###### Abstract  
Periodontal patients may face orthodontic problems because of bone support loss, such as maxillary incisor proclination, spacing, rotation, extrusion, pathologic tooth migration (PTM) or traumatic occlusion. Orthodontic treatment is therefore an element within the comprehensive treatment of periodontitis after the periodontal condition has stabilized. The presence of fixed appliances (FAs) promotes the accumulation of bacterial biofilm and impedes hygiene procedures. The increasing popularity of clear aligner (CA) treatment is due to the convenience of use, less discomfort, better esthetics, easier hygiene, lower failure rate, and shorter, less frequent visits. Therefore, the question arises whether treatment with aligners is a good solution for periodontal patients. To answer this question, the PubMed/Medline, Cochrane Library and EMBASE databases were searched using the following keywords: periodontitis, orthodontic treatment, clear aligners, multibracket orthodontic appliances, fixed appliance, root resorption, gingival recession and pathologic tooth migration. The search strategy identified 18 relevant studies. A total of 1090 participants took part in the analyzed studies. The available literature was analyzed in terms of the occurrence of root apex resorption, the possibility of treating pathologic tooth migration, the occurrence of gingival recession, periodontal health status and occlusal stability in patients treated with CAs and FAs. Despite statistically significant differences in terms of Plaque Index (PI), probing depth (PD), apical root resorption and gingival recession favor the use of CAs. However, these values are mostly of no clinical significance. It is possible to treat PTM with CAs, but it is limited by the high degree of tooth mobility and incisor inclination. Obtaining perfect occlusion is comparably difficult in both CA and FA treatment. When planning orthodontic treatment in patients with reduced periodontitis, the use of both CAs and FAs should be considered. The choice of method would ultimately depend on the patient's dental condition. periodontitis; orthodontic treatment; clear aligners; fixed appliances; pathologic tooth migration +
Footnote †: journal: Medical  
and occlusal trauma with concomitant inflammation contribute to further loss of bone support, and hence, orthodontic treatment may be recommended, not only to improve dental esthetics but also to maintain periodontal health and function [3]. Orthodontic treatment performed in periodontal patients affects their quality of life by improving the functions of the stomatognathic system, which translates into improved chewing function, smile symmetry, its esthetics, oral health and improved well-being [4]. The conditions necessary for the safe orthodontic treatment of periodontal patients are the absence of subgingival biofilm [5], previously performed periodontal treatment--both non-surgical and surgical phases--a stable periodontal condition with pockets \(\leq\) 4 mm and no bleeding on probing (BOP) [3]. In these cases, orthodontic treatment allows for further shallowing of the pockets, reduction in attachment loss and vertical and horizontal bone defects, as well as reduction in tooth mobility [5]. Periodontal health during orthodontic treatment depends on many factors: the immune system, systemic diseases, smoking, gingival phenotype, bone morphotype, the amount and qualitative composition of dental biofilm and, above all, the patient's oral hygiene regimen [6]. It is acknowledged that the presence of fixed appliances (FAs) promotes the accumulation of bacterial biofilm and impedes hygiene procedures. Also, the mere presence of dental appliances changes the amount and composition of the bacterial biofilm [6; 7].