ChiCTR‐TRC‐07000454.

Trial name or title	The impact of the Hawley's removable retainer and clear overlay removable retainer on orthodontic patients' oral hygiene
Methods	Parallel RCT
Participants	Males and females up to 30 years of age Inclusion criteria 1. Patient is resident and impossible to leave in two years; 2. When ended active orthodontic treatment, patient will receive periodontal treatment until the periodontia recovery, the color of the gingival returned normal and the blood of periodontal (BOP) index is negative; 3. The age: the minimum age is a stage that patient's second molars have been erupted and have occlusion when ended active orthodontic treatment. The maximum age is 30 years old Exclusion criteria 1. Whole body factors 1) Systematic diseases: Diabetes, AIDS, Osteoporosis, Leukemia; 2) Sex Hormone: pubertal gingivitis, gestational period gingivitis; 3) Genetic factor: gingival fibromatosis; 4) Medicine: Phenytoin, cyclosporine; 5) Habit disturbance: brygmus, the custom of biting hard‐thing, smoking and being addicted to drink, unilateral mastication, mis‐brushing habit, oral respiration. 2. Local factors 1) Severe periodontal disease; 2) Local in false dental prosthetic restoration; 3) Mis‐designed partial prosthodontics; 4) Fixed prosthodontics; 5) born‐missed teeth or abnormal extraction.
Interventions	Group 1: Hawley's removeavble retainer Group 2: transparent retainer Group 3: normal comparison observation group
Outcomes	PLI; Bite the number of the comtact point; GBI; ALI; CI (meaing of acronyms not provided)
Starting date	Registered 2007
Contact information	Yu Yongchun , sjxj.558@163.com
Notes	Department of Orthodontics, the College of Stomatology of West China, Sichuan University