“The mucogingival complex” is formed by the portion of the oral mucosa that covers the alveolar process including the gingiva (keratinized tissue) and the adjacent alveolar mucosa [1]. Clinically, the gingiva (“the fibrous investing tissue, covered by keratinised epithelium, that immediately surrounds a tooth and is contiguous with its periodontal ligament and with the mucosal tissues of the mouth”) [1] can be found around the cervical portion of the teeth and is characterized by (a) a pink and opaque color, (b) scalloped appearance/contour, (c) a stippling texture that reminds an “orange peel,” and (d) firm consistence, (e) may present melanic pigmentation, and (f) may vary in width, and (g) it usually assumes its definitive shape and texture following the eruption of permanent teeth (Fig. 2.3) [12, 13].

In terms of clinical anatomic limits, the gingiva is delimited by the free/marginal gingiva (“that part of the gingiva that surrounds the tooth and is not directly attached to the tooth surface/the most coronal portion of the gingiva that forms the wall of the gingival crevice in health”) [1] and the attached gingiva (“the portion of the gingiva that is firm, dense, stippled, and tightly bound to the underlying periosteum, tooth, and bone”). The free/marginal gingiva includes the interdental papilla (“that portion of the gingiva that occupies the interproximal spaces [the interdental extension of the gingiva]”) [1] and the col (“a valley-like depression of the interdental gingiva that connects facial and lingual papillae and conforms to the shape of the interproximal contact area”) [1]. Within anterior interproximal sites, the interdental papilla assumes a triangular shape, whereas at the posterior teeth these are more “smooth-edged” given the impression that the posterior papilla is formed by two parts, one buccal and one lingual separated by the col area [13, 14]. Usually, the free/marginal gingiva extends to the gingival groove (“a shallow, V-shaped groove or indentation that is closely associated with the apical extent of free gingiva and runs parallel to the margin of the gingiva”) [1] where it “connects” to the attached gingiva [13, 14]. Regarding the attached gingiva it extends from the apical limit of the free/marginal gingiva to the mucogingival junction, its width may vary between the anterior and posterior teeth, and it may increase with age (Fig. 2.4) [13, 14].

Microscopically, the gingiva is formed by three epithelial (oral, oral sulcular/crevicular, and junctional) and one connective tissue layer (Fig. 2.5). With the assistance of biopsy samples of human teeth sectioned in a buccal–lingual plane, it can be seen that the buccal gingiva facing the oral cavity presents a layer of keratinized stratified squamous epithelium denominated “oral epithelium” that extends from the mucogingival junction to the gingival margin (Fig. 2.6). This epithelium is formed by four layers/stratums (Fig. 2.7):

Within the oral epithelium, different types of cells may be found, such as melanocytes (cells that produce the dark, amorphous pigment of the skin, hair, and the choroid coat of the eye and that give the darkish color of the gingiva – Fig. 2.8) [1], Langerhans (defense cells originated of macrophages), and Merkel (sensorial/tactile) cells [13, 15].

At the gingival margin, the oral epithelium “continues” through the interior of the gingival sulcus/crevice (i.e., the shallow fissure between the marginal gingiva and the enamel or cementum) [1], and there it becomes the oral sulcular/crevicular epithelium, a nonkeratinized stratified squamous epithelium formed by three layers (basale, spinosum, and granulosum) [13–15]. Despite being described as “nonkeratinized,” there has been evidence of areas/portions of keratinization mainly close to the entrance of the crevice (Fig. 2.9). Additionally, in the presence of gingival health, it will allow the formation of a gingival sulcus/crevice of 0.69 mm that extends from the gingival margin to the bottom of the crevice all around the tooth [16].

The bottom of the gingival crevice separates the sulcular of the junctional epithelium, which is defined as “a single or multiple layer of nonkeratinizing cells adhering to the tooth surface at the base of the gingival crevice” [1]. It is formed by 15–30 parallel layer cells at its most coronal portion adjacent to the oral sulcular/crevicular epithelium to just a few cells at its most apical position [15]. Despite presenting just two strata (basale and suprabasale), the junctional epithelium is characterized by its capacity of sealing the internal or the external environment and by its high capacity of cellular turnover (as provided by its basal layer) and bigger intercellular spaces than the other two epitheliums (Fig. 2.10) [13, 15]. These features provide the ability not only of attachment, but of protection because of cell desquamation at its most coronal portion (i.e., close to the base of the gingival sulcus/crevice) and permeability to polymorphonuclear neutrophils (which are quite evident) [13, 15].

All epitheliums are underlined by a connective tissue layer of the lamina propria (“the connective tissue coat just beneath the epithelium and the basement membrane”) [1]. For the oral epithelium, the interface formed with the connective tissue is irregular and comprises “fingerlike projections” of connective tissue from the papillary layer (“connective papilla”) that extends into depressions on the undersurface of the epithelium (“epithelial crests”) [16]. These ridge-like projections of epithelium into the underlying stroma of connective tissue [1] (or rete pegs when seen in histological sections– Fig. 2.11) improve its attachment to the lamina propria [16]. The sulcular/crevicular epithelium also presents such “rete ridges” but in a diminished number, while at the junctional epithelium these are not present [17].

Regarding the components of the gingival connective tissue, it is formed by fibroblasts (65 % of all tissues) and other cells (i.e., mast cells, macrophages, undifferentiated mesenchymal cells, neutrophils, and plasma cells), fibers, blood vessels, and nerve fibers that are intended to act for cell nutrition, tissue healing, as well as mechanical (by the group of collagen fibers and the viscosity of the amorphous intercellular substance of the extracellular matrix) and phagocytic (via macrophages, neutrophils, antigen–antibody reactions, and activation of the complement system) mechanisms of defense [13, 15] Figs. 2.12 and 2.13.

Although parts of the fibers are irregularly distributed through the connective tissue layer, most of them consisting of a dense network of collagen fiber bundles form an organized supra-alveolar fiber apparatus. Their function and location are illustrated in Figs. 2.14 and 2.15 (notes 1–9) and depicted as follows [1, 13, 15]:

Additionally, other types of fiber bundles such as oxytalan (“fibers found in all connective tissue structures of the periodontium that appear to consist of thin, acid-resistant fibrils – their function is unknown”) [1], reticular (type III collagen fibers secreted by reticular/fibroblast cells that give support to the lamina propria of the gingiva), and elastic (around blood vessels) are present at the gingival connective tissue.

With respect to the neurovascular composition of the gingival connective tissue, the vascularization of the gingiva is primarily supplied by blood vessels located at the periodontal ligament and at the supraperiosteal portion of the lamina propria (i.e., supraperiosteal vessels) and by the intra- septal artery [13, 15]. These vessels/artery and capillary loops will originate from two vascular networks of arteriovenous anastomoses, the subepithelial and the dentogingival plexus (Fig. 2.16) [15]. Regarding the neural elements, these are its great majority surrounding/close to blood vessels and composed by myelinated fibers that play a sensory part [15].

The clinical role of the cementum, the alveolar bone, and the periodontal ligament conditions is briefly depicted below [1, 18]:

Together with the knowledge of the soft tissue anatomy, the characteristics of these tissues, mainly of the alveolar bone, play an important role on the development of soft tissue deformities even without the presence of dental biofilm. Anatomical features of the alveolar bone, such as bone fenestrations (i.e., window-like apertures or openings in the alveolar bone over the root of a tooth without comprising the marginal crestal bone) [1, 19–22] and dehiscence (i.e., areas in which the root is denuded of bone and portions of the root surface are covered only by soft tissue, and this area extends to through the marginal alveolar bone) [19–22], may be important for the development of periodontal disease and non-plaque-induced gingival lesions, as well as for the prognosis of a periodontal plastic surgery procedure (Fig. 2.20). For instance, approximately 10 % of the teeth may present fenestrations or dehiscence of the bone, but when accounting the presence of such defects “per subject,” this value increase up to 60 % [19]. Also, 12 % of maxillary central incisors may present lack of bone covering the root surface beneath the gingival tissues [20], and in the presence of malocclusions, the frequency of fenestrations and dehiscence may significantly increase to approximately 35 and 50 %, respectively, especially in the anterior region of the mandible (Figs. 2.21 and 2.22) [21, 22]. In addition, it should be noted that histological information indicates that the buccal bone wall is thinner than the lingual wall and both crests are located at a similar distance from the cementoenamel junction [23].

The palatal vault may play an important role during the decision-making process due to its inherent anatomical characteristics, in terms of potential damages and complications (e.g., small bleeding up to hemorrhage) that may occur to the greater palatine artery and their major branches [24, 25]. Known as the main artery supplying blood to the masticatory mucosa of the palatal vault, the greater palatine artery emerges on to the inferior surface of the hard palate through the greater palatine foramen and follows anteriorly close to the alveolar ridge up to the incisive foramen, where it leaves the palate (Fig. 2.23) [24–27]. Also, the greater palatine nerve accompanies this artery, and it is related to anesthetic procedures of the anterior teeth and palatal mucosa [24–28].