Technology

The evolution of technology in dentistry has made a significant impact on orthodontic diagnosis, treatment planning, and treatment. Digital photos, radiographs, and record keeping have all become commonplace in many orthodontic practices. The use of digital records improves communication between practitioners and makes it easier to store information. Most records taken for orthodontic diagnosis are 2 dimensional, providing limited information to the practitioner. The majority of 3 dimensional information is collected via clinical examination and models.

The use of digital models now provides practitioners the ability to evaluate the dentition in three dimensions, while improving storage capabilities (Figure 6). A number of methods exist for generating digital models including holographic scanning, stereophotogrammetry capture, phase-shifting optical triangulation and cone-beam computed tomography (CBCT). The models can be made by scanning the teeth intraorally, scanning polyvinyl siloxane or alginate impressions and bite registrations, or scanning the actual plaster or stone models. Companies providing such services include OrthoCAD™, RexcanDS™, and OrthoInsight™. OrthoCAD™ uses alginate impressions of both dentitions combined with a bite registration to generate the 3 dimensional digital study models. Digital models have improved diagnosis by making it possible to measure teeth digitally and generate tooth size analyses quicker and with more ease.84 Using models generated via laser scanning for tooth size measurements has been found to be similar to measurements on plaster casts.85 These models can also be used to fabricate appliances84 and for indirect bracket set ups86 when appropriate model quality is achieved.

Figure 6.
Example of models generated via alginate impressions mailed to OrthoCAD
Example of models generated via alginate impressions mailed to OrthoCAD™.

The use of cone beam computed tomography (CBCT) has become increasingly more common in recent years in the orthodontic field. CBCT has been noted as being particularly useful in cases with impacted teeth, skeletal asymmetries, suspected temporomandibular joint changes, suspected airway problems, and various pathologies.87 When evaluating airway, CBCT allows a 3 dimensional rendering, allowing one to determine the antero-posterior and transverse dimensions and come up with a volumetric assessment (Figure 7). This is one area with surrounding controversy, as no method has been developed to standardize how this is measured.88

Figure 7.
Example of an airway assessment using a CBCT in InVivo software
Example of an airway assessment using a CBCT in InVivo™ software.

CBCT can also be used to evaluate inclination of the teeth and their boney support in the transverse and antero-posterior dimensions by looking at slices of the image. A method has been developed to use CBCT to evaluate the fusion of the midpalatal suture.89,90 It has also been determined that while CBCT can be helpful in determining the presence of fenestrations and dehiscences on anterior teeth, it may result in overestimation (Figure 8).91 CBCT can also be used to develop digital models. The accuracy of models generated from CBCT in orthodontic treatment is unclear and requires further research.85 Some literature has claimed that the accuracy of the tooth crown from models generated by CBCT is low in comparison to the accuracy of the roots from CBCT or of the tooth crowns in laser generated models.92

Figure 8.
Evaluation of boney support of the lower incisors using a localized CBCT in KODAK software
Evaluation of boney support of the lower incisors using a localized CBCT in KODAK™ software.

Intraoral scanning is another major area of development in digital orthodontics (Figure 9). Some of the current scanners on the market include the iTero® Element™ by Align Technology, Trios® by 3shape, and CS 3500 by CareStream. Models generated from intraoral scanners have been found to have similar accuracy to those made from alginate impressions.93 Some of the benefits of using an intraoral scanner include less retakes of impressions, improved patient comfort, and quicker turnaround time for obtaining digital models. Another advantage is the ability to send the model digitally to an orthodontic lab for appliance fabrication, which greatly shortens the time needed between appointments. There are currently four different ways that scanners obtain information to generate the digital models. These are triangulation, parallel confocal, accordion fringe interferometry, and three-dimensional in-motion video. Some units also require an extra step of powdering the teeth.94

Figure 9.
Initial appearance of an iTero scan
Initial appearance of an iTero® scan prior to processing for Invisalign™.

Stereolithographic (STL) files holding the digital model information can be used to 3D print models. Current technology methods used to print include stereolithography, fused deposition modeling, digital light processing, and polyjet photopolymerization. Currently the Objet30 OrthoDesk, Ultra® 3SP®, and the MakerBot Replicator 2 are 3D printers available for orthodontic office use.95 While the cost of these machines and their materials are currently high, several orthodontic laboratories also have the ability to print models for a much smaller fee. 3D printing is projected to become more common and more affordable in the future, and will likely evolve in similar ways to the evolution we have seen thus far with CBCT and intraoral scanners.