INTRAORAL SCANS FOR CAD / CAM APPLICATION idea was to make restorations without the need for dental laboratory. A chairside system means that every step of the workflow is in the hands of the dentist. Digital impressions are taken in the dental office with an intraoral scanner, designing the restoration is done chairside and even the milling and finishing is done in the office. Its great advantage is that it offers One Day Dentistry. Inlays, onlays, solo crowns can be made for patients within a few hours. Monoblocks restorations are milled with the CAM unit, which need small adjustments( staining, polishing, sintering) before cementation. The main difference between those restorations milled by labside and chairside systems are the extension and the materials used. Chairside systems are made for solo restorations as mentioned before( veneers, crowns, inlays, onlays, small full contours), and temporaries. Labside milling in the dental laboratory or in the milling centres offers you more options due to the precision of 5-axis milling and high-strength materials, labside offers extended prosthetic appliances.
4. Discussion 4.1. Features of taking digital impressions- accuracy, time factor, patient’ s comfort There are numerous factors that can easily describe the clinical use of the digital impression procedure. The investigation of some of these factors can be measured objectively, for example accuracy and scanning time. This is a well-researched area in literature. Other features of intraoral scanners can be described with subjective parameters for example patient’ s comfort and dentist’ s satisfaction.
4.1.1. Accuracy of digital impressions The fit of the final restoration depends on the quality of the impression, therefore accuracy of intraoral scanners is one of the most important features. Accuracy consists of trueness and precision. Trueness describes how close our data are to the original true value. Precision shows the relative deviation of the repeated measurements [ 10 ]( Fig. 11). In a blind study, crowns developed using intraoral scanning technology were preferred over crowns generated using conventional impressions and criteria of marginal fit, contacts, occlusion, and time of adjustment in nearly 70 % of cases [ 11 ]. It was found that digital quadrant impression methods achieve a level of precision, comparable to the conventional impression techniques( precision ranged from 18.8 to 58.5 μm). However, there are significant differences in terms of absolute values and deviation pattern [ 12 ]. The direct digitalisation with Lava C. O. S. showed statistically significantly higher accuracy compared to the conventional procedure of impression-taking and indirect digitalisation when datasets were generated and superimposed by a best fit algorithm. It could be shown that direct digitalisation accomplished the most accurate results, followed by digitized polyether impression, and indirect digitalisation [ 13 ]. According to a study in 2015 the following scanners were found acceptable in clinical practice when
scanners were evaluated in terms of trueness and precision( an acrylic model with the embedded typodont teeth was scanned and datasets were superimposed): 3Shape trios, 3M True Definition, iTero, CS3500, CEREC Omnicam, Planmeca, Planscan [ 14 ]. The accuracy of virtual data gained from intraoral scanners is influenced by many factors. For example, the palatum and toothless areas do not give enough information to make a useful digital model [ 15, 16 ]. Virtual models obtained by digital impressions were shown to be more accurate than their conventional counterparts when Polyvinyl-siloxane impressions and digital impressions with three intraoral scanners( iTero,
Figure 7. Polymer model made by 3D printing from digital data.
Figure 8. Polymer models are printed with pins holding the ICP position and mounted on an adjustable articulator for veneering.
Figure 9. CAM / Computer Assisted Manufacturing: Blocks for zirconiumdioxide frameworks, lithium disilicate monolithic restorations and PMMA temporary restorations.
Figure 10. PMMA block manufactured in Roland DG DWX-50 milling machine. Advantage of PMMA temporary restorations fabricated by CAD / CAM technology is that they last long. Polymer’ s resistancy is much better than temporary materials used for conventional chairside technique.
Original Article
Stomatology Edu Journal
113