Functional Coatings for Orthodontic Archwires-A Review

Abstract

In this literature review, the current state-of-art of coatings for orthodontic archwires' increasing antimicrobial and relevant mechanical properties, such as surface topography, friction or corrosion resistance, has been presented. There is a growing request for orthodontic appliances, therefore, most researchers focus on innovative functional coatings to cover orthodontic archwires and brackets. Orthodontic appliances are exposed to the unfavorable oral cavity environment, consisting of saliva flow, food, temperature and appliance force. As a consequence, friction or biocorrosion processes may occur. This can affect the functionality of the orthodontic elements, causing changes in their microstructure, surface topography and mechanical properties. Furthermore, the material which the orthodontic archwire is made from is of particular importance in terms of the possible corrosion resistance. This is especially important for patients who are hypersensitive to metals, for example, nickel, which causes allergic reactions. In the literature, there are some studies, carried out in vitro and in vivo, mostly examining the antibacterial, antiadherent, mechanical and roughness properties of functional coatings. They are clinically acceptable but still some properties have to be studied and be developed for better results. In this paper the influence of additives such as nanoparticles of silver and nitrogen-doped TiO₂ applied on orthodontic brackets by different methods on the antimicrobial properties was analyzed. Future improvement of coating techniques as well as modification of the archwire composition can reduce the release of nickel ions and eliminate friction and bacterial adhesion problems, thus accelerating treatment time.

Keywords: antiadherent; antimicrobial; archwire; coating; orthodontics; surface modified.

Figure 1

Classification of thin film coating techniques [34].

Figure 2

PVD Processing Techniques including categories of vacuum evaporation (a), sputter deposition in a plasma environment (b,c) and in a vacuum (d), ion planting in a plasma environment with a thermal evaporation source (e), with a sputtering source (f) and with an arc vaporization source (g) and ion-assisted deposition (IBAD) (h) [35].

Figure 3

Schematic diagram of a chemical vapor deposition (CVD) system [44].

Figure 4

Stages of the sol-gel process [56].

Figure 5

Scanning electron microscopy analysis of Streptococcus mutans and Porphyromonas gingivalis [11].

Figure 6

Antibacterial effect of TiO₂ thin film with 1–5 coating layers against Lactobacillus acidophilus and Candida albicans [69].

Figure 7

Three-point bending test—scheme; A: thermal screen, B: indenter, C: wire sample, D: supporting points, E: temperature sensor, F: hot-air circulation temperature controller [106,107].

Figure 8

The archwire position in the brackets slot: an initial position (A), maximum wire displacement and contact points—greatest abrasive wear areas (B) [111].

Figure 9

Potentiodynamic polarization curves of CAW, TiO₂ coat-CAW and N-TiO₂ coated CAW [15].