THE ETIOLOGY AND MANAGEMENT OF PAIN IN DENTURE WEARERS R.J.C.Wilding. BDS, Dip Pros. M.Dent. Ph.D

Soreness of the mucosa under a denture is one of the most common reasons patients seek treatment.¹ Denture soreness, like all pain, is a complex experience, in which a multitude of factors interact. In order to discover the possible origins of denture pain, it will be necessary to examine all these factors, from the emotional to the physical.

We are all familiar with the patient whose alveolar mucosa is deeply rutted with ulcers and hyperplastic tissue, but is quite unaware of the damage. At the other extreme is the patient whose mouth burns with pain, but looks normal. These example illustrate a paradox about pain; it is possible to have tissue damage without pain and pain without obvious tissue damage. Much depends on how the brain/mind processes the incoming sensory messages. The processing involves memories of previous pain, cultural attitudes, feelings, and giving meaning to the sensory messages.²

Pressure is probably the initial cause of irritation to denture bearing tissue. However once the tissue is damaged, substances released by the damaged tissue (histamine and prostaglandins), and substances released by the nerve endings themselves (substance P), contribute to causing swelling and increased sensitivity. So, when bruised and swollen mucosa is pinched between a denture and a hard sharp ridge of bone, the exquisite tenderness is understandable.

We have two broad processes to examine when we set out to relieve denture pain, the first is clearly, to prevent tissue damage, and the second is to listen to the brain/mind to hear signs of increased vulnerability to pain.

What makes denture bearing mucosa susceptible to pain?

Let us recall some anatomy and physiology of the denture supporting tissues. Firstly, there are different types of mucosa covering the ridge. These range, on the one hand from robust, well keratinized masticatory mucosa which may still cover the crest of the ridge, to fragile, non-keratinized lining mucosa covering the floor of the mouth and including the genial tubercles and mylohyoid ridge.^3,4 The masticatory mucosa may be as much as 4 mm thick while the lining mucosa is only 0.3mm thick.⁵ This difference in thickness has a disturbing effect on the ability of the mucosa to spread the pressure applied by the denture base. The thin mucosa becomes compressed before the thick mucosa, just as the bony bits of our bodies complain first if we spend a night on a hard floor (Fig 1)

Figure 1. A section through the edentulous mandible in the molar region. Arrow length and thickness indicate the resilience of the mucosa to loading. The mucosa (a) over the buccal (B) shelf of bone is mobile, resilient, and fairly thick. The mucosa (b) is firmly attached to the underlying bone, and less resilient. The lingual (L) mucosa (c), is very thin and mobile. Over some areas it is resilient, but over sharp ridges of bone (d) there is no resilience.

The contour of the underlying bone varies from rounded to sharp, depending on the pattern of resorption. Sharp underlying ridges are like needles sticking into the mucosa .

The area of mucosa available to receive the load from a complete lower dentures is about half that available to support an upper denture, and that is about half the area of the periodontal ligament (PDL).⁶ So the pressure on the lower denture bearing mucosa is four times that on the PDL.

The blood supply of the PDL is from three sources. These include vessels at the apex of the tooth, from the tooth socket and from the gingival vessels. Anastamosis between these three sources, provides for a collateral blood supply, should one source become reduced by compression.⁷ In contrast, the blood supply of the residual alveolar mucosa is primarily from mucosal, supra-periosteal vessels. At the crest of the ridge, there is a collateral supply to the overlying mucosa from the underlying bone, but on the buccal, labial and lingual shelves, there is very little . Compression of mucosa thus restricts the blood supply as there is poor collateral supply from bone. When mucosal damage is followed by exudate, the resultant oedema further reduces the circulation.

The difference between the support offered by mucosa and the periodontal ligament have been well studied in order to solve problems when these two forms of support have to be used together in distal extension partial dentures.⁸ The problems arise because oral mucosa is displaced under load about 10 times more than the periodontium. Like the PDL, mucosa is viscoelastic, which is to say that there is an aspect of elasticity together with an aspect of viscosity in the support, although mucosa has less elasticity than the PDL.^9,10 Both support systems are similar to the suspension of a car. The springs resist compression and provide rebound after the wheel is displaced. The shock absorbers act as dampers, slowing down the rate of displacement. The periodontal ligament is well supplied with fibres which are elastic and act as springs. They resist loads well and return the tooth to its pre-loaded position quite rapidly , especially if the load is applied rapidly and briefly. But even if a light load is applied for some time, like an orthodontic appliance, the tooth recovers quite slowly to its original position (Fig. 2).

A slow recovery to sustained loads is even more noticeable in oral mucosa which lacks the elastic fibre content of the PDL and is poorly vascularised . Recovery of the oral mucosa to prolonged loading may take several hours, and in the elderly it may take days. Hence even light continual clenching causes displacement of the mucosa, ischaemia, and widespread damage (Fig 3).

Figure 3 The lower mucosa is swollen and bruised by repeated clenching. No amount of adjustment to the denture will prevent this source of denture pain

In summary, the denture supporting tissues may be thin, inelastic, uneven in thickness, poorly vascularised overlying sharp underlying bone.

What makes dentures most likely to cause pain?

Oral mucosa is trapped between a bone and a hard denture. If the pressure were distributed evenly, sore spots would be less common. But as we have seen, in places the bone is sharp and the mucosa is thin. How do we make a denture base which accommodates these differences? The most permanent solution is to surgically reduce the sharp bone spikes on the alveolar ridge.(Fig 4).

Figure 4 The lower mucosa has been reflected to reveal the sharp underlying bone which needs to be reduced to provide comfortable denture support

The ideal impression material would have, amongst many others, two important qualities. Firstly, it would record the difference in resiliency of the mucosa so that all areas could contribute to supporting the denture. This would require a fairly stiff, mucocompresive material, like impression compound. Secondly, the ideal material would be fluid enough to be moved away by the muscles and soft tissue during mouth movements, so as to develop a periphery for the denture base which was not over extended. This would require a flowing, mucosatic material like plaster of paris, or zinc oxide paste. It is clear that these two qualities are not to be found in one material. Mucosatic materials are often preferred, as they avoid overextending the denture. But impressions made with compound, using a lower fusing compound such as Kerr's green stick for the periphery, make a very comfortable denture base which is not overextended. Plaster of paris has the most unusual property of flowing when vibrated, but being quite viscous when pressure is slowly applied. Lower impressions made with plaster of paris require that the water/powder ratio of the mix be carefully controlled, but they are certainly worth the trouble. One of the most effective methods of making a comfortable and stable denture base, is to rebase the denture after making it, using a mucocompressive tissue conditioner, such as De Trey's Viscogel. All these methods compress the tissue while the impression is made, and record differences in resiliency of the supporting mucosa ¹¹ (Fig 4).

Figure 5 a) A lower denture relined using a tissue conditioner as a functional impression material. The resilient parts of the mucosa (green) are compressed. b) the fitting surface of the rebased denture, pre-loads the resilient areas, so that as the base begins to transmit greater loads, the entire denture-bearing mucosa contributes to transmitting the bite force to the underlying bone

Heat cured dentures do warp a little during processing, and affect the fit, particularly of lower dentures. This warpage is the reason we are sometimes disappointed to find that the finished lower denture does not have as good retention as the impression. A little pressure indicating paste will confirm that the finished lower denture needs some adjusting so as to prevent soreness developing An inexpensive supply of pressure indicating paste can be made by mixing zinc oxide powder into a little lanolin cream. Cut the hairs of a paintbrush off short, and apply the cream evenly to the denture base.

Distribution of the chewing loads is greatest when the teeth make simultaneous contact, at least close to the area of maximum intercuspation. If tooth contact is consistently premature in one area of the occlusal table, the load is concentrated, and pressure on the mucosa is raised in a local area. Accurate jaw registration is clearly critical, as uneven pressure on the occlusal rims will produce premature contacts in the denture. One of the most important requirements for jaw registration materials, is that they have little resistance to being displaced by the occlusal rims. For this reason, impression plaster between the rims is ideal, but low fusing, metal-containing waxes (Aluwax) also seem to work well. Remounting the denture after deflasking is always essential, so that errors due to warping may be corrected. At the final visit, the occlusion is again checked using occlusal indicating wax. Articulating paper is less revealing, particularly if the bases are not stable. Indicating wax provides additional information about the amount of tooth material which must be removed to make the occlusion even.

An excessive vertical height often leads to clenching, as if to get the jaws closer together. It is also a prime cause of general discomfort and difficulty in chewing and swallowing. It may be worth making a denture with a reduced vertical height in order to prevent the patient using their maximum bite force, and to allow better food management for the less coordinated patient.

What makes dentures most likely to cause pain?

There are some patients who never seem to be able to adapt to wearing dentures.¹² They appear to be unwilling, or unable to learn to habituate, or to tolerate some initial discomfort. It is important that we try to assess patient tolerance and motivation, as we are unlikely to be able to eliminate denture complaints if our patient is determined to cling to negative attitudes.

Some habits increase the risk of denture pain. While the modern diet seldom calls for hard chewing, there are some health enthusiasts who start the day with a plateful of muesli and spend the rest of the day suffering. We have mentioned clenching as a potent cause of denture pain. Wearing a denture at night may contribute to denture pain, and impairs healing, so a general rule would be to take dentures out at night.

Patients with a lower single denture are at risk of developing a painful lower mucosa¹³. The reason for this may be, that the periodontal ligament provides positive feedback to the masticatory muscles, increasing the power of contraction. When the teeth, and the PDL are lost, the bite force is reduced. While this reduction limits the chewing performance of denture wearers, it does at least protect the mucosa from damage.

The oral mucosa may be affected by systemic disorders such as diabetes, anaemia, nutritional deficiency and old age ¹⁴. Dryness of the mouth combined with reduced cell turnover, makes the mucosa susceptible to injury and slows down healing. Many of these conditions are beyond our control, but we can suggest dietary supplements for the elderly, particularly when we suspect protein and vitamin deficiency. It is worrying and troublesome to elderly folk, to have a painful ulcer that will not heal. It is worth a few moments to explain why and how their healing process is impaired. A major problem is reduced cell energy and nutrition due to reduced vascularity. This contributes, amongst other changes, to reduction in secretion of salivary glands. Another problem is a reduced rate of cell division and maturation, and this reduces the thickness and repair capacity of the epithelium of the oral mucosa. If you advise them, that the best thing is to take the denture out for most of the day, except meal-times, they may be quite relieved, that this is the experts advice. Of course it is the most comfortable thing to do, but many patients feel torn between the desire for comfort and the desire to keep up appearances. It is much easier for them to explain to the family.. "the dentist told me I had to take them out, otherwise my mouth will not heal" . We can understand the frustration of a daughter who brings her mother in to see us, because the old lady refuses to wear her teeth. Perhaps we need to imagine ourselves at eighty something, doing anything uncomfortable, just for appearance, or to satisfy anyone else.

In summary, three main factors can be identified which can cause denture pain (Fig 6.).

1. UNEVEN DISTRIBUTION; this includes sharp underlying bone, poorly fitting denture base, excessive vertical height, uneven occlusion.

2. ABNORMAL FORCE; this includes chewing hard foods and clenching, and the single denture.

3. POOR RESISTANCE ; this includes, systemic factors and ageing.

When a patient presents with denture pain, we need to find out which of these three factors is present. The presence of a single factor, on its own, may not cause pain but when combined with one or two other factors, pain becomes increasing likely and more difficult to reduce. Our first step is to listen to the history and ask some searching questions. The history may take us 90% of the way to a diagnosis.

A Pain History

A pain history may be more comprehensive than what follows, which are but a few questions of particular importance.

Have you always had trouble with dentures? This question helps to identify whether there is an old problem, like a sharp ridge, which keeps on recurring, or whether the pain is confined to a recent denture.

When did they start hurting? Dentures which have always hurt, may have not been made well. More recent episodes of pain may be related to tissue changes, or current habits.

What can you eat and what can you not eat? It is useful to introduce some objectivity to a complaint which may tend to be catastrophic in its entirety. Despair can be modified by a realisation that all is not lost. The question also allows the patient to begin to take responsibility for restricting certain foods.

Does anything you do make the pain better? This question helps the patient to recognise that they do have some sort of control over their pain, however little. Self help must be encouraged.

How have you been feeling in general lately? Pain is too complex, to restrict this interview to a history limited to the effects of tissue damage. The question may allow powerful moderators of pain perception, such as resentment, anxiety, and grief to emerge.

How are you coping? Our inability to cope with life and its challenges is stressful. A high stress level does not imply that a patient's denture pain is imaginary or psychological. All pain is real.. But it is also certainly worse, when we are tired and feeling depressed. It is important for our patient to acknowledge the role of stress in pain, as there is much that can be done to reduce stress. Identifying stress also alerts us to the possibility of clenching, a direct causes of denture soreness.¹⁵ If we can help our patient, to identify feelings, to talk about them, and to acknowledge the effect they have on their lives, we have helped a great deal.

Denture examination

Before we look in the mouth, it is easy to check of a few features of the dentures.

Is there enough freeway space? Whatever measuring device you use, now is the time to evaluate the vertical height of occlusion, with calipers, Willis gauge, or just watching the closure from a resting position to intercuspation. Perhaps the most revealing method of all, is to watch and listen to a string of "S" sounds produced by counting from 60 to 70. Less than a millimetre space between incisors, or clattering sounds of the back teeth are a sure sign that there is not enough freeway space.

Is the occlusion even? Articulating paper seldom reveals occlusal slides and prematurities as well as occlusal indicating wax.

Is the fit good? Pressure indicating paste is the most important single item of equipment in examining for denture pain.⁽¹⁾

Intra-oral examination

Dry, sticky oral mucosa is a sign that there are systemic factors predisposing to tissue damage and poor healing. It is well to refer such patients to an oral medicine clinic unless you feel competent to investigate and treat this problem.

Finger pressure over the ridge may reveal sharp underlying bone in some well defined areas, or a more diffuse and general tenderness which suggests habitual clenching or chewing hard food.

Diagnosis and management of denture pain

It should be possible to identify which of the major etiological agents is causing the pain. It is possible that there is more than one factor. Further explanation to the patient, perhaps using a simple chart may be necessary (Fig 5). When there is more than one factor, the chances of eliminating the pain decrease. The essential biology of the problem needs to be explained, not in order to absolve us from action, but to reinforce the challenge facing the patient (not the dentist) and to encourage their participation in improving the situation.

Management of uneven distribution

Management of abnormal force

Management of poor resistance

In almost all cases, a painful lower denture can be temporarily improved by the addition of tissue conditioner provided it can be thick enough to relieve pressure. If Viscogel(De Trey) is used, the lower denture, loaded with material, should be placed in hot water for several minutes. When it is stiff and tacky, like chewing gum, the denture can be placed in the mouth and seated with gentle pressure. It should be taken out and trimmed of excess, at the same time checking that there is at least a millimetre thick layer of material covering the base. In situations of reduced freeway space, tissue conditioners are not appropriate, as they further increase the vertical height. Tissue conditioning can become a tiresome routine as the material must be frequently replaced. It does however provide the opportunity for assessing the problem and developing a more permanent solution.

Denture pain is usually visible ,or palpable and the tenderness is evident. Being able to manage or at least explain pain, helps defend us against the patient determined to render us helpless. But making dentures, takes us deep into uncharted territory, and we will need other skills for managing the demanding patient.¹⁶

REFERENCES

1. Marstad, A T (1968): Postinsertion denture problems. Journal of Prosthetic Dentistry. 19. 126-132.

2. Melzack, R and Wall, P (1988). The Challenge of Pain. 2nd Ed. Penguin Books. London.

3. Muller, N and Proschel, P (1988). Histological investigation of tissue reactions in anterior and lateral ridges of the mandible induced by complete dentures. Quintessence International, 20, 37-42.

4. Van Mens, P R., Pinkse-Veen, M J & James J (1974): Histological differences in the epithelium of denture bearing and non-denture bearing palatal mucosa. Archives of Oral Biology. 20:23-28.

5. Kydd W L, Daly C H & Wheeler, J B (1971): The thickness measurements of masticatory mucosa in vitro. International Dental Journal 21:430.

6. Watt, D M, MacGregor, A R, Geddes A, Cockburn, A & Boyd J L (1958). A preliminary investigation into the support of partial dentures and its relationship to vertical loads. Dental Practitioner 9 : 2-15.

7. Roth, G (1975). Micro-circulation in Oral Biology. Ed. Roth G and Calmes. C V Mosby. Page 90.

8. Leupold R.J and Kratochvil F.J (1965) An altered cast procedure to improve tissue support for removable partial dentures. J. Prosth Dent. 15,672-677.

9. Picton, O C A & Willis, D J (1978). Visco-elastic properties of the periodontal ligament and mucous membrane. Journal of Prosthetic Dentistry. 40 : 263-272.

10. Moxham, B J (1985). Studies on the mechanical properties of the periodontal ligament in current Topics in Oral biology. University of Bristol Press.

11. Goolam R. and Wilding R.J.C. (1985) Displacement characteristics of impression materials on residual alveolar ridge morphology. (Unpublished)

12. Basker R.M., Davenport J.C. and Tomlin H.R. Prosthetic treatment of the edentulous patient. Macmillan Press.

13 Thompson, J C (1971). The load factor in complete denture intolerance. Journal of Prosthetic Dentistry. 25, 4-11.

14 Bates J.F, Adams D. and Stafford G.D. (1984) Dental Treatment of the Elderly in Dental Practitioner Handbook 35. Wright. Bristol.

15. Yemm, R (1972). Stress-induced muscle activity: A possible etiologic factor in denture soreness. Journal of Prosthetic Dentistry. 28, 133-140.

16 Wilding R.J.C The demanding denture patient. Dental Practice. Vol 36, no 3, 1988.

This page was prepared by Robin Wilding and last updated on March 14 2001. Write to RobWilding@eclipse.co.uk with comments or visit Moorland Dentistry