## 2 Materials and Methods  
A double-blinded randomized controlled trial was conducted at the department of operative dentistry and endodontics, Altamash Institute of Dental Medicine, for 11 months from 1 January 2020 to 1 December 2020. The study was previously approved by the Ethics Committee (protocol number: (AIDM/ERC/12/2019/01). The Helsinki Declarations' ethical aspects were followed.  
The sample size was calculated using the WHO sample size calculator, considering a mean discomfort score of 1.13 \(\pm\) 1.08 of potassium nitrate and sodium monofluorophosphate, with a power of test 80. The confidence interval was set at 95% and 5% margin of error. The estimated sample size in each group was 67 participants [10].  
A simple random sampling technique was used for the recruitment of participants in this study. Patients of both genders and aged between 18 to 45 years who required in-office vital bleaching in teeth with normal pulp response and no history of previous tooth sensitivity were included. Smokers, pregnant or lactating mothers, root canal-treated anterior teeth, anterior teeth with gingival recession or dentin exposure, active root carious lesion, and patients with known allergy to milk protein \"casein\" were excluded.  
After obtaining informed consent, patients were randomly and equally divided into three groups by a certified dental hygiust using the lottery method: the CPP-ACP group (group 1), PNSMP group (group 2), and placebo gel group (group 3). To begin with, a cheek retractor was placed, and petroleum gel was applied on the exposed lip surface. Upper/lower anterior teeth including the first premolar were dried and isolated by a gingival barrier. After that, a thin layer of bleaching agent, 35% hydrogen peroxide (Fluorescent Express White, Vista Dental, USA) was applied on the labial surface of all isolated teeth, followed by light activation for 15 min. The procedure was performed 3 times for 8 min, as per manufacturer instructions. A certified dental hygiust was responsible for handing over the desensitizing or placebo gel in an unmarked (blinded) syringe to the patient with a written instruction to apply it immediately and every 12 h up to 36 h after the procedure.  
A questionnaire designed to obtain information on any incident of pain after bleaching treatment was given to the patients. Patients were thoroughly educated about the questionnaire and were asked to mark the intensity of pain five minutes after the application of gel on a discomfort interval scale (DIS) [12], which was explained to the patients, and instructions were given to mark the score from 0 to 4 according to the intensity of pain experienced, such as 0: no pain, 1: mild pain, 2: moderate pain, 3: severe pain, and 4: intolerable pain.  
Data were entered and analyzed using SPSS version 25. Mean and standard deviation was calculated for age and sensitivity score. Frequency and percentage were calculated for qualitative variables such as gender and efficacy. Efficacy of the desensitizing agent was compared in all groups by using an ANOVA test and post hoc Tukey's test. Pearson correlation was applied to find an association of desensitizing agents with age. An independent \(t\)-test was applied to find gender disparity in discomfort level, keeping \(p\leq 0.05\) as significant.