What is the value of pH of the mouth when tooth decay starts?

pH < 5.5

The correct answer is option 2. pH < 5.5.

To understand why tooth decay begins when the pH of the mouth drops below 5.5, it's essential to understand the role of pH in dental health and the process of tooth decay.

Tooth decay, also known as dental caries, is caused by the demineralization of tooth enamel, which is the hard outer layer of the tooth. This demineralization occurs when acids produced by bacteria in the mouth dissolve the minerals (primarily calcium and phosphate) in the enamel, leading to the formation of cavities or holes in the tooth structure.

The pH scale measures the acidity or alkalinity of a solution, with values ranging from 0 to 14. A pH of 7 is considered neutral, while values below 7 indicate acidity, and values above 7 indicate alkalinity.

The bacteria in the mouth feed on sugars and starches from food particles, producing acids as byproducts through fermentation. These acids, particularly lactic acid and acetic acid, lower the pH of the dental plaque that forms on the tooth surface after eating. As the pH of the plaque drops below a critical value of approximately 5.5, the enamel begins to demineralize.

At a pH below 5.5, the acidic environment becomes conducive to the dissolution of the minerals in the enamel, primarily calcium hydroxyapatite. This demineralization weakens the enamel and leads to the formation of microscopic pores and lesions, which eventually progress into cavities if left untreated.

Therefore, when the pH of the mouth drops below 5.5, it indicates an acidic environment that promotes the demineralization of tooth enamel, initiating the process of tooth decay. Maintaining proper oral hygiene, including regular brushing, flossing, and limiting sugary and acidic foods, can help prevent tooth decay by controlling plaque formation and maintaining a neutral pH in the mouth.