What Percentage of Production Should a Dentist Pay an Endodontist?

I was hoping for some
recommendations for how to pay my Endodontist. 

We are a GP practice, and for
the past year we’ve hired an Endodontist to work a couple days a month for us.
We have given him 37% of production of his specialist fees; however recently he
wanted to know if we would give him 50% of production of his specialist fees. 
I guess this is what he is used to receiving as an associate at endodontic
offices, however I didn’t know what was standard when an endodontist works in a
GP office.  

He pays for no instruments, materials, equipment etc, and has
his own chairside assistant at no expense to him. 

Thanks!

Generally 45-50% of COLLECTIONS. 
If they want payment on
production make it adjusted production.