Removable prostheses fit over the gums and remain in place only with suction or with the use of a specific glue. The fixed prostheses (ALL – ON – 4/6) are fitted onto the implants and fixed, which does not require any use of glue for this purpose. One of the problems in the use of removable prostheses is related to the fact that the supporting bone is absorbed, over time, because of the absence of teeth. This will cause the dentures to fall out and not be supported to hold, which means they will have to be replaced regularly to avoid discomfort and problems when eating. Removable dentures also increase the rate of bone loss.   The upper removable prosthesis covers the complete roof of the mouth and the lower one is horseshoe shaped to allow space for the tongue. Cleaning is usually done overnight (hence the cliché of “false teeth” in a glass of water on the bedside table). Fixed dentures are custom-made so that they fit precisely in the patient's mouth. and should act like natural teeth in terms of appearance, chewability and comfort. There is no risk of them moving around while talking or eating. Removable prostheses offer a clear cost advantage over any type of implant, however they need to be replaced, on average, once every five years.