Fracture resistance and 2-body wear of 3-dimensional–printed occlusal devices

Statement of problem

Polymeric material for 3-dimensional printing can be used to fabricate occlusal devices. However, information about fracture resistance and wear is scarce.

What Approaches are Most Effective at Addressing Micronutrient Deficiency in Children 0–5 Years? A Review of Systematic Reviews

Introduction Even though micronutrient deficiency is still a major public health problem, it is still unclear which interventions are most effective in improving micronutrient status. This review therefore aims to summarize the evidence published in systematic reviews on intervention strategies that aim at improving micronutrient status in children under the age of five. Methods We searched the literature and included systematic reviews that reported on micronutrient status as a primary outcome for children of 0–5 years old, had a focus on low or middle income countries. Subsequently, papers were reviewed and selected by two authors. Results We included 4235 reviews in this systematic review. We found that (single or multiple) micronutrient deficiencies in pre-school children improved after providing (single or multiple) micronutrients. However home fortification did not always lead to significant increase in serum vitamin A, serum ferritin, hemoglobin or zinc. Commercial fortification did improve iron status. Cord clamping reduced the risk of anemia in infants up to 6 months and, in helminth endemic areas, anthelminthic treatment increased serum ferritin levels, hemoglobin and improved height for age z-scores. Anti-malaria treatment improved ferritin levels. Discussion Based on our results the clearest recommendations are: delayed cord clamping is an effective intervention for reducing anemia in early life. In helminth endemic areas iron status can be improved by anthelminthic treatment. Anti-malaria treatment can improve ferritin. In deficient populations, single iron, vitamin A and multimicronutrient supplementation can improve iron, vitamin A and multimicronutrient status respectively. While the impact of home-fortification on multimicronutrient status remains questionable, commercial iron fortification may improve iron status.

     

Protection of short-time enamel erosion by different tetrafluoride compounds

OBJECTIVE: This in vitro study aimed to analyse the protective effect of differently concentrated titanium (TiF(4)), zirconium (ZrF(4)) and hafnium (HfF(4)) tetrafluoride on enamel erosion. METHODS: Polished enamel surfaces of 36 bovine crowns were covered with tape leaving 4 enamel windows each 3mm in diameter exposed. The crowns were randomly assigned to six groups (each n=6) and pretreated with 4% TiF(4), 10% TiF(4), 4% ZrF(4), 10% ZrF(4), 4% HfF(4) or 10% HfF(4) for 4 min (first window), 10 min (second window) or 15 min (third window). The fourth window of each crown was not pretreated and served as control. Erosion was performed stepwise with 1% HCl (pH 2) in five consecutive intervals of each 15 s (total 75 s). Enamel dissolution was quantified by colorimetric determination of phosphate release into the acid. For each tooth, cumulative phosphate loss of enamel pretreated with one of the tetrafluoride compounds was calculated as percentage of the respective control and statistically analysed using two-way ANOVA. RESULTS: Enamel erosion was significantly reduced by TiF(4), ZrF(4) and HfF(4) application. Cumulative phosphate loss (mean % of control, 75s erosion) after 4-15 min application was significantly lower for 4% ZrF(4) (7-11%), 10% ZrF(4) (2-6%), 4% HfF(4) (11-9%) and 10% HfF(4) (12-16%) compared to 4% TiF(4) (42-27%) and 10% TiF(4) (54-33%). Only for 4% and 10% TiF(4), phosphate loss decreased with increasing duration of application, but also increased with increasing acid intervals. CONCLUSION: TiF(4), ZrF(4) and HfF(4) might protect enamel against short-time erosion, but protection was more enhanced by ZrF(4) and HfF(4) compared to TiF(4) application overtime.     

Expression of tropoelastin in human periodontal ligament fibroblasts after simulation of orthodontic force

The ability of elastic fibers to respond to mechanical stimuli suggests that they play a central role in physiological adaptation to external stimuli including application of orthodontic force. The purpose of this study was to examine the effect of external pressure simulating orthodontic force on tropoelastin gene expression in cultured human periodontal ligament fibroblasts (hPDLF). External pressure simulation was achieved by centrifugation for 10, 30, 60, 90 and 120 min of hPDLF in a horizontal microplate rotor. Semi-quantitative RT-PCR analysis of tropoelastin mRNA was performed and beta-actin was used as an internal invariant control. While centrifugal force on mRNA levels of beta-actin showed almost no change, the mRNA levels of tropoelastin increased significantly to a peak level of more than four-fold after 30 min. Thereafter, at 60 min, the mRNA levels remained at more than three-fold. After 90 min, mRNA levels decreased to control levels. The finding that no changes in mRNA levels of beta-actin occurred during the first 90 min of centrifugation validates its use as an invariant control gene in such an experimental model. This study demonstrated that tropoelastin is expressed in hPDLF and that the pressure caused significant time-dependent upregulation of the tropoelastin gene. The responsiveness of the tropoelastin gene to force shows its possible clinical importance in orthodontic tooth movement. Further studies, however, are essential in order to learn whether the high expression of the gene in vitro will also be followed by corresponding protein synthesis and deposition in vivo in the extracellular matrix (ECM) of the periodontal ligament (PDL).