Hi there 0ozma, good to see you and Hachi.
I can't reassure you about distemper though - it's an important vaccination. It's the P in the FVRCP combined vaccine. If Hachi got the kitten series vaccinations, then he should be ok, although many vets seem to still go with the 3-year booster protocol.
I stopped all vaccinations a few years ago after Celia had an adverse reaction, and my vet was not happy. My kitties used to get the FVRCP booster every year, then every 3 years once the guidelines changed. But I've heard some rumblings about vaccinations potentially being associated with kidney disease (which Celia has) though I haven't looked too much into this. Many people are hesitant to give vaccinations, usually because of the risk of injection site sarcoma (ISS). It is a small risk, but it is a risk, and an unnecessary one if vaccinations confer lifelong immunity as they should.
That said, if your vet requires it before a dental, personally I would do it and go ahead with the dental while it's just a cleaning. I'd rather take my chances with ISS rather than with gingivitis or teeth that need to be extracted. And then I'd stop further vaccinations.
There is less risk with non-adjuvanted vaccines. I know Merial is the only one that makes a non-adjuvanted rabies, but I don't know about for distemper. My kitties have always gotten the combination FVRCP, also by Merial I believe.