Aljabo, AFH; (2015) Development of anti-bacterial, re-mineralising and selfadhesive dental composites. Doctoral thesis , UCL (University College London).

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Abstract

The project aim was characterisation of antibacterial releasing, remineralising and self-adhesive novel dental composites. Commercially available bulk filling and flowable composites were tested in order to provide benchmark properties for successful dental composite materials. 20 wt. % of light curable urethane dimethacrylate based liquid was mixed with 80 wt. % glass filler containing 10 wt. % CHX and 0 - 40 wt. % CaP. Conversion versus depth with 20 or 40 s light exposure was assessed by FTIR. Solidification depth and polymerisation shrinkage were determined using ISO 4049 and 17304 respectively. Subsequent volume expansion and biaxial flexural strength and modulus change upon water or simulated body fluid (SBF) immersion were determined over 4 and 6 weeks respectively. Precipitation of hydroxyapatite on the surfaces of light cured discs after storage in water versus SBF was assessed weekly up to 4 weeks using SEM with EDX, Raman and XRD. Mass of precipitate that could be scraped from the surfaces was determined gravimetrically after 12 weeks. CHX release into solution or associated with the hydroxyapatite layer over 12 weeks was determined using UV spectrometry. Biaxial flexural strength and modulus were determined after 1 month immersion in SBF. The shear bond strength between experimental formulations and Ivory dentine etched with phosphoric acid was assessed. Separate adhesive agent ‘iBond’ was applied to dentine and the shear strength was compared with that when experimental composite was attached directly to the dentine without iBond use. Conversion decreased linearly with both depth and CaP content. Shrinkage was ~3% for experimental materials. Early water sorption increased linearly, whilst strength and modulus decreased exponentially to final values when plotted versus square root of time. Maximum volumetric expansion increased linearly with CaP rise and balanced shrinkage at 10-20 wt. % CaP. Experimental composites initial strength and modulus decreased linearly with increasing CaP. Hydroxyapatite layer thickness / coverage from SEM images, Ca/Si ratio from EDX and normalised 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. Early CHX release was proportional to the square root of time and to CaP level and twice as fast in water compared with SBF. After 1 week, CHX continued to be released into water. In SBF, however, any released CHX became entrapped within the precipitating hydroxyapatite layer. At 12 weeks HA entrapped CHX was proportional to the CaP filler wt. % and up to 14% of the total in the sample. CHX formed 5 to 15% of the HA layer with 10 to 40 wt. % CaP respectively. Shear bond strength has increased upon addition of CaP up to 20 wt. %. Formulations with 0 wt. % CaP and no adhesive monomer exhibited the lowest shear strength of ~ 3 MPa. Upon addition of 4Meta and still absence of CaP, the shear strength increased up to 13 MPa. Formulations with 20 wt. % CaP experienced the highest shear strength of ~ 25 MPa irrespective of the addition of adhesive monomers. 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.

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