The Stephan curve depicts the evolution of the pH of the plaque after the consumption of a meal rich in sugars. This curve is often taken up by chewing gum commercials without sugar and other useful aids when it is not possible to perform a correct oral hygiene with a toothbrush and toothpaste.
In the 40s of the last century, Stephan carried out a series of in vivo experiments measuring the pH of the plaque through electrodes placed on the tooth surface. The data collected by Stephan showed how, immediately after rinsing with a sugar solution, the pH of the plaque drops sharply within 5 minutes, and then gradually rises to baseline values in the next 30 minutes. This shows how acidity levels that are harmful to the enamel are reached in the 20-30 minutes after a meal, which starts to suffer from pHs below 5.5, demineralising itself with the loss of calcium and phosphate. The pH is restored over the next 30 minutes by increasing the concentration of bicarbonates in the saliva.
The curve of the Stephan curve is similar in subjects with healthy teeth and in those with caries; however, in the latter the pH values are on average lower, both at basal levels and in the acidity peak after the sugary meal.
Stephan's curve explains why it is important to avoid close consumption of sugary snacks and sweets, very common in children. Indeed, such habits lead to an increase in the period of time in which the enamel is exposed to critical acidity levels. For this, it is preferable to consume a sweet food during the main meals, avoiding snacks between meals.
