america's dentists are alarmed by a trend for mouth adornments which encase teeth in precious metals and jewellery.

　　grills, as the removable mouthpieces are known, have been popularised by rappers who spend tens of thousands of dollars on gold, platinum or silver tooth coverings with diamond inlays.

　　dental experts say the close-fitting ornaments can trap bacteria, causing decay and gum disease, and health officials in some states have barred their manufacture.

　　the mouthpieces recently gained nationwide fame thanks in part to the singer nelly's hit single grillz, which refers to his costly coverings as a "smile on the rocks". since the song's release, the new york website goldteethusa.com has seen a 30 per cent increase in business.

　　the houston rapper paul wall, who describes his $25,000 (￡14,000) oral bling as "a disco ball", has teamed up with a texan jeweller to launch a line of custom-made mouthpieces.

　　to make a grill, an impression of the teeth is taken and a cast made. but matthew messina, of the american dental association, warned that using cheaper metals may expose wearers to allergic reactions.