11: Surgical aids to prosthodontics, including osseointegrated implants

11 Surgical aids to prosthodontics, including osseointegrated implants

INTRODUCTION

Although many advances in dental health have been made over the past few decades, it is nevertheless rare for an individual to retain a full complement of natural teeth for life. Teeth are lost for various reasons, notably periodontal disease, dental caries, pathological conditions of the jaws and trauma. Prosthodontics aims to restore not only the function and aesthetics of the dentition after tooth loss but also the aesthetics of the facial form.

A well-constructed removable prosthesis that replaces missing teeth will restore function and appearance. A removable prosthesis should be stable and have adequate retention and stability. To achieve this, the prosthesis should be seated onto well-shaped alveolar ridges with adequate basal bone and a healthy oral mucosa. There will ideally be no major vertical or horizontal skeletal discrepancy, which can compromise denture stability.

Preprosthetic surgery is a term used for surgical procedures that aim to improve the condition of the oral tissues to enable a removable denture to rest on a sound base, free from marked bony protuberances or undercuts, with no interfering muscle attachments, flabby soft-tissue excess or hyperplastic oral mucosa. To achieve the best results, the skills of the oral surgeon and the prosthodontist are combined in a team approach.

Endosseous implants are commonly placed in suitable patients to improve the stability and retention of removable dentures as well as fixed prostheses. Implants may avoid the need for more complex surgery to improve an otherwise unsatisfactory edentulous ridge.

PHYSIOLOGICAL CHANGES IN THE ORAL TISSUES AND MASTICATORY APPARATUS ASSOCIATED WITH AGE

The oral tissues undergo physiological changes with advancing age, some of which may influence the outcome of prosthodontic rehabilitation:

As we age the blood supply to the jaws becomes increasingly dependent on the circulation in the periosteum, rather than from the arteries. This is largely due to age changes leading to narrowing of the lumen of vessels such as the inferior alveolar artery. Consequently, it is important to preserve the periosteum and its blood supply wherever possible, to minimize the risk of ischaemic necrosis of under-lying bone.

Physiological changes in the oral tissues are sometimes a consequence of hormonal changes. For example, oral discomfort may occur in women without overt clinical signs, and denture wearing may aggravate the symptoms in some patients. In a few cases, oral discomfort may be attributed to the menopause, and the symptoms may resolve after hormone replacement therapy. It is therefore necessary to obtain a comprehensive history from the patient in order to identify accurately the cause of any oral discomfort associated with denture wearing. Nutrition can also play a part in oral discomfort; some patients with sore mouth may be anaemic.

ANATOMICAL CONSEQUENCES OF TOOTH LOSS

Loss of alveolar bone

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.

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.

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)

TREATMENT PLANNING

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:

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.

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.

Jan 14, 2015 | Posted by in Oral and Maxillofacial Surgery | Comments Off on 11: Surgical aids to prosthodontics, including osseointegrated implants
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