This is a good question--wish I had a good answer for you.
For those insurance companies that have reduced-fee participating
dentist programs (PPOs) the fee schedules can sometimes be obtained on
line (though I'm not sure you can access these if you aren't a member).
    But as far as what insurance companies consider reasonable (so-called
UCR--usual, customary and reasonable) are usually secret.  It is usually
defined as the 90th percentile (that fee at and beneath which 90% of
dentists' fees fall--sometimes broken out by locale).
    Problem is, some insurance companies maintain UCR lists that are years
(sometimes many years) out of date.  In a rare instance of candor, years
ago an insurance company rep admitted to me that they used a UCR list
that was about 15 years old, but that the next year they were upgrading
to a UCR list that was only 5 years old!
    The most absurd instance of this secrecy is the Delta Dental system.
If a dentist wishes to participate, they must sign a contract accepting
the delta fees.  Problem is, they don't tell you what the maximum
allowable fee is.  You submit your fee profile, and when you send in a
claim if your fee is over their max they reduce the fee to their max.
That is the only way you ever find out what their maximum reimbursement is.
    The only other thing I can tell you is that there are some throwaway
magazines that are sent to just about every dentist in creation--one
called Dental Economics (come to think of it, I don't think I get it
anymore) that once a year does a statistical survey of fees by region.
If you're near a dental school you might want to try to sneak into their
library and see if you can find a copy.  There is no way to tell of
course if their informal survey is truly representative, and my
impression is that the fees are generally quite high.  There are also
some practice management companies that survey and keep these statistics
(available for a fee).
    I found something on the web, and it may help you.  If you e-mail me at
dentaltwin@earthlink.net I can send it to you as an attachment.

Steve