The Current State of Chairside Digital Dentistry and Materials

This article describes and illustrates the current state of chairside computer-aided design computer-aided manufacturing technologies and materials. It provides a historical background and discusses the different components of the chairside digital workflow: intraoral scanners, design software, milling machines, and sinter furnaces. The material range available for chairside digital dentistry is broad and includes polymethyl methacrylates, composite resins, and a large variety of ceramics. Clinical applications and success rates of the different material groups are summarized and discussed based on the current scientific evidence.

Key points

  • Chairside computer-aided design (CAD) computer-aided manufacturing (CAM) technologies have emerged into user-friendly and patient-friendly, versatile, and accurate clinical assets.

  • Current intraoral scanning technologies are as accurate as, or even more accurate than, conventional impression techniques, at least for single-span and short-span multiunit restorations.

  • Design software has been simplified with excellent features to produce natural esthetics and function.

  • Milling machines have become smaller, more accurate, and more versatile for a large variety of materials.

  • Most modern materials fabricated in the laboratory can also be fabricated chairside in a single visit: composite resins and various types of ceramics, even zirconia.

Introduction

Computer-aided design (CAD) computer-aided manufacturing (CAM) systems were initially developed in 1950 by the defense arm of the United States Air Force for use in aircraft and automotive manufacturing. It took 3 decades until such technologies were applied in dentistry, when Francois Duret developed a dental CAD/CAM device that included an optical impression of the abutment tooth and a numerically controlled milling machine. The first restoration was milled in 1983 and the system demonstrated at the French Dental Association’s International congress in November 1985. Werner Mormann is known as the developer of the first commercial CAD/CAM system: CEREC (Dentsply Sirona), an acronym for ceramic reconstruction or chairside economical restoration of esthetic ceramics. The first CEREC chairside treatment was performed in 1985 at University of Zurich Dental School. That this system could, based on an optical scan, fabricate indirect same-day ceramic dental restorations in the dental office was revolutionary.

Laboratory-based CAD/CAM systems that included an optical or mechanical scan of a master cast, digital restoration design, and a CAM system either in the dental laboratory or a centralized milling center followed shortly. In the meantime, digital planning, design, and manufacturing technologies have been the common standard in dental laboratory technology for many years now. The digital work flow and its manufacturing components provide high accuracy and precision, predictability, efficiency, cost-effectiveness, and a wide range of restorative and prosthetic materials with physical, optical, and biological properties that often exceed those fabricated conventionally. Digital tooth design and treatment planning have changed fundamentally. Independent of the wax-up skills of the practitioner or the dental technician, so-called digital wax-ups allow the use of scan files of natural teeth and smiles and, therefore, the ability to mimic nature. Combined with current face-scanning technologies, artificial intelligence and machine learning tools will allow automated generation of individual digital smile designs and treatment plans in the near future.

Early CAD/CAM systems were limited to fabricating inlays, onlays, and single crowns. Now, with the plethora of CAD/CAM technologies, systems, milling machines, and other tools available, there is virtually no limit to the type of dental restoration that can be fabricated, from single-unit inlays, onlays, crowns, veneers, implant abutments, and restorations to fixed and removable dental prostheses for partially and completely edentulous patients. Although currently the most prominent method of fabrication is subtractive through milling processes, additive technologies such as three-dimensional (3D) printing are becoming increasingly popular and are already applied for printing models, impression trays, night guards, surgical guides, orthodontics aligners, dentures, provisionals, and other devices. With the development of better printers and additional restorative materials in the future, 3D printing may well become the manufacturing process of choice.

The spectrum of restorations that can be fabricated with a chairside system depends on the size of the milling machine, the size of the material block, and the properties of the selected material. However, the lines between chairside digital manufacturing and laboratory-based CAD/CAM technologies have become blurred. Most chairside systems provide the possibility to send a scan file to any manufacturing site with the option to either produce a restoration in the office, often within minutes, or delegate this responsibility to the dental laboratory. The material choices for both options are increasing steadily, ranging from composite resins and polymethyl methacrylates (PMMAs) to silica-based and high-strength ceramics such as zirconia. Many laboratories mill wax or acrylic pattern resin copings and frameworks for casting metal alloys.

Despite its advantages, common application of chairside CAD/CAM technology has not yet been fully embraced by the dental community. The main reasons cited for that are related to high initial and maintenance cost, a steep learning curve, and the need to change procedures that practitioners have learned in dental school and become used to.

Chairside computer-aided design computer-aided manufacturing systems

The list of intraoral scanners, milling machines, sintering furnaces, 3D printers, and other CAD/CAM equipment available on the market is growing exponentially at an unexpected rate. At present, the 2 most popular systems that offer the entire range of equipment from scanning to in-house milling are CEREC (Dentsply Sirona, York, PA) and Planmeca (Planmeca Oy, Helsinki, Finland). The current portfolio of the CEREC system includes the CEREC Omnicam scanner and CEREC MC, X, and XL 4-axis milling units. These milling units can accommodate material blocks of up to 20 mm (MC), 40 mm (MCX), or 85 mm (MCXL) and mill either wet or dry. The Planmeca chairside work flow offers the Emerald camera and the PlanScan intraoral scanner in combination with the PlanMill 40s or the smaller PlanMill 30s milling machine. Other manufacturers that offer total chairside solutions are Carestream Dental (Atlanta, GA) with the CS 3600 intraoral scanner and the CS 3000 milling machine, Dental Wings (Montreal, Canada) with its DW IntraOral scanner and the DW Lasermill, and Zfx (Dachau, Germany) with the IntraScan scanner and the Inhouse5x milling unit.

Several manufacturers offer various components of the chairside digital workflow; for example, 3Shape (Copenhagen, Denmark) with its popular Trios 3 Wireless scanner or Ivoclar Vivadent (Schaan, Liechtenstein), which recently introduced the PrograMill One chairside milling machine.

Tooth preparation

Keeping in mind the type of restoration material used, mostly brittle ceramics, and that different milling parameters, such as size of bur, greatly affect the internal fit of the ultimate restoration, any abutment tooth preparations intended for CAD/CAM restorations should provide adequate space and be rounded. Sharp corners and edges are not likely to be properly represented in intaglio surfaces of the restoration. Inadequate space and thin margins may lead to fractures. The preferred preparation finish line design is an internally rounded shoulder or a chamfer. It was shown that the preparation quality has a direct effect on the marginal fit of chairside CAD/CAM crowns.

A provisional restoration becomes unnecessary when the complete chairside approach is applied and the definitive restoration is fabricated and inserted in 1 visit. The clinician may choose to immediately seal the prepared dentin tooth surfaces with a bonding agent (immediate dentin sealing technique), even before scanning.

Intraoral scanners

Different technologies are used to obtain a digital impression of teeth and surrounding intraoral tissues. These technologies are constantly updated and refined, and so are the actual scanners to make them smaller, user and patient friendly, as well as easy to navigate and handle in the oral cavity. A strategic scanning technique that subsequently captures all areas and angles has to be used and become routine for maximum scanning efficiency and quality outcomes. Current intraoral scanners do not require the once-necessary antireflective powder and have the ability to scan colors as well as determining tooth shades. Besides eliminating uncomfortable aspects of a conventional impression, one of the great advantages of intraoral scanning is that select areas that may not have been adequately captured can simply be rescanned without having to retake the entire impression.

Intraoral scanners function by projecting structured light (white, red, or blue), which is recorded as individual images or video and compiled by the software after recognition of specific points of interest. Different coordinates are used, the first 2 (x and y) of each point are evaluated on the image, and the third coordinate (z) is then calculated depending on the distance of each object to the camera. A 3D model is then generated by matching the points of interest taken under different angles. Extreme points can also be statistically eliminated to reduce noise.

The accuracy of the restorations is independent of the impression technique, analog or digital. However, the time needed for taking a digital impression is less than that for a conventional impression. In addition, patients clearly prefer the digital scan. It is also interesting that dental students favored the scans rather than traditional impressions, whereas trained clinicians were split evenly regarding their preferences. This finding may be related to habits and experience with a technique they were familiar with since dental school.

Digital full-arch impressions taken with an intraoral scanner seem to have slight deviations in respect to cross-arch accuracy. Other researchers found similar accuracy levels for full-arch scans between scanners. A recent literature review concluded that, currently, the literature does not support the use of intraoral scanners for long-span restorations on teeth or implants and that there are still areas in respect to digital impressions of dental implants that need further investigation. However, new intraoral scanning technologies, such as photogrammetric imaging, allow high accuracy even for full-arch implant restorations.

Because chairside-fabricated CAD/CAM restorations are typically limited to single-span or short-span units, the questions related to long-span restorations on multiple teeth and implants may not be critical. However, scanning technique and sequence also play a major role in the accuracy of the scan. When properly applied, the digital impression technique seems to be more accurate than a conventional impression. Fig. 1 depicts the clinical application of an intraoral scanner.

Fig. 1
Intraoral scanners have become significantly smaller as well as user and patient friendly.

In the past, intraoral scanners were connected to mobile carts as a complete unit with the computer and monitor. More recent versions of scanners are connected directly or wirelessly to a laptop computer. Companies that produce scanners as well as dental chairs offer the option of incorporating the scanner into the dental chair.

Computer-aided design computer-aided manufacturing design software

The ability to visualize and analyze digital impressions immediately after scanning is one of the key advantages of the chairside work flow ( Fig. 2 ). Unlike conventional impressions, where errors are often only detected after fabricating the mastercast, an erroneous or deficient digital impression can be analyzed and corrected immediately. Specific software (eg, PrepCheck, Dentsply Sirona) is available to detect errors in the tooth preparation, such as inadequate occlusal clearance, undercuts, unclear preparation margin, sharp corners, and rough surfaces. These features are specifically useful in a teaching environment.

Fig. 2
The quality of the tooth preparation and the digital impression can be evaluated immediately. Files of natural teeth and smiles can be applied to digitally designed esthetic and functional restorations.

Different software is available for each type and intended use of CAD/CAM systems: clinical or laboratory. The reason is that restorations and materials for chairside CAD/CAM are more limited because of time restrictions. The main objective of the chairside work flow is to complete a definitive restoration in 1 visit, avoiding the need for a temporary restoration and a second patient appointment for final restoration delivery. With the developments in high-strength ceramic materials and implant prosthetic solutions, the latest chairside CAD/CAM software versions are able to design and produce fixed dental prostheses and implant-supported restorations. Dental restoration design software has become increasingly user friendly, with many features like preparation finish line detection and tooth digital wax-up now automated. Clinicians can select from digital libraries of natural tooth shapes and morphologies or create a mirror image of an existing tooth in the patient’s mouth. With these features, esthetic and natural tooth shapes that are not hand made by a dental technician can be applied based on the individual esthetic needs and desires of the specific patient. STL or other files and tooth libraries can be imported from other sources. Advanced options include digital smile design features and face scan technology to optimize esthetic outcomes.

Clinicians who want to incorporate digital impressions in their practices but do not want to mill and finish the restorations in house select a semichairside workflow, which includes the intraoral scan without the design and milling of restorations. After review of the scan images and definition of the preparation margins, the digital impression is sent electronically to the dental laboratory where the restorations are fabricated. System-specific software is available for that feature (eg, Sirona connect, Dentsply Sirona). The laboratory can then use compatible laboratory-specific software for the design and manufacturing (eg, exocad, exocad GmbH, Darmstadt, Germany).

Archiving stone study models and mastercasts requires ample space. Digital scans and data sets can be stored and archived virtually on a designated server. However, it is important to understand and follow patient data privacy rules and regulations when deciding where and how to store patient data and scan files. With most systems, CAD data are handled and transmitted in an STL format, which has become the standard file format in 3D printing and rapid prototyping. Other formats that are currently used are PLY, DCM, and UDX. To communicate with a milling machine, these file formats are translated into millable data file formats (CNC [computer numerical control]). STL files describe only the surface geometry of a 3D object without any representation of color, texture, or other common CAD model attributes.

Chairside milling machines

A large number of milling machines with a small footprint, intended for use in the dental office, have entered the market in recent years and are geared toward the ability to mill all different kinds of restorative material blocks ( Fig. 3 ). Compact milling units are indicated for dental offices that want to scan, mill, and deliver restorations in 1 appointment. This type of milling unit is typically a 4-axis mill, which means that the milling bur moves in the 3 axes, x, y, and z, and the material block can rotate in 1 additional axis (also termed 3 + 1 axis milling machine). Some units use 2 burs on 2 separate motors to mill the material block at the same time, making the process faster, with an average milling time of 8 minutes for a single crown and with an accuracy of 25 μm.

Fig. 3
Chairside milling machines have a small footprint and are adequate for a variety of restorations types and materials.

Accuracy and milling time are determined by various factors, such as number of axes and spindles, bur size and abrasiveness, milling speed, and the material. Silica-based ceramics are typically milled in a wet environment, whereas composite and zirconia blanks are dry milled. Not all milling machines offer both wet and dry milling. It is therefore critical to carefully consider specific material needs and preferences before selecting a milling machine.

Four-axis (3 + 1) milling machines have long been the standard for small in-office milling and are perfectly adequate for most clinical applications, such as veneers, inlays/onlays, crowns, and fixed dental prostheses. Milling machines with 5 or more axes can rotate the material block in additional axes, which enable milling of more complex designs, even with undercuts such as implant superstructure where the implant screw access opening may be angulated in different directions. They also seem to provide greater accuracy. Rotary cutting instruments with a smaller diameter lead to greater accuracy but require longer milling times.

The more compact chairside milling units can accommodate material blocks of up to 20 mm, 40 mm, and 85 mm. Five-axis milling units are able to process polymer, hybrid ceramic, glass ceramic, silicate ceramic, and zirconium oxide from discs of 98.5 mm in diameter and up to 30 mm in thickness. With a multiblock holder, they can also mill up to 6 blocks at the same time for maximum productivity and efficiency.

Laser milling of dental restorations uses millions of short, high-intensity laser pulses to remove small amounts of material from a standard block to complete the restoration. The extremely small laser spot size allows a high resolution, resulting in improved morphology and microtexture on the restorations. The advantages of laser milling are the cost reduction of in-office production of restorations by eliminating cutting tools and coolants. The integrated 3D scanner has the ability to perform in-process quality control before the restoration is finished.

Sinter furnaces

A furnace is needed for materials that require sintering or ceramic glazing. The CEREC Speedfire (Dentsply Sirona) and the Programat CS4 (Ivoclar Vivadent) are chairside furnaces with a small footprint that can be used for sintering zirconia, glazing ceramics, and crystallization/processing of lithium disilicates. They feature specific speed sintering cycles for timely finalization and delivery of all-ceramic restorations.

Chairside computer-aided design computer-aided manufacturing materials

One of the key benefits of chairside CAD/CAM technologies is the ability to fabricate indirect restorations in the dental office without the involvement of an external laboratory and within a short period of time. Various factors limit these restorations to single-span or short-span multiple units. The material range includes acrylics, indirect resin-based composites, and various ceramics. Proper selection of these materials based on indication as well as specific esthetic and functional needs is essential for clinical longevity. Several clinical studies indicate very high long-term success rates of chairside CAD/CAM restorations. Table 1 gives examples of popular commercial products in each material group. After milling, the sprue has to be removed from the restoration ( Fig. 4 ) with adequate rotating instruments. Some materials, like composite resins and resin matrix ceramics, only need polishing ( Fig. 5 ) or application of light-cure stains and glaze. Silicate and oxide-based ceramics need to be crystallized or sintered either with or before staining and glazing ( Fig. 6 ). Both of these steps require a special sinter furnace ( Fig. 7 ).

Table 1
Examples of dental materials for chairside digital dentistry
PMMA-Based Materials Composite Resins Resin Matrix Ceramics Silicate Ceramics Oxide Ceramics
Resin-based Ceramics Hybrid Ceramics Feldspathic Ceramics Lithium Silicate Ceramics Zirconium Dioxide Ceramics
Traditional Feldspathic Ceramics Leucite-Reinforced Glass Ceramics Lithium Disilicate Ceramics Zirconia-reinforced Lithium Silicate Ceramics
Telio CAD (Ivoclar Vivadent)
VITA CAD-Temp MonoColors/MultiColor Blocks (VITA Zahnfabrik)
VITA CAD-Waxx Blocks (VITA North America)
CEREC Guide Bloc/inCoris PMMA (Densply Sirona)
artBloc Temp (Merz Dental)
Paradigm MZ100 (3M ESPE).
Tetric CAD (Ivoclar Vivadent)
BRILLIANT Crios (Coltene)
Cerasmart (GC)
Lava Ultimate (3M ESPE)
Grandio Blocs (VOCO)
HC Block CAD/CAM Ceramic-Based Restorative (Shofu)
KATANA AVENCIA Block (Kuraray Noritake Dental, Inc)
BRILLIANT Crios (Coltene)
VITA ENAMIC (VITA Zahnfabrik) VITABLOCS Mark II (VITA Zahnfabrik)
VITABLOCS RealLife ceramic blocks (VITA)
VITABLOC TriLux Forte (VITA)
CEREC Blocs (Densply Sirona)
CEREC Blocs C/C In/C PC (Densply Sirona)
IPS Empress CAD (Ivoclar Vivadent) IPS e.max CAD (Ivoclar Vivadent) VITA SUPRINITY PC (VITA Zahnfabrik)
Celtra Duo (Densply Sirona)
CEREC Zirconia/Zirconia meso (Densply Sirona)
inCoris TZI/TZI/C/ZI/ZI meso (Densply Sirona)
KATANA Zirconia Block (Kuraray Noritake Dental, Inc)
VITA YZ XT/ST/HT White /HT Color /T (VITA Zahnfabrik)
Lava Zirconia Blocks (3M ESPE)
IPS e.max ZirCAD (Ivoclar Vivadent)
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Aug 9, 2020 | Posted by in General Dentistry | Comments Off on The Current State of Chairside Digital Dentistry and Materials
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