Determinants of preterm delivery in the central zone of Tigray, northern Ethiopia: a case-control study

Background. Preterm birth remains one of the most serious problems in obstetrics care globally. In Ethiopia preterm delivery is a direct cause of 28% newborn deaths. However, little is known about the risk factors of preterm birth.Objective. To determine risk factors of preterm birth in Tigray, Ethiopia.Methods. A hospital-based, unmatched case-control study was conducted among 288 respondents (cases=96; controls=192). Data were collected during individual interviews and through a chart review. Statistical analysis included descriptive statistics and bivariate and multivariate binary logistic regression analysis (significance level p<0.05). Results. The response rate was 100%. The mean (standard deviation) age of the respondents was 26.1 (5.9) years. Urban residence (adjusted odds ratio (aOR) 3.11; 95% confidence interval (CI) 1.181 - 8.168)), gynaecological problems (aOR 8.9; 95% CI 1.580 - 50.252), hard physical work during pregnancy (aOR 3.85; 95% CI 1.622 - 9.144), being younger than 18 (aOR 4.56; 95% CI 1.702 - 12.215) and being a first-time mother (aOR 4.66; 95% CI 1.635 - 13.254) were identified as statiscally significant risk factors of preterm delivery. Micronutrient supplementation (aOR 0.26; 95% CI 0.008 - 0.084) and nutritional counselling during pregnancy (aOR 0.24; 95% CI 0.067 - 0.862) were identified as protective factors against preterm birth. Conclusion. The study identified various factors associated with an increased risk of preterm birth and also some protective factors against preterm birth. Programmes to improve maternal and newborn healthcare are recommended to reduce the incidence of preterm births in this region

Effect of casting method on castability of titanium and dental alloys.

Titanium, once considered to be difficult to cast because of its relatively high melting point (1670 +/- 50 degrees C) and strong chemical affinity, can now be acceptably cast using newly developed casting apparatus. The objectives of this study were to examine the castability of commercially pure (CP) titanium using an ultra high-speed centrifugal casting machine and a pressure difference-type casting unit and to compare the castability of titanium with that of conventional dental casting alloys. To determine castability, two types of patterns were used: a mesh pattern of 22 x 24 mm cut polyether thread sieve, and a saucer pattern (24 mm diameter) perforated to create four T-shaped ends. The casting equipment significantly affected the mold filling of both patterns (p < 0.001). The castability indices obtained from both patterns of CP titanium cast in the centrifugal casting machine were significantly (p < 0.05) better than the indices of the castings produced in the pressure-difference casting unit. The radiographs of the saucer pattern cast in the centrifugal casting machine showed some pores that were fewer and smaller in size than the pores found in castings made in the pressure-difference unit. When the ultra high-speed centrifugal casting machine was used with the manufacturer's recommended mold material, the castability of titanium was similar to that of gold alloy or Ni-Cr alloy cast by conventional means.

In vitro corrosion resistance of titanium made using different fabrication methods.

The corrosion of cast or milled ASTM Grade II CP titanium with different surface conditions was studied by potentiodynamic anodic polarization and immersion testing. Specimens were fabricated using three dental titanium casting systems and from machined titanium. Three surface conditions were tested: (1) sandblasted with surface reaction layers remaining; (2) polished surface without surface reaction layers; and (3) sandblasted surface without surface reaction layers. An acidic saline solution (0.1 M lactic acid/0.1 M NaC1 [pH = 2]) and an artificial saliva were used as the corrosion media. Anodic polarization was performed starting at 50 mV below the rest potential and terminating at +2250 mV vs Ag/AgCl. Two surface conditions (sandblasted with the surface reaction layers and polished without such layers) were examined in the immersion test. Specimens were immersed in the corrosion media at 37 degrees C for six months. The recovered solution was analyzed by an atomic absorption spectrophotometer for titanium dissolution. A distinctive passive region on the polarization diagram, ranging from approximately 0 to approximately +1300 mV, was observed for all specimens in both media. Great similarity was observed for all the sandblasted specimens which had larger primary passive current densities and passive regions compared to the polished ones. A current density peak at approximately +1600 mV seen for all the specimens with sandblasted surfaces was less well defined for the polished specimens. Immersion testing in the acidic saline solution revealed no significant differences among the polished specimens. A significant increase (P < 0.05) in titanium dissolution was found for the sandblasted specimens with surface reaction layers remaining on the surfaces made with phosphate-bonded SiO2/Al2O3 investment compared to the polished ones. Significant differences were also found between sandblasted specimens with the surface reaction layers resulting from different investment materials and different casting methods. Measurable amounts of titanium were not found for all specimens in the artificial saliva after six months. It is evident that the corrosion behavior of cast CP titanium is similar to that of machined titanium. The surface roughness appears to be a more prominent factor than do the surface reaction layers on the polarization behavior of the CP titanium under the present experimental conditions. Surface roughness and the presence of the surface reaction layers both affect the dissolution of titanium.

Strength and microstructure of gallium alloys.

This study investigated the physical and mechanical properties and the microstructure of four different gallium alloys. For all gallium alloys, the compressive strengths measured at one hour (86-223 MPa) and 24 hours (265-286 MPa) after specimen preparation were found to be well within the range exhibited by many high-copper amalgams. The creep values and dimensional change of the gallium alloys were comparable to those of leading amalgams, except for the dimensional change value of one alloy. The set gallium alloys consisted of a multi-phase structure including beta-Sn, CuGa2, In4Ag9, Ag72Ga28, and Ga5Pd (except for one product that did not contain Pd) that was more complicated than the structure of dental amalgams. Although the gallium alloys had physical and mechanical properties comparable to those of high-copper amalgams, the microstructure, coupled with the instability of the element gallium itself, could make these materials more prone to corrosive attack compared to amalgams.

Effect of Pd and In on mercury evaporation from amalgams.

The amount of Hg vapor released from "synthesized" gamma 1 with 1% (wt) Pd was reported to be less than 30% of that from gamma 1 with no Pd. This study tested the hypothesis that Hg evaporation from Pd-containing amalgams decreases with Pd concentration and that In also reduces Hg vapor. Specimens (4 mm dia, 8 mm long) were prepared by triturating Ag-Sn(25%)-Cu(12%) alloy powder containing 0.5-9.0% Pd with pure Hg and by triturating 3% Pd alloy powder with Hg containing 1-5% In (all residual Hg approximately equal to 62%). The total amount (ng/mm2) of Hg vapor released at 37 degrees C from freshly prepared amalgams was measured. Pd (3-9%) in the powder significantly (p < 0.05) decreased Hg vapor release from amalgams during setting. Use of In-containing Hg also reduced Hg vapor release (5% In, p < 0.05). The reduction in the Hg vapor pressure by adding Pd and the rapid oxide film formation on the In-containing amalgam appear to work together to reduce Hg vaporization from these amalgams.