The New Face of Milling Materials in Esthetic/Restorative Dentistry

When digital dentistry first emerged onto the market, dental professionals were introduced to the concept of digitally capturing patient data and transferring that information to an in-office milling machine that would create a full-contour restoration for the dentist. These initial systems provided a glass-ceramic restoration that was very basic in tooth shape and occlusal anatomy. With subsequent improvements made in the last 30 years, CAD/CAM systems can now produce restorations that rival conventionally fabricated restorations produced in many dental laboratories.

When CAD/CAM technology perfected framework and full anatomic contour design and delivery, dental technicians were able to create digital data to fabricate increasingly complex restorations. As with any technology, second- and third-generation CAD/CAM systems have continued to improve on the initial concept and design, resulting in the creation of laboratory-based systems that can provide increasingly comprehensive results for single- or multiple-unit restorations. Today’s CAD/CAM systems are being used to design stronger restorations with improved marginal accuracy and fit with enhanced esthetics as compared with restorations fabricated using traditional methods. These systems have evolved to allow for fabrication of full-crown, veneer, inlay/onlay, and complex implant framework designs. The introduction of CAD/CAM to the laboratory has significantly improved the overall output provided by these systems for restoration of increasingly complex cases with better predictability.

Advancements within digital dentistry are now developing rapidly, drawing on the existing capabilities of modern systems and seeking to improve the dental technician’s ability to provide optimal care within a fraction of the time. As the software and fabrication processes continue to evolve, new generations of technologies will enable increased diagnostic capabilities that will allow the user to deliver comprehensive dentistry with increased predictability, while taking into account critical functional concerns such as occlusal and anatomic nuances.

Along with the new scanning technology, design software, and manufacturing machines, the materials companies have also been working diligently to stay current with the technological developments. The first laboratory CAD/CAM systems were designed to mill only zirconia (Figure 1 and Figure 2). From CAD design to copy milling, the introduction of these systems and materials created immediate excitement in the laboratory profession. Today zirconia is available in all shapes and sizes. The esthetics of this material have progressed from opaque white to an ever-expanding offering with a multitude of shades and translucencies available in both mono-colored discs and multilayered disks that provide a gradual transition from dentin to incisal coloration. New zirconia systems also enable the technician to have the ability to custom stain during the green stage to achieve a wide range of esthetic possibilities. Research and product development continues today to provide a higher range of translucency and esthetics.

One of the technology and materials systems that changed the laboratory profession, in regards to workflow, esthetics and function, was the Ivoclar IPS Empress® system. This system was the first to offer a technique that allowed technicians the ability to press high-strength ceramics to create full-contour restorations, hybrid-layering designs, and frameworks. Today, CAD/CAM systems and the new waxes that have been developed for proper milling or 3D printing now allow technicians to use standardized tried-and-true technologies to efficiently create pressed ceramic restorations. These waxes are presented in a multitude of colors, opacities, and hardness levels that can be chosen based on the technician’s preferences. In addition to the pressing of ceramics, based on the hardness of the wax, precision frameworks for the casting of alloy can also be created very predictably.

Technological and materials advancements have also provided techncians with the tools to more efficiently create value-based products. The diagnostic wax-up offers laboratories the opportunity to provide great service to dentist-clients and their patients (Figure 3). In the past, even though the diagnostic wax-up was vital to the success of the restorative case, the process itself took many hours for a highly skilled technician to manually accomplish a proper functional, esthetic result. New milling waxes offer the laboratory a predictable and efficient way to offer this service to the dentist and patient, while still retaining the artistic skills of the individual technician.

The next step after proper diagnosis, treatment planning, and a diagnostic waxup is creating the provisional restorations. This service represents another area in which laboratories have struggled to offer this service to clients and still make a fair profit.

Polymethyl methacrylate (PMMA) has been long used in dentistry for a variety of applications (Figure 4). Typically, PMMA materials were in a powder-liquid form. The powder was mixed by hand with the liquid monomer to form a dough of uncured plastic that could either be heated or self-cured. Problems associated with this technique included residual monomer, excessive shrinkage, porosity, and the color instability of the final appliance. Labor costs associated with this material and technique were high, and a fair profit was difficult to achieve. The new millable PMMA materials reduce or even eliminate most of the challenges associated with liquid-powder processing of PMMA materials. Most any appliance or restoration that could be created from traditional PMMA techniques can now be fabricated more efficiently, and at a higher quality using these new higher-strength, low-porosity, lower-monomer CAD/CAM-enhanced materials. Applications for these materials include long-term provisional restorations, occlusal splints, implant surgical guides, full dentures, and denture bases. Many laboratories may overlook the restorative possibilities offered by these new PMMA materials; however, today’s generation of CAD plastic materials provide all laboratories the ability to offer new products and services to their dentist-clients.

Another material that has allowed laboratories to move from a traditional workflow to a digital process is acetyl resin. Acetyl resin is a thermal plastic monomer-free polymer; it has high resistance to abrasion, excellent tensile strength, and high elastic memory. For almost 20 years, these resins have been used in dentistry to develop a wide range of prosthetic solutions: esthetic clasps on metal partial frameworks, entire partial frameworks, provisional bridges, and the ever-popular Snap-on Smile® (Den-Mat Holdings, snaponsmile.com). This material is offered in a variety of shades to allow technicians artistic control over the final prosthetic.

Another new entry into the millable plastics arena would be the thermal plastic composite polymer known as polyether ether ketone, or more commonly known as PEEK. This material has long been used in medicine for the creation of different medical implants, including cranial, knee, and spinal prosthetics. PEEK has many potential uses in our digital CAD/CAM workflow. In dentistry, this material is commonly used in the fabrication of implant scan bodies that are recognized by both intraoral and desktop scanning. These geometrically shaped scanning bodies, when coupled with the correct computer design software, tell the operator and computer which type of implant was used, as well as its inclination and depth within the tissue and bone surrounding the implant. Additonal applications of this material for the laboratory include fabrication of partial denture frameworks, fixed bridge frameworks, and the possibility of producing implant-supported bars.

As metal usage in the laboratory continues to decline, metal is being replaced by ceramics, plastics, and fiber-reinforced composites (Figure 5). As with other materials, the fiber-reinforced composite category has been used in dentistry for many years. This material has been offered to the market in the form of endodontic posts, and in the laboratory it was offered in a ribbon form for the internal strengthening of traditionally hand-applied composite restorations. This material is now offered in disc form, which has been modified to allow the precision milling of dental prosthetics. Again, fiber-reinforced composites have the potential to also replace metal frameworks in many dental applications. Indications include the creation of frameworks that support milled PMMA restorations for long-term provisional use, as in the use of sequenced implant surgery. Expanded uses may also include the fabrication of implant-supported bars.

Technological advancements have always progressed from an initial design concept that is improved upon in several iterations until an ideal format is achieved. While CAD/CAM technologies evolved, dental professionals continued to use tried-and-true methods for data transfer, incorporating digital dentistry to fill some of the blanks that familiar methods left. As digital dentistry further expands, the use of CAD/CAM systems will be increasingly applied for treatment planning procedures, implemented from initial treatment phases, and used throughout the entire restorative process. By incorporating advanced systems in the diagnostic phase, dental professionals will continue to reduce the margin for error inherent in traditional protocols, and further enable the dental professional to replicate natural esthetics while focusing on proper function and occlusal harmony using CAD/CAM technology.

The most intriguing factor surrounding these technologies is not in the potential applications imagined by dental professionals, but in the fact that these hypothetical applications are becoming reality today; some are even in the final stages of development. These are advancements that will not “eventually” emerge in the market—they are realities that will be released within a relatively short time to further revolutionize the quality of dental care that is being delivered in modern practice.

Lee Culp, CDT, is the CEO of Sculpture Studios, a dental laboratory and research and product development center in Morrisville, North Carolina.