Edward B. Seldin

Evaluation of a Semiburied, Fixed-Trajectory, Curvilinear, Distraction Device in an Animal Model

PURPOSE This study evaluated a new small, buried distractor, capable of curvilinear movement while following a fixed trajectory. The geometrical basis for such devices and the 3-dimensional treatment planning system required to make buried distractors practical are discussed. MATERIALS AND METHODS A curved rack and worm-gear device, based on the design of a hose clamp, was constructed to produce a curved distraction path, and this distractor was tested in 2 minipigs using a protocol with zero latency and 1 mm/d x 7 days of distraction. Serial standardized lateral cephalograms were used to verify distractor function and path. RESULTS Curvilinear distraction was documented by clinical examination and serial cephalometric analysis in the 2 minipigs. Observed angulation of the margins of the wedge-shaped distraction gap conformed to the calculated angulation based on the fixed radius of curvature of the distractor. CONCLUSION Distraction along a curved trajectory using a small, semiburied, curvilinear device of novel design is feasible in the minipig mandible.

A 3-D System for Planning and Simulating Minimally-Invasive Distraction Osteogenesis of the Facial Skeleton

Three-dimensional planning tools will enable the use of minimally-invasive distraction osteogenesis for the correction of craniomaxillofacial deformities by simulating treatment, precisely quantifying movement vectors, and aiding pre and post-treatment evaluation. Current techniques extrapolate 3D surgical movements and outcomes based on standard 2D radiographs. Surgical planning and outcome evaluation would be greatly improved by an accurate, reproducible and reliable 3D treatment planning system. Building upon a software foundation that includes the 3D Slicer of the Brigham & Women’s Hospital, and the Visualization Toolkit (VTK) of Schroeder, Martin & Lorensen, we add algorithms that support interactive cutting of large triangulated surface models, collision detection, landmark-based registration, and cephalometric analysis. The oriented bounding-box tree (OBB tree) structure is used throughout to enhance the interactivity of selection, collision detection, and cutting. The cutting tool is notable for its generality and preservation of topological closure in the resultant models. In a retrospective case study, the collision of the proximal fragment of the distracted mandible with the skull base is detected and the resulting 3D bone movements are quantified. The distracted bone volume is computed. In prospective cases, this system will be used to compute the placement and configuration of appropriate buried distractor(s).

Multilocularity as a radiographic marker of the keratocystic odontogenic tumor.

PURPOSE The purpose of this study was to answer this clinical question: When a patient presents with a radiolucent lesion of the mandible presumed to be an odontogenic cystic lesion, to what extent is the radiographic finding of multilocularity predictive of a final diagnosis of keratocystic odontogenic tumor (KCOT)? MATERIALS AND METHODS The study sample was derived from the population of patients who presented to the Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital for evaluation and management of suspected mandibular lesions from January 1991 through January 2009. Subjects were eligible for study inclusion if there was a final histologic diagnosis of KCOT or dentigerous cyst. The predictor variable was radiographic appearance of the lesion and was grouped into 2 categories (unilocular or multilocular). The outcome variable was lesion type (KCOT or dentigerous cyst). Appropriate univariate, bivariate, and multivariate statistics were computed. Statistical significance was defined as P < .05. RESULTS The study consisted of 130 subjects. Multilocular lesions were 1.7 times more likely to be KCOTs than unilocular lesions (P = .0001). The sensitivity, specificity, and positive and negative predictive values were 0.48, 0.87, 0.86, and 0.49, respectively. In the multiple logistic regression model, a multilocular radiographic appearance was associated with a 12-fold (95% confidence interval, 3.7 to 38) increased risk of KCOT. CONCLUSION The results of this study confirm the hypothesis that radiographic multilocularity is predictive of a KCOT because it is associated with a 12-fold increased risk for the diagnosis of KCOT.

Design and experimental evaluation of adjustable bone plates for mandibular fracture fixation

Conventional bone plates are commonly used for surgical mandibular fracture fixation. Improper alignment between bone segments, however, can result in malocclusion. Current methods of fixation require a surgeon to visually align segments of bone and affix a metal plate using bone screws, after which little can be done to adjust alignment. A method of adjusting fracture alignment after plate placement, without screw removal, presents an improvement over costly and risky revision surgery. A modified bone plate has been designed with a deformable section to give surgeons the ability to reduce misalignments at the fracture site. The mechanics of deformation for various adjustment mechanisms was explored analytically, numerically, and experimentally to ensure that the adjustable plate is comparable to conventional bone plates. A static force of 358.8 N is required to deform the adjustable bone plate, compared with predicted values of 351 N using numerical simulation and 362 N using a simple beam theory. Dynamic testing was performed to simulate in vivo loading conditions and evaluate load-capacity in both deformed and un-deformed bone plates. Results indicate that bending stiffness of a rectangular bone plate is 709 N/mm, compared with 174 N/mm for an octagonal plate and 176 N/mm for standard plates. Once deformed, the rectangular and octagonal plates had a stiffness of 323 N/mm and 228 N/mm, respectively. Un-deformed and deformed adjustable bone plates have efficacy in bone segment fixation and healing.

Mandibular Fracture Fixation and Reconstruction Using the Lower-border Threaded Rod: An Eleven-year Follow-up Study

Twenty-five cases in which a lower border threaded rod was used for fracture fixation and mandibular reconstruction were reviewed. These cases were performed during the last 11 years and have been followed for periods of up to five years and ten months. The fixation technique, originally reported in 1978, is well tolerated and provides excellent mechanical stability when enhanced security of fixation is indicated. Three unusual cases are reported in detail.

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.

A computer-assisted system for reporting of dental radiographs

A computer reporting system in radiology at the Massachusetts General Hospital (MGH) uses the direct transcription of dictated reports into the computer with the option of standard reports. This article describes a system in regular use at MGH for reporting dental radiographs in which both the clinical history and the radiographic findings are assembled from canned subunits of standard text. The system covers 80 to 90 percent of all dental radiographs and results in a clear report requiring far less production time than previously.

Analysis and design of rolling-contact joints for evaluating bone plate performance.

An apparatus for testing maxillofacial bone plates has been designed using a rolling contact joint. First, a free-body representation of the fracture fixation techniques utilizing bone plates is used to illustrate how rolling contact joints accurately simulate in vivo biomechanics. Next, a deterministic description of machine functional requirements is given, and is then used to drive the subsequent selection and design of machine elements. Hertz contact stress and fatigue analysis for two elements are used to ensure that the machine will both withstand loads required to deform different plates, and maintain a high cycle lifetime for testing large numbers of plates. Additionally, clinically relevant deformations are presented to illustrate how stiffness is affected after a deformation is applied, and to highlight improvements made by the machine over current testing standards, which do not adequately re-create in vivo loading conditions. The machine performed as expected and allowed for analysis of bone plates in both deformed and un-deformed configurations to be conducted. Data for deformation experiments is presented to show that the rolling-contact testing machine leads to improved loading configurations, and thus a more accurate description of plate performance. A machine for evaluation of maxillofacial bone plates has been designed, manufactured, and used to accurately simulate in vivo loading conditions to more effectively evaluate the performance of both new and existing bone plates.