Research On The Vertical Control Effect Of The Vertical Holdin G Appliance In Treatment Of Hyperdivergent Patients

Objectives:During orthodontic treatment,it is important to control the vertical dimension of the hyperdivergent patients.The hyperdivergent cases are associated with weaker musculature,which can induce extrusion of both the maxillary posterior teeth and mandible posterior teeth.And the mandible tends to rotate downward and backward,which causes the increase of the lower anterior facial height.In this research,we tried to explore the effects of a modified transpalatal arch-the vertical holding appliance(VHA) through cephalometric analysis of the hyperdivergent patients who accepted orthodontic treatment with premolars extraction.Methods:A total of 40 patients with high mandibular plane angles and four first premolars extracted were selected from patients in the Department of Orthodontics,Hospital of Stomatology,He Bei Medical University.The patients met the following criteria:mandibular plane angle:(MP-SN)≥40°,S-Go/N-Me<62%,skeletal ClassⅠmalocclusion(ANB>0°),normal or deep overbite.The 40 patients were seperated into two groups:the VHA group(7 females,13 males;average age 13.35 ± 1.44 years,range from 11 to 16 years)and the control group(6 females,14 males;average age 13.14±1.35 years,range from 11 to 16 years).During treatment,the patients in the VHA group were treated with the VHA to control the vertical dimension.However,the patients in the control group had no special measurement to control the vertical dimension.The VHA was fabricated with banded maxillary permanent first molars connected with a 1.2mm stainless steel wire with a dime-size acrylic batton positioned at the middle of the first molars.The distance from the palatal mucosa to the surface of the acrylic button was set at 5mm and the thickness of the acrylic button was about 2mm.Pretreatment and postreatment lateral cephalometric radiographs were dotted and measured digitally by Winceph 8.06.All the radiographs were measured three times and the mean values were used as the ultimate values.The following cephalometric variables were used to evaluate skeletal and dental treatment changes:MP-SN:The angle formed by the mandibular plane and the SN plane.FMA:The angle formed by the mandibular plane and the Frankfort horizontal plane.MP-PP:The angle formed by the mandibular plane and the palatal plane.PP-SN:The angle formed by the palatal plane and the SN plane.Y-axis:The angle formed by points sella-Gn and the Frankfort horizontal plane.U6-PP:Perpendicular distance from the mesial cusp of maxillary first molar to the palatal plane.L6-MP:Perpendicular distance from the mesial cusp of mandibular first molar to the mandibular plane.U1-PP:Perpendicular distance from the incisal edge of the maxillary incisor to the palatal plane.L1-MP:Perpendicular distance from the incisal edge of the mandibular incisor to the mandibular plane.The lines through points N,ANS,Me,S,Go parallel to the Frankfort horizontal plane represents the fiduciary lines.Measuring the distance between these lines.Anterior facial height(N-Me):the vertical distance between the point N to the point Me.Anterior upper facial height(N-ANS):the vertical distance between the point N to the point ANS.Anterior lower facial height(ANS-Me):the vertical distance between the point ANS to the point Me.Posterior facial height(S-GO):the vertical distance between the point S to the point Go.The ratio of ANS-Me and N-Me:ANS-Me/N-Me×100%The ratio of S-Go and N-Me:S-Go/N-Me×100%SPSS13.0 statistics analysis software was used to make normality test and to make description via mean and standard deviation if the statistics obeyed the normal distribution.All intragroup treatment changes of the two groups were evaluated with paired t tests.Intergroup comparisons of changes between the two groups were done by Independent sample t-test.On the contrary,we made description via median(M) and interquartile range(Q) and made analysis by Wilcoxon rank and inspection(inspection level α=0.05).Results:1 VHA group:During the treatment,the L6-MP, S-Go, N-Me, ANS-Me increased by 1.60 ± 0.51 mm,1.33 ± 0.91 mm,1.91 ± 1.32 mm,1.36 ±0.70 mm,respectively,(P<0.05).There were no significant differences in other variables,(P>0.05).2 Control group:During the treatment,the MP-SN, Y-axis, U1-PP, U6-PP, L6-MP increased by 1.03±0.56°, 1.72±0.42°, 0.91±0.91 mm, 2.03±1.23 mm, 3.06±1.61 mm,respectively.p<0.05.The S-Go, N-ANS, N-Me, ANS-Me, ANS-Me/N-Me increased by 1.42±0.91 mm, 1.27±0.77 mm, 5.34±2.64 mm, 4.07±2.28 mm, 0.96%±0.79%, respectively,(P<0.05).The S-Go/N-Me decreased by 1.69%±1.59%,(P<0.05).There were no significant differences in other variables,(P>0.05).3 The comparison of the treatment changes of the VHA group and the control group:the treatment changs of the MP-SN, Y-axis, U6-PP, L6-MP,N-Me,ANS-Me,ANS-Me/N-Me were smaller in the VHA group than in the control group,and the S-Go/N-Me was larger in the VHA group than in the control group,(P<0.05).There were no significant differences in other variables of the treatment changes,(P>0.05).Conclusion:1 The mandibular plane angle of the hyperdivergent patients tend to be steeper and the lower facial height of them tend to be higher if no special measurements are used to keep the posterior teeth height.2 The vertical holding appliance can prevent the maxillary first molar to extrude during treatment and as the fewer usage of the ClassⅡelastic,the extrution of the mandibular first molar is also prevented.So the vertical holding appliance can keep the mandibular plane angle and the anterior lower facial height stable.