International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The purpose of the present paper is to evaluate the geometric accuracy and surface roughness of polymeric samples manufactured by Digital Light Projection (DLP) Stereolithography. The standard cubic samples with dimensions 5 mm х 5 mm х 5 mm were printed of two polymers: NextDent C+B (white-yellowish color A3.5, VITA shade guide) and NextDent Cast (dark-red color), in two ways of placement to the base – horizontally and inclined at 45^о. The samples were printed with two different layer’s thickness – 35 μm and 50μm. It was established that the samples of both polymers, manufactured in horizontal position with the lower layer’s thickness (35μm) possess highest dimensional accuracy and lowest interval of deviation. The most accurate are the dimesons parallel to the basis, while these, parallel or inclined to the print direction, have the highest deviations. The interval of the deviations of the dimensions of samples, manufactured inclined at 45^o, is nearly 2-3 times higher, as the interval of the samples, made of NextDent Cast, is more than 50% higher than that of NextDent C+B. The horizontally printed samples have 1.5-2 times lower surface roughness compared to the samples, printed inclined at 45^o. The surface roughness of the samples, made of NextDent Cast, is 30-50% higher than that of NextDent C+B independently of the layer’s thickness. The increase of the thickness from 35 μm to 50μm leads to 1.5-2 times higher surface roughness in the two samples’ positions. The optical properties of both polymers in the research strongly influence the geometric characteristics, dimensional accuracy and surface roughness of the objects, manufactured by DLP stereolithography.

Cobalt-chromium based alloys are widely used in dental applications due to their excellent mechanical properties, high corrosion resistance and good biocompatibility. Although they are generally fabricated by casting for dental restorations, recently selective laser melting (SLM) has become an attractive production method since it allows complex geometries. Recent studies revealed that Co-Cr alloys formed by SLM, provided better corrosion resistance as well.

In this study, tribo-corrosion behavior of a Co-Cr-Mo alloy produced by casting (Biosil-Degudent) was compared with the one (Co212-f ASTM F75) produced by SLM. The wear properties were investigated by tribo-corrosion tests in a Fusayama-Meyer artificial saliva solution using a “ball-on-disc” type tribometer. Polished surfaces were tested against zirconia balls at the same sliding speed, distance and load. Friction coefficient values were determined and the worn surfaces were evaluated using microscopes to compare the wear and tribo- corrosion resistance through wear tracks. SLM proved to be a promising manufacturing method for dental applications.

The aim of the present paper is to investigate the mechanical properties (hardness and tensile strength) of dental Co-Cr alloys fabricated via casting and selective laser melting (SLM). Two groups of metallic specimens (four-part dental bridges and standard tensile test specimens) made of Co–Cr dental alloys were produced by lost-wax casting and SLM processes. Vickers hardness distribution along the depth of the dental bridges as well as the Rockwell hardness and tensile strength of the samples were studied out. The hardness of Co–Cr dental alloys are dependent on the manufacturing technique employed. It was established that the average Vickers hardness of the samples, produced by SLM, was higher than that of the cast samples 382 HV and 335 HV respectively. The nearly even hardness distribution in the bridges, produced by SLM, and fluctuations of the hardness values along the depth of the cast bridges were observed. The Rockwell measurements confirmed the higher hardness of the SLM samples – 39 HRC in comparison with that of the cast ones – 33 HRC. The tensile strength is in good agreement with the hardness values. Due to the unique microstructure, the yield strength and tensile strength for the SLM samples were higher than those of the as-cast alloy.