Comparative Study of the Trueness of the Inner Surface of Crowns Fabricated from Three Types of Lithium Disilicate Blocks

Abstract

This study set out to compare the three-dimensional (3D) trueness of crowns produced from three types of lithium disilicate blocks. The working model was digitized, and single crowns (maxillary left second molar) were designed using computer-aided design (CAD) software. To produce a crown design model (CDM), a crown design file was extracted from the CAD software. In addition, using the CDM file and a milling machine (N = 20), three types of lithium disilicate blocks (e.max CAD, HASS Rosetta, and VITA Suprinity) were processed. To produce a crown scan model (CSM), the inner surface of each fabricated crown was digitized using a touch-probe scanner. In addition, using 3D inspection software, the CDM was partitioned (into marginal, axis, angular, and occlusal regions), the CDM and CSM were overlapped, and a 3D analysis was conducted. A Kruskal–Wallis test (α = 0.05) was conducted with all-segmented teeth with the root mean square (RMS), and they were analyzed using the Mann–Whitney U-test and the Bonferroni correction method as a post hoc test. There was a significant difference in the trueness of the crowns according to the type of lithium disilicate block (p < 0.001). The overall RMS value was at a maximum for e.max (42.9 ± 4.4 µm), followed by HASS (30.1 ± 9.0 µm) and then VITA (27.3 ± 7.9 µm). However, there was no significant difference between HASS and VITA (p = 0.541). There were significant differences in all regions inside the crown (p < 0.001). There was a significantly high trueness in the angular region inside the crown (p < 0.001). A correction could thus be applied in the CAD process, considering the differences in the trueness by the type of lithium disilicate block. In addition, to attain a crown with an excellent fit, it is necessary to provide a larger setting space for the angular region during the CAD process.

Effects of Trueness and Surface Microhardness on the Fitness of Ceramic Crowns

“…When using dental CAD/CAM systems, it is important to evaluate the consistency between the designed crown and the fabricated crown [4,5,9,10]. Low consistency may affect the marginal and internal fit of a prosthesis [4,9,10].…”

“…When using dental CAD/CAM systems, it is important to evaluate the consistency between the designed crown and the fabricated crown [4,5,9,10]. Low consistency may affect the marginal and internal fit of a prosthesis [4,9,10]. Trueness indicates the similarity of the prosthesis designed first in CAD software (CAD reference model) with the fabricated prosthesis (CAD test model) [4,9,10].…”

“…Low consistency may affect the marginal and internal fit of a prosthesis [4,9,10]. Trueness indicates the similarity of the prosthesis designed first in CAD software (CAD reference model) with the fabricated prosthesis (CAD test model) [4,9,10]. A prosthesis exhibiting excellent trueness may offer the advantage of time for the patient to adjust to the prothesis [4,10].…”

“…Trueness indicates the similarity of the prosthesis designed first in CAD software (CAD reference model) with the fabricated prosthesis (CAD test model) [4,9,10]. A prosthesis exhibiting excellent trueness may offer the advantage of time for the patient to adjust to the prothesis [4,10]. The trueness of the fabricated crown may differ depending on the type of lithium disilicate block used due to the differences in processability [10].…”

“…A prosthesis exhibiting excellent trueness may offer the advantage of time for the patient to adjust to the prothesis [4,10]. The trueness of the fabricated crown may differ depending on the type of lithium disilicate block used due to the differences in processability [10]. However, few studies have investigated the correlation between the surface microhardness of the ceramic material and the trueness of the resulting crown.…”