RESUMEN
This study was carried out to compare the capability of K-files with Mtwo rotary file in terms of negotiation as well as depth of penetration in second mesiobuccal [MB2] canal of maxillary first molar. A total of 32 MB2 canal of maxillary first molars having different root curvatures [not more than 30 degree] and root lengths were selected and then detected by K-file no. 10, no.8 and no. 6. Based upon file penetration the samples were assigned into four groups. Group A: K-file no. 10 penetrate>2mm into coronal third, group B: K-file no. 10 could penetrate2mm penetration, group C: K-files no. 10 and 8 could penetrate