CHAPTER 2
Anatomy and histology of the periodontium

Aditi Chopra and Steph Smith

Contents

• Introduction
• Gingiva
  • Gingival/periodontal phenotype
  • Histology of the gingiva
  • The dentogingival complex
• Cementum
• Alveolar bone
  • Composition of alveolar bone
  • Supporting alveolar bone
  • Alveolar crest position
• Periodontal ligament
• Blood supply of the periodontium
• Lymphatic system of the periodontium
• Nerve supply of the periodontium
• References

Learning objectives

• Macroscopic anatomy of the periodontium.
• Histology of the anatomic structures of the periodontium.
• Understanding of gingival and periodontal phenotypes.
• Dimensions and histology of the dento-gingival complex.
• Blood supply, lymphatic drainage, and nerve supply of the periodontium.

Introduction

The oral cavity consists of two types of tissues: hard tissues, comprising 32 teeth and alveolar bone, and soft tissue, comprising the oral mucosa. The oral mucosa consists of three zones: masticatory mucosa, which includes the gingiva and the soft tissue covering of the hard palate; specialized mucosa, which covers the dorsum of the tongue; and the oral mucous membrane, lining the remainder of the oral cavity.

The root of each tooth is embedded into a socket of the alveolar process of the mandible and maxilla, called a gomphosis, also known as a dentoalveolar syndesmosis. It is a joint that binds the teeth to the sockets, and the fibrous connection between a tooth and its socket is a periodontal ligament. The tooth is furthermore supported in its position by the help of the tissues surrounding the tooth, i.e. the periodontium. The periodontium anchors the teeth in position and provides interdental linkage of the teeth within the dental arch. The periodontium, also called "the attachment apparatus" or "the supporting tissues of the teeth," undergoes certain changes with age and is also subjected to morphological changes related to functional alterations and alterations in the oral environment (Newman et al. 2019). The developmental, biological, and functional unit of the periodontium consists of four types of tissues: gingiva, root cementum, alveolar bone proper, and the periodontal ligament (Ainamo & Löe 1966; Cho & Garant 2000; Cleaton-Jones et al. 1978; Lindhe & Lang 2015; Listgarten 1964; Melcher & Bowen 1969; Newman et al. 2019; Ten Cate 1975, 1994) (Figure 2.1).

Gingiva

The gingiva is that part of the masticatory mucosa that covers the alveolar process of the jaw and surrounds the neck of the tooth (Ainamo & Löe 1966). Macroscopically, the gingiva is divided into three parts: interdental gingiva (Table 2.1), marginal (free) gingiva (Table 2.2), and attached gingiva (Table 2.3) (Ainamo & Löe 1966; Cho & Garant 2000; Cleaton-Jones et al. 1978; Lindhe & Lang 2015; Newman et al. 2019). The clinical characteristics of the gingiva are depicted in Table 2.4.

Gingival/periodontal phenotype

The gingival phenotype is determined by gingival thickness and the keratinized tissue width. The periodontal phenotype is determined by the gingival phenotype and the bone morphotype, i.e. the thickness of the buccal bone plate (Jepsen et al. 2018). Determination of the periodontal phenotype is necessitated for assessing therapy outcomes in periodontal and implant therapy, prosthodontics, and orthodontics. Three categories of periodontal phenotypes have been classified, i.e. thin scalloped, thick flat, and thick scalloped (Chambrone & Tatakis 2016; Cortellini & Bisada 2018; Kan et al. 2010; Zweers et al. 2014). For the diagnoses and factors determining the gingival/periodontal phenotypes, see Chapter 10.3.

Histology of the gingiva

Histologically, the gingiva is comprised of two parts: the gingival epithelium and the underlying connective tissue (Ainamo & Löe 1966; Cho & Garant 2000; Cleaton-Jones et al. 1978; Listgarten 1964).

Figure 2.1 The periodontium.

Courtsey of Dr. Abdulqader Alhammadi.

Table 2.1 The interdental gingiva.

• Also known as the papillary gingiva, it is a pyramidal-shaped tissue found between the two teeth, filling the space in the gingival embrasure below the contact point of adjacent teeth.
• In anterior regions of the dentition, the interdental papilla has a pyramidal form, while in molar regions, the papillae are flatter in the buccolingual direction (Newman et al. 2019).
• The shape of the interdental gingiva is determined by the contact relationships between the teeth; the width of the approximal tooth surfaces; the course of the cementoenamel junction; the distance between the contact point and the osseous crest; and the presence or absence of some degree of recession (Lindhe & Lang 2015).
• The facial and lingual surfaces are tapered toward the interproximal contact area, whereas the mesial and distal surfaces are slightly concave. The lateral borders and tips of the interdental papillae are formed by the marginal gingiva of the adjoining teeth. The intervening portion consists of attached gingiva.
• If a diastema is present, the gingiva is firmly bound over the interdental bone to form a smooth, rounded surface without interdental papillae (Lindhe & Lang 2015).
• The papillary gingiva between the buccal and lingual side is connected to form a valley of tissue, called the "col." In the premolar/molar regions of the dentition, the teeth have approximal contact surfaces rather than contact points. Thus, the interdental papillae in these areas often have one vestibular and one lingual/palatal portion separated by the col region.
• The col region is covered by a thin non-keratinized epithelium. This epithelium has many features in common with the junctional epithelium (Newman et al. 2019).

Table 2.2 The marginal gingiva.

• Also known as the free gingiva or unattached gingiva, as its inner surface is not attached to the tooth or periosteum of the alveolar bone (Ainamo & Löe 1966; Cleaton-Jones et al. 1978; Listgarten 1964; Melcher & Bowen 1969).
• In the coronal direction, the coral pink gingiva terminates in the free gingival margin, which has a scalloped outline (Newman et al. 2019).
• The gap between the marginal gingiva and tooth structure is known as the gingival sulcus. The depth of the sulcus can be examined using a periodontal probe, by estimating the distance the probe penetrates. The depth of the gingival sulcus corresponds to the free gingival groove on the outer surface of the gingival epithelium.
• The free gingival groove is positioned at a level corresponding to the level of the cementoenamel junction. The free gingival groove is not always clinically visible, and may only be present in about 30-40% of adults (Newman et al. 2019).
• The free gingival groove appears most frequently in the vestibular incisor and premolar regions of the mandible, and least frequently in the mandibular molar and maxillary premolar regions (Newman et al. 2019).
• Histologically, the free gingival groove represents a point between the free gingiva and the attached gingiva. Under ideal conditions, the depth of the gingival sulcus is 0 mm or close to 0 mm (Ainamo & Löe 1966). However, as determined in histological sections, the depth of the gingival sulcus in humans is approximately 1.8-3 mm (Cleaton-Jones et al. 1978; Listgarten 1964; Melcher & Bowen 1969; Ten Cate 1975, 1994).

Table 2.3 The attached gingiva.

• It is that portion of the masticatory mucosa that is firmly attached to the underlying alveolar bone (periosteum) and cementum by connective tissue fibers, thus being comparatively immobile in relation to the underlying tissue (Newman et al. 2019; Ten Cate 1994).
• It extends from the free gingival groove to the mucogingival junction. The mucogingival junction is an imaginary line that separates the alveolar mucosa and the attached gingiva, and can be visually identified by the distinct color change between the alveolar mucosa and attached gingiva.
• The alveolar mucosa is red, smooth, and shiny due to the presence of increased vascularity and a thinner non-keratinized epithelium, and contains no rete pegs.
• The color of the attached and marginal gingiva is generally described as "coral pink," being produced by the vascular supply, the thickness and degree of keratinization, and the presence of pigment-containing cells (Newman et al. 2019).
• The width of the attached...