Reconsider lip injections Your teeth aren't the only things that affect your smile. Your lips are a big part of the equation. As we age, the collagen in our lips starts to break down, causing our lips to thin and flatten, making the corners of our mouth start to droop, says Singh. While lip injections or fillers can successfully plump and shape thin lips, giving a more youthful appearance, they can also give you the dreaded "duck lips" stars like Lisa Rinna and Meg Ryan have fallen victim too. Over injecting your lips will ruin your smile no matter how perfect your teeth are.