Fig. 1. a Erosive tooth wear, b dental caries, c oral cancer, d periodontal disease.

      Oral conditions are included among the non-communicable diseases, which also include diseases such as cancer, cardiovascular disease, diabetes, and chronic lung disease. These are regarded as the leading causes of the disease burden and mortality worldwide. Today, it is also known that there is a strong connection between oral disease and the 4 main non-communicable diseases.

      Oral health cannot be looked upon in isolation. The mouth is a window into the health of the body and signs of nutritional deficiencies may be seen in the mouth at an early stage, in the form of mouth lesions or other oral disorders. The global aim is lifelong oral health for everyone! Diet, nutrition, tobacco use, harmful alcohol use, and oral hygiene should be regarded as modifiable risk-behaviour factors. Methods are currently available to prevent a large number of oral diseases. To control oral health, it is important to increase our knowledge of oral disease aetiology, develop standardised measurement tools, and focus on oral health promotion and preventive strategies including the effective control of diet and nutritional risk factors. This chapter aims to discuss in greater detail dental caries, dental erosion/erosive tooth wear, periodontal diseases, oral cancer, and dry mouth condition from this perspective. Figure 1 shows examples of the first four conditions.

      Dental Caries

      Introduction and Prevalence

From a historical perspective, dental caries is one of the most widespread diseases, and is the most common oral condition globally. The caries prevalence was low among prehistoric individuals, while a dramatic increase has been witnessed since the middle 19th century. This more recent change in disease pattern is due to dietary changes, particularly an increase in sugar intake. Even if the disease prevalence has been reduced in most countries since the middle of the last century through extensive preventive strategies, in the 21st century it still constitutes a major problem from the perspective of the individual, dental profession, and society. Untreated caries in permanent teeth is currently the most common condition, with a global prevalence of 35% (all ages combined) exceeding conditions such as headache, skin diseases, and low back pain [3]. Moreover, untreated caries in the deciduous teeth is ranked among the 10 top conditions affecting 9% of the global population [3]. For some time now, interest has focused on paediatric oral health and, over the years, different targets have been set with the aim of achieving an improvement in oral health. Many European countries have already realised the WHO goals for oral health in 2020, with the target of >80% caries-free 6-year-old children and a DFT of <1.0 for 12-year-olds [4]. However, large disparities can still be seen among children from both an international and a national perspective. Caries disease occurs in all age groups, and an increased prevalence can be seen in relation to different risk factors, such as diseases and medication, but also in relation to socioeconomic status [5]. The disease is also known to be clearly linked to overall quality of life and well-being [6].

      Aetiology and Pathogenesis

Dental caries is the result of an ecological imbalance in the oral domain. There is a dynamic relationship between the environment and the oral microflora, where disease development and progression occur, after repeated episodes of low pH caused by the bacterial breakdown of fermentable carbohydrates [7, 8]. In conjunction with low pH, a shift towards an increase in the number of acidogenic and aciduric species, such as mutans streptococci and lactobacilli, takes place. The weak organic acids, particularly lactic and acetic acids, formed from the metabolism of fermentable carbohydrates include both sugars and starches [9, 10]. This is followed by the demineralisation of the enamel and dentine, if the pH falls below the critical level for the hard tissues (ca. pH 5.7 for enamel and pH 6.2 for dentine, respectively). The balance between demineralisation and remineralisation determines whether or not further progression will occur. This aetiological triad, consisting of the tooth, cariogenic microflora and fermentable carbohydrates, is influenced by a large number of inherited (e.g., genetic) and acquired (e.g., lifestyle and socioeconomic) risk factors. Together with protective elements such as fluoride and oral hygiene, this determines whether or not the disease will occur [11].

      Disease Prevention

      Individual risk assessment and the early diagnosis of disease symptoms are important factors in disease management. Special attention should be paid to high-risk individuals within populations. Following the ecological principles of disease, a holistic approach to caries control should be adopted with the emphasis on disease prevention, where the establishment of a stable, positive oral condition may reduce the risk for the onset of disease and slow the disease progression. Strategies for creating an oral environment of this kind include inhibiting biofilm development and the enhancement of the host defence factors, where fluoride application, oral hygiene performance and dietary changes in particular play a key role. Tooth brushing twice daily with fluoridated toothpaste is the basic recommendation for individuals of all ages, with the amount of fluoride modified according to age and risk level. The stimulation of salivary flow to adequate levels is important for individuals with dry mouth conditions. Restorative treatment may be necessary for more advanced carious lesions, but this does not reduce the risk of disease. As diet plays a central role in disease initiation and the further development of disease, it is considered important to include other health professionals such as dieticians and nutritionists in caries-prevention programmes.

      Erosion and Erosive Tooth Wear

      Introduction and Prevalence

In recent years, dental erosion has evolved as a major threat to tooth integrity. It entails a gradual loss of tooth substance, due to repeated acidic insults on the enamel and dentine over time, and it is therefore often recognised late in the process. Dental erosion can be regarded as a common condition, with prevalence rates of between 4 and 82% in the