The FDA has recently cleared a fractional laser for treating stretch marks. In clinical studies the Lux1540 produced an average of 51-75% reduction in stretch marks. This is the first fractional laser that I know of which has been cleared to treat stretch marks.
I find it extremely rare to see stretch marks after breast augmentation. In the past five years I think I've seen maybe three of my patients who've developed stretch marks after breast implants. Surprisinglyall three patients did not have large implants placed. All the implants were around 350cc. In these situations we've utilized a pulse-dye laser with pretty good results. It usually takes several treatments though. Unfortunatelythere is no way to completely erase stretch marks without actually cutting them out (and trading them for a scar).