The relationship between the cusps,impacted type and roots of mandibular third molar tooth

Objective To study the relationship between the cusps,impacted type and roots 1090 mandibular third molar tooth.Results The cusps of the mandibular third molar tooth can be divided into 6 types,they are 3 cusps (0.55%),4 cusps (26.42%),5 cusps (53.58%),6 cusps (18.16%),7 cusps (0.83%)and 8 cusps (0.46%).The root of the mandibular third molar tooth can be divided into 4 types,they are 1 root (35.14%),2 roots (57.34%),3 roots (7.34%) and 4 roots (0.18%).The less the cusps of teeth crown,the higher the proportion of one root.The cusps is increase,the proportion of one root is decrease and the proportion of two roots or three roots is increase.7 and 8 cusps have not 1 root.The proportion of impacted type are as follow:mesioangular impaction is 31.65%.Vertical impaction is 29.08%,buccoangular impaction is 16.88%,distoangular impaction,linguoangular impaction and horizontal impaction is less then 9%.The proportion of one root of distoangular impaction is the largest (47.06%),the proportion of two roots of mesioangular impaction.Vertical impaction,horizontal impaction is 64.35%,58.04%,57.73%.Respectively.The proportion of three roots of buccoangulaz impaction and vertical impaction separately reach 13.04% and 11.35%.The proportion of three roots of rest types is less than 9.5%.