Cremation is the physical reduction, by intense heat, of the body to its basic element: carbon (bones). Cremation is performed in a retort that looks somewhat like a large pizza-oven.
What happens to prostheses, teeth, gold or silver fillings? What about pace-makers? Most crematories require the funeral director to remove any prostheses prior to deliving the body to the crematory. Gold and silver fillings actually contain very little of the precious metal, and are vaporized along with the rest of the body's soft tissue. Though it is apocryphal, some people believe that if a body containing a pace-maker is cremated, the battery can explode causing a nuclear incident. Again, though it is apocryphal, crematories still require the pace-maker to be removed prior to accepting the body.
What is left when the cremation is completed? See cremated remains. Depending on the size of the body, between five and eight or so pounds of bone fragments. Some of the larger joints (e.g. hips) may remain largely intact, as may portions of the skull. Crematories in most states are required to pulverize the bone pieces and fragments to a minimal size such as 5 MM or less. A machine similar to a grist-mill is used.