The study linked below (via Mashable) found that social media widgets that generate customer interaction, such as polls or discussion groups, do not neccesarily predict future buying. For dentists this is interesting as it indicates social media may be more powerful as a method to support existing patients than to find new ones.
Of course if you have a satisfied patient (who is supported via a facebook page) and she decides to make a facebook posting about you, then instantly her 130 friends (the facebook average) get the mesage and some of those will re-post it to their 130 and so on. Word of mouth 2.0.
Surprisingly, the study suggests that banner ads may be the best choice for advertisers that want to push a product. However, for campaigns that want to build engagement, corporate profiles or sponsored content is the better option.