## 4 Discussions
There was no significant difference after etching between the group of teeth moistened with water and the dry enamel group. The very similar results not as absolute values but as differences between the studied groups could be explained by the fact that these authors used acid etching and subsequent contamination with distilled water and saliva in ways similar to our research [18]. Their study demonstrated that saliva prevents micromechanical bonding between Fuji Ortho LC and tooth enamel to a great extent in the etched groups because of deposition of salivary constituents [18]; this must be the reason why we also found the lowest adhesion in the group where the contamination after etching was done with saliva. Other studies, such as that of [PERSON] et al. [27], demonstrated that \"etching the tooth surface with phosphoric acid produced a significantly poorer bond to the enamel\" [27]. [PERSON] and [PERSON] have demonstrated that Fuji Ortho LC bonded without any enamel conditioning gives a significantly lower shear bond strength compared with that made by glass ionomer cement on enamel etched with 37% phosphoric acid [16; 28]. Using acid etching creates a layer of porous enamel that ranges in depth from 5 to 50 \(\upmu\)m [29], which is more suitable to achieve a stronger micromechanical adhesion by increasing the accessible areas for bonding. The acid application eliminates the organic biofilm and increases the enamel surface's free energy [30]. It is well known that the adhesion of glass ionomer cements to enamel is also one of a chemical nature [16; 18]. [PERSON] et al. [31] found that in the case of using stainless steel lingual brackets, Fuji Ortho LC had a significantly higher bond strength after application on saliva-moistened enamel, after enamel conditioning with polyacrylic acid, when compared to all other tested enamel conditions: nonetched and dry, nonetched and wet, etched with polyacrylic acid and water-moistened. The hydrophilic monomer HEMA (2-hydroxy ethyl methacrylate) which is a main component of Fuji Ortho LC, may be responsible for infiltration and hydration [18]. Many studies have been done to compare the bond strengths of glass ionomer cements and composite resins [32; 33; 34]. [PERSON] et al. [32] showed that the bond strength of the composite resin was better than that of glass ionomer, and the adhesion given by both bonding materials decreased after contamination with blood. [PERSON] and [PERSON] [33; 34] also demonstrated that Transbond XT had a better shear bond strength than Fuji Ortho LC. In our study, we found no significant differences between the two bonding systems on dry enamel and enamel moistened with saliva. The difference between the two bonding systems was statistically significant in their application on water-moistened enamel; Fuji Ortho LC exhibited better shear bond strength. The laboratory conditions may greatly differ from those in vivo; the debonding forces may act in different directions. Moreover, water and saliva contamination varies in quantity and cannot be controlled as finely as in our study. It would be useful to test other parameters that reflect the adhesion of the brackets, such as the tensile bond strength [35].