The effects of feed size distribution on confined-bed comminution of quartz and calcite in piston-die press

Packing characteristics of particle beds, determined mainly by the particle size distribution, exert a critical influence on the interparticle breakage of minerals in confined beds under compression. This paper is concerned with the effects of feed size distribution on characteristic phenomena of confined-bed comminution. Minus 3.35-mm quartz and calcite feeds were prepared by proportionately mixing previously classified narrow-size fractions so as to construct particle size distributions having the Gaudin-Schuhmann functional form with distribution modulus values of 0.5, 0.7, and 0.9. These feeds were comminuted in a piston-die press at five levels of applied pressure ranging between 26.5 MPa and 283 MPa, generating specific energy inputs in the range 0.65 J/g to 8 J/g depending on the material and feed size distribution. The size distributions of the comminuted solids were analyzed for self-similarity, comminution kinetics and reduction ratios. Force-displacement data were analyzed for bed compaction, energy absorption and energy utilization phenomena. The results showed definite effects of feed size distribution on these latter phenomena and product particle size distributions. The relationship between the specific energy absorbed and applied pressure is linear. Self-similarity does not hold for the coarse-size range of the products, indicating greater deviations for feeds with greater proportions of the coarse material. Breakage fraction of the top-size class (3.35 x 2.36 mm) particles and production of fines (minus 75 mu m) are significantly high with feeds having the size distribution modulus of 0.9. Reduction ratio-specific energy input relationship is curvi-linear; energy utilization becomes better with increasing value of the distribution modulus. The observed effects are explicable in terms of the packing density of particle beds and the amount of fines in the feeds

Fusion of the permanent maxillary right incisor to a supernumerary tooth in association with a gemination of permanent maxillary left central incisor: A dental, genetic and dermatoglyphic study

The relationship between fusion of the permanent maxillary right central incisor to a supernumerary tooth in association with gemination of permanent maxillary left central incisor and dermatoglyphics were investigated.</jats:p

Root canal morphology of maxillary premolars

The objective of this study was to investigate further internal anatomy of maxillary premolars. Six hundred recently extracted maxillary first and second premolar teeth were used in this study, One-half of the teeth were maxillary first premolars, the other half were maxillary second premolars. The teeth were stored in 10% formalin solution, and a standard clearing technique was applied with some modifications. Finally, ink-dyed root canal systems were evaluated by a dissecting light microscope, Each tooth was examined as to the number of roots and root canals and their types, ramifications of the main root canals, and location of apical foramina and transverse anastomoses, Examination of the root canal systems of the teeth was based on Vertucci's classification. The incidence of type I canals (one canal) for the maxillary first premolars was 8.66%, whereas 89.64% of the total samples demonstrated two canals (from type II to type VII), Only 1.66% of maxillary first premolars were type VIII or type IX (three canals). Regarding maxillary second premolars, the incidence of type I (one canal) was 48.66%, whereas it was 50.64% for type II to type VII (two canals), Type VIII (three canals) was found in 0.66% of the total sample