I currently have no dental insurance. I have been looking at options, however, in the last year the only thing I would have used it for would have been cleaning or routine x-rays, nothing really necessary. I'm fortunate to have good dental health at the moment. The only "real" work I've needed in the past 2-3 years was crowns. I had to get 2 a couple years ago, though I only needed one, because it was my front tooth and I wanted the two front to match. The one had chipped off a corner and though the second had a surface crack in about the same place as the one had chipped off, insurance would not pay unless it actually broke off too. So, I had to pay myself.
It's definitely a gamble. It seems to be a decision of what do you think you will need and when. The cheapest dental insurance I've found was $35/month. Crowns in my area run $800-$1000. Most insurance will only pay 50% on a crown. That means you will pay at least $400 on one. Further, most insurance won't pay for a crown in the first 12 months of coverage. So, even if you get a crown in month 13 (as soon as allowed) you will have paid $420 in premiums and you'll pay $400 of the cost of the crown. That's the full cost of the crown. If you don't need it that soon, then you may have paid enough premiums for 2 crowns before you need them. So, maybe you should just put that $35/mo into savings for when you do need dental work. And some dentists give a discount for cash, as well as for seniors.
On the other hand, if you think you're going to need a lot of work or don't want to take the chance of an emergency, then insurance can give you real peace of mind and be beneficial. It's a more difficult decision for people trying to live primarily on social security than those who have been able to save enough to live well in retirement and see SS as pocket change.