You can do dofollow blogs for that particular keyword and participate in forums. Use that keyword in the signature fields. It will helps to increase higher rankings in search engine.
Oh geez, come on people. The number 1 way to increase your SERPS is with quality links from relevant authority sites. There is no way to get natural rankings that surpasses the effect a good link with the right anchor text from an authority site. Blog comments are garbage for the most part when just trying to increase your links. Most sites will mark as spam any comment that uses a Keyword Phrase as the 'Name.' My advice is to seek out other dentists, medical groups, insurance websites, etc. and petition a link from them, you'd be surprised on the response when asked nicely. I recommend participating in Dental Forums, etc. and giving sound advice/recommendations and using your website as a signature (if allowed). If your dental website is associated with a Physical Location, by all means add it to the Google Local Search, Business Directories (that aren't Link Farms/Crap), submit to the Google Directory (well worth the $299 fee). Best of luck.