July/August 2011, Volume 7, Issue 7
Published by AEGIS Communications
Several developments in 2010 and early 2011 regarding CAD/CAM materials and applications may have a significant impact on implants and fabricating bridges without the need for a physical impression or model. The Rapid Layer Technique (RLT) from VITA (www.vident.com) uses software on the Sirona CEREC system to create two files for fabricating a full-contour bridge. One file is used to mill the zirconia framework, and a second file mills a corresponding full-contour veneer from a fully dense Triluxe block that is then bonded onto the zirconia framework using composite resin cement. Ivoclar Vivadent (www.ivoclarvivadent.com) has a similar technique, called CAD-on, through which an IPS ZirCAD zirconia framework is joined to a veneer milled from IPS e.max® lithium disilicate using a fired glass.
Materials recently approved by the FDA for use in the CEREC system may significantly impact the fabrication of custom abutments. Several companies are developing or planning for integration of intraoral digital impressions with cone beam data. Sirona’s application allows dentists to treatment plan implant placement and restoration design to maximize esthetic results, as well as ensure proper placement in the bone. This system enables fabrication of custom zirconia abutments for a variety of implant brands using a special zirconia block (Meso) with a corresponding titanium intermediate element (Ti-base). Currently the dental laboratory must fabricate the abutment, but there will likely be further system refinements to facilitate chairside fabrication. The data may also be sent for fabrication of a custom surgical template.
A new block from VITA, called Real Life, allows chairside milling of restorations that have a layered structure similar to hand-layered porcelain produced by dental laboratories. The block consists of an internal dentin core with an enamel outer shell. The crown can be positioned in the block to vary the ratio of enamel to dentin to match adjacent teeth.
At the IDS meeting, DENTSPLY (www.dentsply.com) introduced a machinable, chromium-cobalt–based porous metal block. Milled in a porous state and then sintered in a special furnace, this block further expands CAD/CAM capabilities for directly milling metal frameworks for PFM restorations.
Materials used in CAD/CAM systems that are approved by the manufacturer tend to demonstrate superior mechanical and physical properties compared to pressed or hand-layered porcelain. The ceramic blocks are fabricated in a consistent manner, so porosity is minimized and the material is more homogeneous. Many variables can affect the quality of hand-fabricated restorations, including how well the porcelain is compacted, humidity level of the room, technician experience, furnace calibration, etc. All of these variables are controlled when fabricating CAD/CAM blocks.
Millions of milled restorations have been produced, and a large number of clinical trials demonstrate that restorations fabricated from CAD/CAM blocks outperform “conventional” restorations. Therefore, dentists can use this technology to provide esthetic and more reliable restorations.
However, in order to take full advantage of CAD/CAM material developments, dentists should get involved in digital dentistry. This may involve buying a complete digital impression/milling unit, or just purchasing an intraoral impression system.
Even though CAD/CAM materials rely on computerized technology for fabrication, the clinician’s skill is still required to produce a quality restoration. If a chairside milling unit is purchased, seek additional training and start slow, not with a full-mouth reconstruction. It’s important to practice using the system, and it may take several cases or additional training to master the technique. Learn by doing inlays first and then progress to more complicated restorations and treatment plans.
A careful evaluation of the different systems available is required to determine which fits best with your practice philosophy. Ideally, purchase from a company that will let you return the system if it doesn’t work for you.
About the Author
Russell Giordano, DMD, CAGS, DMSc
Associate Professor of Biomaterials
Director of Biomaterials
Henry M. Goldman School of Dental Medicine