The aim of this investigation was to determine colour compatibility between dental shade guides, namely, VITA Classical (VC) and VITA 3D-Master (3D), and human teeth in quinquagenarians and septuagenarians. Tooth colour, described in terms of L*a*b* values of the middle third of facial tooth surface of 1391 teeth, was measured using VITA Easyshade in 195 subjects (48% female). These were compared with the colours (L*a*b* values) of the shade tabs of VC and 3D. The mean coverage error and the percentage of tooth colours being within a given colour difference (DeltaE(ab)) from the tabs of VC and 3D were calculated. For comparison, hypothetical, optimized, population-specific shade guides were additionally calculated based on discrete optimization techniques for optimizing coverage. Mean coverage error was DeltaE(ab) = 3.51 for VC and DeltaE(ab) = 2.96 for 3D. Coverage of tooth colours by the tabs of VC and 3D within DeltaE(ab) = 2 was 23% and 24%, respectively, (DeltaE(ab)

The purpose of this study was to evaluate, for both genders and two elderly age groups, differences in lightness, chroma, and hue of pairs of natural anterior teeth, so that more accurate information on color would be available for the production of dentures with a natural appearance. The subjects in the younger group (YG) were 54 to 56 years of age, those in the older group 73 to 75 (N = 195, 48% women). Tooth color was measured using a spectrophotometer. Mixed models were calculated for each pair of teeth, with gender as a fixed factor. Gender did not have a significant effect in either age group. In both groups, differences in chroma between upper canines and lateral incisors and in lightness and hue between upper and lower canines were observed. In the YG, additional differences were found, with the only exception of the comparison between upper central and lateral incisors. The nongender-specific color differences observed should be considered when producing denture teeth for these groups of patients, in order to come as close as possible to the natural color ideal.

Corcodel N, Helling S, Rammelsberg P, Hassel AJ. Metameric effect between natural teeth and the shade tabs of a shade guide. Eur J Oral Sci 2010; 118: 311–316. © 2010 The Authors. Journal compilation©2010 Eur J Oral Sci The objective of this study was to evaluate metameric effects, that is, the dependence of the colours of teeth and shade tabs on the illuminant used. The colours of 49 teeth of 37 participants and of the corresponding shade tabs of the 3D‐Master (VITA Zahnfabrik; colour match ΔEab< 2) were measured using an intra‐oral spectrophotometer (VITA Easyshade). Spectral reflectance data (from 400 to 700 nm) were recorded. Commission Internationale de l’Éclairage (CIE) L*a*b* values were calculated for D65 (reference daylight), A (incandescent light), and TL84 (store/office light) as reference illuminants. A modified metamerism index (Mod‐M) and hue‐angle ratios were calculated to express differences between tooth and tab colour relative to the difference observed under D65 illumination. The Mod‐M for teeth and tabs was greater than unity (indicating a greater colour difference relative to D65) by 57.1% for A and by 49.3% for TL84. Hue‐angle ratios of teeth and tabs using the test illuminants were different from those obtained using the standard illuminant D65. If teeth and shade tab matching is conducted using daylight illumination, the colour difference may not be the same under other lighting conditions, leading to perceptible, or even unacceptable, colour differences under these conditions.

Device gamuts are commonly defined for output devices, such as monitors or printers. In this paper, a definition of gamuts of input devices will be examined, considering multispectral cameras as examples. A method appropriate to calculate them as a function of the camera model and the spectral reconstruction algorithm will be proposed.The method will be applied to multispectral camera models with a variable number of channels. The characteristics of the resulting gamuts will be shown and examined as a function of the number of channels. Implications on the minimum number of channels needed will be derived.The method proposed here to characterize input devices can be used in addition to common quality criteria such as color distances like ∆E 00 , spectral errors, etc. The advantage of the proposed method is the independence of any given spectral data set. This makes it a quality criterion universal for linear (multispectral) cameras and reconstruction algorithms.

We set up a multispectral image acquisition system using a flash light source and a camera featuring optical bandpass filters. The filters are mounted on a computer-controlled filter wheel between the lens and a grayscale sensor. For each filter wheel position, we fire the flash once within the exposure interval and acquire a grayscale image. Finally, all grayscale images are combined into a multispectral image. The use of narrowband filters to divide the electromagnetic spectrum into several passbands drastically reduces the available light at the sensor. In case of continuous light sources, this requires powerful lamps producing a lot of heat and long exposure times. In contrast, a flashgun emits its energy in a very short time interval, allowing for short exposure times and low heat production. Our detailed colorimetric analysis comparing the color accuracy obtainable with our flashgun and a halogen bulb shows that our acquisition system is well suited for multispectral image acquisition. We computed a mean color error of 1.75 CIEDE00 using the flashgun. Furthermore, we discuss several practical aspects arising from the use of flash light sources, namely the spectrum, repeat accuracy, illumination uniformity, synchronization and calibration of the system. To compensate for intensity variations of the flash, we propose two calibration methods and compare their performance.