Optical Methods To Measure Shape and Size

Abstract

A number of methods are available to quantify exterior size and shape of living and non-living objects. Relevant items for dentistry are the exterior of face and skull and the surface of dental casts. To the best of our knowledge, dentitions have not yet been measured in situ. The optical methods using incoherent light are mechanical sensing of casts, visual stereometry (on the subject or on stereophotographic pairs), moire techniques, and optical-sensor morphometry. It will be shown that the three latter systems in fact rely on the same physical principles, although they involve quite different technologies. On the other hand, coherent optical techniques, such as holography and contouring holographic interferometry, are presented. The basic principles of the different techniques are shown, and their main features in relation to applications to the dental object discussed. Main features include: resolving power, range, time needed for a measurement, requirements for the surface of the object, and ease of selection and collection of data. Examples of methods from the literature and from work by the author are given.