Michael Miller, DDS
Your information lends doubt to the viability of dual-cure core materials. Do you foresee them being removed from the market? What can we expect from all the buildups we've done using these materials? Would you recommend going back to total self-cure buildup materials such as Core Paste from Den-Mat? I prefer self-cure in the posterior (especially in deeper preps), although I do use light-cured in the anterior. Do you recommend discontinuing the use of the dual-cure materials?
We are not quite ready to tell you to trash all your dual-cure products, but our tests are definitely showing that most of them are not doing what they are supposed to do. For example, in our latest round of tests, the results of which can be found in our 2004 annual edition, we found virtually all the dual-cure core materials polymerized more thoroughly in the self-cure mode rather than the dual-cure mode. This shows that light-activation interferes with the self-curing mechanism. Therefore, maybe a moratorium on these materials is warranted rather than an outright ban. Nevertheless, stocking a deep-curing light-cured product such as Clearfil Photo Core (Kuraray) and a reliable self-cure product such as the aforementioned Core Paste should cover you for most situations.
When cementing a PFM crown, is there much advantage in using RelyX Unicem over RelyX Luting cement? Are they similar in both strength and solubility?
RelyX Unicem, a resin cement, should be more insoluble and retentive than RelyX Luting Cement, which is a resin ionomer. Nevertheless, the former is new and unproven, while the latter product has a solid track record. For metal-based crowns with adequate mechanical resistance and retention form (not "teepees"), RelyX Luting is tough to beat from a performance standpoint, but being powder/liquid and hand-mixed, its convenience factor is quite low. On the other hand, RelyX Unicem, packaged in an automix capsule, is easy to use. Just be aware that our tests reveal that its hardness doubles when you allow it to self-cure (which it would do anyway under a metal-based restoration) compared to light-activation. Paradoxically, its bond strength after 24 hours is higher when you do light-activate it. So, the best way to use this product is still uncertain when light-curing is possible (metal-free restorations).
Any new research regarding 4 Seasons by Ivoclar Vivadent?
We have indeed completed a full-scale evaluation of this product, with all the details in our 2004 annual edition. In summary, we found it to have one of the best, if not the best, shade selection among the hybrids on the market. In addition, it is quite sculptable — you'll never have to worry about it slumping. Be warned, however; if your preference is to use a brush to manipulate composite, especially smoothing the surface layer, this product is too stiff.
I received a sample of "Shimmer," a new polishing paste from Dentsply Professional. It says it is great for all restorations. What is the real story?
Nupro Shimmer (its official name) is supposed to be a polishing paste for restorations during routine hygiene visits. It contains submicron aluminum oxide plus sodium fluoride. It has a good consistency — it's nonrunny and the splatter is controllable. Our preliminary polishing test on composite finished with an Enhance disc showed Shimmer is capable of producing a high shine on composite, but only if it is used on a FlexiBuff by Cosmedent or a similar instrument. It was not able to improve upon the Enhance surface with a typical prophy cup.
For quite some time, I have used both resin cements and glass ionomer cements in my practice. My strategy was to use resin cements as much as possible for lower solubility and adhesive properties, but to select glass ionomer (with the appropriate restorative material and retentive preparation design) if I thought the clinical circumstances revealed that moisture control or "bondability" might be compromised.
To that end, I selected PermaCem from Zenith/DMG a few years ago as a resin/glass ionomer solution that could be used for the cementation of all-ceramic crowns that had high-strength, highly sintered cores (i.e In-Ceram Alumina and Procera.) The color, low expansion, and glass ionomer "self-adhesion" component seemed like a good alternative. I read the instructions, which implied that the glass ionomer component of the cement would be "enough" to "bond" to underlying tooth structure without the application of additional etchant and adhesive. To my recollection, etching/adhesive application wasn't discouraged, but it certainly wasn't required. When the clinical circumstances warranted it, I selected one of these all-ceramic restorative systems and cemented the final restorations with the cement alone — no "bonding." I cemented dozens of units that way.
Now, nearly three years later, I have seen intensely dark gray chroma showing through at the margins of some of the patients with whom I used that technique. Clearly, the cement is leaking and there was (for all intents and purposes) no glass ionomer "bond" to the preparations at all. I have been informed that Zenith/DMG has since "changed its tune" and now definitely recommends adhesive techniques when using PermaCem. Am I correct in my recollection of the initial PermaCem instructions that claimed using an adhesive was optional?
The original instructions stated that use of an adhesive was optional, but suggested using an adhesive if you wanted the highest possible adhesion. We thought this was strange and noted, "When do you not want the highest possible adhesion?" in our 2000 annual edition (when we first evaluated it). Your experience underscores why we advise not to jump in headfirst with any new product. In any event, this is a difficult call as far as establishing whether Zenith/DMG should have been more definitive and insistent in its directions concerning the use of an adhesive from the beginning. It was stated that an adhesive would help performance, but it left the final decision to you, the clinician. While we believe manufacturers should be less equivocal in their directions, we find numerous ambiguous statements across the board. We try to point them out for our readers, but we also believe to play it safe when in doubt.
Dr. Michael Miller is the publisher of REALITY and REALITY Now, the information source for esthetic dentistry. He is an international lecturer and a fellow of the American Academy of Cosmetic Dentistry, as well as a founding member. He maintains a private practice in Houston. For more information on REALITY and to receive a complimentary issue of his monthly update, REALITY Now, call (800) 544-4999 or visit www.realityesthetics.com.