Introduction: Achieving good results in orthognathic surgery depends largely on precise and accurate model surgery, which in turn depends on the type of the articulator used. Standard model surgery has inherent drawbacks; there is inaccuracy and time consuming. There have been many trials to introduce special articulators for model surgery planning but none of them reached the popularity to be used routinely. I am introducing an orthognathic surgery simulating instrument (OSSI) which is a new device that allows free movement of the dental casts in all three planes of space without detaching the model from the articulator. Both linear and rotational movements could be achieved and measured.

Patients and methods: The appliance has been used in ten patients planned to have bimaxillary surgery in the form of Le fort I and sagittal split osteotomy. The time needed for model surgery was estimated using OSSI and compared with, the same model surgery movements using dental casts mounted on Hanau semi-adjustable articulator for the same patients. To assess the accuracy of the new instrument, the postoperative cephalometry was compared with the prediction tracing.

Results and conclusions: In all cases, intra-operative occlusion was achieved exactly as in preoperative planning. The time needed for model surgery was shorter in OSSI group. Furthermore, statistical analysis revealed no significant difference between the planned (prediction tracing) and the post-operative cephalometry for all the measured points. The appliance carries the following advantages over the standard model surgery; it is time saving, precise, easy to use and cost saving.

Conflict of interest: None declared.