how does dental billing work?

Hi, I went to my primary dental office and they quoted me $25 for the first root canal and $385 for the second. I have two different insurances. One from work and one from the university. They both have a $500 max and the one from work has $360 remaining. The bill shows that the first root canal costs $610-$360-$225(2nd insurance) = $25 out of pocket expense. The second one would be $610-$225(2nd insurance) = $385. However, I just went to another dentist office (a root canal specialist) and gave them both insurances. They claim to be in-network for both of them. However, they told me that the first canal would cost $610-360 = $250. And the second one would cost 610-225=$385. It seems like they did not split bill the first root canal to BOTH insurances but instead to only the 1st insurance. Then they billed the second root canal to the second insurance. I was wondering if you think the first dentist office made a mistake or if the second one did? I am going to call the second dentist office tomorrow to kindly ask them to review it and let them know about the first dental office billing estimate to see if they split billed it properly. I really want to go to the second dentist but if it is going to cost me hundreds of dollars more then I refuse. I work in a pharmacy and I know about how billing two different insurances can sometimes be tricky and sometimes mistakes occur where if the patient does not speak up they would have ended up paying over a hundred dollars extra. However, I have no insight to how dental billing works. Thank you for your advice/insight! Also I was wondering what happens if you cancel your appointment? I know the first dental office has a policy that you must cancel before 24 hours prior to the appointment or you are charged $10 for each 1/2 hour. However, I do not know about the second dentist. I would be canceling several days in advance so what do you think would be the reasonable consequence?
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You never quite know how the insurances work until you submit your claims. It should work the same at either office if your sure they are both in-network for your insurance. Our offices cancellation policy is 48 hours before appointment or a $45 per hour charge. Wasted time means lost money.
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