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Prosthodontics

Authors: Dr. Nabeel, Dr. Sameera Y, Dr. Rathika Rai

Abstract

Modern day Prosthodontics has set its foot firm on the concept of digitization. With the evolution of technology in all fields of life, the dental science is also turning it up by incorporating digital treatment protocols in regular dental procedures. Compared to conventional clinical procedures these digital alternatives are convenient for the dentist to perform and provide a comfortable experience to our patients. One such advancement is the digitizing the process of making a dental impression. This article describes the evolution, working principal, workflow, benefits and drawbacks and the shortcomings of digital dental impressions.

Key Terms: Digital Dentistry, Digital Impression, CAD-CAM

INTRODUCTION

Today’s era has seen the world move towards a faster, easier and convenient mind set. Dentistry also has seen a rapid shift towards this convenient mind set. With the advent of technology, gone are those days when dentists had to rely on laboratory and clinical manpower to run the show. We dentists have shifted to fancier gadgets that enable us to provide comprehensive care to our patients in a fastest and most convenient possible way. The basis of most of these revolutionary innovation has been the incorporation of CAD CAM (Computer aided designing – Computer aided machinery) in everyday dental practise, so much that among dental fraternity CAD – CAM is now being referred to as Computer aided Dentistry – Computer aided Manufacture. Among the numerous innovations that have eased the work of the dentist and convenient for the patient is the digital impression. From using impression trays we have shifted to these sophisticated sensors which are convenient to both the dentists and their patients.

EVOLUTION

As early as 1970, Duret explored how digital technology could be incorporated into dentistry, and in 1987, Mormann introduced the first chair-side CAD/CAM system, CEREC 1.1

The first intraoral scanner came to the market about 20 years ago however; the popularity of these systems in regular dental practice is very recent. In the last few years, multiple new brands of intraoral sensors have been developed and introduced in the market.2

CONVENTIONAL VS DIGITAL IMAGING

Accurate impressions depend on proper technique and materials. Elastomeric impression materials (polyethers, polyvinyl siloxanes, and hybrids) are popular because of their excellent physical and mechanical properties, including precise detail reproduction, high elastic recovery, and dimensional stability.

The decision to use one over the other varies among clinicians and is based upon personal preference. Although it is clear that elastomeric materials have improved over the years, their use continues to present some challenges.

Traditional impression technique involves multiple steps, which increase the chances of error.3 Patient comfort is a major concern due to tray accuracy, taste and odour of impression material and time of the impression procedure. Consequently, digital impressions provide an alternative to overcome some of the obstacles seen with conventional impression materials and

techniques. Studies have shown that restorations fit more accurately with digital impressions compared to conventional impressions.4 The technological advancement is so good that it has now almost eliminated the need for conventional impression materials and techniques, also from the patient’s perspective, increasing comfort and decreasing apprehension.5

Apart from basic crown and bridge and restorative work, literature has proven that digital impressions are now also being used for construction of maxillafacial prosthesis.6 Also, the accuracy of these prosthesis have proven to be better than the conventional impression techniques. A case study by Elbashti et al evaluated the feasibility and accuracy of using an intraoral scanner to digitize edentulous maxillectomy defects. The study included a total of 20 maxillectomy models for which conventional and digital impressions were made using silicone impression material and a laboratory optical scanner as well as a chair-side intraoral scanner and the 3D data were analyzed using 3D evaluation software. The study concluded that digitizing edentulous maxillectomy defect models using a chair-side intraoral scanner appeared to be feasible and accurate.7

Some systems require the use of titanium dioxide powder as a contrast medium, whereas others do not. Data collection methods, strategies, and size of scanner head may vary between scanners, but each procedure culminates in a digital model of the patient’s dentition.

What will digital impressions help avoid?
  • Impression trays and tray selection
  • Impression material
  • Strenuous impression procedure
  • Dental casts
  • Patterning and Investment materials
  • Casting procedure and finishing
What will digital impressions involve?
  • Intra-oral scanner
  • Designing software
  • CAD-CAM machinery
WORK FLOW

Compared to the strenuous procedure in fabricating a restoration with the conventional work flow, the digital work flow is much simpler as major technique sensitive steps can be avoided during the fabrication process (Fig.1). Rather than the avoiding it can be said that most of the steps are now carried out in human free environment. Post tooth preparation the steps in digital fabrication of the restoration are as follows:

  • Application of contrast spray
  • Digital scanning of prepared tooth
  • Digital scanning of occluding tooth
  • Pattern fabrication on CAD-CAM machine
  • Milling / Printing
STRUCTURE AND WORKING PRINCIPLE

The Device works on the principle of triangulation. The light source and the receptor unit are positioned at defined angulations to emit and receive the light rays (Fig. 1).8

The device contains a light source which produces optic light rays. These light rays are collimated to produce a beam which is reflected and exits the device through the head. The efferent light rays are reflected off the surface of the tooth and form the afferent light rays. These afferent light rays enter the device and are reflected through a series of mirrors and finally reach the sensor camera.

 
DATA FILES AND DESIGNING

There are two important categories of digital impression systems in terms of data files created during scanning.

  • The open architecture [ Standard Tessellation Language (STL File)]
  • The Closed architecture.

Open-architecture files, typically termed STL files, are not dependent on the manufacturer, and can be used in virtually any design software to fabricate a final restoration.9 For example, data obtained by an “open” scanner can be designed and milled (CAD/CAM) with many different systems, regardless of manufacturer. For laboratories that are skilled in customizing their own settings or configurations, open architecture offers more potential business opportunities. For example, a laboratory with an open-architecture digital impression system may become an outsourcing partner for other laboratories or choose to integrate new interfaces with emerging CAD software platforms.10 Open-architecture systems allow individual dentists to work with several different laboratories and maximize the potential of their investment with options such as implant restorations and orthodontics.

Closed-system software architecture collects and manipulates data by the same manufacturer, offering laboratory owners security and a one-stop shop for resolving problems. One company controls both the CAD and CAM configurations, knows the milling unit’s performance specifications and capabilities, and is able to adapt the CAD and CAM software accordingly.11 For example, using Sirona Connect, participating Sirona Connect laboratories can receive files from any CEREC® device, design and mill on an InLab system (Sirona), and deliver a restoration to a dentist using CEREC. Manufactures always insist on closed architecture files for better accuracy and ease of use

AVAILABLE SYSTEMS
  1. CEREC® – Sirona Dental System
  2. iTero – CADENT
  3. E4D –D4D TECHNOLOGIES, LLC
  4. Lava™C.O.S. – 3M ESPE
  5. IOS FastScan – IOS TECHNOLOGIES, INC.
  6. DENSYS 3D – DENSYS LTD.
  7. DPI-3D – DIMENSIONAL PHOTONICS INTERNATIONAL, INC.
  8. 3D Progress – MHT S.p.A. (IT) and MHT Optic Research AG
  9. DirectScan – HINT - ELS GMBH (DE) 10.
ACCURACY

A study by Quimby et al determined the accuracy, reproducibility, efficacy, and effectiveness of measurements made on computer-based models with a plastic model occlusion as control. The study concluded that, measurements made from computer-based models appeared to be generally as accurate and reliable as measurements made from plaster models. Efficacy and effectiveness were similar to those of plaster models.12

However, accuracy depended on the quality of the digital scanner used. An invitro study by Schaefer et al investigated the effect of digital impression procedures in three dimensional fit of ceramic partial crowns. The study compared digital impressions were taken using iTero (ITE), cara TRIOS (TRI), CEREC AC with Bluecam (CBC), and Lava COS (COS) systems, and restorations were designed and machined from lithium disilicate blanks. The results revealed that mean marginal (internal) discrepancies were, ITE 90 (92) mm, TRI 128 (106) mm, CBC 146 (84) mm, and COS 109 (93) mm and concluded that, marginal and internal fit of milled lithium disilicate partial crowns depended on the employed digital impression technique.13

However, some studies showed that when conventional impression techniques were combined with newer crown fabrication technology, the results proved to be better than digital impressions. A study by Anadioti et al evaluated the 3D and 2D marginal fit of pressed and computer-aideddesigned/ computer-aided-manufactured (CAD/CAM) all-ceramic crowns made from digital (Lava C.O.S.) and conventional (poly vinyl siloxane) impressions. The result concluded that combination of PVS impression method and press fabrication technique produced the most accurate 3D and 2D marginal fits.14

EASE OF USE

The ease of usage of the technically challenging digital impressions however, is perceived differently between different age groups. A study by Lee et al to evaluate the difficulty level and operator’s perception between dental students and experienced clinicians when making digital and conventional implant impressions concluded that in a VAS score of 0-100 the student group scored a mean difficulty level of 43.1 for the conventional impression technique and 30.6 for the digital impression technique. On the other hand, the clinician group scored a mean difficulty level of 30.9 for conventional impressions and 36.5 for digital impressions. As far as the preference to the technique 60% of the students preferred the digital impression while only 33% preferred the digital impression.15

PATIENT PERSPECTIVE

On a broader perspective it is obvious that patients will be inclined towards the more comfortable digital impression. Patient satisfaction is one of the core concepts considered in development of technology in dental practise. A study by Wismeijer et al measured patient’s perception of the difference between a conventional and an intra-oral scan concluded that the preparatory activities, taste of the impression material and overall preference of the patients were significantly in favour of the intra oral scanned impressions.16

Wismeijer D, Mans R, Genuchten M, Reijers HA. Patients’ preferences when comparing analogue implant impressions using a polyether impression material versus digital impressions (Intraoral Scan) of dental implants. Clinical oral implants research. 2014 Oct 1;25(10):1113-8.

COST ANALYSIS

Cost although is a deciding factor in selection of impression technique, on a long term basis digital impressions have proven to be more economic than the conventional impression procedures. A prospective cohort was performed by Tim Joda and Urs Bragger analysed cost for implant-supported singleunit reconstructions in the digital workflow compared to the conventional pathway, where a total of 20 patients were included for rehabilitation [costs was measured in Swiss Francs (CHF)]. The results of the study showed that, treatment costs were significantly lower for the digital workflow 1815.35 CHF compared to the conventional pathway 2119.65 CHF and the an 18% cost reduction within the digital process.17

CONCLUSION

Digital impressions today have been very useful to us by providing a platform to the dentists and laboratory technicians by enabling us to achieve greater accuracy in our restorative procedures. As far as the patient’s perspective is considered, saving time and a lot lesser mess is what inclines them towards the newer digital methods of impression making. Ultimately the target of any development in the dental field is to provide better patient care and it can be said with authority that these digital impressions have achieved what they were intended to do. However, the initial installation cost of the digital scanner being high, have put a barrier in the unified use of this modern tool. One should consider that on a long run the digital impressions will be more economical than the conventional methods of impression.

REFERENCES
  1. Bunek S, Brown C, Yakas M. The evolving impressions of digital dentistry. Inside Dentistry. 2014;10(1):30-9.
  2. Logozzo S, Franceschini G, Kilpelä A, Caponi M, Governi L, Blois L. A comparative analysis of intraoral 3D digital scanners for restorative dentistry. The internet journal of Medical Technology. 2011;5(1).
  3. Powers JM, Wataha JC. Dental materials: properties and manipulation. 10th ed. St. Louis, MO: Mosby Elsevier; 2013
  4. Farah JW, Brown L. Comparison of the fit of crowns based on digital impressions with 3M ESPE Lava Chairside Oral Scanner C.O.S. vs. traditional impressions. The Dental Advisor Research Report. 2009;(22):1-3.
  5. Lowe R. CAD/CAM dentistry and chairside digital impression making. http:// intl.invisaligngallery.com/wp-content/uploads/2012/01/Cad-Cam-Dentistry-and- Chairside-DigitalImpression-Making-by-Dr-Bob-Lowe-062609.pdf. Accessed September 11, 2013.
  6. Park JH, Lee KS, Lee JY, Shin SW. Fabricating a Maxillary Obturator Using an Intraoral Digital Impression: A Case History Report. The International journal of prosthodontics. 2017;30(3):266.
  7. Elbashti ME, Hattori M, Patzelt S, Habil MD, Schulze D, Sumita YI, Taniguchi H, Patzelt SB. Feasibility and Accuracy of Digitizing Edentulous Maxillectomy Defects: A Comparative Study. International Journal of Prosthodontics. 2017 Mar 1;30(2).
  8. Wu Q, Bin HU, Gong X, Li J, Jianpang ZH, inventors; Shenzhen University, assignee. Intra-oral scanner for digital impression and real-time reconstruction system for inner surface topographic image of oral cavity. United States patent US 9,149,348. 2015 Oct 6.
  9. Fasbinder DJ. CAD/CAM. Inside Dentistry. 2011;7(7):82.
  10. Brown C. Major factors to consider before making a CAM milling machine purchase. Inside Dental Technology. 2011;2(2):52-54
  11. Feuerstein, P. An overview of CAD/CAM and digital impressions. In: Feuerstein P, Puri, S. CAD/CAM and digital impressions. www.ineedce.com/courses/1593/ PDF/CAD_CAM_DigitalImpressions.pdf. Accessed September 11, 2013.
  12. Quimby ML, Vig KW, Rashid RG, Firestone AR. The accuracy and reliability of measurements made on computer-based digital models. The Angle orthodontist. 2004 Jun;74(3):298-303.
  13. Schaefer O, Decker M, Wittstock F, Kuepper H, Guentsch A. Impact of digital impression techniques on the adaption of ceramic partial crowns in vitro. Journal of dentistry. 2014 Jun 30;42(6):677-83.
  14. Anadioti E, Aquilino SA, Gratton DG, Holloway JA, Denry I, Thomas GW, Qian F. 3D and 2D marginal fit of pressed and CAD/CAM lithium disilicate crowns made from digital and conventional impressions. Journal of Prosthodontics. 2014 Dec 1;23(8):610-7.
  15. Lee SJ, MacArthur RX, Gallucci GO. An evaluation of student and clinician perception of digital and conventional implant impressions. The Journal of prosthetic dentistry. 2013 Nov 30;110(5):420-3.
  16. Wismeijer D, Mans R, Genuchten M, Reijers HA. Patients’ preferences when comparing analogue implant impressions using a polyether impression material versus digital impressions (Intraoral Scan) of dental implants. Clinical oral implants research. 2014 Oct 1;25(10):1113-8.
  17. Joda T, Brägger U. Digital vs. conventional implant prosthetic workflows: a cost/time analysis. Clinical oral implants research. 2015 Dec 1;26(12):1430-5.

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