The word rapid prototyping (RP) was first used in mechanical engineering field in the early 1980s to describe the act of producing a prototype, a unique product, the first product, or a reference model. In the past, prototypes were handmade by sculpting or casting, and their fabrication demanded a long time. Any and every prototype should undergo evaluation, correction of defects, and approval before the beginning of its mass or large scale production. Prototypes may also be used for specific or restricted purposes, in which case they are usually called a preseries model. With the development of information technology, three-dimensional models can be devised and built based on virtual prototypes. Computers can now be used to create accurately detailed projects that can be assessed from different perspectives in a process known as computer aided design (CAD). To materialize virtual objects using CAD, a computer aided manufacture (CAM) process has been developed. To transform a virtual file into a real object, CAM operates using a machine connected to a computer, similar to a printer or peripheral device. In 1987, Brix and Lambrecht used, for the first time, a prototype in health care. It was a three-dimensional model manufactured using a computer numerical control device, a type of machine that was the predecessor of RP. In 1991, human anatomy models produced with a technology called stereolithography were first used in a maxillofacial surgery clinic in Viena.

No abstract

Many methods have been used to establish the occlusal plane in complete denture prosthodontics. However, no single method seems to be fully accepted. Anteriorly, esthetic considerations help define the occlusal plane, and posteriorly the tongue, retromolar pad, and Stenson's duct are considered. Some dentists bisect the space between the residual ridges. The technique of using the ala-tragus line (Camper's line) to establish the occlusal plane is well documented. However, definitions of the ala-tragus line cause confusion, because the exact points of reference do not agree. For example, the glossary of prosthodontic terms states that the ala-tragus line runs from the inferior border of the ala of the nose to the superior border of the tragus of the ear while Spratley’ describes it as running from the center of the ala to the center of the tragus. This article concerns us the exact relationship between the occlusal plane and ala-tragus line in dentate individuals.