Preparation Of Nano-micro Structured Hydroxyapatite For Dental Restorative Composite Resin

Dental resin-based composites have been used for more than 50 years.The size and the structure of inorganic filler have a great effect on the mechanical properties of the composite resin.Hydroxyapatite is a commonly used inorganic filler that exhibits high biological activity and reduces the occurrence of secondary caries.Larger particles(microparticles)can allow higher filling amount,and then produce superior mechanical properties,whereas difficult to polish and impossible to retain surface smoothness.Smaller particles(nanoparticles)can be more effectively polished,and exhibit higher wear resistance.However,nanoparticles have a large surface area and tend to severe agglomeration owing to the nanosize effect.This will result in less filler loading,a significant increase in viscosity,and the corresponding reduced mechanical propertie.Therefore,a kind of novel micro-sized clusters of hydroxyapatite nanorods(MCHN)was thus designed,which was fabricated by spray drying nano-hydroxyapatite.The effects of various factors on MCHN preparation and the mechanical properties of dental restoration composite resin and in vitro activity were investigated.Further,an antibacterial dental restoration composite resin was obtained based on Ag-HN nanoparticles,which were prepared by high-gravity reactive crystallization combined with hydrothermal process.The main contents were as follows:(1)A novel micro-sized MCHN were prepared by spray drying combined with heat treatment.The effects of the aspect ratio of primary hydroxyapatite nanorods(HN),suspension solid content,feed temperature,nozzle gas velocity,calcination temperature on the preparation of MCHN were investigated.The optimal process conditions were as follows:The solid content of the suspension was 2%,the feed temperature was 120?,the gas velocity of the nozzle was 473 L/h,the aspect ratio of the primary nanorod was 2,and the heat treatment temperature was 500?.With the optimal conditions,high-performance MCHN(MCHN-2)were prepared,and the particle size distribution was 1-4 ?m.As the feed rate increased,the particle size of the obtained MCHN becomed smaller and the distribution becomed narrower.With the increase of the primary HN aspect ratio,the particle size of the obtained MCHN gradually increased,the surface was rough,and the morphology becomed irregular.(2)The obtained MCHN was further modified by y-MPS and used as a filler in the oral resin.The effects of modifier dosage,HN aspect ratio,filling amount,heat treatment temperature and SiO2/MCHN-2 with different mass fraction on the mechanical properties of the composite resin were investigated.The results indicated that y-MPS was successfully grafted onto the surface of MCHN.The grafting rate was 4.25%.The obtained flexural modulus increased as the filling amount of MCHN-2 increased(0 wt%-60 wt%),and the flexural strength and compressive strength first increased and then decreased.When the filling amount of the inorganic filler was 50 wt%,the amount of the modifier was 10 wt%,the heat treatment temperature was 500?,and the aspect ratio of the primary HN nanorods was 2,the mechanical properties of the composite resin was superior,and the flexural strength reached 119.5 MPa,flexural modulus reached 5760.6 MPa and the compressive strength reached 414.9 MPa.Compared with the composite resin filled with HN-2,the improvements were 36.3%,11.4%and 56.6%,respectively,and the filling amount was also increased by 10 wt%.Compared with only MCHN-2(60 wt%),when the mass fraction of MCHN-2/SiO2 was 2:4,the flexural strength,compressive strength and flexural modulus were increased by 27.3%,17.5%and 10.3%,respectively.In vitro activity test and EDS analysis showed that hydroxyapatite had strong remineralization function and showed superior biological activity,while the composite resin containing only silica nanoparticles had weak remineralization function.(3)Hydroxyapatite loaded with different mass fractions(0-2 wt%)of silver ions(Ag-HN)was prepared by high gravity technology combined with hydrothermal method.Further,they were filled into the oral resin with a ratio of 50 wt%to obtain an antibacterial dental restoration composite resin.The results indicated that the silver ion loading had almost no effect on the morphology and size of HN.With the increase of silver ion loading(0 wt%-2 wt%),the mechanical properties of the composite resin gradually decreased The antibacterial property was tested by solid agar disk diffusion method.By measuring the size of the inhibition zone,pure hydroxyapatite had almost no antibacterial property.With the increase of silver ion loading(0 wt%-2 wt%),the inhibition zone became more and more obvious,indicating that the antibacterial effect of the resin tablets gradually increased with the increase of the release amount of silver ions.Based on the mechanical properties and antibacterial properties of the integrated dental composite resin,the optimal loading of silver ions was 1.5 wt%.As the time of the soaking resin sheet in PBS buffer increased(0 d-10 d),the diameter of the zone of inhibition was reduced from 11.86 mm to 11.55 mm.