Adhesion of Hydroxyapatite Nanoparticles to Dental Materials under Oral Conditions

Hydroxyapatite nanoparticles (nano-HAP) are receiving considerable attention for dental applications, and their adhesion toenamel is well established. However, there are no reports concerning the effects of HAP on other dental materials, and most ofthe studies in thisfield are based onin vitrodesigns, neglecting the salivary pellicle-apatite interactions. Thus, thisin situpilotstudy aims to evaluate the effects of three hydroxyapatite-based solutions and their interactions with different dental materialsurfaces under oral conditions. Hence, two volunteers carried intraoral splints with mounted samples from enamel and fromthree dental materials: titanium, ceramics, and polymethyl-methacrylate (PMMA). Three HAP watery solutions (5%) wereprepared with different shapes and sizes of nano-HAP (HAP I, HAP II, HAP III). After 3 min of pellicle formation, 10 ml rinsewas performed during 30 sec. Rinsing with water served as control. Samples were accessed immediately after rinsing, 30 min and2 h after rinsing. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterizethe particles, and SEM evaluated the pellicle-HAP interactions. SEM and TEM results showed a high variation in the size rangeof the particles applied. A heterogeneous HAP layer was present after 2 h on enamel, titanium, ceramics, and PMMA surfacesunder oral conditions. Bridge-like structures were visible between the nano-HAP and the pellicle formed on enamel, titanium,and PMMA surfaces. In conclusion, nano-HAP can adhere not only to enamel but also to artificial dental surfaces under oralconditions. The experiment showed that the acquired pellicle act as a bridge between the nano-HAP and the materials’surface