Why didn't my cavity show up on my x-rays?
Dental x-rays are not perfect detection tools. They are just that—tools. That means that occasionally you could have a condition that does not readily show itself in our digital imaging.
A few explanations may be accurate. First, your cavity may be so small it did not show up on your dental x-rays. A very small cavity has not yet caused enough damage to be visible through x-ray technology.
Secondly, your cavity could be hiding behind an existing filling. When you get decay near an existing filling, we call this secondary decay. Fillings are opaque and may actually block out part of your tooth from being x-rayed, rendering it invisible.
Thirdly, your teeth could overlap. If you have very close teeth, taking an x-ray without overlap may be impossible. Additionally, when you have very close teeth, getting decay between them is more likely.
Another reason decay may not show up on your x-ray is that it could have started after your last set of x-rays. Your teeth are susceptible to decay all of the time, especially if you eat sugary or high acid foods. It is quite possible your decay did not develop until after your last dental exam and last set of x-rays.