For this area a very fine filler such as Juvederm Volbella would be ideal. It would be safe to inject in this area with the right filler.
If your concern is accidental injection into blood vessels, staying superficial or using a cannula is much safer than injecting blindly into the deeper tissue of the lips. However, superficial injections pose more risk aesthetically if not performed correctly. The choice of fillers matter. Thinner fillers like Restylane Silk, Volbella or Belotero are best for superficial injections. Juvederm and Restylane are also good for injecting superficially but you may see little balls form along the border if the injector is not very experienced. It can still happen even with expert injectors but less likely. There is a way to dissolve it if it comes out uneven but it is much better to get it right the first time. The bottom line is, for safety and for best results choose your injector carefully. An expert injector will know where, how and which product to use to give you the best results and avoid mishaps.
