| dc.description.abstract | The purpose of the in vitro study was to evaluate and compare marginal fit & internal fit of digitally designed lithium disilicate crowns manufactured by the computer-aided design/computer-aided manufacturing (CAD/CAM) technique and the conventional lost-wax heat-pressed technique. The method used for analyzing the crowns was based on 3D metrology using advanced hardware and software. A high resolution industrial non-contact scanner with an accuracy of 4 microns was used to generate point cloud data which was converted to a polygonal mesh as a 3D surface representation. This data was subsequently analyzed using engineering software with over 145,000 points of measurement for each sample in both groups.
A Master Die was scanned with a 3Shape D900 Laboratory Scanner and a ‘Standard Tesselation Language’ (STL) crown file was generated using Amann Girrbach’s Ceramill Mind design software (Ver 3.6.1). From this crown STL, two groups were milled with Amann Girrbach’s Ceramill Motion 2 (5-axis) milling machine: one group consisting of 15 crowns using Ivoclar Vivadent’s ProArt CAD Wax Pucks; and the second group consisting of 15 crowns with Ivoclar Vivadent’s IPS e.max© CAD blocks. The ProArt CAD Wax crowns were subsequently pressed with IPS e.max© Press Ingots and the IPS e.max© CAD block crowns were crystallized per Ivoclar Vivadent’s specifications.
The crowns from the two groups were evaluated using a ‘triple-scan protocol’ described by Holst et al. Each sample was scanned 12-13 times with the ATOS III Scanner (GOM, Germany), generating 8 million data points per scan. Using an in-built software (ATOS Professional, Germany), macros were designed to separately analyze the marginal fit and internal fit. The marginal zone comprised of 63,960 points of measurements, and the remaining internal fit comprised of 82,263 points of measurement.
After calculating the means for each area of each sample, a paired t-test was used to determine the differences between the two groups (P˂0.05). For the conventional heat-pressed technique, the mean values were 93.07 µm (± SD 9.58 mm) for marginal adaptation and 127.20 µm (± SD 10.44 mm) for the internal fit. For the CAD/CAM milled technique, the mean values were 83.13 µm (± SD 7.50 µm) for marginal adaptation and 103.00 µm (± SD 7.45 µm) for the internal fit. The results indicated that the marginal adaptation and internal fit were statistically significant with the CAD/CAM manufacturing technique when compared to the conventional lost-wax heat-press technique. The average measurements with the ‘CAD/CAM’ group were smaller than those with the ‘Pressed’ Group. The results are consistent with recent publications showing that CAD/CAM milling is of greater accuracy. | en |
