It seems to me that the exposed nerves may be due to inflammation caused by bacteria. When I had my mercury fillings removed from 5 teeth in 1998, those teeth became very sensitive. It took me more than a month to get over the sensitivity with daily use of the herbal mouthwash. The chief ingredient of this mouthwash, Saussurea , is anti-bacterial and also helps energy flow according to traditional Chinese medicine. Herbs generally have different anti-bacterial actions than chemicals.
Herbs simply create an environment unfavourable for bacterial survival.
Since the normal bacteria require different environment than pathogenic bacteria, they are not affected by herbs. After using our anti-bacterial mouthwash preparation for about a month, her tooth sensitivity disappeared. Other people who had teeth sensitive to cold and heat also had similar favourable experience with the mouthwash. A 43-year old man had a sensitive tooth that bothered him for years. He found only temporary relief with Sensodyne, which he used daily for four years.