# The Impact of Orthodontic Treatment on Pre-Existing Gingival Recessions: A Retrospective Study
## 1 Introduction  
Gingival recession (GR) is defined as the apical shift of the gingival margin with respect to the cement-enamel junction. It is also associated with attachment loss and exposure of the root surface to the oral environment [1, 2]. The consequences of GR include tooth sensitivity, root caries, hypermobility of the affected tooth and poor aesthetics [3, 4]. Several GR classifications are available in the literature, with [PERSON]'s four categories of GR being the most widely used in orthodontics: Class I, where marginal tissue recession does not extend to the mucogingival junction (MGJ); Class II, where marginal tissue recession extends to or beyond the MGJ, but with no interdental periodontal attachment loss; Class III, where marginal tissue recession extends to or beyond the MGJ, with interdental bone or soft tissue loss or malpositioning of teeth, and, finally, Class IV, where marginal tissue recession extends to or beyond MGJ, with severe interdental bone or soft tissue loss and/or severe malpositioning of teeth [5]. In 2018 a new classification was introduced, in which GR is described by three categories based upon the interdental clinical attachment loss and predictability of root coverage outcomes [4, 6]. Literature about the prevalence of different extent of GR is scarce, but GR of Miller class III and IV with interdental attachment loss is usually associated with the inflammatory periodontal disease and therefore is often not included in orthodontic research of periodontally healthy subjects [7]. The overall prevalence of GR affecting at least one tooth ranges from 11% to 90% in the adult population, being more frequent in adults aged 50 years and above [8, 9, 10]. The severity of GR has been observed to increase with age [8, 11]. GR is more prevalent on vestibular surfaces and in mandibular teeth [9]. It is usually observed on one orseveral teeth; however, GR can be more widespread when the gingiva of multiple teeth is affected [12]. Although the pathogenesis of gingival recession remains unclear, there are several predisposing and precipitating factors, e.g., coronally attached fronulum and muscles, absence of attached gingiva, abnormal tooth position, overhanging restorations, proclination of teeth, thin mandibular alveolar bone, fenestration, dehiscence or mechanical trauma [2,13]. It has been observed that GRs greater than 3 mm are associated with facially aligned roots extending beyond the alveolar bony envelope [14]. As labial bone and creestal soft tissue thickness are highly associated, they may also influence the outcome of GR during different kinds of orthodontic movements [15,16]. To sum up, usually the main factors for GR development are presence of gingival retraction before orthodontic movement, poor oral hygiene, gingivitis and/or a thin gingival/bone biotype together with proclination of incisors [17]. Several clinical characteristics have been described for defining gingival biotype: crown width and length ratio, the width of keratinized tissue, papilla height and gingival thickness, which may be assessed by transgingival probing, ultrasonic measurement or probe visibility test [18]. However, method of visual inspection of the probe transparency through the gingiva is mostly recommended [19]. Studies have shown that subjects with a thin biotype are more prone to gingival marginal alterations, irrespective of the type of orthodontic movement. Thin periodontal biotype and proclination of teeth have been shown to correlate with loss of keratinized tissue [16]. It has also been found that the risk for the development of GR grows by 9.7% with each year after orthodontic treatment (OT) [20]. Canines, first premolars and first molars are most prone to GR after OT in the maxilla, while the highest risk of GR in the mandible was observed for the central incisors and first premolars [20]. The management of GR involves the elimination of etiological and predisposing factors and, if needed, surgical root coverage [3,13].