My immediate thought is that it’s not the action of smoking cannabis causing these cavities, instead…

It’s fairly commonly accepted that habitual cannabis use can lead to demotivation. I’m a very regular dry herb vaper and with exception of a few strains, I have to make a great effort to make sure I do daily tasks when I’m high.

I’d also suggest that ppl who are self medicating due to depression are less likely to brush their teeth twice a day. Finally, perhaps cannabis users are more likely to consume sugary snacks?

In a nutshell, these findings don’t surprise me! But I would be surprised if cannabis was causative and not just a correlated factor.