forty teeth diagnosed with white spot lesions in children aged between 10-14 years old were selected to compare between the effect of using nanohydroxyapatite paste applicatio either alone or preceded by the application of HCl (hydrochloric acid) or microabrasion

This study was designed as a randomized controlled double blinded clinical trial in which forty teeth clinically diagnosed with white spot lesions collected from children of both sexes with age range between 10-14 years old was selected from the outpatient clinics of the National Research Centre.

Ethical approval was obtained from the Medical Research Ethics Committee, National Research Centre with number 0343 Written informed consent was taken from the legal guardian of each participating child willing to participate in the trial, prior to the start of the clinical procedure after explaining the whole procedure in a simple way. The consent form was written in Arabic. verbal approval was taken from the child . Parallel allocation design was adopted for the intervention and control arms with allocation ration 1: 1 (i.e. 10 cases each).

The sample size was calculated considering the previously published studies with 80% power in detecting the true statistical significance among the four groups.

The inclusion criteria dictated that the patients should be in the age range of 10 to 14 years, presenting at least 1 White spot lesion on the labial surface of one or more permanent upper or lower anterior teeth.

The exclusion criteria involved patients who had hypoplastic enamel and those with dentine caries, patients who had systemic diseases and also uncooperative patients.

. All children involved in this study was instructed to brush their teeth under the supervision of the researcher before the application of the studied agent.

The buccal surfaces of the study-group teeth was cleaned with water slurry of pumice and rubber prophy cups. After cleaning and drying with a cotton roll, the application of the agent was done for 5 minutes using an applicator tip. After each application, children was instructed not to eat or drink for 1 hour

The same process was repeated in three separated visits in periods of one week, two weeks and six weeks on teeth in each of study and control group.

Grouping of samples:

Group 1: No treatment was applied (negative control). Group 2: Nano hydroxyapatite paste (Apagard primo toothpaste) was applied for 5 minutes.

Group 3: Pretreatment with 2% HCL for 20 sec then nano hydroxyapatite paste (Apagard primo toothpaste) was applied for 5 minutes.

Group 4: Pretreatment with microabrasion with oplasture for 60 sec then nano hydroxyapatite paste (Apagard primo toothpaste) was applied for 5 minutes.

Assessment:

A) Assessment of color change:

Color change of white spot lesions was assessed; before treatment, immediately after treatment, 2 weeks and 6 weeks after the onset of treatment on each tooth in each of study groups and control group using Vita easy shade device.

Prior each measurement, the device was calibrated according to the manufacturer's instructions.

B) Remineralization assessment:

Remineralization assessment was done using Laser fluorescence device "DIAGNOdent® (KaVo)".

All the teeth of the patients included in the study was examined using DIAGNOdent® (KaVo) as recommended by the manufacturer to assess the remineralization process.

All the measurements was performed using the Type B tip, which are designed for flat surfaces like the buccal one. Prior to each measurement, the device was calibrated using a ceramic standard according to the manufacturer's instructions.

The mineralization of the lesion was measured using DIAGNOdent laser fluorescence device before the application and another reading was recorded after 10 min of application. Other recordings was taken at one week, two weeks and six weeks on teeth in each of study and control group

Inclusion criteria:

• age range of children is 10 to 14 years
• presence of at least 1 White spot lesion on the labial surface of one or more permanent upper or lower anterior teeth.

Exclusion criteria:

• hypoplastic enamel
• dentine caries,
• patients with systemic diseases
• uncooperative patient

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Blinding was done to the outcomes assessor and the child and care provider. the outcome assessor has assessed the outcome of each treatment without knowing the type of treatment done. the child was blinded as he was not aware of the type of treatment applied to him. The care provider was blind and he was not allowed to accompany the child during treatment application