Rob Gronkowski has a lot to smile about during the coronavirus pandemic ... the retired NFL superstar's teeth whitening business has seen a MASSIVE increase in sales ... and now he's paying it forward.
TMZ Sports has learned ... Snow -- which is part-owned by Gronk and UFC legend Chuck Liddell -- has been inundated with orders for the teeth whitening kits since the outbreak.
Josh Elizetxe tells us sales have increased by 240% and the orders are still coming in strong -- most likely due to an influx in video chatting while people work from home.