Yes, dentists wear stethoscopes for a number of reasons. If the patient has to have surgery of any kind, the dentist needs to wear a stethoscope to check blood pressure. This is important because if there is a particular spike in the blood pressure then the dentist should know this, especially if the person is under any anesthesia.
The stethoscope can be used in conjunction with checking body temperature. If the patient has an infected tooth, or has symptoms of being hot or tired, the dentist takes the temperature of the patient, and as a part of the exam might use the stethoscope.
The stethoscope can also be used to examine the lungs and the heart. Typically, dentists will listen to the heartbeats to listen for elevated heartbeat and listen to the upper and lower lobes of the diaphragm to check the condition of the lungs. Interestingly, while dentist only look at teeth, the whole body can affect our oral health.