PSI - Issue 42

Tsanka Dikova et al. / Procedia Structural Integrity 42 (2022) 1520–1528 8 Tsanka Dikova, Angel Anchev, Vladimir Dunchev, Dzhendo Dzhendov, Yavor Gagov / Structural Integrity Procedia 00 (2019) 000 – 000

1527

should be used, which are fired at temperatures below 882 °C, because at this temperature phase transformations occur in the pure titanium (Haag and Nilner (2010), Antanasova et al. (2018)). The bonding agents, developed for titanium and its alloys, have firing temperatures between 795-830 o C (Chakmakchi et al. (2009), Zinelis et al. (2010)). The layer thickness of different bonding agents varies depending on their viscosity and shrinkage during firing. The excessive thickness and composition of the bonding agent can affect the adhesion between the metal and the ceramic (Al Hussaini and Al Wazzan (2005). It is found that the weakest bond occurs in layer thickness of the bonding agent between 30- 40 μm. The highest adhesion strength obtained in the combined treatment of the surfaces of cast pure titanium and Ti6Al4V alloy made by milling and SLM can be explained by the better wetting of the sandblasted bond treated surface (Al Hussaini and Al Wazzan (2005), Antanasova et al. (2020)). The bonding agent, used in our experiment, is developed to reduce the difference between the coefficients of thermal expansion of titanium alloy and feldspar ceramic. It is applied in an even layer on the surface of the samples and fired at temperature of 960 °C according to the manufacturer's instructions. Four layers of leucite-reinforced glass ceramic are successively applied onto it and fired at temperatures between 800-750 o C. Most probably, at these lower temperatures, good adhesion between the bonding agent and the first opaque layer cannot be established, resulting in lower adhesion of the ceramic to the metal substructure. In order to confirm these assumptions, it is necessary to perform more detailed studies of the fracture mechanism of the porcelain coating from the metal substrate. 5. Conclusion Experimental study of the adhesion strength of dental ceramic to Ti6Al4V alloy, fabricated by milling and selective laser melting, is carried out in the present paper. It is found that the adhesion strength of the porcelain coating to the titanium alloy produced by both methods has close values: 17.63 – 30.89 MPa for the milled and 22.12 – 31.04 MPa for the SLM alloy. Milled samples treated with the given bonding agent, and SLM specimens with combined surface treatment do not meet the required 25 MPa of the standard. The surface treatments of the metal substrate have a different effect on the adhesion strength. Sandblasting and combined treatment increase the adhesion strength of the porcelain to the milled samples, but decrease it in the SLM ones. The application of the given bonding agent decreases the adhesion strength of the ceramic to the Ti6Al4V alloy produced by both technologies. In the milled alloy, the highest adhesion strength is in the sandblasted samples, followed by these with combined treatment, the control group and the application of bonding agent. In the SLM samples, the adhesion strength in the control group is the highest, followed by the sandblasted samples, treated with bonding agent and combined processing. In order to establish the influence of different surface treatments on the adhesion strength of dental ceramic to Ti6Al4V alloy fabricated by different technologies, it is necessary to carry out additional studies on the fracture mechanism of the coating. Acknowledgements The authors express their gratitude to: 1) Desislava Vlasakieva and Miroslav Simeonov from 3D MEDICAL PRINT (Pleven, Bulgaria), who produced the samples by SLM and provided them free of charge for the purposes of this study; 2) Plamen Atanasov and the team of dental laboratory "SMTL-Plamen Atanasov EOOD" (Varna, Bulgaria) for the active free assistance in discussing the experiment and processing the samples. References Al Hussaini, I. and Al Wazzan, K.A., 2005. Effect of surface treatment on bond strength of low-fusing porcelain to commercially pure titanium. The Journal of prosthetic dentistry, 94(4), 350-356. Antanasova, M., Kocjan, A., Abram, A., Kovač, J. and Jevnikar, P., 2021. Pre -oxidation of selective-laser-melted titanium dental alloy: effects on surface characteristics and porcelain bonding. Journal of Adhesion Science and Technology, 35(19), 2094-2109. Antanasova, M., Kocjan, A., Hočevar, M. and Jevnikar, P., 2020. Influence of surface airborne -particle abrasion and bonding agent application on porcelain bonding to titanium dental alloys fabricated by milling and by selective laser melting. The Journal of prosthetic dentistry, 123(3), 491-499. Antanasova, M., Kocjan, A., Kovač, J., Žužek, B. and Jevnikar, P., 2018. Influence of thermo -mechanical cycling on porcelain bonding to cobalt –