對於假牙贗復醫師來說, Centric relation(CR)是個很難以捉摸的東西. 在這篇Dr. Becker 這篇精辟的文章中我們來回顧一下CR的歷史定義以及哪個時候要取怎樣的CR.
1929年 Hanau:condylar heads are resting upon the menisci in the sockets of the glenoid fossa
1932年 Schuyler:place the tip of the tongue far back on the palate to hold it there while closing
1934年 Niswonger:clench the back teeth
1946年 Thompson:condyles are in the most retruded position in the fossa
1951年 Robinson:mandible can be retruded beyond what we should consider centric into a starined retruded position
1955年 McCollum:rearmost, uppermost, regrettable. CR is bone to bone and MIP is tooth to tooth.
1966年 Glickman:the most retruded position to the mandible to be carried by musculature
1966年 Graber:unstarined neutral position of the mandible
1968年 Goldman:most posterior relation of mandible to the maxilla from which latral movement can be made
1977年 Schluger:the condyles are in their most rearmost ad midmost position in the glenoid fossa
目前咬合學派多半以1955年McCollum的定義為主, 那什麼時候的假牙要取CR而哪時要用MIP? 作者的建議如下
MIP: individual crown; 3-4units of posterior FPD or RPD; 3-6units of anterior FPD and RPD
CR: only 2-3 posterior teeth in contact; no posterior contacts
最後要講到The principles of biologic occlusion:
1. CR和MIP中間沒有interference
2. Working movement 時沒有 balancing side interference
3. Cusp to fossa
4. 每顆牙齒至少有一點接觸
5. Canine or group function
6. 前突運動時沒有後牙干擾
7. 沒有cross-arch balancing contacts
8. 沒有fremitus