An in vitro study of the accuracy of a new protocol for planning distraction osteogenesis of the mandible

PURPOSE

The purpose of this study was to determine the in vitro accuracy of a new protocol for distraction osteogenesis of the mandible that involves a planning process and a surgical technique.

MATERIALS AND METHODS

An experimental design was developed to simulate distraction osteogenesis on stereolithographic models of patients with craniofacial deformities. All patients had previously undergone 3-dimensional computerized scans of the craniofacial skeleton. The data from these scans were used to generate stereolithographic models. Before the fabrication of the models, the computed tomography (CT) data were manipulated to add a series of rulers and markers to the models. The 3-dimensional computerized scans were also used as the basis of the planning process. They were imported into an animation software (3D-Studio Max; Discreet, Montreal, Canada), and a virtual distractor was built and installed on the model, and the osteotomies and distraction processes were simulated. Finally, a recipe for sequencing the linear and angular changes of the distractor were calculated. A surgical technique was developed to facilitate the precise installation of the distractor as indicated in the presurgical plan. The transfer of information regarding pin position and orientation from the computer model to the patient was accomplished by creating a surgical template. This template was designed in the computer and fabricated by use of stereolithography. Mock surgery was performed on the stereolithographic models, and the results were compared with those predicted by the computer. The difference between the actual position and the predicted position was recorded.

RESULTS

On the X-axis, the difference between the predicted position for the condylar marker and the actual position of the marker on the stereolithographic models was 0.6 +/- 1.1 mm. On the Y-axis, the difference between the predicted position for the condylar marker and the actual position of the marker on the stereolithographic models was -0.9 +/- 2.6. On the Z-axis, the difference between the predicted position for the condylar marker and the actual position of the marker on the stereolithographic models was 0.04 +/- 0.8 mm. There was excellent correlation between the predicted and the actual measurements for the X, Y, and Z axes: 0.98, 0.93, and 0.98, respectively.

CONCLUSIONS

The results indicate that the combination of this planning process and surgical technique was very accurate. This in vitro study is the first step in determining the clinical usefulness of this protocol. If the results of this study are validated in clinical practice, this protocol will allow clinicians to improve the clinical outcomes of patients treated with distraction osteogenesis.

Cephalometric values for adult Mexican-Americans

Cephalometric studies of adult Mexican-Americans are incomplete. The purpose of this study was to evaluate whether significant cephalometric differences exist between adult Mexican-American, black American, and white patients. Lateral cephalometric radiographs were taken of 48 Mexican-American adults (23 men, 25 women). All subjects met the following criteria: parents, grandparents, or great-grandparents were born in Mexico; 18 to 50 years of age; Class I occlusion with minor or no crowding; good facial balance; no significant medical history or history of facial trauma; no previous orthodontic treatment or maxillofacial surgery. Twenty-five cephalometric measurements were analyzed. Significant racial and sexual differences were found in the following areas: skeletal measurement (SNA, ANB, PO-N perpendicular, Co-A, Co-Gn, ANS-Me, MP-FH, MP-SN); dental measurement (U1-A perpendicular, L1-APo, U1-L1, IMPA); soft tissue measurement (NLA, FCA, UFH (pu), ULL). Orthodontists and oral surgeons will find the cephalometric values of help in the diagnosis and treatment planning of potential orthognathic surgery patients.

Structural responses of orthodontic wires in flexure from a proposed alternative to the existing specification test

To be reaffirmed in 1987 for lack of a ready replacement, the flexural (elastic-bending) test protocol of ADA Specification No. 32 is judged inadequate. The protocol is problematic because of potentials for erroneous use of the theoretical component, incompatible with the flexible titanium alloy and multistrand stainless steel wires marketed subsequent to the preparation of the specification, and obscure to the clinician because it dictates quantifications of mechanical (pertaining to material only) rather than structural properties (including wire shape and size influences). A five-point elastic-bending test is proposed that stimulates wire activation toward engagement of a single, malaligned tooth crown. An experimental study was undertaken to determine values of transverse stiffness and corresponding elastic range for a broad sample of orthodontic wires and in the process to evaluate the proposed alternative test. Reduced test results are presented; comparisons of rankings and ratios from available theoretical developments and other experimental outcomes, including findings from the existing standard test, were completed. The difficulties with the existing protocol are largely eliminated with the alternative test; a test fixture and procedures are relatively straightforward to fabricate and follow, and the structural characteristics quantified are more meaningful to the practitioner.