Creating an artificial replacement that matches the unique esthetic characteristics of a single maxillary central incisor can be one of the biggest challenges in restorative dentistry. While a variety of factors contribute to this challenge, it is important to understand the clinical considerations that will help clinicians select a good esthetic match. Furthermore, dentists need a basic knowledge of light-science nomenclature. Additionally, practitioners must be able to determine what happens to a tooth’s appearance when light reflects off its surface. The aim of this literature review is to examine the efficacy of cross-polarized photography as an affordable and accurate method for assessing tooth color.
By reducing metamerism, afterimages, and other visual distortions in the oral cavity, clinicians can enhance what is seen visually or photographically.1 To improve the shade matching processes, several shade assessment modalities have been described.2 While the visual analog technique is often used in restorative procedures, additional shade matching technologies have been developed as part of ongoing efforts to enhance color matching, dentist-laboratory communications, and reproduction of tooth characteristics.3 By reducing or eliminating specular reflections, cross-polarizing filters help correct the overestimation of white opacities with flash photography.
Cross-polarizing filters also help when discriminating between color differences in shade guides (Figure 1).4 Comparing digital images taken with, and without, a polarizing filter under different conditions demonstrates superior results with the filter, especially in areas with excess light. This makes digital photography with polarizing filters a valuable tool for dental shade matching.5
The Commission International de l’Eclairage (CIE) developed a system for defining color based on the quantification of wavelength distributions. The CIELab and ΔΕ coordinate system relies on the standardization of light sources and observers.6–8 CIELab locates a specific color in space by using three coordinates: L* (which is related to value); a* (which refers to red to green); and b* (which refers to yellow to blue). Scientists use ΔΕ to evaluate the measured differences between colors.9 In the CIELab system, ΔΕ 3.7 is a clinically acceptable threshold for comparing different methods of color assessment in dentistry.3,10
Search Strategy — The authors conducted a literature search to compare the utility of cross-polarized photography as a tool for shade matching in direct restorations and prostheses. The goal was to compare CIELab and ΔΕ coordinate shade assessment with other shade-matching modalities. The team also looked at additional studies related to cross-polarized photography that used other factors to evaluate shade matching performance.
Following a comprehensive keyword search, an additional hand search was performed based on references from the final relevant articles.
Study Selection Criteria — Only articles published in English were considered, and the selected studies included reviews, cohort studies and case reports. Nondental articles, such as dermatological, ophthalmological, and animal studies, were excluded, as were articles that used cross-polarized photography as a tool for any dental purposes other than color assessment. As a matter of record, no systematic reviews were found in the searches.
Two independent researchers checked the keywords and search results for relevance. They screened the articles by title, abstract, and the full text. Any disagreement regarding the inclusion/exclusion criteria was resolved through discussion. After the final selection, 15 articles were included in this study.
Clinical Implications — The use of cross-polarized photography, as well as postprocessing calibration using a gray reference card, may yield precise color quantification, regardless of ambient lighting conditions.11 This could enhance documentation, shade selection, and communication with laboratory technicians.
Based on six included articles, Table 1 evaluates the different methods of color assessment compared with cross-polarized photography.
Lazar et al5 assessed the influence of polarizing filters on the accuracy of dental shade matching by taking digital images under two different conditions (with direct light and polarized light) from 26 shade samples from the VITA 3D-Master shade guide, and comparing them with the values from a dental spectrophotometer — which is considered the gold standard for shade assessment. They concluded, “Digital photography with polarizing filters might be a useful tool for dental shade matching.”
In another study, Yamanel et al10 used a colorimeter and cross-polarized photography to compare ΔΕ values in two different composite shade tabs and reported no significant differences between the two methods, lending credence to the utility of cross-polarized photography for shade matching.
Using a polarization filter on a digital single-lens reflex (DSLR) camera, Gurrea et al12 evaluated color variability for hue, chroma and value for five tabs (A1 to A4) from five different shade guides, including the Vita Classical guide, which was used as the control. The results showed no significant difference in values of hue, chroma and value for each shade guide.
In another study, a comparison of ΔΕ was assessed at the cervical one-third, middle one-third, and the incisal one-third by taking polarized and nonpolarized photos of the subjects. The nonpolarized images revealed different glare patterns caused by specular reflection from the tooth surface. In contrast, the use of cross-polarization presented glare-free images due to the complete removal of specular reflection. The researchers found that polarized tooth images offer significantly superior ΔΕ values compared to nonpolarized imaging.13
A 2021 investigation by Jorquera et al14 enrolled 45 patients who needed ceramic crowns in an experiment that compared different methods of shade selection, two of which utilized polarization filters — one with a digital camera, and the other with a smartphone camera. These two methods yielded ΔΕ values of 2.75 and 2.34, respectively, which is within the range of acceptable color assessment accuracy.
Similarly, Sampaio et al4 compared various photography techniques to assess the accuracy of final shade assessment by using a DSLR camera with different flash setups, as well as a smartphone. Comparing the results with different equipment, an ΔΕ of 3.4 for images that used polarization filters was achieved. They further noted, “The use of a cross-polarizing filter results in more color-standardized photographs, while the ring flash system and smartphone camera result in less standardized photographs.”
Using a standardized cross-polarized photographic shade analysis and visual shade matching, Rondón et al15 asked 50 observers (35 undergraduate and 15 graduate students) to evaluate the color of two maxillary left central incisors, one of which had a light tooth color, while the other had a dark tooth color. Shade tab selections from visual shade matching and photographic shade analysis agreed only for the light tooth. Overall, cross-polarized photography showed a higher total percentage of what the researchers called “match,” as well as a higher percentage of agreement among the observers.
Color registration and color matching were compared in a young Chilean population with three different methods: visual analysis with a shade guide, digital visual evaluation using cross-polarizing photography, and analysis via spectrophotometer.3 Significant differences were detected between the coordinates recorded by the visual analog method in comparison with the other two modalities. In contrast, no significant differences in ΔΕ were found between color assessment with the spectrophotometer or the digital visual method using a cross-polarization filter.3
Lately, interest in the use of mobile dental photography (MDP) has grown among the provider community. With the use of recent high-tech devices, dentists can easily capture professional-grade dental images. One of the features of MDP is polarized photography, which aids in accurate shade selection when using composite restorations.16
A paper from Villavicencio-Espinoza et al17 presents a clinical report describing the restoration of a maxillary right incisor utilizing cross-polarized photography as a guide for composite shade selection. The team observed this technique allowed highly accurate color matching.
In another restorative case involving a resin veneer on a maxillary right incisor, cross-polarized photography was used to select the most accurate shade to reconstruct a discolored previous restoration. By eliminating the superficial glare that blocks key color information, this technique allowed the unobstructed visualization of surface and subsurface enamel characteristics, aiding in the final restorative shade choice.18
Another productive use of cross-polarized photography involves the treatment of enamel defects.19 Researchers note this method eliminates imaging glare from the tooth — a result that aids in clinical assessment before and after treatment. In addition, enamel thickness varies in different anatomical points, which further complicates choosing an exact shade when treating defects. The use of cross-polarized photography helps address this by removing the frosty appearance and other distractions, which results in more accurate shade selection.
Shade matching is a preliminary step in restorative dentistry, and color selection and reproduction pose challenges to clinicians and laboratory technicians.20 As noted at the outset, the aim of this review is to determine the efficacy of cross-polarized photography as an affordable and reliable method for assessing tooth color.
With the understanding that precise shade selection is critical for a natural-looking smile and patient satisfaction, a nonhomogeneous color choice can be counted as a failure. While tools such as the spectrophotometer and colorimeter are useful, these are not always widely available — which makes alternative shade-matching technologies attractive to restorative practitioners.
As previously noted, one of the obstacles encountered when choosing a shade with the unaided eye is light reflection from the tooth surface, which can hinder accurate color selection. The same phenomena can negatively affect conventional dental photography. In these situations, the use of polarizing filters helps eliminate excess light reflecting back to the camera’s sensor; this results in images that facilitate better interpretation of tooth color.
- Shade selection that matches the unique characteristics of a single maxillary central incisor is challenging.
- Thus, it is important to understand the clinical considerations that will help clinicians select a good esthetic match.
- Various shade matching technologies have been developed as part of ongoing efforts to enhance color matching, dentist-laboratory communications, and reproduction of tooth characteristics.3
- Comparing digital photographs taken with a polarizing filter demonstrates superior results with the filter.5
- Lazar et al’s5 analysis of the influence of polarizing filters on the accuracy of dental shade matching, and comparison of these results to a spectrophotometer, led them to conclude that cross-polarized photography is a reliable way to conduct color evaluations.
- Yamanel et al10 compared shade assessment values with a colorimeter and cross-polarized photography and found no significant difference between the two.
- Evidence suggests that cross-polarized photography represents a reliable and cost-effective alternative to the use of colorimeters and spectrophotometers in dental shade matching.
This review includes studies that evaluated cross-polarized photography techniques for tooth color assessment. To recap, Lazar et al’s5 analysis of the influence of polarizing filters on the accuracy of dental shade matching, and comparison of these results to a spectrophotometer, led them to conclude that cross-polarized photography offers a reliable method for conducting color evaluations. Yamanel et al10 found no significant difference between ΔΕ shade assessment values with a colorimeter and cross-polarized photography. And in the papers reviewed for this article, all values in cross-polarized photography were below ΔΕ 3.7, which suggests this approach matches the reliability of the other color assessment tools currently available.
While cross-polarized photography is a more affordable alternative, the spectrophotometer is still the gold standard for shade selection. In fact, combining these two methods might result in even more accurate color matching.21 Additionally, the use of polarizing filters on smartphone cameras or MDP devices represents another economical approach to shade analysis.16,22
Ultimately, the varied methodology of the reviewed studies underscores the need for well-designed research that evaluates all shade assessment techniques in a manner that allows for precisely comparable results.
- Fondriest J. Shade matching in restorative dentistry: the science and strategiesJ J Prosthet Dent. 2003;23:467–480.
- Stevenson B. Current methods of shade matching in dentistry: a review of the supporting literature. Dent Update. 2009;36:270–276.
- Mahn E, Tortora SC, Olate B, Cacciuttolo F, Kernitsky J, Jorquera G. Comparison of visual analog shade matching, a digital visual method with a cross-polarized light filter, and a spectrophotometer for dental color matching. J Prosthet Dent. 2021;125:511–516.
- Sampaio CS, Atria PJ, Hirata R, Jorquera G. Variability of color matching with different digital photography techniques and a gray reference card. J Prosthet Dent. 2019;121:333–339.
- Lazar R, Culic B, Gasparik C, Lazar C, Dudea D. The accuracy of dental shade matching using cross-polarization photography. Int J Comput Dent. 2019;22:343–351.
- Robertson AR, Lozano RD, Alman DH, et al. CIE recommendations on uniform color spaces, color-difference equations, and metric color terms. Color Res Appl. 1977;2:5–6.
- Kim-Pusateri S, Brewer JD, Davis EL, Wee AG. Reliability and accuracy of four dental shade-matching devices. J Prosthet Dent. 2009;101:193–199.
- Pecho OE, Ghinea R, Alessandretti R, Pérez MM, della Bona A. Visual and instrumental shade matching using CIELAB and CIEDE2000 color difference formulas. Dent Mater. 2016;32:82–92.
- Johnston WM, Kao E. Assessment of appearance match by visual observation and clinical colorimetry. J Dent Res. 1989;68:819–822.
- Yamanel K, Caglar A, Özcan M, Gulsah K, Bagis B. Assessment of color parameters of composite resin shade guides using digital imaging versus colorimeter. J Esthet Restor Dent. 2010;22:379–388.
- Farah RI, Almershed AS, Albahli BF, Ali SN. Effect of ambient lighting conditions on tooth color quantification in cross-polarized dental photography: a clinical study. J Prosthet Dent. 2021;128:776–783.
- Gurrea J, Gurrea M, Bruguera A, et al. Evaluation of dental shade guide variability using cross-polarized photography. Int J Periodontics Restorative Dent. 2016;36:e76–e81.
- Kim E, Son T, Lee Y, Jung B. Development of polarization dental imaging modality and evaluation of its clinical feasibility. J Dent. 2012;40:e18–e25.
- Jorquera GJ, Atria PJ, Galán M, et al. A comparison of ceramic crown color difference between different shade selection methods: visual, digital camera, and smartphone. J Prosthet Dent. 2021;128:784–792.
- Rondón LF, Ramírez R, Pecho OE. Comparison of visual shade matching and photographic shade analysis. J Esthet Restor Dent. 2022;34:374–382.
- Hardan LS, Moussa C. Mobile dental photography: a simple technique for documentation and communication. Quintessence Int. 2020;51:510–518.
- Villavicencio-Espinoza CA, Narimatsu MH, Furuse AY. Using cross-polarized photography as a guide for selecting resin composite shade. Oper Dent. 2018;43:113–120.
- Ntovas P, Papazoglou E. Digital selection of composite resin shade using cross polarized photography and a standardized white balance gray reference card. J Clin Exp Dent. 2021;13:e1061–e1066.
- Robertson AJ, Toumba KJ. Cross-polarized photography in the study of enamel defects in dental paediatrics. J Audiov Media Med. 1999;22:63–70.
- Schwabacher WB, Goodkind RJ. Three-dimensional color coordinates of natural teeth compared with three shade guides. J Prosthet Dent. 1990;64:425–431.
- He WH, Park CJ, Byun S, Tan D, Lin CY, Chee W. Evaluating the relationship between tooth color and enamel thickness, using twin flash photography, cross-polarization photography, and spectrophotometer. J Esthet Restor Dent. 2020;32:91–101.
- de Bragança RMF, Moraes RR, Faria-e-Silva AL. Color assessment of resin composite by using cellphone images compared with a spectrophotometer. Restor Dent Endod. 2021;46:e23.
The authors have no commercial conflicts of interest to disclose.
From Decisions in Dentistry. June 2023;9(6):14-16, 18.