Study The Application Of Cone Beam Computed Tomography In Dowel Preparation For Maxillary First Molar In Baotou

Objective The aim of this study was to observe and measure the root of left and right maxillary first molars in Baotou,Inner Mongolia by Cone-beam computed tomography,so as to understand the anatomical morphology of the maxillary first molars and provide some clinical recommendations for post space preparation.Methods CBCT data were all obtained from the Department of Oral Radiology,Hospital of The Third Affiliated to Inner Mongolia medical university.A total of 120 maxillary first molars from 74 patients who needed CBCT for various reasons were selected,including fifty-five left and sixty-five right,forty male and thirty-four female.Patients age from thirty-one to forty years old,the mean age was 36.21±2.81.Three-dimensional reconstruction and measurement of the root of maxillary first molar were carried out by CBCT built-in software:1)The cross-sections at 4,5,6,7,8,9 mm distant from the radiologic apex were used to measure the BL and MD diameters of the root and the thicknesses of root walls,and the root lengths were measured from one point which at 4mm distant from the radiologic apex to the enamel-dentinal junction（EDJ）.2)The datas at different levels were analyzed by statistical software.3)The probability that the residual root wall thickness（RRT）being not less than 1.0 mm in BL and Md directions after post space preparation by 1#,2#,3#peeso reamers was analyzed.4)Bucco-lingual（BL）and Mesio-distal（MD）diameter of each canal were measured at 4,7,9 mm distant from the radiologic apex,and then the taper was calculated and analyzed.5)The morphology of the mesiobuccal canal was observed and the number of the second mesiobuccal canal was recorded.Results 1.The effective length of mesial buccal root,distal buccal root and palatal root of maxillary first molars were 5.37±1.16mm,5.81±1.27mm and 7.73±1.61mm,respectively.2.The thickness of root canal wall increased with the distance from the radiologic apex.P₂₅5 of root walls thickness was less than 1 mm as following:the buccal and lingual thickness of root walls at 4-5 mm distant from the apex in mesial buccal root;the mesial and distal thickness of root walls at 4-6 mm distant from the apex in mesial buccal root;the buccal,lingual,mesial and distal thickness of root walls at 4 mm distant from the apex in distal buccal root;the buccal and lingual thickness of root walls at 4mm distant from the apex in palatal root.The other root walls thicknesses(P₂₅)were not less than 1mm.The buccal-lingual thickness of root walls were significantly larger than the mesial-distal thickness of root walls in mesial and distal buccal roots.The mesial-distal thickness of root walls were significantly larger than the buccal-lingual thickness of root walls in palatal root.3.The probabilities that the residual root thickness（RRT）≥1.0mm were up to 100%as following:the thickness of the buccal and lingual root walls in mesial buccal root at 6⁹mm distance from the apex after post preparation by 1#peeso reamer;the thickness of the buccal and lingual root walls in mesial buccal root at8⁹mm distance from the apex after post preparation by 2³#peeso reamer;the thickness of the buccal and lingual root walls in distal buccal root at 7⁹mm distance from the apex after post preparation by 1²#peeso reamer;the thickness of the buccal and lingual root walls in distal buccal root at 8⁹mm distance from the apex after post preparation by 3#peeso reamer;the thickness of the root walls in palatal root at 6⁹mm distance from the apex after post preparation by 1³#peeso reamer.The probabilities that RRT≥1.0mm of the mesial and distal root walls in mesial buccal root at 4mm distance from the apex was only 49.20%,after post preparation by 1#peeso reamer.The probabilities that RRT≥1.0mm of the mesial and distal root walls in distal buccal root at 5mm distance from the apex was only 65.17%,after post preparation by 1#peeso reamer.4.The mesial and distal root canal taper of maxillary first molar in buccal-lingual direction was greater than that in mesial-distal direction,while the palatal root canal taper of maxillary first molar in mesial-distal direction was greater than that in buccal-lingual direction.5.The total incidence of MB2 in maxillary first molars in this study was 72.50%.There was no statistical significance between the incidence of MB2 and gender or tooth position（P>0.05）.The Vertucci Type IV（37.5%）canal configuration was the most prevalent in the MB roots of maxillary first molars,following by Vertucci TypeⅡ（26.67%）and Vertucci Type III型（3.33%）.Conclusion 1.Three dowels can be prepared in maxillary first molars,palatal root was the first choice,followed by distal buccal root,the last was mesial buccal root.2.Before the post space preparation,we should observe and measure the thickness of the root canal wall by CBCT,so as to avoid lateral penetration or perforation.3.The result indicate that canal taper and configuration of the maxillary first molar is complicated.We should choose instrument carefully in root canal therapy and dowel preparation.Dowel should be prepared cone-shaped.4.The maxillary first molar in this study have high incidence of MB2 canal.The Vertucci Type IV（37.5%）canal configuration was the most prevalent in the MB roots of maxillary first molars,following by Vertucci TypeⅡ（26.67%）and Vertucci Type III型（3.33%）.