A validation of two orthognathic model surgery techniques.

In order to create an evidence-based orthognathic surgery planning protocol, an investigation of two popular model surgery techniques, the Lockwood keyspacer and the Eastman anatomically-orientated system was carried. This determined (a) the accuracy of positioning of the maxillary cast according to the prescribed treatment plan and (b) the relocation of the maxilla after a simulated Le Fort I down fracture osteotomy using the intermediate wafer as a guide. Fifteen patients-five Class II division 1, five Class II division 2, and five Class III-were included in the study. All the measurements were taken with Erickson's vertically mounted electronic caliper and variations from the treatment plan were analysed. The mean model surgery positioning errors +/- SD (mm) were: (i) vertical plane-Lockwood -0*8 +/- 1*6 and Eastman 0*00 +/- 1*0 (P = 0*0001); (ii) anteroposterior plane-Lockwood 1*2 +/- 1*8 and Eastman -0*1 +/- 1*4 (P = 0*05); and (iii) transverse plane-Lockwood 0*9 +/- 0*9 and Eastman 1*0 +/- 0*9 (P = 0*34). After the simulated osteotomy, the mean errors +/- SD were: (i) vertical plane-Lockwood -0*5 +/- 1*5 and Eastman 0*3 +/- 1*1 (P = 0*001); (ii) in anteroposterior plane-Lockwood 0*8 +/- 2*0 and Eastman 0*7 +/- 1*0 (P = 0*89); and (iii) transverse plane-Lockwood 0*8 +/- 0*6 and Eastman 0*7 +/- 0*5 (P = 0*83). The Eastman technique was relatively better especially in the vertical plane. The variations from the treatment plan were on the whole anatomically small, but in some cases could be clinically significant.