Pits and fissures have been considered as the single most important feature leading to the development of occlusal caries; About 90 % of carious lesions are found in the pits and fissures of permanent posterior teeth .Several materials and techniques have been developed to enhance the longevity of pit-and-fissure sealants, including the use of flowable composite resins as pit-and-fissure sealants

Pits and fissures have been considered as the single most important feature leading to the development of occlusal caries; About 90 % of carious lesions are found in the pits and fissures of permanent posterior teeth . The complex morphology of occlusal pits and fissures makes them an ideal site for retention of bacteria and food remnants, rendering the performance of proper hygiene difficult or even impossible .

Several materials and techniques have been developed to enhance the longevity of pit-and-fissure sealants, including the use of flowable composite resins as pit-and-fissure sealants . However, the clinical longevity of flowable composite as fissure sealants is directly related to their retention, where the percentage of rate of retention differ on a 12-month follow-up examination were the partial loss rate of flowable composite material ranges from 15.5% to 16.5% and total loss were ranged from 12.7% to 13%, while on a 24-month follow-up examination the partial loss rate ranged from 18.1% to 20% and total loss rate ranged from 15.6% to 17%, and that depends on morphology of pits and fissures, adequate isolation, conditioning of enamel, application techniques, particular material characteristics like viscosity, surface tension, adequate adhesion and penetration of the material into the previously etched system of fissures.

In order to overcome the shortcomings of traditional dental composites, nanofibers or nanotubes fillers are broadly used in the academia and industry. The type of Nanofibers and Nanotubes used to reinforce dental resin composites include polymeric nanofibers, metallic nanofibers, and inorganic hydroxyapatide (HAP) nanofibers. The Hydroxyapatite Nanofibers are calcium phosphates fillers that allow the release of mineral from dental resin composite. Also HAP nanofibers possessing sufficiently high slenderness ratios and relatively long and thin structure, and create a lot of bonding points in the interface with polymeric matrix. When the composites suffer from huge pressure this allow tremendous stress transfer from weak polymeric matrix to tough HAP nanofibers; and consequently increase the mechanical properties of resin composite. So this study will examine the effect of adding HAP nanofibers on the clinical performances and retention rate of flowable resin composite.

Inclusion Criteria:

Patients should be over 18 Years old. Patient should have good oral hygiene and general health. Patient with at least 2 non-cavitated initial occlusal carious lesion in first and/or second molar teeth in each quadrant of maxilla or mandible.

Exclusion Criteria:

Known allergy to any of the resins used. Clinically detectable cavitated carious lesion. Previously placed sealants or restorations. Bruxism or malocclusion.

The primary assessors will not be blind to intervention/control material due to different in material shade. However, the other assessors will be blind from the type of material they will evaluate the retention rate of the restoration; it will not be allowed amongst the assessor to exchange any information throughout the entire study period.