Edited Excerpt from Wikipedia on Cremation:
Not all that remains is bone. There may be melted metal lumps from missed jewelry; [ ]dental fillings; and surgical implants, such as hip replacements. Large items such as titanium hips [ ] (which tarnish but do not melt) or casket hinges are usually removed before processing, as they may damage the processor. [ ] Implants may be returned to the family, but are more commonly sold as non-ferrous scrap metal. After the remains are processed, smaller bits of metal such as tooth fillings, and rings (commonly known as gleanings) are sieved out and may be later interred in common, consecrated ground in a remote area of the cemetery. They may also be sold as precious metal scrap.