Tridimensional Evaluation of Maxillary and Mandibular Movements in Orthognathic Surgery

Localization of basicranium midline by submentovertex projection for the evaluation of condylar asymmetry

The purpose of this research was to compare the reliability of two different methods for cranial midline localization through cephalometric analysis of mandibular condyle asymmetries. A retrospective cohort study was performed analyzing consecutively the SMV radiograms of 47 patients undergoing oral surgery before orthodontic treatment at the Dental School, University of Trieste (Italy) from 2003 to 2008. Two different cephalometric analyses were used to identify the basicranium midline (Tracing 1: initial landmarks = craniostat ear rods; Tracing 2: initial landmarks = spinosum foramina), and the left/right symmetry ratio (SR) for four parameters (condylar length, condylar angle, intra-condylar hemidistance, extra-condylar hemidistance) was calculated. The main result showed that no significant statistical difference between the SRs of the intra-condylar and extra-condylar hemidistance obtained with the same tracing was found (t-test; P = NS; C.I. 95%). Conversely, the difference between the SRs obtained with the two different tracings was statistically significant (t-test; P < 0.000; C.I. 95%). In conclusion, if the analysis of condylar asymmetries is performed in growing subjects, utilization of anatomic references such as the neurovascular foramina seems to guarantee a lower error compared to non-fixed references such as ear rods.

Three-dimensional facial surface analysis of patients with skeletal malocclusion

Three-dimensional (3D) laser surface scanning analysis has taken hold in orthodontics, as well as craniomaxillofacial and plastic surgery as a new tool that can navigate away from the limitations of conventional two-dimensional methods. Various techniques for 3D reconstruction of the face have been used in diagnosis, treatment planning and simulation, and outcomes follow-up. The aim of the current prospective study was to present some technical aspects for the assessment of facial changes after orthodontic and orthognathic surgery treatment using 3D laser surface scanning. The technique proposed for facial surface shape analysis represented three-dimensionally the expected surgical changes, and the reduction of the postoperative swelling was verified. This study provides technical information from the data collection to the 3D virtual soft-tissue analysis that can be useful for diagnostic information, treatment planning, future comparisons of treatment stability or facial postoperative swelling, and soft-tissue profile assessment.

The accuracy of two-dimensional planning for routine orthognathic surgery

Two-dimensional cephalometric planning software should be helpful for prediction of hard tissue outcome after bilateral sagittal split ramus osteotomy (BSSRO) or bimaxillary osteotomy, but transferring two-dimensional data to three-dimensions (including mock operation and surgery) may result in errors. The objective of this retrospective study was to analyze deviations between predicted results and postoperative outcome using cephalometric analyses, and to evaluate this procedure for daily use. Fifty-four subjects (mean (SD) age 26 (8) years) had a BSSRO (n=21) alone or in combination with Le Fort I osteotomy (n=33). Predictions were made for each case by cephalometric planning software and mock operations done with study models. Postoperative cephalograms were obtained after 14 days and compared with predicted cephalograms for sagittal (SNA, SNB, ANB,) and vertical (ArMeGo, ML-NSL, NL-NSL) measurements. Mean (SD) differences for all measurements varied between 1.3 degrees (1.1 degrees) and 2.2 degrees (1.6 degrees) for BSSRO; and between 1.1 degrees (1.3 degrees) and 2.2 degrees (1.6 degrees) for bimaxillary osteotomy. There were no significant differences between measurements or operations, indicating that the predictions were accurate. A difference of up to 8.5 degrees could be measured in a single case. Cephalometric prediction therefore remains an accurate tool for planning, particularly maxillary rearrangement in the vertical and sagittal dimension for routine operations. If greater shifts in the transversal dimension are necessary, exact planning should be adapted with three-dimensional planning devices to avoid significant differences.

Use of three-dimensional medical modeling methods for precise planning of orthognathic surgery

Stereolithographic (medical rapid prototyping) biomodeling allows three-dimensional computed tomography to be used to generate solid plastic replicas of anatomic structures. Reports in the literature suggest that such biomodels may have a use in maxillofacial surgery, craniofacial surgery, orthopedics, neurosurgery, otology, vascular, and nasal research. A prospective trial to assess the usefulness of biomodeling in orthognathic surgery has been performed. In 12 patients with mandibular prognathism and/or maxillary retrusion, in addition to routine preoperative cephalometric analysis, preoperative high-resolution (cutting slice thickness of 1 mm) three-dimensional computed tomography scan of the patients was obtained. Raw data obtained from computed tomography scanning was processed with a Mimics 9.22 Software (Materialise's Interactive Medical Image Control System, Belgium). Fabrication of three-dimensional medical models was obtained through a process called powder depositional modeling by use of a Spectrum Z 510 3D Color Printer (Z Corporation, Burlington, MA). Alveolar arches of the maxilla and mandibula of the models were replaced with orthodontic dental cast models. Temporomandibular joints of the models were fixed with Kirschner wire. Maxillary and mandibular bony segments were mobilized according to preoperative orthodontic planning done by analysis of cephalometric plain radiographs. The relation between proximal and distal mandibular segments after bilateral sagittal split osteotomies were evaluated on models preoperatively. The same surgeon had a role in both model cutting preoperatively and as an instructor preoperatively. The same bony relation was observed both in preoperative modelsand in the perioperative surgical field in all patients. Condylar malpositioning was not observed in any of the patients. Studying preoperative planned movements of osteotomized bone segments and observing relations of osteotomized segments of mandibula and maxilla in orthognathic surgery increased the intraoperative accuracy. Limitations of this technology were manufacturing time and cost.