The study aims to investigate the effectiveness of a new treatment for demineralized white spot lesions (WSLs) after fixed appliance therapy. The trial will consist of four parallel groups: control, Fluoride Varnish (FV), Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP), and Resin Infiltration (RI) groups. Patients will be recruited from Riyadh Elm University's electronic record system and contacted by phone. They will be given an appointment to visit the dental clinic.

A total of 22 patients with WSLs will be selected for the study. Two examiners will perform dental examinations using a dental mirror and a ball-ended probe to code the WSL against the ICDAS system. The level of agreement between the two examiners will be assessed using reliability analysis, with an agreement level of above 80% considered.

Buccal WSLs will be defined as those that extend from the center of the buccal to either the mesial or distal surface. WSLs coded 3 or higher will be excluded from further examination and treated accordingly.

Trial design The study will be conducted as a prospective clinical controlled trial with an experimental design, consisting of four parallel groups. Individuals who experienced the development of demineralized white spot lesions after undergoing fixed appliance therapy will be invited to participate in the study and will be assigned to one of the following groups: control group, Fluoride Varnish (FV) group, Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) group, or Resin Infiltration (RI) group.

Participants Patients will be recruited by navigating the electronic record system of Riyadh Elm University from 2023 files backward up to 2022, identifying patients who completed orthodontic treatment reaching up to the required sample size. Those patients will be contacted by phone call from the dental clinic of Riyadh Elm University official number, inviting them to participate in the current study. Patients will be given an appointment to visit the dental clinic at specific time. Before enrollment, every patient or parent/legal guardian of a patient younger than 18 years of age will receive an informational letter and verbal communication about the objectives and protocol of the study. All enrolled patients and/or their parents or legal guardians will be asked to provide a written informed consent following their initial approval. All patients who got treatment in Riyadh Elm University signed consents to share their information for research purposes will be enrolled in the study.

Calibration exercise A total of 22 patients with WSLs attending dental clinics of REU will be selected and two examiners will perform dental examinations using a dental mirror and a ball-ended probe on wet and dry debris-free teeth to code the WSL against the ICDAS system. Whenever in doubt regarding the coding of the WSLs, the third expert examiner decision will be considered final. The level of agreement with regard to the ICDAS codes between the two examiners will be assessed using reliability analysis and the agreement level of above 80% will be considered.

Two examiners will perform dental examinations using a dental mirror and a ball-ended probe on wet and dry debris-free teeth. Each WSL will be identified by visual inspection of mesiobuccal, buccal, or distobuccal tooth surfaces and recorded. An ICDAS code will be assigned to each WSL. A digital photograph will be taken by keeping 45 cm distance between subject and camera. The digital image of WS can be captured with a digital camera (Canon EOS 2000D (NIS) DSLR Camera 18 - 55 mm NIS Lens) held almost perpendicular to the buccal surface. Light is supplied by a flash mounted around lens. The camera system setup was adjusted as follows; the quality of image is Fine, ISO is 200, and white balance is speed light mode. Moreover, dental status of the participants also recorded.

Buccal WSLs will be defined as those that extend from the center of the buccal to either the mesial surface or the distal surface. WSLs that will be coded 3 (denoted by localized enamel breakdown caused by caries without the presence of dentin and underlying shadow), or higher (denoted by the presence of underlying dark shadow caused by dentin, whether enamel-depleting or not, to a large distinct cavity containing visible dentin), in accordance with ICDAS reference, are excluded from further examination and will be appropriately treated.

Following the determination of the 0 LF value for each tooth on a healthy surface, the maximum LF value for each WSL coded tooth (either 1 or 2) will be determined using a DIAGNODent flat tip (KaVo dental, GmbH, Biberach, Germany). Measurements will be done according to the manufacturer's instructions. Each tooth will be dried for 5 seconds, and the tip will be pointed in the opposite direction from the examination area. The measurement will be done using the DIAGNOdent Scale; values 0±13: no caries, values 14±20: enamel caries and values >20: dentinal caries. (Lussi et al., 2001).

Eligibility criteria for participants Inclusion criteria

1. Post orthodontic patients with one WSLs on buccal surface of tooth with ICDAS Code 1 or 2.
2. Agreeing to participate in the study by singing the study informed consent.
3. For younger patients parents agree to provide consent for child participation in the study.

Exclusion criteria

1. Developmental defects of dental hard tissue
2. Patients who have systemic disease or under medications that usually cause an increased risk of oral caries.
3. Patients who are allergic to Fluoride varnish, CPP-ACP and resin infiltration. Study settings Data will be collected from orthodontic clinics of Namouthajya and Muneseya hospitals at Riyadh Elm University, Riyadh, Saudi Arabia.

Intervention In group I (Control group): FV EnamelastTM (a flavored xylitol-sweetened, 5% sodium fluoride in a resin carrier delivered in a 1.2 ml syringe or in a 0.4 ml unit, Ultradent, USA) will be applied on all teeth according to the manufacturer's instructions: compressed air and cotton rolls will be used to dry the teeth. A mini brush will be used to apply varnish to all teeth surfaces. The varnish will be left to dry for one minute. Patients should avoid eating, drinking, or brushing for a period of 3-4 hours following the application of varnish. In the test groups (group II): Intensive FV will be applied three times a week for a week (every two days). For group III: (CPP-ACP), Tooth Mousse® (MI Paste®) (GC Corporation, Tokyo, Japan) for 12 weeks. A thin layer from Tooth Mousse™ will be applied to the teeth after daily brushing with traditional toothpaste and left intact for 180 seconds before rinsing with distilled water (Thierens et al., 2019). For group IV: ICON® (DMG, Hamburg, Germany) resin infiltration will be applied as specified by the manufacturer: the 15% hydrochloric acid (HCL) solution will be sprayed for 2 minutes, followed by rinsing with water for 30 seconds and drying. Application of ICON-Dry (Ethanol) for 30 seconds, followed by air drying. Subsequently, ICON-Infiltration will be applied to the tooth surface and left for 3 minutes. The excess resin will be removed using a cotton roll, followed by a light curing process lasting for 40 seconds. Finally, the enamel surface that has been roughened will be polished with composite resin polish discs and polish cups.

Inclusion Criteria:

1. Post orthodontic patients with one WSLs on buccal surface of tooth with ICDAS Code 1 or 2.
2. Agreeing to participate in the study by singing the study informed consent.
3. For younger patients parents agree to provide consent for child participation in the study.

Exclusion Criteria:

1. Developmental defects of dental hard tissue
2. Patients who have systemic disease or under medications that usually cause an increased risk of oral caries.
3. Patients who are allergic to Fluoride varnish, CPP-ACP and resin infiltration.

A web based research randomizer software will be used to generate a random sequence number to allocate the participants to different groups. The allocation will be kept concealed from patients and examiners using sequentially numbered identical containers containing experimental materials (remineralizing agents) to ensure the double blindness of the study.