Adaptation of lateral pterygoid and anterior digastric muscles after surgical mandibular advancement procedures in different vertical craniofacial types: a magnetic resonance imaging study.

OBJECTIVE: Surgical mandibular advancement procedures induce major adaptations of jaw-closing muscles. In this study, adaptation of antagonist muscles, the lateral pterygoid (LPM) and anterior digastric (DigA) muscles, was evaluated. STUDY DESIGN: Eighteen adult patients with mandibular retrognathia and individually varying vertical craniofacial dimensions were treated with bilateral sagittal split osteotomies (BSSO), in some cases combined with a Le Fort I osteotomy (LF Bimax). The sample was divided into 1 short-face (SF, n = 7) and 2 long-face groups (LF BSSO, n = 3; and LF Bimax, n = 8). Pre- and postoperative maximum cross-sectional areas (CSA) and volumes were compared in these groups. RESULTS: Postoperatively, CSA and volume of LPM increased in BSSO cases and decreased in bimaxillary cases. Inconsistent increases and decreases of CSA and volume of DigA were seen in all groups. CONCLUSIONS: The LPM became larger in SF and LF BSSO patients and smaller in LF Bimax patients. The DigA adapted unpredictably.

Adaptation of jaw closing muscles after surgical mandibular advancement procedures in different vertical craniofacial types: a magnetic resonance imaging study.

OBJECTIVE: Surgical mandibular advancement influences the biomechanics of the mandible and as a result may provoke relapse. In this study, the adaptation of the masseter (MAS) and medial pterygoid muscles (MPM) after surgical mandibular advancement was evaluated. STUDY DESIGN: Of 12 patients with mandibular retrognathia and varying vertical craniofacial morphology, axial and 30 degrees angulated magnetic resonance imaging (MRI) scan series were taken preoperatively and 10 to 48 months postoperatively. Using cluster analysis, subjects were assigned to a long-face (LF) and a short-face (SF) cluster. Subsequently, preoperative and postoperative maximum cross-sectional areas and volumes of the MAS and MPM were compared in these groups. RESULTS: The cross-sectional area and volume of the MAS decreased significantly in both the SF and LF cluster (up to 18%). Although not significantly, this phenomenon tended to be more pronounced in LF patients. The cross-sectional area of the MPM showed less adaptation. CONCLUSION: The jaw-closing muscles become significantly smaller after surgical mandibular advancement, irrespective of the vertical craniofacial type.

Masticatory muscle right-left differences in controls and hemifacial microsomia patients.

One aim of this study was to assess right-left differences in the volume of masticatory muscles in controls so as to be able to distinguish between normal variations and pathological differences. The other aim was to compare the masticatory muscle volume of the nonaffected side of hemifacial microsomia patients with the smaller side of controls so as to test the compensation hypothesis. The study group consisted of 39 children with hemifacial microsomia and the control group of 52 children. Computed tomography scans were made using a Philips Tomoscan 350 and a Pro Speed S Fast Spiral General Electric scanner. The normal right-left differences in volume of the masticatory muscle of the controls, calculated as a percentage of the total, demonstrated small mean differences of 2.57% to 2.88% (SD:1.98-2.74). For hemifacial microsomia patients, the relative difference was about 10 times the difference for controls. For controls, the averages of the right-left differences (%) were all below the generally accepted SEM of 4%. Testing the compensation hypothesis of all effects, only the age effect was multivariately significant (P < 0.001). No overcompensation of the masticatory muscles of the nonaffected side of hemifacial microsomia patients could be demonstrated.

Perception of symmetry in the face.

One purpose of this study was to assess the perception of (a)symmetry of the face by professionals, lay persons, and sculptors using the ratio estimation scale technique. The other purpose was to compare the perceptions of the faces of patients with those of the controls. Three groups of examiners were involved in this study: lay persons (n = 37), professionals (5 orthodontists and 11 surgeons, n = 16), and sculptors (n = 22). The total number of examiners was 75. All groups agreed on the ordering of the patients according to the severity of the affliction. The stage of asymmetry by group identity interaction effect (lay persons, professionals, and sculptors) was significant (P = 0.004). The between-examiner consensus was high for the original asymmetrical photograph, but the groups diverged further and further over the next steps. The subject identity by stage of asymmetry interaction effect was significant (P = 0.001), whereas the examiner's main effect was not. For all patients, each step resulted in a smaller need for treatment. A need for treatment was not found for any of the control subjects, with 1.5 being the highest need for treatment score for controls. The subject identity effect (patient/control) was significant (P < 0.001). Even at step 5 (the reconstructed symmetrical photograph), all patients were perceived to have an inferior appearance to that of control subjects. It is possible to obtain reliable assessment using the ratio estimation scale technique. Professionals, lay persons, and sculptors have different perceptions of the degree of asymmetry but not of the need for treatment. All patients were scored as asymmetrical compared with controls. Asymmetry of the patients was obvious for all the examiners.