Changes occur in the morphology of the jaws after tooth loss (Fig. 11.1). The jaws are composed of alveolar and basal bone. The alveolar bone and periodontium support the teeth, but neither have a physiological function once the teeth are lost, and are therefore resorbed. Alveolar bone changes shape significantly with tooth loss, in both the horizontal and vertical planes, but the overall pattern of resorption is largely predictable. In the maxilla and in the anterior aspect of the mandible bone loss occurs typically in both the horizontal and vertical planes. In the posterior mandible the bone loss is mostly in the vertical plane.

Fig. 11.1 (a) A dentate mandible, illustrating the extent of supporting (alveolar) bone around the teeth. (b) An edentulous mandible, illustrating the extent of resorption of alveolar bone that occurs following loss of the teeth. Note also that the angle between the ascending ramus and body of the mandible is more obtuse than in (a), and the mental foramen is also closer to the crest of the edentulous ridge. The shaded areas in this illustration indicate areas of resorption of mandibular bone with advancing age.

After physiological resorption has occurred, the remaining jaw structure is termed the ‘residual ridge’. The bone that remains after alveolar bone has resorbed is termed ‘basal bone’. Marked resorption sometimes affects the entire mandible (Fig. 11.2). Basal bone does not change shape significantly unless it is subjected to excessive local forces, for example, in the edentulous anterior maxilla in association with retained natural lower incisors.

Fig. 11.2 Gross resorption of the mandibular alveolar ridge gives rise to denture instability, due in part to the reduced surface area of the alveolar ridge, but also to the prominence of the mandibular muscle attachments (e.g. genioglossus), which displace the denture during tongue movements.

Other affected anatomical structures

Other anatomical structures may become more prominent with tooth loss. The genial tubercles and their muscle attachments may become prominent in a patient with extensive resorption of the mandible, sometimes compromising denture stability. Maxillary or mandibular tori may also cause instability of a denture, or may be traumatized by it. A prominent fraenum (Fig. 11.3) can displace a denture during function, and may weaken the denture base so that it fractures through flexing.

Fig. 11.3 A prominent labial fraenum causes displacement of the denture. If the denture flange is eased to fit round the fraenum, the denture may be weakened. Excision of the fraenum (fraenectomy) is indicated.

Forces transmitted through the teeth during mastication are absorbed by the supporting structures (the periodontium and alveolar bone). In an edentulous patient, forces exerted by a denture are transmitted through the oral mucosa to the underlying bone. A denture must therefore fit well if trauma to the oral mucosa overlying an edentulous ridge is to be avoided.

Facial aesthetics are affected by tooth loss. The facial profile collapses (the nose and chin appear too close together) after tooth loss and consequent edentulousness. The loss of face height can be restored with dentures.

CLASSIFICATION OF THE EDENTULOUS JAWS

Cawood and Howell (1988) classified the edentulous jaws according to the state of ridge resorption after tooth loss (Table 11.1). There are other classifications, but this one has been adopted internationally as a means of assisting communication and assessment of a patient’s edentulous state.

Table 11.1 A classification of the edentulous jaws

Class	Description
I	Dentate
II	Immediately postextraction
III	Convex ridge form, adequate in height and width
IV	Knife-edge ridge form, adequate in height but inadequate in width
V	Flat ridge form, inadequate in height and width
VI	Loss of basal bone, which may be extensive but follows no predictable pattern

From Cawood and Howell (1988)

THE IDEAL EDENTULOUS RIDGE

A removable denture requires a firm bone support with a smooth contour, adequate to provide stability, with access to the vestibule for a peripheral seal, and without any soft-tissue excess (e.g. flabby maxillary tuberosities) likely to cause displacement or weakness of the denture.

Most patients tolerate the loss of their natural teeth and subsequent denture wearing without difficulty. However, there may be extensive loss of alveolar bone after tooth extraction, resulting in an atrophic (flat or knife-edged) edentulous ridge (Fig. 11.4). In some patients this can make denture wearing difficult or uncomfortable. The prosthodontist may be able to modify a denture design to enhance its stability and retention, but this is not always possible. Surgery may therefore be required to enhance retention and stability of the prosthesis.

Fig. 11.4 This 32-year-old patient has difficulty in wearing a denture. The alveolar ridge has a ‘knife-edge’ profile, and there is a loss of sulcus depth.

TREATMENT PLANNING

History

The history will indicate the patient’s principal concerns and expectations of treatment. The age and health of the patient influence the treatment plan’a young person with severely resorbed alveolar ridges might tolerate more complex surgery than would a mature patient with similar jaw morphology.

Clinical examination

This will include general extraoral and intraoral assessment of the hard and soft tissues, and specific analysis of the denture-bearing areas.

The height, width and general shape of the alveolar ridges are assessed, with an emphasis on the presence of bony undercuts and the position of anatomical structures such as the mental neurovascular bundle. The depth of the buccal sulci, the position and size of fraenal and muscle attachments and the condition of the alveolar ridges are documented. The dentures should be technically acceptable before considering preprosthetic surgery.

Special investigations

Radiographs are taken to assess the condition of the underlying bone. A panoramic film is useful to assess the overall condition of the edentulous ridges and to identify any retained dental roots or other pathology (e.g. cysts of the jaws). A lateral cephalostat may be taken to demonstrate the anteroposterior skeletal relationship and the height of the alveolar ridges anteriorly. Periapical views are desirable if retained roots are to be removed before construction of a denture.

Articulated study casts facilitate treatment planning and are helpful when explaining the surgical procedure to a patient. A diagnostic wax-up of the prosthesis is desirable to demonstrate the anticipated final aesthetic result to the patient, and as a medicolegal record of the proposed treatment.

PREPROSTHETIC SURGERY PROCEDURES

Various techniques may be used, either alone or in combination, to preserve or improve the denture-bearing area. There are three broad categories of preprosthetic surgery procedure:

1. Soft-tissue surgery

2. Bone-contouring (or augmentation) procedures

3. Endosseous implant surgery.

Summary of treatment planning

• Consider the patient’s concerns and expectations

• Assess their medical fitness

• Examine both extraorally and intraorally

• Assess the height, width, regularity and relationship of the ridges

• Consider whether improvement can be achieved by prosthetic means

• Radiographs may be needed to exclude other pathology and to determine the quantity and quality of bone

• Study casts and a diagnostic wax-up may be of value

Some of the procedures described below may be included in more than one category.

Soft-tissue procedures

Excision of hyperplastic tissue

Hyperplastic oral mucosa under or adjacent to a removable denture usually arises in response to chronic irritation, for example, from an overextended denture flange or a deficiency in the fitting surface of a denture, trauma from a sharp cusp on an acrylic tooth or an ill-fitting denture clasp. Poor denture design may also cause mucosal hyperplasia (Figs 11.5, 11.6). Surgery may be unnecessary if the cause of the hyperplastic tissue is identified and eliminated; the hyperplastic tissue will then usually diminish in size or resolve completely. Any residual tissue that inter-feres with denture construction can be removed via an elliptical incision as for an excision biopsy (see Ch. 8, p. 109). Where possible (e.g. in the buccal sulcus or on the cheek), the incision may be closed by suturing the wound edges together (primary closure). On the edentulous ridge, the periosteum is elevated to undermine the edges of the wound, and the edges of the mucoperiosteal flaps can then be advanced to achieve wound closure. A split-thickness skin graft may be required to cover extensive areas of denuded oral mucosa. A keratinized-free mucosal graft may be harvested from the hard palate for smaller areas. It is often beneficial to place a temporary soft lining in the existing denture after surgery, to minimize the likelihood of further irritation, prior to remaking the prosthesis.

Fig. 11.5 This is an extensive ‘leaf fibroma’ of the hard palate. The lesion was attached to the hard palate by a small stalk (a peduncle) and resembled the outline of a relief chamber incorporated into the fitting surface of the denture.

Fig. 11.6 Fibroepithelial hyperplasia associated with the irritant margin of an ill-fitting lower denture.

Prominent labial fraenum

The flange of a denture may traumatize a prominent labial fraenum or muscle attachment (Fig. 11.3). If the fraenum is relatively small, this may be managed by trimming back the labial or lingual denture flange. However, the denture may be weakened and it might fracture if extensive trimming is undertaken to relieve the fraenum. Excision of the fraenum (fraenectomy) may be indicated to avoid this.

For the fraenectomy procedure (also described in Ch. 12) vertical incisions are made parallel to the fraenum, extending into the sulcus from the residual ridge to form a rhomboid-shaped wound (Fig. 11.7). The incisions are widest at the base of the labial sulcus. The insertion of the fraenum into the alveolar ridge is held with either a suture or a pair of toothed tissue forceps and the fraenum is dissected, leaving periosteum covering the surface of the bone. Interrupted sutures are inserted through the mucoperiosteal flap to achieve wound closure. A modification of this procedure incorporates a Z-plasty, to preserve sulcus depth (Fig. 11.8). However, the Z-plasty can be technically more difficult than the fraenectomy technique described above.