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OPT-In Tests a New Zirconia: The Results

A few months ago a new zirconia from Germany came our way for testing. It claimed to be a higher grade of 1400 MPa purity with more translucency and improved esthetics. Sound too good to be true? We thought so, however, after a few months of testing, we became believers.

Doceram Medical provided a couple of our labs with various samples of Nacera® zirconia, including Pearl 1 (white), and various value shades capable of reproducing 16 vita classic shades. After making the necessary adjustments to sintering and glazing times and temperatures, the results were in, all exceptionally positive. Nacera® zirconia was kinder to milling burs (lasted up to 15% longer), milled more precisely and smoothly, had less shrinkage variations (each lot/batch has its own shrinkage factor), and was more translucent than other high strength zirconia.

OPT-In member, Dennis King, CDT, has used the full line of Nacera® zirconia, including the multi shade pucks that come in A, B, C, and D shades. He has successfully provided several large full mouth cases of full contour Nacera® restorations that included anteriors, one case for a dentist’s wife. Dennis noticed that Nacera® mills far easier than e.max® and other zirconia, and that his burs have been lasting longer. He also stated that fit is consistently better due to more predictable shrinkage and smoother milling. With his successes fully documented, other OPT-In lab members have also commented positively on the same points.

Top photo of Nacera® Pearl 1.5 (A2), with  ceraMotion®, is courtesy of Master ceramist, Roberto Rossi, MDT, who has echoed Dennis’ comments. In a month of testing several different pucks and ceramMotion® (Dentaurum), Roberto noticed more translucency without sacrificing higher strength, better margins with less effort, and predictably better esthetics when compared to competing products. Of particular note, single-step stain & glaze ceraMotion®, distributed by Nacera US, not only improved esthetics, it saved time by requiring only a single stain & glaze bake.

Doceram Medical is establishing the Nacera® brand through a new US subsidiary, Nacera US. OPT-In members are excited about working with Nacera US through a special pricing program, exclusive for OPT-In members. Additionally, the Dental Lab Group, in Staten Island, will provide special Nacera®  outsource pricing [only] for those members without milling machines, as well as for custom milled titanium abutments.

Nacera US will be at booth L-22, Lab Day, Chicago, and provide continuous seminars in a private suite. Guests at the suite will enjoy food and beverages, and be able to test stain & glaze the new ceramMotion®  on samples of Nacera® zirconia. Roberto Rossi, and others, will be guest lecturers and guiding hands-on experiences. Nacera US has also promised important announcements in February, including the launching of their new website. For inquiries and more information about the entire line of Nacera® products, visit: Doceram Medical. For immediate questions, or to register for courses in Chicago, please call Nacera US at, 215-345-5283.

etched porcelain

All-ceramics and Self-adhesive Cements: Is it a Good Idea?

In spite of the inherent brittleness and limited flexural strength of silica-based ceramics, final adhesive cementation with composite resin increases the fracture resistance of the ceramic restoration and the abutment tooth.

Bonding to silicate-based ceramics is usually obtained by two simultaneous mechanisms: 1) micromechanical retention provided by acid-etching of the ceramic surface, and 2) chemical coupling by the application of a silane coupling agent.

During acid etching (above photo, left), the hydrofluoric (HF) acid reacts with the glassy matrix that contains silica, dissolving the surface to the depth of a few microns. This glassy matrix is selectively removed and the crystalline structure is exposed. The silane coupling agent presents bifunctional characteristics, promoting a chemical interaction between the silica in the glass phase of ceramics and the methacrylate groups of the resin through siloxane bonds.

It has been demonstrated that silane primers may confer a resistance to the degradation of the ceramic-resin bond exposed to moisture and intraoral thermal changes. Etching and silanization increase the surface energy and the wettability of the ceramic substrate.

RelyX™ Unicem can achieve high or comparable bond strength to other investigated cements without any pretreatment steps such as etching, priming or bonding. However, other studies observed higher shear bond strength values after etching with HF acid and silanized. In a study by Kumbuloglu et al. RelyX™ Unicem showed lower shear bond strengths than the other resin cements investigated when no pretreatment of the ceramic surface was performed. In the study by Reich et al., only the RelyX™ Unicem, in contrast to Variolink (Ivoclar, Vivadent) and Calibra (DeTrey Dentsply, Konstanz, Germany), was able to survive the whole thermocycling procedure in the case of no pretreatment. This indicates that besides mechanical interlocking, additional bonding mechanisms with RelyX™ Unicem to the ceramic surface are possible.

The specific phosphoric acid methacrylates have the ability to provide physical interactions with the ceramic surface and are able to provide strong hydrogen bonding with hydroxyl groups present on the ceramic surface.  An increase in the bond strength after pretreatment with hydrofluoric acid and silane was also observed. This is in agreement with the study by Piwowarczyk  who reported that, in comparison with 10 cements from different classes, only RelyX™ Unicem exhibited high shear bond strength after 14 days of water storage followed by thermal cycling. In the same study, it was reported that the light polymerization of the self-adhesive resin cements enhances shear-bond strength when compared to auto polymerization.

The above doesn’t take into account, self-adhesive bonding to dentin and enamel. That is a related, but a separate consideration.

 

Zirconia, Cleaning Contaminates: What Works?

As most of us know, zirconia crowns and bridges are healthy, esthetic, and nearly indestructible. However, in certain conditions, long term cement retention can be unpredictable. This is especially true if the internal surfaces have been exposed to saliva. Unfortunately, there is not a lot of information about the best ways to eliminate contamination. Below, we try to bring more clarity to this topic.

Aladag, et al conducted research to determine the effect of saliva on the cementing surface of untreated zirconia. They reported that different cleaning methods, water spray, sodium hypochlorite, or Ivoclean® produced few improvements to bond strengths. The first point to note is that in this investigation, the tested zirconia surface was not air abraded.

Tunc’s team obtained different results from Aladag’s. Their research included Ivoclean, phosphoric acid, alcohol , water rinsing, steam cleaned, and air abrasion (after) saliva contamination. Their findings proved air abrasion to be best followed closely by Ivoclean. But that doesn’t answer the question about saliva contamination after zirconia has been air abraded.

Wille’s prosthodontic team from Germany tested the affect saliva has on zirconia surfaces that have been air abraded prior to contamination. Their testing included silicone disclosing agents, GC Fit Checker white or GC Fit Checker II for checking the fit of zirconia copings. Uncontaminated zirconia surfaces used as controls were compared to contaminated copings cleaned with “…water spray or ultrasonically in 99% isopropanol or using a newly developed cleaning paste (Ivoclean® from Ivoclar) .” Their findings showed that using a secondary application of isopropanol increased reduction of carbon residuals on the zirconia surfaces, more so than did an additional application of Ivoclean. However, none of the cleaning agents or additional applications removed all the silicone contaminants. This could be due to air abrasion increasing retention of the contaminants.

Feitosa’s group also looked at saliva contamination, but included the effects of aging on resin bond strengths. Their investigation included “one hundred and eighty zirconia specimens sandblasted with 50 μm aluminum oxide particles, immersed in saliva for one minute (with the exception of the control group, [C]), and divided into groups according to the cleansing method, as follows: water rinse (W); 37% phosphoric acid gel (PA); cleaning paste (ie, Ivoclean®) containing mainly zirconium oxide (IC); and 70% isopropanol (AL).” Resin SBS was evaluated “…after 24 hours, 5000 thermal cycles (TC), or 150 days of water storage.” The results”…showed that PA < AL and W < IC and C. SBS ranged from 10.4 to 21.9 MPa (24 hours), from 6.4 to 14.8 MPa (TC), and from 2.9 to 7.0 MPa (150 days). Failure analysis revealed a greater percentage of mixed failures for the majority of the specimens and a smaller percentage of adhesive failures at the ceramic-resin cement interface,” and that Ivoclean® was able to sufficiently clean saliva contaminated zirconia surfaces to maintain acceptable long term bond strengths.

Kim, et al’s research, in 2015, also examined saliva contamination of air abraded zirconia surfaces. Their testing included cleaning with “…water-spray rinsing (WS), additional air abrasion (AA), and cleaning with four solutions (Ivoclean® [IC]; 1.0 wt% sodium dodecyl sulfate [SDS], 1.0 wt% hydrogen peroxide [HP], and 1.0 wt% sodium hypochlorite [SHC].” A sample with no contamination (NC) was used as the control. Each zirconia sample was bonded to resin with Panavia F 2.0 prior to aging with 5000 thermocycles. Their results showed “…groups NC, AA, IC, and SHC had hydrophilic surfaces. Groups IC and SHC showed statistically similar bond strengths to groups NC and AA (P>.05), but not groups SDS and HP (P<.05). For groups WS, SDS, and HP, blister-like bubble formations were observed on the surfaces under SEM. Test results reiterated the cleaning effectiveness of Ivoclean®, and also supported the use of sodium 1.0 wt% hypochlorite.

Dentists Feeling Global Slowdown: What’s it Mean?

Thanks to falling oil prices and increased employment, consumer confidence is improved and pent up demand is in bloom. They have also adapted to a new socio economic normal: economic stability with less income. Unfortunately, in 2014 the middle class earned 4% less than in 2000 (Pew), and fell from 61% of earners in 1971 to 50% in 2015. Similarly, the US Census Bureau reported that median income fell 9% from 2007 to 2014. That means, heading into 2016, confident consumers may be working their way up from negative territory. But, there’s more to this story.

As a risky undercurrent to consumer confidence, the economic pullback in China has led US manufacturing and exports to contract, other economies to slow, and raised fears of a new global recession. While the US economy is believed to be less affected than others, the now stronger dollar is impeding exports and causing some to wonder if layoffs are far behind? While there is little belief the US is on the brink of another recession, there is plenty of disagreement about the economic strength of 2016 going forward.

The New Consumer

The recent recession shaped consumer attitudes and habits into a new normal: “If my income is flat or less, then what I pay must be flat or less.” With support from the digital age, price conscious consumers expect and demand discounts in everything they buy. Moreover, with the internet, consumers are faster, better, and more efficient at finding value, making most everything a commodity.

The new normal caused 2015 retail sales to drop 8%, and prices to fall 2.9% from 2014 levels (Bureau of Economic Analysis). Additionally, mid priced retail stores are losing sales to “off-pricers,” such as Kohls and Marshalls.  Meanwhile, “fast design,” high production, low cost chains such as H&M and Forever 21 are expanding. Is dentistry seeing the same price pressures? This past Christmas, online shopping grew 20% while retail bricks and mortar sales fell 10%. In response, Macy’s will close 40 stores in 2016, and open 6 new low cost discount stores. Radio Shack, Staples, and Sears/KMart are closing a combined 1,800+ locations. Yes, in some ways, this is very similar to what we are seeing in dentistry: changes driven by consumers are forcing retailers to change or close.

Impacting Dentistry

Today, new technology provides consumers with consistently higher quality, mass produced (non distinct) products at lower costs. While we see this kind of innovative technology aiding dental labs, commoditized private practice dentists continue to operate without cost-saving scalability. Meanwhile, consumers often tell dentists the very same things they tell retailers: “Yes, expensive is nice, I would like it but I don’t need it, can’t afford it, and I’m not going to pay for it.” For many, dentistry has become a reluctant victim of consumerism’s commoditization.

The market, in general, isn’t as wealthy as it once was and doesn’t see dentists as it once did. Because the market is always 100% correct, dentists and lab owners need to see themselves as their markets see them and either provide what their markets want, or together, convince consumers they need and deserve better. That means, some dentists and lab owners might need to adjust their approach to how they deliver services and set fees. But remember, people pay for what they want. Dentists and their labs can provide what many consumers want, commodity care at a lower cost, or, help them to want something better. It’s entirely up to the professional team.

With pressures never before experienced, dentists, lab owners, manufacturers, and distributors need to look at new ways of collaborating and working together. To help, OPT-In is leading the way in building an alliance community of stakeholders. Nacera US, known for its high quality zirconia products, was first to provide financial support for the OPT-In national public relations campaign supporting private practice. We invite all dentists, laboratory owners, manufacturers, and distributors to contact us and participate.