Location of the mandibular center of autorotation in maxillary impaction surgery

Mandibular autorotation: a critical virtual parameter in clinical decision-making regarding maxilla-first versus mandible-first sequence

Large degrees of mandibular autorotation during intermediate splint design are prone to transfer error and decrease accuracy. The purpose of this study was to evaluate the amount of mandibular autorotation necessary to design intermediate splints for maxilla- and mandible-first sequences using virtual planning software, to help the clinical decision-making regarding the most adequate sequence for each patient. The influence of specific orthognathic movements (different vertical and sagittal changes at the Le Fort I level, cant correction) and the type of maxillofacial deformity (skeletal Class II, III, anterior open bite) were evaluated to identify those that would require higher levels of autorotation for each sequence. Three-dimensional virtual surgical planning data of 194 patients were reviewed (126 female, 68 male; mean age 26.5 ± 11.0 years; 143 skeletal Class II, 51 skeletal Class III) and subgroup analyses were conducted using the Kruskal-Wallis test and post-hoc pairwise comparisons. As an additional parameter (mandibular autorotation), maxilla-first is indicated for bimaxillary osteotomies with Le Fort I posterior intrusion, anterior open bite, and skeletal Class III, while mandible-first is recommended for Le Fort I global extrusion, especially with maxillary cant correction.

Long-term Stability Over 2 Years After Isolated Maxillary Orthognathic Surgery Combined With Mandibular Autorotation in Risk Patients for Condylar Resorption

OBJECTIVE

Counterclockwise rotation of mandible can cause condylar resorption and condylar displacement posteroinferiorly after maxillary orthognathic surgery with mandibular in patients with high-angle mandibular retrognathism. This study was aimed to evaluate long-term stability >2 years and postoperative changes of condylar displacement.

MATERIALS AND METHODS

In 15 patients who underwent Le Fort I osteotomy with mandibular autorotation, postoperative stability was cephalometrically investigated until 2 years. Condylar changes were analyzed with transcranial temporomandibular joint projection. Correlation between condylar displacement and surgical movement was analyzed.

RESULTS

Significant clockwise relapse of mandible ( P <0.01 for SNB reduction and backward movement of point B) was observed between 6 months and >2 years after surgery, even though the values were small (0.5±0.1 degrees and 1.14±0.13 mm, respectively). The condyle was displaced posteroinferiorly immediately after surgery; however, it achieved a stable position at postoperative 6 weeks. The amount of vertical condylar displacement was significantly correlated with surgical change in mandibular posterior border sagittal angle, palatal plane angle, facial height ratio, and point B in the horizontal dimension. Greater mandibular rotation prompted more vertical condylar displacement.

CONCLUSIONS

Small mandibular relapse in long term should be considered after maxillary orthognathic surgery with mandibular autorotation, although it is regarded as a surgical maneuver to minimize mandibular instability in patients susceptible to postoperative condylar resorption.

Considerations for vertical control with microimplants in a idiopathic condylar resorption patient: A case report

Idiopathic condylar resorption (ICR) is a rare, destructive temporomandibular joint disease characterised by progressive resorption of the condyles. This case report presents a record of an orthodontically treated patient with ICR with favourable posttreatment remodelling of the condyles. An 18-year-old woman sought treatment for ICR. A severe Class II high-angle facial pattern with resorption of bilateral condyles was evident. The treatment plan was determined after careful examination of condylar radiographs and comprised forward rotation of the mandible through full-arch intrusion with microimplants after extraction of the four premolars. The treatment was completed in 35 months, and the patient was noted to have a straight profile, good interdigitation and slightly increased condylar volume. Two years after retention, the condyles were stable, and the patient's profile and occlusion remained acceptable despite a mild relapse of the mandibular position. ICR was successfully corrected with orthodontic treatment. Counter-clockwise mechanics applied during the ICR remission period not only improved facial aesthetics but were also suitable for condylar unloading.

Predictability of Mandibular Autorotation After Le Fort I Maxillary Impaction in Case of Vertical Maxillary Excess

A retrospective study of 20 patients treated for vertical maxillary excess between 2009 and 2010, solely by superior surgical repositioning of the maxilla. Clinical and radiological cephalometric parameters were analyzed statistically and their impact on achieving the predicted postoperative mandibular autorotation and on relapse. According to our study, patients presenting with an anterior open bite and a low occlusal plane angle might fail to achieve the predicted mandibular autorotation and are prone to postoperative relapse. No correlation was found between the extent of maxillary impaction and the presence of autorotation.

Spatial changes of the chin in the vertical and sagittal planes after superior repositioning of the maxilla

PURPOSE

The mandible autorotates after maxillary superior repositioning. The aim of this study was to address the changes in chin position in the vertical and sagittal planes after maxillary superior repositioning.

MATERIALS AND METHODS

This cross-sectional study assessed participants who had class I occlusion with vertical maxillary excess and underwent maxillary superior repositioning. Two lateral cephalograms were taken in central occlusion and natural head position. The amount of maxillary superior repositioning was documented for every participant according to lateral cephalometric indices. The distance between the most prominent point of the chin and a perpendicular line from N to the Frankfort line was used to determine the sagittal changes of the chin before and after surgery. The distance from the N point to Me was used to assess the vertical changes of the chin before and after operation. The Pearson correlation test was used to determine the correlation between the amount of maxillary superior repositioning and the vertical and horizontal changes of the chin. The linear regression model was applied to predict the changes of the chin (dependent factor) according to the vertical change of the maxilla (predictive factor). The occlusal plane angle change, mandibular length, and mandibular plane angle were considered as variable factors.

RESULTS

Twenty participants were studied. Analysis of the data demonstrated a significant correlation between the maxillary superior repositioning (predictive factor) and the horizontal and vertical changes of the chin. For every 1  mm of vertical change in the maxilla, the chin could be expected to move 0.21  mm horizontally. For a standard deviation increase of 1 in the maxillary position, the chin advanced by 0.753 of the standard deviation (β = 0.753). For every 1-mm change of the maxilla vertically, it could be estimated that the chin moved 0.71  mm vertically when the amount of maxillary impaction was 8  mm or less. For an increase in standard deviation of 1 in the position of the maxilla, the chin moved superiorly by 0.711 of a standard deviation (β = 0.711). In maxillary superior repositioning greater than 8  mm, for every 1  mm of superior repositioning, the chin moved 0.44  mm superiorly. There was a positive correlation between the occlusal plane change, mandibular length, mandibular plane angle as well as the vertical and horizontal changes of the pogonion (P = 0.001).

CONCLUSIONS

The chin position after maxillary superior repositioning can be predicted according to the amount of maxillary vertical changes. The vertical change of the chin is more predictable than the horizontal change.

Simulation of the human TMJ behavior based on interdependent joints topology

The temporomandibular joint (TMJ) is one of the most important and complex joints of the body and its pathologies affect a great percentage of the human population. The simulation of the TMJ behavior during opening, closing and chewing movements can be very useful to the understanding of this articulation by physicians, helping them to prevent or fix problems due to accidents or diseases. This work proposes a model to simulate the human TMJ behavior based on the concept of two interdependent joints. The model was conceived using multimodal information acquired from CT and MRI images of a live person, as well as motion data acquired from this same person with a magnetic motion capture device. Simulation of movement of other TMJs, based on different morphology of bones and teeth, is obtained by adapting the regular captured motion data through collision detection and treatment methods. The proposed model was evaluated through image registration techniques by comparing our simulated results with real, captured motion data. We also validate the model showing how it can be used to predict TMJ behavior in the presence of different--normal or abnormal--bones and teeth morphologies.

Factors influencing the accuracy of cephalometric prediction of soft tissue profile changes following orthognathic surgery

The cephalometric prediction of orthognathic treatment outcome is an important part of the surgical planning and the process of informed consent. The orthodontic and surgical changes must be described accurately prior to treatment in order to assess the treatment's feasibility, to optimize case management and to increase patient's understanding and acceptance of the recommended treatment. The aim of the present article was to investigate on the factors that could influence the accuracy of cephalometric prediction in planning orthognathic surgery. Review of the literature revealed that, besides factors directly related to the prediction method and its use, there exist a considerable number of factors which could affect significantly the accuracy of soft tissue response. These factors could be biological ones such as relapse, centre of mandibular rotation and individual variation in response to treatment and others such as gender, race, pre-operative soft tissue thickness and data bases for mean ratios of soft to hard tissue movement changes. Some of the factors affecting the accuracy of prediction of soft tissue response following orthognathic surgery are inevitable and there are others, difficult to control and predict. However, patients should be informed that predictions are only a guide, may not represent the actual result of the surgical outcome, and as such they should be implemented.

The relation between pogonion advancement and posterior maxillary impaction

Controversy exists about the relation between the amount of posterior maxillary impaction and pogonion (P) advancement. The aims of the current study were to (1) propose a formula to predict the amount of P advancement due to posterior maxillary impaction surgery, (2) predict the amount of posterior maxillary impaction by means of a formula to achieve the best facial harmony, and (3) identify the compatibility between proposed formulas and the actual resultant mandibular position after posterior maxillary impaction surgery. For obtaining the formulas, 2 cephalograms were taken from 1 patient in centric occlusion and rest position. Afterward, mandibular rotational center was obtained by superimposing the cephalograms; by the help of which the 2 formulas were obtained. To check the reliability of the formulas, 10 patients with the mean age of 21 +/- 1.5 years who had undergone posterior maxillary impaction were selected. The presurgical and postsurgical cephalograms of patients were obtained. These cephalograms were superimposed to find the center of mandibular rotation. Pearson correlation coefficient test was used to evaluate the relation between the suggested formulas and the clinical data. This test showed that there were significant correlations between maxillary impaction and P advancement in both the formulas and clinical evaluation. This correlation (r) was 0.993 (P < 0.001) based on formulas and r = 0.806 (P < 0.005) based on tracing. This study showed that the amounts of anterior facial height reduction and P advancement were almost the same, and the anterior facial height was reduced 1.5 times more than the amount of maxillary impaction.

Nonextraction treatment of an open bite with microscrew implant anchorage

A 16-year-old girl with an anterior open bite was treated with nonextraction therapy that included intrusion of the maxillary and mandibular posterior teeth with microscrew implants. Implants (diameter, 1.2 mm; length, 8 or 6 mm) were placed into alveolar bone near the posterior teeth and used as anchorage for intrusive force. To prevent adverse side effects of buccoversion or linguoversion of the posterior teeth during intrusion, a transpalatal bar and a lingual arch were placed. The 3-mm anterior open bite was corrected in 11 months of treatment, after intrusion of the maxillary and mandibular posterior teeth and autorotation of the mandible. The posterior intrusion relapsed in the early stage of retention, at 8 months; thereafter, no obvious relapse was evident in the vertical position of the molars and the FMA. The treatment mechanics of anterior open bite with posterior intrusion by using microscrew implants were effective but still require a proper retention protocol.

The Inter-relationship Between Mandibular Autorotation and Maxillary LeFort I Impaction Osteotomies

The purposes of the present investigation were to: 1)locate the instantaneous rotation center of mandible autorotation during maxillary surgical impaction; 2) identify the discrepancies between the resultant mandibular position following by maxillary surgical impaction and presurgical predictions, which use the radiographic condylar center as the rotation center for mandibular autorotation; and 3)find the interrelation between the magnitude of maxillary surgical impaction and the sagittal change of mandible. Ten patients underwent maxillary LeFort I impaction without concomitant major mandibular ramus split osteotomies were included. The preoperative (T0) and postoperative (T1) lateral cephalograms were used to evaluate the surgical changes and locate the center of rotation of mandibular autorotation with Reuleaux method. Prediction errors were measured by comparing the predicted (Tp) and postoperative (T1) cephalometric tracings. The magnitude of the maxillary surgical impaction was compared to the positional changes of mandible after mandibular autorotation with correlation and regression analysis. The results demonstrated that the centers of mandibular autorotation located 2.5 mm behind and 19.6 mm below the radiographic condylar center of the mandible in average with large individual variations. By using the radiographic condylar center of the mandible to predict the mandibular autorotation would overestimate the horizontal position of chin by 2 mm and underestimate the vertical position of chin by 1.3 mm following an average of 5 mm surgical maxillary impaction. The magnitude of maxillary impaction was highly and positively correlated to the horizontal displacement of chin position. The rotation centers of mandibular autorotation following by maxillary LeFort I impaction osteotomies might not usually locate at the radiographic condylar center of the mandible also with large individual variations in their positions. Surgeons and orthodontists should be aware of the horizontal and vertical discrepancies of chin positions while planning a two-jaw surgery by using the radiographic center of mandibular condyle as the rotation center in mandibular autorotation.

Prediction of mandibular autorotation

PURPOSE

The purpose of this investigation was to test the hypothesis that the mandible rotates around the same point during maxillary impaction surgery as during initial jaw opening. This point, called the center of mandibular autorotation (CAR), could then be used to predict mandibular position and to decide whether only maxillary impaction would be needed to correct the occlusion and the facial profile.

PATIENTS AND METHODS

Preoperatively, two lateral cephalograms were obtained from a consecutive series of 20 patients who underwent maxillary impaction without concomitant mandibular ramus osteotomy. One cephalogram was taken with the mandible in centric relation using a wax bite wafer and another with a jaw opening of 10 mm using a fabricated acrylic bite block with the mandible manipulated to its most retruded position. The CAR was calculated before and after jaw opening using the Rouleaux method on the lower incisor and gonion point. A third lateral cephalogram was taken within 2 days postoperatively. The postoperative lower incisal point was then transferred to the first cephalogram using cranial base superimposition.

RESULTS

When the preoperative and postoperative distances between CAR and incisal point were compared, there was no significant difference between these distances, proving the hypothesis.

CONCLUSIONS

The method used is a practical and precise way to determine the center of mandibular autorotation on an individual basis. The center of rotation during initial jaw opening is the same as during impaction surgery.

Condylar movement and mandibular rotation during jaw opening

Inaccurate description of mandibular rotation can have profound effects on orthognathic surgical treatment planning and surgical outcome, as well as affect the precision of appliances fabricated on articulators. Disagreement exists concerning movements of the condyle during jaw opening. Although mandibular function is often described as rotation around an instantaneous center located outside of the condyle, many believe that jaw opening occurs around an axis of rotation that remains fixed at the center of the condylar head. In this study, condylar movements and centers of mandibular rotation during jaw opening were examined in normal subjects with the Dolphin Sonic Digitizing System. All of the subjects demonstrated both translation and rotation of the condyle during initiation of jaw opening, and none had a center of mandibular rotation located at the condylar head. The findings support the theory of a constantly moving, instantaneous center of jaw rotation during opening that is different in every person. There were also differences in movement within the subjects between experimental trials. The uncertainty of predicting mandibular rotation for a given patient should be considered when planning surgical treatment and fabricating orthodontic appliances.