Abstract
The study aim was to develop light-curable, high strength dental composites that would release calcium phosphate and chlorhexidine (CHX) but additionally promote surface hydroxyapatite/CHX co-precipitation in simulated body fluid (SBF). 80 wt.% urethane dimethacrylate based liquid was mixed with glass fillers containing 10 wt.% CHX and 0, 10, 20 or 40 wt.% reactive mono- and tricalcium phosphate (CaP). Surface hydroxyapatite layer thickness/coverage from SEM images, Ca/Si ratio from EDX and hydroxyapatite Raman peak intensities were all proportional to both time in SBF and CaP wt.% in the filler. Hydroxyapatite was, however, difficult to detect by XRD until 4 weeks. XRD peak width and SEM images suggested this was due to the very small size (~10 nm) of the hydroxyapatite crystallites. Precipitate mass at 12 weeks was 22 wt.% of the sample CaP total mass irrespective of CaP wt.% and up to 7 wt.% of the specimen. Early diffusion controlled CHX release, assessed by UV spectrometry, was proportional to CaP and twice as fast in water compared with SBF. After 1 week, CHX continued to diffuse into water but in SBF, became entrapped within the precipitating hydroxyapatite layer. At 12 weeks CHX formed 5 to 15% of the HA layer with 10 to 40 wt.% CaP respectively. Despite linear decline of strength and modulus in 4 weeks from 160 to 101 MPa and 4 to 2.4 GPa, respectively, upon raising CaP content, all values were still within the range expected for commercial composites. The high strength, hydroxyapatite precipitation and surface antibacterial accumulation should reduce tooth restoration failure due to fracture, aid demineralised dentine repair and prevent subsurface carious disease respectively.
Highlights
Dental composites have been used for over 50 years as restorative materials [1]
The aim of this study was to develop methods that provide a quantitative assessment of any hydroxyapatite layer on the surfaces of systematically varying new MCPM, β-TCP and CHX-containing light curable composites
From scanning electron microscopy (SEM) it was noticeable that the percentage of the surface covered by HA and the average size of the HA spheres increased with raised CaP content in the samples or time in simulated body fluid (SBF)
Summary
Dental composites have been used for over 50 years as restorative materials [1]. Compared to dental amalgam, they trigger less safety concerns and provide improved aesthetics. Polymerisation shrinkage and lack of anti-bacterial activity, are continuing issues as they enable micro-gap formation between the tooth and restoration followed by bacterial microleakage. These bacteria can cause continuing disease and de-mineralisation of dentine underneath a restoration. Subsequent action by matrix metalloproteinases (MMPs) degrades the demineralised dentinal collagen further widening the micro-gap. Recurrent caries is the major reason for the shorter median survival lifespan (5–6 year) of composites in comparison with more antibacterial dental amalgam (13 years) [1,2,3,4]. Dental composites are typically composed of four major components: an organic polymer matrix
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