How do Cavities REALLY form? The (Gross) Truth

A little girl brushes her teeth.

Many children have heard the phrase from their parents or dentist, “you have to brush to get all those sugar bugs off!” The image that comes to mind is often a plump green monster with sharp fangs and some sort of pitchfork that is directly attacking and eating away at the beautiful white tooth. While this narrative works (sometimes) to motivate children to brush and floss better, it’s often difficult to motivate older children and adolescents to improve their oral hygiene. If you fall into this camp, this post is for you. Plus, the classic sugar bug narrative is not actually the truth. Sure, sugar bugs have a major role in cavity formation, but it’s not as direct as many people think.

Three things are needed for a cavity to form: 

  1. a susceptible host – the tooth 
  2. bacteria aka sugar bugs
  3. a substrate – something for the sugar bugs to eat


Two of these three are always in our mouth and at this time we have relatively little to no control over them. We will always have teeth (hopefully!) and no mater how much we brush, floss, or use mouth rinse, we always have bacteria in our mouth. However, it’s been proven that our plump green monster cannot cause holes with just his pitchfork and pointy teeth. He NEEDS something to eat to cause a cavity. Why is this? Because the real thing that causes cavities is the waste product of the sugar bugs,

I know…it’s a real shocker. But the truth of the matter is that the proliferative bacteria in our mouth process foods just like we do. And just like we do, they have waste products. This waste product is an acidic plaque that sits on our teeth and simply dissolves/erodes the tooth. If the plaque sits in one place long enough, the dissolving will progress until a hole is formed. This is called a cavity. Definitely not as glamorous as the plump green monster with a frontal attack. Brushing and flossing don’t directly affect the sugar bugs that much. They are resilient, plentiful, and always present. What brushing and flossing actually does is remove their acidic waste products. By not allowing the plaque to sit on the tooth, we prevent erosion and therefore cavities. 

Knowing the “how” of cavity formation isn’t just educational, but also extremely motivational. I find that explaining this truth to older kids is much more effective than the watered-down, plump green monster, toddler version. If you are having trouble motivating your pre-teens or teenage children to take better care of their teeth, consider sharing the (gross) truth of how cavities form. After all, nobody wants to have sugar-bug-waste-stuff sitting on their teeth.

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Blake McDonald, DDS

Blake McDonald, DDS

Blake practices dentistry in our Bluffdale Pediatric Dental office.

a happy father receives a kiss from his son

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