Search

Only by the use of scanning electron microscope in investigations concerning the metal-porcelain interface of ceramic masses upon metal frames (approx. 160 crowns since 1967), essential differences in the reason of mistakes have been revealed recently. Primarily, methodic mistakes are to be declared relevant. Independent of their veneering origin, they contribute to fractures within the ceramic layer or to crack-offs of the fired ceramic masses from the metal frame. Obviously, the systemic causes for mistakes in metal ceramics revealed to be dependent on the groups of veneers. Veneering involves non-manageable reasons for mistakes. These qualities in the material are the coefficient of thermal expansion or the share of palladium in the veneer. Very often, palladium is responsible for the formation of bubbles in the ceramic layer, and thus it is the reason for the development of cracks. The so-called pure titanium is quite extraordinary, when covered with ceramic mass, because the so-called alpha case layer cannot be bridged, despite 10 years of permanent research in that field. The clinical critical examination of systemic mistakes, however, proves to be mild. Clinical reasons for mistakes in metal ceramics remain disregarded in this paper.

This review is based on an extensive study of the literature, various investigations of clinical and dental materials, experience as well as long-term observations. Our understanding of the behavior of the gingiva at the margins of artificial crowns has been widely extended within the last two decades. Some of these findings are discussed. However, complete absence of inflammation at the gingival margins can hardly ever be expected. What is usually present is rather "an acceptable state of marginal periodontitis" (Ketterl). Continuous and deliberate oral hygiene on the part of the patients is a decisive prerequisite for an acceptable oral condition.

Materials for metal-ceramic crowns have been developed further in the last few years and the use of this type of crown increases steadily. Numerous investigations concern themselves with binding and other properties of this material as well as with its favourable moulding capacity. The present investigation is oriented towards establishing the order of magnitude and limits of confidence of fracture resistance which has to be reckoned with when using a metal-ceramic crown in the mouth.

The therapeutic possibilities of conservative and prosthetic rehabilitation procedures are set out in this survey. In particular the aim was to find out whether these are suitable for retaining functional dentition into old age. The anatomical characteristics (Figs. 1 and 3) and secondary dysgnathic alterations of the dentition in the period of senescence make dental therapy considerably more difficult. The tooth-coloured filling materials do not behave as permanently in the mouth as could be wished. They are unsuitable for use in posterior teeth, and are in urgent need of improvement. The amalgam filling should still be regarded as the agent of choice for treatment of the cheek teeth, although cast precious metal inlays have been successful over a long period of time (Fig. 6). Too little use is made of veneer crowns in the anterior area with increasing age (Fig. 7), although the prospect of long term success is good. It was possible to establish statistically that tooth-coloured plastics are inferior to ceramic and metal ceramic crowns because of the greater retention of plaque. Ceramic should accordingly be preferred even with bridges in the anterior area. The replacement of missing teeth with removable partial dentures is the typical method of dental treatment for the period of senescence (Figs. 10-12). An attempt was made by bringing together various principles of planning and construction to lay down guidelines for dentures in older patients. With prosthetic care the fact that there are large differences in the physical and mental vitality of the older person, and that vitality frequently decreases rapidly for the most varied reasons, should not be overlooked. Even at this stage dentures should still prove functional.

Both cross-sectional and longitudinal studies have contributed data which provide a scientific basis to the prediction of outcome in prosthodontic treatment. 'Standard' cases have a more favourable and more predictable prognosis than those in which tooth loss is scattered about the mouth. However, the variability of patients' problems and the wide range of their abilities to adapt to denture wearing and the regular maintenance of their oral tissues significantly influence outcome. Long term success with partial prostheses lies in the time scale of 5-10 years. A prerequisite for this is a standard of oral hygiene better than practised before the loss of the dentition. Adverse factors are inadequate diagnosis and treatment planning, undetected errors in denture construction, failure of materials, thermal and abrasive effects of foods, behavioural changes in the patient and ageing. In planning the restoration of abutment teeth by inlays or crowns their suitability for attachments must be considered. As yet, there are no clear guidelines to determine when fixed or removable prostheses should be used. The design of partial dentures should be as simple as possible; they should be stable, easy to clean and, if required, easily modified. Success is most likely to attend the efforts of those dentists who use techniques with which they and their technicians are thoroughly familiar.