Development of Experimental Dental Resin Composites with Potential Bioactivity

Abstract

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 °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 °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 °C. Flexural strength and elastic moduli of rectangular specimens (25x2x2 mm) were obtained via 3-point bending after 24-h storage at 23 °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 °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 °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
Original language	English
Awarding Institution	The University of Manchester
Supervisor	David Watts (Supervisor), Joanne Cunliffe (Supervisor) & Xiaohui Chen (Supervisor)