Leslie A. Will

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 crowns 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.

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.

Editor's Summary and Q&A: Accuracy of reconstructed images from cone-beam computed tomography scans

INTRODUCTION The aim of this study was to determine whether 2-dimensional (2D) images produced from cone-beam computed tomography (CBCT) images taken with an iCAT scanner (Imaging Sciences International, Hatfield, Pa) can substitute for traditional cephalograms. METHODS Lateral and frontal cephalograms were taken of a radiographic phantom with known dimensions. Landmarks on the 2D images were traced and measured manually by 2 examiners and then digitally in Dolphin 10 (Dolphin Imaging Sciences, Chatsworth, Calif) by the same examiners. A CBCT scan was taken of the phantom, and orthogonal and perspective projections were created from the scans. Frontal and lateral cephalograms were created by using the 3-dimensional function in Dolphin 10, digitized into Dolphin, and traced by the same 2 examiners. Linear measurements were compared to assess the accuracy of the generated images from the CBCT scans. RESULTS Measurements on the orthogonal projections were not significantly different from the actual dimensions of the phantom, and measurements on the perspective projections were highly correlated with those taken on standard 2D films. CONCLUSIONS By constructing a perspective lateral cephalogram from a CBCT scan, one can replicate the inherent magnification of a conventional 2D lateral cephalogram with high accuracy.

Dental and skeletal changes in the transverse dimension

Abstract Many methods are available for achieving maxillary expansion. Dentalexpansion can be accomplished using a variety of appliances depending on the amount of expansion desired and the age of the patient. Significant skeletal expansion may be achieved with a fixed jackscrew expander, though the amount of skeletal expansion and the stability of such expansion is variable. No skeletal expansion should be expected in a patient who has reached skeletal maturity.

Mentoring: The value of a personal connection

d Atop priority of the American Association of Orthodontists (AAO) is recruiting and retaining orthodontic faculty. For the past 2 years, the Task Force on Recruitment and Retention of Orthodontic Faculty has worked on strategies to attract interested people to academic careers and then keep them there by facilitating their development. One factor that many senior faculty members list as important in helping them flourish in their career is a mentor. What is a mentor? Instinct tells us that a mentor is someone older and more experienced who guides a younger person. But is there more to it? It is worth examining this model to see how it might be used to assist young faculty members. The term “mentor” originated in Homer’s Odyssey, when Odysseus, leaving for the Trojan wars, asked his friend Alimus whether Alimus’s son Mentor could act as an advisor to his own son, Telemachus. 1 Whether structured or spontaneous, mentorship arrangements contain some common elements: guidance, support, and advice. The specific information conveyed during the mentoring depends on the people involved. Mentoring a faculty member begins with recruitment, either uncovering a latent desire to enter academia or inspiring a talented student to do so. The mentor can provide help in 3 important areas: The junior faculty member must be carefully nurtured as a teacher and researcher, and should have a structured program to develop skills, be evaluated, and gain experience. The mentor can also pave the way for a junior faculty member’s involvement in outside organizations, as long as these activities do not distract the young academician from primary responsibilities. Identifying resources is also an important aspect of mentoring, particularly financial resources. The mentor should be able to direct the junior faculty member to the AAO, the AAOF, the home institution, and other resources for research seed money, continuing education, or salary supplement.