DMO plans are typically not the greatest. My suggestion is to read your benefits booklet throughly and be sure to go to a dentist who participates in the plan. The more you educate yourself of your coverage the less you'll be surprised by unexpected charges.
Is there a waiting period on major dental work? If he needs it now sometimes there are anywhere from 6-12 month waiting periods for things other than your routine cleanings. Also co-pay might be per service some dental plans are on a fee schedule where you pay different amounts depending on procedure. If you have a really good dentist they should run the procedures through your insurance and make you aware up front of the cost.
Re: Healthcare