BACKGROUND:The establishment of model is very crucial in the orthodontic tooth movement experiment. The selection of force and control ing of anchorage may greatly affect experimental results.
OBJECTIVE:To establish an animal model for orthodontic tooth movement.
METHODS:Twenty Wistar rats were included in this study. The root of incisor teeth at upper jaw was dril ed and then threaded with a ligature wire (0.3 mm diameter), therefore the alveolar bone and two incisor teeth were ligated. The first molar at right upper jaw was also ligated using a ligature wire (0.2 mm diameter). The experimental teeth were randomly divided into four groups. A Sental oy closed-coil spring (10 g, 25 g, 50 g) was placed between the maxil ary incisors and the maxil ary first molar, respectively. Taking the incisor as the anchorage, the molars were given a mesial movement, and control group received no force. On day 14, the dental pulp, dentin and enamin resorption was analyzed with Image-Pro Plus software.
RESULTS AND CONCLUSION:A light force (10 g Ni-Ti coil spring) produced irregular enamel resorption and narrowed periodontal membrane space, whereas heavy force (25 g Ni-Ti coil spring) produced irregular dentin and enamel resorption, even heavier force (50 g Ni-Ti coil spring) produced apparent resorption at dental root, which affected the dentin. No statistical difference of the relative depth of dentin resorption was found between the 10 g group and the control group (P>0.05). The data between other groups showed statistical y significant differences (P<0.05). The mechanical union of the incisors and the mandibular bone efficiently prevents the continuous eruption of the upper incisors, which maintains the anchorage stability. Using Ni-Ti coil spring, a stable, scientific and reliable model of orthodontic tooth movement can be established through mesial movement of the first molars. The optimal force of 10 g is used to move the rat first molar mesial y.

BACKGROUND: At present, composite resin has been dominantly applied on bonding brackets, but dental enamel is prone to the injury on the surface when the brackets are removed, resulting from the high bonding strength. OBJECTIVE: To compare the shear bond strength and adhesive remnant index of three orthodontic bonding adhesives at 5 minutes and 15 minutes after bonding orthodontic brackets. DESIGN, TIME AND SETTING: A randomized grouping control experiment was completed in the Laboratory of Stomatology, General Hospital of Shenyang Military Area Command of Chinese PLA from June to October in 2007. MATERIALS: For the sake of orthodontic, 90 premolars were extracted from the volunteers, who signed the informed consents to the study. Buccal surface enamel was observed under 10-power magnifying glass to be intact and untreated, without crack or dental caries, excluding tetracycline stained teeth and dental fluorosis. Jingjin enamel adhesive (Tianjin); light-cured resin modified glass ionomer cement (RMGIC) adhesive (Fuji, GC, Japan); Transbond XT and self-etching primer (3M Uniteck). METHODS: Ninety teeth were randomly allocated into three groups (n=30) as follows: Jingjin enamel adhesive group, light-cured RMGIC adhesive group, and self-etching adhesive group. After bonding, the brackets of the three groups were removed at 5 minutes and 15 minutes, respectively. There were 15 teeth at each time point. MAIN OUTCOME MEASURES: The shear bond strength and adhesive remnant index were measured and scored as 1-5 points (higher scores indicated higher bonding strength between the adhesives and the teeth, whereas lower scores indicated higher bonding strength between the adhesives and the brackets). RESULTS: After the bracket removal, the shear bond strength of light-cured RMGIC adhesive group was the lowest. No significant difference was found in the shear bond strengths between Jingjin enamel adhesive group and self-etching adhesive group. The remnant adhesives equally distributed on the teeth surface and bracket surface in Jingjin enamel adhesive group and self-etching adhesive group, while mainly distributed on the bracket surface in light-cured RMGIC adhesive group. The adhesive remnant index scores showed statistically significant differences among three groups (P