Tooth whitening the human eye and brain. Teeth are composed of a surface enamel layer, which is whiter and semitransparent, and an underlying dentin layer, which is darker and less transparent. These are calcified, hard tissues comparable to bone. The natural shade of teeth is best considered as such; an off-white, bone-color rather than pure white. Public opinion of what is normal tooth shade tends to be distorted. Portrayals of cosmetically enhanced teeth are common in the media. In one report, the most common tooth shade in the general population ranged from A1 to A3 on the VITA classical A1-D4 shade guide.
Eggshell the uterus. The egg can take up fluids and grow in size during this process, and the final, most rigid layer is not added until the egg is full-size. Hatching birds, amphibian and egg-laying reptiles have an egg-tooth used to start an exit hole in the hard eggshell. Eggshell waste is fundamentally composed of calcium carbonate, and has the potential to be used as raw material in the production of lime. Eggshell An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats. Insects and other arthropods lay a variety of