History and Evolution of digital impression systems

Fabrication of models from impressions had been there since 18th century. 9, 10 In 1856 Dr. Charles Stent9 used an impression material for fabrication of device under his name for correction of oral deformities. Sears11 introduced agar- impression material for crowns. Impregum – 1st polyether elastomeric material was introduced by ESPE in 1965.12

Condensation Silicone was developed but the drawbacks were dimensional inaccuracy. With the advent of Polyvinyl Siloxane it solved many of the problems like modulus of elasticity, dimensional accuracy, tear strength, poor odor, taste and superior flow. 12

CAD/CAM(Computer Aided Design/Computer Assisted Manufacturing) had been used since 1960’s in the manufacture of airplanes and automobiles. The First application of CAD/CAM in dentistry was by Dr. Francois Duret in 1970’s in his thesis “Optical Impression”. In 1984, Duret invented and patented a CAD/CAM device and illustrated the crown fabrication in 4 hours. At the same time, Dr. Mormann and Dr. Brandestini originated, the first profit oriented digital impression system the CEREC1, in 1985. 13

CEREC 1 combined a 3-dimensional (3D) digital scanner with a milling unit to create dental restorations from commercially available blocks of ceramic material in a single appointment. CEREC 1 was designed for the fabrication of ceramic inlays and Onlays. Dr. Mormann also licensed today Sirona Systems. Cerec 2, cerec 3, cerec 3D were introduced in 1994, 2000 and 2003.12

Conventional vs Digital Impressions

Abutment – tray selection – gingival retraction – impression – disinfection – laboratory shipping – cast pouring – restoration fabrication 14

Abutment – gingival retraction – scanning – digital transfer of impression to lab – digital designing – restoration fabrication 14

IOS technologies

IOS is composed of a camera that is handheld, computer and software. The goal is to record three-dimensional geometry of an object with precision. STL(Standard Tessellation Language) is the extensively used digital format. Other formats include PLY files, Polygon File Format. Regardless of imaging technology used by IOS. After identification of POI (point of interest) software assembles individual images or videos recorded by the camera under a light projection.15

Light Capture and Projection: In 3d reconstruction field there are two techniques. Active and Passive techniques, Active techniques involve Triangulation a procedure and uses red, white or blue light for real texture and color of tissues for reconstruction by projecting the light from the camera onto an object. Intraoral tissues are illuminated only by ambient light and reliant to a certain level of the texture of the object in passive technique.16, 17

Laser Confocal microscopy Scanning: It is a microscopic technique for scanning 3-dimensional objects by fluorescent microscopy. Marvin Minsky in 1957 introduced the basic principle in confocal scanning. 14

Optic triangulation: It is a method of measuring object to the distance without touching them in microns to millimeters. 14

Optical coherence tomography: It uses light instead of sound, and it is similar to ultrasound imaging. 14

Active Wavefront Sampling (AWS): Active wavefront sampling (AWS) is a surface imaging technique, which uses only a single camera and optical path. 14

Various Commercially available Scanning systems

iTero

Cadent inaugurated iTero in 2007 later it is obtained by Align Technology, Inc in 2011. It utilizes Confocal parallel scanning microscopy principle.18

Lythos

Ormco Corporation inaugurated Lythos in 2013. It utilized Accordion Fringe Inferometry principle, specially designed for Orthodontic purpose.20

Fast Scan

Glidewell laboratories, IOS Technologies inaugurated Fast Scan in 2010. It utilizes the active triangulation principle.16

Plan scan

E4D Technologies(Richardson introduced Planscan in 2008 It utilizes Optical Coherent Tomography principle.16

True definition

3M ESPE inaugurated True definition scanner in 2013. It utilized 3D in-motion video imaging technology.18

Trios

3Shape inaugurated Trios in 2010 It utilizes confocal microscopy principle.16

CS 3500

Care stream Dental inaugurated CS 3500 in 2013. It utilizes confocal microscopy principle.16

CEREC and Apollo systems

Sirona Dental System introduced CEREC in 1987. It utilizes Active Triangulation and Confocal Microscopy principle.23, 24

Accessories: Currently three digital systems are available which include

CEREC Omnicam produces full arch and half arch impressions with full color, 3D and 2D images. It has a small camera tip, handpiece with a rounded camera tube. The clearance between scanner and tooth must be 0 to 15 mm.16

CEREC Bluecam has a blue light-emitting diode for detail capturing. It can be used for scanning full jaw, quadrant and a single tooth. The camera is placed directly over the tooth.16

Apollo DI utilizes Apollo DI software and Apollo DI intraoral camera. These scans are black and white and the camera is mover 2-20mm over the tooth surface during scanning.16

Advantages

Minimizes discomfort: Digital impressions by IOS minimizes the transient discomfort by the placement of impression materials and trays in the patient mouth.25 It terminates the use of impression trays, materials, etc. As per literature reports patients to opt to optical impressions rather than conventional impressions.26

Time-saving: Through the scanning of the patient's soft and hard tissues chairside time is reduced. Time-consuming procedures like pouring the casts etc. are eliminated.27

Easier workflow: Procedure of impression is simplified for complex cases for example severe undercuts, multiple implants which enable conventional impression procedure difficult, and the procedure for repeating the impression is easier without remaking the entire procedure. 28, 29

Communication with Laboratory Personnel: IOS enables the clinician to communicate with the laboratory personnel instantaneously after the scan, if the laboratory personnel is not satisfied clinician can make an instant remake of the scan without a second appointment for the patient. 25, 28, 29

Improved Patient relationship: With the advent of IOS the relationship between the clinician and the patient was improved and the patient is more involved in the workflow and has a positive outcome on overall treatment. 25, 28, 29

Disadvantages

Sub-gingival margin detection: There was a problem of detection of deeply placed gingival margins and also IOS scanning is a little bit troublesome in case of bleeding as it may conceal the prosthetic margins and makes the scan inaccurate.30 IOS cannot displace the soft tissue margins and cannot register dynamic tissue relationships.31

Learning Curve: Learning Curve adaptation for IOS is difficult for Older Clinicians with less desire and experience with computers and technology. Also, it is important to note that there is a debate on which scanning technology is better than the other, as there was little information provided by the manufacturer. 32

Cost-sensitive: The initial purchase costs of IOS are very high, even after the release of many new models into the market.25, 30

Also, additional managing costs like software up-gradation, etc were also present. In addition to the above, the laboratory personnel also must be familiar with digital workflow.25, 30