Hello

i work with maya 4
1 i have make a half human face with subdivisions
But when imake duplicate or copy the all head is ok but there is a seam

2 i try to use the polygon mirror & subdiv surface /mirror but i see a distrub to the new half

by the way when i try the command extude face i read is nonmifold

but my problem is to erase the seam

thank you all for your help