My understanding is that nipple inversion occurs in fetal life  around the
time when the breast bud folds in on itself.
Adhesions are tough bands of tissue. I'm not sure they can be broken.
Stretched might be a more correct term. The nipple can then be pulled into
the baby's mouth because the adhesions are stretched. In many of the cases
I've seen, the nipple is inverted again after feedings.
I have noticed that inverted nipples tend to be very rough and "scaly" when
they first evert. When the "scale" wears off the nipple becomes very tender,
often bleeding. The nipple hasn't seen the light of day for a long time ;-).
(Remember how sensitive the navel becomes when it everts in late pregnancy)
For true inversion, I do suggest shells early in pregnancy but I still
recommend Hoffman's and nipple rolling with a small amount of lanolin twice a
day in the last 3 weeks of pregnancy. I give strict instructions to stop if
there's any contractions.  This gives the "scaly" skin a chance to slough off
slowly and be replaced by new skin before the mom has to nurse every two
hours or less.
Marie Davis, RN, IBCLC