1：Experimental Design and Method Selection:

An in-vitro study design was used to compare different surface conditioning treatments (phototherapy, sodium ascorbate, no treatment) and bonding systems (total etch and self-etch) on bleached enamel. The rationale was to evaluate the efficacy of phototherapy as an alternative to sodium ascorbate for reversing bleaching effects. Methods included bleaching with hydrogen peroxide, surface treatments, bonding of orthodontic brackets, shear bond strength testing, and microleakage assessment using dye penetration. Statistical analysis with ANOVA and Tukey tests was employed.

2：Sample Selection and Data Sources:

120 intact maxillary permanent premolars free from restorations, caries, cracks, and endodontic treatment were used. Teeth were stored in thymol solution and distilled water before preparation. Data were derived from laboratory measurements of bond strength and microleakage.

3：List of Experimental Equipment and Materials:

Equipment included a periodontal scaler (Sonic flex 2000, Biberach, Germany), polishing machine (Automet 250 Pro, Buehler), Er,Cr:YSGG laser (Biolase-Waterlase I-Plus), universal testing machine (Instron Model 4400), isomet (Buehler Isomet 2000), polishing machine (Buehler Polishing Machine type: 49-5100-230), binocular microscope (Olympus SZH10), and light-curing unit (Bluephase C8, Ivoclar Vivadent). Materials included 35% hydrogen peroxide (Total Blanc Office H35/Nova DFL), 10% sodium ascorbate (Merck, Germany), phosphoric acid (3M ESPE), Transbond XT adhesive (3M Unitek), Transbond Plus self-etching primer (3M Unitek), metal brackets (Gemini 3M Unitek), composite paste (Transbond XT, 3M Unitek), methylene blue dye, acrylic resin (Meliodent, Heraeus/Kulzar), and artificial saliva.

4：Experimental Procedures and Operational Workflow:

Teeth were cleaned, mounted, and polished. 90 samples were bleached with hydrogen peroxide. After bleaching, samples were divided into groups for surface treatment: Group 1 (ECL) treated with Er,Cr:YSGG laser, Group 2 (SA) treated with sodium ascorbate, Group 3 (BO) no treatment, and a no-treatment control group (NT). Subgroups were created based on adhesive type: total etch (TEP) or self-etch (SEP). Brackets were bonded, light-cured, and samples underwent thermocycling. Shear bond strength was tested with a universal testing machine, and microleakage was assessed by dye immersion and microscopic examination.

5：Data Analysis Methods:

Data were analyzed for normality using the Kolmogorov-Smirnov test. One-way ANOVA and Tukey multiple comparisons tests were used to compare bond strength and microleakage among groups, with a significance level of p<0.05.