Residual sand particles as a cause of chipping of ceramic cladding

Abstract

Despite the fact that the clinical and technological stages of prosthetics with porcelaine fused to metal constructions are deeply grounded with long-term results of their use, complications arise during the operation of these constructions that require their repair or replacement. First of all, this applies to the chipping of ceramic cladding, which are associated with both errors in clinical planning and violations of the laboratory stages of their manufacture, including adhesion of ceramics and metal. The aim was to study the surface of cast alloy samples for the content of sand particles after sandblasting.
Materials and methods.
Experimental studies of the surface of cast cobalt-chromium alloy samples with a scanning electron microscope at various magnifications were carried out, the roughness parameters after sandblasting with a diameter of 250 μm, 50 μm and a dental milling cutter were studied.
Results.
Microscopic analysis of the surface after processing samples with sand with a diameter of 250 μm showed the absence of contamination, the formation of a three-dimensional structure of the surface with ledges and holes. At 1000 magnification, electrocorundum residues ranging in size from 0.5 to 3 μm were observed, at 5000 magnification, contamination with a size less than 1 μm, and at 20,000 magnification, foreign inclusions with an average size of 100 nm. After processing with a milling cutter, a clean surface from foreign inclusions was revealed, the presence of micro-grooves from 1.0 microns to 10 microns. However, with this type of processing, the minimum roughness parameters are achieved: Ra=0.8 μm, Rz=1 μm. When sandblasting with a size of 50 μm, roughness parameters Ra=1.498 μm, Rz=7.237 μm are achieved, microscopic examination shows the formation of a characteristic locally scratched three-dimensional structure. At 20,000 magnification, foreign inclusions with an average size of 200 nm are observed.
Conclusion.
The presence of large holes and ledges during sandblasting with a size of 250 μm under cyclic dynamic load due to transverse compression will lead to different longitudinal stretching. Milling prevents the occurrence of future stress concentrators, however, the specific surface area is three times smaller, which greatly affects the amount of adhesion of ceramics with a metal frame. When sandblasting with an abrasive of 50 μm, sand particles with a size of 150—300 nm remain on the metal surface, large-range particles are also observed in places, imprinted into the metal, and which are quite difficult to remove by existing methods.