1. The goodwill is of no value because the dentists will leave after their 5 year lock-ins;
2. The revenues are propped up by government subsidies.
Let's examine proposition two. I am sure you are not implying that all OTC revenues comprised of government subsidies. After all, even a simple BUPA family health cover reimburses 100% of an annual clean and check-up. So the question is how much? 50%, 70%?
Let's also take one step further and say that all government subsidies are abolished tomorrow. So the whole industry takes a 50% haircut. The reality then is that individual dental practices will be unprofitable, so why would the dentists leave? Where are they going to go and make a living?
In summary, your two main propositions are in contradiction. Either one or the other can occur, but not both.
In reality, there is a fundamental demand for dental work, much of which is pretty inelastic to any government subsidies. If your teeth hurts, you will pay to get it fixed. I think you might have overlooked this fundamental issue.
p/s I understand that you say ONT may be pricey. But before we arrive at figures to underpin valuations, we need to get the basics right first.