Fig 1-2 The gingiva.
Free gingiva
Free gingiva is the portion of the gingival epithelium that extends from the free gingival margin to the gingival groove (see Fig 1-2). The gingival groove is defined as the “shallow linear depression on the gingiva surface that demarcates the free gingiva and the attached gingiva.”1 The free gingiva covers the teeth at the vestibular and lingual sites following the contour of the tooth and the dental papilla. In normal conditions, the free gingiva presents as a coral pink color. The location of the gingival groove is determined by the position of the CEJ, and it is present in 4% to 54% of teeth with differences based on tooth type.15,16
Attached gingiva
Attached to the tooth and/or alveolar bone, the attached gingiva is delimited by the gingival groove at the coronal end and the mucogingival junction at the apical end. In healthy conditions, it also presents with a coral pink color. A morphologic characteristic of the attached gingiva is the stippling or orange peel appearance. The stippling corresponds to small epithelial ridges and is developed in areas of high keratinization. When the attached gingiva is inflamed, it loses the superficial stippling, and the color turns to a darker red.15,17,18
The mucogingival junction, which is the interphase between the attached gingiva and the oral mucosa, is located between 3 to 5 mm apical to the alveolar crest, and it has been shown to be stable over the years in reference to the base of the mandible or floor of the nose. Consequently, an increase in attached gingiva with age has been associated with the continuous eruption of the dentition.19,20 The dimensions of the attached gingiva have been investigated in classic studies by Bowers21 and Voigt et al.22 In the maxilla, the sites with the greatest width of attached gingiva are the central and lateral incisors. There is a decrease in canines and first premolars, and a slight increase over the second premolar and molar locations. In the mandible, the incisors also present with the greatest amount of attached gingiva with a sharp decrease around the canines and first premolars. At the second premolar site, the attached gingiva increases, and a decrease at the mandibular molar area is also observed. On the lingual aspect, the molar area presents with the greatest attached gingiva followed by premolars, incisors, and canines.
Based on the location and microscopic appearance, the gingival epithelium can be classified into three types: oral, sulcular, and junctional epithelium.
Oral epithelium
The oral epithelium is a keratinized stratified squamous epithelium that extends from the mucogingival junction to the free gingival margin. In some areas of the most superficial layer, the stratum corneum, the cells maintain their nuclei and are considered parakeratinized. If no nuclei are present in the stratum corneum, this epithelium is considered orthokeratinized. In addition to the keratinocytes, other cells can be found in the oral epithelium, such as melanocytes, which give pigmentation to the epithelium; Langerhans cells, which play a role in the immune response; and Merkel cells, which are important for sensory function.
Sulcular epithelium
This is the epithelial tissue located in the sulcus, and it extends from the free gingival margin to the most coronal portion of the junctional epithelium. It is a nonkeratinized stratified squamous epithelium.
Junctional epithelium
The junctional epithelium extends apically from the base of the gingival sulcus following the tooth structure, and it is a nondifferentiated stratified squamous epithelium.23 In healthy situations with no history of periodontal disease or gingival deformities, the deepest portion of the junctional epithelium is located around the CEJ. It has a triangular shape with the base at the bottom of the sulcus and a vertex located apically. The base of the junctional epithelium has a layer 20 to 30 cells thick, which decreases in number to become a bilayer at the level of the CEJ.24 The junctional epithelium is attached to the tooth surface through hemidesmosomes, while the connections in between the epithelial cells are established by desmosomes, adherents, gaps, and tight junctions.25
The gingival epithelial tissue lies over connective tissue establishing finger-type indentations of epithelial tissue termed ridges. This connective tissue subjacent to the epithelium of the attached gingiva is known as lamina propria. The lamina propria is a highly vascularized tissue with two known portions: the papillary layer, which is the most superficial, and the reticular layer. In the papillary layer, the interphase between the connective tissue of the lamina propria and the epithelium follow a wavy morphology with projections of connective tissue called papillae and epithelial ridges known as rete pegs. The interface between the sulcular epithelium, the junctional epithelium, and the connective tissue is characterized by the absence of rete pegs. The lamina propria consists of 57% to 60% connective tissue fibers/fibrous proteins, 5% to 8% cells, and 35% other components such as blood vessels, nerves, and ground substance of the intercellular matrix.5,26
The main cell type in the lamina propria is the fibroblast, which is the main cell responsible for the formation and remodeling of the connective tissue. The main fibers of the lamina propria are comprised by collagen type I, III, IV, and V, with minor presence of elastic fibers and oxytalan fibers. The fibers in the gingiva follow a specific orientation and are classified into different bundles. The main connective tissue fibers are dentogingival, alveologingival, circular, dentoperiosteal, and transseptal (Table 1-4 and Figs 1-3 and 1-4).5,27,28 In addition, secondary connective tissue fibers are periosteogingival, interpapillary, transgingival, intercircular, semicircular, and intergingival.29 The main as well as the secondary fibers are part of the connective tissue attachment.
Fig 1-3 Dentogingival fibers in a mouse model (100× magnification).
Fig 1-4 Gingival fibers.
TABLE 1-4 Main connective tissue fibers5,28
| Subclassification | Origin | Direction | |
| Dentogingival fibers | Subgroup A | Cementum | Free gingiva |
| Subgroup B | Cementum | Attached gingiva | |
| Subgroup C | Sweep down and across the crest | NA | |
| Alveologingival fibers | NA | Periosteum | Free gingiva and attached gingiva |
| Circular fibers | NA | Encircle each tooth within the connective tissue | |
| Dentoperiosteal fibers | NA | Cementum apical to the dentogingival fibers | Crest of the alveolar bone. Some fibers may insert into muscles of the vestibule. |
| Transseptal fibers | NA | Cementum | Cementum of adjacent tooth |
NA, not applicable.
The interface between the connective tissue and the epithelium is a specialized form of extracellular matrix named the basement membrane or basal membrane. The basal membrane consists of a highly crosslinked matrix of collagen and glycoproteins such as laminin, perlecan, and entactin, and it is composed of several layers. Under electron microscopy, three components can be differentiated: the lamina lucida, the lamina