15.3 Dry Mouth, Altered Taste and Halitosis
Key Takeaways
- Xerostomia is the symptom of dry mouth while hyposalivation is the objective finding of unstimulated flow below 0.1 mL/min or stimulated flow below 0.5 to 0.7 mL/min.
- Drugs are the commonest cause of hyposalivation and the effect of multiple xerostomic drugs is additive, so medication review is a legitimate first step.
- Patients with hyposalivation aged 16 and over should receive prescription 5,000 ppm fluoride toothpaste together with varnish and short recall intervals.
- Taste buds turn over every 10 to 14 days, so many drug-related and post-infective taste disturbances recover spontaneously.
- About 85% to 90% of genuine halitosis is oral in origin, most often from volatile sulphur compounds produced on the posterior tongue dorsum.
Xerostomia Versus Hyposalivation
Xerostomia is the symptom of a dry mouth. Hyposalivation is the objective finding of reduced salivary flow. They overlap but are not the same: some patients complain bitterly of dryness with normal measured flow, and some patients with severe hyposalivation do not volunteer the symptom at all.
Objective thresholds, as set out in the salivary physiology chapter, are an unstimulated whole salivary flow below 0.1 mL/min or a stimulated flow below 0.5 to 0.7 mL/min.
Causes
| Category | Examples |
|---|---|
| Drugs (much the commonest) | Tricyclic antidepressants, SSRIs, antihistamines, antipsychotics, antimuscarinics for overactive bladder, opioids, diuretics, antihypertensives |
| Autoimmune | Primary and secondary Sjogren's syndrome |
| Irradiation | Head and neck radiotherapy; salivary tissue is highly radiosensitive |
| Systemic | Poorly controlled diabetes, dehydration, chronic kidney disease, sarcoidosis, HIV |
| Psychogenic | Anxiety, depression, somatoform disorders |
| Obstructive | Sialolithiasis, duct stricture (usually unilateral and meal-related) |
Polypharmacy is additive. A patient on four xerostomic drugs is far more likely to be symptomatic than a patient on one, and medication review with the general practitioner is a legitimate and often effective first step.
Consequences and Management
Loss of saliva removes buffering, clearance, lubrication and antimicrobial protection simultaneously. The consequences are predictable and severe:
- Rapidly progressive cervical and root caries, often at sites normally considered low risk
- Candidiasis, including angular cheilitis and denture stomatitis
- Difficulty with denture retention, speech and swallowing
- Mucosal soreness, fissured tongue and ulceration
- Ascending bacterial sialadenitis where flow is very low
Management follows four strands:
- Treat the cause where possible — medication review, control of diabetes, referral for suspected Sjogren's syndrome.
- Intensive prevention — this is not optional. Prescription 5,000 ppm fluoride toothpaste for patients aged 16 and over, fluoride varnish, dietary advice on frequency of sugars and acids, and short recall intervals.
- Stimulation where residual gland function exists — sugar-free chewing gum, sugar-free sialogogues; pilocarpine is available on specialist advice for radiation-induced and Sjogren's xerostomia.
- Substitution where it does not — saliva substitutes, gels and sprays. Patients with natural teeth should avoid acidic saliva substitutes, which can be erosive.
Altered Taste
Taste disturbance is classified as hypogeusia (reduced), ageusia (absent), dysgeusia (distorted) or phantogeusia (a taste with no stimulus). Causes include:
- Drugs — metronidazole gives a characteristic metallic taste, as do ACE inhibitors, metformin and many chemotherapy agents
- Zinc deficiency
- Chorda tympani injury after middle ear surgery, or lingual nerve injury after third molar surgery
- Upper respiratory infection, where the deficit is largely olfactory rather than gustatory
- Xerostomia, because tastants must be dissolved in saliva to reach the taste pore
- Neurological disease, including Bell's palsy affecting the chorda tympani
Because taste buds turn over every 10 to 14 days, many drug-related and post-infective disturbances recover spontaneously, and reassurance with review is often the correct answer.
Halitosis
Roughly 85% to 90% of genuine halitosis originates in the mouth, and the dominant source is the posterior dorsum of the tongue, where anaerobic Gram-negative bacteria degrade sulphur-containing amino acids to volatile sulphur compounds — hydrogen sulphide, methyl mercaptan and dimethyl sulphide.
| Source | Clues | Management |
|---|---|---|
| Tongue coating | Thick posterior coating, otherwise healthy mouth | Tongue cleaning, oral hygiene, chlorhexidine or zinc-containing rinse |
| Periodontal disease | Bleeding, pocketing, interdental plaque | Periodontal therapy |
| Other oral | Deep caries, food packing, unclean dentures, dry mouth | Treat the specific cause |
| Extra-oral (about 10% to 15%) | Persists despite excellent oral hygiene | ENT for sinus or tonsil disease; medical referral for diabetic ketoacidosis, hepatic or renal failure |
| Halitophobia | Complaint persists with no detectable odour and no objective finding | Avoid repeated irreversible dentistry; psychological referral |
Rule. Do not prescribe antibiotics or perform extractions for halitosis. Treat the tongue and the periodontium first, and only consider an extra-oral cause once oral sources have been properly excluded.
Drug-Induced Xerostomia and Polypharmacy
Medication is the single most common cause of dry mouth in UK practice, and the risk is dose-related and cumulative, so an older patient on several drugs is at greatest risk. The examinable drug groups are tricyclic and other antidepressants, antipsychotics, antihistamines, antimuscarinics for overactive bladder, opioids, diuretics, antihypertensives including beta-blockers and calcium channel blockers, and inhaled anticholinergic bronchodilators. The dentist's role is to recognise the pattern, to discuss with the prescriber whether an alternative or a dose adjustment is possible, and never to stop or alter a prescription unilaterally.
Managing Salivary Hypofunction
Management follows a predictable order and is worth learning as a sequence. Identify and, where possible, remove the cause. Advise frequent sips of water, avoidance of caffeine, alcohol-containing mouthwashes and smoking, and use of sugar-free chewing gum to stimulate residual flow. Provide saliva substitutes — noting that patients with natural teeth should avoid acidic, low-pH products because they demineralise enamel. Consider a salivary stimulant such as pilocarpine in specialist settings, contraindicated in uncontrolled asthma, chronic obstructive pulmonary disease and narrow-angle glaucoma. Above all, intensify prevention with high-concentration fluoride toothpaste, dietary advice and shortened recall intervals, because these patients develop rapid cervical and root caries and are prone to candidosis and denture-related stomatitis.
Halitosis: A Structured Diagnosis
Halitosis is classified as genuine, pseudo-halitosis or halitophobia, and about 85 to 90 per cent of genuine halitosis is intra-oral in origin, arising from volatile sulphur compounds produced by Gram-negative anaerobes on the posterior dorsum of the tongue and in periodontal pockets. Management is therefore mechanical — tongue cleaning, interdental cleaning and periodontal therapy — supplemented by chlorhexidine or zinc-containing rinses. Extra-oral causes, which need referral, include chronic tonsillitis and tonsilloliths, sinusitis, respiratory infection, gastro-oesophageal disease and the systemic odours of diabetic ketoacidosis, hepatic failure and uraemia.