| Objective:1、Using the implant markers-superimposition method as standard,study the stability of the parietal bone in 6-9 months old beagles.If the parietal bone is relatively stable,then evaluating the validity of parietal bone-superimposition method to provide a simple and effective superimposition method for expansion experiment in growing beagles.2、Studying the maxillary growth changes in 6-9 months old beagles to provide the reference for later experiments.Method:6 prepubertal male beagle dogs aged 6 months were included in this study,three implant markers inserted into the left and right sides of the parietal bone,while two implant markers were placed into the palatal bone bilaterally away from the palatal suture and along the lines connecting the two upper first premolars(PM1)and two upper forth premolars(PM4)respectively in each dog as markers.CBCT images were taken at T0(6 months old)and T1(half and 7 months old)and T2(9 months old).With the help of the three dimensional software,three-dimensional implant markers reconstruction was performed,and the distance variation between the implant markers were measured to determine whether or not the implant markers had dropped or displaced.Then,with the help of the three dimensional software again,threedimensional skull models were reconstructed and respectively registered at T0,T1、T1,T2 and T0,T2 using at least three stationary implant markers to obtain the color map of skulls.If the color map indicates the distance deviation of the bilateral parietal bone between the any two models of on beagle was smaller than 0.5mm,so the parietal bone was extracted as the relatively stable region;on the contrary,this experiment can’t determine that parietal bone region is stable or not.All skull models at T0 and T1、T1 and T2 were respectively registered using the implant markers-superimposition and the parietal bone regional superimposition,the displacement of the implant markers along the lines connecting PM1 and away from the palatal suture were measured.All statistical analyses were performed using the SPSS software(ver.21.0).If all data are in accord with the normal distribution and homogeneity of variance,using Paired t-tests to determine the statistical significance of the differences of the displacement of the same implant markers which was used the two different superimposition methods between T0,T1 and T1,T2,Inspection standards for the α = 0.05.Evaluating the validity of the parietal bone as stable region for 3D skull model superimposition.Obtaining the maxillary superimposition map by implant markers-superimposition and the parietal bone regional superimposition respectively,qualitatively observe the growth changes of the maxillary between T0 and T2.Three-dimensional skull models were reconstructed again,quantitatively measure the natural growth changes of the maxillary in 6-9 months old beagles.Measurement items are as follows:(1)Length index: bilaterally the distance between the front of the alveolar process of the maxillary first molar and the posterior margin of the alveolar process of the same side maxillary second molar(A-D),bilaterally the distance between the front of the alveolar process of the same side maxillary first molar and the right Zygomatic arch root(A-H);(2)Width index: the distance between the front of the alveolar process of the bilateral maxillary first premolars(Ar-Al),the distance between the front of the alveolar process of the bilateral maxillary third premolars(Br-Bl),the distance between the front of the alveolar process of the bilateral maxillary first molars(Cr-Cl),the distance between the posterior margin of the alveolar process of the bilateral maxillary second molars(Dr-Dl);(3)Height index: bilaterally the distance between the posterior margin of the alveolar process of the maxillary second molar to the nasal root point(D-J),bilaterally the distance between the front of the alveolar process of the maxillary first molar and the front of the nasal bone(A-I).All statistical analyses were performed using the SPSS software(ver.21.0).If all data are in accord with the normal distribution and homogeneity of variance,using Paired t-tests to determine the statistical significance of the differences of measurements between T0,T1 and T1,T2,Inspection standards for the α = 0.05.Result:After the experiment,3 of the 36 implant markers had displaced during the 3 months experiment.The three displaced implant markers were observed in different beagles,the other implant markers remained stable.The average distance between any of the two implant markers in the same beagle at T1-T0 and T2-T1 respectively was 0.18 + 0.13 mm,0.16 + 0.15 mm.All the color maps by the 3D skull models superimposition indicates that the distance deviation of the parietal bone between any two skull model of on beagle was smaller than 0.5mm.Comparing the difference of the displacement of the same implant markers by the implant markerssuperimposition and the parietal bone regional superimposition to evaluate the validity of this stable region for 3D skull model superimposition.Displacements of the right implant markers between PM1(ar)at T0-T1 and T1-T2 respectively were 0.64±0.21 mm,0.33±0.10 mm,and displacements of the left implant markers between PM1(al)at T0-T1 and T1-T2 respectively were 0.66±0.20 mm,0.34±0.09 mm,measured by implant markers-superimposition;While displacements of ar at T0-T1 and T1-T2 respectively were 0.65±0.22 mm,0.35±0.09 mm,and displacements of al at T0-T1 and T1-T2 respectively were 0.67±0.21 mm,0.36±0.08 mm,measured by the parietal bone regional superimposition method.The displacement of implant markers between the PM1 using the implant markerssuperimposition or the parietal bone regional superimposition had no statistically significant difference(P>0.05).Qualitative results: the maxillary superimposition map between the T0 and T2 by the implant markers-superimposition or the parietal bone regional superimposition both show that The length,width of the maxillary and the width of the Zygomatic arch of All beagles from T0 to T2 were increased a little,but the height of the maxillary from T0-T2 period had no obvious change.Quantitative results: There were statistically significant differences in the length and width of T0-T1 and T1-T2 in all Beagles(P < 0.05),but there was no significant difference in the height of the maxillary height from T0-T2(P > 0.05).Conclusion:(1)The development of parietal bone of the beagles from 6 months old to 9 months old is relatively stable,which can be used as a stable region for threedimensional CBCT skull model superimposition.(2)Maxillary length、width and Zygomatic arch width of the Beagles from 6 to 9 months old after 3 months were increased a little,but the maxillary height had no significantly change. |
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