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. 4-10) is a horseshoe shape white line on a dental radiograph  that  roughly  corresponds  to  the  alveolar bone proper. PERIODONTAL  LIGAMENT The  periodontal  ligament  (fig.  4-8)  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: no  submucosa  lies  under  the  masticatory mucosa, held in place firmly to bone and does not move, has a dense, hard covering, and functions to withstand the active process of chewing and swallowing food. HARD  PALATE.—The hard palate or roof of the mouth (fig. 4-9) is covered with masticatory mucosa and is firmly adhered to the palatine process (bone). Its 4-7 Figure 4-9.—Masticatory mucosa of the hard palate. color is usually pale pink. Important structures of the hard palate are: Incisive  papilla—Located  at  the  midline, directly posterior of the maxillary central incisors (pear-shaped  in  appearance). Palatine  raphe—Extends  from  the  incisive papilla posteriorly at the midline (may be ridge shaped in appearance with a whitish streak at the midline). Palatine  rugae—Extends  laterally  (along  side) from the incisive papilla and from the palatine raphe (wrinkled, irregular ridges in appearance). GINGIVA.—The gingiva, shown in figure 4-10, 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). 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