The aim of this chapter is to discuss issues in the management of cases that require advanced implant treatment.
After reading this chapter the reader should have insight into the many varied complexities of using implants in more complicated cases.
Good implant therapy results should be expected when a single tooth or a small number of teeth that have been removed atraumatically are to be replaced. The prosthetic management conforms to the existing dentition and supportive tissues.
As the number of teeth to be replaced increases so does the complexity of planning and the provision of treatment. The time required is not proportional to the number of units to be replaced. More time will be required in more extensive cases for both the clinical and laboratory stages. If the dental arch is edentulous, multiple fixtures will be required. It may be that a number of teeth can be saved. In such cases a decision has to be made as to whether to link the implants to the teeth or to provide a number of independent implant retained units.
It is simpler to achieve a good aesthetic result if a full arch superstructure is wholly implant-supported. The most predictable way of achieving a good aesthetic result in such situations is by means of an implant-retained over-denture. There is good opportunity to control the aesthetics at the wax tryin stage of treatment. The clinician and the technician have full control over the position and arrangement of the teeth, together with the gingival margins and contours of the prosthetic soft tissues. If there has been limited alveolar resorption, there will be problems accommodating the bulk of an over-denture.
When implant-retained fixed bridges are provided, there is less room for manouvre, as the fixtures dictate the shape of the superstructure. If there has been minimal alveolar resorption, it can be difficult to create ideal gingival contours and emergence profiles, unless the implants have been placed in an ideal position. With further alveolar resorption, pink porcelain is required to simulate gingival tissues. Some fluting of the periphery of the superstructure is important to allow effective cleaning of the implants and mucosa.
When teeth and implants are used to support a superstructure, it becomes particularly difficult to provide a continuous gingival margin and uniform emergence profile for the teeth included in the prosthesis. If very few teeth remain, and they have a dubious prognosis, a case can be made for their removal to simplify implant treatment, improve the aesthetic outcome and enhance long-term success.
The use of temporary superstructures in full arch cases can be of considerable assistance in developing an acceptable aesthetic outcome. As it is difficult to make durable all acrylic temporary superstructures, their period of placement should be limited to a period of weeks. If the time required for refining the temporary superstructures needs to be longer than this, it is prudent to consider some form of metal or glass fibre-reinforced temporary superstructure. Such superstructures involve more laboratory work and higher costs, but are sometimes essential.
Impression procedures are complicated if prepared teeth and implants are included in a single impression. Often multiple impression procedures are required, involving the use of impression copings or, in some cases, Duralay acrylic bonnets on teeth. The aim of a pick-up impression is to locate dies of teeth and implant analogues within a single master working impression from which a master working cast can be produced. It is prudent, and good practice, to verify the accuracy of a working cast. This will reduce the risk of errors in fit and occlusion at later stages. Verification bars to link implant abutments can be made on the working cast, which can then be checked in the mouth. In some circumstances a verification bite fork can serve the same purpose. These are important measures to avoid errors being compounded during the laboratory phase of treatment.
In the past it was difficult to provide large gold-alloy castings of appropriate accuracy for implant superstructures. Casting difficulties are reduced if small units are planned. Various soldering and laser-welding techniques have been developed to join small castings to form large full-arch units, and casting techniques have also improved to accommodate the fine tolerances required. More recently, titanium-milled castings have provided good fit when used with a fixture-head impression technique.
Maintenance of a full mouth reconstruction is simplified if small units have been employed. A porcelain fracture in a three-unit component is much easier to deal with than the same fracture in a 12–14-unit full arch reconstruction. Back-up dentures or temporary fixed bridges are always useful when the replacement or maintenance of such superstructures is required. It therefore follows that the construction and maintenance of a full arch reconstruction, using two fixtures in the mandible and an implant-retained overdenture, is simpler than a full arch fixed bridge supported by eight to 10 implants.
Traditional teaching has advocated avoiding the joining of implants and natural teeth. It is known that teeth have some 3D physiological mobility, but implants have none. It had been thought that joining implants to teeth might result in the early failure of implant screws or the cement lute. Joining implants to teeth can, however, be successful. Gold copings on implants and teeth followed by a cemented superstructure has been found to be a successful approach. A stress-broken design using a fixed-movable joint has also been employed successfully. Another combination is to use conventional cementation of the retainer on the tooth and screw retention only on the implant. It is not known which arrangement will perform best in the long term, but clinical experiences indicate that these combinations are not as problematic as first thought.
There are two main problems when considering the placement of dental implants in patients who have or have had periodontal disease:
There is an uncertain prognosis for the remaining teeth.
There are concerns that a persistent pathogenic periodontal bacterial flora may adversely affect some dental implants, leading to a loss of osseointegration.
In common with all sound treatment planning, primary dental treatment needs should be met before definitive treatment is carried out. In a patient who has severe periodontal disease, with many teeth having a poor prognosis, it is not unreasonable to consider a dental clearance followed by implant therapy. This is a more predictable treatment option than alternatives i/>