# Use of Hydrogels to Regulate Orthodontic Tooth Movement in Animal Models: A Systematic Review
## 4 Discussion  
Hydrogels are cross-linked three-dimensional hydrophilic polymeric networks [28] that have shown very good properties for drug loading; they are biocompatible and exhibit  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline  & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & \\  & **2020** & **2019** & **2019** & **2000** & **2018** & **2020** & **2020** & **2018** & **Total** \\  & [20] & [21] & [22] & [23] & [24] & [27] & [25] & [26] & \\ \hline
1. Title & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
2. Summary & 1 & 0 & 1 & 0 & 0 & 1 & 1 & 0 & 50\% \\ INTRODUCTION & & & & & & & & & \\
3. Background & 0 & 1 & 0 & 1 & 0 & 1 & 1 & 1 & 62.5\% \\
4. Objectives & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\ METHODS & & & & & & & & & \\
5. Statement of Ethics & 1 & 0 & 1 & 1 & 1 & 1 & 1 & 1 & 87.5\% \\
6. Procedures & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
7. Experimental animals & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
8. Housing and agriculture & 1 & 1 & 1 & 0 & 1 & 0 & 0 & 0 & 50\% \\
9. Sample Size & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
10. Assignment of animals to & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\ experimental groups & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
11. Experimental results & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
12. Statistical methods & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\ RESULTS & & & & & & & & \\
13. Reference data & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
14. Numbers analyzed & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
15. Results and estimation & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
16. Adverse events & 1 & 1 & 0 & 1 & 0 & 0 & 0 & 0 & 37.5\% \\ DISCUSSION & & & & & & & & \\
17. Interpretation/scientific & & & & & & & & & \\ implications & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
18. Generalization/Translation & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 100\% \\
19. Financing & 1 & 1 & 1 & 1 & 0 & 0 & 0 & 0 & 50\% \\ \hline \end{tabular}  
* Percentages of the evaluation of the quality of the studies. The number 1 indicates that the study meets the evaluation criterion and 0 indicates the absence of the evaluated criterion.  
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Table 4: Quality assessment of included studies. ARRIVE criteria.  
Figure 2: Risk-of-bias summary for each of the included studies (\(n=8\)). The green color indicates low risk of bias; the yellow color indicates an unclear risk of bias, and the red color indicates high risk of bias.  
swelling properties in aqueous media [29], making them a good option for use as smart carriers of active substances [11; 30].  
Of the eight studies included in this review, three of the studies sought to accelerate orthodontic tooth movement [21; 22; 23], while the other five studies evaluated the ability to inhibit orthodontic tooth movement after treatment had been completed, i.e., during the retention phase [20; 24; 25; 26; 27]. We observed a great diversity in the composition of the eight hydrogels used in the included studies: gelatin-based [20; 24; 25; 26; 27], chitosan hydrogel [20], polyethylene glycol-polycaprolactone-polyethylene glycol [21], hydroxyethylcellulose [22] and methylcellulose [23]. The active ingredients released by the hydrogels were equally diverse: (a) carbonated hydroxyapatite [24; 25], (b) curcumin [20], (c) sclerostin [21], (d) a formulation of RANKL [22], (e) Risedronate bisphosphonate [27], (f) epigallocatechin [26] and (g) parathyroid hormone [23].  
The biological effects of the drugs used in the articles included in this review are among the most important aspects to consider; although they have previously demonstrated their influence on the OTM, for the purposes of this review their effectiveness is contrasted based on how favorable their release was as a consequence of the physicochemical properties of the hydrogel synthesis materials, which is why the influence of the material on drug release will be discussed first.