Orthognathic Surgery Distance Screws

Konrad Wangerin and Henning Gropp

Introduction

The simultaneous osteotomy of the maxilla and mandible, first described by Obwegeser in 1970, runs the risk of incorrect positioning of the maxilla, the mandible, and both condyles, if the opration is done without full supporting actions, including (but not limited to) an exact diagnosis, preoperative orthodontics, operation planning (method and simulation), and careful postoperative control. The use of miniplates and microplates in the midface and the mandible has led to greater convenience for patients; nevertheless, without the additional supporting activities referred to above the results will be dependent solely on the experience of the surgeon. Throughout the last quarter of the 20th century, significant developments in fields such as operation planning, operation simulation, and support skills and services have led to reproducible, lasting, and stable results from this operation.

The double-splint method (Lindorf, 1977) is frequently used to control the horizontal dimension during the step-by-step positioning of maxilla and mandible in reaching a neutral occlusion. Controlling the vertical dimension is done intraoperatively by direct measurements between screwholesabove and belowthe Le FortIosteotomy line, or indirectly with extraoral appliances (Speculand and Jackson, 1984; Neubert, Bitter, and Somsiri, 1988; Luhr and Jäger, 1994), or intraorally using positioning plates (Wangerin, 1990).

Technique

After preoperative orthognathic treatment, extensive clinical diagnosis, planning, and simulation of the operation are performed.

Clinical Diagnosis

First of all, the necessary clinical aesthetic parameters are considered and recorded, including the vertical facial symmetry that embraces the harmony of the three parts of the medial section of the face, the laugh line of the upper lip and the profile of the face. The stomatognathic system is evaluated, including the chewing function, tongue and mimic muscle activities, the condition of the teeth and the periodontium, and function of both temporomandibular joints.

Radiographic Diagnosis

A panoramic radiograph is taken to judge the position of the mandibular canal and the wisdom teeth, where present. A lateral cephalogram is made for the Bergen analysis (Hasund, 1974), which provides information about maxillary and mandibular growth. In cases of asymmetries of the face a posterior–anterior cephalogram is necessary to determine the skeletal dimensions of abnormal jaw growth. These analyses are the basis for planning the operation.

Model Diagnosis

The unstable malocclusion leads to an undefined position of the condyles (Fig. 24.1). Therefore, a check bite in centric occlusion is performed to put the condyles in a physiological position (Fig. 24.2). These condylar positions are monitored radiographically while using the check bite. Plaster models of the maxilla and mandible are made to analyze the orthodontically aligned upper and lower dental arches.

Planning

Cephalometric measurements on the lateral cephalogram determine the planned maxillary displacement. The aesthetic parameters are considered. The mandible is then placed in neutral occlusion to the maxilla. After analysis of the new facial profile a decision is made to determine the chin correction.