2

Factors Influencing the Outcome of Prosthetic Treatment

The successful outcome of prosthetic treatment depends upon the combined efforts of three people:

• The clinician – who makes a diagnosis, prepares a treatment plan and undertakes the clinical work.
• The dental technician – who constructs the various items, which culminate in the finished dentures.
• The patient – who is faced with coming to terms with the loss of all the natural teeth, having to adapt to the dentures and accepting and accommodating their limita-tions.

This chapter will:

• focus on the patient’s contribution to the success of complete denture treatment,
• review the information on the success rate of this treatment, and
• consider whether it is possible to predict treatment outcome.

The patient’s contribution

The patient needs to know, with the clinician’s help, what to expect when new dentures are provided and to be motivated to wear them long enough for adaptation to take place. This willingness, even determination, of the patient to persevere with new prostheses in the face of initial difficulties – so that adaptation can occur – is vital to success for two main reasons:

• There is nothing ‘normal’ about having to wear conventional complete dentures. The change to the oral environment when two large foreign bodies are inserted into the mouth is so great that a substantial positive effort has to be made to come to terms with it.
• The wearing of these foreign bodies is under the complete control of the patient. When difficulties are experienced with the new dentures they can be removed from the mouth, considered, discussed, compared and even set aside. If this is the patient’s main response to the feeling of strangeness then adaptation will not occur and the treatment is likely to fail.

To cope with the drastic change within the oral cavity, the patient must:

• be able to come to terms with the loss of the natural teeth and their artificial replacement,
• become accustomed to the sensation of the dentures, a process known as habituation,
• learn to control the dentures, and
• accept and hopefully appreciate the new appearance.

The psychological effects of tooth loss

Chapter 1 discussed the effect that tooth loss had on the residual ridges. Whereas a lot of research work has been undertaken on that topic, it is only in more recent years that investigations have been carried out to discover the effect of tooth loss on people’s feelings (Fiske et al. 1998; Davis et al. 2000; Hyland et al. 2009).

In an investigation of patients receiving prosthetic treatment, most having lost their remaining natural teeth several years previously and seeking replacement dentures, 45% admitted to having found it difficult to accept the loss (Davis et al. 2000).

Many of those who had difficulties took longer than a year to get over the loss, and more than one-third had still not accepted it by that time. They expressed feelings of sadness, anger and depression and many felt that these last extractions had made them feel prematurely old and that they had lost a part of themselves. There was loss of confidence, a restriction in choice of food and a lowered enjoyment of that food. Relationships with others were affected and many patients avoided looking at themselves without their dentures in place. The impact of the limitations of complete dentures imposed on edentulous patients was also highlighted in a qualitative study comparing patients treated with either conventional complete dentures or implant-supported overdentures (Hyland et al. 2009). The findings again demonstrated that the functional limitations of complete dentures often impose significant restrictions on edentulous patients, particularly in terms of limiting social participation with family and friends and in the choice of foods, especially when eating with others.

The disturbing picture for edentulous patients painted by these studies was reinforced by findings from a national survey of adult dental health (Walker & Cooper 2000), which revealed that 61% of those who still retained their natural teeth found the idea of complete dentures a very upsetting one. More women were upset than men and those people who attended their clinicians on a regular basis were more likely to be troubled than those who did not. Interestingly, the older the dentate person the more likely they were to find the idea of complete dentures very upsetting. It is as if the longer a person has been able to put off the evil day the more troubled they will be if, in spite of every effort, they succumb.

From the above account, it may be concluded that total tooth loss has a profound effect on a significant proportion of the edentulous population and may well introduce added complications to the process of successful rehabilitation. The following points clearly emerge from the research work:

• Prevent total tooth loss if possible.
• If total loss is inevitable, plan the transition from the remains of the natural dentition to the artificial dentition with great care (see Chapter 3).
• Ensure that the patient is properly prepared for treatment and that everything possible is done to reduce the inevitable feeling of anxiety.
• Remember that many wearers of complete dentures are still likely to have profound worries some considerable time after becoming edentulous, and that if these worries are addressed in a sympathetic and encouraging manner, there will be a greater chance of the course of treatment being successful.

Habituation

Habituation has been defined as follows: ‘A gradual diminution of responses to continued or repeated stimuli.’

When new dentures are placed in the mouth, they stimulate mechanoreceptors in the oral mucosa. Impulses arising from these receptors, which record touch and pressure, are transmitted to the sensory cortex with the result that the patient can ‘feel’ the dentures. For the first-time denture wearer this bombardment of the sensory nervous system almost inevitably results in pronounced salivation which, fortunately, only lasts for a few hours. The continuing stimulation of these receptors does not result in a corresponding continuous stream of impulses. The receptors adapt to this stimulation and as a consequence the patient begins to lose conscious awareness of the new shapes in the mouth. Of course, if replacement dentures are constructed whose shape is dissimilar to existing ones, a new set of stimuli will be evoked and the process of habituation starts all over again. This concept is one of the main reasons for copying dentures, using a method such as that described in Chapter 8.

In addition to the mechanoreceptors in the oral mucosa being stimulated by the shape of the new dentures, further stimulation arises as a result of contact between the occlusal surfaces during function. The forces generated by contraction of the muscles of mastication are transmitted through the dentures to the underlying tissues, resulting in a pattern of stimulation of the mechanoreceptors which enables the patient to recognise the presence or absence of occlusal harmony. This is dealt with in greater detail in Chapter 14.

Control of the dentures

A discussion of the behaviour of sensory receptors is equally relevant when considering the patient’s ability to control dentures. This is because the successful manipulation of dentures depends upon purposeful and effective muscular activity, which in turn is dependent on adequate sensory feedback. When sensory nerve endings in the oral cavity are anaesthetised, the retention of complete lower dentures is reduced. In other words, loss of sensory input results in a lower level of purposeful muscle activity directed at keeping the dentures in place.

The patient’s ability to control dentures involves a learning process that, initially, is a conscious endeavour. The first few faltering steps of the inexperienced denture wearer are often discouraging both to the patient and to the clinician. However, it is comforting to realise that the vast majority of these patients return to the surgery after a few days showing few signs of their initial difficulty. The learning process has come to the rescue. As a result of repetition, new reflex arcs have been set up in the central nervous system and the conscious effort has been replaced by a subconscious behaviour pattern. Constant repetition of impulses lowers the synaptic resistance and facilitates the formation of conditioned reflexes. At the same time, however, it must be realised that the synaptic resistance will be increased in the absence of these repeated stimuli. In other words, practice makes perfect whilst idleness leads to decay.

The observation that the first few faltering steps are usually quickly overcome does not provide a license to ignore a more staged transition to the edentulous state through both partial dentures and more particularly overdentures as outlined in Chapter 3.

Appearance

The patient’s perception

‘Beauty is in the eye of the beholder’, and in the prosthetic context one is concerned with the patient assessing the appearance of the new dentures in a mirror. Because a pleasing appearance is a subjective evaluation, there is obviously room for the clinician and patient to have differing opinions. However, open disagreement does not predispose to successful treatment and so it is vitally important that the clinician should take careful notice of a patient’s views on appearance. However, this does not mean that the clinician should blindly follow the patient’s requests if they are likely to lead to a poor aesthetic result. Indeed, advice and particularly demonstration may well succeed in convincing the patient that a more pleasing appearance can be obtained by introducing features such as slight irregularities in the positioning of the anterior teeth and a more natural shade. However, if demonstration of such modifications fails to convince the patient of their merits then it is likely that the patient’s mind is made up and that success will be obtained only if an appearance is produced which conforms to the original request.

The clinician’s judgement

Although the patient clearly has the final word on the appearance of the dentures, there are some situations in which clinical judgement is particularly important. Examples of these are as follows:

• The patient may be tolerating an upper denture whose tooth position has been placed too near the crest of the resorbed ridge. It is often possible to improve the appearance of replacement dentures by a judicious expansion of the upper dental arch. However, if the dental arch is expanded too far, the increased lip pressure on the labial face of the upper denture can lead to instability.
• Patients may request that new dentures are designed to ‘iron out’ creases around the mouth or generally to provide more facial support. Occasionally under such circumstances, it is possible to reduce the creases and so improve the appearance by expansion of the upper dental arch or by thickening the denture border as mentioned above. In both these situations, if it has proved possible to expand the upper arch the possibility of placing the mandibular denture teeth further buccally and/or labially arises and so avoids, or reduces, the dangers of ‘tongue cramping’.
• The clinician may recognize that there would be an advantage in constructing replacement dentures with a lower occlusal plane so that the tongue, by resting on the occlusal surface of the mandibular denture, can be more effective in stabilising it. However, this lowering of the occlusal plane will alter the appearance and may lead to objections from the patient.

On occasions such as those described above, it is advisable for the clinician to explain, test and demonstrate the possible denture changes to the patient. This demonstration can be carried out on the />