Keratinized Tissue Width

Ensuring the long‐term success of dental implants heavily relies on maintaining healthy peri‐implant tissues. However, the role of peri‐implant soft tissue and the necessity of having a minimal amount of keratinized mucosa around dental implants have been a subject of controversy in the literature [9–12].

Different studies have presented conflicting views on the importance of the width of keratinized mucosa (KMW) around dental implants. Some researchers have suggested that a KMW of less than 2 mm is associated with increased inflammation and plaque accumulation compared to sites with a KMW of 2 mm or greater [13, 14]. However, other studies have failed to establish a clear association between the lack of a minimum width of keratinized mucosa and inflammation [15–18].

A recent meta‐analysis reported significantly lower plaque scores, bleeding indices, mucosal recessions, and attachment loss for sites with wider keratinized tissue (KT) [14]. In an observational study involving 110 implants and 36 patients, significantly more plaque accumulation, peri‐implant inflammation, mucosal recession, and bleeding were reported after six months at sites with a KMW of less than 2 mm [19]. Ueno and colleagues also observed that implants with a KMW of less than 2 mm exhibited significantly higher plaque accumulation, bleeding on probing, and pocket depths compared to sites with a KMW of 2 mm or greater [19]. Similar findings, with statistically significantly higher plaque levels, bleeding, and patient discomfort, were reported by Souza et al. for implants with less than 2 mm of keratinized mucosa [20].

Even when patients were highly motivated and able to maintain long‐term low full‐mouth plaque scores for over 10 years, significantly higher plaque accumulation occurred at sites with insufficient keratinized mucosa [21]. In another long‐term observational study spanning eight years, implants with a KMW of less than 2 mm showed significantly higher bleeding and plaque scores than sites with sufficient keratinized tissue width (KTW) [22].

Some authors have observed a positive association between the lack of a minimal band (<2 mm) of keratinized mucosa and the occurrence of PIM [23] as well as a higher prevalence of PIM in such cases [24–27]. However, other studies have found no association [18, 28, 29].

The width of sufficient KT also appears to have an impact on diseased implants, specifically peri‐implantitis. In a cross‐sectional study involving 534 patients, 53 (10.3%) were affected by peri‐implantitis. These implants showed significantly more plaque accumulation and bleeding on probing and were more likely to have an attached mucosa width of less than 2 mm [30].

From a clinical standpoint, it is important to highlight that when the peri‐implant KT is less than 2 mm, there is greater plaque accumulation, bleeding on probing, and more gingival recessions are diagnosed around these implants, particularly in cases with irregular maintenance protocols. However, these differences are not statistically significant when patients have regular recall appointments with professional cleaning every six months, regardless of whether the KTW is less than 2 mm or greater than 2 mm [31]. This clinical study involved 118 patients with 320 dental implants utilizing platform switching.

A recent study has examined the natural regeneration of the implanto–mucosal and dento‐gingival units following the complete removal of KT [32]. The results of the study revealed that after the excision of KT at implant sites, the spontaneous regeneration of the soft tissue is characterized by a non‐keratinized epithelium similar to alveolar mucosa. On the other hand, at tooth sites, the spontaneous regeneration resulted in soft tissue resembling gingiva. These findings are clinically significant as they demonstrate, for the first time, that once KT is lost at implant sites, it does not regenerate naturally. Therefore, the restoration of KT can only be achieved through soft tissue grafting (Figure 10.1a–h).

Mucosal Thickness

In recent years, emerging evidence supports the idea that peri‐implant mucosal thickness represents an important factor in the maintenance of peri‐implant health. Historically, soft tissue thickness has been shown to play a critical role in peri‐implant marginal bone loss [33]. Greater stability of the interproximal bone in cases with adequate mucosal thickness has been reported in a recent systematic review [34]. Nonetheless, the adequate amount for tissue thickness has not been clearly defined yet [35], but a threshold of 2 mm thickness has been proposed [8]. The assessment of peri‐implant mucosal thickness may vary depending on the implant location (e.g. lingual or buccal) and is commonly determined as 1–2 mm apical to the mucosal margin [8]. Most studies assessing horizontal mucosal thickness focused on esthetic outcomes in relation to the transparency of the abutment material [36–38], and a minimum thickness of about 2 mm is necessary for masking restorative materials [37, 39]. However, a thickness >1 mm was reported as beneficial against mucosal recessions following immediate implant placement [40, 41]. On the other hand, augmentation of mucosal thickness has been proposed for compensating expected bone remodeling after immediate implant placement and for stabilizing the mucosal margin [42–45].

Moreover, tissue thickness influences majorly esthetic outcomes [43]. Recent evidence indicates that a thick mucosa assures a more stable mucosal margin as compared to a thinner one [43, 45]. Thin mucosa is also considered an etiological factor for the development of peri‐implant mucosal recessions [41, 46].

Additionally, current studies have also reported that vertical mucosal thickness plays an important role in maintaining/preventing marginal bone loss. Cases with a thin supracrestal tissue (<2 mm) height (measured from the bone crest to the mucosal margin in apico‐coronal direction) were associated with greater marginal bone loss than those with thick mucosa [47, 48], especially at bone level implants [49]. Surgical thickening of the vertical peri‐implant mucosa resulted in reduced marginal bone loss over time [34].

Implants with a thin soft‐tissue phenotype with a reduced horizontal mucosal thickness seem to be more often associated with PIM and peri‐implantitis compared to implants with a thick phenotype [50].

Nonetheless, there seems to be limited evidence to support the thickening of the peri‐implant soft tissue in order to lower the incidence of peri‐implant diseases [51–53].

In conclusion, peri‐implant tissue thickness, in both horizontal and vertical direction, appears to represent important structural components for maintaining peri‐implant tissue health, thus affecting marginal bone remodeling, esthetic outcomes, restorative material transparency, and patient satisfaction.

Peri‐implant Mucosal Recessions

Peri‐implant mucosal recessions can significantly impact esthetic outcomes and patient satisfaction. The etiology of these recessions includes factors such as the mucosal phenotype [41], inadequate width of keratinized mucosa, the height of peri‐implant marginal bone [54], improper oro‐vestibular implant positioning [55, 56], characteristics of the implant abutment and prosthetic superstructure (emergence profile), and the angle of the implant fixture [46].

There are limited data available on the prevalence of peri‐implant mucosal recessions. A systematic review reported peri‐implant recessions in 0–64% of implants, based on data from only four studies [57]. Other studies have observed recessions occurring as early as one‐year post‐implant placement in 24% of cases [58].

Improvement of Keratinized Tissue Width Around Dental Implants

In a consensus report and accompanying systematic review, four randomized controlled clinical trials (RCTs) were included. These studies indicated a positive association between soft tissue grafting aimed at increasing the KTW and greater reductions in plaque and gingival indices compared to non‐augmented sites [34, 62].

Techniques based on apical shifting (i.e. apically positioned flap [APF]) [63–65], or bilaminar procedures like the tunneling technique [66–69] have been the subject of investigation.

In a systematic review and meta‐analysis conducted by Tavelli et al. [52], which included 23 RCTs, it was reported that both autogenous soft tissue grafts and soft tissue substitutes in combination with an APF, can lead to a statistically significant increase in KTW. When compared to non‐augmented control sites, the use of APF and various graft types (FGG, CTG, ADM, and CM) resulted in superior outcomes. Notably, FGG demonstrated the highest improvements in KTW, with the following results: APF (2.48 mm, 95% CI [1.35, 3.62], p = 0.04), CM (2.96 mm, 95% CI [1.82, 4.19], p = 0.002), CTG (2.82 mm, 95% CI [1.91, 4.14], p = 0.007), FGG (3.67 mm, 95% CI [3.03, 4.31], p = 0.01), and ADM (3.02 mm, 95% CI [1.87, 4.17], p = 0.03) [52].

Moreover, the combination of APF with grafting procedures resulted in a statistically significant increase in KTW, leading to reductions in pocket depth, plaque accumulation, and mucosal recessions [52]. In some cases, although unpredictable, there may be observed a slight gain in attachment level when autogenous grafts are used for augmentation procedures [61, 70].

Interestingly, when comparing different treatment approaches including grafting procedures to APF alone, only FGG demonstrated a statistically significant increase in KTW. In contrast, bilaminar techniques did not achieve significant gains in KTW [52].

Increasing KTW has been shown to result in greater reductions in plaque accumulation (WMD = 0.344, 95% CI [0.179, 0.509], p < 0.001) and gingival indices (WMD = 0.863, 95% CI [0.658, 1.067], p < 0.001), but it has no significant effect on bleeding on probing when compared to non‐augmented sites [34, 62]. Moreover, an increase in KTW appears to contribute to a more stable position of the marginal bone levels, particularly when using APF with autogenous grafts (WMD = −0.175 mm, 95% CI [−0.313, −0.037], p = 0.013).

Improving KTW also has a positive impact on peri‐implant marginal bone stability. In the meta‐analysis conducted by Tavelli and colleagues, augmentation procedures involving APF and soft tissue grafts not only improved oral hygiene and reduced plaque accumulation but also resulted in less marginal bone loss [52]. Similar results have been reported by other authors who observed a positive association between KTW improvement and proper plaque control [21, 68, 69].

The timing of soft tissue augmentation procedures seems to have no impact on the gain in KTW with either the bilaminar technique or APF. Therefore, soft tissue augmentation can be performed at the time of implant placement, during the second stage, or at any delayed time [52, 71].

Improvement of Peri‐implant Mucosal Thickness

Soft tissue augmentation procedures are commonly recommended to increase peri‐implant mucosal thickness for esthetic improvements and to address volume deficiencies [42, 72, 73] as well as to facilitate tissue adaptation during implant placement [74].

In a recent meta‐analysis utilizing a network model to assess mucosal thickness as an independent parameter, it was found that all evaluated augmentation methods (CTG, ADM, and CM) used in combination with a bilaminar surgical technique resulted in a statistically significant increase in mucosal thickness. CTG demonstrated the highest improvements (1.13 mm, 95% CI [0.94, 1.31], p < 0.001), followed by ADM (1.08 mm, 95% CI [0.80, 1.35], p < 0.001), and CM (0.76 mm, 95% CI [0.55, 0.97], p < 0.001) [52]