After obtaining informed consent, 32 premolar teeth were collected from patients undergoing orthodontic treatments. The teeth were sound, without any signs of restoration, decalcification, or apparent caries. The sample size was determined using power analysis where n = 2(1.96 + 0.84)2(2)2/(1)2 ≈32. The study was conducted following ethical approval (REC-77723). An ultrasonic scaler and slurry pumice were used to clean the teeth thoroughly and remove any remaining soft tissues, calculus, and plaque before storing them in normal saline for the study. All samples were randomly allocated to four groups where each tooth was sectioned in a mesiodistal direction into equal halves, and each half was divided into two halves. Each quarter was embedded in chemically activated acrylic resin to expose the enamel. Four groups were prepared as per treatment modality:

All samples were demineralized by being immersed and stored in a demineralizing solution (2.2 mM calcium chloride, 2.2 mM monopotassium phosphate, 0.5 mM acetic acid with pH adjusted to 4.4 and 1 M potassium hydroxide) for 96 h to produce a WSL. All the teeth were thoroughly washed with distilled water and then air-dried [17].

The teeth of groups A and C were etched using 37% phosphoric acid for 30 s. Subsequently, they were rinsed with water and left to air-dry for 3 s. Next, a thin coat of Clinpro (3 M ESPE, Pymble, New South Wales, Australia) was administered and exposed to light curing for 20 s [18].

For the Icon resin application (groups B and D), the teeth were treated with a 15% hydrochloric acid gel (Icon-Etch, DMG) for 2 min. They were washed with water and dried using moisture-free air for 30 s. A solution of 99% ethanol (Icon-Dry, DMG) was used, which was applied for 30 s and then allowed to dry in the air. Icon (DMG America, Englewood, NJ, USA) was applied and left to sit for 3 min, after which it was subjected to light curing for 40 s. A second layer of Icon was administered, allowed to sit for 1 min, and then exposed to light cure for 40 s [18].

A commercially available diode laser (Gallium–Aluminum–Arsenide [Ga AIAs] diode laser, Simpler, Doctor Smile, Italy) of 980 nm wavelength and power output of 2 W was used in a continuous mode. Following the application of the materials, the laser was immediately applied to the prepared tooth surfaces for a duration of 15 s per specimen. It was attached to a 220-micron optic conductor fiber as a transmission element. The optic fiber was moving uniformly and longitudinally over the treated tooth surface by the same operator for all the specimens, ensuring consistent application across the study [19].

The color of each sample was assessed at three time points: baseline before WSL, after WSL, and after the application of each of our study materials. The apparatus used in measurements is the Cary 5000 Spectrophotometer provided by Agilent Technologies (USA). Agilent Cary 5000 UV–Vis–NIR spectrophotometers are manufactured using a quality management system certified to ISO 9001.

The measurements were conducted in the same examination room with standardized lighting conditions. To guarantee precision, the spectrophotometer was calibrated before each test using a white calibration plate supplied by the manufacturer. This calibration accounted for any discrepancies in the illumination output from the internal light source. The spectrophotometric data of each tooth were obtained through two separate measurements. This involved placing the measuring head on the tooth’s surface, removing it, and then repositioning it. Consequently, the device produced a definitive numerical value for each tooth, resulting in accurate readings. The color measurements were quantified using the coordinate values L*, a*, b* specified by the Commission Internationale de l’Eclariage, 1978 (CIE) [20].

The microhardness measurements were taken at three randomized indentations on the treated enamel surface of each sample. The indentations were made approximately 0.3 mm away from each other using a Vickers Microhardness Tester (Model HVS-50, Laizhou Huayin Testing Instrument Co., Ltd. China) with a Vickers diamond indenter and a 20× objective lens. Each measurement used a 200-g load for 10 s, oriented perpendicularly to the tooth surface [21].

All samples were examined under a scanning electron microscope (SEM; Model FEI Quanta 3D 200i). Samples were fixed on aluminum stubs with standard diameter using a carbon double sticky tape attached to the EDX Unit (Energy-Dispersive X-ray Analyses/Thermo Fisher pathfinder) that was employed to investigate the morphological structures and elemental composition of the samples under operating conditions of accelerating voltage 30 K.V, resolution for Gun.1 nm, and magnification × 2000 and × 3000 [22]. Images were gathered at the following time points: baseline, after WSL, and after applying the study materials.

The color change and microhardness results are presented as means ± standard deviations. The Shapiro–Wilk test was used to assess the normality of the data. A one-way ANOVA with Tukey’s post hoc test were used to determine the statistical significance between the experimental groups. A value of p < 0.05 was considered significant. GraphPad Prism 9.0 (GraphPad Software, San Diego, CA, USA) was used for the statistical analysis.