Beyond the Block: Techniques and Materials Critical to Achieving CAD/CAM Success

The first CAD/CAM chairside treatment recently celebrated its 35th anniversary. On September 19, 1985, after several years of research and development, Dr. Werner H. Moörmann and electrical engineer Dr. Marco Brandestini completed the first functional CEREC chairside treatment in the University of Zurich Dental School. The material of choice was VITA Mark I feldspathic ceramic.

“We had assembled a complete material set and had a reliable material partner in VITA Zahnfabrik,” Dr. Moörmann wrote in 2006. “At that time, we relied solely on the adhesion between etched enamel and etched ceramic. This method has proven itself in private practice for 10 years.”

In 2004, Naren Rajan, DMD, had just completed his residency and began practicing with CAD/CAM.

“Earlier in my career, I had a few years when I was doing CAD/CAM dentistry routinely. At that time, the materials we were using had not yet evolved into what’s available today,” Dr. Rajan wrote in a 2020 article for Dental Product Shopper. “I was milling a lot of feldspathic porcelain, which definitely had its limitations, and we were starting to see breakages. It was frustrating that the technology was not living up to what I hoped for, and I eventually just gave up and went back to analog dentistry. I didn’t want to hear about digital or even think about computerized dentistry.”

This was a strong, adverse reaction from a young dentist. Dr. Rajan wasn’t technology-averse; rather, he was clinically frustrated by material performance. The first generation of CAD/CAM, designed with the focus of fabricating immediate chairside inlay and onlay ceramic restorations, wasn’t the big “selling point” for him. He found the process lost diagnostic integrity. Thankfully, manufacturers are continuously improving materials, and by the time Dr. Rajan returned to digital dentistry several years later, he had access to improved intraoral scanning with emphasis on diagnostics and better materials for restorative longevity. According to one material review, first-generation monoblocks made of feldspathic ceramic material were largely replaced by reinforced ceramic with silica (feldspar, leucite, and lithium disilicate), non-silica (alumina and zirconia), and a combination of resin-ceramic-based materials, resulting in a 3- to 11-fold increase in flexural strength.

Given the significant improvements in milling materials in recent years, restoration longevity depends on other factors – preparation, cementation, and slight differences in the milling unit itself – that were not experienced in traditional fabrication methods.

For example, let’s consider the milling of a typical crown. The final internal shape must allow complete and passive seating of the restoration, with acceptable margins after milling is complete, according to research. Marginal fit, discrepancy, and adaptation, regardless of the type of restoration, are critically important for the longevity of the restoration.

When using digital design software, two distinct surfaces, the outer shell and inner shell, must be taken into consideration. While the outer shell is the proposed anatomic shape of the restoration that can be altered with software editing tools, the inner shell is automatically designed by the computer software. This design is influenced by operator-determined parameters, such as the cement gap and horizontal margin excess, as well as the shape and diameter of the milling tools.

Clinicians can change parameter settings on the design software to influence the shape of the inner shell, but they typically can’t use tools to edit selective areas. This can result in a space between the inner and outer shells, which can define the thickness of the final restoration. The thickness may impact the finish line configuration, which research suggests is the most significant component affecting success or failure of CAD/CAM crowns.

One study of zirconia crowns with two different preparations found that a thicker cervical collar provided greater fracture load. Another study evaluated tooth preparations for zirconia crowns and fixed partial dentures and found only 13 out of 305 abutment teeth met the clinical requirements for adequate preparations for zirconia restorations established using evidence-based criteria. The study identified two primary areas of difficulty dentists experienced: finish-line design around the entire circumference and angle convergence. The researchers concluded that inadequate tooth preparation for CAD/CAM zirconia crowns will lead to premature failure.

The takeaway

For years, researchers have studied various CAD/CAM issues across a range of clinical scenarios and have made suggestions for how to avoid common pitfalls. You’ll be best served by taking in their findings and advice, and carefully considering your options for preparation and finishing tools, CAD/CAM blocks, and adhesive materials. Whether you’re new to digital dentistry or a seasoned expert, you’ll be able to provide the best treatment to patients by making sure you have options at every stage of the CAD/CAM process.

Here are some recommended products for CAD/CAM restorative success.

Preparing the site

Let’s start off with preparation basics. Before you can deliver a same-day restoration, you must quickly and safely anesthetize the patient.

Patterson Articaine HCl 4% (hydrochloride) and Epinephrine provides a vasoconstrictive effect, and is indicated for local, infiltrative, or conductive anesthesia in simple and complex dental procedures. Available as 1:100,000 or 1:200,000 injections, it offers a fast onset, between 1 and 9 minutes; preparation duration with up to 60 minutes for infiltration injections and 120 minutes for nerve blocks; and no methylparaben in the formulation.

Another effective option is Patterson Lidocaine Anesthetic HCl 2% and Epinephrine, which provides a numbing effect for various dental procedures. Epinephrine is added to the formulation in two strengths – 1:50,000 and 1:100,000.

After injection, the body must raise the pH of the local anesthetic towards physiologic (7.4) before the patient can achieve pulpal anesthesia. Onset (Onpharma) can create a quicker, more predictable experience with anesthesia. The Onset Mixing Pen makes it easy to load the cartridge of local anesthetic and buffer it toward neutral pH in approximately 3 seconds. After the cartridge is buffered, it’s loaded into the syringe for immediate injection. Clinicians can use their own standard dental cartridges of local anesthetic as well as their own syringes.

Traxodent Hemodent Paste Retraction System (Premier Dental) provides predictable hemostasis and soft-tissue management in minutes. The soft paste produces gentle pressure on the sulcus while it absorbs excess crevicular fluid and blood. The aluminum chloride creates an astringent effect without irritating or discoloring surrounding tissue. Traxodent rinses away clean without leaving material behind that could interfere with downstream products and procedures, such as bonding agents.

Choosing the block

Here are two high-performing materials you’ll want to consider for milling:

IPS e.max CAD blocks (Ivoclar Vivadent) are lithium disilicate glass-ceramics that represent a groundbreaking material advancement. IPS e.max CAD combines highly esthetic qualities with user-friendliness and covers a comprehensive spectrum of indications. A wide range of translucency levels, shades, and block sizes offer flexibility for challenging clinical situations.

KATANA Zirconia STML (Super Translucent Multilayered) blocks (Kuraray Noritake) are specialized for fabricating full-contour zirconia prosthetics chairside. KATANA consists of four layers of zirconia in graduated shades for natural tooth-colored restorations and eliminates a time-consuming, challenging process of staining the restoration. For use exclusively with the Dentsply Sirona CEREC system, KATANA can be sintered in just 30 minutes with the SpeedFire furnace.

Delivering the restoration

Material choice for delivery and cementation are critical factors in CAD/CAM restoration longevity. The following products are up for the challenge:

3M Rely Universal Resin Cement works both as a standalone, self-adhesive cement and as an adhesive cement when combined with 3M Scotchbond Universal Plus Adhesive. Together they eliminate the hassle and confusion of multiple resin cements, primers and adhesives, simplifying your direct and indirect restorative workflows, with fewer products to stock and replenish.

RelyX™ Universal Resin Cement (3M) works both as a standalone, self-adhesive cement and as an adhesive cement when combined with 3M™ Scotchbond™ Universal Plus Adhesive. Together they eliminate the hassle and confusion of multiple resin cements, primers and adhesives, simplifying your direct and indirect restorative workflows, with fewer products to stock and replenish.

3M offers another solution in RelyX Unicem 2, a next-generation, self-adhesive cement that combines convenience and easier mixing with reliable clinical performance and enhanced bond strength. The cement is formulated to offer well-balanced mechanical properties and long-lasting esthetics, along with virtually no postoperative sensitivity.

SpeedCEM Plus (Ivoclar Vivadent) is a self-adhesive, self-curing resin cement with optional light-curing. Its formulation has been optimized to make it particularly suitable for use in conjunction with restorations made of zirconium oxide and metal-ceramics, and for the cementation of restorations on implant abutments made of oxide ceramics such as zirconium oxide, metal and metal-based restorations, and lithium disilicate glass-ceramics.

Multilink Automix (Ivoclar Vivadent) is an adhesive luting system for the cementation of indirect restorations made of silicate and oxide ceramics, including IPS e.max, metal and metal-ceramics, as well as composites. The optimized formula now offers an additional “white” shade, try-in pastes, and optimized handling. For demanding ceramic and composite restorations, Variolink Esthetic is Ivoclar Vivadent’s esthetic light- and dual-cure luting composite offering excellent shade stability thanks to the patented and reactive light initiator Ivocerin, which is 100% amine-free.

KaVo Kerr continues to expand upon its excellent reputation in adhesive dentistry with some innovative solutions. Introduced one year ago, Nexus Universal cement allows the clinician to cut their procedure steps by up to half while delivering up to two times higher bond strength on any substrate, according to the company’s data on file. It also offers a flexible workflow to accommodate a clinician’s preferred cementation technique and helps achieve a strong bond. Nexus Universal followed NX3 Nexus Third Generation, an auto-mixing dual-cure cement that can be used for all indirect applications, including veneers. With Kerr’s proprietary amine-free initiator system and optimized resin matrix, NX3 is a truly color-stable adhesive resin cement. For those who prefer a visual indication, Maxcem Elite Chroma (KaVo Kerr) offers a self-etch and self-adhesive resin cement with a color cleanup indicator, which dispenses pink before fading at the gel state, to indicate the optimal time to clean up excess cement.

Further expanding upon Nexus material technology, Nexus RMGI (KaVo Kerr) is the first resin-modified glass ionomer available with advanced Nexus technology, which provides an optimal gel state and 2- to 3-second tack cure capability to ensure easier cleanup. Delivered in an auto-mix syringe, the self-adhering paste/paste system delivers excellent bond strength to tooth structures and common substrates.

Calibra Universal (Dentsply Sirona) is a self-adhesive resin cement designed for easy, one-step cementation, meaning no additional etchant or adhesive is needed for a wide range of indications. This material is designed to remove the stress of over-curing thanks to the wide tack cure window of up to 10 seconds and an extended 45-second gel phase that allows for thorough and effective removal of excess cement. Calibra Universal offers high immediate 6-minute bond strength.

ZR-Cem (Premier Dental) is a dualcured, self-adhesive universal resin cement specially formulated for zirconia restorations. ZR-Cem enables a strong bond to all ceramic materials, dentin, and enamel for excellent retention and marginal integrity. Unlike other cements, ZR-Cem’s BPO/amine-free initiation system translates to lasting color stability.

GC FujiCEM Evolve is GC America’s next-generation RMGI cement. Built on the legacy of FujiCEM 2, GC FujiCEM Evolve is a radiopaque resin-reinforced glass ionomer cement in a syringe delivery with a tack-cure feature and high radiopacity. It can be used for cementing a variety of substrates and different types of indirect restorations.

Dental bur selection is a critical consideration for marginal integrity. Be sure to invest in high-quality burs that can stand up against high-strength materials.

Patterson burs are made from tungsten carbide, diamond, and steel, and are available in all three shank types: friction grip, right-angle latch, and handpiece. The carbide burs are used to remove material and tooth structure, and while steel burs share many of the same characteristics, they’re softer and more flexible. Diamond burs are used for precise drilling and finishing as well as for grinding, where material removal is not a concern. Diamond discs are used primarily for contouring, fabricating, finishing, and shaping of dental restorative materials.

Midwest (Dentsply Sirona) is another clinician-preferred brand. Midwest Trimming and Finishing carbide burs have finely ground edges available in 12- and 30-blade configurations. Their gold-plated shank helps resist corrosion during sterilization. Helpful for COVID-19 considerations, Midwest Once Sterile Diamonds are sterilized in individual pouches, and are sharp and ready to use out of the box. They’re available in standard and spiral configurations.

Selected references

Atlas A, Isleem W, Bergler M, Fraiman HP, Walter R, Lawson ND. Factors affecting the marginal fit of CAD/CAM restorations and concepts to improve outcomes. Curr Oral Health Rep. 2019;6(4):277-283.

Brandt PR, Sterlitz SJ, Fasbinder DJ. Tooth preparation considerations for CAD/CAM materials in restorative dentistry. Decisions in Dentistry. March 13, 2020.

Harsono M, Simon JF, Stein JM, Kugel G. Evolution of chairside CAD/CAM dentistry. Inside Dentistry. 2012;8(10).

Moörmann WH. The evolution of the CEREC system. J Am Dent Assoc. 2006;137(Suppl 1):7S-13S.

Rajan N. Why I Use TRIOS Smile Design. Dental Product Shopper. 2020;14(7):62.

Skjold A, Schriwer C, Øilo M. Effect of margin design on fracture load of zirconia crowns. Eur J Oral Sci. 2019;127(1):89-96.

Winkelmeyer C, Wolfart S, Marotti J. Analysis of tooth preparations for zirconia-based crowns and fixed-dental prostheses using stereolithography data sets. J Prosthet Dent. 2016;116(5):783-9.

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This blog post originally appeared in the January 2021 edition of OnTarget. To read the latest issue and view current promotions, visit pattersondental.com/dental/ontarget.