Influence of finish line design on the marginal fit of nonprecious metal alloy coping fabricated by 3D printing, milling and casting using CAD/CAM

Abstract

Purpose: The purpose of this study was to examine the correlation between the finish line designs and the marginal adaptation of nonprecious metal alloy coping produced by different digital manufacturing methods. With this view, one master model with deep chamfer margin and another master model with rounded shoulder margin were fabricated and this study was aimed to compare the correlation depending on the three different manufacturing methods of selective laser sintering, milling and casting. Materials and methods: For fabrication of two master models with different finish lines, the master models were designed by 3-D designing software program based on the abutment preparation principle and titanium master models were milled by computer aided manufacturing. Nonprecious metal alloy copings were made respectively from each master model with three different methods

selective laser sintering (SLS), milling and casting by CAD/CAM. 12 copings were made by each method resulting in 72 copings in total. The marginal fit was evaluated by measuring the gap between the cavosurface margin of the abutment die and the edge of the crown margin on mesial, buccal, distal and lingual site of each specimen. The measurement was conducted at 40 determined reference points along the circumferential margin with the confocal laser scanning microscope at magnification x150. Results: Mean values of marginal gap of laser sintered copings were 11.8±7.4 μm for deep chamfer margin and 6.3±3.5 μm for rounded shoulder margin and the difference between them was statistically significant (p<.0001). Mean values of marginal gap of milled copings were 53.9±27.8 μm for deep chamfer margin and 48.6±30.1 μm for rounded shoulder margin and the difference between them was not significant (p=.279). Mean values of marginal gap of casted copings were 18.8±20.2μm for deep chamfer margin and 33±20.5 μm for rounded shoulder margin and the difference between them was significant (p=.0004). Meanwhile, the marginal fit depending on the manufacturing method was significantly different regardless of finish line design. Selective laser sintering group exhibited the best marginal adaptation among three manufacturing methods and digitalized casting group showed better marginal fit than milling group. Conclusion: Within the limitation of this study, the following conclusions were drawn. 1. The variation of finish line design influences the marginal fit of laser sintered metal coping and casted metal coping. 2. Laser sintered copings with rounded shoulder margin had better marginal fit than deep chamfer margin. 3. Casted copings with deep chamfer margin had better marginal fit than rounded shoulder margin. 4. No significant difference on the marginal fit was found between deep chamfer margin and rounded shoulder margin in milled metal coping. 5. According to the manufacturing method, SLS system showed the best marginal fit among three different methods. Casting and milling method followed that in order.