Sorry to say but you don't have a very good dentist. One of my good friends is a dental hygienist, and I worked in the dental office for almost 2 years.
Looking at tooth enamel is an indication of your general health. Degraded enamel (piited and scarred), and increased tooth sensitivity to hot and cold can be an indication of bulimia.
Hormonal flucuations caused by puberty, perimenopause and pregnancy increase the likelihood of gingivitis. This can lead to heart problems in the future (honest! Not an old wives' tale! Has something to do with the bacteria that causes gingivitis and that is has been linked to HD).

Getting your teeth treated with fluoride will help with future decay. taking care of your gums - flossing or, like me, waterpicking (don't like putting my hands in my mouth!!) - will guard against gingivitis. Also try using a Sensodyne - type toothpaste to help with any discomfort.
If you have your teeth whitened the sensitivity may increase. Fluoride helps to decrease it.

ClearSkies