Dental insurance: Benefit Limit and 50% co-insurance. Explain?

I have dental insurance which states that for "Routine Dental Treatment" that a "50% Co-insurance applies". There is then "Benefit Limit" of $400. Can some please explain what this means and how the Benefit limit and 50% Co-insurance are related. Thanks!
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Your Co-insurance means your insurance will pay 50% of your dental bill. The benefit limit means that the insurance will pay 50% of your bill up to $400. That means if you have a dental bill of $600, the insurance will pay 50%, or $300. If the bill is $800, the insurance pays $400. If the bill is $1000, it will pay $400 even though 50% is $500 because the "limit" is only $400.
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