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Dentistry Moving Up To Nanofabricating

                       by John Stipek, CDT
                                                   Wol-Ceram Center of the Palm Beaches
                    December 10, 2004

From earliest times, dentists and fabricators have struggled against processing errors inherent in the dental fabricating technologies.  In an oral environment teeming with bacteria and bite-related stress, traditional fabricating technologies are, in a word, gross.

Recently, however, an advanced technology called electrophoretic deposition (EPD) has found a dental application - Wol-Ceram - a German made EPD dental CAD/CAM system.  Now Bio-CAM has enhanced Wol-Ceram to create a high resolution nanoprocess.  The prefix “nano” means billionth - one nanometer has a diameter 10,000 times smaller than a human hair.  By controlling and manipulating materials, at the molecular level, nanoprocessing technologies are used in manufacturing a wide range of high tech products such as DNA identification, thin film lens coating, and smart structure in-vivo robotics (see fig 1: red blood cell getting injection from nanorobot).  Advanced engineering dynamics set the new enhanced Wol-Ceram apart from other dental fabricating technologies, including the recently emerging block-cutting CAD/CAM systems. 

The enhanced Wol-Ceram nanoprocess is a particle-by-particle build-up process.  Micro- and nano-crystalline particles of alumina, spinell, or zirconia are deposited on the original die with a controlled electric field.  Stringent processing standards include; (1) slip rheology and precursor maintenance by Baumé nanohydrometer monitoring; (2) slip viscosity maintenance by comb flow-meter monitoring; (3) electrolyte crystalline deposit control by salinity refractometer monitoring; (4) electrolyte ion activity assurance by pH meter monitoring; (5) relative humidity measurement by hygrometer monitoring; (6) electrical current and dissipation factor control by Amp/Lcr meter monitoring;   (7) infiltration-glass-to-sintered-material ratio using a 0.01g precision balance and digital powder dispenser; (8) precision and contaminant-free core surface assurance by regulated bottled nitrogen abrasive blasting.  Our proprietary process produces a high-density, seamless core that flawlessly fits die margins.  Occlusal surfaces of posteriors and lingual surfaces of anteriors are also engineered to be 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.

Traditional dental fabricating technologies consist of molding, casting, injecting, build-up, and cut-down processes.  These processes always introduce expansion, contraction, or distortion at some level of measurable performance.  Fabricating by means of a wax-up or a brush build-up, for example, is like dumping a load of blocks, leveling and smoothing the surface - to create what is essentially a random pile construction.  Fabricating at the molecular level is like sorting and laying blocks, according to size and shape, one upon another, to create an organized, solid construction.

Block-cutting CAD/CAM systems, such as Procera, Cerec and DCS, develop internal fitting surfaces by milling.  Milling technologies utilize cutting tools (burs) to cut down blocks of material.  Procera mills a die from a Titanium block and processes alumina against this milled die surface.  Cerec and DCS mill the core directly from an alumina or zirconia block.  Computer-visualized surfaces are calculated to tool path and subsequently honed down by moving the cutting tool back and forth across the surface.  Milling continues until the designated die or core is “carved out” of the block.  Milled surfaces have “corn rows” and other defects left behind, resulting from the shape and path of the cutting tool (see fig 2: “corn rows” shown on inside surface of milled crown).  This is why critical, close-fitting surfaces, such as margins, seldom fit well.  Such surfaces have defects that result in open margins.  To avoid the potential for other interferences, less critical fitting surfaces, such as occlusal and lingual fitting surfaces, are programmed to have lots of space.  Although these crown and bridge products have recently emerged as viable restorative modalities, end-products fabricated in this way are not likely to hold up over time, because biting forces are transferred to margins with no occlusal/lingual support.  This, irrespective of the fact, the most popular all-ceramic CAD/CAM materials are Vita materials.

Vita materials, alumina, zirconia and spinell, are dimensionally stable in all processing stages - liquid slip, to the dried solid form (stage-1 copings/bridges), to the somewhat delicate sintered form, to the high-strength glass-infiltrated form.  With 2312 MPa of mean value test strength (Critical Stress Test Wol-Ceram Study, 2004, University of Aachen, Dr. J. Tinschert) and 98.1% success rate over 12 years (All-Ceramic Restoration with the In-Ceram System, Georg-August University, October 1996, Dr. A. Huls), In-Ceram glass-infiltrated alumina has been shown to outperform other crown and bridge restorative materials.  That having been said, the chief difference between Vita In-Ceram and enhanced Wol-Ceram is:

o      In-Ceram is a brush build-up on a duplicated (refractory) die.

o      Enhanced Wol-Ceram is an EPD nanoprocess build-up on original die.

Because of inherent differences between brush build-up and nanoprocessing, enhanced cores made by Wol-Ceram Palm Beaches have been shown to consistently outperform In-Ceram, cast-gold and CAD/CAM milled products.  With high critical break-strength of up to 3200 MPa, independent studies have shown our nanoprocessed material may be stronger than any other cosmetic C&B material.  At the chair, dentists notice and appreciate enhanced Wol-Ceram.

Today, more patients are asking about all-ceramic treatments.  Built on sound engineering principles, Wol-Ceram metal-less crown and bridge restorations help patients get what they really want - a more natural-looking smile, biocompatible materials, and long-term results.