You don't need pain meds for dental care unless you've had some pretty major surgery imo.
I've gone through having two teeth reset from pointing back down my throat to the normal position with no pain relief (which was excruciating), a double root canal with no after-care pain relief (lidocaine for the session only), a session of 5 fillings with no aftercare pain relief (lidocaine only), and a session of four fillings and a wisdom tooth extraction (which snapped as he was removing it) with no pain relief (lidocaine only).
No you will have no withdrawal symptoms at all.
It doesn't matter whether you fell off the wagon, what are you doing now? Not putting drugs in your body? Not planning on putting drugs in your body? You're all good then, no need to worry.
I've just detoxed from bupe and I've got to have my shoulder reconstructed in the near future. Pretty much no way around some form of pain meds for that unfortunately, but it is what it is. I don't intend on leaving myself in excruciating pain because I used to enjoy (and not enjoy) taking opiates. I'll fill whatever script I get given and try and do my best with otc meds but if I have to use the stronger stuff then so be it. I recognise the clear and present danger that represents but as long as I follow the prescription set out for me I'm happy that I'm living my life in the way I want to and not making it worse by taking drugs. I'm in the UK though, I won't get anything major scripted. I imagine in the US I would probably be given months worth of oxy or something silly like that, over here I doubt I'll get anything more than a handful of DHC, maybe oramorph at best.
Still. It doesn't matter whether you took that one pill, just ask yourself whether you are happy with what you are doing now.