The phrase "do dentists know if you have given" refers to the ability of dentists to detect whether a patient has engaged in certain behaviors or habits based on their oral health. For example, dentists can often tell if a patient smokes, uses tobacco products, or has a poor diet by examining their teeth and gums.
This information can be important for dentists in making treatment decisions and providing preventive care. For example, a dentist may recommend more frequent cleanings or fluoride treatments for a patient who smokes or uses tobacco products. They may also recommend dietary changes to improve the patient's oral health.