Melbourne Dental School - Theses
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ItemEffect of exposure of glass ionomer cements to acid environments( 2016)This research focused on evaluating the effect of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) incorporated into a glass ionomer cement (GIC). Two conventional GIC materials were the main focus of the study, Fuji VII and Fuji VII EP (containing 3% w/w CPP-ACP), these materials were made into rectangular blocks and subjected to various acidic media (lactic, citric and hydrochloric acids), while daily observations of surface hardness, mass loss and ion release were carried out over a three day period. Acid storage solutions were specifically chosen to approximate conditions the materials would be exposed to in an oral environment; bacterial acid challenge, food acid challenge and stomach acid reflux. Later stages of the study also included topical CPP-ACFP (casein phosphopeptide-amorphous calcium fluoride phosphate) treatment of GIC surface, as well as a more detailed analysis of ion release of Fuji VII EP compared to other materials (Shofu Beautifil). Blocks of GIC material were prepared and allowed to set in an incubator (37C, 95%+ relative humidity) for 24 hours. Surface hardness was determined using micro-indentation using a microscope-aligned indenter. Acid storage media were changed every 24 hours and all solutions were kept for further analysis of ion release. Fluoride ion concentrations were measured using an ion selective electrode, phosphate ion concentrations were determined using a UV spectrophotometry assay and calcium ion concentrations were measured using atomic absorption spectroscopy (AAS). Mass loss was determined using an analytical microbalance. Later stages of the study also measured aluminium ion concentrations, which were acquired using AAS. Data from sample groups was found to follow the normal distribution, χ2 test was used to test normality. Single factor ANOVA was used to analyse the results using Bonferroni-Holm multiple comparison. Two-way ANOVA was used to determine the interaction between incorporation of CPP-ACP and exposure to different acids. Level of significance was set at α = 0.05. Over the course of three days of storage the surface hardness of both materials reduced significantly in all acid solutions as well as a control water solution. Results showed significant increases in calcium and phosphate ion release in Fuji VII EP groups compared to Fuji VII in the vast majority of acid solutions. Fluoride release remained stable for both materials with no significant differences measured between them. Further topical treatment provided additional increases in calcium and phosphate ion release for both materials. Exception to this were groups stored in citric acid, which exhibited far greater mass loss compared to other groups, very high phosphate ion release and an increase in surface hardness. Analysis of aluminium ion release to indicated that aluminium ions are possibly chelated from the GIC matrix, leading to additional release of phosphate ions and increased mass loss. Formation of a crust surface layer seems to be the cause of increased surface hardness in topically treated citric acid groups. Comparison of fluoride, phosphate and aluminium ion release between Fuji VII EP and Shofu Beautifil showed that ion release profiles are significantly and fundamentally different between the two materials, which may be due to the level of maturation (age) of the glass and structure differences between the materials.