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The Use of a Standardized Gray Reference Card in Dental Photography to Correct the Effects of Five Commonly Used Diffusers on the Color of 40 Extracted Human Teeth

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The Use of a Standardized Gray Reference Card in Dental Photography to Correct the Effects of Five Commonly Used Diffusers on the Color of 40 Extracted Human Teeth HEIN/ZANGL CLINICAL RESEARCH CLINICAL RESEARCH The use of a standardized gray reference card in dental photography to correct the effects of five commonly used diffusers on the color of 40 extracted human teeth Sascha Hein, MDT Private Dental Laboratory Michael Zangl, MDT Private Dental Laboratory Correspondence to: Sascha Hein, MDT Dentaltechnik Christ & Hein GmbH, Karl-Benz-Str. 25, 86825 Bad Wörishofen, Germany. Tel.: 0049 8247 5320 Fax.: 0049 8247 31965; E-mail: [email protected] 2 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY VOLUME 11 • NUMBER 2 • SUMMER 2016 HEIN/ZANGL Abstract ter software (Ricci Adams, version 1.6 (122)) was used to obtain CIE L*a*b* Objective: The aim of this in vitro study values of the specimens before and af- was to investigate the color changes of ter white balancing and exposure cor- human teeth caused by five different dif- rection. fuser materials commonly used in dental Results: All diffusers caused visually photography, as well as software influ- perceivable color changes on the ex- ence, and to confirm whether the use tracted teeth: White Frost (∆E* 1.24; of a standardized gray reference card sd 0.47), 80 gsm printing paper is effective in correcting these color (∆E* 2.94; sd 0.35), LumiQuest polyam- changes during digital postproduction. ide (∆E* 3.68; sd 0.54), PET (∆E* 6.55; Materials and method: Forty extracted sd 0.41), and 3M linear polarizing fil- human teeth were obtained from a spe- ter sheet (∆E* 7.58; sd 1.00). The use cialized oral surgery practice in Cham, of a standardized gray reference card Germany. Five commonly used diffuser (WhiBal) could correct these values be- materials were chosen to be investi- low the visually perceivable threshold: gated, which included: polyethylene White Frost (∆E* 0.58; sd 0.36), 80 gsm (PET), White Frost photographic paper, printing paper (∆E* 0.93; sd 0.54), Lu- LumiQuest polyamide (nylon) mater- miQuest polyamide (∆E* 0.66; sd 0.58), ial, 80 gsm white printing paper, and PET (∆E* 0.59; sd 0.33), and 3M linear 3M linear polarizing filter sheet used for polarizing filter sheet (∆E* 0.53; sd 0.42). cross polarization. A digital single-lens Significance: The use of a standard- reflex camera (Canon EOS 5D MKII) was ized gray reference card with specified used, together with a twin flash suitable CIE L*a*b* values should be considered for macrophotography (Canon MT-24EX when diffusers are used in dental pho- Macro Twin Lite). Images were tethered tography in order to reveal the color of into Adobe Lightroom CC using the preoperative situations (ie, shade docu- RAW format. A standardized gray refer- mentation) and document postoperative ence card (WhiBal, Michael Tapes De- results accurately. sign) was used for exposure calibration and white balancing. Classic Color Me- (Int J Esthet Dent 2016;11:XXX–XXX) 3 THETHE INTERNATIONALINTERNATIONAL JOURNALJOURNAL OF ESTHETICESTHETIC DENTISTRYDENTISTRY VOLUME 11 • NUMBER 2 • SUMMER 2016 CLINICAL RESEARCH Introduction wavelengths will pass through. Due to absorption, only specific wavelengths The use of dental photography plays an that are characteristic of the material will increasingly important role in everyday be transmitted. Hence, all the power that dental practice as an effective tool for is transmitted is concentrated in a few communication between the dental sur- narrow wavelength regions,7 causing gery and the dental laboratory. Modern large color distortions, since they affect digital single-lens reflex (DSLR) camer- both the Correlated Color Temperature as are in common use to document im- (CCT) and the Color Rendering Index portant restorative aspects such as the (CRI) of the emitted light, making it diffi- preoperative situation, the tooth shade, cult to judge shade differences between the final result, and long-term perfor- a shade tab or dental restoration and the mance.1 Photographic documentation surrounding natural dentition on a digi- for purely medical purposes requires lit- tal image. Preliminary relative irradiance tle more than basic equipment, such as measurements of five commonly used a DSLR camera paired either with a ring diffuser materials which were included or twin flash.2 In the field of esthetic den- in this study, using a radiospectrometer tistry, however, elaborate assemblies (Sekonic C-700, Sekonic), in conjunc- are often used to depict the restorative tion with a commonly used electronic process and especially the final result in flash (Canon MT-24EX Macro Twin Lite), a rather “emotional” way, with the use of revealed that different diffuser mater- various bouncers and diffusers and ad- ials did indeed influence CCT and CRI, justable brackets.3 On the other hand, but only slightly. However, the visually cross polarized photography is a useful perceivable effects appeared notice- method to reveal intrinsic shade varia- able in the digital images, suggesting tions of natural teeth for the purpose of that software interpretation might play shade analysis.4 This is achieved with a significant role (Fig 1). The use of a the help of a linear polarizing filter sheet standardized gray reference card prom- that is placed over the electronic flash ises to overcome this limitation through a in an orientation which is perpendicular remapping process of the original RAW to that of another linear polarizing filter image to a defined standard. However, simultaneously placed over the lens, re- natural teeth are heavy light scatter- sulting in the exclusion of diffuse light ers, and irradiation with an intermittent and specular reflection from the labial spectral power distribution may affect surface of natural teeth and dental res- their color within the threshold of visual torations alike.5 perception. The aim of this study was Clinical experience has shown that to determine the effects that five com- in vivo photographs of natural dentition monly used diffuser materials have on routinely show significant color altera- tooth color, to identify their origin, and tions of teeth and soft tissue when cer- to determine if the use of a gray refer- tain types of diffusers are used.6 When ence card is effective in correcting these a diffuser is placed in front of an illu- changes. minant (ie, an electronic flash), not all 4 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY VOLUME 11 • NUMBER 2 • SUMMER 2016 HEIN/ZANGL Canon MT-24EX Macro Twin Lite 380 780 6400 K (CRI Ra 100) Linear polarizer Printing paper LumiQuest SoftBox White Frost Polyethylene PET (80 gsm) 380 780 380 780 380 780 380 780 380 780 CRI Ra 97.2 CRI Ra 92.4 CRI Ra 96.0 CRI Ra 97.6 CRI Ra 97.6 5864 K 5971 K 5775 K 6108 K 5407 K Fig 1 Relative irradiance measurements reveal small influences on the Color Rendering Index (CRI) and Correlated Color Temperature (CCT) caused by five diffusers when placed in front of an electronic flash. Note that a variance in the rendering of the images occurs due to software interpretation of the DSLR camera. Materials and method the RAW format and a USB 2.0 cable. The screen (Cinema Display, Apple) Camera set-up was calibrated using a spectrophotom- eter (ColorMunki, Pantone). The working A digital single-lens reflex camera (Can- distance between the front of the lens on EOS 5D MKII) was used, together and the labial surface of one randomly with a twin flash suitable for macro pho- selected test specimen was varied to tography (Canon MT-24EX Macro Twin achieve life-size magnification (1:1) at a Lite) (Figs 2 and 3). Images were teth- constant distance of 130 mm, as would ered into Adobe Lightroom CC using be the case in a clinical situation, and 5 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY VOLUME 11 • NUMBER 2 • SUMMER 2016 CLINICAL RESEARCH hence this value was chosen as the standard distance for all measurements. Using the camera’s manual mode, ex- posure time and aperture were set to a constant value of 125/sec and f 32. The twin flash normally operates with four AA Mignon batteries (Energizer Ultimate Lithium, +AA 1.5 V, 3000 mAh). However, preliminary tests showed noticeable var- iations in flash intensity after a few meas- urement cycles due to battery depletion and increased recycle time. In order to overcome these limitations, a compact battery pack which normally holds eight additional AA Mignon batteries (Canon CP-E4) was modified to be attached to a 12 V, 1500 mAh direct current trans- former (Yumatron, Model NT6), ensuring steady flash intensity and short recycling times (< 5 s). The camera was attached to a microcomputer (Stack Shot, Cogn- isys) that was programmed to trigger the Figs 2 and 3 The experimental setup consisted camera shutter nine times in a row, with of a DSLR camera paired with a twin flash com- a precisely timed interval of 15 s. monly used for dental photography. In order to mini- mize specular reflection from the labial surface of the teeth, both electronic flash guns were arranged Diffuser materials in two azimuthal illumination angles correspond- ing to 0 degrees/45 degrees geometry using two Five commonly used diffuser materials aluminum rails and two custom 3D-printed variable sled assemblies. were chosen for the study: polyethyl- ene (PET), White Frost photographic paper (ProTech Lighting), Mini SoftBox polyamide (nylon) material (LumiQuest), 80 gsm white printing paper, and 3M lin- ear polarizing filter sheet used for cross polarization. The materials were cut into squares and attached to a set of cus- Fig 4 Five commonly used diffuser materials were chosen for the study. They included polyethylene (PET), White Frost photographic paper, LumiQuest polyamide (nylon) material, 80 gsm white printing paper, and 3M linear polarizing filter sheet used for cross polarization. Each frame had an open window of 80 mm x 55 mm.
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