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.

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.

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.

Clinical application of curvilinear distraction osteogenesis for correction of mandibular deformities.

PURPOSE: To report the use of a semiburied curvilinear distraction device, with a 3-dimensional (3D) computed tomography treatment planning system, for correction of mandibular deformities. MATERIALS AND METHODS: This was a retrospective evaluation of 13 consecutive patients, with syndromic and nonsyndromic micrognathia, who underwent correction by curvilinear distraction osteogenesis. A 3D computed tomography scan was obtained for each patient and imported into a 3D treatment planning system (Slicer/Osteoplan). Surgical guides were constructed to localize the osteotomy and to drill holes to secure the distractor's proximal and distal footplates to the mandible. Postoperatively, patients were followed by clinical examination and plain radiographs to ensure the desired vector of movement. At end distraction, when possible, a 3D computed tomography scan was obtained to document the final mandibular position. RESULTS: Of the 13 patients, 8 were females and 5 were males, with a mean age of 11.9 years (range 15 months to 39 years). All 13 underwent bilateral mandibular curvilinear distraction. Of the 13 patients, 8 were 16 years old or younger and 5 were younger than 6 years of age. The diagnoses included Treacher Collins syndrome (n = 3), Nager syndrome (n = 3), craniofacial microsomia (n = 2), post-traumatic ankylosis (n = 1), and micrognathia (syndromic, n = 3; nonsyndromic, n = 1). The correct distractor placement, vector of movement, and final mandibular position were achieved in 10 of 13 patients. In the other 3 patients, the desired jaw position was achieved by "molding" the regenerate. CONCLUSIONS: The use of a semiburied curvilinear distraction device, with 3D treatment planning, is a potentially powerful tool to correct complex mandibular deformities.

How do feedback and instructions affect the performance of a simulated surgical task?

PURPOSE: This study was conducted to objectively evaluate the effect of feedback and instructional material on the acquisition of surgical psychomotor skills for a model system based on mandibular fracture repair. MATERIALS AND METHODS: This study was a prospective cohort study comprised of students in the preclinical years of dental or medical education. The students were divided into 4 groups and exposed to different levels of feedback/written instructions (including none) in the testing environment. Each subject was given a pair of aluminum bars, representing a fractured human mandible, and a standardized set of tools, including a fixed length of stainless steel wire to fix the bars together. The strength of fixation was measured, using a calibrated testing apparatus, as the amount of load that the fixed sample could tolerate to the point of failure. All subjects completed 5 successive trials under the same conditions. Descriptive statistics were recorded to provide comparisons between groups. Bivariate statistics were computed to compare the different study groups; multiple-comparison testing was used to evaluate differences among the groups. A P value

Comparison of wound management methods after removal of maxillofacial osseous lesions.

PURPOSE: To evaluate outcomes associated with choice of wound management, ie, primary closure or healing by secondary intention, of osseous defects after excision of maxillofacial bone lesions as a guide to clinical practice. PATIENTS AND METHODS: Using a retrospective cohort study design, we enrolled a sample composed of subjects treated for jaw lesions between 1995 and 2003. The primary predictor variable was the wound management choice of the residual jaw defect, classified as primary closure or healing by secondary intention. The primary outcome variable was postoperative inflammatory complications. Other study variables were grouped as demographic, medical/dental history, lesion information, preoperative complications, operative treatment, and follow-up information. Appropriate uni-, bi-, and multivariate statistics were computed. RESULTS: The sample was composed of 93 subjects with 126 jaw lesions, of which 90 (71.4%) were managed by primary closure. In the bivariate analyses, tobacco use was statistically associated (P < .05) with wound management and near statistically associated (P = .06) with complications. In the multivariate model, after adjusting for the presence of multiple cysts and tobacco use, there was not a statistically significant difference between the 2 wound management choices in terms of postoperative complications. CONCLUSIONS: Our results suggest that the choice of managing the osseous wound, ie, primary closure versus secondary intention, was not associated with increased risk of postoperative inflammatory complications. The implications of these findings are discussed below.

Range of curvilinear distraction devices required for treatment of mandibular deformities.

PURPOSE: The purpose of this study was to determine the range of fixed trajectory curvilinear distraction devices required to correct a variety of severe mandibular deformities. MATERIALS AND METHODS: Preoperative computed tomography (CT) scans from 18 patients with mandibular deformities were imported into a CT-based software program (Osteoplan). Three-dimensional virtual models of the individual skulls were made with landmarks to track movements. An ideal treatment plan was created for each patient. Upper and lower boundaries for the dimensions of curvilinear distractors were established based on manufacturing and geometric constraints. Then, anatomically acceptable distractor attachment points were identified on the models using proximal and distal grids. Treatment plans were simulated for a series of distractors with varying radii of curvature, elongations (arc-length of device), and placements along the grids. The outcomes using these distractors were compared with the ideal treatment plans. Discrepancies were quantified in millimeters by comparing landmarks in the simulated versus ideal movements. RESULTS: Approximately 400,000 simulated 3-dimensional movements, based on the distractor parameters and variations in placement were computationally evaluated for the 18 cases. It was determined that, by varying distractor placement, a family of 5 distractors, with 3, 5, 7, and 10 cm radii of curvature and a straight-line device, could be used to treat all 18 cases to within 1.8 mm of error. CONCLUSIONS: The results of this study indicate that a family of 5 curvilinear distractors may suffice to treat a broad range of mandibular deformities.

Analysis of skeletal movements in mandibular distraction osteogenesis.

PURPOSE: The purpose of this study was to use geometric parameters of movement, calculated from 3-dimensional computed tomography (CT) data, to determine the curvilinear distractor dimensions required to correct mandibular deformities in a series of patients. MATERIALS AND METHODS: Preoperative CT scans from 15 patients with symmetric (n = 5) and asymmetric (n = 10) deformities were imported into a CT-based software program (Osteoplan; an open-source visualization application developed by Gering et al at the Surgical Planning Laboratory [SPL, Brigham and Womens Hospital, Boston, MA]). The software was used to reconstruct virtual 3-dimensional models from these scans. Two experienced surgeons, working with a computer scientist, then used Osteoplan to create an ideal treatment plan for each patient. In each case, the 3-dimensional curvilinear movement was quantified using 4 "parameters of movement" (POMs). These parameters were then used to prescribe a distraction device capable of executing the planned skeletal correction. Curvilinear distractor dimensions calculated by Osteoplan included the radius of curvature of the prescribed device, and the distractor elongation, pitch, and handedness. RESULTS: Treatment plans including POMs were developed for each patient. The radii of curvature for the prescribed distractors ranged from 2.3 to 14.1 cm, the distractor elongation dimensions ranged from 0.7 to 3.2 cm, and the pitch (horizontal plane) dimensions ranged from 0.005 to 0.8 cm. Handedness was either a left (n = 12) or right (n = 8) turning helix. CONCLUSION: The results of this study indicate that, using geometric parameters of movement calculated from 3-dimensional CT scans, curvilinear devices could be prescribed for correction of the range of skeletal deformities in this group of patients.

Types, frequencies, and risk factors for complications after third molar extraction.

OBJECTIVES: The study objective was to identify the types, frequency, and risk factors for complications after third molar (M3) extractions. STUDY DESIGN: This retrospective cohort study consisted of patients who had 1 or more M3s removed between 1996 and 2001. Risk factors were grouped into demographic, general health, anatomic, and operative. Outcome variables were operative or inflammatory complications. Data were analyzed using descriptive, bivariate, and multivariate statistics. RESULTS: The study sample was composed of 583 patients (57.0% male) with a mean age of 26.4 +/- 8.4 years. The overall complication rate was 4.6%. Increasing age, a positive medical history, and the position of the M3 relative to the inferior alveolar nerve were associated with an increased risk for complications. CONCLUSION: While age, medical history, and M3 anatomy cannot be altered directly, these factors may be modified indirectly, resulting in a potential decrease for postoperative complications.