Changes in the mechanical advantage of the masseter and temporal muscles following surgical correction of mandibular prognathism.

The purpose of this study was to determine if the mechanical advantage of the masseter and temporal muscles is altered and improved as expected in patients subjected to surgical correction of mandibular prognathism. It aimed also to detect any relationship between (1) the moment arms of the masseter and temporal muscles, the moment arm of the bite force, and any morphologic characteristics considered to be factors in determining the size of the moment arms; and (2) the changes in the moment arms and the changes that the combined orthodontic-surgical treatment could induce in the morphologic characteristics. Presurgical and postsurgical lateral cephalograms of 51 consecutive orthognathic surgery patients with severe mandibular prognathism were used. The radiographs were taken 1 week before surgery and approximately 1 year after surgery. The results indicated that the mechanical advantage of the masseter and temporal muscles had a tendency to increase following correction of the dysplasia. The changes in the moment arms of the masseter and the bite force seem to be dependent on the changes in some morphologic parameters such as the angle between the mandibular line and ramal line, the angle between the anterior cranial base and the mandibular line, and the angle between the anterior cranial base and the functional occlusal plane. The combination of changes in these angles together with the shortening of the mandibular length could also lead to a decrease of the advantage of both muscles.

Financial consequences of reducing treatment availability in a publicly-funded orthodontic service. A decision analysis problem.

When a third party is responsible for funding a component of the health service, cost/benefit assessments become important. Such assessments become urgent when the budget is reduced. In this paper decision analysis has been applied to evaluate potential savings by reducing the proportion of children offered free orthodontic treatment through the National Health Service in Denmark. Data for the development of the decision tree was acquired using the Delphi technique. The results suggest that a reduction in the proportion of children offered early treatment might ultimately lead to an increased consumption of resources. Further investigation of the issue is needed before definitive recommendations can be made.

Skeletal stability after surgical correction of mandibular prognathism by vertical ramus osteotomy.

The purpose of the study was to assess skeletal stability following combined surgical-orthodontic management of 52 adults with severe mandibular prognathism. Lateral cephalograms taken 1 week before surgery, within 1 week post-surgery and approximately 1 year after operation were studied by means of eight variables and a constructive stable reproducible reference system. The surgical procedure of choice was a bilateral vertical ramus osteotomy through an extra-oral approach. In all cases the condyles were left passively in the articular fossa and no attempt at their active repositioning was made. The patients were randomly allocated to an osteosynthesis or non-osteosynthesis group with regard to intramandibular fixation. Intermaxillary fixation lasted 6 weeks and an interocclusal wafer was used in all cases during this period. The findings of this study showed that during the post-operative period there was a trend for posterior rotation of the mandibular corpus (P less than 0.001). This pattern was also characterized by an increase (P less than 0.001) of the lower anterior face height and an improvement of the angle of convexity (P less than 0.001). These changes occurring in a direction so that the dentoskeletal profile became less concave, did not tend to reverse the goal of operation and cannot be considered as detrimental. No significant differences (P greater than 0.05) were found between the groups without and with osteosynthesis.

Tomographic assessment of alterations of the temporomandibular joint after orthognathic surgery.

The aims of the study were: (1) to identify absolute condylar displacements and glenoid fossa changes; (2) to assess alterations in the condyle-fossa relationships following orthognathic surgery, by means of linear temporomandibular joint tomography. The sample consisted of 44 adults who received pre- and post-operative orthodontic therapy and management of their dentofacial deformities with various osteotomies (maxillary: 10; mandibular: 24; combined: 10). The material consisted of the tomograms of the right temporomandibular joints taken within 1 week pre-operatively, immediately post-surgery, and 6 months postoperatively. The X-rays were taken with the mouth closed. Tracing, superimposition, and interpretation of the tomograms were made according to a new method. The findings of the study regarding the groups which received mandibular or combined osteotomies indicated that immediately post-operatively there was a tendency for the condyle to be distracted downward and anteriorly from its original position in the fossa. However, in the 6 months follow-up the condyle showed a tendency to re-establish its initial position. Large variation in posterior space was observed among the patients of the mandibular osteotomy group who were also examined individually. In the maxillary osteotomy group no significant post-operative changes were observed on the average. Remodelling was noticed in both condylar and fossa surfaces of all groups.

Alterations of hyoid bone position and pharyngeal depth and their relationship after surgical correction of mandibular prognathism.

The present investigation studied changes of hyoid bone position and pharyngeal depth at the levels of the second and fourth cervical vertebrae and their relationships in mandibular prognathism patients who received combined orthodontic-surgical treatment. The material consisted of presurgical and 1-year postsurgical profile cephalograms of 52 adult orthognathic surgery patients (40 females and 12 males) who initially had mandibular prognathism and had undergone bilateral vertical ramus osteotomy through an extraoral incision in the retroangular area. Hyoid bone position and pharyngeal depth were assessed on the profile radiographs with 10 cephalometric variables. Paired t tests were used to evaluate the operative changes in all cephalometric parameters. The relationships between pairs of variables describing hyoid bone position and pharyngeal depth were assessed by means of Pearson's product-moment correlation analysis. Significant differences (p less than 0.01) were observed for the distances of the hyoid bone to the maxilla and the mandible. The distances of the hyoid bone with the anterior cranial base, the vertebral column, and the anterior pharyngeal wall, and the measurements representing pharyngeal depth exhibited no significant changes (p greater than 0.05). Moderate correlations were seen between (1) the depth of the pharynx at the fourth cervical vertebra and the hyosymphyseal distance (r = 0.34) and the distance between the point of the projection of the hyoid bone to the mandibular line with its posterior border (r = -0.34), and (2) the depth of the pharynx at the second cervical vertebra and the distance of the hyoid bone with the anterior pharyngeal wall at the level of the fourth cervical vertebra (r = -0.33).(ABSTRACT TRUNCATED AT 250 WORDS)

Tomographic assessment of alterations of the temporomandibular joint after surgical correction of mandibular prognathism.

The aims of this study were to identify absolute condylar displacements and temporal fossa changes and to assess alterations in the condyle-fossa relationships after bilateral vertical ramus osteotomy for correction of mandibular prognathism. Twenty-four patients had linear tomograms taken of their temporomandibular joints within 1 week preoperatively and 6 months postoperatively. To ensure identical orientation of the focusing plane, a custom-made headholder was constructed and the head of the patient was positioned on the x-ray table in a standardized way. All radiographs were traced, and superimposition was made on stable structures, such as the mastoid cells of the temporal bone, the auditory meatus, the zygomatic arch, and the anterior cranial base. The results of the study indicated that, 6 months postsurgery, the only statistically significant change existed in the posterior joint space, which showed an average increase of 0.7 mm (P = .003). All other variables showed that the condylar position within the joint tended to approach its preoperative value. Small resorptive alterations in the glenoid fossa were also noticed.

[Segmented arch technique and incisor intrusion for deep overbite correction]. / Embythise tomeon gia te diorthose tes auxemenes katakoryphes protaxes, me ten technike "segmented arch".

The mechanisms which will be selected for the correction of deep overbite depend exclusively on the choice of the clinician for: 1. Gennine anterior teeth intrusion. 2. Eruption of posterior teeth. 3. Combination of anterior intrusion and posterior extrusion. Principles of incisor intrusion have been presented as well as the use of intrusive springs in the segmented arch technique. Six principles must be considered in incisor intrusion: 1) the use of forces of optimal magnitude and constancy, 2) the use of a single point contact in the anterior region, 3) selection of the point of force application with respect to the center of resistance of the anterior segment, 4) selective intrusion based on anterior tooth geometry, 5) control over the reactive units and 6) inhibition of eruption of the posterior teeth and avoidance of undesirable eruptive mechanics.

[Soft tissue profile changes following mandibular rami osteotomies]. / Metaboles sto "prophil" ton malakon morion asthenon meta apo osteotomies tou kladou tes kato gnathou.

Rami osteotomies used to correct mandibular prognathism and retrognathism is a well known fact that produce also changes at the shape and position of the soft tissues. These changes in the relationship of hard tissue to soft tissue are reported as well as predicting formulas. All these information can be used as a guide in planning orthognathic surgery once their limitations is well understood.

Stomatognathic function of patients who seek orthognathic surgery to correct dentofacial deformities.

To determine the craniomandibular functional status of patients who seek orthognathic surgery, 48 adults with various dentofacial deformities were examined, and the functional parameters of the patients were compared with those of a normal population. The relationship between function and morphology was also studied. The method of study included a clinical examination of dysfunction, an evaluation of the number and intensity of occlusal contacts, a kinesiographic analysis of mandibular movements at the incisors, an evaluation of ramal and condylar vertical symmetry by means of dental rotational panoramic radiography, and an examination of profile and frontal cephalograms. Results of the examinations showed that the patients seeking orthognathic surgery showed craniomandibular functional patterns different from those of the normal group or healthy population. However, because no significant correlations were found among specific morphologic and functional characteristics and dysfunctional status (with the exception of condylar asymmetry, the maximal deviation of a maximal opening-closing movement defined on the sagittal plane, and the inclination of the maxillary central incisor in relation to the anterior cranial base), no clear cause-effect relationship was proved.