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Management of oral problems associated with cancer treatment: Radiotherapy  David Hay

It may seem surprising that the question of dentistry and dental treatment needs to be considered as part of the management of radiotherapy. The reasons are, however, quite simple.

Radiotherapy and mouth problems

Radiotherapy can affect the tissues in the mouth because the X-rays and electrons which are used to destroy the active tumour cells also, regrettably, injure the normal tissues through which they pass. Irradiation is particularly effective when it acts on the tumour cells if they are actually dividing - but there is also a similar effect on other normal cell divisions which are occurring in nearly all other body tissues. The skin linings [mucosal surfaces] of the mouth and throat are thus particularly vulnerable to the effects of radiotherapy because these surfaces are very active. The whole thickness of the mucosa [skin] of the mouth is completely replaced about every 10-12 days! The effect of radiotherapy therefore inhibits or stops normal cell divisions in the lower layers of the mucosa, which means that new cells are not produced quickly enough to replace those shed from the skin surfaces. The overall result is that the mucosa becomes damaged and thinned and as the treatment continues, progressive damage often means that the mucosa becomes so thin that it breaks down and painful ulcers develop.

The Oral Environment

The mouth, like the rest of the outside surfaces of the body, contains a very large population of bacteria [micro-organisms] which live there all the time and which can never be completely removed. They become established shortly after birth and are known as the 'normal resident micro-flora' - rather like the normal population of birds and animals which live in a forest. In fact, up to 27 different species ['racial groups'] of micro-organisms are commonly found in the mouth and some authorities believe there could be up to 200 different species, although not all of them are necessarily present in all people all of the time. Nevertheless, this constitutes a real 'international community' which mostly lives in a state of of balance with the host. But under some circumstances the equilibrium can change and various infections of the gums and the other oral tissues can occur. This is particularly likely to happen when the defence systems of the body become defective or are prevented from working properly by malignant disease, radiotherapy or by drugs which are used in the treatment cancers and which suppress the immune system.

Many of the micro-organisms in the mouth are able to use the food materials which are eaten as part of the person's normal diet and if food debris is allowed to remain around the teeth, this very rapidly - in the space of only a few hours - becomes heavily colonised by micro-organisms. It is also important to remember that this will continue to happen by the normal process of bacterial cell division, even although dietary food may not be supplied. In other words, even though the patient or person may not be eating, bacterial numbers will continue to build up. This 'compost heap' of debris is known as dental plaque and it is plaque which is responsible for the two commonest diseases in the world, periodontal [gum] disease and tooth decay [dental caries]. It has been estimated that 1 gram of plaque contains up to 1,000,000,000,000 [one thousand billion] micro-organisms, which is about 200 times the present world population!! Obviously then, if the mouth is permitted to become dirty, the potential for infection to develop becomes very much greater when the mouth is damaged or ulcerated. Good oral hygiene is necessary at all times but is of major importance during the time when the malignant disease is active, during treatment with radiotherapy if the treatment fields involve the mouth and during the recovery period following treatment.

The basis of any mouth care program is, therefore, strict plaque control which should consist of a basic routine of careful toothbrushing, using any of the commonly available the toothpastes, after meals.

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Effects of Radiotherapy on the Oral Tissues

A) Effects arising during the course of treatment.

During the first week of treatment not very much appears to happen in the mouth. If the areas of the major salivary glands are involved however, there may be a thickening of the saliva which becomes more mucoid and stickier, making it more difficult to clean the mouth. This may be particularly noticeable upon waking at night and in the morning. In general, this problem tends to worsen during the course of treatment and is caused by damage to the saliva glands caused by the radiotherapy. The most effective way of overcoming this, is to use a salt/bicarbonate of soda [baking soda] mouth rinse very frequently during the day and, if required, during the night. Salt/bicarbonate of soda rinse is an extremely useful 'mucolytic' [mucous dissolving] mouthrinse and enables these sticky secretions to be mobilised, washed away and spat out. A suitable regimen is:

- In a container [eg a margarine plastic pot] put equal volumes of salt and bicarbonate of soda powder. Mix the powders together and keep the container in the bathroom or somewhere convenient. Dissolve 1 teaspoonful of the mixture in a glass of very warm water and use as a vigorous rinse/gargle frequently - up to 6-8 times a day if necessary.

As treatment progresses, the skin inside the mouth which falls within the irradiation fields becomes progressively more affected by the treatment, first becoming swollen, then usually breaking down to form painful ulcerations. This may make talking, eating and swallowing very difficult and unpleasant. When ulcerations develop, it may be necessary to add a variety of antiseptic and pain relieving mouthrinses or medications, to supplement the basic oral care routine and these would generally be specifically prescribed by a dentist attached to the treatment centre of the hospital. A supplementary mouth care program needs to be effective, simple to use and acceptable - the latter being difficult to

achieve sometimes! Some of the options are:

Antiseptic: Chlorhexidine gluconate 0.2% mouthrinse.

10ml used as a rinse/gargle for 1 minute once or twice daily. The rinse may be diluted 50/50 [chlorhexidine is a rather bitter tasting chemical] and it should not be swallowed. It is therefore not suitable as a mouthwash for youngsters. However, an alternative is to soak a large cotton wool bud/swab in the mouthrinse preparation and rub this around the mouth and teeth, or the toothbrush can be dipped into the solution instead of toothpaste. This material is an excellent, safe, oral antiseptic - a good chemical toothbrush! - and is available as 'Savacol' [Colgate], or 'Chlorhexidine Mouthwash' [Delta West, marketed by Upjohn]. Both products differ only in the flavour.

- Antifungal preparations: eg Nystatin liquid drops; Nystatin lozenges; Miconazole gel. Additional systemic antifungal medication [eg Ketoconazole, Fluconazole] is sometimes needed if topical treatment cannot control the problem.

- Topical pain relief: a) Benzydamine [Difflam] mouthrinse or lozenges. This drug is not recommended by the manufacturers for young children.

b) Xylocaine topical preparations - these need to used with care otherwise the mouth and throat can be made quite numb and the cheeks or tongue can be accidentally bitten which rather defeats the purpose of the exercise.

c) For young children, Promethazine HCl elixer, 5mg/5ml [Phenergan] has excellent topical analgaesic properties and can be carefully wiped around the mouth on a small cotton bud and thus applied to painful ulcers when required. Care must be taken not to exceed to recommended doseage and the additional sedative effect may be advantageous.

d) Topical treatment may need to be supplemented by systemic pain relief eg paracetamol preparations. Occasionally narcotic analgaesia is required.

Adequate food intake is very important during treatment if undue weight loss is to be avoided. Dietary advice is readily available and liquid supplements such as Complan, Ensure and other foods may be recommended.

Such a program needs to be well supervised and undertaken properly for maximum benefit to be achieved. Communication and consultation between the dental personnel and the patient's medical and nursing team has to be an integral part of the cooperative effort during the management of these often very unpleasant mouth problems. During this time interventive dental treatment should be avoided. Occasionally it may be necessary to deal with an acute toothache but this can usually be solved by palliative treatment such as a temporary dressing. Extraction of teeth should be avoided if possible. Definitive dental treatment can almost always wait until treatment has finished and the mouth has healed.

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B) Long Term Effects of Radiotherapy.

i) Dry Mouth (xerostomia).

There is one important long-term effect of radiotherapy which can affect the dentition. The doseage of irradiation required for treatment of many head and neck cancers has the additional effect of destroying a considerable proportion of the salivary gland tissue. This leads to a degree of permanent dry mouth [xerostomia - pronounced 'zerro-stow-meeuh']. How does this affect the teeth? Tooth structure is rather like reinforced concrete. There is a framework of tough, strong collagen fibres [like the steel framework of a building], around which is deposited the crystal minerals of the tooth [concrete] that gives the structure its rigidity and toughness. The crystal/mineral part can be dissolved out by acids but normally there is a balance between the minerals contained in the saliva [which is saturated with calcuim salts], and tooth structure. That is, should a small amount of mineral be dissolved out of the tooth by, say, an acid lemon juice drink or by acid production from bacterial activity on dietary sugar [see below], then calcium crystals will tend to be deposited back into the tooth via the saliva. This process is greatly enhanced by the presence of 'fluoride ion' [which is the reason for the incorporation of fluoride in water and toothpastes] and the re-formation of tooth mineral crystals is rather like the way in which crystals of alum or copper sulphate can be built up in a school chemistry experiment. Indeed, it is largely due to this mechanism that tooth decay has been reduced so dramatically in the community over the last 30 years.

Acid waste products are excreted by some species of oral bacteria which use dietary sugars for their own energy requirements. The acids soak into the plaque lying up against the teeth and when the acidity drops below a certain level, the tooth mineral will dissolve out of the tooth structure. If this process occurs too quickly, then there is not enough time for mineral to be replaced in the manner described above and holes appear in the teeth. This, in fact, is how tooth decay occurs and the acidity at which this takes place is technically described as: 'below pH 5.5'. The pH scale is simply a way of measuring the degree of acidity or alkalinity of a solution.

It is also important to know that commercially available carbonated fizzy drinks, eg Coke, Fanta, lemonade, L&P etc, range from about pH 3.8-2.4. Similarly, commercially available fruit juices eg Fresh Up, Just Juice, McCoy, Twist etc, range from pH 3.7-2.5. In other words all these products are capable of dissolving tooth structure and, of course, such beverages tend to be drunk frequently by people with dry mouth. Usually, in a person with normal salivary flow, not much damage occurs because saliva also contains buffering ['acid soaking up'] systems and together with its washing and diluting action, any adverse effects of food or drink acids is rapidly eliminated. But tooth mineral loss in a person who has xerostomia can be significant because these compensatory mechanisms are absent or reduced. So the action of the oral bacteria on the sugar sweetners in food and drinks and the acidity of the drinks themselves can thus cause an additive effect and the end result can be an increase in dental decay. Once again, careful attention to regular mouth hygiene will go a long way to preventing such dental problems.

Of course people who have full dentures are spared the tooth problems but dry mouth can significantly add to the difficulties of retaining and eating with the dentures which invariable become loose.

Xerostomia and its sequelae are managed according to severity.

1. First, if there is some secretory glandular tissue working, it can be stimulated by chewing gums or sucking sweets. This may be sufficient to maintain adequate lubrication in the mouth between meals for talking and normal activities. However, it is vital that if you have your own natural teeth, such gums or sweets are sugar free [otherwise dental decay via conversion of sugar to acids by the microflora in the mouth will occur]

Products: Sugar free gums by Wrigley

V6 gum - this product contains urea which leads to an alkaline environment in the mouth, which in turn, actively neutralises acid production and discourages tooth mineral loss.

Sugar free sweets

2. The drug Pilocarpine appears to be a useful sialogogue [salivary stimulant] but, as with all drugs, there are side effects and the patient needs to be carefully screened for heart disease, diabetes and othe medications first. Although thie drug may increase salivary flow, patients can find the side effects unacceptable.

3. Saliva replacements. Generally these are compounded from methylcellulose [the base which contains the lubricant] plus a variety of other compounds designed to mimic true saliva as much as possible. Patients complain that these feel greasy. A mucin based artificial saliva has been introduced which more closely resembles saliva itself but, unfortunately, has been withdrawn

Products: Luborant [methylcellulose base]

Salube [methylcellulose base]

The price tends to put people off these and many resort to carrying a small container of water

around, taking sips when required. These saliva substitutes are not suitable when eating and at the present time there is little available except to increase fluid intake during meals.

4. In patients with dry mouth denture wearing can be a major trial because retention of dentures relies considerably on the good fit of the prosthesis but also on the surface tension effect of the viscous saliva solution under the denture. So the saliva 'seals' the edges of the denture preventing air from getting under the appliance which allows it to drop. In xerostomia this component of denture retention can be largely absent. There are some aids for retaining the dentures which rely on the application of a thick sticky material which causes a semi-adhesion of the denture to the underlying tissues.

Products: Polygrip

Fixodent.

5. It can be seen that in order to prevent as much as possible the problem of extensive and rapid dental decay and to ensure that dentures are maintained, regular dental examinations are a priority. In the case of those who have their natural dentition a dentist should be able to advise in appropriate oral hygeine techniques eg brushing flossing, antiseptics, fluoride applications/rinses. Use F' toothpastes.

Avoid acid swabs etc. Avoid acid juices. Many people resort to using fruit juices/carbonated fizzy drinks to make the mouth feel nice and to keep it damp. ALL these products havs a pH less that 4.5 - often in the 3.2 - 3.8 range. Coke pH = 2.5! So unfortunately all of these drinks will demineralise the teeth.

Regular checks 4-5 monthly in the initial stages to ensure good control of the oral environment.

Dentures require somewhat less attention but an annual or biennial review would be indicated.

ii) The effect of radiotherapy on the blood supply

The long term effect of radiotherapy on the regional blood supply within the irradiated fields is to reduce it dramatically. This is dose related, permanent and continues after treatment has been completed, so that many years later, the blood supply to the affected area is still diminishing slowly. The process of devascularisation has an adverse effect on the ability of the local tissues to heal. In other words, if a further operation is performed on the jaws - such as the extraction of teeth - then the bone and surrounding tissues may not heal properly and the jaw bone in the area may become 'dead'. This is called 'osteoradionecrosis' and is very difficult to treat satisfactorily. Good treatment planning in the initial stages of treatment can avoid these problems to a large extent, for example decayed, broken down or unsound teeth should be extracted before radiotherapy is started.

However, it is not always possible to predict the degree of xerostomia which may occur or to judge how committed a patient may be to ensure that impeccable oral hygiene and regular dental care is maintained and sometimes the remaining teeth break down more quickly that expected - often to the point where further repair is impractical. In cases where it is then necessary to remove teeth from a previously irradiated area it is considered mandatory for the patient to undergo a course of Hyperbaric Oxygen Therapy before the extractions are done. This treatment [which can only be done in a hospital with such a machine or at a special unit such as the Devonport Naval Base in Auckland which has a dive chamber] involves lying in a special chamber into which oxygen is pressurised at about 2 atmospheres, for 2 hours per day for 20 successive days. The therapy tends to cause blood vessels to open up and 'revascularise' the previously poorly vascularised tissues and thus increasing the healing ability of the area. The teeth may then be removed with much less risk of failure to heal. A further 10 'dives' in the oxygen chamber is usually recommended after the extractions or operative procedure.

SUMMARY

- The application and maintenance of a careful oral hygeine program is of primary importance. Patients who begin radiotherapy and cancer treatment with no plaque, develop significantly fewer problems and oral complications last for a shorter period of time.

- In the initial period of radiotherapy, dental treatment should be avoided until healing has occurred - except for emergencies .

- When disease is in remission routine dental treatment can be undertaken by a dentist, who must be advised of the patient's previous medical condition and details of the treatment areas and involvement of the teeth and jaws.

- Teeth which have previously been included in the treatment fields should not be extracted until after a course of hyperbaric oxygen therapy.

- Advice must be sought from the medical or dental team if, at any time, unusual problems occur or if there is any concern about the advisability of undergoing a dental procedure.

 


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