$40/month for family coverage? Jesus. Neither my firm nor my wife's offers anywhere near that. That's a fraction of what we'd pay.
For many years, I bought "insurance" on DentalPlans.com -- it's not really insurance but, rather, a discount schedule that some dentists honor. My dentist took it for almost 15 years, allowing me to get $39 cleanings four times a year. He finally walked in after a cleaning and told me I was ripping him off. Now they're $100 more. But I ran the numbers and it still doesn't make sense to sign onto my wife's dental insurance or use my firm's.