Hydroxyapatite nanoparticles (nano-HAP) are receiving considerable attention for dental applications, and their adhesion to enamel is well established. However, there are no reports concerning the effects of HAP on other dental materials, and most of the studies in this field are based on in vitro designs, neglecting the salivary pellicle-apatite interactions. Thus, this in situ pilot study aims to evaluate the effects of three hydroxyapatite-based solutions and their interactions with different dental material surfaces under oral conditions. Hence, two volunteers carried intraoral splints with mounted samples from enamel and from three dental materials: titanium, ceramics, and polymethyl-methacrylate (PMMA). Three HAP watery solutions (5%) were prepared with different shapes and sizes of nano-HAP (HAP I, HAP II, HAP III). After 3 min of pellicle formation, 10 ml rinse was performed during 30 sec. Rinsing with water served as control. Samples were accessed immediately after rinsing, 30 min and 2 h after rinsing. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the particles, and SEM evaluated the pellicle-HAP interactions. SEM and TEM results showed a high variation in the size range of the particles applied. A heterogeneous HAP layer was present after 2 h on enamel, titanium, ceramics, and PMMA surfaces under 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 oral conditions. The experiment showed that the acquired pellicle act as a bridge between the nano-HAP and the materials’ surface.

Synthetic hydroxyapatite-based solution is a bioinspired material that may present anti-adhesive properties, restraining the dental biofilm formation without causing adverse effects. This in situ study aims to evaluate the effects of three different hydroxyapatite (HAP) watery solutions as a mouthwash against biofilm adhesion on different dental material surfaces under oral conditions. Hence, four volunteers carried maxillary splints containing enamel, titanium, ceramics, and polymethyl-methacrylate resin (PMMA) samples. Three HAP watery solutions (5%) were prepared with HAP particles presenting different shapes and sizes (HAP I, HAP II, HAP III). During 24 h, the volunteers rinsed two times with one of the following selected tested solution: HAP I, HAP II, HAP III, water, or chlorhexidine 0.2% (CHX). The first rinse was performed 3 min after pellicle formation; the second rinse occurred after a 12 h interval. The surface analysis was performed by scanning electron microscopy (SEM), fluorescence microscopy (FM), and transmission electron microscopy (TEM). Statistical and microscopic analysis showed that most samples treated with any HAP solution revealed reduced biofilm coverage presenting comparable results to CHX treated samples, however without altering the microorganisms’ viability. In conclusion, the results of this investigation showed that a pure hydroxyapatite-based mouthrinse could be a promising bioinspired adjunct solution for biofilm management.

Oral biofilms play an essential role on peri-implant disease development. Synthetic hydroxyapatite nanoparticles (nHAP) are a bioinspired material that has structural and functional similarities to dental enamel apatite and may provide preventive properties against biofilm formation. This study aimed to investigate the effects of an experimental nHAP solution on biofilm formation on polished and non-polished titanium under oral conditions. Five volunteers carried maxillary splints with non-polished and polished titanium and followed a 48 h rinsing protocol with the proposed nHAP solution, and with chlorhexidine 0.2% (CHX) and water, as controls. Samples were analyzed by fluorescence microscopy (FM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FM showed a significant reduction of biofilms on polished samples treated with nHAP (p = 0.0485) compared with water, without differences between nHAP and CHX (p > 0.9999). Analyzing biofilm viability, polished samples rinsed with nHAP showed significantly fewer dead bacteria than CHX (p = 0.0079), but there was no significant difference in viability between polished samples rinsed with water and nHAP (p = 0.9268). A significantly higher biofilm coverage was observed on the non-polished surfaces compared to the polished surfaces when nHAP was applied (p = 0.0317). This difference between polished and non-polished surfaces was not significant when water (p = 0.1587) or CHX (p = 0.3413) rinsing were applied. SEM and TEM analysis supported the FM findings, that polished samples rinsed with nHAP presented fewer biofilm coverage compared to samples rinsed with water. In conclusion, the nHAP solution reduced the biofilm formation on polished Ti surfaces without altering bacterial viability, providing a novel approach for the management of biofilm formation on biomaterials.