A better way to look at it is... If you put your users first, and create a site with enough utility and value to bring in a massive network of people..You'll be worth much more even if you have to start by monetizing with ads...but don't worry, eventually you can sell products and services between dentists and patients, dentist and vendors, and patients and retailers.

TL;DR put people first, your users are your defense. Monetization will fall into place if you have a network effect.