What are dental impressions?
Dental impressions are ‘intraoral’ -(i.e. “within the mouth”) negative imprints of hard (e.g. teeth) and soft tissues (e.g.gums) in the mouth from which a positive reproduction (or cast) is formed as illustrated in the diagram.
A metal or plastic horseshoe shaped tray is chosen to fit the teeth and gums comfortably, over the top or bottom teeth. The tray is then filled with an impression material – alginate is the most commonly used impression material in dental practice, supplied as a powder and is mixed with water .
Dental impressions conventionally taken this way – also called indirect impressions – have, for decades, been used in prosthetic dentistry to create custom mouth guards, whitening trays, retainers, crowns, bridges, veneers, dentures and models for diagnostic study. The impression is subsequently poured in dental stone that forms the basis for the lab to manufacture these prostheses. .
History has shown problems with these conventional techniques. First, well-fitting indirect dental restorations can only be made if there are accurate models of the oral tissue. And common technical flaws include: impressions taken where a finish line is not visible; air bubbles in critical places; impressions with voids or drags; and unset impression material on the surface of the impression and/or cast . Misfits of casts from dimensional changes can result in stress forces on the underlying teeth .
For patients undergoing a dental impression, some report experiencing a gag reflex – often uncomfortable, but which is a normal, involuntary defence mechanism that serves to warn humans about foreign bodies entering the trachea, pharynx or larynx.  Still somewhat unpleasant.
Digital dental impressions
Today in 2017, conventional methods are giving way to digital dental impression techniques, and digital has excitingly come to the fore.
New advances in technology allow dentists to create a virtual, computer-generated replica of the hard and soft tissues of the mouth with the aid of lasers and other optical scanning devices. Without the mess of alginate powder. This digital technology enables the capture of clear and highly accurate impression data in minutes compared to days, and bypass traditional impression materials altogether.
With direct digitalization using intraoral scanners, an accurate digital record of the contours of the soft and hard tissues is possible and a ‘virtually perfect’ 3D model can be produced [5, 6]. The impression data is transferred to a computer and used to create restorations without the use of traditional stone models. The procedure is starts the workflow so the data collected during this phase is critical to produce a reliable and precise impression result . [7, 8]
Benefits of digital techniques
Contemporary intraoral scanners use CAD/CAM to build 3D models, combining several 3D images made of the same section of the model, but from different angles. The result is a ‘stereolithographic’ (STL) file – an industry standard file format – and when transferred to an automated production device such as a dental milling machine, enables – at the end of this e CAD/CAM workflow – the final dental prosthesis fabricated.
Digital technology, with new restorative materials e.g. zirconia, enables the patient to take advantage of a layered, deeper and more natural look when wearing the prosthesis. And a brilliant, authentic smile.
3M True Definition (TD) Scanner
There are many commercially available intra-oral scanners that employ different scanning technologies to obtain the 3D images. A recent study conducted by Guth, et al (2017)  attempted to evaluate the accuracy of a number of high-end intraoral scanners – such as (1) CS 3500 (CS), (2) Zfx Intrascan (ZFX), (3) CEREC AC Bluecam (BLU), (4) CEREC AC Omnicam (OC) and (5) True Definition (TD).
The results highlighted that the process of direct digitalization using the TD showed the significant highest overall “trueness”, followed by CS. The study found that expressing the accuracy as ‘trueness’ is a common method applied in many studies where a reference dataset is used in comparison with a test dataset for measurement of precision.
It is clear that as digital systems in dentistry become more developed, arguments for continuing with older methods will make even less sense 
Dentserve is actively integrating digital dentistry into our workflows to save time, costs and increase the accuracy of our patient treatments.
For our patients, improved efficiency (cost and time); accuracy; and a high level of predictability of outcomes mean that we can better serve you.
At Dentserve – we love caring for your smile.
- Nandini, V.V., K.V. Venkatesh, and K.C. Nair, Alginate impressions: A practical perspective. J Conserv Dent, 2008. 11(1): p. 37-41.
- Meer, W.J.v.d., et al., Application of Intra-Oral Dental Scanners in the Digital Workflow of Implantology. PLoS ONE, 2012. 7(8): p. 43312.
- Wassell, R.W., D. Barker, and A.W.G. Walls, Crowns and other extra-coronal restorations: Impression materials and technique. British Dental Journal, 2002. 192: p. 679-690.
- Al-Nuamy, K.M., Gag Problem in Dental Treatment Assessment and Methods to Control it. Al–Rafidain Dent J, 2010. 10(2): p. 27-291.
- Ahrberg, D., et al., Direct versus indirect digitalisation for CAD/CAM fabricated all-ceramic restorations: a double-blinded, randomised clinical trial. Clin Oral Invest, 2016. 20: p. 291-300.
- Rondon, N. Digital Impressions: Virtually Perfect. Consumer Guide to Dentistry [cited Jul 31, 2017; Available from: http://www.yourdentistryguide.com/digital-impressions/.
- Branemark, P., Osseointegration and its experimental background. Journal of Prosthetic Dentistry, 1983. 50: p. 399-410.
- Ongül, D., et al., A comparative analysis of the accuracy of different direct impression techniques for multiple implants. Australian Dental Journal, 2012. 57: p. 184-189.
- Güth, J.-F., et al., Accuracy of five intraoral scanners compared to indirect digitalization. Clin Oral Invest, 2017. 21: p. 1445-1455.