Evaluation On Palatal Bone Thickness In Different Vertical Skeletal Facial Types Of Adolescents With Cone Beam Computerized Tomography

ObjectiveBased on CBCT 3D data reconstruction,this study compared the palatal bone thic-kness in the first premolar level,the second premolar level and the first molar level,and the cortical bone thickness in the first premolar level between different teenage patients with different vertical facial skeletal types to explore the connection between the bone thickness of the palate and facial skeletal features.It provides theoretical basis for choosing the site of implant anchorage in the palate.Materials and MethodsWe randomly selected 90 cases of teenage patients in orthodontic division in DentalHospital of Shandong University from 2012 to 2015.Criteria:1)Age:12-16 years old;2)Substantially symmetric face;no harelip and cleft palate;no surgery history;3)No impacted tooth on back teeth segment on upper jaw;teeth are complete(except wisd-om tooth);no obvious congested teeth;4)Healthy periodontium;no absorption of alv-eolar bone;5)No disease that can affect metabolism.We scanned the patients with CBCT(NewTom 5G,QR,Verona,Italy)and reconstructed the craniofacial three dim-ensional images.We also took lateral cephalograms and measured the cranio facial morphology.On the basis of Frankfort-mandibular plane angle(FMA),the patients were divided into three groups:high angle group,average angle group and low angle group.We further grouped the patients’ sagittal skeletal patterns by ANB angle.Specifically,there were 30 cases in high angle group(15 males and 15 females;10 cases with Class I sagittal skeletal pattern,13 cases with Class II and 7 cases with Class Ⅲ),32 cases in average angle group(14 male and 18 females;15 cases with Class I sagittal skeletal pattern,11 cases with Class Ⅱ and 6 cases with Class Ⅲ),and 28 cases in low angle group(13 males and 15 females;11 cases with Class Ⅰ sagittal skeletal pattern,7 cases with Class Ⅱ and 10 cases with Class Ⅲ).We collected scanned images of different patients and reconstructed images with software MIMICS 17.0.Then we separately measured the bone thickness on five common implantation sites in the first premolar level,the second premolar level and the first molar level,which are the midpalatal suture of palate area,3mm and 6mm on the left and right of the midpalatal suture of palate.We also measured the cortical bone thickness in the four sites of the first premolar area,3mm and 6mm on the left and right of the midpalatal suture of palate.Data were analyzed using SPSS 18.0.The bone thickness was presented by average number±standard deviation(X±SD).Chi-square test was used to examine the difference in gender and sagittal skeletal patterns between the three groups.The analysis of variance was used to compare the difference in age,palatal bone thickness,cortical bone thickness in different and the same measurement sites between the three groups.Two-two comparisons among the means were done by LSD method(Least significant Difference).T test is used to compare means between gender in each group.P<0.05 is considered as statistically significant.Result1)No obvious differences were observed in age(F=1.20;P=0.356),gender(x2=0.48;P=0.97)and saggital skeletal pattern(χ2=0.698;P=0.86)among the high angle group,average angle group and low angle group.2)Differences in bone thickness at different sites of the same vertical facial skeletal pattern on the palateIn the anterior posterior direction,the bone thickness gradually decreases from the first premolar to the first molar in the midpalatal suture area in the high angle group(P<0.05).However,no significant difference was observed in the average angle group and the low angle group(P>0.05).Bone thickness at 3mm and 6mm on the left and right of the midpalatal suture of palate gradually decreases from the first premolar to the first molar in all the groups(P<0.05).In the transverse direction,the bone thickness in the first premolar area gradually increases from the midpalatal suture to both sides.In the second molar and the first molar area,the bone thickness decreases from the midpalatal suture to both sides(P<0.05).The overall trend was consistent among three groups.3)Differences in bone thickness at the same site of different vertical facial skeletal pattern on the palateThere was no significant difference in bone thickness in the midpalatal suture among all the groups(P>0.05).However,significant difference in bone thickness was obser-ved in the lateral palatal area among the three groups(P<0.05),with the minimal value in the high angle group,followed by the average angle group and the maximal value in low angle group.4)Difference of cortical bone thickness between different sites in palate of the first premolar levelThe cortical bone thickness between the 3mm and 6mm of the lateral palatal area in the same vertical skeletal group was not statically significant(P>0.05).No significant difference was observed in cortical bone thickness in the same sites between high angle group and average angle group(P>0.05),while the cortical bone thickness of both the high angle group and the average angle group were significantly lower thanthat of the low angle group(P<0.05).The minimal value of cortical bone thickness among all the measurement sites was 1.81±0.38mm,with the minimal value of 2.26±0.49mm in the low angle group.Conclusions1)Bone thickness varies among adolescent patients with different vertical skeletal pattern in the first premolar,second premolar,and the first molar level of the palate,with high angle group the lowest,followed by the average angle group and low angle group the highest.The cortex bone thickness of both high angle group and average angle group is less than that of low angle group.2)The bone thickness in the lateral palatal area is greater than that of midpalatal suture area in the first premolar level.3)The bone thickness decreases from the first premolar level to the first molar level in the lateral palatal area in the sagittal direction.