Cheekimplants are solid. Or are you talking about silicone injections?
Medpor implants 'attach' themselves to the natural cheekbones within a few months. Uneven? Other probs? Impossible to remove or to revise.
Silicone implants are screwed to the bone. Can cause bone erosion over time.
Both types of implants can create undereyehollows because the implants don't reach up to the undereyelids.
Both types of implants can make your temples look narrower and your eyes closer set.
Both types of implants can cause a strange looking, 'wooden' face, barely able to move when talking, laughing, smiling etc. Can look very nice in pictures but very strange when animated. Very negative attention grabbing in public.
Both types of implants can make a GG's or a TS's face look very, very harsh.
Both types of implants can make a face look 'off'.
Both types of implants can throw a face off balance.
When placed early in transition: hormones cause facial fat to redistribute to the cheekbones. When this happens over both types of implants you'll wind up with an overstuffed, strange looking, matronly 'pillowface'.
I've only once seen a soft, nice looking cheekbone augmentation: this TS had her adamsapple shaved and the surgeon used the shaved cartilage for cheekbone augmentation.
Probably because the surgeon used small pieces of cartilage instead of 'solid shells'/implants.
