Review article

Advances in color matching

A modern paint/coating (P/C) is a complex mixture of many interacting compatible chemicals. Its properties depend on the properties and amounts of the chemicals as well as the processes by which the chemicals are combined. The main components of paint include a solvent as a carrier, pigments, a polymer/resin as a binder and/or aid in dispersing the pigments, and additives. The relationships between (1) the quality attributes of a P/C product and (2) the properties and amounts of the chemicals that the product is made from and the process type and conditions are complex and difficult to fully describe using physiochemical models. This chapter describes a study of capturing, describing, and predicting the relationships using machine learning (ML) models trained on formula data from Axalta coating systems’ historical P/C data. It also discusses advances necessary in ML methods to better capture the relations.

Shade selection has become more important and challenging as it becomes more emphasized in esthetic dentistry. It would be beneficial to screen dental students early in their predoctoral education for any deficiencies in color discrimination. Specific tests that reliably predict dental shade-matching ability have not been fully established.

The purpose of this study was to determine whether the Farnsworth-Munsell 100 Hue Test (FM-100), Perceptual Ability Test (PAT), ethnicity, age, sex, and time to complete the tests affect dental shade-matching ability and value discernment in first-year dental students. Secondary aims were to determine whether correlations exist between performance on the PAT and FM-100 and between FM-100 and dental shade matching.

The FM-100 test was administered to 98 first-year dental students in a Judge II booth (color temperature=6500 K, color rendering index=90). The Vita Toothguide 3D-Master shade guide was used in this study. For the Value Test, students arranged 3 sets of 5 masked shade tabs from lightest to darkest. In all 3 sets, the value ranged from 1 to 5. In set #1, each shade tab had the same hue and chroma. In set #2, the hues were constant, but the chroma varied. In set #3, the hue and chroma varied. For the Matching Test, students matched together 11 pairs of masked shade tabs from 2 shade guides. Ethnicity (white, African American, Hispanic, Middle Eastern, and Asian), PAT scores, age, sex, and time to complete tests were recorded. Data were analyzed by using least square means, Wilcoxon Rank Sum, Kruskal-Wallis, and Spearman correlation tests (α=.05).

FM-100 total error scores (TES) ranged from 0 to 188. Forty-three students had superior color discrimination (TES 0 to16), 51 had average (TES 20 to 100), and 4 had poor color discrimination (TES>100). Ethnicity, age, and sex did not significantly affect performance on any tests. Longer completion time resulted in better performance on FM-100 (P=.002) and Matching Tests (P=.032). However, increased time resulted in fewer correct answers on the Value Test (P=.016). There was a significant effect of PAT on FM-100 results (P<.001). As PAT scores increased, TES scores decreased, indicating better color discrimination. Similarly, lower TES scores resulted in higher Matching Test results (P<.001). However, this was not observed on the Value Test (P=.302). Correlation between the PAT and FM-100 was weak (r=-0.217), as well as between the FM-100 and Matching Test (r=-0.364).

Ethnicity, age, and sex did not affect dental shade-matching ability. Participants with higher PAT scores demonstrated higher color discrimination on the FM-100 and were better at matching dental shade tabs. Time had different effects on the Matching and Value tests.

A silicon carbide (SiC) protective coating has been developed for dental ceramics, but whether the coated ceramics can match the classical VITA shades is unclear.

The purpose of this observational in vitro study was to evaluate the color adaptability of SiC-coated dental ceramics by testing the hypotheses that SiC-coated disks can be fabricated to match standard tooth shades and have a perceptible color match rate of at least 50% for disks with a color difference (ΔE)<2.0. The effects of ΔE, shade hue, shade value, observer sex, years of experience, profession, and shade guide orientation on color perception were studied.

SiC-coated disks were fabricated to color match (ΔE_ab<3.3) all 16 VITA classical shades. Uncoated disks of each VITA shade were used as the reference materials to determine whether the SiC-coated disks were color matched to the classical VITA shade guide. Three ΔE formulas (76, 94, and 2000) were applied and compared. Participants (N=120) with an average of 22 years of experience included dental school students, dental faculty members, and dental assistants. Pseudoisochromatic plate and the Farnsworth D-15 Panel test for assessing color deficiency and color blindness were administered. Participants then attempted to match SiC-coated disks to standard shade guides arranged by value or hue. All spectrophotometer readings and color matching were conducted in a light booth with standardized daylight illumination. Statistical analysis used the Fisher's exact test to determine factors associated with improved matching performance (α=.05).

A significant difference in color match rate was found between disks with ΔE<2.0 (63.9%) and ΔE≥2.0 (41.7%) (P<.001). Arranging shade by value (72.2%) instead of hue (67.2%) produced better color matching (P<.001). Sex (P=.430), profession (P=.708), and years of experience (P=.902) had no significant influence on color matching.

SiC-coated disks were successfully fabricated to match all VITA classical shades, and clinical visual color matching results confirmed that ΔE was a useful metric in optimizing color matching for the SiC-coated dental ceramics.