Do dentists still need impressions with the same degree of accuracy for CAD/CAM as we needed for traditional casting, or is CAD/CAM more forgiving?
It is even more important to have an accurate impression for CAD/CAM restorations. Handmade restorations have a built-in "fudge" factor, whereas to get a quality restoration with CAD/CAM, everyone has to be on the same page. You can always burnish or weld a metal margin. However, with all-ceramic restorations, the only option is to use pure porcelain and compromise strength.
What preparation margin do you suggest for a full-coverage lithium disilicate restoration, and why?
For full-coverage lithium disilicate restorations, no bevel margins are preferred. We will often recommend chamfer or shoulder margins. For CAD/CAM restorations, chamfer margins ensure the best fit. Truthfully, though, we find that the best advice is to adhere to the manufacturer's specifications.
In your opinion, what are the advantages of lithium disilicate over zirconia?
Lithium disilicate offers some of the best strength, coupled with strong esthetic results. It can easily match existing tooth opacity, shades, and translucency without sacrificing strength or needing any veneering porcelain. Furthermore, as a technician, pressed lithium disilicate is the closest an all-ceramic restoration comes to matching a traditional wax-and-cast restoration. This allows us to have more control and margin integrity, enabling us to have, in essence, a tooth-colored full-cast crown.
How do you treat a lithium disilicate restoration before you send it to dentists? What should dentists do with them after they take them out of the bag?
We do our final quality control inspection, checking the margins, contact, and fit. We apply a ceramic etching gel to the internal surface. We apply the IPS Ceramic Etching Gel for about 20 seconds, as per the manufacturer's specifications. It is sealed in a pouch with alcohol to prevent contamination and sent to the doctor.
After the doctor tries it, the surfaces become contaminated by saliva and the strength of the resin bond is compromised. Washing with water or phosphoric acid only restores some of that bond strength, but Ivoclean from Ivoclar has shown to be very effective. Ivoclean was developed specifically for decontaminating the inner surface of the restoration prior to cementation.
Do you have a preference for a type of resin cement to be used with lithium disilicate?
Several of our clients seem to prefer self-etch adhesive resin cement, such as Multilink Automix, for its high strength and reduced sensitivity for the patient. Self-adhesive resin cements will work, as well, but the bond strength is lower than that of a self-etch adhesive.
Lenny Marotta, CDT, MDT, PhD, is a graduate of the Kerpel School of Dental Technology, Fairleigh Dickinson University, Farmingdale State College - State University of New York, and Leeds Metropolitan University. He is the owner of Marotta Dental Studio and MDS Cranial Facial Engineering. Dr. Marotta also teaches at Farmingdale State College - State University of New York and the New York University College of Dentistry. To contact him, email [email protected].
