Hyalinization during orthodontic tooth movement: a systematic review on tissue reactions

The purpose of this study was to perform a meta-analysis on the literature concerning hyalinization in relation to experimental tooth movement in animals and humans. A structured search of electronic databases as well as hand searching retrieved 70 publications concerning the subject. After application of inclusion and exclusion criteria, 39 studies remained, of which three were in humans. Articles on animal experiments were in the majority with most studies performed in rats. Among other data force magnitude, type of tooth movement, duration of the experimental period, and moment of first and last appearance of hyalinization were extracted from the included studies. The heterogeneity of the published studies and the limited data on appearance of hyalinization made it impossible to perform a meta-analysis. Therefore, the literature was systematically reviewed. It appears that there are no major differences in tissue reaction between species during experimental tooth movement. Although hyalinization is considered to be an undesirable side-effect of orthodontic tooth movement, little attention has been paid to the phenomenon itself and its possible relationship with stress/strain levels in the periodontal ligament (PDL) and alveolar bone or the rate after the initial phase of tooth movement. There is a need for well-designed experimental studies to elucidate the role of hyalinization in orthodontic tooth movement.