<P> The cause of caries is acid from bacteria dissolving the hard tissues of the teeth (enamel, dentin and cementum). The acid is produced from food debris or sugar on the tooth surface . Simple sugars in food are these bacteria's primary energy source and thus a diet high in simple sugar is a risk factor . If mineral breakdown is greater than build up from sources such as saliva, caries results . Risk factors include conditions that result in less saliva such as: diabetes mellitus, Sjogren's syndrome and some medications . Medications that decrease saliva production include antihistamines and antidepressants . Caries is also associated with poverty, poor cleaning of the mouth, and receding gums resulting in exposure of the roots of the teeth . </P> <P> Prevention of dental caries includes regular cleaning of the teeth, a diet low in sugar, and small amounts of fluoride . Brushing the teeth twice per day and flossing between the teeth once a day is recommended by many . Fluoride may be from water, salt or toothpaste among other sources . Treating a mother's dental caries may decrease the risk in her children by decreasing the numbers of certain bacteria . Screening can result in earlier detection . Depending on the extent of destruction, various treatments can be used to restore the tooth to proper function or the tooth may be removed . There is no known method to grow back large amounts of tooth . The availability of treatment is often poor in the developing world . Paracetamol (acetaminophen) or ibuprofen may be taken for pain . </P> <P> Worldwide, approximately 2.3 billion people (32% of the population) have dental caries in their permanent teeth . The World Health Organization estimates that nearly all adults have dental caries at some point in time . In baby teeth it affects about 620 million people or 9% of the population . They have become more common in both children and adults in recent years . The disease is most common in the developed world due to greater simple sugar consumption and less common in the developing world . Caries is Latin for "rottenness". </P> <P> A person experiencing caries may not be aware of the disease . The earliest sign of a new carious lesion is the appearance of a chalky white spot on the surface of the tooth, indicating an area of demineralization of enamel . This is referred to as a white spot lesion, an incipient carious lesion or a "microcavity". As the lesion continues to demineralize, it can turn brown but will eventually turn into a cavitation ("cavity"). Before the cavity forms, the process is reversible, but once a cavity forms, the lost tooth structure cannot be regenerated . A lesion that appears dark brown and shiny suggests dental caries were once present but the demineralization process has stopped, leaving a stain . Active decay is lighter in color and dull in appearance . </P>

Write the ph value after which teeth start decaying