Plane Cant Research Articles

Change of lip-line cant after 1-jaw orthognathic surgery in patients with mandibular asymmetry

The purpose of this study was to investigate the change of lip-line cant (LLC) after 1-jaw orthognathic surgery in mandibular asymmetry patients. Preoperative and postoperative data of 22 patients having 1-jaw orthognathic surgery, with menton deviation over 2 degrees before the surgery, were our subjects. LLC was measured in the preoperative and postoperative frontal photographs, and its change was correlated with various craniofacial measurements obtained from preoperative and postoperative frontal cephalograms and maxillofacial 3-dimensional computed tomography images. Although these subjects had 2.4 degrees of LLC on average before surgery, LLC improved to 0.5 degrees after surgery, and the change (1.9 degrees ) was statistically significant. In the correlation analysis, preoperative LLC showed positive correlations with menton deviation and mandibular anterior occlusal plane cant. In the correlation analysis of LLC change, it had positive correlations with preoperative LLC and mandibular anterior occlusal plane cant and preoperative and postoperative change of menton deviation. These results suggest that LLC is present with chin deviation, even without significant maxillary canting, and can be improved considerably by 1-jaw surgery alone.

Characteristics and Corrective Outcome of Face Asymmetry by Orthognathic Surgery

This study was conducted to identify the characteristics of facial asymmetry before surgery and to evaluate the facial skeletal changes and stability after 2-jaw orthognathic surgery. The ideal "double-cross grid" as fitting the key landmarks to the reference planes on posteroanterior cephalograms was set as the treatment goal. Twenty-seven adult patients, 18 female and 9 male subjects, were evaluated before and after surgery and at completion of orthodontic treatment. Cephalometric measurements of posteroanterior and lateral cephalograms were obtained at 3 timings. Measurements of frontal facial photographs were recorded before and after treatment. Data from each time set were compared to evaluate surgical achievement and postsurgical stability. All patients had original malocclusion of Class III in at least 1 side of the dentition except 1 patient. Total treatment duration was 15 +/- 3.5 months on average. Laterality of the patients demonstrated left-side dominance in 18 patients and right-side dominance in 9 patients. After surgery, face symmetry was improved by correction of the occlusal plane cant, incisal dental axis, and chin deviation. Symmetry of bilateral gonial width was also improved significantly with good stability. Intergonial width was reduced by 3.4 mm during treatment. Soft tissue presented similar correction by leveling oral commissures and correcting chin deviation. The maxilla was moved forward 1.25 mm and upward 1.20 mm, and the mandible was setback 4.3 mm and upward 1.5 mm as measured from lateral cephalograms. All sagittal changes remained stable after surgery. Fitting skeletal landmarks into a double-cross grid on posteroanterior cephalogram is an attainable guide and goal for 2-jaw orthognathic correction of facial asymmetry. Symmetry was achieved and facial profile was improved after surgery and remained stable afterward. The decrease of intergonial width indicated considerable remodeling of the bilateral gonial angle after surgery.

Simultaneous Maxillo-Mandibular Distraction Osteogenesis in Hemifacial Microsomia: A New Technique Using Two Distractors

The goal of this study was to prospectively evaluate the use of two distractors for a simultaneous maxillo-mandibular distraction osteogenesis without the use of intermaxillary fixation in the restorative treatment of hemifacial microsomia. The authors analyzed the clinical and radiological data of five patients with type I hemifacial microsomia (one patient), type IIa hemifacial microsomia (two patients), and Goldenhar syndrome (two patients). Follow-up examinations were performed at 1, 3, 6, and 12 months. All the patients had satisfactory correction of the facial asymmetry without complications. Complete horizontalization of the occlusal plane was achieved in three patients, whereas a cant of 2 degrees persisted in two patients. None of the children in this study were noncompliant with the prescribed duration of the active distraction period, nor did they experience technical problems with the two devices. Simultaneous maxillo-mandibular distraction osteogenesis resulted in a high rate of success in correcting facial asymmetry as well as occlusal plane cant. It offered good aesthetic satisfaction.

Correction of Facial Asymmetry with Multiplanar Mandible Distraction: A One-Year Follow-Up Study

To assess the effectiveness of multiplanar mandibular distraction by evaluating the treatment effect and 1-year stability, measuring changes on the affected and nonaffected sides, and evaluating correction of the occlusal plane and oral commissure cant. Eleven patients aged 5 to 9.4 years (mean 6.7 years ) who underwent unilateral multiplanar mandibular distraction were included, 10 with hemifacial microsomia and one temporomandibular joint ankylosis. Intermaxillary elastics were applied to intraoral dental devices during and after distraction until bony consolidation and occlusal interdigitation were achieved. Radiographs were taken and measured before distraction, after vertical distraction, after completion of distraction, and 1 year after treatment. Frontal facial photographs were obtained to analyze the changes in the position of the oral commissure. The facial profile was improved by sagittal mandibular advancement. Although the facial height increased 6.6 mm during vertical distraction, with a net gain of 5.8 mm in follow-up, the mandibular plane angle was maintained. The affected mandibular length increased 8.3 mm after distraction and remained unchanged after 1 year. Ramus height increased 12.7 mm after distraction and relapsed 3.8 mm at follow-up (30%). The affected body length demonstrated postoperative growth of 3.1 mm. Correction of the chin deviation was 9.8 mm after distraction and relapsed 1.6 mm (16.3%) after 1 year. Canting of the occlusal plane and oral commissure was corrected and remained stable. Multiplanar mandibular distraction is an effective treatment for correcting facial asymmetry in young children. The 1-year follow-up revealed that the new sagittal jaw relation and mandibular body length were stable, and the achieved occlusal interdigitation was well maintained. However, the ramus height and chin deviation demonstrated some relapse.

Upper lip asymmetry in adults during smiling

Purpose: This study examined the incidence of upper lip asymmetry in adults while smiling. Patients and Methods: Two-hundred ten students between the ages of 21 and 44 years were examined. Subjects determined to have an occlusal plane cant were eliminated from the study. Repeated smiles were then evaluated in the remaining subjects to check for upper lip asymmetry. Results: Fifteen subjects were observed to have occlusal plane cants and were eliminated from the study. Of the remaining 195 subjects, 17 (8.7%) were found to have an asymmetrical smile secondary to canting of the upper lip. Conclusions: Although there was not a high incidence, the results of this study indicate there is clinically evident upper lip canting associated with smiling in the adult population that needs to be considered in patients undergoing orthognathic and cosmetic surgery. © 2001 American Association of Oral and Maxillofacial Surgeons

An explicit closed-loop guidance for launch vehicles

An explicit, near optimal, closed-loop steering logic common to both, 2- and 3-dimensional launch trajectories is presented. This scheme uses a single steering angle in a canted plane, which can then be resolved as pitch and yaw angles in any inertial frame. New, exact formulations for integrating the steering thrust acceleration are presented along with the existing series approximation. Using Enke's method, two uniform gravity vectors are evaluated to account for the actual effects of inverse square gravitational force field in the propagation of position and velocity vectors, during the future guided trajectory. An iterative differential corrector to solve for the guidance parameters that decide the steering angles and thrust cut-off is discussed. Also, means of overcoming the difficulties faced by the closed-loop guidance logic close to injection is presented. Simulations are conducted for a typical launch mission. The computational load for the onboard computer are estimated in order to explore the feasibility of realizing this guidance logic. Simulation study of the effects of computational delay is also presented.

Optimal explicit guidance of multistage launch vehicle along three-dimensional trajectory

Details of an efficient optimal closed-loop guidance algorithm for a three-dimensional launch are presented with simulation results. Two types of orbital injections, with either true anomaly or argument of perigee being free at injection, are considered. The resulting steering-angle profile under the assumption of uniform gravity lies in a canted plane which transforms a three-dimensional problem into an equivalent two-dimensional one. Effects of thrust are estimated using a series in a recursive way. Encke's method is used to predict the trajectory during powered flight and then to compute the changes due to actual gravity using two gravity-related vectors. Guidance parameters are evaluated using the linear differential correction method. Optimality of the algorithm is tested against a standard ground-based trajectory optimization package. The performance of the algorithm is tested for accuracy, robustness, and efficiency for a sun-synchronous mission involving guidance for a multistage vehicle that requires large pitch and yaw maneuver. To demonstrate applicability of the algorithm to a range of missions, injection into a geostationary transfer orbit is also considered. The performance of the present algorithm is found to be much better than others.

Optimal explicit guidance for three-dimensional launch trajectory

The paper presents an exoatmospheric near-optimal explicit guidance algorithm for a satellite launch vehicle following a two- or three-dimensional trajectory. The unified steering law has been developed in a vector form using an equivalent gravitational field in an inertial coordinate frame. The resulting steering law follows a linear tangent law in a canted plane for a three-dimensional trajectory. The principle is based on the concepts of optimal transfer between non-coplanar orbits. The guidance parameters are determined by solving three simultaneous algebraic equations envolving thrust integrals which are computed recursively. Two constant gravity related vectors are defined which account for change in velocity and position due to the spherical Earth. The solution is obtained by a differential correction method after finding the required partial derivatives analytically. A predictor corrector approach is suggested where the trajectory is predicted using the Encke's method. This also enables consideration of other effects such as oblateness. The simulation results for typical multistage launch vehicles show that the guidance algorithm is extremely accurate, robust and yet simple enough for on-board implementation. It can be used for a variety of missions.