The simple answer is no; dentures will not correct a thin upper lip. However, there are ways to improve the appearance of a thin upper lip with the help of dentures.
Dentures can be used to add support to the lips, which can in turn, make the lips look fuller. In addition, teeth can be made with a lip-supporting design that helps to keep the lips from looking sunken in.
If after your teeth are made you are still unhappy with the appearance of your lips, you may want to consider an injectable hyaluronic acid dermal filler. Dermal fillers can be used to add volume to lips, giving them a fuller, more youthful appearance.