Diagnostic Accuracy of Innovative Photo-Analysis Software in Resin Composite Shade Matching

Shade Matching

diagnostic accuracy, spectrophotometer, Computer assisted software, visual assessment

This study aims to assess the agreement between new computer software using dental photographs, digital spectrophotometer and the visual technique, in achieving accurate resin composite shade matching.

* Custom composite resin shade tabs are fabricated and catalogued to serve as reference standards during shade matching. * Teeth are professionally cleaned on dental chair using a nylon prophylaxis brush with polishing paste to ensure complete removal of extrinsic stains and to reveal the native tooth color. * Participants will be seated on an adjustable chair in an upright posture, with the head oriented perpendicular to the floor and be stabilized by a headrest. The chair will be positioned against a matte white wall adjacent to a clear window to standardize a neutral background and exploit consistent daylight illumination. * Patients will be instructed to maintain an upright head posture with the interpupillary line parallel to the floor. All measurements will be performed under daylight, while extraneous light sources and environmental interferences to be minimized. * Computer-Assisted Software A standardized Computer-assisted photographic shade-matching workflow will be employed using a novel photo-analysis software that first receives the photos and balances each photo to suppress unrealistic colors using a standard gray reference card (WhiBal; Michael Tapes Design), with nominal colorimetric targets of L\* =75, a\* = 0, b\* = 0, will be included in every photograph within the plane of the teeth. The Photo is firstly captured with a Nikon D3400 DSLR crop-frame camera (Nikon Corp) mounted on a stable tripod to avoid movements during capturing the photo and set the proper angulation and parallelism. All camera parameters will be standardized. The program establishes a pixel-to-metric conversion scale (cm) from known distances and overlays orthogonal reference axes to fix landmark orientation and reproducible measurement geometry. Using these guides, tooth height and width are annotated, and the region of interest is consistently defined at the central area of the middle third of the labial crown of either the tooth or shade tabs. Candidate shades are then quantitatively compared to the region of interest by computing CIEDE2000 color-difference values (ΔE₀₀), which incorporate corrections for lightness, chroma, and hue; the final selected shade is the one yielding the smallest ΔE₀₀. Where: ΔL', ΔC', ΔH' are the lightness, chroma, and hue differences in the CIEDE2000 framework; SL, SC, SH are weighting functions; kL, kC, kH are parametric factors (set to 1 unless otherwise justified); and RT is the rotation term accounting for interaction between chroma and hue differences. * Spectrophotometer assessment A pre-calibrated spectrophotometer (per manufacturer guidelines) independently measures tooth and shade-tab color. Measurements are reported as CIE L\*, a\*, b\* values. For each tooth-tab combination, the CIEDE2000 color difference (ΔE00) is calculated; the tab yielding the minimal ΔE00 is accepted as the selected shade. 9 * Visual Shade Matching Under the same conditions (lighting and patient positioning), experienced assessors independently determine the matching shade. Agreement between their own assessments and between the other assessors' assessments, as well as the extent of their discrepancies, is quantified using kappa test.

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