INTRAORAL SCANS FOR CAD / CAM APPLICATION
Original Article
CEREC, TRIOS) were made from a PMMA model for comparison [ 17 ]( Fig. 12).
4.1.2. Time efficiency( factor) of digital impressions We have found numerous studies comparing the time needed for digital and conventional impressiontaking techniques. When investigating the whole treatment time an average of 260 s is needed for a digital impression and 620 s for a conventional one. Bite registration with intraoral scanner took five times less than with the conventional technique [ 18 ]. Although scanning time extends when there are abutment teeth in the arch. Scanning 1 abutment is 23 minutes, 2 abutments 22 minutes and the whole arch is 13 minutes faster than conventional impression-taking. As the number of prepared teeth increases, the time of the intraoral scanning gets closer to the conventional impression-taking time. In these studies participants had experience in taking conventional impressions [ 19 ]. In Lee and Galucci’ s study dental students had no previous experience on taking impressions. Intraoral scanning took half the time of the conventional technique. Consequently, the study shows that without experience intraoral scanning is still a time saving technique. It seems that digital technology reduces patients’ time spent in the dental office [ 20 ].
4.1.3. Evaluation of the digital impression-taking procedure based on the dentist’ s and the patient ' s subjective comfort In 2016 Joda et al. investigated digital and conventional implant impression procedures. They found the usability and the efficiency of intraoral scanners more favourable by students( 88 %) and dentists( 64 %) compared to conventional methods [ 21 ]. According the previous studies patients prefer digital impressions to conventional ones. During conventional impressions patients reported breathing difficulties and they felt vulnerable, especially when upper impressions were taken. They were afraid of repeating conventional impressions rather than repeating digital ones [ 22 ]. Overall both dentists and the patients found it less stressful when impressions were taken digitally.
4.2. Intraoral scanning possibilities; advantages and difficulties In the next session we would like to introduce the features of the new technology, which can be a benefit or an initial difficulty when we use an intraoral scanner [ 23 ].
4.2.1. Difficulties of intraoral scanning Learning the process of intraoral scanning is not an easy task, it is important to follow the instructions given by the manufacturers. Digital impression taking is very different from conventional impression procedure. During scanning as the scanner-head goes above the surface of the tooth the software adds new data to the images that have already been taken. The inappropriate use leads to insufficient or inaccurate virtual model. For implant scanning scan bodies are used, which are supported by the manufacturers( Fig. 13). These scan bodies should be compatible with the
Figure 11. Fit of the final restoration depends on the quality of the impression. Accuracy consists of trueness and precision. Trueness shows how close is our data to the original true value. Precision shows the relative deviation of repeated measurements.
Figure 12. Less time is needed for a full arch intraoral scan compared to the conventional impression taking procedure.
Figure 13. Scan bodies are used for implant scanning, they provide the necessary information for designing the prosthetic appliance.
CAD software in order to plan the digital prosthetic appliance. Manufacturers have already faced the need to start production of hybrid scan bodies, which are compatible with different systems. If we are not properly informed about the scanners’ features prior to the purchase, it may be an unpleasant surprise that some companies charge a data management fee. In such a case, after scanning the data, it is entered into the cloud operated by the company, from which it can only be sent to the laboratory after payment of the fee. However, most manufacturers provide an open system, which allows to export the STL files for free. Limitation of intraoral scanners is that they are very expensive, however the cost of equipment is expected
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Stoma Edu J. 2018; 5( 2): 110-117 http:// www. stomaeduj. com