The accuracy of positioning the osteotomized maxilla during orthognathic surgery was assessed in 26 patients, comparing the use of an external reference point placed on the forehead skin (SERP), and an external reference point consisting of a bone screw placed at the forehead bone (BERP). In all cases, the unoperated mandible was used to provide an anteroposterior and transverse maxillary position, through use of an intermediate splint. In 14 cases, the distance between the SERP and the maxillary central incisor was measured, to determine the maxillary vertical dimensions. In 12 cases, measurements between the BERP the and maxillary central incisor were made.
All preoperative lateral cephalometric radiographs were traced by one investigator, and these tracings were superimposed on postoperative lateral chephalograms (3 to 6 days after surgery), respectively. The actual changes in the vertical and horizontal position of U1 were measured perpendicular and parallel to the Frankfort horizontal plane. The actual change of the palatal plane angle was also measured. These values of actual change were compared with the prediction tracings made by measurements obtained from model surgery, and the difference between planned and actual movements was calculated.
The mean difference of U1 anteroposterior movement was 1.5±2.0mm in the SERP group, and 1.2±1.1 mm in the BERP group. The mean difference of U1 vertical movement was 1.8 ±2.8mm in the SERP group, and 0.5±0.3mm in the BERP group. And the mean difference of palatal plane angle rotation in the SERP group was 2.7±6.2°, and 1.6±1.8° in the BERP group. Statistical analysis showed a significant difference between the SERP group and the BERP group in the U1 vertical difference (t-test, p<0.05).
The results of this investigation revealed less accuracy in the actual three-dimensional maxillary movements of the SERP group, compared with the BERP group. And this study also showed that use of the BERP will allow accurate three-dimensional control of the maxillary position, especially in the vertical dimension. However, the maxillary repositioning technique using BERP still remains subject to operator error, and other numerous possible sources of error were identified, which may lead to an incorrect result.
