Relapse revisited-Animal studies and its translational application to the orthodontic office

Real orthodontic relapse is only a minor component of the changes that take place after orthodontic treatment. Continued facial growth and aging play a major role in the process. The biological basis of dental relapse after treatment is still not very well understood. Most studies on this topic are descriptive, suggesting that collageneous fibers in the supporting tissues of the teeth are involved in the etiology of relapse. This has led to the hypothesis that retention is needed until these structures are completely reorganized. However, there is considerable evidence that collagen turnover in the PDL is extremely fast, and that the gingival and transseptal fibers remodel only slightly slower. Therefore, it is concluded that stresses and strains evoked by collagen fibers are probably not the most important factor in the etiology of dental relapse, and that other extracellular matrix components may contribute significantly to the process. There is an urgent need for well-designed experimental and clinical studies to elucidate the etiology of relapse. Only then it will be possible to design evidence-based retention protocols.