Technical Considerations for Laboratories
Combining advantages of fit, esthetics, strength, biocompatibility and radioluscency, enhanced Wol-Ceram helps dentists get what they really want – consistent marginal integrity, more natural-looking treatments and trouble-free restorations. Here’s why:
o Fit – Wol-Ceram Center of the Palm Beaches has pioneered a process we call high resolution Nanofit™. Our proprietary electrophoretic deposition nanoprocess achieves a coveted 5-micron fit on original die at the margin. Occlusal surfaces of posteriors, lingual surfaces of upper anteriors and labial surfaces of lower anteriors are also close fitting. Space for cement is provided on axial surfaces. Specified surface-fitting is key to optimal pressure distribution and a stress-free, long-lived restoration.
o Esthetics – All Wol-Ceram crowns and bridges are internally shaded, the core imparting a life-like translucent base-shade. Opaque is not required so internal luminescence can be achieved. Opaque lines commonly showing at the gum-line just don’t exist on Wol-Ceram crowns and bridges. Unlike conventional crowns and bridges, Wol-Ceram does not display dark metal or white zirconia and opaque lines and the gum-line.
o Strength – The 2004 Tinschert study at Aachen Germany found glass-infiltrated alumina processed by Wol-Ceram electrophoretic deposition to have mean value test strength of 2312 MPa. That’s 2.2 times stronger than alumina processed by other means – stronger than industrial-pressed alumina used by the block-cutting CAD/CAM systems – at least as strong as yttria-stabilized zirconia. Enhanced Wol-Ceram assures you of treatments engineered to last.
o Biocompatibility and Radioluscency – With significantly better biocompatibility and radioluscency, Wol-Ceram restorations aid the dentist in providing a higher standard-of-care. Conventional porcelain-fused-to-metal crowns and bridges have black and white lines at the gumline. The black lines produce toxic oxides that lead to periodontal disease and gum tissue die back. The white lines are common to computer-made all-ceramic restorations commonly having fit problems that can lead to tooth decay caused by bacteria living at the gum-line and under the margin. Wol-Ceram fits very closely to the prepared tooth so that bacteria is sealed out.
In implementing any new technology, the potential for satisfying dentists and their patients is contingent upon a lab’s commitment to (1) establishing consistent means for producing trouble-free products and (2) creating reasonable timetables and fees for making it happen. By following the protocol outlined here, a lab can achieve the high standards of performance that dentists are looking for:
o Indications – Crowns, splinted crowns, veneers, onlays, inlays, and bridges up to 38mm and crowns/bridges on implants are appropriate Wol-Ceram treatment modalities.
o Contraindications – Inlay bridges, onlay bridges and Maryland bridges are contraindicated, as are cases that will require temporary cementation. Also contraindicated are undercut, irregular or rough feather-edge margins which significantly compromise processing. If a margin has tiny bur-marks, for example, the core can lock onto the die during processing. Fit resolution is that good. Die margin edges must, therefore, be well defined. Slight undercuts and irregular or rough areas must be trimmed prior to processing – otherwise cores would have broken, cracked and open margins.
o Shades –Vita’s Vita-Lumin and Vita-Pan 3D-Master from Vita (www.vident.com) are the preferred shade guides. Wol-Ceram shades are derived from infiltration glass. Material-specific infiltration glass is fired into alumina, zirconia and spinell cores, respectively, to impart color and strength. With 16 life-like shades, Wol-Ceram Palm Beaches blends Vita In-Ceram infiltration glasses to produce a broader range of shades than are commercially available. Bridge cores can be ordered with a different shade on each bridge unit.
o Tooth Preparation – Most dentists prefer a light to medium chamfer margin. Conventional PFM preparations are good, provided that feather-edge margins are not undercut, irregular or rough. Incisal reduction should be 1.5mm and occlusal reduction should be 2mm. To avoid risk of premature fracture, sharp angles should always be avoided. To avoid hairline glass-filled cracks, or, the delay that is required to repair them, margin areas should not be undercut, irregular or rough.
o Die Materials – Dies should be poured in a chip-resistant stone (do not add die-hardener liquid to stone). Never coat dies with spacer or sealer. Always re-pour dies with missing incisal and occlusal areas because, any all-ceramic restoration will not be successful when incisal or occlusal areas have been arbitrarily formed (telephone Wol-Ceram Center for tips on how to pour bubble-free ultra-thin incisal areas). Cyanoacrylate glue should be used to fill very small bubbles in the pour.
o Die Trimming – Trim bulk areas with an arbor band. Then ditch dies with a large carbide bur suitable for stone and plaster. Always ditch to the finish line. After years of searching for the right cutting tool, capable of ditching (not chipping) the ideal Wol-Ceram processing contour, we use the Standard Universal Cutter #5410-060HP from Cardinal Diatech (www.cardinaldental.com). To avoid delivery delays, always provide dies that are neatly trimmed and ditched with a red margin line. No block-out, no spacer, no sealer.
o Labial Identification – Please inscribe the shade of your core on the labial and bottom surfaces of your die. This will aid us in identifying and locating the labial margin and this will assist in confirming the shade you need. Mesial and distal sides are utilized by us to inscribe your case number, due date and shade, thereby reducing the possibility of delays.
o Bridge Models – Bridges require special models. The master model is fabricated with dowel pins in the usual way – except do not saw out, or ditch, the die and pontic units involved in the bridge. Send us the master model and the opposing model, unmounted but indexed. Market demand for Wol-Ceram bridge frames is greater than our capacity to produce them and production deadlines are first come first serve. A Wol-Ceram bridge core can take 7 working days to as long as 3 weeks.
o Modifying Cores – Adjust cores with light-pressure and constant circular motion at 18,000 RPM. Support margin areas with finger pressure to muffle vibration. Use only diamond-filled stones, such as Diagen wheel #34000180 from Bredent USA (www.xpdent.com) and diamond-filled rubber wheels, such as the Cardiglaze knife-edge wheel #6125-250-1R from Cardinal Diatech (www.cardinaldental.com). Take care when opening the interproximal areas of bridges, never to cut into the underlying core material (such as when using a thin or ultra-thin diamond disk). Small-diameter diamond-filled stones, such as Diagen cone point #34000150 from Bredent USA (www.xpdent.com), may be used for very miner internal adjustments; as with any all-ceramic alumina, spinell, or zirconia core restoration, generally try to avoid internal adjustments. Avoid all conventional cutting tools, including carbide burs and other cutting tools commonly found in the dental lab, including, sintered diamond, aluminum-oxide and carborundum (heatless) abrasive wheels, disks and points.
o Sandblasting and Cleaning – If modified, always sandblast the build-up surface with 50-micron aluminum oxide abrasive at 50 PSI. All build-up surfaces should be a matt finish. Use Anhydrous Ethyl Alcohol or Acetone to remove oil and contaminants. Hold copings during build-up with the Bredent USA (www.xpdent.com) spot-clip instrument. To obtain a good bond, coat core build-up surfaces with dentin (body-porcelain) slurry wash and fire to full glaze. Subsequently build and fire according to manufacturer’s recommended procedure. After glazing, sandblast your crown inside.
o Build-up Porcelains – Compatible porcelains that can be used on Wol-Ceram alumina, spinell and zirconia are All-Ceram from Degussa (www.neytech.com), Cerabien from Noritake (www.darbylab.com), CreationAV from Jensen (www.jensenindustries.com), InitialAL from GC America (www.gcamerica.com), RondoAL from Nobel Biocare (www1.nobelbiocare.com), VintageAL from Shofu (www.shofu.com) and VitaVM7 from Vita (www.vident.com). Take care not to use other porcelains because the coefficient of thermal expansion is as significant with all-ceramic restorations as it is with porcelain-fused-to-metal restorations. Porcelain build-up may be safely striped as follows; (1) reduce bulky areas with heatless stone but, positively avoid grinding the core with the heatless stone in any way; (2) ultrasonic clean in new Strip-It for not more than 30 minutes; (3) sandblast at 50 PSI; (4) clean in Anhydrous Ethyl Alcohol or Acetone.
With 1,100 to 1,540 MPa independently tested strength (Dr. J. Tinschert, University of Aachen, Germany) and with more than 1.2 million delivered units, Wol-Ceram has been shown to be an effective restorative modality when treatments are provided in accord with established laboratory and clinical protocol:
o Modifying Cores – Cores may be modified using a good, no chatter, electric handpiece such as Osada, and light pressure at 18,000 rpm. Use XPDent Bredent USA Diagen Wheel 34000180 and Diagen cone point #34000150 to modify contours. Use Cardinal Diatech Knife-Edge Coarse Rubber+Diamond Wheel 6125-250-1R to modify margins. Modifying margins requires considerable care and skill; (1) to shorten a thin margin, apply firm pressure to edge while keeping wheel and edge midplanes parallel and the direction of rotation aligned with the edge; (2) to shorten a collar margin, reduce collar axial surface using firm sweeping strokes at a 90° angle to the edge; (3) to thin a margin, use circular motion to slowly build abrasive-heat on a broad axial surface area, reducing with short, controlled, soft strokes at a 45° angle to the edge. When modifying cores do not make sharp notch or score lines, especially at interproximals – these can cause fault-line fractures. Do not grind a crown or bridge abutment inside – this can create micro- and nano-cracks and fractures. If a fit problem exists, ask the doctor to adjust the prep.
o Core Surface Prep – Always be sure that core surfaces are thoroughly sandblasted with unrecycled aluminum oxide and degreased using anhydrous ethyl alcohol or acetone. Build-up porcelain bond can fail if core surfaces are not consistently prepped.
o Separate Brushes – Mark new porcelain build-up brushes for Wol-Ceram/In-Ceram. Do not use these brushes for PFM or zircon build-ups. Build-up porcelain for Wol-Ceram/In-Ceram has a specific CTE. Cross contamination with other porcelains will cause cracks in build-up porcelain.
o Core Prefiring – Coat cores with a thin wash of slurry porcelain and fire to a full glaze. This will “wet” the core surface for bonding to future build-ups. Core surfaces that were not prefired in this way have had occurrences where the entire build-up separated and lifted off of the core after cementation in the mouth.
o After Each Firing – Allow all-ceramic crowns and bridges to cool completely after each firing. All-ceramic will fracture if hot and handled with a cold instrument. Like a hemostat, XPDent Bredent USA Spot Clip 310-000-07 can clip-attach a core to hold it for build-up and staining procedures, but without risk of fracturing the core edge.
o Finishing Margins – Contour build-up porcelain at margin with Cardinal Diatech Knife-Edge Fine Rubber+Diamond Wheel 6225-250-1. Mounted points and many other conventional porcelain cutting tools can chip core margins, creating micro- and nano-cracks and fractures.
o Sandblast When Done – After glazing, always sandblast your crown or bridge abutments inside. Failure to do so can cause cementation problems and fractures.
Predicated on standard-of-care excellence, enhanced Wol-Ceram has become the hallmark for metal-free crown and bridge treatments. Wol-Ceram Center of the Palm Beaches, a division of Bio-CAM, LC, proudly offers enhanced Wol-Ceram crown and bridge core services to dental laboratories.