Esthetic, adhesive restorations are increasingly becoming the restoration of choice for many clinical situations. And ceramic inlays, onlays, veneers, and crowns are a primary treatment option for chairside CAD/CAM systems. CEREC AC (Sirona Dental) and E4D (D4D Technology) systems predominantly utilize ceramic materials for their esthetic qualities, surface finish, and long-term durability.1 A number of feldspathic porcelain (Vita Mark II/Vident, Sirona Blocs/Sirona Dental), leucite reinforced porcelain (EmpressCAD/Ivoclar), and lithium disilicate porcelain (emaxCAD/Ivoclar) blocks are available for use with the CEREC AC and E4D Dentist systems. Many long-term clinical studies have documented the longevity, durability, and clinical success of these types of restorations.2
Composite resin blocks (Paradigm MZ100/3M ESPE) have also been available for over ten years for both chairside systems, though they are not used with the same frequency as the ceramic materials. One of the primary reasons for this is the general perception dentists have of “composite” materials in general. Dentists believe composites are not as strong as ceramic restorations, will undergo more general surface wear, and are generally not as useful for rehabilitating posterior occlusion. Lastly, ceramic materials are believed to have a longer lasting surface finish than composites.
A randomized clinical trial compared the clinical longevity of chairside CAD/CAM composite inlays (Paradigm MZ100/3M ESPE) to porcelain inlays (Vita Mark II/Vident).3 After ten years of clinical function, there was no significant difference in margin finish, surface finish, proximal contact, and anatomic form, all remaining essentially unchanged from baseline for both materials. This finding reveals a much different clinical result for prepolymerized blocks of composite that are used by chairside CAD/CAM systems by comparison to what many dentists would believe to be the outcome for compositionally similar materials used in a traditional restorative technique. Six porcelain inlays fractured over the course of the study with only one fracture of a composite inlay reported. Chairside CAD/CAM composite inlays performed as well as porcelain inlays with significant advantages in shade match and inlay fracture over the ten years of the study. Clinical evidence of this type encourages dentists to reconsider their “perceptions” of a restorative material based on its category or name rather than the clinical outcome. A laboratory study reported that adhesively bonded Paradigm MZ100 molar crowns were more crack resistant than adhesively bonded Vita Mark II porcelain crowns.6 The industrial fabrication of the composite block potentially offers a significant clinical advantage to what may be expected of a typical composite that is placed incrementally and cured intraorally.
An alternative, monolithic esthetic material has been recently introduced in a block form for CAD/CAM fabrication using both chairside and laboratory systems. The new material is based on the integration of nano-technology and ceramics. A stated advantage of the material is to offer easier clinical finishing and polishing, without the need for a porcelain oven, with the strength, surface gloss and finish retention similar to ceramic materials. Lava Ultimate (3M ESPE) contains a blend of nano particles agglomerated in clusters and individual bonded nano particles embedded in a highly cross-linked polymer matrix. It is a combination of aggregated zirconia/silica clusters (comprised of 20 nm silica and 4 to 11 nm zirconia particles), non-agglomerated/non-aggregated 20 nm silica, and non-agglomerated/non-aggregated 4 to 11 nm zirconia with approximately an 80% ceramic load.
The physical property of strength must be sufficient to resist the forces and stresses of mastication over time. Common in vitro tests of material strength include flexural strength and fracture toughness. With a manufacturer reported flexural strength of 200 MPa, the nano-ceramic block has a higher initial strength than feldspathic and leucite reinforced porcelain blocks, as well as veneering porcelains for PFM crowns. The fracture toughness of the nano-ceramic material is reported by the manufacturer to be greater than feldspathic materials and direct composites while being less brittle than feldspathic glass-ceramics, and therefore less prone to fracture during try-in and function.
A purported improvement in the nano-ceramic block is the ability to retain a high gloss surface finish over time. This has been a problematic limitation of composite blocks when used for larger restorations such as crowns. The inclusion of nano particles in the Lava Ultimate block allows for easy contouring and creation of a high gloss surface finish similar to porcelain. (Figs. 1 & 2). In vitro studies by the manufacturer indicate that Lava Ultimate has a resistance to toothbrush abrasion and retention of the initial glossy surface finish similar to glass ceramics. Only long-term clinical evaluation will confirm this desirable property of the material.
CASE REPORT
A patient presented with an amalgam restoration on tooth #18 with caries along the occlusolingual margin with significant wear (Fig. 1). After discussing treatment options, risks and benefits, the patient elected to have a nano-ceramic onlay fabricated in a single appointment with a chairside CAD/CAM system (CEREC AC). Lava Ultimate restorative (3M ESPE) is available in eight popular shades in both low and high translucency forms. The high translucency shade block was selected for the onlay to allow for a chameleon effect allowing the underlying tooth color to blend in the final color of the restoration.
After local anesthesia, the tooth was prepared for the nano-ceramic onlay. The manufacturer recommends a somewhat more conservative tooth reduction in the cavity preparation due to the improved strength of the nano-ceramic material. The axial reduction was 1.0 mm and the cuspal reduction was 1.5 mm with both dimensions being about 0.5 mm less than what is conventionally recommended for porcelain restorations. The proximal contacts of the tooth were maintained intact as the marginal ridge areas were well supported by dentin and the proximal surfaces were free of caries (Fig. 2).
Digital image scans of the preparation quadrant and opposing teeth were made with the CEREC AC system and the virtual models were aligned with a buccal scan. The preparation details were readily visualized on the virtual model in the design software (Fig. 3). The restoration proposal was calculated based on the unique anatomy of the adjacent teeth using the Biogeneric Individual design process, and the final design was transmitted to the milling chamber (Fig. 4). A Lava Ultimate I14 block (shade A2 HT) was inserted into the MCXL milling chamber and the onlay was milled from the prefabricated block of nano-ceramic (Fig. 5). Upon recovery of the milled restoration from the milling chamber, the restoration was tried in and adjusted for optimum internal adaptation and marginal fit to the cavity preparation.
Ceramic restorations require considerable time and effort to polish effectively. However, this is not the case with the nano-ceramic material. It is optimally contoured and polished using light pressure and low speed as for composite or acrylic materials rather than the high torque and high pressure required for polishing ceramics. Conventional composite contouring wheels and points are useful for initial contouring. Final polishing is best achieved with a soft brush and diamond polishing paste.
Unlike ceramic materials, etching the intaglio surface of the restoration will not create a good bonding surface since there is no glass component that can be dissolved by the acid. Air abrasion of the intaglio surface with 30-50 micron particles in a microetcher will create an effective bonding surface.
The nano-ceramic material is not as brittle as ceramic materials and has a modulous of elasticity similar to den
tin allowing it to absorb more stress rather than immediately fracture. This property also may be a reason to create an enhanced adhesive bond to the tooth for resistance and support of the restoration since additional stress may be imparted to the tooth interface that could result in a debond of the restoration. Self-etching, self-adhesive cements are best avoided. A self-etch, selective etch, or total etch process with an adhesive bonding agent and resin cement are optimal choices for adhesive cementation of the nano-ceramic.
Scotchbond Universal Adhesive (3M ESPE) is a self-etching bonding adhesive that can be used with a selective-etch or total etch process to enhance the bond strength. In this case, a selective etch process was used on the preparation enamel, rinsed, dried and Scotchbond Universal Adhesive was applied and dried with air. The onlay was seated with RelyX Ultimate dual cured resin cement and allowed to initially self-cure for 1 minute to allow a gel set to facilitate cleaning of the cement from the margins. An alternative technique is to use a 1-2 second light cure to “tack cure” the cement prior to cleaning the margins.
Following visible light curing, the margins were finished and polished with a 40 ìm microfine diamond, low speed single grit abrasive polisher (40 ìm aluminum oxide-impregnated silicon), followed with a latch-head soft brush with impregnated abrasive silicon carbide particles and a 5 ìm diamond polishing paste (Diashine by VH Technologies) (Fig. 6).
This clinical case illustrates the high gloss finish that can easily be achieved with the nano-ceramic material with a very efficient finishing and polishing sequence without the need for firing the restoration in a porcelain furnace. The clinical indication and application of the nano-ceramic material will ultimately be determined by long-term clinical research. Previous studies of chairside CAD/CAM composite restorations have documented the durability and fracture resistance of the material as well as the wear resistance compared to feldspathic porcelain.5 The degree to which the new nano-ceramic material duplicates these features with a more conservative tooth reduction and improved retention of the surface finish and gloss will ultimately determine the expanded utilization of the material. The nano-ceramic CAD/CAM block Lava Ultimate will surely challenge the thoughtful provider to reconsider the misperception that this is “just another composite.”OH
Dr. Fasbinder is a Clinical Professor and the Director of the Advanced Education in General Dentistry Program at the University of Michigan School of Dentistry where he also maintains a part-time private practice. He directs the Computerized Dentistry (CompuDent) Unit at the University of Michigan that is dedicated to research and education on CAD/CAM dentistry.
Dr. Poticny is an Adjunct Associate Clinical Professor at the University of Michigan School of Dentistry. He maintains a private practice in Grand Prairie, Texas.
REFERENCES
1. Fasbinder, DJ. Restorative materials for chairside CAD/CAM restorations. Compend Cont Educ Dent 2010; 31(9):2-17.
2. Fasbinder DJ. Clinical performance of chairside CAD/CAM restorations. JADA 2006; 137:22S-31S.
3. Fasbinder DJ, Dennison JB, Heys D. Clinical Evaluation of CAD/CAM-Generated Composite Inlays: Ten-Year Report, AADR 2011, Abstract #379.
4. Kassem AS, Atta O, El-Mowafy O. Combined effects of thermocycling and load-cycling on microleakage of computer-aided design/computer-assisted manufacture molar crowns. Int J Prosthodont 2011 Jul-Aug;24(4):376-8.
