Generation of 3D digital models of the dental arches using optical scanning techniques

Abstract

Due to a number of benefits mainly concerning orthodontic treatment planning and issues of documentation and sharing of patient records, digital models of the dental arches are more and more replacing conventional stone models in clinical orthodontics. To date, the most common approach for generating digital models of the dental arches comprises the digitization of stone models mostly by using optically-based desktop scanner systems. This indirect approach is sufficiently accurate and achieves a largely complete model surface with relatively low equipment acquisition costs. In the recent decade, however, intraoral scanners are becoming ever more established and proven in clinical practice. The great advantage of this direct approach for generating digital models is that the intermediate step of stone cast fabrication can be omitted which eliminates material and space requirements for casts. The various commercially available intraoral scanning systems are based on the application of different optical measurement techniques. Fringe (i.e., structured-light) projection and two or more camera systems lead to a bulky arrangement and to shadowing effects which limit the accessibility of undercuts and thin volume fractions such as incisal edges. Moreover, they usually require powder coating of the teeth. Confocal laser scanners eliminate these disadvantages, although the three-dimensional (3D) movement of the scanner handpiece is disadvantageous with regard to scanning speed, accuracy and reliability. Intraoral scans generally contain a source of risk for inaccuracy, because multiple single 3D images are assembled to a complete model. Recent studies, however, have shown that the trueness and precision of intraoral scanners of commercially available scanning systems is already sufficient for orthodontic applications. Current development of novel scanner technologies, e.g. based on multipoint chromatic confocal imaging and dual wavelength digital holography, will further improve the accuracy and clinical practicability of intraoral scanning. Hence, it is likely that in future intraoral scanning combined with 3D printing will completely replace conventional stone models of the dental arches.