50 Theories and techniques of oral implantology

ORAL EPITHELIUM

Bone is not the only tissue important to the implantologist. Overlying the bone are various soft tissues. Generally, if these are in good health, they are not a prime factor in performing an endosseous implant intervention. However, they are a vital consideration when contemplating a subperiosteal implant, for they must he parted to expose the implant site and they must heal properly to hold the implant firmly in place. The subperiosteal technique is intimately involved with the structure, function, and relationship of the soft tissues to other tissues in the oral cavity, particularly bone.

Of interest to the implantologist are the mucosa, submucosa, and nerve and vascular bundles. The nerves and their associated blood vessels have al-ready been discussed in detail. The same consideration, namely avoiding impinging upon or in any other way interfering with the major routes, applies here. As for the mucosa and submucosa, a detailed study is appropriate.

Mucosa

Any body cavity that communicates with the outer environment is lined with a specialized soft tissue, the mucosa, or mucous membrane. The oral mucosa is composed of two layers, the surface epithelium and the lamina propria, which are separated from one another by a basement membrane.

Surface epithelium. Surface epithelium consists of several kinds of cells: basal, prickle, granular, and keratinous. These names describe the location, con-tour, or appearance of the cell. The cells lie in strata named after the characteristics of the cells. The basal cells form a thin stratum that is lowest in the tissue. They lie right next to the basement membrane and attach the epithelium to it. Because these cells are cuboidal in shape, they are also called cuboidal cells. On top of the basal, or cuboidal, stratum is the prickle cell stratum, which is composed of irregularly shaped cells stacked one on top of the other, several cells deep.

Both the basal and prickle cells are capable of mitosis. They undergo frequent division, and the uppermost prickle cells are pushed upward by the new additions. They become flatter and granular and form the granular stratum of the epithelium. As they are pushed to the surface, they become keratinized and die. The degree of keratinization depends upon the location in the mouth. Those around the gingiva of the teeth, where a great deal of abrasion occurs, become heavily keratinized and tough. Those under the tongue are less keratinized. These

superficial keratinized cells slough off individually and very easily.

Lamina propria. The lamina propria is a layer of dense connective .issue in which are embedded blood vessels and nerves. Papillae, or protrusions, of this tissue extend upward into the epithelium, in-creasing the amount of contact between the two layers. Blood vessels in the papillae nourish the epithelium and carry away its metabolic wastes. Some of the nerves in the papillae actually pass into the epithelium.

The height of the papillae, and thus the thickness of the lamina propria, varies. In the alveolar mucosa, for example, the papillae are short and few in number. In the gingiva, the papillae are tall and numerous. Naturally, the height of the papillae corresponds closely to the depth of the epithelium; where the epithelium is thick, the lamina propria is also thick.

As has been discussed, the oral mucosa may vary in degree of keratinization of the epithelium, thickness of the epithelium, and structure of the lamina propria, particularly the density and height of its papillae. Of particular importance in the performance of a subperiosteal implant is the way in which these tissues are held to the underlying structure, which is a function of the submucosa.

Submucosa

The submucosa consists of connective tissue containing glands, blood vessels, nerves, and adipose tissue. Here the vessels and nerves divide into smaller branches that pass into the lamina propria and its papillae.

To the implantologist, the most important function of the submucosa is that it serves to attach the mucosa to underlying structures. The submucosa may be thick or thin, dense or of the loose alveolar type, and it may contain fibers of various tensile capacity. These characteristics determine whether the attachment will be loose or firm.

The mucosa over the alveolar ridge is firmly attached to the bone by a thin layer of dense submucosa containing short thick fibers. The mucosa forming the buccinator surface is held by a relatively thick submucosa filled with elastic fibers. When the underlying muscles move and change shape, the mucosa remains firmly held to the altering contour of the muscles by the fibers. When elastic tissue loses its elasticity, as in old age, the mucosa is less tightly held and can be bitten. This is a consideration in planning the bridge.

In areas where the mucosa and its underlying