Implant systems are designed based on the principles described in Chapter 2. Irrespective of the system, the design features aim to provide reduced healing times and rapid integration to provide patients with faster reconstructions. An implant-retained prosthesis is made up of three parts, and each part connects to the other like a piece in a jig saw (Figure 3.1). The precision with which each component is made to fit determines the successful outcome of the restoration. A number of compatible replicas are available; however, it is good practice to use the designated components whenever possible. The growing demand for implants has been driven both by patients and clinicians who are trying to satisfy their patients with manufacturers providing solutions to these demands with newer designs and configurations emerging many of which have little or no published data. A number of the mainstream implant companies have also produced new implant and restorative product lines with limited evidence supporting their success. The focus of these products is to address the demand from patients wanting more rapid solutions for tooth replacement. It is, however, important to remember that these developments cannot overcome the limitations imposed by the biological factors which are integral to successful osseointegration. Whilst every system has specific nuances, making it unique, the majority have features that are common and follow the basic principles related to osseointegration and its success. These features are categorised below.

• Components

All implant systems have four components (described below) that are essential for the provision of implant-retained restorations (Figure 3.2).

• A. The Fixture Component (also known as the implant or screw)

This is the part that replicates the root of the tooth and has to be surgically placed into the jaw bone to allow osseointegration into the bone. The different design features and surfaces of the screw that play a role in enhancing osseointegration have been covered in the previous chapter. The screw is designed to facilitate placement into the jaw bone with ease, without causing any trauma to the bone. Some systems have specific designs apically to facilitate atraumatic placement. The top part of the screw on which the prosthesis sits is called the ‘platform’. The platform contains the connection into which the prosthesis is connected. The type of connection will influence the marginal bone stability. The microgap at the platform–prosthetic interface is reported to affect the marginal bone loss; however, if this was shifted medially, then the marginal bone around the implant is noted to remain stable. This concept is called ‘platform switching’ (Figure 3.3a, b). The junction at which the connection on the platform links the prosthesis to the implant screw, is called the ‘implant abutment connection interface’.

This interface is crucial in preventing rotational movement of the prosthesis which usually inserts into the implant screw by the use of either a slip fit or friction fit connection.

There are two main types of connections with different configurations (Figure 3.4). These are:

• External:

This was the first type of connection which protrudes beyond the top of the platform. It is a slip fit connection which can be a hexagon often called the ‘external hex’ or an octagon with the former being more common. This connection has a higher centre of rotation thus reducing mechanical stability leading to an increased frequency of screw loosening of the prosthesis resulting in its reduced use. Although implants with this type of connection are available, the majority of systems have moved away from this connection due to the stress distribution which occurs largely at the apical area and the marginal area.

• Internal:

This connection sits within the body of the screw. It offers a close and tight fit which prevents micromovement of the abutment, prevents microleakage and distributes forces and mechanical stress generated during function through the body of the implant screw and out towards the bone. There are different internal connection configurations associated with the various implant systems; however, all aim to offer the same function. The configurations include the following:

• the six point hexagon,
• 12 point double hexagon,
• internal cylinder hexagon,
• the trichannel lobe,
• the morse taper design with a mechanically locking friction fit connection with a 5.7^o degree or 8^o taper and
• the morse taper design with a mechanically locking friction fit connection with a 11.5^o cone screw connection.

Figure 3.5 shows the different types of connections.

Although these different connections are used, they do not influence the implant survival or complication rates, however, the internal connection systems have shown slightly lower marginal bone loss. The majority of implant systems today have moved to the internal connection with moderately rough implant surfaces. Table 3.1 shows the connections associated with different implant systems. The surgical technique needs to be modified depending on the connection and is covered in Chapter 5.

• B.
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