Cone-beam computed tomography transverse analyses. Part 2: Measures of performance.

INTRODUCTION: The aim of this study was to compare the predictability of the cone-beam transverse (CBT), jugale (J-point), and transpalatal width measurement (TWM) analyses in identifying clinical crossbite. METHODS: From a pool of patients with cone-beam computed tomography scans who came for orthodontic treatment, a sample of 133 patients was identified, with 54 in posterior crossbite (28 boys, 26 girls) and 79 not in crossbite (77 boys, 110 girls). No patient had dental compensation in this sample. After correcting for lateral mandibular shift, 33 of the 54 posterior crossbite patients had a bilateral crossbite, and 21 had a unilateral crossbite with no shift. The CBT, J-point, and TWM analyses were done for each patient from a coronal cross-section through the middle of both the maxillary and mandibular first molar crowns. The landmarks and measurements used were described in detail in a previous study. Posteroanterior cephalograms were constructed to simulate the geometry of the conventional cephalometric radiographs. All 3 analyses were performed on the same data set to predict whether crossbite was present. We used 2 assessments of diagnostic predictability: sensitivity and specificity, and positive and negative predictive values. While the 2 methods answer different questions, the prevalence of crossbite in a population will affect the positive and negative predictive values, but the sensitivity and specificity will not change. RESULTS: Of the 133 patients studied, 54 had a clinical crossbite, and 79 had no crossbite. The J-point analysis accurately predicted that 38 patients would have a crossbite, and 45 would not. This resulted in a positive predictive value of 52.78%, a negative predictive value of 73.77%, sensitivity of 70.4%, and specificity of 57%. The TWM analysis accurately predicted that 53 patients would have a crossbite, but it falsely predicted that an additional 68 patients would have crossbite. This resulted in a positive predictive value of 43.8%, a negative predictive value of 91.67%, sensitivity of 98.1%, and specificity of 13.9%. The CBT analysis correctly predicted a crossbite in 47 patients and accurately predicted no crossbite in 73 patients. This resulted in a positive predictive value of 88.68%, a negative predictive value of 91.25%, sensitivity of 87.0%, and specificity of 92.4%. CONCLUSIONS: This study showed that although the TWM analysis had slightly better negative predictive and sensitivity values, the CBT analysis was overall better at both predictive value and sensitivity/specificity because of the limitations in J-point landmarks and the extent of the TWM analysis. Furthermore, the CBT analysis can distinguish between skeletal and dental discrepancies. Further work will test the analysis on additional samples with differing prevalences of crossbite.

Cone-beam computed tomography transverse analysis. Part I: Normative data.

INTRODUCTION: The application of cone-beam computed tomography (CBCT) in orthodontics ushered in a new era in 3-dimensional analysis that promises to provide more comprehensive understanding of craniofacial skeletal anatomy. That promise is now being realized in multiple studies. The purposes of this study were to investigate a portion of transverse dimension relationships by using CBCT and to propose a transverse analysis to assist practitioners with treatment decisions. METHODS: The CBCT scans of 241 patients with and without crossbite were analyzed to assess the width of the jaws and the inclination of the first molars. The dental and skeletal measurements were compared between the noncrossbite and the crossbite groups. RESULTS: The noncrossbite group included patients who had apparently normal transverse relationships, but also a surprising number of patients with an obvious skeletal transverse discrepancy masked by dental compensation. The noncrossbite patients with molar inclinations within 1 SD of the mean were defined as the control group, and those with dental compensations were identified as either superior convergent or inferior convergent. The obvious unilateral crossbite patients demonstrated dental compensation in the maxillary first molar on the noncrossbite side, whereas the obvious bilateral crossbite patients had normal dental inclinations. CONCLUSIONS: Skeletally, both the bilateral and unilateral crossbite groups had narrower maxillary widths than did the controls, but also wider mandibles, with more severe bilateral crossbites. Dentally, the unilateral crossbite group had more upright teeth on the noncrossbite side. In the noncrossbite groups with dental compensations, the superior convergent and inferior convergent differences in both dental and skeletal characteristics were marked. Patients without crossbites can have significant discrepancies that might warrant treatment.

Comparison of the mandibular dental and basal arch forms in adults and children with Class I and Class II malocclusions.

INTRODUCTION: The mandibular arch form at the levels of both the application point of the orthodontic bracket and the basal bone in adults and children with Class I malocclusion and Class II Division 1 malocclusion was investigated. METHODS: One hundred thirteen pretreatment mandibular casts were scanned to generate a 3-dimensional computer model of each cast. The casts were divided into Class I and Class II Division 1 malocclusion groups, and were further divided into adults (age, > or =25 years) and children (age, < or =18 years). Two reference points, FA and WALA, were assigned for each tooth. The FA and WALA arch forms were compared, and the distances between corresponding points and intercanine and intermolar widths were analyzed. RESULTS: The mandibular intercanine FA point widths were significantly greater in the Class II Division 1 malocclusion group than in the Class I malocclusion group (P <0.05) and were also significantly greater in the Class I adults than in the Class I children (P <0.05). Both the canine FA and WALA point distances and the molar FA and WALA point distances were moderately to highly correlated (R(2) >0.55) and highly significant (P <0.001) for all groups. The FA and WALA curves for all groups had individual differences, especially in the premolar and molar areas. CONCLUSIONS: The Class II Division 1 mandible is essentially the same as the Class I mandible with respect to basal bone and dental arch dimensions. WALA points can be used to predict individual dental arch forms in adults and children. Dental and basal arch forms were not significantly different between adolescents and adults.

Comparison of dental and apical base arch forms in Class II Division 1 and Class I malocclusions.

INTRODUCTION: The purpose of this study was to compare the mandibular dental arch form and the mandibular basal bone arch form of patients with Class I malocclusion with those of patients with Class II Division 1 malocclusion. Our aims were to determine differences in dental and basal transverse dimensions and arch forms between the 2 groups, and to determine the usefulness of WALA points as a reference for predicting a stable dental arch form in Class II Division 1 patients. METHODS: Three-dimensional graphic representations of mandibular casts from 35 Class I malocclusion patients and 32 Class II Division 1 patients were created by using a laser scanning system. Anatomic reference points were subjectively identified and used to represent the dental arch form (FA points) and the arch form of the basal bone (WALA points). RESULTS: The FA point intercanine width was found to be significantly larger in the Class II Division 1 sample compared with the Class I sample, whereas the basal arch form, represented by the WALA ridge, was not significantly different. No significant difference was found in the FA points for intermolar width or in the arch form of the basal bone between the 2 groups. A highly significant correlation between basal and dental arch forms was found at the canine and molar areas in the Class II Division 1 sample, and the FA and WALA point arch forms were highly individual in the Class II Division 1 sample. CONCLUSIONS: The mandibular dental arch forms for both the Class I and Class II samples were essentially the same, except at the canines; this is likely due to the nature of the occlusion in Class II Division 1 patients. There was no difference in arch forms of the basal bone between the 2 groups. The use of WALA points or other anatomic landmarks of the basal bone to predict the ideal dental arch form for a patient seems possible and could ensure a more stable orthodontic treatment outcome.

Accuracy and reliability of linear cephalometric measurements from cone-beam computed tomography scans of a dry human skull.

INTRODUCTION: The purpose of this study was to determine the accuracy and reliability of 3-dimensional craniofacial measurements obtained from cone-beam computed tomography (CBCT) scans of a dry human skull. METHODS: Seventeen landmarks were identified on the skull. CBCT scans were then obtained, with 2 skull orientations during scanning. Twenty-nine interlandmark linear measurements were made directly on the skull and compared with the same measurements made on the CBCT scans. All measurements were made by 2 operators on 4 separate occasions. RESULTS: The method errors were 0.19, 0.21, and 0.19 mm in the x-, y- and z-axes, respectively. Repeated measures analysis of variance (ANOVA) showed no significant intraoperator or interoperator differences. The mean measurement error was -0.01 mm (SD, 0.129 mm). Five measurement errors were found to be statistically significantly different; however, all measurement errors were below the known voxel size and clinically insignificant. No differences were found in the measurements from the 2 CBCT scan orientations of the skull. CONCLUSIONS: CBCT allows for clinically accurate and reliable 3-dimensional linear measurements of the craniofacial complex. Moreover, skull orientation during CBCT scanning does not affect the accuracy or the reliability of these measurements.

Mandibular arch form: the relationship between dental and basal anatomy.

INTRODUCTION: We investigated mandibular dental arch form at the levels of both the clinically relevant application points of the orthodontic bracket and the underlying anatomic structure of the apical base. The correlation of both forms was evaluated and examined to determine whether the basal arch could be used to derive a standardized clinical arch form. METHODS: Thirty-five mandibular dental casts (skeletal and dental Class I) were laser scanned, and a 3-dimensional virtual model was created. Two reference points (FA, the most prominent part of the central lobe on each crown's facial surface, and WALA, a point at the height of the mucogingival junction) were selected for each tooth from the right to the left first molars. The FA and WALA arch forms were compared, and the distances between corresponding points and intercanine and intermolar widths were analyzed. RESULTS: Both arch forms were highly individual and the tooth values scattered. Nevertheless, a highly significant relationship between the FA and WALA curves was found, especially in the canine (0.75) and molar (0.87) areas. CONCLUSIONS: Both FA and WALA point-derived arch forms were individual and therefore could not be defined by a generalized shape. WALA points proved to be a useful representation of the apical base and helpful in the predetermination of an individualized dental arch form.

Newly defined landmarks for a three-dimensionally based cephalometric analysis: a retrospective cone-beam computed tomography scan review.

OBJECTIVES: To identify two novel three-dimensional (3D) cephalometric landmarks and create a novel three-dimensionally based anteroposterior skeletal measurement that can be compared with traditional two-dimensional (2D) cephalometric measurements in patients with Class I and Class II skeletal patterns. MATERIALS AND METHODS: Full head cone-beam computed tomography (CBCT) scans of 100 patients with all first molars in occlusion were obtained from a private practice. InvivoDental 3D (version 5.1.6, Anatomage, San Jose, Calif) was used to analyze the CBCT scans in the sagittal and axial planes to create new landmarks and a linear 3D analysis (M measurement) based on maxillary and mandibular centroids. Independent samples t-test was used to compare the mean M measurement to traditional 2D cephalometric measurements, ANB and APDI. Interexaminer and intraexaminer reliability were evaluated using 2D and 3D scatterplots. RESULTS: The M measurement, ANB, and APDI could statistically differentiate between patients with Class I and Class II skeletal patterns (P < .001). The M measurement exhibited a correlation coefficient (r) of -0.79 and 0.88 with APDI and ANB, respectively. CONCLUSIONS: The overall centroid landmarks and the M measurement combine 2D and 3D methods of imaging; the measurement itself can distinguish between patients with Class I and Class II skeletal patterns and can serve as a potential substitute for ANB and APDI. The new three-dimensionally based landmarks and measurements are reliable, and there is great potential for future use of 3D analyses for diagnosis and research.

Transverse skeletal and dental asymmetry in adults with unilateral lingual posterior crossbite.

BACKGROUND: Posterior unilateral lingual crossbite (PUXB) is a common malocclusion in children. However, the extent to which PUXB affects the dentition and craniofacial structures in adults has not been fully defined. We investigated dental and skeletal asymmetry in adults with PUXB. METHODS: We randomly selected 15 crossbite subjects (mean age, 26.2 years) and 15 matched controls (mean age, 30.6 years) from 3000 records. Mounted pretreatment dental casts were measured to assess dentoalveolar asymmetry, and posteroanterior radiographs were used to evaluate left-right skeletal asymmetry and positional deviations of the mandible. RESULTS: A statistically significant difference in mandibular transverse dental asymmetry was observed between adults with PUXB and the control group. However, no significant differences were found in the right-left skeletal asymmetry, although the PUXB group showed more positional deviation of the mandible. Moreover, condylar position analysis indicated that the crossbite group did not show any greater functional shifts than the control group. CONCLUSIONS: We concluded that PUXB in adults is primarily due to dentoalveolar asymmetry and positional deviation of the mandible and not simply to right-left skeletal asymmetry of the mandible. These data suggest that untreated PUXB in children might lead to progressive asymmetric compensation of the condyle-fossa relationship and result in a positional deviation of the mandible, which, along with a distinct dentoalveolar asymmetry, maintains the crossbite occlusion in adults.