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For the last 45 years, the dental ceramic industry has been in the midst of a revolution. Materials have evolved from the early 1970s with the introduction of the glass-ceramic material Dicor® by Corning Glass Works1 to the current zirconia-containing lithium silicate (ZLS) (Celtra® Duo/Press, Dentsply Sirona, dentsplysirona.com; Suprinity®, Vita, vita-zahnfabrik.com) and zirconium oxide (zirconia), which includes the following products: ArgenZ™, Argen®, argen.com; BloomZir, Bloomden®, bloomden.com; BruxZir®, Glidewell Laboratories, glidewelldental.com; Cercon®, CEREC® Zirconia, and Zirconia InCoris® TZI, Dentsply Sirona; e.max® ZirCAD, Ivoclar Vivadent, ivoclarvivadent.us; Katana™, Kuraray Noritake Dental, kuraraynoritake.com; Lava™ Plus/Esthetic, 3M, 3mespe.com; Nacera®, Doceram Medical Ceramics, doceram-medical.com; Zenostar®, Ivoclar Vivadent; and Zirlux® FC2, Zirlux, zirlux.com.
This article reviews the dental ceramic materials (Table 1) that have been available through in-office chairside CAD/CAM (blocks) and dental laboratory (press, pucks, and blocks) ceramics in relation to esthetics, strength, and durability. The article concludes with a focus on the ZLS pressed material, including case studies.
History and Types of Dental Materials
Adhesive Ceramic Feldspathic
Vitablocs® Mark II (Vita North America); CEREC/Sirona Blocs (Dentsply Sirona).2-5 Vitablocs Mark II is the most researched monolithic block in history, introduced in 1991 with over 25 years of scientific study. This monochromatic feldspar ceramic block was originally used in all areas of the mouth because it was the original CAD/CAM chairside block, and the survival rate of this block was enhanced when there was proper occlusal reduction of the tooth. Vitablocs Mark II has a flexural strength of 130 MPa and must be hydrofluoric (HF) acid-etched for 60 seconds before bonding for maximum strength. Several positives for using the material are its nonabrasiveness against the natural dentition, its similar wear pattern to enamel or gold, and the fact that the material can be polished and/or glazed before cementation. This fine-grained (4 µm) feldspathic porcelain is esthetically pleasing, which make it suitable for inlays, onlays, crowns, and veneers. Today, the material is usually used from the second premolar forward and not used in the molar regions due to its lower flexural strength. In 2007, Sirona introduced its version of this feldspathic porcelain, CEREC Blocs. Vitablocs Mark II and CEREC/Sirona Blocs continue to be used in the chairside environment for selected cases, especially inlays and veneers.
Adhesive Ceramic Leucite-Reinforced
IPS Empress® CAD/Press (Ivoclar Vivadent).6 IPS Empress CAD was introduced in 1998 and was similar to Empress I but with a finer particle size. Empress CAD (160 MPa) is a leucite-reinforced ceramic that is used like Vita Mark II but with slightly higher flexural strength. The leucite adds strength to the material and blends well in the mouth with the surrounding dentition. The blocks are available in low translucency (LT) and high translucency (HT). The material can be glazed or polished and requires etching with HF acid for 60 seconds before bonding. The material is highly esthetic with excellent shade adaptation and was used in the late 1990s/early 2000s as the material of choice. A potential drawback to Empress CAD is its strength, which is less than desirable in heavy occlusion areas. In selected areas, Empress CAD is still a highly esthetic and appropriate material to use for crowns and veneers.
Multi-Shade Blocks
Vita North America, Ivoclar Vivadent, and Dentsply Sirona have made multi-shade blocks available to the clinician using chairside in-office milling. These blocks demonstrate an attempt to address issues of the inherent shading in natural teeth but have limitations to their effectiveness. These blocks have a gradient of opacities where the top part of the block is more translucent and the bottom part is more opaque. The main advantage is that the software allows adjusting the restoration position within the block to maximize whether the practitioner wants to mill a more translucent or more opaque restoration.
Multi-shade blocks are available in many forms:
• Vitablocs TriLuxe Forte- Displays more intensive chroma (intensity) and fluorescence at the cervical with increased layering to the enamel.7,8
• Vitablocs RealLife® - Gives more natural vitality to a tooth. The internal-to-external shade transition simulates the natural tooth transition from dentin to enamel. The crown design is manually positioned in block for fabrication.9
• CEREC Blocs PC - Integrates three color saturation levels (chroma) and translucency.5
• IPS Empress CAD Multi - Incorporate gradients of chroma and translucency in an Empress block.6
• CEREC Blocs C In- Similar to Vitablocs RealLife but the user selects the shade and the software will automatically position the restoration in the block. The CEREC C In consists of only one block, and the shade (preset translucency) of the restoration can be adjusted by adjusting the amount of enamel and dentin that appears.10
High-Strength Ceramic
e.max CAD.11,12 e.max CAD is a pre-crystallized lithium-disilicate block with particle sizes of 1.5 µm and 70% by volume. The e.max block is milled in the "blue phase" (pre-crystallized) where its strength is approximately equal to Vita and Empress blocks. After firing, e.max goes through a "crystallization" (from blue phase to enamel shade) where it reaches its final color and strength. e.max can be stained and/or glazed to achieve a 3-point flexural strength test of 360 MPa and a biaxial flexural strength test of 500 MPa. The material needs to be etched with 4.5% HF acid for 20 seconds before bonding for a non-retentive preparation and bonded/cemented for a retentive preparation. e.max has been a successful block over the years, with a documented 10-year success rate of 97.8% for a single crown and 88% for 3-unit single-visit bridges, limited from second premolar and forward with a connector size of 16-mm squared. Bridges can be cemented or bonded at the same success rate.13 e.max can also be used for custom implant abutments or screw-retained hybrid crowns with an anti-rotational notch inside the e.max block to increase stability and accuracy of fit. Lithium disilicates can be fabricated using several methods, such as milled from an in-office block or pressed in a dental laboratory.
Obsidian® (Glidewell).14 This translucent lithium-silicate ceramic has a flexural strength of 385 MPa. It is mainly used for inlays, onlays, or crowns.
High-Strength Ceramic: Zirconia-reinforced Lithium Silicate
This ZLS material contains a finer microstructure, resulting in a higher glass content that results in improved esthetics due to more light conductivity. The natural vitality of the ZLS material is displayed in its opalescence, translucence, and fluorescence, which contributes to the "chameleon effect" the restoration has with the rest of the surrounding dentition.15, 16
Celtra Duo.15 This chairside block was launched at the March 2013 International Dental Show (IDS) in Cologne, Germany. Celtra Duo is a fully crystalized ZLS chairside block. It allows the clinician the option of polishing or firing the material. Polished Celtra Duo results in a 3-point flexural strength test of 210 MPa and a biaxial flexural strength of 413 MPa. Fired Celtra Duo results in a 3-point flexural strength test of 370 MPa and a biaxial flexural strength of 560 MPa. The material comes in HT and LT.
Celtra Press with Celtra Ceram.16,17 Celtra Press establishes a blend of esthetics and strength in a glass-ceramic. Celtra Ceram is a veneering porcelain used when cutbacks are performed on Celtra to enhance esthetics. It presents in shades and translucencies that include enamel opal, enamel opal transparent, enamel opal HT, enamel opal LT, enamel effect, enamel effect fog, enamel effect ivory, power dentin, opaceous dentin, dentin effect, and dentin gingiva.
Vita Suprinity.18 Vita Suprinity was launched in 2014 as an un-sintered block requiring an oven to convert to final shade and strength (400 MPa). The material can be milled very thinly and comes in HT and translucent (T) blocks. Currently, Vita Suprinity ZLS material is not available in the US market.
High-Strength Ceramic: Zirconium Oxide
High-strength zirconia ceramics can be divided into two categories: traditional and translucent. Traditional zirconia options include ArgenZ Ultra, BloomZir HT, BruxZir, CEREC Zirconia Block, Katana HT, Katana ML, Katana STML, Lava Plus, Nacera Pearl, Zenostar MO, Zenostar T, and Zirconia InCoris TZI Blocks. Translucent zirconia options include ArgenZ Anterior, ArgenZ Esthetic, ArgenZ HT+, ArgenZ ST Multilayer, BloomZir ST, BloomZir UT, Cercon HT, Cercon XT, e.max ZirCAD, Katana UTML, Lava Esthetic, Zenostar MT, and Zirlux FC2.
Argen.19 ArgenZ Ultra Disc presents with high strength (1,400 MPa) and 0% translucency, making it an ideal solution over implants and posterior restorations. ArgenZ Esthetic Disc offers high translucency (40%) along with 100% stain absorption for esthetics and a strength of 1,100 MPa. ArgenZ HT+ has a strength of 1,260 MPa and translucency of 45%, both greater than the traditional HT zirconia. ArgenZ Anterior comes in a disc that represents the highest translucency (50%) with optimum strength (765 MPa). ArgenZ ST Multilayer presents an accurate match to the 16 Vita Classical shades. It has seven blended layers that provide 50% translucency with a strength of 850 MPa.
BloomZir.20 BloomZir HT Plus is a high-translucency zirconia with a strength of 1,350 MPa used for copings and restorations. BloomZir ST (super translucent) has a strength of 1,200 MPa and is used for crowns and copings in the esthetic zone. BloomZir UT (ultra-translucent) has a strength of 1,350 MPa and is used for anterior and posterior crowns.
BruxZir Blocks and Pucks.21 BruxZir has been used approximately 10 years for crowns, bridges, veneers, and implant abutments. This zirconium oxide is used in anterior cases for esthetic demands and bridge frameworks for strength, with values ranging from 600 to 1,400 MPa.
CEREC Zirconia Blocks, Zirconia InCoris TZI Blocks, and Cercon XT and HT Pucks.22 Zirconia InCoris TZI is a translucent zirconium- oxide sinter ceramic and represents the strongest material the dentist can fabricate chairside. The advantages of zirconia include an exceptionally high flexural strength (> 1,000 MPa), precise-fitting milled margins, more conservative preparations, and the fact that it can be cemented. However, it can be challenging to achieve the desired esthetics due to the inherent opaqueness of the material. Cercon XT (extra-translucent, 750 MPa) is used for crowns and 3-unit bridges; Cercon HT (1,200 MPa) is used for crowns, multiunit bridges, and abutments. Both provide a wide range of restoration options while maintaining esthetics.
e.max ZirCAD Blocks and Pucks.23 e.max ZirCAD is a zirconium-oxide monolithic block that can be milled chairside or fabricated in the laboratory, producing a flexural strength of between 850 to 1,200 MPa. The material is ideal for crowns, 3-unit bridges, and implant-supported superstructures. IPS e.max ZirCAD comes in three levels of translucency and also as a "multi" option that displays gradated chroma and translucency.
Katana Blocks and Pucks.24 Katana represents a relatively new zirconia that displays a gradual chroma and translucency like enamel. It is reported that Katana has a comparable translucency to lithium disilicate but is 30% to 75% stronger. The material comes in monochromatic and multilayer blocks and can be fabricated in approximately 45 minutes. Katana is available in several translucencies, meeting a wide range of strengths and translucencies: ultra-translucent multi-layered (UTML), flexural strength 550 MPa; super-translucent multi-layered (STML), flexural strength 750 MPa; multi-layered (ML), flexural strength 1,100 MPa; and HT, flexural strength 1,100 MPa. Katana has many applications, from veneers, inlays, onlays, crowns, and 3-unit bridges to long-span bridges.
Lava Esthetic.25 Lava Esthetic possesses an inherent, tooth-like fluorescence with a strength of 800 MPa that can be used for full-contour crowns, inlays, onlays, veneers, and bridge cases. This material has good matches with Vita Classical shades and an inherent translucency that works well in anterior and posterior cases.
Lava Plus.25 Lava Plus can be used for splinted crowns up to 4 units, including long-span, curved, and cantilever bridges. Implant abutments (screw-retained and hybrids), primary tooth crowns, and Maryland bridges can also use Lava Plus.
Nacera Pearl.26 Nacera Pearl is available in pucks for full and partial crowns, inlays, onlays, and veneers up to 14-unit bridges. The Pearl color range allows for seven basic colors plus white. This esthetic material is suitable for frameworks that require cutbacks for veneering purposes in high cosmetic-demand areas, monolithic crowns and bridges, telescopic and attachment technology, and abutments and screwed constructions. Nacera Pearl Multi-shade pucks have a flexural strength (biaxial) of 1,200 MPa and match well with Vita shades. An additional option is the hybrid ceramic puck (Nacera Hybrid) for permanent restorations.
Zenostar.27 These products address a variety of esthetic and strength needs. Zenostar MT (high translucency, flexural strength ≥ 550 MPa) is used for single crowns as well as 3-unit bridges. Zenostar T, which can be used for patients with signs of bruxism, has a flexural strength ≥ 900 MPa and is used for single-unit restorations as thin as 0.4 mm as well as long-span bridges. Zenostar MO, for veneering (flexural strength ≥ 900 MPa), can be used for long-span bridges and masking discolored preparations or titanium abutments.
Zirlux FC2.28 Zirlux FC2 is available in pucks and millable blocks indicated for full-contoured crowns and bridges, inlays, onlays, frameworks, and layered ceramics. Its high translucency along with its high strength (>1,100 MPa) make it an excellent choice for highly esthetic cases. The flexibility of the shade pastes and modifiers help the laboratory technician to achieve all 16 Vita Classical shades as well as three bleach shades.
Hybrid Ceramic
Vita Enamic.7 Vita Enamic, introduced as a variation of Vitablocs Mark II, was released in 2013 as a hybrid ceramic containing composite and porcelain. It consists of a polymer network 14% by weight and feldspathic porcelain 86% by weight with a flexural strength of 150 MPa. The composite contributes to a flexibility that allows the material to bend but not break, and the abrasion behavior is superior to direct composites. Vita Enamic is less brittle than a conventional ceramic and only requires an occlusal thickness of 1.0 mm. This material should be polished only and not placed in an oven due to the polymer component. Vita Enamic can be milled faster than other ceramics with less bur wear (+50 mills/bur) and should be etched internally with HF acid for 60 seconds before bonding. Vita Enamic wears like enamel, making it an ideal material for inlays, onlays, and selected crowns.
Shofu Blocks and Pucks HC.31 Shofu HC blocks and pucks are relatively new to the industry. They are force-absorbing hybrid ceramics that display natural fluorescence with color stability plus a flexural strength of 191 MPa. The blocks are two-layered for esthetics, which gives a lifelike, natural opalescence. The material is easy to polish, resulting in a high-gloss finish, and is highly stain- and wear-resistant. Shofu HC is commonly used for inlays, onlays, veneers, full crowns, and implant-supported restorations.
Laboratory-processed Resin Composites
Lava Ultimate.29 Lava Ultimate was introduced in 2011 as a nano-ceramic combining aggregates of zirconia/silica clusters (20 nm silica + 4 to 11 nm zirconia particles) and a resin matrix. This material is not indicated for full-coverage crowns and, due to the resin component, should not be glazed. The material can be easily polished with no firing and is commonly used for inlays and onlays. It is essential to not use HF acid before bonding, but to internally micro-etch with light sandblasting using 30-µm to 50-µm alumina particles to prepare the internal surface of the restoration, and apply silane for the ceramic component.
GC Cerasmart.30 GC Cerasmart was introduced in 2013 as a nano-ceramic with similar applications to Lava Ultimate. This material is very flexible due to the composite content intertwined with zirconia/silica clusters. GC Cerasmart should be micro-etched only with 30 µm to 50 µm alumina and not placed in an oven. GC Cerasmart is a quick-mill, easy-to-polish, flexible material that works well for inlays and onlays.
Composite
Paradigm™ MZ 100 (3M ESPE).32,33 Paradigm MZ 100 was introduced in 2000 and was mainly used for inlays. The material is 85% filled by weight of 0.6-µm zirconia-silica filler particles. Paradigm MZ 100 requires no etching or air abrasion and is easily reparable with composite, highly polishable, and low-wearing to the opposing; it was used because it was a softer material for implants and bruxers.
Temporary Acrylic
Telio® CAD.34 Telio CAD is a monolithic poly methyl methacrylate (PMMA) material for temporary crowns, bridges (up to two connected pontics), and implant-supported temporary hybrid abutment crowns. One of the main advantages of this temporary material is highly polished margins on crowns or bridges that are critical when the clinician must keep the temporary long-term for tissue response, such as in an immediate implant placement with a temporary crown. This material has high color stability, with natural fluorescence. The internal surface of the temporary should be air-abraded with 30- to 50-µm silica particles before temporary cementation.
Vita CAD-Temp.7 Vita CAD-Temp is a cross-linked acrylate polymer with micro-filler used as a long-term (wearing up to 3 years) temporary material. This material also has high color stability, is resistant to abrasion, is cost-effective, and possesses desirable optical properties. Vita CAD-Temp comes in monoColor (monochromatic) and multiColor (multichromatic). The internal surface of the temporary should be air-abraded with 30- to 50-µm silica particles before temporary cementation.
Zirconia-containing Lithium Silicates: A Closer Look
ZLS has several characteristics that clinicians may find advantageous.16 The chameleon effect is readily apparent due to the blending with the natural dentition, and the graying effect is reduced due to the inherent natural opalescence of the material. Precise Vita shade matching makes the conversation with the dental laboratory technician more accurate, which becomes extremely important when dark, banded, or cast-prepared stump forms are present. The balance between translucency and natural opalescence makes the crown look not like a restoration, but like a tooth. ZLS represents a new standard not only in esthetics but in survivability. It is easy to adjust chairside and in the mouth, and it gives the dentist the option to bond or cement the final restoration.
It is advisable to take a preoperative photograph with the Vita shade tab that matches most closely to the tooth. This step should be followed with two photographs of Vita shade tabs that are very close to the shade, with one slightly lighter and one slightly darker. Subsequently, the dentist can have a "visual conversation" with the laboratory technician that allows the technician to see the variation of what the shade is, and more importantly, what the shade is not.
The ultrafine microstructure displays crystallites four to eight times smaller than the crystallites found in lithium disilicates.16 The smaller crystal size is significant because it reflects ZLS's high average flexural strength, better compressibility and flowability, and ability to be polished more simply and quickly.16The smaller crystal size is designed within the visible light wavelength to mimic the light-scattering behavior of natural teeth (enamel).16 The marginal fit and integrity of ZLS is highly robust due to its microstructure and allows the clinician to adjust and polish intraorally or before cementation, if needed.16Pressable ZLS can be cemented conventionally with a glass-ionomer using a self-adhesive cement or bonded with a fully adhesive dual-cure, depending on the clinical situation.35
From a dental laboratory point of view, the fabrication of pressed ZLS is less time-intensive because there is little to no reaction layer inside the crown.16 This is the result of faster divesting time and sandblasting steps needed to produce the restoration. Consequently, up to 50 minutes can be saved when using ZLS for a 3-unit bridge, with minimal cleanup (due to eliminating the surface acidification steps in the dental laboratory). Additionally, the need to reproduce all Vita shades while reducing the inventory of individual pressing materials that the dental laboratory technician must stock is decreased due to the chameleon effect and high shade fidelity of ZLS. There is a 100% coverage rate with fewer shades and simple staining-six shade ingots (of 16 total) can cover almost 100% of all Vita shades. Accurate shade representation is reflected in the ingot from the laboratory; thus, fewer adjustments of hue (color), value (brightness), and chroma (strength or intensity of hue) are necessary. Pressable ZLS has increased flowability due to low viscosity and pressing behavior for all types of restorations.16 Even in bridge work, only one sprue is necessary, resulting in a minimal reaction layer and smooth surface inside the crown or veneer, leading to a better fit, no unnecessary acid treatment, and less laboratory time.16
Case Study 1
A patient wanted to change the shade, shape, and symmetry of her maxillary anterior teeth. Even after going through orthodontics to align the long axes of the anterior teeth, the patient wanted to "fine-tune" her smile by changing the overall shade and shape while eliminating the unsightly "dark triangles" present, especially between teeth Nos. 8, 9, and 10. Another concern was to preserve as much natural existing tooth structure as possible because there were no preoperative caries present on teeth Nos. 4 through 13. Conservative veneers were chosen to achieve her preoperative goals. The plan was to place pressable ZLS veneers from teeth No. 4 through No. 13 to take advantage of the chameleon effect of the natural teeth (Figure 1 through Figure 6).
Case Study 2
A 45-year old male patient presented with tooth No. 21 that had an intermediate restorative material (IRM) restoration on the facial aspect after a pulpotomy due to a carious lesion into the pulp from the facial (Figure 7 and Figure 8). The patient had root canal therapy and a post-and-core buildup placed on No. 21 before the crown. The patient was involved in the decision-making for the enamel shade on No. 21. He wanted to make sure that the clinicians did not match No. 21 with No. 20 because he felt the shade on No. 20 was too dark. Instead, the patient wanted to match the new ZLS that had been planned on No. 21 with the natural shade of No. 23 and No. 24. The facial and occlusal views revealed the obvious differences in shade between No. 21 and No. 20. The plan was to use pressable ZLS due to its esthetics, shade-matching abilities, strength, and ease of finishing, so it was decided to involve the dental laboratory technician with the shade-taking process. In planning the discussion with the laboratory technician, the author felt that the best shade would be a Vita A3.5. However, because the laboratory technician worked about 90 minutes away, the author wanted to get his input on the shade by sending him several photographs using the shade the author felt tooth No. 21 was (ie, Vita A3.5) plus shades that were close (ie, Vita A3 and Vita A4). Laboratory technicians are more familiar with shading techniques and may see something that the dentist did not see in the surrounding teeth. This is important when using ZLS to take full advantage of the blending ability that this material displays. The final crown displayed a vibrant match of hue and chroma (Figure 9 through Figure 13).
Conclusion
The evolving dental ceramic industry continues to search for the ultimate combination of strength and esthetics. The challenge lies in finding the unique material that not only provides the desired esthetic result for the clinical situation but that also has enough strength to survive and endure the demands of the oral environment. A variety of materials have been available through in-office chairside CAD/CAM and dental laboratory ceramics in regard to esthetics, strength, and durability. The intent of this article was to provide a survey of the landscape and contribute to informing clinician's decisions as they look to optimize patient care and practice efficiencies.
About the Author
J. William Claytor, Jr., DDS, MAGD
Senior Associate
Shelby, North Carolina
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