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Subject: search.filters.subject.Dental acrylic resins

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    The efficacy of Hibiscus sabdariffa as a fibre-reinforcement material for denture base acrylic resins
    (2017) Okeke, Kenneth Nkemdilim; Vahed, Anisa; Singh, Shalini
    The poor mechanical properties of denture base acrylic resins can cause dentures to fracture either through impact or stress fatigue. Various metal reinforcing materials such as powders, nets, plates and wires together with synthetic fibres are therefore used to improve the strength properties of denture base acrylic resins. Despite their benefits, they are difficult to apply during fabrication, are costly, non-recyclable, and not environmentally friendly. The suitability of Hibiscus sabdariffa (H. sabdariffa) as a fibre reinforcement material for denture base acrylic resins was therefore investigated. A quantitative research paradigm and a two-phased experimental research design was used. The preliminary study used Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and field emission scanning electron microscope (FE-SEM) to assess the characteristics of, and the effect of, mercerisation on H. sabdariffa fibres. In determining the suitability of H. sabdariffa fibres, fibre diameter, fibre density, moisture content and absorption were examined. The main study investigated the mechanical and physical properties of two sample groups namely: the unreinforced (control) group and the H. sabdariffa fibre-reinforced (test) group denture base acrylic resins. The flexural strength, impact strength, specific wear rate, hardness and water absorption behaviour were determined in line with ASTM D 790 and D 256, G 99, D 2583 and D 570 methods of testing, respectively. Parametric and non-parametric tests were used to analyse the mean differences (p = 0.05) between the unreinforced and the H. sabdariffa fibre-reinforced denture base acrylic resins. The preliminary study revealed that H. sabdariffa fibres favourably compared to other lignocellulosic fibres in terms of fibre diameter, fibre density, water content and absorption behaviour. In the main study, a t-test revealed that there were significant differences in flexural strength at 0oC (p < 0.0001) and at 65oC (p < 0.0025) between the two sample groups. Similarly, there were significant differences in the impact strength between the two sample groups at 0oC (p < 0.031) and at 65oC (p < 0.0001). In contrast to the 200g load, there were significant differences (p < 0.044) in the specific wear rate of the unreinforced and the H. sabdariffa fibre-reinforced denture base acrylic resins at the 500g load. The hardness values revealed no significant differences (p > 0.707) between the two sample groups. There were however, significant differences (p < 0.041) in the water absorption rate between the two sample groups. Overall, the prominent features of this study showed that H. sabdariffa fibre is a suitable reinforcement fibre material for denture base acrylic resins and is in compliance with ISO 1567: 1999. Although this study found that H. sabdariffa fibres can be used as reinforcement material for denture base acrylic resins, the results cannot be generalised to clinical conditions, therefore in vitro and in vivo investigations are recommended.
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    Using eggshell for the development of a quality alternative material to pumice in reducing the surface roughness of heat-cured acrylic resins.
    (2016) Onwubu, Stanley Chibuzor; Vahed, Anisa; Singh, Shalini; Kanny, Krishnan
    Pumice is used in the polishing of dental appliances to remove surface irregularities. It is usually used in a slurry form that is pumice powder mixed with water. In Nigeria, the increased cost of pumice as a result of its limited supply into the country has encouraged dental technicians to re-use pumice slurry for longer periods than advocated when polishing acrylic dentures, whether new or old dentures which have been worn in the mouth. Consequently, this is likely to increase cross-infection of communicable diseases in the dental technology laboratory. Although materials such as white sand, black sand and porcelnite can be used, literature documents that these materials are less effective in the polishing of acrylic dentures (Areeg 2011). The focus of this study was to use eggshells, a natural waste product, to develop and test the quality of an alternative material to reduce the surface roughness of heat-cured acrylic resins. A quantitative research paradigm and an experimental research strategy were adopted. The research design included two phases. In phase one of this study, different characterisation techniques such as Brunnae-Emmer Teller (BET); Fourier Transform Infrared Spectroscopy (FTIR); X-ray Diffraction (XRD); Energy Dispersive X-ray Spectroscopy (EDX) and Scanning Electron Microscope (SEM); Transmission Electron Microscopy (TEM); Laser Scattering Particle Size Distribution Analyser (PSA); Thermo-Gravimetric Analysis (TGA); and Induction-Coupling-Optical Emission Spectroscopy (ICP-OES) were used to assess the suitability of the new abrasive material (NAM). In addition, the level of microbial contamination of the NAM was assessed in line with the specified microbial limits for cosmetic products. In contrast, phase two investigated the product-based quality of the NAM as an abrasive material for removable dental appliances. There were two sample groups, that is, the NAM (test group) and Pumice (control), and each sample group had 50 PMMA acrylic specimens. The surface roughness (Ra) was measured using a Talysurf profilometer. An Independent Tukey test was used to analyse the Ra values (p=0.05). A Scanning Electron Microscope (SEM) and Optical Microscope (OEM) were further used to support the results of the profilometer in terms of the quality of surface finish and polish. Validity of the study was achieved following the ISO 20795-1 (2013) methods of preparation and fabrication of the acrylic specimens. The reliability was determined via reproducibility and repeatability of tests. The BET analysis showed that the NAM is predominantly a mesoporous powder. The FTIR and XRD analyses confirmed that the NAM is pure calcite with unique water absorbing characteristics, and is free of bacteria. The EDX and ICP-OES analyses revealed calcium, oxygen and carbon as the major elemental composition of the NAM. The SEM and TEM images revealed irregular shaped particles in the NAM. The PSA analysis of the particle distribution showed the NAM to be superfine (50nm to 0.3µm) and medium (44µm powder), respectively. The TGA analysis revealed a high-grade carbonate product in the NAM (>66.0 mass% of calcium carbonates). In addition, and in terms of in the qualities of the NAM in reducing the surface roughness of PMMA resins, the test group and the control group produced Ra values that were significant different (p<0.0001). The SEM and OEM analyses further confirmed the differences in the surfaces between the polished sample groups at different magnifications. Overall, the control showed the highest mean average (0.1056±0.03688µm), whereas the test group had the lowest Ra values (0.0476±0.01379). The lowest Ra values measured with the test group indicated that the NAM improves the surface smoothness of PMMA acrylic specimens. Notably, this study conclusively showed that the NAM effectively reduces the surface roughness to below the threshold limit value of 0.2µm. Significantly, and in associating the Ra values to the threshold limit value of 0.2µm, the NAM produced better results than pumice. Hence the use of the NAM as a polishing material for acrylic dentures is highly recommended. Finally and in line the NAM being a suitable alternative to pumice as it effectively reduces the surface roughness of PMMA specimens, future investigation into the use of eggshell nanoparticles to develop dental prophylaxes will be encouraged.
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    An in vitro investigation of the flexural strength and microstructure of "stick glass fiber" and "wire mesh" reinforced heat cured denture base acrylic
    (2008) Kiilu, Paul Muli; Vahed, Anisa; Lachman, Nirusha
    Globally in the field of Dental Technology, polymethyl methacrylate (PMMA) resin continues to be the popular material for the fabrication of denture bases in removable prosthodontics. However, the mechanical strength of the denture base is a concern due to fractures occurring intra-orally or when accidentally dropped. The objective of this in vitro investigation was therefore to evaluate and compare the flexural strength and microstructure of stick® glass fibre and wire mesh reinforced PMMA resin after thermocycling. The selection of the materials used in this study was based primarily on their popularity and availability in South Africa. These materials were selected to ensure that the results of this study would have further implicational value in the commercial dental industry when published. This investigation was conducted by means of fabricating a total of 90 PMMA resin specimens and divided in three groups consisting of 30 specimens each. Sample groups 1 and 2 were reinforced with stick® glass fibres and wire mesh respectively. The un-reinforced sample group was the control. All 90 specimens were thermocycled in water at temperatures between 5˚C and 55˚C for 2100 cycles. The flexural strength of each specimen was tested using a universal testing machine and the microstructure of the fractured surfaces was then analysed using scanning electron microscopes (SEM). SPSS version 15.0 was used for data analysis. A p-value of <0.05 was considered as statistically significant. Data were analysed using parametric and non-parametric statistical methods. Statistically significant differences in flexural strength existed between the three sample groups (p<0.001) with the stick® glass fibre and wire mesh sample groups being significantly superior to the control. Furthermore there was a significant association between fracture modes and sample groups. Microscopic analysis revealed the presence of voids. Statistically, in terms of microstructure (% of voids present), a significant difference existed between all sample groups. With regards to surface texture of the compression and tension sides of the test specimens, significant differences existed between the three sample groups. Furthermore microscopic analysis revealed partial impregnation and distribution of the fibres to the PMMA resin matrix and un-bonding between the wire mesh and PMMA resin matrix. Statistically, the Mann-Whitney test was conducted to compare flexural strength between sample groups with and without voids. The flexural strength was higher in sample groups with voids than those without. This is an important finding from the clinical perspective because, in some structures of dentures, toughness is a desired property. Nevertheless in order to find the long-term data especially on clinical behaviour of these new fibre reinforcement systems, more studies should be conducted.