November 2015
Volume 11, Issue 11

Peer-Reviewed

CAD/CAM Materials in Dentistry

Rapidly evolving products and processes give clinicians better treatment options

Andrew Koenigsberg, DDS

Every aspect of the CAD/CAM process—data capture, design software, materials, and production method—will continue to evolve, resulting in greater accuracy, more applications, and increased efficiency with both new and existing materials.1 CAD/CAM processes are now used with every type of restorative material: ceramic, polymers, and metal. These materials are used to fabricate everything, including single copings, crowns, complex full-arch restorations, removable appliances, temporaries, positioners, surgical guides, and dentures. In laboratories, CAD/CAM materials are used to fabricate models as well as to create burnout patterns before conventional casting or pressing. Tables outlining the applications and indications of CAD/CAM materials and ceramics are available at dentalaegis.com/go/id1119.

CAD/CAM ceramics are most relevant to restorative dentists and where the greatest changes in clinical practice have been realized. A majority of crown-and-bridge (C&B) restorations are now produced through CAD/CAM, often with new ceramic materials. CAD/CAM ceramic materials evolved from traditional feldspathic porcelain, an esthetic but low-strength, brittle material, to a range of materials with different strength, resilience, and esthetic properties. They are clinically successful2 and are replacing porcelain-fused-to-metal (PFM) restorations.

Until recently, a clinician’s decision was simple when choosing CAD/CAM ceramics, as high strength meant poor esthetics and excellent esthetics meant low strength.3 C&B ceramics are rapidly changing as the esthetics of the high-strength materials has improved to the point where it is now possible to make anything from a single unit to full-arch monolithic ceramic restoration. Monolithic restorations are less prone to failure as there is no weaker outer layer. They are also much easier, quicker, and cheaper to fabricate, as the restoration is made through CAD/CAM and there is no labor intensive, highly skilled layering process.

Glassy Phase Ceramics

This is the original chairside CAD/CAM material, which has been used for CAD/CAM inlays, crowns, and veneers, and we now have about 30 years of data.4 When this material is used properly (prep design, handling of ceramic, and bonding technique), it has a high success rate and is the most esthetic option. However, if there are thin margins, extensive adjustment, or inadequate bond to the underlying tooth, the failure rate dramatically increases. There are more forgiving or stronger materials for most indications. However, these materials can still produce the most esthetic, well-fitting veneers. They are available in multi-shade blocks and can be custom stained and layered.

Nano-Ceramics

These materials combine the resilience of resins with the strength of ceramic. They cannot be stained in an oven, but there are resin surface stain kits available. This is a serious limitation to their use in the anterior region where the restoration cannot be characterized. Recently, 3M ESPE (www.3mespe.com) withdrew the crown indication from Lava™ Ultimate due to excessive debonding. Inlays and onlays are the best indications for this material, because thin margins are less prone to chipping and there is less flexion and debonding of the restoration. Chairside advantages are fast fabrication, clean milling, and easy polishing.

Lithium Silicate Glass Ceramics

Lithium disilicate was introduced by Ivoclar Vivadent (www.ivoclarvivadent.com) as Empress II in 1998. Initially, the material was too opaque for full-contour restorations so a layering porcelain had to be baked over the substructure. Ivoclar continued to improve the esthetics and it is now available in various translucencies, making it appropriate for all single-crown and veneer applications, as well as three-unit bridges up to the bicuspid region. It is also available for custom implant abutments and screw-retained implant crowns. There is excellent data on its durability and it can be custom stained and layered. While it can be cemented with conventional cements, it also has excellent adhesion to composite cements.

A number of companies have introduced chemically similar materials with comparable strength properties. These products include Obsidian® (Prismatik Dentalcraft Inc., www.obsidianceramic.com), a lithium silicate, and CELTRA™ Duo (DENTSPLY International, www.dentsply.com), a zirconia-reinforced lithium silicate. They have their final color before the oven cycle; however, they do not have the long-term data of IPS e.max® (Ivoclar Vivadent). They also cannot be layered and are not available in as wide a range of translucencies. These materials are often the best choice for single-unit restorations anywhere in the mouth and anterior three-unit bridges.

Zirconia

Zirconia was originally a substructure material because of its lack of translucency and its opaque white color. Zirconia potentially has the flexural strength of metal. While zirconia can be layered with translucent porcelain, there have been issues with chipping. Over the past decade, manufacturers have figured out how to shade the material and increase the translucency to the point where esthetic anterior crowns and bridges can be fabricated. There are now multilayer discs so that the restorations have more chroma at the gingiva and more translucency at the incisal, reducing the need to layer. Typically, the more esthetic the zirconia, the weaker it is, though even the weaker materials exceed the strength requirement for anterior bridges. Advantages include strength and conventional cementation, while disadvantages are difficulty in chairside adjustment and modification. The dentist must be aware of which zirconia is being used, especially for large and posterior bridges, as there are significant strength differences between products.

Milling Processes

All three categories of CAD/CAM materials (polymers, metals, and ceramics) can be processed by subtractive techniques where material is removed from a block or disc, leaving the planned shape, which is usually achieved by milling or grinding away excess material, though some metals can be shaped by “spark erosion.” A significant advantage of the subtractive technique is that the blocks and discs have been produced under industrial conditions. For ceramics, this avoids the defects, stresses, and shrinkage that come with layering and multiple oven cycles. With metals, this avoids porosities and other stresses and distortion that result from casting and the heating and cooling of metal. Therefore, the same material is stronger and has better properties when processed by CAD/CAM vs traditional techniques. There are an increasing number of materials that have been developed specifically for CAD/CAM that cannot be fabricated with traditional techniques.

Subtractive processing can be wasteful, as a majority of material is ground away and discarded. Milling burs wear with use, which can introduce inaccuracy. For porcelains, the grinding process can introduce stresses and fractures. Even with these limitations, milling produces stronger, accurate, and economical restorations.

Additive technologies build the restoration, appliance, or model and can currently be used with resins and metals in dental applications. The process involves fusing thin layers (about 30 microns) to create a 3D object. The fusing can be accomplished by different techniques, including printing, light activation (stereolithography), and laser welding. A new additive method, continuous liquid interface production (CLIP), shows promise of being even more accurate and efficient. This method has the final product “emerge from a pool of liquid.”5 At first, only prototypes could be produced but as the technology and materials advance, 3D printing is becoming an efficient method of production. With the ability to print plastics in color, it is not hard to imagine a full, monolithic denture being printed. The possibilities for C&B are even more exciting, as additive techniques and materials should have improved mechanical properties, customization options, and reduce the stress and waste of milling.

Final Thought

CAD/CAM materials are rapidly evolving, giving dentists and patients new treatment choices. Dentists must be aware of the available materials so they can offer their patients the appropriate material for each clinical situation. Undoubtedly, existing materials will continue to evolve and entire new CAD/CAM restorative materials will emerge.

About the author

Andrew Koenigsberg, DDS
Gallery57 Dental
New York, New York

Cofounder and Clinical Director
CAD/CAM Excellence

References

1. Goswami R, Arora G, Priya A. CAD/CAM in restorative dentistry: a review. British Biomedical Bulletin. 2014; 2(4):591-597.

2. Della Bona A, Kelly JR. The clinical success of all ceramic restorations. J Am Dent Assoc. 2008;139 Suppl:8S-13S.

3. Li RW, Chow TW, Matinlinna JP. Ceramic dental biomaterials and CAD/CAM technology: state of the art. J Prosthodont Res. 2014;58(4):208-216.

4. Otto T, Schneider D. Long-term clinical results of chairside CEREC CAD/CAM inlays and onlays: a case series. Int J Prosthodont. 2008;21(1):53-59.

5. Johnson P. Breaking barriers: new breakthroughs in 3D printing speed and flexibility. Inside Dental Technology. 2015;6(7):34-35.

CAD/CAM Showcase

A | IPS e.max® CAD

IPS e.max CAD from Ivoclar Vivadent is an innovative lithium disilicate glass-ceramic for CAD/CAM applications that combines highly esthetic quality with exceptional user-friendliness. IPS e.max CAD covers a comprehensive spectrum of indications.
800-533-6825
ivoclarvivadent.com

B | CS 3000

The CS 3000 milling machine from Carestream Dental is a CAM tool featuring a 4-axis brushless motor that produces high-quality restorations with ± 25 µm accuracy. The average milling time for a crown is less than 15 minutes.
888-679-0153
carestreamdental.com

C | TRINIA CAD/CAM Block

Trinia, a CAD/CAM fiber-reinforced composite from Shofu, is a resilient and ultralight biocompatible resin material that provides clinicians with a more efficient and cost-effective alternative to metal bars milled in titanium, or cast in semi-precious and precious metals.
800-827-4638
shofu.com

D | Prettau® Zirconia

Zirkonzahn’s Prettau Zirconia is for cases where there is not sufficient space available for ceramics. It enables the creation of full-zirconia crowns and bridges, eliminating the problem of chipping, with minimal abrasion to opposing natural dentition.
678-441-9419
zirkonzahn.com

E | LAVA™ Ultimate

Lava Ultimate from 3M ESPE is a unique CAD/CAM material that is resilient, not brittle, and incredibly durable and shock absorbent. It offers a polish that lasts, is designed for precision and speed, and is backed by a 10-year warranty.
800-634-2249
3mespe.com

F | TS150™

The TS150 chairside mill from IOS Technologies is a fast, efficient, and affordable open-source milling unit that uses an orbital precision milling strategy to provide excellent marginal integrity. It could reduce your turnaround time to less than two hours.
858-202-3360
ios3d.com

G | CEREC MC XL

Sirona’s CEREC MC XL milling unit creates the same restorations as the CEREC MC (inlays, onlays, crowns, or veneers) with the inclusion of bridges, abutments, and surgical guides on blocks up to 40 mm. The unit has four motors and a touchscreen display.
800-659-5977
sironausa.com

H | Dental Wings Laser Mill (DWLM)

With the DWLM clinicians can create restorations using proven materials such as polymers, composites, hybrid, and glass ceramics with unprecedented detail. The DWLM has no burs or spindles to replace, no cutting fluid to manage, and no need for compressed air.
888-856-6997
dentalwings.com

I | PlanMill® 40

The Planmeca PlanMill 40 features a wireless connection and easy touchscreen operation. Dual spindles mill on both sides of the restoration simultaneously, and calculate custom milling paths with micron-precise accuracy.
630-529-2300
planmeca.com

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