Decalcification is an important effect of orthodontic therapy on tooth enamel as orthodontic accessories and their bonding materials create retentive areas around them for bacterial biofilm accumulation . This allied to poor oral hygiene habits and leads to the formation of white stain lesions and marginal gingivitis adjacent to fixed orthodontic appliances [1, 13].
With the intention of minimizing and preventing white spot lesions, there is awareness about the use of new fluoride-releasing materials .
Glass ionomer cements were developed with the aim of uniting biological and chemical properties in one and the same material. In addition to promoting fixation to the tooth surface, they release and are recharged with fluoride, thereby reducing white stain lesions around brackets [6, 14–16].
However, the GICs have lower bond strength to the enamel surface in comparison with orthodontic composites. With the intention of associating important characteristics of the two materials, such as shear bond strength and fluoride release, resin modified glass ionomer cements were developed, which release fluoride without compromising the bond strength to the tooth surface .
The bond strength between orthodontic accessories and enamel may be compromised by the presence of the acquired pellicle at the time when they are being bonded [17–20]. It is well known because it is a biologically important integument on the tooth surface as it constitutes the interface between the enamel surface and the first layer of oral biofilm. It is recognized that at a functional level, it plays a role in mineral homeostasis of tooth enamel. There is ample evidence that this structure is formed by selective adsorption of proteins, peptides, and other molecules present in oral fluid [18, 20]. Therefore, it is of fundamental importance to remove the acquired pellicle by deproteinizing it before performing orthodontic bracket bonding.
With the purpose of eliminating the influence of the organic matrix on the adhesion of composites to the enamel surface, Justus  suggested the use of 5.25% NaOCl for 60 s, and Pithon suggested the use of 10% papain for 60 s as deproteinizing agent before etching with 37% phosphoric acid, showing good results.
The aim of the present study was to verify the hypothesis that deproteinization of the enamel surface with 2%, 4%, 6%, 8%, and 10% papain gel for 60 s increases the shear bond strength of brackets bonded with RMGIC.
Deproteinization performed with papain gel removes the acquired pellicle, which persists after prophylaxis, from the tooth surface .
The gel at concentrations of 2%, 4%, 6%, 8%, and 10% is obtained from an alkaloid enzyme, papain, extracted from the papaya fruit (Carica papaya). It is extracted from the latex in the leaves and skin of the mature fruit. In addition to the proteolytic action, it has antibacterial and anti-inflammatory properties, thus acts as remover of necrotic remainders, and is not cytotoxic [11, 21, 22].
Papacárie® is papain presented in gel form and differs from that used in the present study. It is not formulated from pure papain but is made up of chloramine - a compound of chlorine and ammonia used for root canal irrigation and toluidine blue dye - photosensitizer with antimicrobial properties, and papain . In this study, the gel was used because in this presentation, it is easy to manipulate. In this study, it was perceived that in concentrations of up to 6%, in groups 2, 3, and 4, papain gel showed no statistical differences from the control group, and its use in these concentrations is not clinically relevant, considering that its use adds a clinical step without any real gain in bond strength.
Deproteinization is a prudent step to include when using RMGIC as there is an improvement in marginal sealing at the base of the accessory with the enamel surface, in addition to the formation of white stain lesions being minimized with the use of RMGIC .
The enamel surface etched with 37% phosphoric acid after eliminating the organic elements from it probably produces more tags that penetrate into the enamel. These lead to a significant increase in mechanical retention of adhesives to enamel, particularly RMGICs, as demonstrated in the present study .
The use of papain as deproteinizing agent increases the shear bond strength irrespective of the etching agent .
When comparing the mean shear bond strength values presented by the groups (3, 4, 5, and 6), with the values suggested by Reynolds , these are adequate for the majority of procedures performed in orthodontics (between 5.9 and 7.8 MPa).
Apart from the groups already mentioned, papain gel was also tested at concentrations of 8% and 10%. These obtained better results in comparison with the other groups and presented no statistical differences between them. Thus, the concentrations of 8% and 10% increased the RMGIC bond to the enamel surface, adding another favorable characteristic to this material when one thinks of using it for bonding orthodontic accessories, a result that corroborates Pithon's findings .
As regards the ARI, the control group presented statistical differences from the other groups (2, 3, 4, 5, and 6), and these showed no statistical differences among them. This result is clinically relevant considering that papain gel at all tested concentrations increased the RMGIC bond to tooth enamel and also avoided damage to enamel when the accessories were debonded.
The results presented here are given preliminaries that were coming from an in vitro study. In vivo studies should be performed in order to confirm our findings.
The results presented here are preliminaries given that were coming from an in vitro study. In vivo studies should be performed in order to confirm our findings.