My dear wife unfortunately has had horrible luck with dental problems. She had coverage from her employer, and we continued it, at $49/month, after she retired. For her, it's been a good decision, but even with a huge amount of care required, it's close to being a wash. There are just too many things that they don't cover, like she had a partial denture that broke apart, literally split in half, when it was two years old. They paid half the cost of the device originally, but zero for the replacement, since they will only cover a partial ever three years. We battled them for months when they misread a chart and denied extensive work on her upper teeth, since they claimed that they had already paid to extract the teeth in question. Now they had copies of charts, and current x-rays, and swore that their in house dentist was reviewing the claim, but in reality they were just playing games. In the last three years we probably got a 25% return over the premiums, with a really heavy volume of dental work.
My take, after far too much interaction with the dental insurer, is that IF your dental health is a mess, it's PROBABLY a good idea to have the insurance. If you are pretty normal, then your best bet is to stick that $46 a month in a saving account and pay out of pocket, when the time comes.