RESUMO
OBJECTIVES: Dental resins filled with hydroxyapatite (HAp) nanoparticles have significantly revolutionized restorative dentistry offering advantages such as remineralization potential and increase of polymerization. However, these materials have limited radiopacity hindering the diagnosis of secondary caries. The present study investigated the development of a new radiopaque dental adhesive by incorporating novel pure strontium hydroxyapatite nanoparticles [Sr10(PO4)6(OH)2, SrHAp] synthesized by a simple hydrothermal method. METHODS: Strontium phosphates were prepared using co-precipitation (SrHAp0h) and hydrothermal treatment for 2 and 5h (SrHAp2h and SrHAp5h). The crystallinity, crystallite size, textural and morphology features of the nanoparticles were characterized by XRD, FT-IR, micro-Raman and TEM. Strontium hydroxyapatite (SrHAp) or calcium hydroxyapatite (HAp) nanoparticles were then incorporated (10â¯wt%) into an adhesive resin of a commercial three-step etch-and-rinse adhesive to evaluate the radiopacity of disk-shaped specimens, degree of conversion (DC) assessed by FT-IR and mechanical properties by three-point bending test. The unfilled adhesive was used as negative control. RESULTS: While SrHAp0h and SrHAp2h resulted a phase mixing, the pure and highly crystalline phase of strontium hydroxyapatite free of calcium was obtained with 5h hydrothermal treatment (SrHAp5h). The TEM images revealed nanorods morphology for SrHAp5h. SrHAps incorporated into adhesive showed higher radiopacity, no alteration on DC despite slightly reducing the mechanical properties. SIGNIFICANCE: Although the mechanical properties are slightly impaired, incorporation of SrHAp nanoparticles offers potential method to improve radiopacity of restorative dental resins, easing the tracking of actual remineralization effects and enabling diagnosis of recurrent caries.
Assuntos
Cimentos Dentários/química , Hidroxiapatitas/química , Fenômenos Mecânicos , Nanoestruturas/química , Estrôncio/química , Precipitação Química , Testes MecânicosRESUMO
OBJECTIVES: Enamel resin infiltrants are biomaterials able to treat enamel caries at early stages. Nevertheless, they cannot prevent further demineralization of mineral-depleted enamel. Therefore, the aim of this work was to synthesize and incorporate specific hydroxyapatite nanoparticles (HAps) into the resin infiltrant to overcome this issue. METHODS: HAps were prepared using a hydrothermal method (0h, 2h and 5h). The crystallinity, crystallite size and morphology of the nanoparticles were characterized through XRD, FT-IR and TEM. HAps were then incorporated (10wt%) into a light-curing co-monomer resin blend (control) to create different resin-based enamel infiltrants (HAp-0h, HAp-2h and HAp-5h), whose degree of conversion (DC) was assessed by FT-IR. Enamel caries lesions were first artificially created in extracted human molars and infiltrated using the tested resin infiltrants. Specimens were submitted to pH-cycling to simulate recurrent caries. Knoop microhardness of resin-infiltrated underlying and surrounding enamel was analyzed before and after pH challenge. RESULTS: Whilst HAp-0h resulted amorphous, HAp-2h and HAp-5h presented nanorod morphology and higher crystallinity. Resin infiltration doped with HAp-2h and HAp-5h caused higher enamel resistance against demineralization compared to control HAp-free and HAp-0h infiltration. The inclusion of more crystalline HAp nanorods (HAp-2h and HAp-5h) increased significantly (p<0.05) the DC. SIGNIFICANCE: Incorporation of more crystalline HAp nanorods into enamel resin infiltrants may be a feasible method to improve the overall performance in the prevention of recurrent demineralization (e.g. caries lesion) in resin-infiltrated enamel.