Where did you hear that? It's generally only a problem with movements over 10mm+ or 9.7mm at the osteotomy (>12mm) and over the age of 30, according to a recent study. Who said you need implants? You can graft the gap with bone. It's actually a rare complication after a year, bones don't like discontinuities. Dr Wolford does an inferior border osteotomy to avoid the problem, which reduces the notch rate from 20% down to 5%. It also has the disadvantage of ligating the facial artery/vein, safe to do but all things being equal, better not to compromise blood supply to things. A&G use PRP grafts, I hear it doesn't work that well but they'd know better.