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.
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.
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:
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: