Dentists have tried to perfect the ultimate way to reproduce the intraoral condition extraorally since the early days of the profession. One only needs to study the development of articulators to gain appreciation for the different theories, and means employed to reproduce mandibular movement on a laboratory bench.
Central to recreating the intraoral condition extraorally is to have an accurate cast of the dentition and corresponding soft tissue (or strictly the edentulous ridges). Until recently, the only available means to accomplish this was by taking a physical intraoral impression, which enabled the dentist or technician to make a stone model of the teeth, gingival, and/or edentulous areas. Our predecessors used impression plaster, compound in copper bands, reversible and irreversible hydrocolloid, and polysulfide rubber base. At times they even fabricated wax patterns directly in the tooth preparation. Today, the most commonly used impression materials in the world are polyether and vinyl polysiloxane (VPS).
ERRORS IN PHYSICAL IMPRESSIONS CAN BE COSTLY
Inherent errors exist in the making of an analog impression as well as errors introduced in making the corresponding cast. Dimensional changes, in both the impression material and the stone with which the cast is made, can produce inaccuracies. Even in the best practitioner’s and dental technician’s hands, air bubbles, voids, tears, blood/saliva/other contamination, and distortion due to a variety of causes, can render a hard fought impression unusable. Pinning the dies can make unstable models. Any of these problems can result in extensive adjustments to get the proper occlusal or interproximal fit, or in the worst case, may make the impression worthless. Compounding the problem are issues that may not be readily apparent, only to be discovered in the process of remaking a restoration or appliance.
ADVANCES IN INTRAORAL SCANNING TECHNOLOGIES
Technological alternatives have existed for many years in the form of digital impression systems. The first to market in 1987 was the CEREC 1 (Siemens), which used a 3-dimensional (3-D) scanner and optical powder on the teeth to create a virtual model. The development of the infrared camera (CEREC 1) was one of the first steps in providing the profession with a digital practice experience. For nearly 20 years, CEREC was the only system capable of direct intraoral digital impression making. In addition, with the CEREC system, the practitioner could use CAD/CAM technology to fabricate one visit inlays, onlays, and crowns. Over the years, software and hardware improvements, as well as restorative material improvements have made it easier for the practitioner to make durable and aesthetic one visit CEREC restorations.
Until the recent introduction of CEREC AC powered by BlueCam (Sirona), in January of 2009, the imaging device remained unchanged. According to the manufacturer’s Web site, the latest “CEREC BlueCam captures highly detailed images using a powerful (short wavelength) blue light-emitting diode.” This technology is 2x faster than infrared scanning, and it can now be done in a few minutes.This new camera system takes exceptionally accurate images, and improves further on the previous version offered by allowing imaging of an entire arch. However, it does continue to require an optical powder medium to properly image the desired area.
More recently, a number of competitive technologies have entered the market. The E4D Dentist System, launched in 2008, also creates a finished restoration in one visit and unlike CEREC, does not require the use of a powder in most instances.
In the field of dedicated 3-D impression scanners, where final restorations are produced at the dental laboratory, there are several systems on the market:
CEREC Connect (Sirona) is a Web-based communication platform designed exclusively for use by CEREC dentists and Sirona inLab laboratories. This allows CEREC dentists to electronically transmit a digitally-scanned impression to the inLab laboratory of their choice.
Lava Chairside Oral Scanner (C.O.S.) (3M ESPE) was launched in 2008. This system produces a digital impression from a recorded video sequence and requires a light powdering. Upon completion, the impression is forwarded to 3M ESPE, where a model is created using stereolithography.
The iTero Digital Impression System (Cadent) was launched in 2006. It uses parallel confocal imaging, which utilizes laser and optical scanning to digitally capture the surface and contours of the tooth and gingival structures. The iTero scanner captures 100,000 points of laser light and has perfect focus images of more than 300 focal depths of the tooth structure. This approach, which differs from the technology employed by CEREC and 3M ESPE, does not require the need for scanning powder. The iTero images are converted by Cadent into a working model that is sent to the dental laboratory of the doctor’s choice.
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