Accuracy of rapid prototype models for head and neck reconstruction

Abstract

Statement of problem: Rapid prototype (RP) models are used in craniofacial reconstructions; however, there are no standards or acceptable limits to ensure accuracy of the fabricated models.

Purpose: The purpose of this study was to assess the accuracy of RP models by validating the accuracy of SLA skull models with a coordinate measurement device.

Material and methods: Stainless steel spheres were located on a dry cadaver skull as fiducial markers, scanned with Multi Detector Computer Tomography (MDCT), and interpreted with software for rapid prototyping. Seven stereolithographic (SLA) models were fabricated and measured with a coordinate measurement device. An Euler rotation transformation calculation was applied to standardize the coordinate system between the control and the models. A paired standard t test (α=.05) was used to compare fiducial marker locations on SLA models with the control.

Results: A significant difference was found between the control and each of the SLA models (P<.001) in the Z axis additive build. Significant dimensional differences were not consistently detected in the X and Y axes. Dimensional deviations fell within the size of the MDCT scans voxel dimensions.

Conclusions: The greatest discrepancies of medical model fabrication correspond to the largest dimension of the orthotropic voxel volume of the MDCT scan, which is related to the slice thickness of the scan and the Z axis of the RP model. However, the absolute magnitude of the error was small, well within the generally accepted tolerance for patient treatment.