The mouth is home to 19,000-26,000 different types of bacteria living together in a moist environment called a biofilm, otherwise known as plaque. There are a number of different types of bacteria within this biofilm that have the propensity to cause dental decay.
While everyone has a range of different bacteria in their mouth, people have differing amounts of good and bad bacteria. People who have active dental decay have elevated numbers of decay causing bacteria in their mouth. This bad bacteria can be transferred to others via a toothbrush, sharing water bottles, lip gloss, kissing, etc.
So you might be curious if you can catch your girlfriend’s or boyfriend’s tooth decay by borrowing their toothbrush. There are a few factors to consider, such as the type and shape of the toothbrush, toothpaste used, how long since they last brushed their teeth and if they have active dental decay.
There have been a few studies which have studied this area in detail and have found interesting results. If someone has active dental decay, they have higher numbers of decay causing bacteria in their mouth and this bacteria sticks to their toothbrush when they brush. Straight after brushing, the toothbrush has the highest amount of bacteria present.
Most people then store their toothbrush dry in a holder or leave it on the sink. Over time, the toothbrush dries out and the numbers of bacteria in the brush decrease. After 24 hours, there are still bacteria present, but lower numbers.
So does this mean that you can catch their decay? No, not necessarily.
Bacteria that causes decay needs to feast on sugar in order to produce acid as a waste product. It is this acid that eats away at the surface of the tooth and eventually leads to a cavity in the tooth.
If you are not feeding this bacteria sugar from your own diet, it cannot produce the acid that causes the cavity. If you are regularly removing the plaque from all surfaces of the teeth by brushing for two minutes, twice daily and flossing to remove it from between the teeth, you will remain cavity free.