I recently went through the need to learn about dental insurance and am happy to share what I learned.
Delta Dental offers numerous plan types, and not all Delta Dental providers accept all the different plans. The one that is best for patients is worst for the dentist, therefore the only dentists that accept that particular plan may provide so-so treatment if you are particular. But you may get 'lucky' and find an office where everyone cares more about dental care than the mighty dollars.
The plan I was going to sign us up for had no waiting period, no annual maximum, no deductible and was around $200 annually for both of us. BUT when I visited the offices within the area (its based on your zip code) I would not want to get dental treatment at any of them. I called a relative who retired from 60 years as a practicing single office and he explained it to me.
Also learned that many of those dental offices 'share' equipment and specialists which is not a good thing.
The dentist I unfortunately went to initially (car accident broke 4 teeth) did such bad work that one year later I've had to have all work redone and pay out of pocket. Hard lesson, hope this helps someone who reads this.