Thermal creep analysis of noble metal alloys for the ceramic-fused-to-metal technique

Abstract

Distortion of metal frameworks for the ceramic fused to metal technique during firing is attributed to thermal creep of the alloys. Usually thermal creep measurements are performed at constant load and constant temperature over varying time periods. Because metal frameworks for the ceramic-fused-to-metal technique are cyclically stressed, a three-point bending test for dynamic measurement of creep in a modified dilatometer was developed. Bending of 14 commercially available noble metal alloys was determined in the as-cast state, as well as after simulation of the firing process. The sag at 950 degrees C, which is the firing temperature of the ceramic, was chosen as an indicator for creep. No correlation of this value to other technical data of the alloys was observed, but it was found that sag correlates with the sum of the Au and Ag content of the alloys. A strong sag was observed with high (Au + Ag) content. The lowest sag values were found with a content in the range of 50 atom % (Au + Ag). At lower (Au + Ag) content Pd becomes the main component in the alloys, and the values for sag increased slightly. The method for dynamic measurement of creep gave reproducible results and offers a possible test for rapid qualitative creep assessment.

Effect of various intraoral repair systems on the shear bond strength of composite resin to zirconia

“…In the metal-ceramic restoration, for the close bonding of metals and porcelain, the CTE of metals is higher than that of veneering porcelain by approximately 0.5 × 10 -6 /℃ 16. Particularly, if the precious metals is used as a core, the difference of CTE may be compensated by the creep deformation caused by metal heat 17,18. However, the strength of zirconia core is very high and such creep deformation is absent.…”

“…As a general porcelain repair system is based on the bonding strength between porcelain and composite resin, in cases with the exposed zirconia core, the prognosis of the intraoral repair would be determined by the increase of the bonding strength of zirconia surface and composite resin. Generally, the methods that improve the bonding strength of porcelain to resin could be divided to mechanical bonding and chemical bonding 12,17. Methods that render roughness by using HF or phosphoric acid, sandblasting, or diamond burs may be considered as mechanical methods.…”

Flexural strength of veneering ceramics for zirconia

“…15 Especially, high-gold alloys show a low sag-resistance. 16 A zirconia substructure in contrast is rigid, which leads to higher stress formation. Hence, compared to metal-ceramics a higher flexural strength of the veneering ceramic is favorable to provide a high reliability of the veneer.…”

“…plastic flow, especially if a high gold alloy is used. 15,16 In all-ceramic systems, the ceramic framework is rigid and does not yield to the stress induced by a thermal mismatch to that extent. Therefore, the risk of destructive stress formed in the veneer layer might be higher in all-ceramic systems and thus would require a high mechanical strength for veneering materials for all-ceramic systems.…”

Metal‐Ceramic Alloys in Dentistry: A Review

“…5 The chief disadvantage of Pd-Co alloys is their tendency to form a dark oxide layer, 16 which can compromise porcelain esthetics. 23 In addition, it has been reported that Pd-Co alloys have lower porcelain bond strengths than do Pd-Cu alloys. 24…”