[Influence of removable thermoplastic appliances and fixed appliances on periodontal status: a meta analysis].

PURPOSE: To evaluate the influence of removable thermoplastic appliances and fixed appliances on periodontal status. METHODS: Cochrane library, PubMed, EMBASE, CBM, CNKI, VIP, Wanfang Database were searched from the date of inception to 2017.10.16，to find clinical trials about removable thermoplastic appliances and fixed appliances on periodontal status. The quality of the included studies was assessed by two reviewers independently, and meta analysis was performed using RevMan5.3. RESULTS: Totally 11 studies including 543 patients were identified. The results of meta analysis showed there were significant difference in PLI and SPD at 3 months and PLI and GI at 6 months between removable thermoplastic appliances and fixed appliances, and no significant difference was observed in GI at 3 months and SPD at 6 months between the two groups. CONCLUSIONS: In the early orthodontic treatment, removable thermoplastic appliances has better effect than the fixed appliance on periodontal health.

[Comparison between the tooth length measured by cone-beam CT and the tooth length measured with vernier caliper].

OBJECTIVE: To evaluate the accuracy of cone-bean CT (CBCT) on the measurement of the tooth length. METHODS: One hundred and sixty single root premolars extracted for orthodontic purposes were selected. The tooth length was measured with vernier caliper. The premolars were divided into 10 groups randomly, 16 premolars in each group.In each group, the teeth were lined in molar area, premolar area, canine area and anterior tooth area in maxilla and mandible. Then CBCT was taken, and the tooth length was measured using the software supplied by the manufacturer in coronal and sagittal plane. Accuracy was compared between vernier caliper measurement and CBCT measurement. RESULTS: The tooth length measured by CBCT was smaller than that measured with the vernier caliper. Significant differences were found in six areas, except the maxillary and mandibular premolar areas. With the increase of mesial-distal inclination or buccolingual torque angle, the difference between tooth length measured by CBCT and that measured with vernier caliper increased. The correlation between buccolingual torque angle (∠X1) and the coronal view of CBCT radiology tooth length (Spearmen index was 7.00, P < 0.001), and the correlation between mesial-distal inclination and the coronal view of CBCT radiology tooth length (Spearmen index was 0.624, P < 0.001) were found. CONCLUSIONS: The tooth length measured by CBCT was smaller than that measured with vernier caliper.

[A scanning electron microscopic study of root surface following mini-implant anchorage for maxillary incisors intrusion].

PURPOSE: To establish an animal model for maxillary incisors intrusion with mini-implant as the anchorage and study the effect on the surface morphology of cementum after the force had been given. METHODS: 9 dogs were selected and randomly divided into 5 groups, group I was the control group(1 dog) with no force given; groups II,III,IV,V were experimental groups (2 dogs each). Mini-implants were inserted into the labial alveolar bone between the roots of second and third maxillary incisors on both sides, 100 gram force was imposed on the first and the second incisors on both sides.The animals were sacrificed at the end of 1, 2, 4,12 weeks (activation for 4 weeks,then retention for 8 weeks after force removal) respectively after activation.Scanning electron microscopy was used to examine the surface of the cementum. RESULTS: In group II, the surfaces of root tip had a little scratch, which was small,confined. In group III, near the apical 1/3 of root, lacunas were fused, but no dentin exposed. In group IV, at the junction of the apical 1/3 and the middle 1/3 of the root, lacunas went deep into the dentin,which were wide and serious. In group V, the surfaces of lacunas were low ,smooth and even. CONCLUSIONS: As the intrusion goes on, the area of absorption expands from the root tip to neck. Root resorption increases with the duration of the applied force prolonged and repair of the cementum occurs at the resorbed area after force removal.