Introduction

The restoration of edentulous and partially dentate jaws using a variety of implant-retained prostheses has become a common clinical procedure in recent years. The implants are usually made of titanium and are described as either:

This chapter concentrates on endosteal dental implants which are more commonly used, particularly since P. I. Brånemark’s clinical research on the concept of osseointegration which he defined as a direct connection between living bone and a load carrying endosseous implant at the light microscopic level. There are many different endosteal implant systems available, and it is beyond the scope of this book to discuss all the systems and their various advantages and disadvantages. The Brånemark system, described here, is probably the best known and has been researched over the longest period demonstrating acceptable 20-year success rates. Most currently used implant systems can be viewed as design modifications to this basic concept.

However, whatever the system used, radiology plays an essential role in preoperative treatment planning, postoperative follow-up and success evaluation.

The Brånemark system

Treatment usually involves either a two-stage or a one-stage (non-submerged) surgical procedure followed by the restorative phase. Initially, in the two-stage technique the fixture is placed in vital bone ensuring a precision fit. The cover screw is screwed into the top of the fixture to prevent downgrowth of soft and hard tissue into the internal threaded area. The fixture is then left buried beneath the mucosa for 3–6 months. (It is important during this initial healing period to avoid loading the fixture although early loading protocols are being used in certain clinical circumstances.) The fixture is then surgically uncovered, the cover screw removed and the abutment (the transmucosal component) connected to the fixture by the abutment screw. An hexagonal anti-rotation device is incorporated into the top of the fixture. The gold cylinder, an integral part of the final restorative prosthesis, is finally connected to the abutment by the gold screw. A standard Brånemark implant is illustrated in Fig. 23.1.

Modifications to this basic design include slightly roughened implant surfaces to improve bone to implant contact and more stable, secure abutment/implant connection systems employing internal connections rather than the classic flat-top hexagon described above. A variety of different abutments and connecting restorative elements are available for different clinical situations.

Main indications

Replacement of missing teeth in patients with:

A thorough clinical examination using study casts and an overall evaluation of the patient are essential, as good case selection is imperative for the long-term success of implants. A multidisciplinary approach involving surgeons, prosthodontists and dental technicians is often adopted because of the many important factors that need to be taken into account, including:

Radiographic examination

In recent years various guidelines have been published in both the USA and in Europe recommending the most appropriate radiographic examination(s) to use in preoperative treatment planning. However, the reliable evidence on which to base recommendations is still limited. In addition, other variables contribute to disagreement on selection criteria in individual clinical situations. Examples of these include:

There are a range of investigations that are suitable in different clinical situations. Clinical choice may well depend on availability of facilities. Investigations include:

• Periapical radiography

• Panoramic radiography (see Fig. 23.2A)

• Lower 90° occlusal radiography (see Fig. 23.2B)

• Lateral cephalometric radiography (see Fig. 23.2C)

• Cross-sectional linear tomography programmes available with some modern panoramic machines

• Cone beam CT. This is ideal for implant assessment and is likely to become the imaging modality of choice when cross-sectional imaging is required (see Figs 23.3 and 23.4). Computer manipulation enables the production of panoramic and cross-sectional (transaxial) images. CBCT data can be imported into specially designed implant planning software programs, such as SimPlant® or NobelGuide®, to create 3-D reconstructions of the jaws and to plan the placement of implants in three dimensions. The software can also be used to design a drill guide so that the implant fixtures can be placed accurately at the proposed sites (see Fig. 23.4).

• Computed tomography (CT). Specific dental computer programs, designed for implant planning, have been written that are compatible with medical CT. This usually involves about 30 axial scans per jaw, each 1.5 mm thick. This information can then undergo computer manipulation to produce reformatted cross-sectional, panoramic and three-dimensional reconstructed images as shown in Fig. 23.5. The CT data can also be imported into implant planning software.

• Magnetic resonance (MR). This offers the advantages of not using ionizing radiation and producing sections in any desired plane without reformatting, as shown in Fig. 23.6.

Postoperative evaluation and follow-up

Postoperative evaluation can be carried out immediately after surgery and usually after the initial 4–6 months healing period. Further clinical evaluation of the success or otherwise of the implant, including radiographic assessment, should be carried out on an annual basis for the first few years and then bi-annually. Geometrically accurate paralleling technique periapicals (either film-based or digital) are most commonly used. Note: The accuracy can be checked by examining the geometric thread pattern of the fixture.

Criteria for success

Ideally, implants should be evaluated against standardized success criteria and not simply assessed for their survival. Several criteria for success have been put forward over the years for the different implant systems. Those favoured by the author, and cited frequently in the literature, are those proposed by Albrektsson in 1986. These include:

1. That an individual, unattached implant is immobile when tested clinically.

2. That a radiograph does not demonstrate any evidence of peri-implant radiolucency.

3. That vertical bone loss be less than 0.2 mm annually following the implant’s first year of service.

4. That individual implant performance be characterized by an absence of signs and symptoms such as pain, infection, neuropathies, paraesthesia or violation of the inferior dental canal.

5. That, in the context of the above, a success rate of 85% at the end of a 10-year period be the minimum criteria for success.

Radiographic evaluation (see Figs 23.7–23.9)

Radiographs allow evaluation of criteria 2 and 3, but also are used to assess:

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• The position of the fixture in the bone and its relation to nearby anatomical structures

• Healing and integration of the fixture in the bone

• The peri-implant bone level and any subsequent vertical bone loss – threaded fixtures allow easy measurement if radiographs are geometrically accurate

• Development of any associated disease, e.g. perimplantitis

• The fit of the abutment to the fixture

• The fit of the abutment to the crown/prosthesis

• Possible fracture of the implant/prosthesis.

Footnote

The limited nature of the information provided by conventional two-dimensional radiographs on the width or thickness of the alveolar bone cannot be overemphasized. Inadequate clinical and radiographic assessment of possible implant sites, before surgery, may lead to implant failure and more seriously, to temporary or permanent nerve damage and possible litigation.

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