The co-cr alloys and their use in the construction of removable partial dentures frameworks

Abstract

Cobalt-chromium alloys are used for the framework fabrication of double-crown, precision-attachment, conventional-clasp – retained, and combined, removable partial dentures. Although some literature data are referred to all types, this dissertation focuses on the third-type, alloys investigation and its comparison with other materials. Frameworks can be fabricated by conventional-casting (C-CST), indirect (I-3DP) and direct (D-3DP) 3d printing patterns [wax/polymeric followed by casting, cobalt-chromium (laser melting/sintering), respectively]. Differences in chemical composition (elements, their role, deviation probability from manufacturer data) are examined. I-3DP creates, microstructure, mechanical properties and good castability, typical for C-CST, dimensional- and adjustment- accuracy higher and ranging from lower to higher respectively. Contrary to cast, D-3DP alloys exhibit, more homogeneous, fine, and defect-tolerant microstructure which defines higher mechanical properties (hardness, strength, ductility), precision, dimensional-accuracy, retentive force stability, biocompatibility, corrosion resistance, patient satisfaction, and other process-dependent benefits, but also higher residual-stresses, adjustment-inaccuracies, and present anisotropy in mechanical properties especially in the fatigue life. D-3DP surface roughness comparing to, C-CST is higher, D-3DP is lower, while differences exist in surface – morphology, structure, elemental ratio and distribution. Basic parameters, in casting (investment, cooling method/rate, melting/casting method/temperature, remelting-recasting) and in D-3DP (powder, build-orientation, support-structures, device-process, device-type), with heat-treatment (necessary only in D-3DP) and final-processing (treatments for cast-resin bond strength, finishing/polishing), improve all the aforementioned when done correctly. Clasps have been also fabricated by wrought wire bending (mainly in the past), hybrid-manufacturing and hard-milling. Despite the limited existing studies, compared to casting and D-3DP, the last two methods exhibit the highest –surface smoothness, retentive forces stability, dimensional-accuracy but lower fitness, and –fitness, respectively. Many materials e.g., platinum, nickel-chromium, stainless steel, Pd- and Ag- based alloys, gold, titanium and their alloys, polymethyl-methacrylate, glass-fiber-reinforced – thermoplastic-polymers and composites, flexible thermoplastic resins, high performance polymers and zirconia, have been compared to cobalt-chromium alloy. Each one has benefits and disadvantages.