Effects of the changes in the condylar long axis angle and condylar position on temporomandibular symptoms after intraoral vertical ramus osteotomy: a preliminary study

Examination of the Safe Zone in Mandibular Ramus Osteotomies

ABSTRACT

In the surgical procedures such as osteotomy to be applied to ramus of the mandible, care should be taken not to damage the inferior alveolar nerve (IAN). The safe zone, which is the area above and behind the mandibular foramen (MF), is the ramus of mandible area, where these surgeries can be performed without damaging the inferior alveolar neurovascular bundle. It was aimed to determine the safe zone in the ramus of mandible in the cone-beam computed tomography (CBCT) images of individuals. The CBCT images of 300 Turkish individuals between the ages of 18 to 65 were bilaterally and retrospectively evaluated. Three parameters on the sagittal and two parameters on the axial plane were measured. Additionally, two ratios were calculated which determined the superior and posterior part of the safe zone through the measured parameters. In this study, the safe zone was determined as the area where 55% of the upper part and 49% of the posterior part of the mandibular ramus. Determining the safe zone in surgical procedures to be applied to the ramus of mandible will help protect the neurovascular structures passing through the MF, reduce complications and increase the success rate of the surgical procedure. However, it is seen that there are few studies on this subject in the literature and there are some differences between these studies. The authors think that preoperative CBCT screening will be safer for each patient in the mandibular ramus osteotomies and more studies should be done on different populations to determine standard values.

Predisposing conditions for condylar sag after intraoral vertical ramus osteotomy

Intraoral vertical ramus osteotomy (IVRO) is used to treat mandibular prognathism and temporomandibular disorders. However, the improvement of temporomandibular disorders after IVRO is considered to be due to the anterior and downward movement of the mandibular condyle, which may lead to condylar sag, and in the worst case, condylar luxation. In this retrospective cohort study, we examined factors potentially associated with condylar sag. Univariate analysis indicated that condylar sag was significantly associated with the following factors: magnitude of setback (P = 0.001), less than 3 mm setback (P < 0.001), presence of temporomandibular joint (TMJ) symptoms (P = 0.002), Wilkes classification (P = 0.039), occlusal cant correction ≥ 2 mm (P = 0.018), and mandibular condyle deformation (P < 0.001). Setback magnitude (P = 0.032) and TMJ symptoms (P = 0.007) remained significant in the multivariate analysis. In the receiver operating characteristic curve, the setback magnitude cut-off value for condylar sag after IVRO was 3.25 mm. Thus, the incidence of condylar sag after IVRO is increased with a smaller setback magnitude (≤ 3.25 mm) and the presence of TMJ symptoms. These factors should be evaluated by surgeons during treatment planning for IVRO to estimate condylar sag, and it may be possible to predict the risk of condylar luxation.

Mandibular condyle displacements after orthognathic surgery-an overview of quantitative studies

The repositioning of bone segments during orthognathic surgeries often results in mandibular condyle positional changes and can also affect jaw muscles, soft tissues and the temporomandibular joint (TMJ). Condylar displacements are considered as one of the factors of bone remodeling and further skeletal relapse. The quantitative approach is commonly used in comparative analyses and evaluations of the relationships between examined factors. The aim of this study is the overview of the current literature including quantitative analysis in the research of mandibular condyle positional changes as a consequence of orthognathic surgeries. Thirty articles were included in the overview. Most of the articles present a comparative and evaluative analysis of treatment results concerning different surgical approaches, fixation methods or types of skeletal defects. The correlation between condylar displacements and bone remodeling, skeletal relapse and TMJ dysfunctions were considered. The most frequently repeated study variables were: short-term changes, Class III malocclusion, yaw rotation, 3D cephalometry measurements. Quantitative data might be useful in the evaluation of patterns and range of condylar displacements for specific treatment conditions. Available literature concerning the analysed topic is characterized by great heterogeneity with regards to the purpose and methodologies of the studies. More systematic approaches and long-term considerations are needed in future research.