The Study Of Maxillary First Molar Access Cavity Design With The Aid Of Cone-beam Computed Tomography

Objectives:The relationship of the size and the location between the traditional endodontic access cavity(TEC)guided by pulp horn and the contracted endodontic access cavity(CEC)guided by root canal orifice on the occlusal surface of the right maxillary first molar were quantitatively compared with the aid of Cone beam computed tomography(CBCT).The aim of this study was to obtain an ideal endodontic access cavity,retain more healthy tooth tissue and avoide the removal of the normal tooth that should be retained,which could increase the resistance of the teeth and improve the long-term survival rate of the teeth after root canal treatment.It could provide anatomical evidence for clinicians when they accessing the cavity.Methods:This study retrospectively analyzed CBCT images of 200 patients between 2015to 2018 in our local Hospital.In the CBCT reading software,the long axis of the right maxillary first molar is adjusted perpendicular to the horizontal plane.And the four pulp horns(Mesiobuccal,Distobuccal,Mesiopalatal,Distopalatal)and three root canal orifices(Mesiobuccal,Distobuccal,palatal)are vertically projected to the occlusal surface.The CBCT self-contained measuring tool is used to establish a coordinate system on the occlusal surface.The tangent to the mesial marginal ridge is the X-axis,the tangent to the buccal marginal ridge is the Y-axis,and the intersection is the origin.The tangent lines of the distal marginal ridge and the lingual marginal ridge are respectively made.And the four tangents wind the teeth to form a rectangle.Firstly,the distance of buccal-lingual and mesial-distal are measured.Secondly,the distance between the four pulp horns and the three root canal orifices to buccal marginal ridge and mesial marginal ridge are measured.Thereby,the coordinate of the pulp horns and root canal orifices are obtained respectively.Two types of endodontic access cavities of the right maxillary first molar are obtained according to the coordinate position:(1)the traditional endodontic access cavity(TEC)which removed the entire roof of pulp chamber according to the pulp horn;(2)the contracted endodontic cavity(CEC)formed by the connection of root canal orifices in the horizontal plane of floor of pulp chamber at the point of projection of the occlusal surface.Results:1.Among the 200 CBCT image datas,there are 88 male people(44%)and 112 female people(56%),and the average age was 31.52±13.60 years.According to the older than 40 and younger than 40,the patients were divided into two groups.There was no statistical difference in the location of each pulp horn and root canal orifice between different age groups and sexes(P>0.05).2.The position of each pulp horn on the occlusal surface:that is the distance from each pulp horn to the buccal marginal ridge and the mesial marginal ridge.The distance from the mesiobuccal pulp horn to the buccal marginal ridge and the mesial marginal ridge was less than one third of the buccal-lingual diameter(P<0.05)and greater than one third of the mesial-distal diameter(P<0.05),respectively.The distance from the distobuccal pulp horn to the buccal marginal ridge and the mesial marginal ridge was greater than one third of the buccal-lingual diameter(P<0.05)and less than two thirds of the mesial-distal diameter(P<0.05),respectively.The distance from the mesiopalatal pulp horn to the buccal marginal ridge and the mesial marginal ridge was less than two thirds of the buccal-lingual diameter(P<0.05)and greater than one third of the mesial-distal diameter(P<0.05),respectively.The distance from the distopalatal pulp horn to the buccal marginal ridge and the mesial marginal ridge were not statistically different from that of two thirds of the buccal-lingual diameter and mesial-distal diameter(P>0.05).3.The position of each root canal orifice on the occlusal surface:that is the distance from each root canal orifice to the buccal marginal ridge and the mesial marginal ridge.The distance from the mesiobuccal root canal orifice to the buccal marginal ridge and the mesial marginal ridge was less than one third of the buccal-lingual diameter(P<0.05)and greater than one third of the mesial-distal diameter(P<0.05),respectively.The distance from the distobuccal root canal orifice to the buccal marginal ridge and the mesial marginal ridge was greater than one third of the buccal-lingual diameter(P<0.05)and less than two thirds of the mesial-distal diameter(P<0.05),respectively.The distance from the palatal root canal orifice to the mesial marginal ridge was less than two thirds of the mesial-distal diameter(P<0.05).4.The area of the traditional endodontic access cavity of the right maxillary first molar was 9.54±2.10 mm~2;the area of the contracted endodontic cavity is 3.48±1.12 mm~2;the difference was statistically significant(P<0.05).The area of TEC was about 2.74 times area of CEC.Conclusions:1.In the study,the trisection of the buccal-lingual diameter and the trisection of the mesial-distal diameter were used to locate the position of the four pulp horns and three root canal orifices of the right maxillary first molar at the tooth occlusal surface for the first time.Clearly showing the positional relationship between every pulp horn and root canal orifice in the Jiugong grid at the tooth occlusal surface,providing a clear schematic view of the two different endodontic access cavities for clinical guidance.2.The contracted endodontic cavity guided by the root canal orifices of the right maxillary first molar was a blunt triangle,and the traditional endodontic access cavity guided by the pulp horns was an oblique quadrangle,which were located in the center of the tooth occlusal surface,and mainly occupies the central square of the occlusal nine square;The common features of the two types of endodontic access cavity:the mesial wall and the distal wall did not exceed one third of the mesial-distal diameter,and the palatal side did not exceed the palatal one third of the buccal-lingual diameter,suggesting that the maximum boundary of the endodontic access cavity of the right maxillary first molar should not exceed the above range.3.The area of the traditional endodontic access cavity guided by the pulp horns of the right maxillary first molar was probably three times that of the contracted endodontic cavity guided by the root canal orifices,and the traditional endodontic access cavity guided by the pulp horns grinding more mesial marginal ridge.Therefore,in the clinical,it was recommended to use a contracted endodontic cavity guided by the root canal orifices to retain more roof of pulp chamber and mesial marginal ridge.