Preliminary Research On The Occlusal Sphere’s Characteristic In Individual With Near Normal Occlusion In North China

Objective: The present research using the reverse engineering software and MATLAB R2016 b to collect the coordinate data of special points on the digital dental models and to fit the occlusal spheres is based on the theory of Monson’s sphere to investigate the occlusal spheres’ characteristic within the individual with near normal occlusion in North China,hoping to provide Chinese patients who need personalized occlusal rehabilitation or occlusion adjustment in orthodontics with some reference.Methods: 1.According to the inclusion criteria,selected 62 individuals(7 males and 55 females,aging from 18 to 22 years old)from North China region from Tianjin Medical College.The super-hard plaster models were made for the volunteer’s dentition.Used the 3Shape R700 scanner to obtain digital dental models.Randomly selected 15 files from all the digital model files,and imported them into Geomagic Studio 2012 software.Stipulated the definition of cusp point and incisal edge midpoint,then two professionals directly selected 28 points needed for fitting from every digital model according to the definition,respectively recorded the coordinates of the selected points(X0,Y0,Z0)and(X0,Y0,Z0),imported the point coordinate data into MATLAB R2016 b,applied least square method to calculate and fit the occlusal sphere of every selected model,and recorded the radiuses(R0 and R1)of the fitted spheres.With fortnightly interval,one of the operators again selected the points needed for fitting from the 15 pairs of digital models selected in the first time and fitted the occlusal sphere using the same method as used before,and recorded the radius of the fitted sphere of each model.The measurement was repeated by the same operator twice respectively.Recorded the sphere radii as R2 and R3 respectively.Paired t-test(α=0.05)was made to evaluate the measurement error between the two different operators and calculated the ICC of the sphere radii fitted by each measurement using the SPSS 22.0 statistical software.2.Imported 62 mandibular digital model files of the volunteers with normal occlusion into the Geomagic Studio 2012 software and directly selected points at the corresponding cusp points and the incisal edge midpoints according to the definition to obtain the coordinates of the points in corresponding position.28 sites were selected on each digital model: midpoint of incisal edge,canine cusp,buccal cusp of the first premolar,buccal and lingual cusps of the second premolar,mesial buccal and lingual cusps and distal buccal and lingual cusps of the first molars,mesial buccal and lingual cusps and distal buccal and lingual cusps of the second molars.Recorded the coordinates of the selected points obtained on each model in the Excel tables.Imported the coordinate data of selected points of each model into MATLAB R2016 b software,and applied the least square method to calculate and fit the occlusal sphere of each model.Recorded the radius and the coordinates of the center of the sphere,and then calculate the distance from the corresponding coordinate of the center of the fitted sphere in each model,and then calculated the deviation distance from each point to the fitted sphere.SPSS 22.0 statistical software was used to analyze the radius and deviation distance.Results: 1.The difference between the two operators was not significant with the paired t-test result showing p=0.098.The intraclass correlation coefficients of the threedimensional coordinates-X,Y,and Z of the selected points are: 1.000,0.999,1.000.The intraclass correlation coefficient of the fitted spheres’ radii in three fitted processes is 0.999.2.The radius of the fitted sphere of the 62 pairs of models is 81.6761 ± 17.6108 mm,of which the median radius of the fitted sphere in the female(55)is 76.8782 mm,and 99.3725 mm in male(7).The statistical result of the absolute values of the distance from all fitted points to the fitted spherical surface is 0.3881 ± 0.3196 mm,the positive maximum deviation value is 0.9606 ± 0.3273 mm,and the negative maximum deviation value is 0.9319 ± 0.2761 mm.In the fitted results of the 62 pairs of models,the distribution of the maximum deviation sites is demonstrated as follows: there are 26 sites on the second molars,accounting for 5.24% of the total number of cusps of the second molar(504),62 sites on the first molars accounting for 12.5% of the total number of cusps of the first molar(504),15 sites on the premolars accounted for 4.03% of the total number of cusps(378),5 sites on the canines accounting for 4.03% of the total number of canines(126),and 16 sites on the incisors accounting for 6.45% of the total number of incisor margin centers(252).Conclusions: 1.It is highly repeatable to select the points on the digital models and the result of the present study showed high reliability.2.The sphere radius of young adults with near normal occlusion in North China is 81.6761 ± 17.6108 mm,which is obviously different from the 4 inches(101.6mm)proposed by Monson.This difference should be considered when applying Monson’s sphere theory in occlusal reconstruction 3.There may be gender differences in the size of male and female occlusal spheres.