If maintained well and an individual does not have a genetic predisposition towards some major dental problem, teeth can last a lifetime. But this is not always true. Human beings tend to lose a few teeth at some point of time in life, and a significant number lose all their teeth in advancing middle age.
A Prosthodontist is a specialist in replacing missing teeth. Most cases requiring either full dentures or partially missing teeth can be treated by general dentists. A Prosthodontist is usually required for the specifically difficult cases of complete dentures and complex rehabilitation of even partial replacements.
A Prosthodontist is of immense value in planning such cases and working out proper designs which will last a life time. Replacements can be fixed or removable. Fixed replacements are generally termed bridges. Bridges take support of existing teeth and replace missing teeth. If natural teeth do not exist on either side of the missing teeth, a bridge cannot be made, and the standard alternative is to make a removable partial denture.