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.