Your financial assumptions for your business will depend greatly on the scope of your marketing efforts. If you plan to rely only on your relationships with your dentist friends, I'd be very conservative in your financial assumptions, on the other hand, if you have a marketing program that is consistent, and makes use of several marketing tools, you can assume a greater income. An idea that's worked out for me is:
1. Assume a very modest income for the 1st year or 2
2. Track your marketing efforts and results, keep a close accounting of them
3. Adjust the projected income figures in your business plan every 3-6 months as you get updated information from your marketing efforts.
Sorry I can't pin it down more than that, but I'm not sure what you're doing to market your business, other than your relationships with your dentist friends. However....If you plan to work for different types of providers, I would suggest at least 2-3 different types of marketing activities.