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Figure 2.1 The subperiosteal implant.

      Although subperiosteal implants were effective, the overall procedure was lengthy and involved a great deal of discomfort for the patient and often were subject to various complications [8, 9]. Further, a high degree of surgical skill was required and necessitated a close collaboration between the surgeon, prosthodontist, and the laboratory technician to ensure optimal clinical results. Provided care was exercised in patient selection, there was good overlying soft tissue and no residual alveolar bone, the prognosis could be very good with reasonably high short‐term success rates.

       Endodontic Implants

      For many years, the most established and longest established implant was the endodontic endosseous pin implant, also known as the endodontic stabilizer, and was particularly useful for rigidly anchoring a mobile tooth to bone. Tooth mobility can have many causes, including an unfavorable crown‐to‐root ratio, gum and alveolar recession, bruxism and an unbalanced occlusion.

      The basis of this approach was that a pin was inserted through the root canal into the underlying bone such that it was anchored in bone but with upper end projecting into the mouth and upon which, a crown or RPD was fabricated [10].

      Typically, the lower end of the pin did not penetrate the cortical plate of the mandible or the antral or nasal floors of the maxilla. Indications for endodontic implants included treatment of root fractures, external or internal root resorption and when better support and stability was required for FPD or RPD abutments.

Although the clinical use of endodontic endosseous pin implants is less common due to the advent of the modern endosseous implant, they were successful, with few contraindications for their use provided correct clinical procedures were followed [11].

       Endosseous Implants

      Endosseous implants, also known as intra‐osseous and endosteal implants, have been in clinical use since the 1960s [12]. There are four main categories of endosseous implant, namely pins, spirals, blades, and screws. Regardless of implant design, endosseous implants are used in edentulous areas where there is sufficient healthy bone to accommodate the implant. Selection criteria for the use of implants are discussed in later chapters of this book.

      The first successful endosseous implants were the Formiggini spiral screw implant and, subsequently, the Cherchève spiral‐post implant, the former dating from 1947 and the latter from the 1960s to 1970 [4, 12]. The most sophisticated, and successful, Cherchève implant consisted of a double hollow spiral mounted on a square post. After the bone was trephined to create a cavity, the implant was placed beneath the alveolar ridge with the shank or post extending into the oral cavity and, upon which, the final prosthesis was constructed. The problem with these early implants was that trephining of the bone created a gap or space between the abutment post and the host hard and soft tissues, and this could sometimes present problems.

      Many workers developed modifications of the spiral implant during the late 1960s and early 1970s. These largely comprised self‐tapping screw implants, often with a vent or port below the threaded portion to permit fibrous tissues and, hopefully, bone to grow through the aperture and promote retention. Although many of these screw implants were successful, numerous failures occurred as the result of tissue irritation, frank infection and epithelial downgrowth preventing adequate retention and sometimes complete evulsion of the implant. Commonly, poor bony attachment to these implants caused stability to be a problem.

An alternative approach to screw‐type endosseous implants was the tripodal pin concept which dated from the same period. In essence, thin tantalum pins were inserted into bone at roughly 120° angulations and the exposed ends of the pins were bonded together using acrylic resin, Fig. 2.2.

      The implanted tripodal system could then be used as a bridge abutment or to support a single‐unit prosthesis. Although pin implants had certain applications, they did not possess long‐term retention, generally were not self‐supporting and the pins often were easily displaced or removed over time.

A major development in endosseous implants was the blade or blade vent implant designed by Linkow in 1968 and subsequently modified by Linkow and others over the period 1970–1971 [12–14]. Blade implants were originally designed for use in areas where there were knife‐edge alveolar ridges, situations where screw‐type implants are contra‐indicated. These implants can be used in virtually all maxillary and mandibular edentulous areas, provided there is sufficient residual alveolar process. Because the implants have greater mesio‐distal dimensions than their vertical heights, the design combines maximal stability, especially against lateral forces, while minimizing risk to underlying tissues and structures.