Effects of Acid Etching and Bleaching on Enamel Stain Retention From Turmeric and Coffee: An In Vitro Study

Dental procedures, such as acid etching and bleaching, are widely used to improve the appearance of teeth. However, dietary chromogens, such as turmeric and coffee, may affect the aesthetic outcomes of these treatments by staining the enamel. Understanding how these procedures influence the interaction between enamel and common staining agents is essential for optimizing dental aesthetics. This in vitro study compared the effects of 37% phosphoric acid etching, 10% hydrogen peroxide bleaching, and their combination on enamel surface roughness and stain retention when exposed to turmeric and coffee, simulating clinical conditions and dietary exposures.

Sixty non-carious human maxillary premolars were sectioned at the cementoenamel junction, and the buccal surfaces were ground flat to create a standardized 5 mm × 5 mm enamel surface. The specimens were randomly divided into three groups (n = 20 each): Group A (control, no etching), Group B (etched for 30 seconds with 37% phosphoric acid gel; Scotchbond Etchant, 3M Company, St. Paul, MN), and Group C (treated with 10% hydrogen peroxide gel for 10 minutes; Opalescence Boost, Ultradent Products, Inc., South Jordan, UT). Each group was subdivided into two subgroups (n = 10) for staining with either turmeric (10 g McCormick Ground Turmeric, McCormick & Company, Hunt Valley, MD) in 100 mL distilled water or coffee (10 g Nescafé Classic, Nestlé S.A., Vevey, Switzerland) in 100 mL distilled water at 37°C for 10 minutes, three times daily for seven days. Surface roughness (Ra and Rz) was measured using a profilometer (Surftest SJ-210, Mitutoyo Corporation, Kawasaki, Japan) before and after staining. Stain retention was quantified via a chemical staining assay using a UV-vis microplate reader (Synergy H1; BioTek Instruments, Inc., Winooski, VT) at 425 nm for turmeric and 275 nm for coffee.

Phosphoric acid etching resulted in significantly higher stain retention (coffee: 25.60 ± 2.10 µg/mL; turmeric: 16.80 ± 1.8 µg/mL) than hydrogen peroxide (coffee: 18.20 ± 1.50 µg/mL; turmeric: 12.70 ± 1.20 µg/mL) and control (coffee: 8.30 ± 0.90 µg/mL; turmeric: 5.10 ± 0.60 µg/mL) (p < 0.001). Surface roughness increased significantly after staining in all groups (p < 0.05), with coffee causing greater changes than turmeric. The phosphoric acid-etched surfaces exhibited the highest roughness (coffee: 2.38 µm; turmeric: 2.05 µm).

Phosphoric acid etching significantly enhanced enamel staining susceptibility and roughness compared to hydrogen peroxide bleaching, with coffee posing a greater risk than turmeric. These findings underscore the need for dietary counseling and post-treatment protective measures to preserve dental aesthetics.