Investigation of Silver Enhanced Dental Restorative Materials by the Development of an In Vitro Oral Biofilm Model

Abstract

Generally, in vitro oral biofilm models are commonly used to help in ‎understanding the complex processes and the factors affecting oral diseases. They help ‎to accurately predict, in a controlled and simplified way, a clinical outcome which can ‎lead us to preventive actions for a disease (Salli and Ouwehand, 2015).‎The complexity of biofilm research requires different approaches to address ‎various questions. Furthermore, models cannot capture all of the details involved with ‎disease formation, however it is considered a way of performing a reproducible ‎experiment under controlled conditions. Obviously there are ethical limitations with in ‎vivo studies in relation to caries and periodontal diseases. Therefore, different in vitro ‎techniques have been developed and are continuously improved to better address the ‎study question, to help interpret the results and to obtain as much information as ‎possible with other than clinical testing (Salli and Ouwehand, 2015).‎This project aimed at developing a robust in vitro oral biofilm model to ‎determine the effectiveness of enhanced dental restorative materials using antimicrobial ‎additives. It is focused on the antibacterial and mechanical properties of novel silver ‎formulations that have been combined with glass ionomer cement. Three out of nine ‎bacterial species considered to be early colonisers (Streptococcus oralis, Streptococcus ‎mutans, & Neisseria subflava) were inoculated at 0.1 OD600 into wells containing ‎sterile glass-ionomer disks. The established artificial saliva media DMM (Defined ‎Medium Mucin) was used for 24-48Hrs studies, conducted under aerobic and anaerobic ‎conditions.‎Following incubation, the disks were washed with PBS (Phosphate Buffer ‎Saline) in a series of up to five, twelve minute steps. The bacterial community within the ‎well, loosely attached to the well surface and the disk, and finally the bacteria intimately ‎attached to the surface were determined using a viable count of Colony Forming Unit ‎Count (CFUs), a MTT metabolic assay and DNA quantification. Three silver solutions ‎were developed with different ionic concentrations, 5mg/ml, 10mg/ml and 13mg/ml. ‎The addition of polyvinyl alcohol to stabilise the 10mg/ml solution was investigated and ‎along with the MIC/MBC and the effect on the ability of three bacterial species to ‎survive and colonise glass ionomer disks was determined. In addition, compressive ‎strength, hardness and adhesive shear bond strength of each glass-ionomer silver disk ‎was assayed and compared with the base line glass-ionomer.‎The biofilm model favoured survival of S. oralis under aerobic conditions and N. ‎subflava and S. oralis under anaerobic conditions. Silver formulations proved to have ‎effects on both strength and antimicrobial activity. Specifically, 5mg/ml proved more ‎antibacterial than 10mg/ml silver. Compressive strength was enhanced for both ‎concentrations of additive, however bond strength became compromised at the higher ‎concentration.‎This model proved its efficiency to test the antibacterial activity of silver ‎enhanced glass ionomer cement in the presence of artificial saliva. Furthermore, addition ‎of 5mg/ml silver to the glass ionomer cement enhanced antibacterial activity and ‎physical properties significantly.‎

Date of Award	2018
Original language	English
Sponsors	University of Jordan
Supervisor	Mark Hector (Supervisor) & David Edwards (Supervisor)