As the focus on mucogingival factors in the orthodontic literature is increasing, it is important to analyse whether the improvement in gingival recession (GR) may be influenced by orthodontic treatment (OT). Previous studies were more focused on the influence of factors, which induce the development of recessions rather than changes (19,20). The aim of the present retrospective study was to evaluate the change of GRs, which were present before OT. Only 5.1% of patients with pre-existing GR were identified from the 12-year clinical material of 2 orthodontists. The included patients were different in the type of malocclusion, number of recessions and other variables, partly explaining the current scarcity of the prospective studies (Table 2, Figure 1). The mean age of the included patients was relatively high (28.7 years), suggesting that GRs are more prevalent in adult patients, and was similar to that described in the literature (8). GRs in teenagers have been described to be associated with atypical tooth position (21). The present study analysed the change of 114 gingival recessions in 37 patients after OT. The results revealed a positive impact of OT on the change in GR (62.3% GRs improved). The mean change of GRs was similar at patient (0.4 mm) and tooth (0.5 mm) levels confirming the positive impact of OT. The high percentage of improved GRs could be influenced by gingival enlargement during OT. However, gingival enlargement is mostly prevalent in teenagers with compromised oral hygiene and this study comprised mostly adults with good oral hygiene, therefore the influence of this factor is not discussed (22). Tooth group was found to be important in GR changes. The present study showed the greatest GR improvement in millimetres in maxillary incisors and maxillary premolars (Table 3). The study by Melsen et al. (2005) showed equal amounts of improved and worsened gingival recessions (42.3%) (23). It is worth mentioning that these authors examined recessions only on mandibular incisors, which did not improve in our study. Mandibular incisors might be described most frequently because of the highest prevalence of new GRs after OT on their labial surfaces. The result that GRs in the mandibular incisors did not improve in the present study may be explained by the fact that the labial alveolar bone is anatomically very thin already before OT and therefore may predispose the development of dehiscences and fenestrations after orthodontic movement of these teeth (24). The percentage of improved GRs in the present study was largest on maxillary canines (84.6%), which is in contrast to the results found by Boke et al. (2014), where only worsening of GR after orthodontic treatment was registered (17). That could be influenced by negative torque, which is usual in Roth prescription of canine brackets, leading to greater labial movement of canine root. In the present study, all patients were treated with maxillary canine torque of 0° or +7°. The careful selection of torque for the treatment of GR, bearing in mind the position of the root in the alveolus, could be have influenced our results. However, this is only a speculation, as the present study had a retrospective design.
As the study patients were different in malocclusions, we found it important to analyse factors, which could have influenced GR change. OT of increased overbite showed positively influence on the GR improvement. This is in line with the results by Zimmer et al. (2007), where an average improvement of 2 mm in gingival recessions was observed in maxillary incisors (25). The sample of the aforementioned study consisted mainly of patients with traumatic deep bite. Therefore, a significant improvement in GR was related to elimination of the causative factor - mechanical load. Based on the results of the present study and earlier studies it may be expected that the treatment of deep bite may favour an improvement of GR. In the study by Zimmer et al. (2007), changes in GRs were measured by changes in the clinical height of the crown before and after the treatment, while we measured the distance between the marginal gingival contour and cementoenamel junction. We chose this method because many patients had undergone restorations of the incisal edge during OT, therefore GR measurements of clinical height of the crown would be inaccurate. Enhos et al. (2012) also found that patients with hypo-divergent vertical growth pattern (deep bite) have a lower prevalence of dehiscence than those with a normo-divergent or hyper-divergent (open bite) growth pattern (26). In cases of GR caused by traumatic occlusal contacts, especially due to deep bite, it was found that orthodontic correction may influence positive changes (25). GR improvement in the present study was also associated with the treatment of increased overjet (≥4 mm). This was also found by Boke et al. (2014), where a decreased incisor proclination had a positive effect on gingival recessions (17). Later studies by Kamak et al. (2015) and Morris et al. (2017) did not find such an association (27,20). Gingival biotype in the univariate analysis was associated with GR improvement; however, in the multivariate analysis, this factor was not significant. In the study by Boke et al. (2014), there was also no association between GR change and gingival biotype reported (17). GR improvement in teeth with the thin gingival biotype was rare in the present study. These findings support the suggestion that GR is less likely to be improved after OT in cases with thin biotype (28). Most of the previous studies show that the extent of GR may be increased when mandibular incisors are retroclined, especially in Class III cases (19). Sperry et al. (1977) observed that Class III patients with excessive dental compensations had more than three times as many teeth with labial GRs after OT in comparison to patients with Class I or Class II (29). The results of the present study support these findings. Patients who had a Class III canine relationship had 3.2-times less chance of GR improvement than those with Class I or II. This can be explained by the anatomically thin buccal cortical plate, and the presence of dehiscences and fenestrations in the mandibular incisor region found in all types of untreated sagittal malocclusions. Therefore, lingual movement of the crowns, in order to compensate Class III malocclusion, may push the incisor roots buccally thereby causing or worsening gingival recession (30). Maxillary anterior teeth usually undergo proclination due to dentoalveolar compensation in Class III patients, which has also been found to induce the occurrence or worsening of GR (28). Therefore, the net effect is that Class III patients have a risk of worsening of GR during orthodontic therapy.
Most of worsened cases were Class III patients with small OB and OJ before OT, which means that probably teeth were moving outside the bony envelope. On the other hand, patients with improved GR, were mostly with thick/normal gingival biotype, normal or deep bite and large pre-treatment OJ, which means that mostly teeth were moving deeper into the bone.
The clinical relevance of the present study is that the tendency of gingival recessions to be improved was noted in deep bite cases, however more in maxillary teeth. Recessions in mandibular, especially anterior, teeth, if present prior OT, may need to be treated periodontally in order to prevent their worsening as their improvement during OT was not observed. Class III cases, especially in planned camouflage movements, might also need periodontal treatment before OT due to the risk of GR worsening.