The Vitro Study Of The Endodontic Access Opening To Mandibular Permanent Incisors

Objective:(1)To research the type of the root canal of mandibular permanent incisors,and evaluate the influence of adopting different methods between labial access opening and lingual access opening to probe incisors with double root canals.(2) To evaluate the degree of instrument curvature between labial access opening and traditional lingual access opening,and study the location of the endodontic access opening when the endodontic path is straight. To apply reference for clinical root canal therapy of the mandibular permanent incisors.Methods:(1)Self-contrast study is applied in this research.80 extracted mandibular permanent incisors are collected to probing root canals separately with two different metheds according the position of the coronal access opening,and the group of traditional lingual access opening is denoted by group A, the group of labial access opening is denoted by group B.Record every tooth's number of root canals.And then all tooth are cut into three sections at the root of the root cervical,middle and apical,aim to observe the number of root canals of every root cross-section under a Stereomicroscope and classify the type of root canals of the mandibular incisors,which is denoted group C.The number of root canals of every teeth is recorded by special recorder using blind method.Make a statistic about the incidence rate of the mandibular permanent incisors with double root canals,and compare the difference of the positive rate using two different endodontic access opening methods to probing the mandibular incisors with double root canals between labial access opening and traditional lingual access opening and make statistical tests.(2)80 extracted mandibular permanent incisors are divided into A group(lingual access) and B group(labial access) according to the position of the coronal access opening.Every teeth of each group is inserted #15K untwisted files into the root canals corresponding to practical probing situation as mentioned earlier and radiographed to obtain digital dental films from proximalview,then import the films into image analysis software system.These images are then studied the information of the instrument curvature including two indexes—canal access angle(CAA)and angle of curvature(AOC)—in order to compare the same teeth by statistical anylysis of the differences of the indexes by group.Then analysis dental images of group A about the position which the K file's pass through the crown in the reverse direction when it is a straight line in the file's middle-lower part,to obtain the ideal endodontic access opening position in mandibular incisors.Results:(1)Influence of different enododntic access opening exerted on probing root canals of mandibular incisors:①The incidence rate of tooth with double root canals in mandibular incisors is 30%.The bifurcation point of a root canal may be located in any part of the root canal with highest proportion in the middle-lower part of them.②The same doctor will come to a relatively stable result when he adopts the same methods to probe root canals of mandibular incisors,which generally does not appear significantly different(P>0.05).③The same doctor will come to different results when he adopts different methods to probe root canals of mandibular incisors,which appears statistically significant(P<0.05),and there is a higher discovery rate of teeth with double root canals using the method of labial access opening.④The Kappa analysis indicates that the same doctor will obtain more higher reliability using the method of labial access opening(K=0.773, P<0.05) to probe root canals of mandibular incisors than that using the traditional method of lingual access opening(K=0.457,P<0.05).(2) Influence of different methods of opening to the pulp exerted on the endodontic path of mandibular incisors:①The ideal position of access opening to the pulp of 80 mandibular incisors are located in the incisor edge accounted for 73.75%,accounted for in the labial side of 25%,in the lingual side are only 1.25%.②The component ratio of bend angle's type of the instruments inserted into root canals including CAA and AOC change a few with using different methods of access opening to the pulp of mandibular incisors,but there are no significant difference (P>0.05).And slight curvature and moderate curvature are the main types.③Between the methods of labial access opening and the method of lingual access opening,the angle difference of CAA (f=2.445,P<0.05)and that of AOC (t=2.552, P <0.05) are both statistical significance. It indicates that there are different bending degrees in the endodontic instruments between the two methods, and the bending angles are reduced after labial access opening.Conclusion:(1) The incidence rate of tooth with double root canals in mandibular incisors is 30%,and the bifurcation point of a root canal may be located mostly in the middle-lower part of them. There is a higher discovery rate of the teeth with double root canals using the method of labial access opening than using the method of traditional lingual access opening,and a higher reliability as well.(2) The ideal position of access opening to the pulp of the mandibular incisors are mostly located in the incisor edge and in the labial side,and rarely in the lingual side.And there are different bending degrees in the endodontic instruments between the two methods of labial access opening and traditional lingual access opening, and the bending angles are reduced with labial access opening.