## 2 Materials and Methods  
### Sample Preparation  
Under the guidelines of the \"ISO 29022:2013\" standard, the samples were subjected to a series of shear-bond-strength tests. A total of 27 maxillary premolars (n = 27) that were extracted for orthodontic purposes and had no defect, a full and healthy crown, no cavities,no fillings, and no fractures or cracks were chosen. Sample size determination in this study was calculated using the Federer formula, which is described as follows:  
\[\left(\mathrm{t}-1\right)\left(\mathrm{n}-1\right)\geq 15\]  
n: number of samples in each group;  
t: number of experimental groups.  
This study used 3 groups (control group, a fluoride-containing desensitizing agent group, and a non-fluoride-containing desensitizing agent group).  
\[\left(3-1\right)\left(\mathrm{n}-1\right)\geq 15\]  
\[\mathrm{n}-1\geq 15/2\]  
\[\mathrm{n}-1=7.5\]  
\[\mathrm{n}=8.5\approx 9\]  
All of the samples were trimmed in the root area so that the distance from the cementoenamel junction to the base was 7 mm using a low-speed handpiece (W & H, Burmoos, Austria) and diamond bur ([PERSON], Neuss, Germany).  
Each selected tooth was then mounted in self-curing acrylic (Hillon, S Court Limited, Lancshire, UK) into a silicone mold (25 mm \(\times\) 25 mm \(\times\) 13 mm) up to the cementoenamel junction based on its vertical axis. The teeth were then subjected to a prophylactic procedure, polished with a rubber cup and pumice using a low-speed handpiece, rinsed with water, and dried with air. All specimens were then stored for 24 h in a saline solution (Otsuka, Malang, Indonesia) prior to the next procedure.  
Then, samples were randomly assigned to one of three groups (n = 9): group 1 (control group, CG), bleached teeth; group 2 (fluoride group, FG), bleached teeth and a fluoride-containing desensitizing agent (CPP-ACFP) applied; and group 3 (non-fluoride group, NFG), bleached teeth and a non-fluoride-containing desensitizing agent (CPP-ACP) applied. The enamel surfaces of all specimens were bleached using 37% hydrogen peroxide (Pola Office, SDI, Bayswater, Australia) as per the manufacturer's instructions. One cycle of bleaching lasted 20 min and was repeated up to three times, for a total bleaching time of 60 min. The samples were then rinsed with distilled water and desiccated with a dental chip blower.  
Group 2 (Tooth Mousse Plus, GC, Tokyo, Japan) and group 3 (Tooth Mousse, GC, Tokyo, Japan) were then given a desensitizing agent. As per the manufacturer's instructions, a desensitizing agent was applied to the enamel surface of each sample with a microbrush for three minutes before being rinsed with distilled water and dried with a dental chip blower.  
A total of 27 ceramic upper premolar brackets (20/40\({}^{\mathrm{TM}}\), American Orthodontics, Washington Ave, Sheboygan, WI, USA) with a surface area of 10.84 mm\({}^{2}\) were utilized in this study. The enamel's surface was etched with 37% phosphoric acid for 20 s (Hexa Etch, Bogor, Indonesia). A TransbondTM XT-bonding (3 M, Minnesota, USA) (TransbondTM XT) was applied to the bracket base, which was then placed on the labial enamel surface and firmly pressed into place to expel excess adhesive. The excess adhesive was removed, and a 10 s light cure was applied to all surfaces using a quartz tungsten halogen light-curing unit (Woodpecker, Guilin, China) with a light intensity of 450 mW/cm\({}^{2}\). Before the subsequent procedure, all specimens were stored for 24 h in a saline solution.