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c. Contains mostly type I collagen, although smaller amounts of type III and XII collagen are also present. d. Has a rich vascular and nerve supply.

Both sensory and autonomic nerves are present.

(1) The sensory nerves in the PDL dif- fer from pulpal nerves in that PDL nerve endings can detect both pro- prioception (via mechanorecep- tors) and pain (via nociceptors). (2) The autonomic nerve fibers are

associated with the regulation of periodontal vascular flow.

(3) Nerve fibers may be myelinated (sensory) or unmyelinated (sen- sory or autonomic).

2. Cells

a. Cells present in the PDL include fibrob- lasts; epithelial cells; cementoblasts and cementoclasts; osteoblasts and osteo- clasts; and immune cells such as macrophages, mast cells, or eosinophils. b. These cells play a role in forming or destroying cementum, alveolar bone, or PDL.

c. Epithelial cells often appear in clusters, known as rests of Malassez.

3. Types of alveolodental fibers (Figure 1–69) a. Alveolar crest fibers—radiate down- ward from cementum, just below the cementoenamel junction (CEJ), to the crest of alveolar bone.

b. Horizontal fibers—radiate perpendicu- lar to the tooth surface from cementum to alveolar bone, just below the alveo- lar crest.

c. Oblique fibers

(1) Radiate downward from the alveo- lar bone to cementum.

(2) The most numerous type of PDL fiber.

(3) Resist occlusal forces that occur along the long axis of the tooth. d. Apical fibers

(1) Radiate from the cementum at the apex of the tooth into the alveolar bone.

(2) Resist forces that pull the tooth in an occlusal direction (i.e., forces that try to pull the tooth from its socket). e. Interradicular fibers

(1) Only found in the furcal area of multi-rooted teeth.

(2) Resist forces that pull the tooth in an occlusal direction.

4. Gingival fibers

a. The fibers of the gingival ligament are not strictly part of the PDL, but they play a role in the maintainence of the periodontium.

b. Gingival fibers are packed in groups and are found in the lamina propria of gingiva (Figure 1–70).

c. Gingival fiber groups:

(1) Transseptal (interdental) fibers (a) Extend from the cementum of

one tooth (just apical to the junctional epithelium), over the alveolar crest, to the corre- sponding area of the cementum of the adjacent tooth.

(b) Collectively, these fibers form the interdental ligament (Figure 1–71), which functions to resist rotational forces and retain adjacent teeth in inter- proximal contact.

(c) These fibers have been impli- cated as a major cause of postretention relapse of teeth that have undergone orthodon- tic treatment.

(2) Circular (circumferential) fibers (a) Extend around tooth near the

CEJ.

(b) Function in binding free gingiva to the tooth and resisting rota- tional forces.

(3) Alveologingival fibers—extend from the alveolar crest to lamina propria of free and attached gingiva.

Apical Oblique Interradicular

Horizontal Alveolar crest

Figure 1–69. PDL (alveolodental) fibers: five groups. (From Brand R, Isselhard D: Anatomy of Orofacial Structures, St. Louis, Mosby, 2003.)

(4) Dentogingival fibers—extend from cervical cementum to the lamina propria of free and attached gingiva. (5) Dentoperiosteal fibers—extend from cervical cementum, over the alveolar crest, to the periosteum of the alveo- lar bone.

C. Alveolar bone (process)

1. The bone in the jaws that contains the teeth alveoli (sockets).

2. Three types of bone (Figure 1–72):

a. Cribriform plate (alveolar bone proper) (1) Directly lines and forms the tooth socket. It is compact bone that con- tains many holes, allowing for the passage of blood vessels. It has no periosteum.

(2) Serves as the attachment site for PDL (Sharpey’s) fibers.

(3) The tooth socket is constantly being remodeled in response to occlusal forces. The bone laid down on the cribriform plate, which also provides attachment for PDL fibers, is known as bundle bone.

(4) It is radiographically known as the

lamina dura.

b. Cortical (compact) bone

(1) Lines the buccal and lingual sur- faces of the mandible and maxilla. (2) Is typical compact bone with a

periosteum and contains Haversian systems.

(3) Is generally thinner in the maxilla and thicker in the mandible, espe- cially around the buccal area of the mandibular premolar and molar. Facial surface of tooth Cross-sectioned tooth Interdental papilla Alveolar crest Alveolodental fibers Cementum CEJ Interdental ligament

Figure 1–71. Interdental ligament. (Modified from Bath-Balogh M, Fehrenbach M: Illustrated Dental Embryology, Histology, and Anatomy, ed 2, Philadelphia, WB Saunders, 2006.) Alveologingival ligament Dentoperiosteal ligament Dentogingival ligament Circular ligament

Figure 1–70. Arrangement of gingival fiber groups in the lamina propria of gingiva. (Modified from Bath-Balogh M, Fehrenbach M: Illustrated Dental Embryology, Histology, and Anatomy, ed 2, Philadelphia, WB Saunders, 2006.)

c. Trabecular (cancellous, spongy) bone

(1) Is typical cancellous bone contain- ing Haversian systems.

(2) Is absent in the maxillary anterior teeth region.

3. Alveolar crest (septa)

a. The height of the alveolar crest is usu- ally 1.5 to 2 mm below the CEJ junction. b. The width is determined by the shape

of adjacent teeth.

(1) Narrow crests—found between teeth with relatively flat surfaces. (2) Widened crests—found between

teeth with convex surfaces or teeth spaced apart.

3.2 Soft Oral Tissues 3.2.1 Oral Mucosa

The oral mucosa consists mainly of two types of tissues: the oral epithelium, which consists of stratified, squamous epithelium, and the underly- ing connective tissue layer, known as the lamina

propria (Figure 1–73). There are three variations of

oral mucosa.

A. Oral epithelium

1. Consists of stratified, squamous epithe- lium.

2. Four layers (Note: Cells mature as they progress from the deepest [basal] layer to the most superficial [cornified] layer) a. Basal layer (stratum germinativum or

basale)

(1) A single layer of cuboidal or col- umnar cells overlying the lamina propria.

(2) Contains progenitor cells and thus provides cells to the epithelial lay- ers above.

(3) Site of cell division (mitosis). b. Prickle cell layer (stratum spinosum)

(1) Consists of several layers of larger, ovoid-shaped cells.

c. Granular layer (stratum granulosum) (1) Cells appear larger and flattened. (2) Granules (known as keratohyaline

granules) are present in the cells.

(3) This layer is absent in nonkera- tinized epithelium.

d. Cornified layer (stratum corneum, ker- atin, or horny layer)

(1) In keratinized epithelium:

(a) Orthokeratinized epithelium— the squamous cells on the surface appear flat and contain keratin. They have no nuclei present. (b) Parakeratinized epithelium—

the squamous cells appear flat and contain keratin; nuclei are present within the cells. (2) In parakeratinized epithelium, both

squamous cells without nuclei and cells with shriveled (pyknotic) nuclei are present.

(3) In nonkeratinized epithelium, the cells appear slightly flattened and contain nuclei.

B. Lamina propria

1. Consists of type I and III collagen, elastic fibers, and ground substance. It also con- tains many cell types, including fibrob- lasts, endothelial cells, immune cells, and a rich vascular and nerve supply.

2. Two layers:

a. Superficial, papillary layer Spongy bone Spongy bone Cortical plate Cortical plate Cortical plate Cortical plate Cribriform plate Cribriform plate A B

Figure 1–72. Alveolar bone. A, Cross-section view through a mandible. B. A longitudinal horizontal section through a mandible. Notice the thickened lamina dura (arrow). (From Brand R, Isselhard D: Anatomy of Orofacial Structures, St. Louis, Mosby, 2003.)

(1) Located around and between the epithelial ridges.

(2) Collagen fibers are thin and loosely arranged.

b. Reticular layer

(1) Located beneath the papillary layer. (2) Collagen fibers are organized in

thick, parallel bundles.

C. Types of oral mucosa (summarized in Table 1–33).

1. Masticatory mucosa

a. Found in areas that have to withstand compressive and shear forces.

b. Clinically, it has a rubbery, firm texture. c. Regions: gingiva, hard palate.

2. Lining mucosa

a. Found in areas that are exposed to high levels of friction, but must also be mobile and distensible.

Submucous layer Artery Vein Periosteum Bone Lamina propria Capillaries Basement membrane Cornified layer Granular layer Spinous cell layer Basal layer

Figure 1–73. Oral mucosa: epithelium and lamina propria. Also shown are submucosal layer and bone. (From Brand R, Isselhard D: Anatomy of Orofacial Structures, St. Louis, Mosby, 2003.)

MUCOSA REGIONS

Masticatory mucosa Thick epithelium Gingiva (free, Keratinized attached) Numerous rete Hard palate

ridges Long papilla

Lining mucosa Thin epithelium* Alveolar Nonkeratinized mucosa Few rete ridges Labial and Short papilla buccal mucosa

Lips

Floor of mouth Ventral side of

tongue Soft palate

Specialized mucosa Nonkeratinized Dorsum of Forms lingual tongue

papillae