**3.8. Biocompatibility**

As mentioned above, monocrystalline brackets have more optical clarity than polycrystalline brackets (**Figure 4**). Whether this difference is of essential importance from an esthetic point

Apart from esthetics, the optical properties of ceramic brackets have been shown to affect the amount of light transmitted through these brackets during photocuring. The amount of light transmitted through ceramic brackets affects the curing efficiency of the light-cured adhesive. Polycrystalline brackets and polycrystalline brackets with a polymer mesh base were found to block direct light transmittance to a greater extent than monocrystalline brackets. It was pointed out that the color-coded holders designed for identification and handling of ceramic brackets also hinder light transmittance. The use of clear holders with colored edges has been

The color stability of ceramic brackets throughout orthodontic treatment is an important characteristic. It has been stated that ceramic brackets, both monocrystalline and polycrystalline, undergo a color change when subjected to coffee, black tea, coke, and red wine [21, 23, 24]. It has to be pointed out that these are in vitro findings. In vivo studies concerning the color

Limited information is available about which bracket material (ceramic versus metal brackets) is less prone to the adhesion of bacteria and plaque accumulation. A clinical study performed by Lindel et al. [25] concluded that ceramic brackets exhibit less long-term biofilm accumulation than metal brackets. It was emphasized that future research should aim to determine whether the difference in biofilm accumulation between ceramic and metal brackets has a clinically significant effect on the development of decalcifications. Lindel et al. [25] pointed out that the results obtained from this type of future research might have a strong effect when

choosing bracket material in patients with insufficient oral hygiene habits.

**Figure 4.** Intraoral image of monocrystalline (A) and polycrystalline (B) ceramic brackets.

of view is a decision to be made by the orthodontist as well as the patient [2].

suggested [22].

**3.6. Color stability**

10 Current Approaches in Orthodontics

**3.7. Plaque accumulation**

stability of ceramic brackets are lacking.

Biocompatibility is the ability of a material to provide successful service in a host while causing minimal response [9]. It has been stated that conventional ceramic brackets are chemically stable (inert) in the oral environment and that they exhibit excellent biocompatibility with oral tissues [5].

In 2012, Retamoso et al. [26] carried out an in vitro cytotoxicity study evaluating various orthodontic brackets. These researchers reported that monocrystalline ceramic brackets had good biocompatibility. On the other hand, polycrystalline ceramic brackets with metal slots demonstrated some toxic effects. It was pointed out that the metallic slot was the essential factor responsible for a decrease of cell viability due to nickel ion release. They [26] concluded that it is essential to continue with studies evaluating cytotoxicity. If toxicity of any material is proven, alternative materials have to be used.
