Fundamentals of
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| 2-4 PERIODONTIUM The tissues that surround and support the teeth are collectively called the periodontium. Their main functions are to support, protect, and provide nourishment to the teeth. Figure 2-8 illustrates the supporting tissues of the periodontium. The periodontium consists of cementum, alveolar process of the maxillae and mandible, periodontal ligament, and gingiva. CEMENTUM Cementum is the only tissue considered as both a basic part of the tooth and a component of the periodontium. It is a thin, calcified layer of tissue that completely covers the dentin of the tooth root. Cementum is forming during the development of the root and throughout the life of the tooth. Cementum functions as an area of attachment for the periodontal ligament fibers. ALVEOLAR PROCESS The alveolar process (fig. 2-8) is that bony portion of the maxilla and mandible where the teeth are embedded and by which tooth roots are supported.
Figure 2-8.—The periodontium. The alveolar socket is the cavity within the alveolar process in which the root of the tooth is held by the periodontal ligament. The bone that divides one socket from another is called the interdental septum. When multirooted teeth are present, the bone is called the interradicular septum. The alveolar process includes the cortical plate, alveolar crest, trabecular bone, and the alveolar bone proper. Cortical Plate Structurally, the cortical plate is composed of lingual and facial plates of compact bone. It is dense in nature and provides strength and protection and acts as the attachment for skeletal muscles. The mandibular cortical plate is more dense than the maxilla cortical plate and has fewer perforations for the passage of nerves and blood vessels. Alveolar Crest The alveolar crest is the highest point of the alveolar ridge and joins the facial and lingual cortical plates. Trabecular Bone Trabecular or spongy bone lies within the central portion of the alveolar process, and is the less dense, cancellous bone. When viewed by a radiograph, trabecular bone has a web-like appearance. Alveolar Bone Proper The alveolar bone proper is a thin layer of compact bone, that is a specialized continuation of the cortical plate and forms the tooth socket. The lamina dura (fig. 2-10) is a horseshoe shape white line on a dental radiograph that roughly corresponds to the alveolar bone proper. PERIODONTAL LIGAMENT The periodontal ligament (fig. 2-8) is a thin, fibrous ligament that connects the tooth to the bony socket. Normally, teeth do not contact the bone directly; a tooth is suspended in its socket by the fibers of the ligament. This arrangement allows each tooth limited individual movement. The fibers act as shock absorbers to cushion the force of the chewing impact of mastication. TISSUES OF THE ORAL CAVITY The oral cavity is made up of specialized epithelial tissues that surround the teeth and serve as a lining. These tissues are called the oral mucosa and consist of three types: masticatory mucosa, lining mucosa, and specialized mucosa. Masticatory Mucosa Masticatory mucosa is comprised of the tissue that covers the hard palate and the gingiva. Masticatory mucosa is usually light pink in color (can vary with skin color) and is keratinized. Keratinized tissue has a horny, tough, protective outer layer of tissue. Characteristics of masticatory mucosa are:
HARD PALATE.—The hard palate or roof of the mouth (fig. 2-9) is covered with masticatory mucosa and is firmly adhered to the palatine process (bone). Its color is usually pale pink. Important structures of the hard palate are:
Figure 2-9.—Masticatory mucosa of the hard palate. GINGIVA.—The gingiva, shown in figure 2-10, is specialized masticatory mucosa covering the alveolar process. In a healthy mouth, gingiva is firmly in place encircling the necks of the teeth. It aids in the support of the teeth, and protects the alveolar process and periodontal ligament from bacterial invasion. Healthy gingiva is firm and resilient. Healthy gingiva under normal flossing and brushing activities does not bleed. The color of healthy gingiva can range from pale pink to darker shades (purple to black) depending on each individual’s pigmentation. The surface of the attached gingiva and interdental papillae may be stippled (resembling the texture of the skin of an orange).
Figure 2-1 0.—Structures of the gingiva. Like the tongue, the gingiva is highly vascular and receives its blood supply from the lingual, mental, buccal, and palatine arteries. Other important aspects of the gingiva are discussed in the following paragraphs. Unattached Gingiva.—The portion of gingiva that extends from the gingival crest to the crest of the bone is called unattached gingiva. It can also be called the free gingiva. It can be displaced and is not bound directly to the tooth or bone. In a healthy mouth, this portion is approximately 1 to 3 mm wide and forms the soft tissue wall of the gingival sulcus next to the tooth. Other structures of unattached gingiva include:
Interdental papilla—The portion of the free gingiva that fills the interproximal embrasures below the contact areas of adjacent teeth. It helps prevent food from packing between the teeth.
Lining Mucosa Lining mucosa is found on the inside of the lips, cheeks, vestibule, soft palate, and under the tongue. It consists of a thin, fragile tissue that is very vascular. Lining mucosa is brighter red in color than masticatory mucosa. Also included in the lining mucosa is alveolar mucosa. It lies apical to the mucogingival junction and is loosely attached. <%%> |
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