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Dental professionals today are functioning in a rapidly-evolving environment that can, at times, be overwhelming. Additionally, the desire to provide the very best treatment for patients oftentimes requires that the dental team take the time to stay abreast of advancements that may currently be out of financial reach. While time can an extremely valuable, but scarce commodity, these technological improvements ultimately will streamline processes to a point of maximum productivity, allowing the laboratory to achieve higher quality and consistency levels than ever previously imagined.
Before delving into the new technologies on the market, the author would like to briefly cover some areas of importance.
Effective communication is the backbone of all successful relationships. It is absolutely essential, yet many times taken for granted or so poorly executed that catastrophic misunderstandings and unacceptable results occur. Our ability to communicate through the use of common digital platforms has changed our daily interactions dramatically. Consider the up-to-the-minute information sharing via social media applications such as Facebook and Twitter, or simply how easy it is to reach someone via text. With so many new kinds of communication platforms, email could soon be considered passé, having been around since 1993.
The rapid development of these communication technologies has had a significant impact on the dental community. The spectrum of communication options that are now available to the members of the restorative team are invaluable for both planning cases and successfully delivering complex treatment.
Contemporary Digital Treatment Planning
The following is an example of typical contemporary digital treatment planning protocol. A patient presents in need of comprehensive oral rehabilitation. The dentist takes digital radiographs and photos and stores the data in the patient’s electronic file. If indicated, the patient undergoes a computerized Cone Beam Volumetric Tomography (CBCT) scan to aid in the planning of implant-supported restorations. The capture of appropriate digital impressions and occlusal registrations completes the pre-operative records. From there, the data is sent to the partnering specialist and laboratory technician. Numerous technologies give these professionals the option to load the digital casts onto a virtual semi-adjustable articulator (Figure 1).
Once the data has been shared, a multidisciplinary meeting is scheduled between the restoring dentist, specialist(s), and technician. Live video conferencing is readily available through web-based services such as Skype, WebEx, and GoToMeeting. One only requires a computer, Internet connection, and web camera to access these services. This type of direct communication minimizes potentially expensive and frustrating miscommunication.
Centralized virtual information-sharing platforms serve as an excellent host for all members of the restorative team to upload information on a specific treatment to one location. These secure email services are HIPPA compliant and provide everyone associated with the treatment plan access to all information involving the case from diagnosis through delivery. This can be especially valuable when treating complex multi-disciplinary cases.
The next step is for the technician to create a virtual diagnostic mock up that meets the previously established occlusal and esthetic case requirements with CAD design software (Figure 2). This data is then returned to the restoring clinician for approval. Upon acceptance, these files can be forwarded to the patient for approval or clarifying discussion. If additional questions arise, the dentist and patient may communicate with the technician and/or specialist via web conference. Once the patient approves the design files, treatment is scheduled. When planned at this level of detail, it may be possible to schedule the entire treatment sequence from beginning to delivery.
After the patient approves the design and treatment is scheduled, the laboratory receives the electronic prescription for the fabrication of provisional restorations. Still working from the original stl file, the technician designs minimum reduction of the abutment teeth and mills provisionals from a disc of PMMA material. Ideal, the PMMA material should exhibit high strength, reasonable esthetics, and bondability to the chairside reline resin of choice.
Digital Shade Communication
Tooth color and characterization communication remain the most challenging aspect of single anterior fixed prosthodontic treatment.1 Digital shade-taking technology provides a mathematical shade measurement of the tooth area. These devices are able to take several shade samples simultaneously, breaking the samples down into cervical, middle, and incisal thirds to offer the restorative team an accurate assessment of tooth color. Digital shade-taking technology can also help the dentist choose the closest matching shade tab for inclusion in digital photographs.
Digital photography has become irreplacable in the dental office, and it is now possible to achieve excellent photographic results with only a smart phone. There are even specialized kits designed to record images under 5500 Kelvin with color correct LED lighting and a magnetic polarizing filter to give the technician a more detailed view of the sample (Figure 3 and Figure 4).
Digitally capturing the patient’s tooth shade, shape, and characterizations offers a significant improvement in dentist/laboratory color communication, whether it be with a high quality 35mm digital camera, digital shade-taking tool, or smart phone. The images help guide the team to select the proper shade and communicate that information using appropriate tooth shade guides. Additionally, partnering laboratories can use the corresponding ceramic materials and denture teeth to complete the accurate match.
Digital Impression Technology
The most dramatic improvement in fixed prosthodontic restorative patient care is the ability to digitally scan prepared teeth or implant scan flags for direct and indirect fixed prosthodontic cases. The improved dimensional accuracy that results in minimal delivery adjustments is well documented.2 Patient comfort and reduced stress levels provide an improved treatment experience compared to traditional impression methods.
The digital capture technology falls into two categories; Capture Only and Capture and Manufacture. Capture Only devices are designed to capture the digital data chairside for laboratory use only. Capture and Manufacture devices are designed to capture the digital data for chairside manufacture or for sending capture data to the laboratory for case completion
Chairside/Laboratory Manufacturing Systems
Chairside manufacturing systems were introduced commercially in 1987.3 In 2007 the sole provider of chairside manufacturing, Sirona, developed technology that allowed the digital capture file to be sent to the laboratory for modeless single crown fabrication. Consequently, other chairside systems, following in the same footpath, have been introduced onto the market.
Software transmit technology inherent to these systems provides an opportunity for laboratories to play an integral role in several ways. One option is that the clinician sends the digital scan file to the laboratory and requests that a design for the restoration be returned within a few minutes for in-office milling and delivery. Another option would be for the technician to use the file to develop a modeless crown in-house the same day, if proximity allows, or within 1, 2, or more days for a sliding scale fee, based on turnaround time. To accomplish the more complex treatment of multiple units, the laboratory can also order a digital model from a central manufacturing facility utilizing 3D printing or milling technology, or use its own CAM system if the investment is logical.
Digital Case Submission
The rate of clinicians ordering prosthetic restorations via online prescriptions is increasing at a dramatic rate. The development of Internet-based portals for submitting case information provides an opportunity for convenient comprehensive dentist-to-laboratory communication and also serves as a conduit for clinicians to access to their specific account data.
Upon receipt of the digital impression stl file, if case complexity dictates, the laboratory has the ability to procure a 3D printed or milled working cast (Figure 5 and Figure 6). Concurrent manufacturing provides the technician with the ability to upload the stl file to a digital workstation for the design of a 3D printed wax pattern or milled zirconia restoration while the model is being digitally developed. This not only decreases working time but ensures an even greater level of accuracy due to the elimination of an additional data transfer from scanning a master cast or impression. Modeless single-unit ceramic restorations may also be milled to full contour, characterized, and fired for expedited delivery.
At this point in the process, the clinician prepares the teeth for the final restorations. The prepared teeth are then digitally scanned and the stl files are sent to the technician for the development of milled or printed working casts.
Upon delivery of the relined and adjusted provisional restoration, the clinician scans the patient-approved modified provisionals and submits that file to the laboratory for overlay onto the image of the prepared teeth. This allows the technician to develop the ideal substrate support for veneering ceramic or full-contour restorations as prescribed. This highly precise data transfer assures an esthetic match and the accuracy of the definitive restorations.
CAM Materials and Fabrication Methods
At its introduction, zirconia was intended for CAM production of a milled substrate that supported veneering ceramic. The clinical community generally lost confidence in this type of restoration due its technique sensitivity, which led to material fracture issues with the veneering ceramics. This has largely been resolved with the understanding that the material must be slow cooled to accommodate the heat sync differential between the core material and the veneering ceramic. Now, full-contour restorative options have taken the marketplace by storm. The low cost of zirconium oxide compared to the cost-prohibitive industry standard precious metal has created a tremendous shift to its use. The recent study published by Burgess, et al, at University Alabama Birmingham shows a favorable wear rate against enamel when polished, which has also contributed to the material’s acceptance in the prosthodontic community.5 The more recently developed technique of designing these restorations with a “window” cutback for the application of veneering ceramic provides esthetic control and custom characterization, greatly improving the esthetics in the anterior.
Other millable materials have emerged and thrived with the introduction of digital technology. The introduction of lithium disilicate as a milled or pressed full-contour restorative material provides improved strength (360 to 400 MPa) and cementability when compared to the original pressed formulation of its predecessors (Figure 13). Additionally, the recent introduction of high-translucency zirconia-reinforced lithium silicate milling materials provide laboratory technicians with improved esthetics at strengths of 370 MPa, allowing adhesive cementation of etched and silane treated restorations.
CAM Wax Patterns
The use of digital technology also eliminates the dimensional inconsistencies associated with hand-0waxed patterns for casting of alloys or pressing of ceramic restorations. Many of the previously discussed CAM systems may also be used for the milling of wax patterns for fixed prosthodontics.
3D printing allows dental technicians to create extremely detailed, intricately-layered structures. This feature is especially important in the development of cast alloy removable partial denture patterns. 3D printing technology also can be utilized for small to large batch sizes, depending upon which system is in use (Figure 7).
The newest innovation arriving on the dental technology scene is Selective Laser Melting (SLM) technology. As a rapid prototyping methodology, this technology develops the intended restoration through the selective laser melting of powdered alloy sequentially from bottom to top, layer by layer. A variety of alloys are available for crown and bridge applications, as well as titanium and CoCr for implant bars (Figure 8). Using SLM for the fabrication of implant bars offers the opportunity to create macro surface retention, thus enhancing the veneering resin bond and dramatically reducing the potential for stress fracture of the veneering resin due to excessive occlusal load (Figure 9).
These applications are available from a variety of centralized production centers, a manufacturing model that enables laboratories to take advantage of the technology without the significant expense of SLM machine ownership and maintenance. The laboratory may ship working casts to the facility or, in some cases, more efficiently scan and design the cases in the laboratory and send the stl file for fabrication.
The final frontier of digital prosthetic treatment comes in the form of complete digital dentures. The author believes that this is the most fertile ground available for the contemporary dental laboratory. The sheer size of the Baby Boomer generation dictates that millions of patients will continue to require denture therapy. Incorporating implants into the treatment assures the demand for more technologically advanced technicians. The massive contraction of the removable prosthetic technician labor pool—due to the aging segment and fewer technical education programs—compound the intensity of the business opportunity for the remaining laboratories. In addition, digital denture technology provides improved solubility, excellent tissue adaptation, and increased strength (Figure 10 and Figure 11).
It is indeed exciting to work in this arena of seemingly unlimited potential to provide the most sophisticated restorations imaginable.
1. Dawson PE. Determining and communicating restorative and esthetic guidelines. St Petersburg, FL: Dawson Center for Advanced Dental Study; 1997.
2. Hassel AJ, Koke U, Schmitter M, et al. Clinical effect of different shade guide systems on the tooth shades of ceramic-veneered restorations. Int J Prosthodont. 2005;18(5):422-426.
3. Birnbaum N, Aaronson H, Stevens C, Cohen R. Digital scanners: a high-tech approach to more accurate dental impressions. Inside Dentistry. 2009;5(4):70-77.
4. Mormann WH, Brandestini M, Lutz F, et al. Chairside computer-aided direct ceramic inlays. Quintessence Int. 1989;20(5):329-339.
5. Janyavula S, Lawson N, Beck P, et al. The wear of polished and glazed zirconia against enamel. J Prosthet Dent. 2013;109(1):22-29.
About the author
David Avery, CDT, AAS
Director of Professional Services Drake Dental Laboratory