SUMMARY Dental fluorosis is a developmental disturbance of enamel caused by excessive fluoride on ameloblasts during enamel formation. Patients often present to the dentist with a main goal of improving their esthetic appearance. This case report describes a minimally invasive technique for treating a severe case of enamel fluorosis with brown surface aspect and small defects. A selective mega-abrasion and microabrasion were used to recreate macro- and micro- surface morphology, followed by power bleaching, home bleaching, and resin infiltration to improve the esthetic appearance.

tang 1,2 ✉ to evaluate tooth behaviours under various maxillary incisor retraction protocols for clear aligner therapy. A three-dimensional finite element model of maxillary dentition was constructed for first premolar extraction. A loading method was developed to mimic the mode of action of clear aligners for incisor en masse retraction. Three protocols with different amounts of retraction and intrusion on incisors were designed. Initial tooth displacements and stresses on periodontal ligaments were analysed with ANSYS software. The central (U 1) and lateral (U 2) incisors exhibited uncontrolled lingual tipping and extrusion upon 0.25 mm retraction. U1 exhibited translation movement, while U 2 underwent less tipping during 0.2 mm retraction and 0.15 mm intrusion. Labial tipping and intrusion of U 1 and bodily intrusion of U 2 were observed during 0.1 mm of retraction and 0.23 mm of intrusion. With the additional intrusion on incisors, canine showed extrusion movement, and higher stresses on periodontal ligaments were shifted from U 2 to canines. Incisors also exhibited different mesial-distal angulation in the three simulations, while posterior teeth all suffered mesial inclination. Incorporating intrusion displacement in clear aligners led to a tendency of lingual root movement during incisor retraction. the complexity of tooth movement should be recognized regarding clear aligner therapy.

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Under the background of the slow recovery of the global economy, strengthening regional cooperation is an important driving force to promote the development of the world economy, and has become a trend. In 2013, President Xi put forward the the strategy of "The Belt and Road" (B&R), which not only sought its own development, but also contributed to the development of other countries in line with the historical trend of Chinese wisdom. Over the past five years, the construction of B&R has gradually changed from planning to practice, from vision to reality, and the progress and achievements have exceeded expectations. On the one hand, B&R provides a new opportunity for the development of higher education in China. On the other hand, higher education provides a guarantee for the implementation of B&R. B&R is the latest development concept of China's reform and opening up and foreign policy. Many scholars study the development of higher education from the perspective of B&R. This topic has become a new hot spot of research. In theory, the strategy of B&R originates from the excellent traditional Chinese cultural thought, is a further explanation of China's foreign policy and foreign concept, and is also a further practice of the new concept put forward since the 18th National Congress of the Communist Party of China (CPC). By studying the cooperation mode of higher education between China and the countries along B&R, it is beneficial to increase the international exchange and cooperation in higher education in the future, and to strengthen the cooperation in higher education. To strengthen the cooperation of higher education is beneficial to the great development of the higher education in China, to realize the great rejuvenation of China's dream, to promote the construction of the human destiny community and to create a better future for mankind.

Objectives To evaluate the accuracy of integrated models (IMs) constructed by pretreatment cone-beam computed tomography (pre-CBCT) in diagnosing alveolar defects after treatment with clear aligners. Materials and Methods Pre-CBCT and posttreatment cone-beam computed tomography (CBCT) scans from 69 patients who completed nonextraction treatment with clear aligners were collected. The IMs comprised anterior teeth in predicted positions and alveolar bone from pre-CBCT scans. The accuracy of the IMs for identifying dehiscences or fenestrations was evaluated by comparing the means of the defect volumes, absolute mean differences, and Pearson correlation coefficients with those measured from post-CBCT scans. Defect prediction accuracy was assessed by sensitivity, specificity, positive predictive values, and negative predictive values. Factors possibly affecting changes in mandibular alveolar defects were analyzed using a mixed linear model. Results The IM measurements showed mean deviations of 2.82 ± 9.99 mm3 for fenestrations and 3.67 ± 9.93 mm3 for dehiscences. The absolute mean differences were 4.50 ± 9.35 mm3 for fenestrations and 5.17 ± 9.24 mm3 for dehiscences. The specificities of the IMs were higher than 0.8, whereas the sensitivities were both lower (fenestration = 0.41; dehiscence = 0.53). The positive predictive values were unacceptable (fenestration = 0.52; dehiscence = 0.62), and the overall reliability was low (<0.80). Molar distalization and proclination were positively correlated with significant increases in alveolar defects at the mandibular incisors after treatment. Conclusions Alveolar defects after clear aligner treatment cannot be simulated accurately by IMs constructed from pre-CBCT. Caution should be taken in the treatment of crowding with proclination and molar distalization for the safety of alveolar bone at the mandibular incisors.

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The 1999 relief plan for China's Minimum Livelihood Guarantee (called, for short, the dibao)-originally designed to assist all of the urban poor-changed by the mid-2000s, emphasizing employment, not handouts, for the ablebodied impecunious. Also, the center ordered that cities should subsidize just the most ill and needy. We find that only some Chinese cities-the less wellendowed and politically less prominent-responded to this shift by cutting back their percentage of merely unemployed recipients and increasing the percentage of the truly needy among their dibao beneficiaries. We suggest that two factors could account for this disparity: politicians in wealthier cities have greater autonomy; and they are closer to fulfilling a momentous career goal-stepping up to a post in the central government, and are thus more ambitious. It could be that in prosperous cities-where politicians have control over their budgets and where their trajectories have already positioned them near the peak of the mobility channel-leaders choose to