Why can the top lip get a ledge after Restylane filler?

In  my opinion, there are three factors that affect the shape of the lip after treatment with a filler. Choice of filler, experience and technique of the injector, and anatomy of the patient's  lip. Prior to injection, one should have a consultation with the physician that includes a discussion of the desired shape. Good luck.Jeff Rapaport MD FAADRealself All-star

The choice of filler and the experience of the injector play an important role in the results of lip filler treatment. The "ledge" maybe the result of overfilling of the vermilion border in a patient who also has a sharply defined border which tends to be the case with younger patients. The vermilion border flattens with aging. 

Hello, 
Restylane has many variants, so depends on the variant’s character and also the technique of injection. This can be happened from other brand too.