five percent sodium fluoride varnish (Charm varnish -Dentkist- Korea).

I. Nano-eggshell powder preparation: After cleaning, A small crack will be made in each eggshell to split it into two halves to evacuate the content. The eggshells will be disinfected in a hot water at 100°C for 10 minutes to facilitate the detachment of the inner membrane. They will be exposed to steam sterilization. Then they will be crushed using a sterile mortar and pestle. The crushed particles will be milled using a zirconia ball-milling machine at 200 rpm . This will result in a nano-sized eggshell powder to incorporate them into a gel form.

II. Preparation of eggshell hydrogel formulations: through dispersing a suitable concentration of egg shell powder in distilled water, followed by dissolving the gelling agent; sodium carboxymethyl cellulose at a concentration of 5-10% under continuous stirring. The formed hydrogel will be kept at 8°C for a period of 24 hours before further use. This will produce a paste of consistency that is appropriate for handling and application.

change in minerals content of the lesion , will be assessed using diagnodent scores ( minimum value is 0 and maximum value is 99 ) higher scores means worse outcome .

whether the lesion is active or in active , will be assessed using Nyvad's criteria ( minimum value is score 0 and maximum value is score 9) higher scores means worse outcome .