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