Third molars are coded in box 24 D of the CMS form
It should look like this:
41899 UL
41899 UR 59
41899 LL 59
41899 LR 59

The UL, LL, LR & UR are placed in the first modifier field, the 59 is placed in the second modifier filed and is appened to the second, third and fourth codes only. In box 19 of the CMS form you need to put what type of extraction along with the tooth number (example D7240 1 & 16 D7230 17 & 32). You will further need a diagnosis code of 520.6placed in box 21.1 of the CMS form.