Hi sushant,
MDS  is master of dental surgery
And MNS is military nursing service

But i think to get into the military through medical.
You should give the NEET first and then AFMC ( best route).
As there is reservation for boys about 85% to 90%.
After NEET you have to go through 80 marks ( written test)  and 50 marks ( personal interview).
If you score incredible you will be in military.
Hope this helps.
Thank you.