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Title: A characterisation of the thermal curing- and mechanical properties of polymethylmethacrylate / hydroxyapatite composites
Authors: Yang, Ming 
Issue Date: 31-Oct-2013
The aim of this study was to investigate the changes in exothermic
polymerisation characteristics and a range of mechanical properties in
PMMA/HA composites (of varying HA concentrations) against a control sample
of pure PMMA.
Specimens of pure PMMA, and 5, 10, 15, 20 and 25 percent HA composites
were made according to the specification of appropriate testing standards using
the flask and packing method. Exothermic polymerisation testing was
conducted on respective samples using an internal j-type thermocouple
temperature sensor. The rate of temperature change and maximum
temperature in relation to time were recorded. Mechanical tests included tests
of flexural strength and modulus, compressive strength and modulus, tensile
strength and modulus and shear strength. All specimens were kept in a
controlled environment prior to testing, which was performed on a LIoyd®
LR30K universal testing machine, and recorded in computer-generated logs.
Exothermic polymerisation testing revealed a decrease in mean maximum
temperature values with increasing HA content. The mean exothermic
temperatures of all six groups were above 100 ̊C, with small relative
temperature reductions as the HA percentage increased.
The results of
mechanical testing revealed that there was a significant reduction in flexural
strength in the range between pure PMMA and 15 percent HA and no statistical
difference in flexural modulus. There was a notable trend toward a decrease in
compressive strength as HA percentage increased, achieving statistical
significance at 20 and 25 percent HA, with no statistical difference in
compressive modulus between samples. The tensile strength test results no
significant difference between pure PMMA and composites containing up to 15
percent HA. A significant difference was noted between the 20 percent- and 25
percent HA composites and those of lower HA concentration with an increased
failure risk as HA concentration was increased above 10 percent. There was a
tensile modulus peak at 15 percent HA, and a significant difference between 15
percent HA composites and pure PMMA and the 10 percent HA composite.
Shear strength was noted to decrease with HA percentage, with significant
reduced strength between the 15 percent HA composite and pure PMMA, as
well as between the 20 and 25 percent HA composites and composites of less
than 10 percent HA.
The study revealed that the addition of HA to pure PMMA negatively affects the
mechanical strength measured in compression, bending or shear. Tensile,
compression and flexural moduli showed a gentle increase with the addition of
increasing amounts of HA. The peak values were noted at 15 percent for tensile
modulus and 25 percent for compressive and flexural moduli. It was
recommended that the best compromise across all properties (mechanical and
thermal) should be based upon the context of composite use. It was further
recommended that PMMA/HA composite materials with 10 – 15 percent HA be
investigated further, with due cognisance of the limitations of the present study.
The researcher recommended replication of the study using a larger sample
size, more refined methodology and the incorporation of additional tests,
including shear modulus testing, impact resistance, bioactivity and composite
Submitted in fulfillment of the requirements of the Degree of Master of Technology: Dental Technology, Durban University of Technology, Durban, South Africa, 2013.
Appears in Collections:Theses and dissertations (Health Sciences)

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