A Comparison Study Between Herbst Appliance Followed By Extraction And Extraction-only Treated Class II Division 1 Malocclusion

Objective: To compare the mechanism and effects between Herbst Appliance followed by extraction and extraction-only treated skeletal class II division 1 malocclusion combind with mandibular retrusion and dentition crowding by cephalometric analysis, in order to provide some information to clinical treatment.Methods: 32 patients of FG-G phase of permanent dentition with skeletal class II division 1 malocclusion combind with mandibular retrusion and dentition crowding were divided into two groups. The first group consisted of 17 patients (10 males, 7 females) , who were treated with cast splint Herbst appliance followed by four first premolars removed and edgewise technique, and the second group consisted of 15 patients (9 males, 6 females), who were treated with edgewise technique and extracted two upper first premolars and two lower second or first premolars at the beginning. The average age were 13 year-5 month and 13 year-8 month respectively. Taking cephalograms two weeks before treatment (T1), immediately after removal of Herbst (T2) and at the end of edgewise therapy (T3) in the first group, and the second group were radiographed at the T1 and T3 stage. Then taking cephalometric analysis and statistical analysis.Results: After T1-T3 period of treatment, the overjet and molar relationship had achieved normal level both the two groups, and had generated some changes as follow:1. The increment of ramus length,mandibular length and mandibular effective length and antedisplacement of pg were 4.16mm,3.15mm,6.14mm and 3.65mm in the first group, they were 1.57mm,1.35mm,2.28mm and 1.84mm more than in the second group respectively (p <0.05).2. In the first group overjet had decreased by 6.05mm, with 44% skeletal changes and 56% dental changes, and molar relationship had improved 4.83mm, with 55% skeletal and 45% dental. In the second group overjet had decreased 4.86mm,with 15% skeletal changes and 85% dental changes, and molar relationship had improved 3.04mm, with 25% skeletal and 75% dental.3. The increment of SNB in the first group were 1.93 o(p<0.001)more than in the second group, and the decrement of ANB and convex angle of hard tissue was 1.64 o(p<0.001)and 1.43o(p<0.05)respectively less than in the second group. The mandibular plane angle and occlusal plane angle were no significant changes in the first group(p>0.05),but they increased by 1.23o and 1.95o in the second group, and the difference between two groups were significan(tp<0.05). The decrement of U1/SN in the second group was 5.60(op<0.001)more than in the second group, the increment of L1/MP and U1/L1 in the second group were 5.47o(p<0.001) and 0.31(op>0.05)more than in the first group.4.The decrement of Ns-Sn-Pos was 1.66o,the increment ofNs-No-Pos and S-Ns-B in the first group were 1.61o and 1.52o(p<0.05)respectively more than in the second group. LL-E,UL-E had decreased 0.71mm,2.34mm in the first group, and 1.09mmm,1.37mm in the second group, but the difference between two groups were no significant.Conclusion: 1. It can achieve better dental,skeletal and profile changes by two phase treatment that was Herbst appliance with extraction when the jaw relationships improved than by extraction-only method when treated Class II division 1 malocclusion with mandibular retrusion.2. It can simplify the treatment difficulty and reduce multiple brackets fixed treatment time by two phase treatment that was Herbst appliance with extraction when treated Class II division 1 malocclusion with mandibular retrusion.