What is difference between flat mid facies and a broad nasal bridge? what is difference between a short philtrum and a smooth philtrum? what is the difference between micrognathia and retrognathia? can micrognathia disappear over time?

These are physically different terms used by those who study "dysmorphology" or the variations in the physical features. Flat mid face is based on the silhouette of the face from the side- the mid face (nose) doesn't come out as far. The philtrum is the structure between the nose & upper lip. It can be tall/average/short and can have tall ridges or short. Micro=small, retro=positioned to the back