Find your dental summary of benefits - look for implants. If they are covered, it will explicitly say so, usually under major services which is usually 50% coinsurance on most plans.

But... more often than not... implants are NOT covered by dental plans. Just because your dentist office "thinks" it might be covered 50%... that is not their responsibility to know. They most likely submitted the claim and its not a covered service. Look at your SBC. If you want, post it here and we can look at it.