Accuracy of rapid prototype models for head and neck reconstruction.

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.

Effect of EDTA preparations on rotary root canal instrumentation.

INTRODUCTION: The aim of this study was to evaluate whether rotary instrumentation using saline, EDTA 17% solution, or RC-Prep (Premier Dental, Philadelphia, PA) resulted in differences in root canal transportation. The secondary objective was to assess if instrumentation using these agents caused changes in the working length and canal volume. METHODS: Moderately curved mesiobuccal roots of 24 maxillary molars were standardized in length and randomized into 1 control and 2 experimental groups. The canals were instrumented with 0.04 taper rotary files to size #30. All groups were irrigated with saline. Group 1 was also irrigated using EDTA 17% solution (Pulpdent Corp, Watertown, MA), and in group 2, RC-Prep was used. X-ray micro-computed tomographic scans and working length measurements were made before and after instrumentation. Three-dimensional models were created from the pre- and postinstrumentation scan data and compared for volume changes. Centroid points were calculated in cross-sectional slices of the canals, and transportation was determined by measuring the distance between the pre- and postinstrumentation points. The data were analyzed with 1-way analysis of variance (α = 0.05) and the Tukey post hoc test. RESULTS: Less transportation was observed in group 2 than in group 1 (P = .001) and the control group (P = .014). Transportation in group 1 and the control group was not significantly different. Canal volume in group 1 was increased relative to group 2 (P = .004) and the control group (P = .022). No significant differences in the working length were observed. CONCLUSIONS: The use of chelating agents during root canal instrumentation did not significantly increase apical transportation.