A {HEAD ~ ledge} or mandible engaging support surface is defined between the upper tier and lower tier and terminates in {TAIL ~ an exterior opening} 
terminates in
A { HEAD ~ ledge } or mandible engaging support surface is defined between the upper tier and lower tier and terminates in { TAIL ~ an exterior opening }
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL