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Objective: To investigate the main reasons of relapse in those orthodontic patients who ask for the retreatment post retention, and to assess the factors affecting the long stability of orthodontic treatment, then to provide better understanding of the diagnosis for retreatment.Materials and methods: 90 retreatment patients (male 20, female 70) were selected from the Stomatological Hospital Affiliated to Dalian University, Department of Orthodontics. The mean age of initial treatment was 15.3 +5.2 years old, from 8.0 to 39.2 years old; the mean age of retreatment was 20.1 +5.3 years old, from 12.5 to 40.1years old. 40 patients were treated with teeth extraction (premolars or molars), 50 patients were treated without extraction. All clinical informations were collected, including age, sex, medical history, retainer type, retain period, extraction/nonextraction, malocclusion pattern, growth pattern, the occlusion at the end of former treatment, wisdom teeth eruption, abnormal oral habit, and etc. The correlation analysis was performed between relapse and those above factors.Results: The main relapse happened in the lower and upper insisors section, mild crowding or malposition were seen in 62 cases (68.9%); calssⅡtendency contributed to the excess overjet, mainly caused by the retro-mandibule, 33 cases (36.7%); calssⅢtendency contributed to the reverse overjet, mainly caused by the extra growth of mandibule, 17 cases (18.9%); space reopening were seen in 6 cases (6.7%), half were in extraction sites, and another half were in initial space; anterior open bite were seen in 4 cases (4.4%), caused by tongue thrusting.The main reason of relapse were as below: 1)Retention problem: shorter wearing time or even no retention; bond failure of lingual retainers and didn’t rebond on time, total 33 cases (36.7%); 2) Improper diagnosis or anchorage loss, 21 cases (23.3%); 3) Inadequate torque or derotation, improper adjacent touch, 17 cases (18.9%); 4) The growth pattern contributed to calssⅡ/Ⅲtendency, 9 cases (10%); 5) The eruption of wisdom teeth contributed to the crowding of lower incisors, 6 cases (6.7%); 6) Malfunction factor (tongue thrusting) remained, directly lead to the open bite, 4 cases (4.4%).Conclusion: The relapse post retention was closely related to the initial diagnosis, anchorage control, malocclusion pattern, growth characteristic, wisdom teeth eruption, abnormal oral habit, and the patients’cooperation. It’s critical essential to achieve excellent and long stable term orthodontic treatment results by fully consideration of the proper diagnosis with growth, the 3-D control of tooth movement, the rebuild of function and the adequate retention as well.
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