Mini tooth,
The DMD and DDS degrees are not separated by the regions of the U.S.! It's actually based on history of how certain schools interpret how they want to name their graduates and their philosophy behind dentistry. I think it's just coincidence that east coast schools has more DMD schools and west coast has more DDS schools! Here's a brief description of how the two degrees come about:
<img src="http://imagehost.auctionwatch.com/preview/sh/shie0023/dmddds.jpg" alt="" />
Above source is from American Student Dental Association publications
For further detailed explaination, visit this site and scroll down to United States section:
<a href="http://www.dental-site.itgo.com/westerndent1750.htm" target="_blank">http://www.dental-site.itgo.com/westerndent1750.htm</a>
Hope this clears up some confusion. 😎