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From Trisha's Desk Trisha E. O’Hehir, RDH, MS, Hygienetown Editorial Director

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What's pH Got to Do with It?
– by Trisha E. O’Hehir, RDH, BS, Hygienetown Editorial Director

Caries is a pH disease, not just a sugar disease. As the pH of the saliva and plaque biofilm drops from a neutral of 7, demineralization begins and if the pH remains below 5.5 for enamel and 6.7 for cementum, cavitation will occur.
Sören Sörensen, a Danish biochemist who was the Director of Chemistry in the Carlsberg Laboratory in Copenhagen, devised the pH scale in 1909. Beer magnate JC Jacobsen founded the Carlsberg Laboratory in 1876, but the focus of the laboratory was science, not beer. Dr. Sörensen received a number of awards and honors for his work.

The scale Dr. Sorensen devised measures the "power of hydrogen," or "pH." The pH scale begins with zero, an extreme acid, and increases to 14, an extreme basic or alkaline. Seven is considered neutral, in the middle of the scale between acid and base. Water has equal numbers of hydrogen (H) ions and hydroxide (OH) ions. The negative logarithm of hydrogen concentration is the pH number. Water has a pH of 7, which has a hydrogen concentration of 1 x 10-7. Remove the negative to the left of the 7, and you have the pH score, 7. Until the pH scale was developed, there was no widely accepted way of expressing hydrogen ion concentrations. The pH scale provides a convenient way to express hydrogen ion concentration. Each pH score increases exponentially by a power of 10, so the pH of 5 is 10 times more acidic than a pH of 6.

Litmus paper is a popular way to measure pH in solution. The word "litmus" comes from an old Norse word meaning "to dye or color." This makes sense as litmus paper is infused with dyes from lichens that have been used for years to dye cloth. When placed in a solution, the paper will turn red in an acid, blue in a base and purple in a neutral solution. For more definitive readings, indicator paper that comes with a printed color guide will provide scores within two pH readings. Electrical pH meters measure even more accurately.

The body functions best within a narrow pH range. For example, human blood is generally within a range of pH 7.35 to 7.45, just slightly more basic than neutral pH 7. Measuring blood pH is now a routine part of blood analysis. Looking for higher or lower blood pH values will indicate alkalosis or acidosis. Identifying pH values beyond normal can help diagnose metabolic and respiratory problems. Urine is also commonly analyzed for indications of diabetes, by acidic pH levels.

Either at home or in the office, resting salivary pH can easily be tested with indicator paper by having the patient spit into a medicine cup or plastic spoon. Simply dip the pH paper strip into the saliva and check the reading against the scale. When heavy plaque biofilm is covering the teeth, an exposure to sugar or other fermentable carbohydrates will drop the pH of the biofilm below 5.5 and hold it there for 20 minutes to an hour. Repeated acid exposures will lead to demineralization and eventually cavitation of enamel or cementum.

Besides testing saliva and plaque for pH, foods, drinks and sour acid candies can be tested to give patients an idea of what they are exposing their teeth to each day. Adding pH testing to your practice will help patients understand the caries process is about more than sugar.

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