The tissues involved in implant procedures 27

Lingula   Mandibular foramen

Alveolar process

Mental protuberance

External

oblique   Mylohyoid   Mental

ridge   foramen

Fig. 2-1. A mandible with all teeth present usually has a considerable amount of alveolar bone above the mental foramen. Considerable amounts of alveolar bone are not typical of the edentulous or partially edentulous areas where endosseous implants are contemplated.

men, which is marked by a spur of bone called the lingula.

In the bone the mandibular canal is located in the spongy cancellous bone (Fig. 2-2). The canal does not have a definite wall. In the area of the molars, it divides into several branches, supplying the teeth and chin with nerves and vessels (Fig. 2-3) . The mental foramen, which can be seen on the outer surface of the mandible near the chin, marks the place where that branch of the mandibular nerve known as the mental nerve, or inferior dental nerve, exits from the bone and passes into the soft tissues.

In an adult with all his teeth, the mandibular canal is approximately midway between the inferior and superior borders of the mandibular body (Fig. 2-4). However, its position changes with age and/or loss of teeth, and the changes directly reflect what happens to the alveolar process.

The alveolar process is an arch of bone on the uppermost part of the body of the mandible. This is the part that bears the teeth. The arch contains sockets, or alveoli, for the roots of the teeth. The alveolus on both the inside and outside surfaces of the mandible is marked by vertical ridges following the contours of the sockets.

The process is composed of several parts that bear mentioning because of their involvement in implant procedures. The walls of the sockets adjacent to the periodontal ligaments comprise the cribriform plate, or alveolar bone proper. Between the cribriform plate and the labial and lingual cortical plates is supporting alveolar bone.

The inner wall of the alveolar bone is made of a thin tissue called the lamina dura. The lamina dura is perforated by many blood and lymph vessels and by nerves that connect the periodontal membrane with the supporting alveolar bone. The alveolar process acts as a single unit, and all its parts join to support the teeth.

The amount of alveolar bone changes markedly during life, as does the appearance of the rest of the mandible (Fig. 2-5). At birth the body is a shell of bone enclosing the developing teeth. The mandibular vessel and foramen are near the lower border, the foramen being opposite the cavity for the first milk molar tooth. The ramus is short and the angle is very obtuse, so that the coronoid process is almost in line with the body. As the teeth erupt and the child begins to chew, the body becomes stronger and deeper, the rami enlarge, and the angle becomes reduced (Fig. 2-6).