The best way to know if your wisdom teeth are decayed is to go to a dentist and have them looked at by a professional. If you need to check by yourself, what you need to check is not whether the wisdom teeth have individual caries, but the eruption position of the wisdom teeth, you can open your mouth and open your cheeks and look in the mirror to see whether the eruption position of the wisdom teeth is normal or not. If the wisdom teeth erupt in the same position as the front teeth, and after biting to achieve a better bite, wisdom teeth exposed in the oral cavity of the tooth surface as well as the crown are more polished, then it is a normal tooth. If you can see that the wisdom tooth is erupting at an angle and there is resistance to forward growth, or there is resistance from soft tissue or bone tissue in the far side of the wisdom tooth, then consider that this wisdom tooth is an obstructed wisdom tooth, which can be called a bad wisdom tooth and is clinically recommended to be removed.