Dentists are our main clients and they are difficult to collect from , they also get offended easy about collections
Reorganize your invoice so instead of the traditional 'penalty' for late payment you offer an incentive for early payment. Same values, reverse labels.
You should also look at automating reminders for payment after a certain date. This should be relatively straight forward depending on the accounting system you are using.
I've provided similar automation solutions for a number of clients and would be open to discuss in more detail if you would like to schedule a call.