Ask the Experts

CLINICAL PERFORMANCE OF LOW FUSING FRAMEWORKVENEERING CERAMIC MATERIALS

Guest ExpertDavid Avery, CDT*

Associate EditorEdward J. Swift, Jr., DMD, MS

QUESTION: I have been told thatthere are problems with the veneer-ing porcelain fracturing from zirco-nia cores. Is this something that Ishould be concerned about?

ANSWER: As with most dentalmaterials, the continued develop-ment of ceramic contributes to theimprovement of patient care.At times, however, “new andimproved” might not be improvedin actuality. There is rising concernthat the newer generation of lowertemperature (750–810°C) porce-lains used to veneer computer-assisted design/computer-assistedmilling-produced zirconium oxideframework systems are exhibitinglower cohesive strengths thanthe traditional highertemperature porcelains.

The rationale for development ofthese low-fusing porcelains is a

desire for a less opposing enamelwear than what occurs with felds-pathic porcelains. However, clinicalfailures have been reported in sub-stantial enough numbers to leadmany laboratories to eliminatethese porcelains from use. Thetypes of failures reported typicallyare of a chipping or intra-porcelainnature rather than a catastrophicinterfacial bonding failure.

Clinical Research Associates con-ducted a study that found anextremely high rate of this type offailure at 1-year recall. However,please note that the zirconiumoxide frameworks performed verywell with no fractures reported.The veneering porcelain failures donot exclusively lead to removal ofthe restoration and total replace-ment. Rather, in many cases, thefracture site can be smoothed andpolished to the satisfaction of the

patient and clinician. Nevertheless,this type of failure raises concernsregarding future performance.

The reader should be aware thathigh-strength, high-fusing (950°C)ceramic materials such as Vita VM9 (Vident, Brea, CA, USA) areavailable for this process. Thegood clinical performance of thesematerials over the same frameworksystems suggests that the concernabout the low-fusing materials is avalid one.

Input from the manufacturingcommunity suggests that the casesin question were the result of theceramist mishandling the materialduring fabrication. This is certainlya valid hypothesis, but it raises theunfortunate possibility that thelevel of training provided forthe use of these materials hasbeen inadequate and must be

*Director of Professional Services, Drake Precision Dental Laboratory, Charlotte, NC, USA

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improved for the sake of thedental public.

As new indirect restorative tech-nologies are introduced to the cli-nician and technician, a learningcurve is always present. To theextent possible, we must beadequately prepared to adjust tonew and different handling charac-teristics so that our patients neednot serve as test subjects for newrestorative options. Unfortunately,history shows that this hassometimes been the case. One

example is the fiber-reinforcedcomposite resin systems that wereintroduced for definitivefull-coverage restorations.

This commentary is not intendedto be critical of our colleagues inthe manufacturing community. Theresearch and development ofimproved methods for patienttreatment is certainly important.This author’s chief concern is thathigher levels of training, perhapswith certification and validation ofproficiency, would be of value in

shortening the learning curve,thereby reducing the likelihood ofearly clinical failures.

S U G G E S T E D R E A D I N G

Clinical Research Associates. Zirconia vs.porcelain-fused-to-metal (PFM)—clinical per-formance at 1 year. CRA Found Newslett2006;30(11):1–4.

McLaren E, Giordano R. Zirconia-basedceramics: material properties, esthetics and lay-ering techniques of a new veneering porcelain,VM9, high-alumina frameworks. Quint DentTechnol 2005;28:98–110.

Denry I, Seghi JR. State of the art of zirconiafor dental applications. Dent Mater2008;24:299–307.

Editor’s Note: If you have a question on any aspect of estheticdentistry, please direct it to the Associate Editor, Dr. Edward J. Swift,Jr. We will forward questions to appropriate experts and print theanswers in this regular feature.

Ask the ExpertsDr. Edward J. Swift, Jr.Department of Operative DentistryUniversity of North CarolinaCB#7450, Brauer HallChapel Hill, NC 27599-7450Telephone: 919-966-2770; Fax: 919-966-5660E-mail: ed_swift@dentistry.unc.edu

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