Mechanical Characterization of Thermoplastic Aligner Materials: Recommendations for Test Parameter Standardization.

Background: Understanding of the different mechanical properties of thermoplastic materials is essential for a successful aligner treatment and further developments. However, data of previous material testing studies are scarcely comparable. Aim of the current study was to evaluate the different test parameters to lay the foundations for guidelines for future, more standardized three-point-bending aligner material tests. Materials and Methods: Several parameters concerning the specimen preparation and experimental three-point-bending setup were varied. The specimens were collected from polyethylene terephthalate glycol (PET-G) Duran® foils with different thicknesses. Both raw foils and foils thermoformed using different geometrical forms were investigated. The three-point-bending tests were performed using span lengths of 8 and 16 mm and variable deflection ranges between 0.1 and 0.2 mm. The influence of water storage on the bending forces was studied using unloaded and loaded specimens. Experimental results were validated using a beam cantilever mathematical model. Results: Local macroscopic cracks after long-term loading could be avoided by keeping the deflections within a thickness-dependent individual range. The mathematical calculations confirmed that these individual deflection ranges lead to local stresses between 14 and 18 MPa. Constantly loaded specimens immersed for 24 hours in water showed a decrease of the bending force by 50%. This reduction was much smaller for the unloaded specimens (14%). Conclusion: During clinical aligner therapy, very small bending deflections are combined with small distances between the tooth surface regions supporting the aligner. In vitro aligner material testing by three-point bending should consider these geometrical aspects, while keeping the material stresses in a range between 14 and 18 MPa to avoid local microcracks. Considering these aspects, thickness-dependent deflections were established for three-point bending of the PET-G specimen for a span length of 8 mm. We recommend the application of these test parameters in future aligner material studies to achieve valid and comparable test results.

A nationwide survey of prevalence of pediculosis in children and adolescents in iran.

BACKGROUND: Since 2005, pediculosis is one of the obligatory reportable diseases from community to the Center of Disease Control. This study is the first nationwide survey on the prevalence of pediculosis and some associated risk factors in Iranian children and adolescents. METHODS: National data of the Ministry of Health and Medical Education were gathered in 2005 through school screening programs and obligatory reports from the country health centers. RESULTS: 12,359,448 Iranian children and adolescents were screened in 2005. Overall, 213,450 students, consisting of 198,947 girls and 14,320 boys were reported to have pediculosis. The prevalence of pediculosis was 581 per 100,000 population that varied from 1/100 000 to 8,303/100,000. In general, the highest prevalence of pediculosis was documented in south-eastern cities. The prevalence of pediculosis was significantly higher in girls than in boys (93% vs.7%, respectively, p<0.0001). In both genders, the highest prevalence of pediculosis was documented in the 6-10- year age group. Of those infected, 62% lived in rural areas, and 32% of those infected with pediculosis had a previous history of this infection. Most (99.37%) infected individuals had head lice, the rest had body and pubic pediculosis. CONCLUSION: The prevalence of pediculosis is low in Iranian children and adolescents, but this infestation is still a health problem in some south-eastern cities with warm climate and low to middle socioeconomic status.

Anaemia control: lessons from the flour fortification programme.

OBJECTIVES: Anaemia is an important public health problem in Iran; therefore, a programme of flour fortification with iron was launched in two pilot provinces. The present study was conducted in January 2009 to evaluate the effectiveness and process of this programme. STUDY DESIGN: A 'before-and-after study' was conducted to evaluate the effectiveness of the flour fortification programme, and the process of the programme was evaluated using a cross-sectional study. METHODS: To evaluate the effectiveness of the programme, blood haemoglobin and ferritin levels were measured in sample populations from Bushehr and Golestan provinces. The target population was women aged 15-49 years. Iron content was measured in samples of flour and bread to evaluate the flour fortification process in these two national pilot provinces. RESULTS: The total study population was 600 women from Bushehr province and 652 women from Golestan province. Similar trends were found in the indicators of anaemia/iron deficiency among the women studied in both provinces. The flour fortification programme only appears to have had a beneficial effect on ferritin levels (iron deficiency) in the two provinces. The prevalence of iron-deficiency anaemia before and after the intervention did not differ significantly in either province. Interestingly, the prevalence of anaemia (low haemoglobin) was significantly higher after the intervention in women from both provinces. The coverage of fortified flour and bread was 90% and 98.7% in Bushehr province, and 94.1% and 95% in Golestan province, respectively. CONCLUSIONS: In areas where anaemia is not mainly due to iron deficiency, an iron fortification programme might decrease the prevalence of iron deficiency without affecting the prevalence of anaemia.