When Kevin asks this lady if a toothbrush has been "approved by the American dental association" she's baffled—it's like she's been hit with the Riddle of the Sphinx. She has to confer with another employee. (Typically, the package would reveal this information, but apparently it didn't.)
Then, Old Man Marley enters and Kevin starts backing towards the door—he runs away, prompting the clerk lady to yell for the stockboy to intercept him. Kevin escapes, and we never learn whether his toothbrush was approved by the American Dental Association or not. It's a sad day for oral hygiene.