Tooth polishing This outermost fluoride rich layer of enamel is removed when tooth polishing is provided. The mineral components of saliva and polishing pastes containing fluoride can assist in remineralizing this outer layer. The enamel surface is strong enough to withstand repeated tooth polishing, but it should be avoided on newly erupted teeth, exposed root surfaces and areas of demineralization. If polishing does occur on these surfaces, fluoride therapy can minimize the risk of dental caries. Excessive pressure can lead to frictional heat that may cause pulpal discomfort or necrosis of the dental pulp. Surfaces of restorations may be damaged by conventional
Active layer in permafrost regions due to the low rate of weathering in the very cold climate. The slow rate of decomposition of organic material means gelisols (permafrost soils) are very important as a sink for carbon dioxide. This carbon dioxide and other greenhouse gases (chiefly methane) forms from the very slow decomposition of the excess organic matter that remains in most gelisols and is mixed down into the pereletok layer during relatively hot summers and below that layer during warmer periods about 5000 to 6000 years ago. This storage of carbon means thawing of permafrost may accelerate global warming - some