PSI - Issue 42

Alla V. Balueva et al. / Procedia Structural Integrity 42 (2022) 9–17 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction In dental implants (Figure 1), titanium is often used due to its tensile strength, bioinertness, and low corrosivity, which, in turn, contributes to osseointegration or, the fusion of a foreign substance with bone and ability to oxidize under normal atmospheric conditions (meaning being in the presence of oxygen) [Tsygankov et. al., 2019]. It, however, is not without its pitfalls. Metal poisoning, allergic reactions, and metallosis are all side-effects that afflict titanium based dental implants. It is therefore a topic of interest to find ways to improve upon the flaws of titanium and coating a titanium sheet by calcium phosphate coatings is one solution to these problems. Calcium phosphate materials are similar in properties to the bone [Tsui et. al., 1998; Ou et. al., 2014], which promotes osseointegration between the titanium implant and the bone. It should be noted that implanted biomaterials should mimic the function and structure of the replaced biological material [Ou and Hosseinkhani (2014), Baheiraei et al. (2015)].

Fig. 1. General view of a dental implant screwed into the jaw. Calcium phosphates recently became the most attractive synthetic biomaterials for dental coatings, and the most common of them are hydroxyapatite (HAp) and tricalcium phosphate. In this research we will concentrate on tricalcium phosphate nano-coatings and investigate the adhesion strength of these coatings on the level of the chemical reactions between their components and titanium dioxide, modelling these reactions using Density Functional Theory (DFT) methods and calculations. 1.1. Tricalcium Phosphate Coatings Tricalcium phosphate, along with HAp, is the most common material used for a dental coating. Tricalcium phosphate, Ca 3 (PO 4 ) 2, in the same spirit of hydroxyapatite, is very osseointegrative. It provides sufficent adhesion to the titanium substrate and bonds well with bone. It was later found by Jalota et. al. (2006) that tricalcium phosphate has a higher solubility in water than hydroxyapatite does, making it more ideal than hydroxyapatite for dental coatings. Even though tricalcium phosphate coating assure good osseointegration between the bone and an implant, some cases of separation of Tricalcium phosphate coatings from titanium substrate were reported in medical practice and that is a reason for a possible implant failure. Therefore, it is important to have methods to evaluate adhesion strength of a tricalcium phosphate coating and titanium. Some experimental results are available in the literature [e.g., Baheiraei et. al., 2015; Suttin and Gubbi, 2007; Huang et. al., 2014]. In this paper, we suggest a method of evaluation of the surface binding energy between tricalcium phosphate nano-layer on titanium as a result of the chemical reaction, by Density Functional Theory. 1.2. Recent Computational Physical Chemistry Calculations of HAP and Ti While the experiments on adhesion properties of Calcium phosphates coatings on titanium are costly and complicated, the computational experiments are easier to carry out. Just only recently, with the formulation of Density Functional Theory and the development of high performance computers, it became possible to tackle the exploration of materials’ properties and their interactions on the ab initio level. In our case, the application of DFT and ab initio calculations are only possible due to the micro scale of tricalcium phosphate coating upon which we are working. For