# Retrospective Study of the Association between Peri-Implantitis and Keratinized Mucosa
## 4 Discussion  
In view of the controversy found in the literature about the role of KM in the development of periodontitis, this study attempts to provide data to help clarify its role in the development of peri-implant diseases. [PERSON] and [PERSON] already pointed out in their studies in the 1980s and 1990s that the absence of KM increased the risk of peri-implantitis in areas with bacterial plaque accumulation, and that the clinical success of the implant depended on the presence of KM and a good plaque control [11; 12]. Proper hygiene is essential for the maintenance of peri-implant health and many authors point out that in the absence of KM, proper hygiene is complicated and plaque retention is highly favored [13; 14]. [PERSON] et al. [15] observed that in patients with proper oral hygiene who received regular implant maintenance therapy, implants with reduced KM (<2 mm) were more prone to plaque accumulation and bleeding, as well as recession. [PERSON] et al. [16] associated an inadequate amount of KM with increased plaque accumulation and gingival inflammation, but not with a higher mean annual bone loss, regardless of implant surface configuration. In a study of 200 implants carried out by [PERSON] et al. [17], it was observed that the increased width of KM around implants was associated with lower mean alveolar bone loss and improved soft tissue health indices. In the meta-analysis by [PERSON] et al. [5], a relation was established between KM and plaque index, gingival index, gingival recession, and clinical attachment loss. However, no significant differences were found with respect to bleeding on probing, probing depth, and radiographic bone loss. [PERSON] et al. [18] conducted a 10-year prospective study and observed that implants that were not surrounded by KM were more prone to plaque accumulation and gingival recession, even in patients with good oral hygiene, receiving periodontal supportive therapy. The lack of keratinized mucosa around dental implants was significantly associated with more plaque accumulation, mucosa recession, interproximal bone level \(\geq\) 3 mm and peri-implantitis. There are even authors who point to KM as an indicator of risk for peri-implant disease even if there is no history of periodontitis in those patients [19; 20]. All these studies coincide to some extent with the results of the present study, where a strong association between the absence of KM and peri-implantitis was observed. The results in this study point out that in the peri-implantitis group there is a higher percentage of absence of KM (49%) than in the control group (2.9%). When relating KM to other clinical parameters, a statistically significant association was observed. Greater gingival recession was observed in implants without KM (1.7 mm in the peri-implantitis group and 0.1 mm in the control group). Therefore, it could be suggested that the presence of KM prevents the recession of peri-implant tissues. The absence of KM is related to a higher plaque index,increased bleeding and suppuration on probing. Hygiene seems to be better in the presence of KM and this is directly related to bleeding on probing and suppuration. In addition, the percentage of multiple implants was higher in the peri-implantitis group, which could complicate hygiene, although these differences were not statistically significant. The better the hygiene, the better the gingival health and the less inflammation. During the study, a series of limitations were encountered. One of them was the heterogeneous nature of the length of time since implant placement, being significantly longer in the test group than in the control group. This indicates that the longer the time since implant placement, the greater the risk of developing peri-implantitis. This is probably due to the prolonged effect of external risk factors which would be related to the results of [PERSON] et al., who concluded that the longer the follow-up period, the higher the risk of implants presenting inadequate KM [21].