X: axial distance from the origin at {HEAD ~ the tooth surface} at {TAIL ~ the center} of the tooth thickness, 
X : axial distance from the origin at { HEAD ~ the tooth surface } at { TAIL ~ the center } of the tooth thickness ,
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH