Well an Overture search shows:
essex dentist 4871
If your looking to sell based on typo traffic, i would'nt anticipate a huge price, if you could find a buyer perhaps £50 - £100, but finding a buyer could be tricky, someone looking to develop a site for revenue could pick up a similar name for reg fee, so unless they are really keen on Essex Dentists, you'll be lucky!
The potential is in possible development yourself, if you could create a simple directory style site listing dentists in Essex with some SEO work to attract some traffic, you could then look to sell based on traffic and income....