The tissues involved in implant procedures 51

muscles move in a great variety of positions, the submucosa is a loose areolar type. It contains a relatively large amount of adipose tissue and a few fine fibers. This type of attachment permits the wide variety of movements characteristic of the lips and tongue.

Evaluating the soft tissues for a subperiosteal implant

It is difficult at times for the implantologist to determine the true characteristics of the mucosa in regard to thickness, amount of adipose tissue, depth, and degree of the protrusions of the papillae from the lamina propria, as well as the elasticity and tenacity of attachment of the deepest layers of the submucosa to the bone. All of these characteristics might very well play an important role in the success or failure of a subperiosteal implant.

A patient having an extremely thin mucosa and submucosa in the oral cavity might be a poor risk for a subperiosteal implant, because the lack of elasticity and density of his tissues might allow the implant borders to eventually perforate the tissues. In contrast to this type of poor risk patient, a patient who has extremely thickened tissue with a heavily keratinizecl mucosa might also be a poor risk for the subperiosteal implant intervention. In such hard, thickened tissues there may be very few blood vessels extending from the submucosa into the lamina propria and, through the papillae, into the outer layers of the mucosa. Such poor circulation hinders the rapid overall healing of the incised tissues. If slow sporadic healing occurs, as it might in such a case, the incised tissues invaginate inward with epithelial tissue, thus exposing the metallic implant substructure and never allowing it to be completely buried by soft tissue. As a result, the implant is not tenaciously held and can be easily dislodged.

The effects on the mucosa and submucosa resulting from interaction with other structures in the mouth should also be carefully evaluated. For ex-ample, in a patient who has a large and unusually thick tongue (macroglossia), the mechanical effect on the mucosa and submucosa from the movements of the tongue during speaking and swallowing must be considered. Normally a person swallows several thousand times a clay; in a patient with macroglossia combined with a thin layer of soft tissues over the implant site, the continual anterior and lateral thrusts of the tongue could dislodge the implant.

Another consideration in evaluating the implant site is determining the shape of the resorbed alveolar crest that will bear the implant. The muscle attach-

ments often fool the prosthodontist into thinking that the mylohyoid ridge, which lies somewhat lingually to the alveolar ridge, is the true ridge. Thickened pads of soft tissue also aid this deception, so palpation of the area is not adequate. The implant must be fabricated to fit exactly over the resorbed alveolar ridge or it will fail. For this reason, it is important to reflect the tissues and reveal the crest so that an accurate wax or stone bone bite impression can be taken. This will help orient the operator, as well as the technician, to the area of the true crest of the ridge.

The last and one of the most vital points in evaluating the implant site is determining the location of the mental nerve   the continuation of the man-
dibular nerve that lies in the soft tissues near the chin. Unlike an endosseous implant procedure, where x-rays show the mandibular canal as the site to be avoided, the subperiosteal procedure involves locating the nerve as it leaves the bone and passes into the soft tissues. In a jaw bearing teeth, the men-

tal foramen   the exit site—lies below and between
the root apices of the bicuspid teeth. In the edentulous jaw, it must be demonstrated by carefully retracting the soft tissues away from the bone.

Because of these soft tissue characteristics   dif-
ficulty in determining the depth and elasticity of the mucosa and submucosa, difficulty in determining the true alveolar ridge, and difficulty in locating

the mental nerve   the tissues should be incised to
reveal the site that will bear the implant.

Healing of the soft tissues

Scar tissue along the crest of the ridge does not form in the same manner as it does, for example, on the face, hands, or any other external surface of the body. In fact, it can hardly be seen in many cases after a carefully performed subperiosteal implant intervention. This is probably caused by the rich blood supply in the mucosa and submucosa. Therefore the rapid reestablishment of the blood supply is of prime importance in suturing the tissues. The suturing must be clone in such a manner that the deeper submucosal layers containing most of the blood vessels are held firmly together, surface to surface, from the deepest layers outward. Merely suturing the cut edges back together may not be adequate, and the implant may fail because of slow healing and improper formation of scar tissue.

Certain incised areas of the soft tissue heal more slowly and are usually extremely uncomfortable post-operatively for the patient. The tissue in the retromolar pad area is an example. This tissue is in the