Expansion and contraction of materials due to temperature changes is an important consideration in all areas of construction. For example, expansion joints are placed in bridges to respond to heating in the summer and cooling in the winter. Expansion and contraction rates are important in something as small as a filling in a tooth. The filling must not expand more than the tooth and crack the tooth, or contract more than the tooth and pull away from the sides of the tooth. Manufacturers of plastic and rubber parts have to allow for size changes after the manufacturing process so that the parts are the proper size after cooling to room temperature.