Complete dentures revisited

Recognition of support problems

It is not the purpose of this article to carry out a resumé of the oral and facial anatomy relevant to complete denture prescription; nevertheless, it could be argued that this facet should be the easiest for the practitioner to identify.

The absence of well-defined ridges means that, in theory, there is less denture-bearing tissue to carry the functional loads and this should highlight problems of support. Careful examination of the denture-bearing areas of both arches is therefore required but this does not mean a reliance on visual scanning. This will give little meaningful information on the ability of the denture-bearing tissues to withstand pressure7 (although it may draw the clinician's attention to potential problems (Figure 2).

Further assessment, for example by digital pressure over the dental-bearing areas, is therefore essential to identify where problems are (Figure 3). This will help the clinician to plan which impression material to use (vide infra) in addition to helping her/him to prescribe appropriate relief if required, eg over a torus or bony prominence (Figure 4).

Recognition of retention problems

Retention of complete dentures is principally achieved via a peripheral seal; anything which prevents/impairs the potential for a peripheral seal therefore should be identifiable as a potential problem in the successful prescription of complete dentures. High muscle attachments, which are attached to the crest of a ridge, therefore will not only affect stability of a denture, but will make the achievement of a peripheral seal impossible (Figure 5). Similarly, the presence of a palatal fissure in the postdam area will present problems which will require modification of the master cast (vide infra) (Figure 6). In the same way that digital pressure is recommended in the identification of support problems, it is recommended that the clinician determines the relative displaceability of the tissues of the post dam, as there tends to be more glandular and connective tissue laterally than there is centrally (Figure 7).

Although it has been stated that the principal factor in retention is peripheral seal, proximity of fit of the denture base to the tissues is also of importance, as is surface tension; factors influencing these may also therefore affect the retention of a complete denture. This will be dealt with later.

Recognition of stability problems

As was described earlier, stability of complete dentures, if achieved, is a paradigm of muscle balance and occlusal balance. The achievement of successful stability is, in the opinion of the authors, the single-most difficult thing for a clinician to achieve. While careful impression techniques may ensure a good peripheral seal, eccentricities of muscle form may displace a proficiently made denture. On the other hand, patients with neuro-muscular diseases/conditions may have uncontrollable tremors which make it almost impossible to achieve acceptable muscle balance. While not all occlusal problems may be overcome, each clinician should be able to identify where occlusal tables are too long (Figure 8) and too broad (Figure 9). In addition, where prosthodontic guidelines are disregarded and inappropriate occlusal planes are prescribed, the result can be instability caused by clinical displacement of the mandibular denture in accordance with the principles of an inclined plane (Figure 10). It is perhaps prudent here to indicate that, while the authors accept that it is highly unlikely that clinicians will be able to prescribe balanced articulation clinically, the minimal requirement, prosthodontically speaking, for complete dentures is balanced occlusion in Retruded Contact Position (RCP). As instability occurs when spaces occur between dentures, then the concept of balanced articulation was introduced as a means of improving stability. This should be achievable on all cases on an articulator. Sadly, semi-adjustable articulators do not equate to the ginglymo-diarthrodial TMJ apparatus of patients and true balanced articulation is probably achieved only rarely. This, however, should not mean that the clinician does not aspire to achieve it!

In addition to the above, good common sense and careful history-taking might alert the clinician to the potential for denture-wearing problems. Figure 11 shows a patient who obviously wears spectacles. The pressure of the spectacles on the keratinized tissues on the bridge of the nose would lead one to be sceptical about the ability of the (non–keratinized) tissues overlying the residual ridges to withstand robust oral function; this is also a useful guide to the biological age of the patient. The mention of function does raise the important question of what functions are being sought. If we include appearance as a function (strictly speaking it is not), then there are four principal functions of complete dentures:

Although the diagnosis of these problems in these areas will be dealt with later, it is important to determine the functional needs of a patient before commencing treatment. Speech problems may not always be treatable via replacement dentures and not all foods may be tackled as with a natural dentition; nevertheless, it would be sensible to know how a patient eats. By giving a patient a biscuit and observing how he/she eats; a guide to posterior tooth form may be gleaned. If mandibular movements are vertical, then it may be quite acceptable to prescribe flat-cusped teeth. If, however, ruminatory movements take place, then cusped teeth will be required to prevent destabilizing spacing between dentures.

In conclusion, although it is recommended that the clinician is aware of the philosophical basis of complete denture prosthodontics, such problems rarely fall into one category and care has to be taken to take into account what the clinician sees but also what he/she palpates and hears. For that reason, the next section in this article will be on diagnosis of symptoms reported by the patient (anamnestic reports).

The symptoms will relate to commonly presenting symptoms such as:

For simplicity, these complaints will be presented in tabular form (Table 1).

As is normal in clinical practice, however, diagnosis is just part of the problem. The next problem is how to manage the problem (more often it is more than one problem) and this article has given a brief introduction to most of the common ones and readers are referred to a standard textbook of Prosthodontics7 for more detailed coverage of the matter.