U of M DENT 6911 - Improved Color Matching of Metal Ceramic Restorations (7 pages)

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Improved Color Matching of Metal Ceramic Restorations



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Improved Color Matching of Metal Ceramic Restorations

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Pages:
7
School:
University of Minnesota- Twin Cities
Course:
Dent 6911 - Prosthodontics I
Prosthodontics I Documents
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THE JOURNAL OF PROSTHETIC DENTISTRY AUGUST 1987 FIXED PROSTHODONTICS l VOLUME 58 NUMBER 2 OPERATIVE DENTISTRY SECTION EDITORS WILLIAM LEFKOWITZ SAMUEL E GUYER JOHN E RHOADS WILLIAM F MALONE ROBERT C SPROULL Improved color matching of metal ceramic restorations Part I A systematic method for shade determination John A Sorensen D M D and Tony J Tomes University of California Los Angeles School of Dentistry Los Angeles Calif S election of the proper porcelain shade and colormatching ceramic restorations to the natural dentition continues to be one of the most perplexing and frustrating problems in fixed prosthodontics Inadequate technology to aid the ceramist and dentist in the appropriate selection of porcelain shades has rendered this part of dentistry more of an art form than a science Unlike science art form is subordinate to the individual abilities of the dentist that influence the predictability and reproducibility of the finished restoration Traditionally communication between dentist and ceramist on color and shade matching has been poor Lack of clarity errors of omission and variability in the amount of information conveyed are just a few reasons for this communication gap As a consequence frustration can be anticipated when the dentist subjectively determines the shade and communicates shade information in an inconsistent manner A ceramic restoration drastically different from that originally prescribed often results This series of articles presents a simplified systematic approach for shade selection improved methods of communication and porcelain application procedure This information will assist the dentist ceramist team in its goal of consistently producing inconspicuous life like ceramic restorations The techniques presented in this series are aimed toward dentists who are willing to exert extra effort and time to achieve the greatest esthetic potential for their patients Some dentists may find these procedures too time consuming to justify their use Assistant Professor Assistant Director Graduate Prosthodontics ResearchAssistant Certified Dental Technician THE JOURNAL OF PROSTHETIC DENTISTRY THE PROBLEM The observer In general dentists have little or no training in vision physiology or color science lV3 A survey in 1967 revealed that only 23 of 112 dental schools had color education in their curriculum More recent surveys are not available but inadequate training in color science is still prevalent Although color perception is subjective and varies between individuals 4 8 Bergen9 demonstrated that color discrimination perception and description can be improved with training in dental procedures Culpepper found disagreement between dentists in shade matching the same tooth and individual dentists could not duplicate their shade selections on different days The problem of determining and communicating shade selections from dentist to ceramist becomes readily apparent These factors in addition to the easily fatigued nature of the cones responsible for color perception would seem to make accurate color matching nearly impossible Viewing conditions Color and shade selection is highly affected by viewing conditions The light sources in the operatory and laboratory color of the walls amount of sunlight the patient s clothing and make up and the viewing angle of the tooth can all affect the selection of a shade Light is composed of different wavelengths dependent on the source Fluorescent light tends to accentuate the blue range of the color spectrum whereas incandescent light accentuates the yellow red range To reduce the effects of metamerism the dentist should evaluate and compare shade determinations under several light sources To standardize lighting conditions both dentist and ceramist should use color corrected lights with a 133 color rendering index of 90 or greater for selecting shades and evaluating completed ceramic restorations I2 Shade guides Commercially available shade guides add another weak link in the shade matching process Several studies have evaluated a large number of natural teeth by using the Munsell color system1 15and CIE LAB system 16Several texts are available to explain the CIE Lab System 7 20When comparing the range of color space for available shade guides and natural teeth Sproull15 found that 1 available guides did not cover the volume of color space required 2 there was no logical or systematic arrangement of the tabs and 3 clustering and duplication of colors existed in some areas of the color space and voids in other regions More elaborate shade matching systems that attempt to adequately cover the color space occupied by natural teeth have been presented but have not been widely used 6 2 22 Another inadequacy of commercial shade guides is in their unrealistic method of fabrication A typical shade tab measures 4 mm buccolingually and is made with high fusing denture tooth porcelain giving an unrealistic representation of the metal ceramic porcelain shade Application of internal and external characterization to the shade tabs by the manufacturer further misrepresents the actual porcelain shade The lack of a metal backing may also mislead the observer Miller reported variation among shade guides produced by the same manufacturer The inherent weakenessesof commercial shade guides motivated individuals such as Muiaz3 to develop custom shade determination techniques Using custom fired shade tabs Muia determined the Four Dimensional Tooth Color System Excellent results can be achieved with this method but few laboratories are willing to expend the time and expense necessary to fire new shade tabs for each new bottle of porcelain and each patient Inadequate technology Ideally the dentist would have a spectrophotometer linked to a computer A fiber optic head held against a tooth would give the formulation of porcelain powders for reproducing the natural tooth color being viewed Presently we lack the technology to perform this function 11 24 25 Clarkz5 listed the properties of teeth that contribute error to measurement with calorimeters and spectrophotometers These are fluorescence metamerism nonuniformity across the surface inhomogeneous internal structure in layers translucency small size irregular shape and conditions preventing close approximation of the measuring port Colorgen Inc Billerica Mass has made advances in swell CW Personal communication Lecture before the American College of Prosthodontists October 1986 Miller L Personal


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