick Ceph 2000 superimpositions to the hand-traced method of superimpositions that are currently accepted by the American Board of Orthodontics (ABO). We used 30 sets of serial cephalometric radiographs of growing patients from 1 orthodontic office. Fiduciary x- and y-axes were drawn in pencil on the T1 radiographs in the regions of the cranial base, the maxilla, and the mandible. The fiduciary lines were transferred to the digital and film serial cephalograms by regionally superimposing the tracings as described in the ABO Phase III examination handbook. A Mann-Whitney test was done to compare the median and Delta of the T1 and T2 values for each measurement acquired by hand and by Quick Ceph. There was no difference in the identification of cephalometric landmarks made manually vs digitally with Quick Ceph 2000. There was no difference in acquiring consistent cephalometric values for the measurements required by the ABO for the Phase III clinical examination manually vs digitally by using Quick Ceph 2000. There was no difference in the regional superimpositions of the mandible, the maxilla, and the cranial base, manually vs digitally with Quick Ceph 2000.

Activator versus cervical headgear: Superimpositional cephalometric comparison

Clinical trials comparing activator and headgear treatment have shown comparable effectiveness in the total result achieved, but the mechanism of correction is still uncertain. Most studies have used conventional cephalometric methods to evaluate treatment effects, and this might be a factor for the inconclusive results. The aim of this retrospective investigation was to compare the effects of activator and cervical headgear treatment with a superimpositional cephalometric method that could discern between vertical and horizontal effects as well as skeletal, dental, and rotational treatment results. The sample consisted of 2 groups of Class II Division 1 patients, treated without extraction by the same clinician (22 patients were treated with a modified activator-type functional appliance, and 30 patients were treated with a combination of cervical headgear and fixed edgewise appliances). Lateral cephalometric radiographs taken at the beginning of treatment and after Class II molar correction were evaluated conventionally and with a superimpositional method. Regarding the conventional cephalometric measurements, the only difference in the anteroposterior dimension between the 2 treatment modalities was the significantly reduced SNA angle in the headgear group. Both appliances appeared to produce minimal changes in FMA and GoGn-SN angles, and there were no statistically significant differences between the treatment groups. Regional superimpositions showed differences in the movement of molars: the maxillary molar was found to move more posteriorly and inferiorly in the headgear group. Conversely, the mandibular molar was found to move toward the occlusal plane more in the activator group. Assessment of mandibular skeletal changes showed that the mandible moved anteriorly by approximately 1 mm more in the activator than in the headgear group. The overall effect of the 2 appliances was found to be clinically comparable. However, the individual components of change showed differences characteristic of each appliance. (Am J Orthod Dentofacial Orthop 2003;123:296-305)

A procedure to average 3D anatomical structures

Creating a feature-preserving average of three dimensional anatomical surfaces extracted from volume image data is a complex task. Unlike individual images, averages present right-left symmetry and smooth surfaces which give insight into typical proportions. Averaging multiple biological surface images requires careful superimposition and sampling of homologous regions. Our approach to biological surface image averaging grows out of a wireframe surface tessellation approach by Cutting et al. (1993). The surface delineating wires represent high curvature crestlines. By adding tile boundaries in flatter areas the 3D image surface is parametrized into anatomically labeled (homology mapped) grids. We extend the Cutting et al. wireframe approach by encoding the entire surface as a series of B-spline space curves. The crestline averaging algorithm developed by Cutting et al. may then be used for the entire surface. Shape preserving averaging of multiple surfaces requires careful positioning of homologous surface regions such as these B-spline space curves. We test the precision of this new procedure and its ability to appropriately position groups of surfaces in order to produce a shape-preserving average. Our result provides an average that well represents the source images and may be useful clinically as a deformable model or for animation.

Cephalometric analysis of changes in occlusal relationship.

One of the main problems in assessing the mode of action of various treatment modalities is the method of measuring the treatment change. The purpose of the present study was to develop a cephalometric method that would permit a detailed evaluation of the individual growth processes (skeletal and dental) that contribute to the overall change in occlusal relationship. The change in molar relationship was resolved in five components, i.e. translation of the maxilla, of the upper molar, of the mandible, of the lower molar, and rotation of the mandible. These movements were recorded using regional superimposition of various structures, with the aid of a computer program. Derotation of the mandible was performed to remove any confounding effects of total mandibular rotation on the interpretation of the measurements. The results show that assessment of treatment effects can be carried out by comparison of the five resulting vectors.

The validity of the prediction of soft tissue profile changes after LeFort I osteotomy using the dentofacial planner (computer software)

The purpose of this study was to examine the validity of the prediction of soft tissue changes after LeFort I osteotomy with the DentoFacial Planner (DFP) (computer software). The preoperative and postoperative lateral cephalograms of 21 white adult orthodontic patients (10 males and 11 females) who underwent only LeFort I osteotomy as part of their overall treatment were digitized. A coordinate system of X and Y axes were used to assess the amount and direction of movement of the maxilla. The SN + 7° was the X axis, and a perpendicular to this plane from nasion was the Y axis. The sample was divided into two groups depending on the amount of forward movement of the maxilla. More than 2 mm of anterior placement of the maxilla comprised the advancement group (13 patients) and less than 2 mm comprised the impaction group (8 patients). The selection criteria for the sample were (1) before and after cephalograms taken with lips in repose and in centric occlusion; (2) all preoperative records taken almost immediately before surgery; (3) postoperative records taken at least 6 months after surgery and checked by regional superimposition of the preoperative and postoperative lateral cephalograms onto the maxilla and the mandible. No tooth movement occurred between the time the records were taken. The following soft tissue landmarks were examined: pronasale, subnasale, stomion superior, middle upper lip, stomion inferior, middle lower lip, labrale inferior, labiomental fold, and pogonion. The results indicate that for some of these landmarks the amount and direction of soft tissue changes differed between the DFP prediction and the actual surgical changes by LeFort I osteotomy. Differences between actual and predicted changes may be partially attributed to the variability of surgical procedures of previous studies that provided the data for the DFP computer software. (A M J O RTHOD D ENTOFAC O RTHOP 1994;105:241-9.)

Three-dimensional reconstruction of myocardial contrast perfusion from biplane cineangiograms by means of linear programming techniques.

The assessment of coronary flow reserve from the instantaneous distribution of the contrast agent within the coronary vessels and myocardial muscle at the control state and at maximal flow has been limited by the superimposition of myocardial regions of interest in the two-dimensional images. To overcome these limitations, we are in the process of developing a three-dimensional (3D) reconstruction technique to compute the contrast distribution in cross sections of the myocardial muscle from two orthogonal cineangiograms. To limit the number of feasible solutions in the 3D-reconstruction space, the 3D-geometry of the endo- and epicardial boundaries of the myocardium must be determined. For the geometric reconstruction of the epicardium, the centerlines of the left coronary arterial tree are manually or automatically traced in the biplane views. Next, the bifurcations are detected automatically and matched in these two views, allowing a 3D-representation of the coronary tree. Finally, the circumference of the left ventricular myocardium in a selected cross section can be computed from the intersection points of this cross section with the 3D coronary tree using B-splines. For the geometric reconstruction of the left ventricular cavity, we envision to apply the elliptical approximation technique using the LV boundaries defined in the two orthogonal views, or by applying more complex 3D-reconstruction techniques including densitometry. The actual 3D-reconstruction of the contrast distribution in the myocardium is based on a linear programming technique (Transportation model) using cost coefficient matrices. Such a cost coefficient matrix must contain a maximum amount of a priori information, provided by a computer generated model and updated with actual data from the angiographic views. We have only begun to solve this complex problem. However, based on our first experimental results we expect that the linear programming approach with advanced cost coefficient matrices and computed model will lead to acceptable solutions in the 3D-reconstruction of the myocardial contrast distribution from biplane cineangiograms.

A Proposal for an Equal Area Map of the Entire World on Mercator's Projection

The superimposition of regions scaled to be correct in area relative to one another on a Mercator map background provides an illustration of area changes on the projection while preserving Mercator shapes; the resulting "world" is discontinuous. Modifying the longitude spacing on the Mercator projection allows one to construct a continuous equal-area map.