A plaque biofilm inhibits the restorative effects of saliva, and low saliva levels increase the risk of dental decay. Dry mouth (xerostomia) may result from a number of causes, including:¹¹

• Medication such as antidepressants, antihistamines, and diuretics
• Diabetes
• A blocked nose resulting in mouth breathing, or sleeping with an open mouth
• Inadequate hydration levels, especially among the frail, elderly, and those with cognitive impairment
• Caffeine, alcohol or nicotine
• Radiotherapy to the head and neck, damaging the salivary glands
• Sjörgen's syndrome, an auto-immune condition which can damage moisture-secreting cells including salivary glands.

Dental decay may also arise from acid erosion due to frequent vomiting or gastric reflux, as well as the normal process of tooth-wear or behaviour such as bruxism (teeth grinding or jaw clenching).¹² Drug abusers and those on methadone maintenance treatment are at increased risk, as €there is a higher incidence of rampant caries, xerostomia, bruxism and poor oral hygiene.€¹³