A common cause of failure of resin-bonded-composite (RBC) dental restorations is recurrent caries, due to bacterial ingress and demineralisation between tooth walls and RBC. RBC systems with potential re-mineralising ability and sufficient flexural strength could address this problem. Nano hydroxyapatite (nHAP) is a candidate filler phase and source of Ca2+ and PO43- ions but used singly may have insufficient properties. Glass Flake (GF) particles may be a suitable adjunct filler system. The aim was to formulate and study RBC systems with systematically varied GF:nHAP ratios and a total (constant) filler mass-fraction of 50 % in a 50:50 w/w Bis-GMA:TEGDMA photo-polymerised matrix. Eight novel RBC formulations were evaluated. Handling properties (packing and stickiness forces) of unset RBC pastes were evaluated by an instrumented probe method at 23 ÃÂ°C, then light transmission through 4 x2 mm thick disks was measured throughout 20-s photo-cure. Degree of conversion (DC%) of C=C bonds was determined by FTIR spectroscopy at different periods during 24-h post-irradiation. Polymerisation-shrinkage kinetics at 23 ÃÂ°C were measured from 0-60 min via a bonded-disk instrument. Top and bottom surface-hardness (VHN) of the cured RBC disks was measured after incubating for 24-h at 37 ÃÂ°C. Flexural strength and elastic moduli of rectangular specimens (25x2x2 mm) were obtained via 3-point bending after 24-h storage at 23 ÃÂ°C. Microstructures of fractured specimens were imaged via scanning electron microscopy (SEM). Sorption, solubility and mass changes of cured RBC disks (15 x2 mm thick) were measured continuously for 16-w during immersion in simulated oral environments of: (i) water and (ii) 3:1 ethanol:water at 37 ÃÂ°C. In parallel, their hygroscopic expansion during sorption/desorption was measured via a laser-scan micrometer (LSM). Ca2+ and PO43- ion release from same-sized disks were measured after immersion at 37 ÃÂ°C in either tris-buffer at pH 7.35 or phthalate buffer at pH 4.0, using ICP-AES for Ca2+ and ion chromatography for PO43-. All data were analysed using one-way ANOVA, and the Tukey HSD post-hoc test. The results obtained show the remineralisation potential of some of these GF:nHAP resin-composite systems as candidate restorative materials, particularly for the lower region in a two-step cavity restorative procedure. Ca2+ and PO43- release was determined mainly from the nHAP proportion while strength properties were dependent upon the GF proportion, thereby demanding selection of suitably chosen proportions of the dual filler system.
|Date of Award||1 Aug 2019|
- The University of Manchester
|Supervisor||David Watts (Supervisor), Joanne Cunliffe (Supervisor) & Xiaohui Chen (Supervisor)|