If ur going to dentist to get work done and ur insurance covers 90% should u have to pay 70 dollars up front ?

Sure: Unless your dentist has worked with you for a long time and knows your insurance well, he (or she) doesn't really know whether or not your insurance will follow through on paying as they say they will. Maybe they take months to pay. Maybe they deny claims frequently. Is it fair that your dentist should work for free while waiting for this to get straightened out? Do you work for free?

Coverage is not. . .: An insurance plan may cover 50%, 60%, 70%, etc..., but that says nothing about what they will pay for. Many people do not realize that coverage is not payment. Most patients with medical insurance have deductibles, from $250 to $4000 dollars. That means the insurance company covers, but does not pay for, the first $250 to $4000 of covered services (the patient pays that out of his own pocket).

It depends: It depends on your insurance's contract with your provider. Some insurances require the provider to submit the bill to them before they are allowed to bill the patient. Some allow the provider to collect an estiamte up front. That is a great question for your insurance company service agent. Either way, you should be the expert on your plan's rules to be able to plan ahead.