Personally I don't drink the stuff, so I respond with some reservations, but it sounds to me more as though the problem were caused by acid rather than sugar. Acid removes the outer layer of basic calcium phosphate and the tooth's layer of mucoproteins and bacteria. It also roughens the tooth's surface by etching it, leaving bare crystalline surfaces exposed.  When you rub those etched, unlubricated surfaces together, the friction is considerable.

You may take it as a warning of what the stuff is doing to your teeth.

"Gritty" teeth

is a phenomenon I know from eating rhubarb.

(caused by the oxalic acid in rhubarb, I think)

The drink You mention contains citric acid and

dihydogenphophate, both are rather acid, but 

I did not find figures about amount of that

acids.

Either this is a common observation (in this case

there should be more on that in Internet) or

Your teeth are extra sensitive.

In any case such "sports" drinks are very fluid,

they are superfluous.

Georg