Stephan Curve

Acid produced by oral bacteria during fermentation of carbohydrates dissolves or demineralizes the enamel and/or dentin during the caries process. The extent to which acid is produced during fermentation of foods with different macronutrient compositions, meal patterns, or intake sequences can be identified and compared using plaque pH studies. Based on the assumption that acid produced by oral bacteria causes caries, the acid produced during fermentation can be quantified and the fall in plaque pH reflects the cariogenicity of the test food. The pH gradually returns to normal following removal of the acid through salivary clearance or buffering. The Stephan curve, the plot of the pH of plaque over time, allows the visualization of the food’s cariogenic potential (Figure 3).¹¹ The critical pH is defined as the pH above which remineralization occurs, and below which demineralization occurs. Although individual critical pHs vary, the critical pH is generally defined as a pH of 5.5.

Figure 3. The Stephan Curve¹¹

Figure 3. The Stephan Curve¹¹

Plaque pH studies have been used to confirm that sugars are readily fermented by oral bacteria. Fibrous foods that require chewing increase the rate of acid removal and reduce caries risk. The impact of the carbohydrate form on the critical pH has also been determined. For example, Naval et al investigated the differences in plaque pH in response to different beverages following a sugary snack (Figure 4).¹² First, they had subjects eat or drink a sugared cereal, a 10% sucrose solution (positive control), or a 10% sorbitol solution (negative control). The subject’s plaque pH fell in response to the sugared cereal and sucrose challenges, but not the sorbitol solution. Navel et al then had the subjects drink whole milk (mixed protein, carbohydrate, fat), 100% apple juice (all sugar) or tap water after eating the sugared cereal (Figure 5).¹² The pH returned to normal faster after milk consumption, followed by water, and finally juice. Similar plaque pH studies have been used to confirm that oral bacteria are unable to metabolize saccharine, aspartame, acesulfame K, or sugar alcohols. As the low/no calorie sweeteners are not acidogenic, they are not cariogenic.

Figure 4. In vivo mean plaque pH after participants rinsed with sucrose or sorbital or consumed Froot Loops (Kellog’s, Battle Creek, Mich.).¹²

Figure 4. In vivo mean plaque pH after participants rinsed with sucrose or sorbital or consumed Froot Loops (Kellog’s, Battle Creek, Mich.).¹²

Figure 5. In vivo mean plaque pH after participants consumed Froot Loops (FL) (Kellog’s Battle Creek, Mich.) followed by FL and whole milk (FL/milk), FL and 100% apple juice (FL/juice) or FL and tap water (FL/water) (n=20). The solid arrow indicates two minutes after complete consumption of FL. The dotted arrow indicates the time of beverage consumption.¹²

Figure 5. In vivo mean plaque pH after participants consumed Froot Loops (FL) (Kellog’s Battle Creek, Mich.) followed by FL and whole milk (FL/milk), FL and 100% apple juice (FL/juice) or FL and tap water (FL/water) (n=20). The solid arrow indicates two minutes after complete consumption of FL. The dotted arrow indicates the time of beverage consumption.¹²