36 Theories and techniques of oral implantology

the sinus floor is usually separated by alveolar bone about 1 cm. deep in the lateral maxillary sinus region and 1.2 cm. in the anterior nasal region. The width of the alveolar crest increases from front to rear, with the maximum width usually at the level of the last molar and wisdom teeth. As teeth are lost, the alveolar hone recedes, lowering the sinus floor. In the edentulous patient with marked alveolar bone resorption, only a thin layer of hone may divide the sinus from the mouth (Fig. 2-16) .

Again, the approach to an endosseous implant procedure is determined by the extent of alveolar bone and the placement of a landmark, this time the sinus. The classification table in Fig. 2-17 indicates which cases are acceptable for an implant procedure and which are not. It should be noted that the amount of alveolar hone between the floor of the sinus and the mouth need not be the only consideration. If there is sufficient bone flanking the sinus, the cavity may be circumvented by the tripod implant procedure (explained in Chapter 1) or with variously shaped blade implants. Generally, however, the resorption of an edentulous maxilla takes place buccopalatally, thereby thinning out to a knife-edge ridge. The amount and direction of resorption can be best seen by reflecting the soft tissues overlying the ridge. Often the tuberosity is wider than the ridge, allowing a blade to be inserted buccopalatally.

As for the front of the maxilla, there may be adequate bone remaining for another type of implant if the maxillary sinus does not extend too far forward or if the nasal cavity is not endangered.

BONE

The gross anatomy of any organ reflects the arrangement of tissues that comprise it and the activities of these tissues. Because an implant procedure involves interrupting the normal continuum of events in these tissues, it is necessary to keep in mind what constitutes normal activities and their deviations in order to evaluate the appropriateness and success of the procedure. As will be seen, an implant intervention is designed not only to cause little abnormal disruption in the tissue involved but also to capitalize on the normal healing and restorative processes inherent in these tissues.

Bones are composed of marrow, various membranes, and bone tissue.

Marrow

The spaces between bone tissue are filled with marrow. Two varieties of marrow exist, red and yel

low. Red marrow has hematopoietic, or blood-forming, functions. In the newborn infant all marrow is red. As the individual matures, many red marrow sites gradually change into a more fatty, yellow mar-row that does not produce red blood cells. However, yellow marrow can revert to red marrow when the body is called upon for increased production of red cells. Red marrow is usually seen in the jaws associated with bone resorption. Yellow marrow is often seen in maxillary tuberosities.

Bone marrow participates in the formation and destruction of bone tissue. Some of the marrow cells can differentiate into bone cells, and nonfunctioning hone cells may disappear into the marrow stroma.

Periosteum

The periosteum is a two-layered membrane covering the outside of the bone. The outer layer consists of dense connective tissue containing blood vessels. In areas where it serves as an attachment site for the muscles, it is thin and strongly attached to the hone. Where it does not serge as an attachment site, it is thick and easily lifted from the bone. The periosteum may not be present when muscles or tendons are attached to the bone itself. The muscle or tendon is bound by its own interstitial connective tissue, which extends into the bone as Sharpey's fibers.

The inner, or cambium, layer of the periosteum contains loosely arranged collagenous bundles, cells with osteogenetic potencies, and a few blood vessels. In a mature adult, the periosteum normally has no osteogenic functions. However, when a bone fractures, its bone-forming potentialities are activated.

Endosteum

The endosteum is the membrane that lines bone marrow and all other cavities of the bone. It has both osteogenetic and hematopoietic functions, and it takes an active part in the healing of fractures.

Bone tissue

Bone tissue is composed of two basic elements—hone cells and an intercellular substance. The cells include osteoblasts, cells associated with the growth and development of bone; osteocytes, mature osteoblasts embedded in the intercellular substance; and osteoclasts, large, multinucleated cells bringing about the destruction of bone tissue. All three are present simultaneously, for bone--in spite of its

hardness   is in a continual state of change.

The intercellular substance, which is also called the matrix or ground substance, is a product of the