How CAD/CAM Materials Differ From Traditional Indirect Materials

Digital dentistry and CAD/CAM has changed how many dentists handle restorative work. Over the past few decades, the materials they use in their machine have changed, too. But how are they different from traditional indirect materials? Here’s what we found out.  

The most significant difference is the effects of the manufacturing process on the material composition. Per the Journal of the American Dental Association (JADA), the improvements in materials, along with advancing technology of CAD/CAM systems, contribute in no small way to clinical success. The fabrication method of these materials enhances their reliability when used for restorations. In other words, the manufacturing process of the blocks results in a  consistent “dense, high-quality material.” Traditional materials are produced by hand. So, although JADA says the restorations from traditional materials are also high quality, they might have less “reliability” regarding mechanical and esthetic properties because they were not mass-produced. For example when you examine a cross-section of block vs. hand-built (traditional indirect) material, there are pores in the hand built but not in the blocks.¹

Furthermore, when comparing the blocks of several manufacturers from the time (2006), the blocks had “fine-particle-sized microstructure,” which helped them in many areas, including:¹

• Resistance to machining damage

• Improvement of mechanical properties

• Reductions of polishing time

• Increased “wear-kindness” of the completed restoration

A concern about some of the block materials is their monochromatic nature. However, improvements to materials over the years have addressed this concern, which includes techniques of staining and glazing as well as shade matching the blocks to match patients’ surrounding dentition to create a chameleon effect.¹

However, many dentists do not find these differences pronounced between the CAD/CAM materials and traditional indirect materials. John Flucke, DDS, and Technology Editor for DPR, says that he isn’t aware of significant differences between the two groups. Moreover, he appreciates that. It means that dentists don’t have to think about it too much or focus on too many factors when choosing how to move forward for treatment. 

“Materials manufacturers do that on purpose to make the whole process easier,” Flucke says.

Some Pros and Cons of the Digital Material Types
Digital dental materials all have their features and related benefits, as well as some drawbacks. For permanent restorations, Nathaniel Lawson, DMD, PhD, assistant professor and director of the Division of Biomaterials at the UAB School of Dentistry, roughly categorized the digital materials into four material types:

• Resin-based materials (composites)

• Porcelain/leucite materials

• Lithium disilicate materials

• Zirconia materials

Resin-Based Materials
Lawson says the resin-based materials are mostly the same composition as composites used for direct restorations. They contain glass or ceramic fillers in a resin matrix. 

“The difference between these materials and direct composites is that they are polymerized under high temperature and high pressure to improve crosslinking and, therefore, mechanical properties,” Lawson explains.

The advantages of resin-based material are suited explicitly for in-office milling, per Lawson. Resin-based materials can be more easily milled, do not require heat treatment in a furnace, polish quickly, and you can repair them with composite. However, he says, they also have disadvantages.

“Resin-based materials do not have the strength of ceramics, and they have a less reliable bond,” Lawson explains. 

Porcelain/Leucite Materials
Porcelain/leucite based materials (e.g., VITA’s Mark II, Ivoclar Vivadent’s IPS Empress, and Dentsply Sirona’s CEREC Bloc) have some of the advantages of ceramics built-in, Lawson says. They not only have a similar bonding ability and high esthetics but also do not require crystallization in a furnace. However, they have a disadvantage, too. 

 “These materials do not have the strength of lithium disilicates,” Lawson says. 

 A hybrid exists of the resin-based materials and porcelain material, called Enamic from VITA. Lawson describes it as “porcelain infused with resin,” which imparts some additional toughness to the porcelain. 

“The advantage of this material is that it can be bonded like porcelain, but it possesses the strength and toughness of resin-based materials,” Lawson says. 

Lithium Disilicate Materials
Lawson describes lithium disilicate as the “workhorse material for CAD/CAM dentists.” Lithium disilicate is a high-strength ceramic material that has the advantages of ceramics (e.g., esthetics, “bondability”) but with a much higher strength than porcelain. Lawson says to achieve these properties you must crystalize the material in a furnace.

“Originally, there was only one material in this category, IPS e.max CAD,” Lawson says of the material from Ivoclar Vivadent. “Recently, there have been additional materials in this category, including Celtra Duo, Suprinity, LiSi, and Amber Mill.”

Flucke says that while lithium disilicate materials are excellent for many types of restorations, they also have strict rules when you use them in a bridge. Its brittle nature means it cannot hold up in a long span.

“You can push the envelope with a longer span than advised, but know that the fracture rate is much  higher,” Flucke says. 

Continue Reading on Next Page

Zirconia Materials
The newest addition to the family of in-office CAD/CAM materials is zirconia. Zirconia is a durable polycrystalline material (contains no glass) and used in many everyday materials, from dishes and servers to lighting and more.¹ Per Lawson, this material requires different process steps than all other materials.  

“It is milled dry in a chalky form. It is then sintered in a special furnace that must achieve a temperature much higher than the furnace used to crystallize lithium disilicate,” he explains. 

Lawson says the advantage of zirconia restorations is that they are significantly tougher than lithium disilicate and can be used for posterior fixed partial dentures (bridges). Moreover, he says they can be cemented with conventional cementation (RMGI).

“The disadvantage of these materials is that they do not have the esthetic properties of lithium disilicate or porcelain, and there is less clinical evidence for the bond between zirconia and resin cement,” Lawson says. 

There are few other considerations with zirconia chairside materials. First, restorations made from zirconia should be over-scaled to allow for shrinkage during sintering.  However, per Cerecdoctors.com, each block carries a unique code to allow for a precise amount of enlargement, which the software recognizes.  Another interesting fact about the materials is that the blocks are shade-matched, which means you do not use dyeing agents as you can sometimes with other zirconia agents. ³ Also, zirconia milling can be wet or dry, although the preferred option is dry. 

Cerecdoctors.com had some additional advice for using the zirconia blocks. In the posterior, the restorations will wear better if they are polished and not glazed, but glazing is a possibility. Also, phosphoric acid should not be used to clean zirconia restorations made from chairside blocks; they should be cleaned with a cleaning solution or sandblasted following try-in.³

Temporary Solutions with CAD/CAM Technology
Flucke says another material you can use in a mill is PMMA (polymethyl methacrylate), which is a temporary material. He says this can be handy when you have a patient that needs to be in a temporary for a long time. For example, if you were treating an occlusal rehab case where you open them up a significant amount, like 3mm, you can use PMMA milled temporary restorations to see if that is going to cause the patient problems. Since the temporaries fit much like the permanent ones, you can let the patient wear temporaries longer to get a better feel for how the restoration will wear and feel. 

“The ability to do that digitally gives you a much better restoration,” Flucke says. 

Also, if there is a chip or a repair needed, you can make a replacement restoration before the patient's next visit. In a post-COVID-19 pandemic world of dentistry, this allows for increased efficiency and reduced exposure repair visit. Moreover, you can work ahead of time, which can be helpful if you are working without an assistant. 

“Fire up the machine and make them a new one and then just have them come in,” Flucke says. “You just pop one out, pop another one in.”

What Is Not Different About CAD/CAM Materials? Performing Proper Prep.
Flucke says that no matter what materials you use for the restoration, prep design is crucial. With porcelain fused to metal restorations (PFMs), he says you could sometimes not do the best prep and still have a decent restoration. However, the new materials are not as forgiving. The physics that goes into these materials and making these esthetic materials long-lasting rely on proper prep design.

“So, spending a few extra minutes at your prep appointment to make everything look good is something that will pay off in the long run as far as durability of the restoration,” Flucke says. “My grandfather had this great expression, ‘there’s never time to do it right, but there’s always time to do it over.’ There’s never been a profession where that applies more poignantly than dentistry.”

References

1. Giordano R. Materials for chairside CAD/CAM–produced restorations. The Journal of the American Dental Association. 2006;137:14s-21s. doi:10.14219/jada.archive.2006.0397.

2. Huot, DDS R. What Are Zirconia Crowns? | Colgate® Oral Care. Colgate.com. https://www.colgate.com/en-us/oral-health/cosmetic-dentistry/bridges-and-crowns/what-are-zirconia-crows-0417. Published 2020. Accessed April 23, 2020.

3. Poticny, DDS, Daniel J. “Exploding on the CEREC® Scene 3M™ Chairside Zirconia.” CERECdoctors.com. multimedia.3m.com. https://multimedia.3m.com/mws/media/1699647O/3m-chairside-zirconia-exploding-on-the-cerec-scene.pdf Published 2019. Accessed via Web. 5 May 2020.