I will paste here my forum posting about the principle behind dermarolling.
It is the same for dermastamping:
There aren't many ways to rejuvenate or remodel skin. One of the best methods is to cause mild skin damage. Our body will renew/remodel the skin by fixing that damage. That is one of the principles of dermarolling.
That is also the principle behind most laser rejuvenation treatments. Laser either evaporates the entire outermost top layer of the skin or it evaporates only fractions of the skin (Fraxel laser).
Have a look how it works, it's interesting:
https://http://www.youtube.com/watch?v=hHvRZ-LPhW8&feature=related A dermaroller makes tiny holes mechanically, whilst a fractional laser makes tiny holes thermically. But in principle it is the same. The collagen production will continue many months after treatment.
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Dermarolling /dermastamping also crushes the scar tissue if used intensively on the scar. Scars often have hardened fibrotic collagen tissue and that is crushed and softened by dermarolling/dermastamping. And yes, this often restores the blood flow into the scar (angiogensis/revascularisation). If you continue the treatment, the scar will start to fill in at least partially by triggering new collagen.
It is possible that the fibrotic wall of the scar collapsed and the scar has that kind of relief from the side that you described. However, collapsing the hardened wall is the first step in improving the scar.
If you just have individual, isolated scars, the single needle is better. A dermastamp is for larger areas with many scars.