University of Iowa
Iowa City, Iowa
Lorenzo Tavelli, DDS, MS
Adjunct Clinical Assistant Professor and Research Fellow
Department of Periodontics and Oral Medicine
School of Dentistry
University of Michigan
Ann Arbor, Michigan
Vivian Petersen Wagner, DDS, PhD
Postdoctoral Researcher
Department of Oral Diagnosis
Piracicaba School of Dentistry
University of Campinas
Campinas, Brazil
Shan-Huey Yu, DDS, MS
Clinical Assistant Professor
Department of Periodontics and Oral Medicine
School of Dentistry
University of Michigan
Ann Arbor, Michigan
Miguel Romero Bustillos, DDS, PhD
DEFINITIONS AND TERMINOLOGY
Alveolar bone proper: Compact bone that composes the alveolus (tooth socket). Also known as the lamina dura or cribriform plate, the fibers of the periodontal ligament insert into it.
Alveolar process: The compact and cancellous bony structure that surrounds and supports the teeth.
Attached gingiva: The portion of the gingiva that is firm, dense, stippled, and tightly bound to the underlying periosteum, tooth, and bone.
Attachment apparatus: The cementum, periodontal ligament, and alveolar bone.
Biologic width: The dimension of soft tissue composed of a connective tissue and epithelial attachment extending from the crest of bone to the most apical extent of the pocket or sulcus. This term was recently redefined as “supracrestal tissue attachment.”2
Bundle bone: A type of alveolar bone, so-called because of the “bundle” pattern caused by the continuation of the principal (Sharpey) fibers into it.
Fibroblast: The predominant connective tissue cell; a flattened, irregularly branched cell with a large oval nucleus that is responsible in part for the production and remodeling of the extracellular matrix.
Free gingiva: The part of the gingiva that surrounds the tooth and is not directly attached to the tooth surface.
Gingival groove: A shallow, V-shaped groove that is closely associated with the apical extent of free gingiva and runs parallel to the margin of the gingiva. The frequency of its occurrence varies widely.
Gingival papilla: The portion of the gingiva that occupies the interproximal spaces. The interdental extension of the gingiva.
Hertwig epithelial root sheath (HERS): An extension of the enamel organ (cervical loop) Determines the shape of the roots and initiates dentin formation during tooth development. Its remnants persist as epithelial rests of Malassez in the periodontal ligament.
Lamina propria: In the mucous membrane, the connective tissue coat just beneath the epithelium and basement membrane. In skin, this layer is known as the dermis.
Mucogingival junction: The junction of the gingiva and the alveolar mucosa.
Osseointegration: A direct contact, at the light microscopic level, between living bone tissue and an implant.
Periodontal ligament (PDL): A specialized fibrous connective tissue that surrounds and attaches roots of teeth to the alveolar bone. Also known as the periodontal membrane.
Periodontium: The tissues that invest and support the teeth, including the gingiva, alveolar mucosa, cementum, periodontal ligament, and alveolar supporting bone. Also known as the supporting structure of the tooth.
Rete pegs: Ridge-like projections of epithelium into the underlying stroma of connective tissue that normally occur in the mucous membrane and dermal tissue subject to functional stimulation.
The periodontium comprises the supporting structures of the dentition. It is composed of four main elements: gingiva, cementum, periodontal ligament (PDL), and bone. Understanding this dynamic network of tissues is pivotal for the proper performance of the many procedures related to periodontal therapy. This chapter describes the different structures of the periodontium from microscopic and macroscopic points of view.
The attachment apparatus, also known as periodontal attachment, is an aggregate of tissues with the main function of anchoring teeth to the alveolus. It consists of cementum, alveolar bone, PDL, and gingiva. Several terms are highly relevant with this regard and are described by the American Academy of Periodontology (AAP) Glossary of Periodontal Terms (see sidebar).1
Periodontium: Attachment Apparatus
PERIODONTAL LIGAMENT
The PDL is a specialized connective tissue located between the bony walls of the dental socket and the dental root. It surrounds the majority of the dental root and attaches the teeth to the alveolar bone. In the most coronal portion, the PDL is continued with the lamina propria of the gingiva. Characterized by its hourglass shape, this specialized connective tissue narrows at the middle part, with an average width ranging from 0.2 to 0.4 mm.3 The PDL space decreases with age and increases under excessive load.
Origin
The PDL develops in a cell population from the dental follicle. As the crown approaches the oral mucosa, fibroblasts produce collagen fibrils without organized orientation. Later, prior to tooth eruption, the fibroblasts adopt an oblique orientation adjacent to the cementum. Finally, after this fibroblast arrangement, fibers with organized orientation are developed at the cementum surface as well as at the alveolar bone proper. These fibers will continue elongating until they reach each other at the middle portion of the PDL. The orientation of the fibers will be determined by the location within the PDL (Table 1-1).4,5
TABLE 1-1 Principal periodontal ligament fibers4,5
CEJ, cementoenamel junction.
Composition
The PDL is formed by different cell types. The fibroblasts are the most abundant as they are responsible for the metabolism of the extracellular components. Within this heterogeneous population of fibroblasts within the PDL, osteoblast-like fibroblasts are also present, and these are rich in alkaline phosphatase.6,7 In addition, the PDL contains stem cells, epithelial cell rests of Malassez, cells from the blood vessels, and cells associated with the immune and nervous systems.
The extracellular matrix of the PDL consists of collagenous and noncollagenous proteins. Collagen type I is the most abundant, and it is also the primary constituent