Henry Hemmendinger

Color distribution of three regions of extracted human teeth

OBJECTIVES Knowledge of human tooth color and its distribution are critical to the understanding of shade matching in esthetic dentistry. The color of human teeth shows a gradation from the gingival to the incisal region. There have been many reports in the literature on the distribution of color in teeth, but not in the CIE 1976 L*a*b* system. This study was conducted to determine the color distribution in three regions in a sample of human teeth and express the results in Munsell notation, CIE 1976 L*a*b* and CIE delta E* color differences. The hypothesis of this research was that it is possible to detect significant differences in the color parameters of the three distinct regions in teeth. METHODS All of the teeth used in this study were extracted, cleaned and stored in artificial saliva. Prior to measurement, the teeth were removed from the solution and mounted in a holder to ensure consistent measurements. Spectral data were collected using a GE recording spectrophotometer, CIE chromaticity coordinates calculated using CIE illuminant C and 1931 observer data, and conversions made to L*, a*, b* and Munsell notation. The results were analyzed by ANOVA and Scheffés multiple comparisons test. RESULTS The mean L*, a*, b*s were 72.6, 1.5, 18.4 for gingival, 72.4, 1.2, 16.2 for middle, and 71.4, 0.9, 12.8 for incisal. Average Munsell parameters were 1.2 Y 7.1/2.7 for gingival, 1.3 Y 7.1/2.4 for middle, and 1.4 Y 7.0/1.9 for incisal. The mean CIE delta E* between the gingival and incisal regions of the 95 teeth showed a clinically significant difference of 8.2. SIGNIFICANCE The distribution of color was identified for three regions of the tooth. A statistical analysis determined that there are statistically significant color differences between the regions, and these differences are also clinically significant. This information is beneficial when esthetic restorations are required.

How the CIE 1931 color‐matching functions were derived from Wright‐Guild data

The principles that guided the founders of the CIE 1931 system for colorimetry are examined. The principles are applied to the Wright-Guild experimental determinations of the color mixture data to show in detail how and why each step in the development of the CIE 1931 system for colorimetry came about. These steps are examined in the light of 65 years advanced knowledge of colorimetry. The necessity for each of these principles in the modern world is examined critically to determine whether one might hold to the same principles if the system were being freshly formulated today.

Stability of ceramic color reflectance standards

This article reviews the long-term repeatability of spectrophotometric color measurements of ceramic color standards calibrated by Hemmendinger Color Laboratory (HCL) since it was founded 25 years ago. A set of twelve BCRA tiles was measured at HCL in 1977, and a few months later at NBS. The CIELAB color-difference, averaged over the twelve tiles, between HCL and NBS was 0.25 units. Measured at HCL about every four months since that time, the repeatability of measurement, averaged over the twelve tiles, has been better than 0.15 CIELAB units. The difference from the NBS measurements has remained at about 0.25 units over two decades. From these data the conclusion can be drawn that the tiles have not changed color during this period of time by an amount exceeding the limits of instrumental repeatability, namely about 0.15 units.

A Transformation Pantograph for the Reduction of Microphotometer Tracings

An instrument is described for the continuous transformation to a scale of linear or logarithmic intensity of a galvanometer tracing representing the density of a photographic image. The instrument has few moving parts, and has proved capable of executing the reductions quickly and accurately.

Leonardo 2000: the softcopy screen book

As part of a larger project that is intended for self-taught color science, we developed a software tool to provide a softcopy simulation of the Munsell Book of Color under varied illuminants and for various observers. This simulation avoids setting up as ideal a particular set of pigments from which to derive spectral reflectances. The color-order database contains a reflectance function for each Munsell aim point. The aim points are the usual ones for Illuminant C and 2° Observer function. For a new illuminant and observer, each reflectance funtion is weighted by appropriate color-matching function and illuminant spectral power distribution, and integrated to produced new X, Y, and Z values. From these values, CIELAB and chromaticity coordinates are computed. Having specified atlast colors in a variety of coordinates, the program next renders them on screen as a color-navigation tool. To illustrate good practice in constructing an atlas of reflectances, the reflectance spectra from a linear series of aim points in Munsell space can be co-plotted to show the requirements for consistency of the series under illuminant and observer change.

The role of opponency in Twentieth Century colorimetry

For decades physicists have described the stimuli originating in the retinal cones as the basis of color, and psychologists accepted the perceptions arising in the brain as the fundamental aspect of color vision. It is now universally recognized that both assertions are correct; the distinction is essentially a semantic one.

Industrial applications of formulation computations: Is the computer the enemy?

The basis of modern computations of colorant formulations is a 1931 article by Kubelka and Munk. Virtually all the subsequent important contributions to the problem were published in the following four decades; if it were the practice for software instructions to include a comprehensive list of published references, it is unlikely that many, if any, would be dated later than the advent of the modern computer. This implies either that no major problems remain unsolved, or that some factor is discouraging further improvements or is inhibiting their publication. This leads to the hypothesis that the accepted practice, in the dissemination of computer documentation, of failing to provide references to relevant published work is a significant basis of stultifying new development. It is accordingly urged that promulgators of software accept the responsibility, universally observed in scientific and technological publication, of disclosing prior work by supplying appropriate lists of relevant published material. The failure to disclose prior published work should be deemed a form of plagiarism.