That's not easy. I mean it's not that hard computationally but you're talking about very specific attack requiring some dedicated tools. Real life you would have two scenarios:
- You trying to break into my specific account like gmail. This will not help you because they will rate limit you, use captcha and eventually just block you.
- You have a leaked list of thousands/millions password hashes and my password is among them. Hackers would just use existing rainbow tables. They will not think 'hey, maybe some of those passwords use song lyrics, let's check'.
This would be bad pretty much only in the very specific scenario of hackers trying to hack my specific account and having leaked hashes of password for this account.
Still I wouldn't really use this method. I'm just saying it's better method than some printed card generating short alphanumeric password.
Dental is tricky in many countries. It's delicate, easy to go wrong and very often painful. In Poland I used to do simple things like fillings using public insurance and I've heard many times that I'm crazy and for sure they will fuck it up. I think it's simply because it's it expensive and will go wrong people will think it was inevitable. But if it's free and goes wrong people will say it's because it was free. So in my experience even if public insurance covers dental people tend to avoid it.