Does anyone know why I developed a noticeable dent on my toenail?

this has never happened to me before.. But I have noticed that there is a significant dent on both nails of my big toe. It is growing out now, but it's as though the part of the nail closest to the cuticle is ';lower'; then a kind of ridge and the rest of the nail sits slightly higher. I have had no change in shoes... I am wondering if this is a deficiency of some sort. I do strive for a healthy diet. I am 33 and healthy, and live a healthy lifestyle.Does anyone know why I developed a noticeable dent on my toenail?
Just an old injury growing out.