Dental Product Test Drive: GC America’s Precrystallized CAD/CAM Blocks Save Time Without Compromise

Image Credit: © GC America

Digital dentistry is no longer a hobby for the tech enthusiast dentist. Many companies provide solutions for your practice that offer improved workflows and enhanced treatment possibilities. I have been fabricating restorations chairside since 2006 and have enjoyed seeing the technology improve almost as fast as you might see a new smartphone come to market.

It remains my firm belief that the category of digital dentistry would not be as profound without a concurrent explosion of growth in available materials. When I started, we had a couple of options including composite and leucite glass-ceramics such as Empress from Ivoclar. Today we have dozens of incredible materials, and recently I had a chance to try out the new material from GC America: the GC Initial LiSi Block.

The GC Initial LiSi Block is a lithium disilicate glass-ceramic. At its core, lithium disilicate has incredible esthetics like the classic Empress but demonstrates a much higher level of strength. This creates an expanded indication for the material that can be used in the anterior as well as the posterior.

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Before I try any material in our office, I look for research to corroborate any claims made by a company. In this case, GC again demonstrated its commitment to excellent peer-reviewed clinical research. I was able to find articles demonstrating the GC Initial block had acid dissolution similar to zirconia restorations, 2-year studies showing 100% longevity, and confirmation of the high compressive strength of the material.^1-5

One advantage of these blocks is that they have been crystallized prior to milling. Another characteristic of this material is the use of High Density Micronization (HDM) in the block fabrication. HDM is significant in that it utilizes smaller crystals that are dispersed in higher density as compared with other lithium disilicate materials. In their research, GC America’s scientists found this reduces the risk of microfracture within the restoration following milling. It also improves resistance to wear and decreases the abrasion against the opposing tooth better than the average ceramic.

The fact that the block is precrystallized is comforting because this means it was fired under the manufacturer’s optimized protocol. This saves time at the practice and reduces the potential for distortion in thin areas of a restoration fired chairside.

Of course, with all this research, I still need to know the real-life clinical impact. Milling a crystallized block improves my time in delivering the final restoration. The workflow goes from scanning, designing, and milling the restoration right into final polishing before seating. It was nice to find that GC America has videos on its website featuring useful tips on how to properly polish the restoration prior to cementation.

With GC Initial LiSi Blocks, the good news is that you can stain and glaze the restoration if you want to add characterization, and the blocks are designed to work cohesively with the GC Initial Spectrum Stain system. With GC Initial LiSi Blocks you have a range of B1, and A shades from A1 down to A3.5. Each is available in high translucency and low translucency.

With research and block choice completed, I finally got a chance to try out the material. The preparation guidelines are like those of other lithium disilicates. Years ago, we found that our preparations improved when we started scanning them. There is nothing like seeing your own crown prep blown up on a computer monitor. The technique that I have found works well is to prep down at least another half-millimeter to a full millimeter. It is not that the Initial LiSi necessarily needs the additional thickness, although it certainly gets stronger in this case. I just prefer additional room to create variable and lifelike anatomy in the restoration for esthetic purposes, especially in the premolar and first molar locations.

While testing the blocks, we tried both polishing and glaze firing in the oven. Polishing simply included removing the sprue, using a rubber wheel for the initial polish, and then using a diamond paste for that final glaze polish. It took less than 5 minutes and is something you can train yourteam to help with. The glaze firing also was under 10 minutes because you do not need to crystallize the material. For me, the choice between polishing or glazing is based on how much characterization I need.

I found the shades matched to the standard VITA shades fairly well. Having used high translucency IPS e.max from Ivoclar in the past, I did not think it was quite as translucent as that material. The GC Initial LiSi HT blocks were closer to the MT e.max blocks in this case. For most of my adult patients, this was plenty of translucency. The low-translucency blocks were a perfect choice if I was adjacent to any classic porcelain-fused-to-metal or zirconia, while still having a bit more lifelike reflection to the material itself.

We were also able to separately evaluate and use GC G-CEM ONE, the universal self-adhesive resin cement from GC. This is a dual-mix resin cement with the same extensive research behind it. Coming in 4 shades, this cement had a usable tack cure stage, which was my favorite thing about it.

I often get stuck on other cements when their “tack cure” stage is anything but that, and I am left with rock-hard cement to clean up. Of course, this destroys any time savings I may have gotten from utilizing CAD/CAM chairside. The G-CEM ONE tack cures to a nice rubbery state that allowed me to do most of the cleanup prior to final curing. We polished the margins a bit at the end as well, and the optical connection between the tooth and the restoration really blended nicely.

After using this new CAD/CAM material for a few weeks, I found little to complain about. I think the GC Initial LiSi block is a welcome addition to the digital dentistry lineup, saving me time without compromising on the result.

References

1. Azuma T, Shigenori A, Fusejima F. Evaluation of acid resistance for novel lithium disilicate glass-ceramic block. Presented at: CED-IADR/NOF Oral Health Research Congress; September 16-18, 2021; Brussels, Belgium. Abstract 0223. https://ced-iadr2021.com/wp-content/uploads/2021/09/Abstract-book_2021-9-20_Adjusted-version.pdf
2. Onodera M, Azuma T, Murata Y, et al. Acid resistance of lithium disilicate glass ceramics. Presented at: 2023 AADOCR/CADR Annual Meeting; March 17, 2023; Portland, OR. Presentation ID: 0760. Accessed January 8, 2023. https://iadr.abstractarchives.com/abstract/52am-3824170/acid-resistanceof-lithium-disilicate-glass-ceramics
3. Azuma T, Onodera M, Murata Y, Akiyama S, Fusejima F. Evaluation of acid resistance for novel machinable lithium disilicate glass-ceramics. Presented at: 2022 AADOCR/CADR Annual Meeting; March 24, 2022; Atlanta, GA. Presentation ID: 0472. Accessed January 8, 2023. https://iadr.abstractarchives.com/abstract/51am-3649098/evaluation-ofacid-resistance-for-novel-machinable-lithium-disilicate-glass-ceramics
4. Cagidiaco EF, Grandini S, Goracci C, Joda T. A pilot trial on lithium disilicate partial crowns using a novel prosthodontic functional index for teeth (FIT). BMC Oral Health. 2019;19(1):276. doi:10.1186/s12903-019-0957-4
5. Miyake T, Kato K, Akiyama S, et al. Microstructure of new lithium-disilicate CAD/CAM block. Dental Materials. 2019;35(suppl 1):e25. doi:10.1016/j.dental.2019.08.050