Retrospective Study On Craniofacial Changes Of Class â…¡ Division 1 Teenage Patients With Non Extraction And Different Extraction Protocols

ClassⅡdivision 1 malocclusion is one of the most common malocclusions in daily practice. It has been reported that the prevalence of this malocclusion is 36.42% among adolescents in China. ClassⅡdivision 1 malocclusion is characterized by proclination of maxillary incisors associated with a pronounced overbite, deep overjet, abnormal stomatognathic function and poor facial appearance, which affects the physical and mental growth of adolescents. The formation mechanism of such malocclusion is complicated and attracts many researches as follows: horizontally, the discrepancy between the width of upper and lower dental arch was about 3-5mm; sagittally, 60% of patients were due to mandibular retrusion and 13% were due to maxillary protrusion; vertically, 27% of patients were low-angle and 23% of patients were high-angle. To correct such malocclusion associated with complicated formation mechanism and negative impacts on teenagers, there are several common clinical protocols of treatment: non-extraction treatment, extraction of four first premolars, extraction of two maxillary first premolars and two mandibular second premolars, and the removal of only two upper premolars. The proportion of these treatment choices was 45%, 19.06%, 5.78% and 2.3% respectively.The impact of four common treatment protocols mentioned above on adolescents was various according to different researches. Moreover, few retrospective studys were reported to systematically compare and analyze the impact of these treatment patterns on adolescents with ClassⅡdivision 1 malocclusion Thus, the objective of the present study was to retrospectively investigate the craniofacial changes of ClassⅡdivision 1 teenage patients with four common clinical treatment protocols and further analyze the effectiveness of different therapeutic mechanisms on correcting ClassⅡdivision 1 malocclusion. This study consists of three parts:PartⅠ: Craniofacial changes of ClassⅡDivision 1 teenage patients with non-extraction treatmentThe completed cases of ClassⅡDivision 1 teenage patients received non-extraction treatment were selected from the department of orthodontics, School of Stomatology, the Fourth Military Medical University during 2008-2010. The Onyx Ceph software system was used to analysis the cephalometric film of pre- and post-treatment. The changes of the hard tissue of AngleⅡ~1 malocclusion teenagers before and after non-extraction treatment were analyzed and discussed.Results: After non-extraction treatment,∠S ArGo,∠SNB,∠NGoMe,∠SN-OP , Go-Me/NS ratio and∠L 1-MeGo were increased significantly (P<0.05), and∠A NB,∠NGoAr,∠U1-SN ,∠U1-L1 were decreased significantly (P<0.05). Other measurements before and after treatment were similar without significant difference (P> 0.05). Conclusion: After non-extraction treatment, deep overjet and sagittal discrepancy between upper and lower dental arch of AngleⅡ1 malocclusion adolescents are improved, however, lower incisor inclination is more obvious, indicating that lower incisors move forward compensatorily after treatment.PartⅡ: Craniofacial changes of ClassⅡDivision 1 Malocclusion with different extraction patterns.The completed cases of ClassⅡDivision 1 teenage patients treated with extraction were selected from the department of orthodontics, School of Stomatology, the Fourth Military Medical University during 2008-2010. According to different extraction patterns, the selected cases were divided into three groups:①removal of four first premolars (group B);②extraction of two maxillary first premolars and two mandibular second premolars (group C)③only extracted the maxillary first molars(D group). The same method as described in part 1 was used for data analysis and processing.Results:①B group changes after treatment:∠S ArGo,∠SN-OP, S-Go/N-Me and Go-Me/NS ratio,∠U 1-L1 were significantly increased (P<0.05), and∠NGoA,∠U1-SN and∠L 1-GoMe were significantly reduced (P <0.05).②C group changes after treatment:∠SArGo, S-Go/N-Me, Go-Me/NS ratio and∠U 1-L1 were increased statistically (P <0.05), and∠N GoAr,∠SN-GoGn,∠U1-SN,∠L 1-GoMe were reduced with statistical significance (P <0.05).③D group changes after treatment:∠S N-OP, Go-Me/N-S ratio,∠L 1-GoMe,∠U 1-L1 were increased significantly (P <0.05); and∠U1-SN was reduced with statistical significance (P<0.05).Conclusion: After different extraction treatment, upper incisor inclination are improved obviously, but other results are different. After the extraction four first premolars ,upper and lower incisors inclination are improved, but occlusal plane are clockwise rotation; After the extraction tow first premolars on maxillary and tow second premolars on mandibular, upper and lower incisors inclination are improved as well, but it is counterclockwise rotation on the jaw; After the extraction tow first premolars on maxillary ,upper incisors inclination are improved, but lower incisors inclination are increased and occlusal plane are clockwise rotation.PartⅢ: Craniofacial changes of ClassⅡDivision 1 malocclusion teenagers with different treatment protocolsThe cephalmetric data from part 1 and part2 were collected to investigate the effect of four treatment protocols, in order to provide basis to the clinical diagnosis and treatment.Results: (see Table 5-1, 5-2)①∠U 1-SN: group A was reduced less than group B, group C, group D by 10.31°, 7.69°, 5.47°respectively; group B was reduced more than group C and group D by 3.62°, 7.84°respectively, group C reduced more than group D by 4.22°;②∠L 1-GoMe: group A increased more than group B, group C, group D by 6.74°,5.14°, 1.11°; group B reduced more than group C, group D by 1.60°, 5.63°; group C reduced more than group D by 4.03°;③∠SNB: group A was increased more than group B, group C by 1.73°, 2.33°, 2.33°;④∠A NB: group A was reduced more than group B, group C by 1.12°, 1.10°, 0.77°; ⑤∠SN-OP: group C was increased less than group A, group B, group D by2.25°, 1.41°, 2.44°;⑥∠SN-GoGn: group C was reduced more than group A, group B by 2.23°, 1.45°, 1.68°.Conclusion:Compared with non-extraction cases,extraction treatment was more conducive to decrease the degree of labial inclination of incisors. When the extraction teeth on maxillary were identical, the extraction teeth in mandibular is closer to anterior region, the more conducive to improve of the labial inclination of upper and lower anterior teeth; the closer posterior tooth area on mandibular, the easier counterclockwise rotation on the jaw.In addition, non-extraction treatment was benefit the improve of classⅡmalocclusion sagittally.