## 1 Introduction  
The possibility of bonding brackets was an important step in fixed orthodontics, resulting in the shortening of working time for the orthodontist, better hygiene and fewer dental and periodontal pathological conditions after wearing the appliances, better aesthetics and the elimination of the working phase in which the interdental spaces were closed after detaching the bands [1]. The bond strength between the brackets and the tooth enamel is an extremely important issue in performing the mechanics of orthodontic treatment; the brackets' detachments cause a series of inconveniences, the reattachment being a difficult, unpleasant maneuver, besides the fact that the detachment of the brackets can cause delays of the treatment results and mechanical injuries of the neighboring soft tissues of the oral cavity [1, 2]. From a chemical point of view, adhesion is the gluing of two materials that can be different by means of a chemical compound called adhesive or bonding. The difference from physical adhesion is that chemical groups which appear on both surfaces can form an intramolecular or intermolecular chemical bond. Chemical adhesion involves a chemo-absorption process in which the adhesive molecules attached by adsorption to the surface of the material can react with its active groups by forming chemical bonds [3]. In our case, the purpose of adhesion is to join the enamel surface with another substrate, represented by the materials used for bonding the brackets. The tooth enamel is the hardest tissue of the body due to its hyperineralization. Its hardness varies depending on the dental area in which the tooth is positioned; in areas with intense functional stress, it can reach 5 degrees of hardness on the Mohs scale. The tooth enamel does not retain water, being consequently easy to wash and dry [4]. Many orthodontists are accustomed to using composite resins for bonding brackets, even if those adhesive systems have high technical sensitivity because they require a completely dry surface throughout the application procedures. The number of clinical steps and the long application time require the patient's cooperation and the focus of the doctor to eliminate the possible technical errors [5]. [PERSON] et al. [6] showed that Transbond Plus Color Change Adhesive (3M Unitek, Monrovia, CA, USA) is an improved resin that has ionized glass particles in its composition; this adhesive is described by the manufacturer as having excellent adhesion with metal and ceramic brackets. TPCC has been described as having hydrophilic properties. Because of the chemical composition of ionized particles, Transbond Plus Color Change is an adhesive that slowly releases fluoride, which results in the reduction in enamel demineralization around the brackets' bases [7]. Its pink-colored component is activated by light-curing or by exposing it to the natural light, and during the polymerization, the initial pink color changes and turns irreversibly into a shade similar to that of the tooth enamel. The color change restores the aesthetic appearance of the bonding agent during the treatment. The initial pink color helps the doctor to remove excessive bonding material from the tooth surface before light-curing [6; 8]. Excess adhesive may cause food retention, dental plaque and injuries of the superficial periodontium or the oral mucosa. Bacterial plaque with a large variety of microbial strains and food debris may produce inflammation and infection of the periodontal tissues and demineralization of the tooth enamel, especially in the cervical region of the vestibular surfaces, above the upper edge of the brackets' bases [8]. These great advantages of bonding procedures and the entire orthodontic treatment are important reasons why the use of TPCC is preferred by many orthodontists.