BACKGROUND: Bracket dropping is often seen in clinic. Can these shed brackets be used again; what should be done to treat these brackets; is the bond strength of these recycled brackets different from those new ones, these questions are often concerned by orthodontists in their clinic and are the purpose of our study as well.OBJECTIVE: To evaluate the shear bond strength and compare two base-cure methods of recycled brackets. DESIGN: Grouping control study. SITTING: Department of Orthodontics, the Affiliated Hospital of Medical College, Qingdao University; Department of Materials, Dental School, Beijing University. MATERIALS: The teeth were collected from Oral Surgery, the Affiliated Hospital of Medical College, Qingdao University. The age was from 11 to 19 years. The gender was half male and half female. Intact enamel of the crown was required, but decayed, fracture, tetracycline pigmentation teeth or fluorosis teeth were excluded. Patients provided the confirmed consent for this experiment.METHODS: The experiment was carried out in Stomatology College of Peaking University in December 2005. Thirty ex vivo teeth were selected randomly from those prepared enamel surfaces, used as sample for rebounding. The edgewise brackets of swallow-tailed brackets were bonded on each tooth and rebonded after 24 hours. The teeth were cleaned and divided randomly into 3 groups. There were 10 teeth in each group. Group 1 was bonded with new brackets; group 2 with recycled brackets whose adhesive remnant were burned and got rid of; group 3 with recycled brackets whose adhesive remnant in the groove of the base were stored. Bracket was provided by Standard edgewise, Orsu Company, Hangzhou, China. After 24 hours, the shear bond strength was tested with material testing machine (Autogragh, Shimadzu, Japan). Adhesive remnant index (ARI) was added up. MAIN OUTCOME MEASURES: Shear strength of old metal bracket after rebonding and adhesive remnant.RESULTS: ① Shear bond strength: The shear bond strengths were (10.094±3.158 9) in group 1, (10.266±2.406 0) in group 2 and (8.898±1.365 9) in group 3. There were no statistically significant differences among the three groups (P > 0.05). ② ARI scores: ARI scores were 51.7%, 58.3% and 35.0% in the three groups, respectively. There were statistically significant differences between group 2 and 3. CONCLUSION: In vitro study indicates that the recycled metal brackets can reach good bond strength and that maybe there is chemical bond between new and old adhesive.

Objective To investigate the effect of orthodontic tooth extraction and non-extraction on dental arch width and esthetical smile. Methods 100 patients treated without extraction and 100 patients treated by 4 first-premolars extraction were selected. The study models of the patients were measured before and after the treatment and compared statistically. Measurements were made in the maxillary and mandibular canine regions from the most labial aspect of the buccal axial surfaces of the canine roots. Results Before treatment, maxillary and mandibular arch widths were the same between both groups (P＞0.05). In non-extraction group, mandibular arch width of posttreatment was 0.88 mm larger than that of pretreatment (P＜0.001), and maxillary arch width of posttreatment was 0.84 mm large (P＜0.001). In extraction group, mandibular arch width of posttreatment was 1.64 mm larger than that of pretreatment (P＜0.001), and maxillary arch width of posttreatment was 1.50 mm large (P＜0.001). After treatment, the width of mandibular arch in the extraction group was 0.59 mm larger than that in the non-extraction group (P>0.05), while the width of maxillary arch in the extraction group was 0.10 mm less (P>0.05).Conclusion Both extraction treatment and non-extraction treatment do not result in narrower dental arch, but wider. The view that orthodontic extraction results in narrower arch widths and unaesthetic smiling is untenable.