Bioactive glass to prevent post-operative sensitivity of vital teeth bleaching

INTERVENTION: The participants will be instructed to apply 20% carbamide peroxide bleaching agent (7 days—04 h each) (Opalescence® PF™, Ultradent Products Inc. USA—20% carbamide peroxide) , delivered by the bleaching custom tray. followed by the application of tooth paste containing Bioactive glass 45S5 (Sensodyne Repair & Protect contains NovaMin® technology) delivered by the bleaching custom tray (7 days—30 min each). The bleaching agent and 45S5 toothpaste will be delivered individually by the participants themselves at their home by the bleaching custom tray. For monitor adherence to the intervention , the researcher will check the bleaching agent and toothpaste containers after 7 days of commencement of intervention to make sure that they are empty. CONDITION: Oral and Gastrointestinal ‐ Other diseases of the mouth, teeth, oesophagus, digestive system including liver and colon Teeth sensitivity;Teeth color changes after bleaching; ; Teeth sensitivity ; Teeth color changes after bleaching PRIMARY OUTCOME: Tooth sensitivity using visual analogue scale.[Follow‐up will be daily for 7 days after application of both the bleaching agent and the Bioactive/placebo toothpaste. The primary outcome will be assessed by the patients themselves using visual analogue scale in the first day of commencement of intervention."] SECONDARY OUTCOME: Color changes using digital spectrophotometer. ; The digital spectrophotometer measures the shade of teeth based on the CIE L*a*b* color space system, allowing the determination of color in a three dimensional space [ Baseline: before the beginning of the intervention. ; Follow‐up will be after 3 days , 1 week ,15 days, 1 month, 3 months and 6 months after intervention commencement of both the bleaching agent and the Bioactive/placebo toothpaste] INCLUSION CRITERIA: 1‐be at least 18 years old, 2‐Have six maxillary anterior teeth with no restorations or carious lesions on their buccal surfaces, 3‐colour shade B2 or darker on the shade guide (Vitapan Classical, Vita Zahnfabrik) 4‐No history of tooth sensitivity or use of a desensitising agent or desensitising toothpaste in the past 3 months.