**1.1 KM width around implants**

The displacement and loss of the KM can be a consequence of—(1) flap mobilization in order to achieve primary flap closure during horizontal or vertical bone augmentation procedures and (2) vertical bone resorption and reduction of distance between the bone crest and mucogingival line [6].

Today, the vast majority of published evidence supports the necessity of at least 2 mm of keratinized mucosa width around the implant.

The presence of an adequate amount of KM around implants (>2 mm) will facilitate maintenance of oral hygiene, which can lead to less plaque accumulation and lower incidence of peri-implant mucositis. Furthermore, KM can be associated with soft and hard tissue stability, resulting in decreased incidence in the recession of periimplant mucosa, marginal bone resorption, and attachment loss (**Figure 1**) [5, 7–13].

KM is fundamental in maintaining health around implants in erratic maintenance compliers patients. Less than 2 mm of KM around implants is erratic compliers seems to be associated with a higher incidence of peri-implantitis [12, 14].

#### **1.2 PIS volume**

In literature, the suggested PIS thickness is at least 2 mm. PIS thickness has a major influence on two factors—(1) esthetic appearance of the implant/prosthetic rehabilitation and (2) marginal bone stability [13, 15].

#### *1.2.1 Esthetic appearance*

The color, texture, volume, level of mucosal margin of the PIS, and presence of papilla has a major influence on the overall esthetical outcome. The aforementioned elements must be in line with those of soft tissue around adjacent teeth in order to obtain a harmonious and natural-looking restoration. These parameters are influenced

**Figure 1.** *Recession of the marginal mucosa caused by inadequate width of KM.*

#### **Figure 2.**

*Visible discoloration of the thin marginal mucosa caused by titanium abutment in the region of the lower right canine.*

mainly by soft tissue thickness. Several indexes were developed to objectively evaluate the esthetical appearance of the implant/prosthetic restoration [16].

In literature, the suggested PIS thickness is at least 2 mm [15].

Inadequate PIS volume can be improved with soft tissue augmentation techniques. Furthermore, thick soft tissue can even mask and hide alveolar bone loss on the buccal side of implants [12, 13, 15]. Therefore, soft tissue augmentation is recommended in esthetical regions where a certain amount of buccal bone remodeling is expected, like immediate implant placement in situations with thin biotype or thin buccal bone plate [17, 18].

PIS thickness is essential for concealing the color of the prosthetic restoration and preventing PIS discoloration caused by prosthetic material. In cases with thin PIS (< 2 mm) titanium abutments will cause a visible color change of the buccal PIS (**Figure 2**) [12, 19–21].

#### *1.2.2 Peri-implant marginal bone stability*

PIS has a predetermined thickness of 2.5–4 mm, termed biologic width [22]. PIS is formed after healing abutment installation. In case when soft tissue is thinner than 2 mm, peri-implant marginal bone resorption will be initiated in order to establish sufficient space for the biological width [22, 23]. Augmentation of PIS volume with soft tissue grafts can prevent marginal bone resorption in the case of thin PIS [5, 14, 24].
