Theses and dissertations (Health Sciences)
Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/12
Browse
9 results
Search Results
Item The efficacy of Hibiscus sabdariffa as a fibre-reinforcement material for denture base acrylic resins(2017) Okeke, Kenneth Nkemdilim; Vahed, Anisa; Singh, ShaliniThe 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.Item Colour stability of three modern ceramic materials after repeated firing(2017) Naidoo, Ansuya; Adam, Jamila Khatoon; Zondi, M.P.P.Background Shade matching is a challenging aspect of aesthetic dentistry (Vichi et al., 2011). For a long time, aesthetically pleasing prostheses have been achieved using the porcelain-fused-to-metal crown whereby the metal is masked with an opaque layer and then consecutive layers of veneering ceramic are built up (McLean, 1979). The growing popularity of all-ceramic restorations has created a need for an understanding of its colour characteristics in preference to porcelain fused to metal restorations. The study aims to assist dental technicians in making a more informed decision when choosing an all-ceramic system in terms of colour stability. Objectives The objectives were to identify colour changes of the zirconia after each firing cycle and defining if there are any microstructural changes in the zirconia cores after subsequent firing. Methods This is a quantitative study with a sample size of eighteen which was used for each experimental group. Green state zirconia blocks from Cercon (Dentsply DeguDent, USA), Lava (3M ESPE,USA), and Zirkon Zahn (Zirkonzahn Gmbh, Bruneck, Italy) were trimmed, finished and sintered to a final thickness of 0.5mm according to the manufacturers’ instructions. Each sample group was obtained directly from the manufacturer. In each group, nine specimens were shaded and nine were unshaded. The colour of each specimen was recorded before being exposed to firing cycles. This data formed the control group. All specimens were subjected to three firings and spectrophotometer reading. After each firing, SEM analysis was done after one and three firings. There was a total of thirty six specimens x three firings; n = 108. The raw data for the statistical analysis was obtained from the spectrophotometer readings recorded after the firings (n=108). The data of the study was analyzed using the SPSS version 22.0. The data were compared among the three groups using Pearsons chi square tests, where the data of the firings were measured as a binary or nominal variable, and using t-tests where a measured normally distributed variable was compared. The general linear model (GLM) looked at combinations of the variables and their effects on the dependant variable. The Multivariate tests table indicates the actual result of the one-way MANOVA. Results The Cercon results for both the control and experimental groups reveal the same result patterns and was maintained before and after firing. Lava also revealed the same results before and after firing, however, the cores in the control group differed in colour. The Zirkon Zahn system proved to be the least stable in colour. Conclusion This study supports the hypothesis that colour differences would occur relative to the number of firings for shaded zirconia. It can be concluded that Cercon displayed the most stable results in terms of colour. The acumen gained in this study may better assist dental technicians in their selection of an all-ceramic zirconia system.Item The evaluation of the applicability of using gold plating to enhance the predictability and strength of base metal post ceramic gold solder joints when using a flux that does not discolour the porcelain(1993) Waddell, John Neil; Coertze, Dirk J.; Engelbrecht, Nick J. H.The unpredictability of solder joints in dental base metal alloys constitute a major problem. This study aimed to establish whether gold plating the joint surfaces of a metal ceramic base metal alloy prior to postceramic soldering would enhance the predictability of the soldering method and joint strength. 150 standardised test specimens were prepared from 3 Oegussa dental alloys, viz Resistal P (Nier), Oegulor M (AUPt) and Realor (PdAU). The Resistal P specimens were subjected to 6 porcelain firing cycles and solder joint surfaces of 40 specimens gold plated prior to soldering, using gold plating equipment and solutions found in the jewellery industry. suitable fluxes were used and all soldering was done in a porcelain furnace. First the soldering method was validated by soldering 20 oegulor M specimens and determining the tensile strength of the 10 joints in an Instron testing machine. The data were then compared with the ISO minimum standards. The soldering method proved sound and a control was thus established. secondly, using 3 alloy combinations without gold plating, 30 solder joints were made and their tensile strengths determined. This established the level of predictability and strength and parameters for comparison. Thirdly, the above procedure was repeated, but the Resistal P specimen joint surfaces were gold plated prior to investing for soldering. The levels of predictability and strength were then compared with the parameters set. The fracture sites of broken joints were examined and photographed using a metallurgical microscope. The data were analysed using 4 statistical tests. The Oegulor M control group solder joints were the strongest and the Resistal P joints the weakest. The success rates for the non-plated joints were; oegulor M to oegulor M = 100%, Resistal P to oegulor M = 90%, Resistal P to Realor = 80% and Resistal P to Resistal P = 60%. The success rates for the gold plated joints were; Resistal P to oegulor M = 60%, Resistal P to Realor = 40% and Resistal P to Resistal P = 80%. This study found, under the circumstances of testing, that gold plating of the base metal alloy prior to investing for postceramic soldering did not enhance the strength, solderability and predictability of the solder joints to an extent that a flux that does not discolour porcelain can be used.Item An evaluation of the colours of base metal alloy oxide layers, and its effects on the shade of base metal alloy metal-ceramic restorations(1997) Somers, Grant Brandon; Waddell, J. N.Globally, difficulties are being experienced by the dental world to match manufactured prosthetic restorations with natural tooth colour. The primary objective of this study was therefore to evaluate the colour of five different metalceramic base metal alloy oxide layers, and the effects of each oxide layer on the shade of the porcelain applied to its surface. The increase in the cost of gold alloys in the dental industry has influenced manufacturers to provide alloys which are cost effective and have adequate mechanical properties for the manufacture of metal ceramic restorations. Five base metal alloys used in the fabrication of metal-ceramic restorations were selected. The selection of the base metal alloys was based on popularity in the industry, availability and cost. The following five base metal alloys were selected for the investigation: Wiron 99 (nickel-chrome) Ceradium V (nickel-chrome-beryllium) Remanium CD (nickel-chrome) \x95 Wirobond (cobalt-chrome) Heranium (nickel-chrome) Bond-on-4 (low noble content alloy {control group; which was gilded}) II Thirty specimens for each alloy group (180 in all) were cast, using the lost wax technique. Three ceramic layers (notably the opaque, dentine and a glaze layer) were applied to the 20mm in diameter surface of each specimen. .\xB7t Finally both sample groups were tested against a custom shade guide the colour being compared specifically with the Vita A 1 shade. The reason for the inclusion of the shade guide was that, clinically, most shade selections are made by comparing the patient's tooth shade with a manufactured shade guide. A wide selection of shades are available to the ceramist. A certain school of thought that recommends that the metal surfaces of semi-precious metals be gilded with a gold gilding paste before the application of ceramics. in order to block out the dark oxide colour and enhance the colour of the ceramic to a more aesthetic and warmer colour. Therefore, prior to the opaque firing of the control group (Bond-on-4), a gilding layer of Spectra Seal Paste was applied to the surface of each specimen. Following each application of ceramic, the appropriate firing cycles were used to fire the ceramic. The following factors affected the selection of the shade of ceramic used in this study: the shade which is most influenced by the dark oxide layer the more popular shades of ceramic ( the A class of shades). It was established, through a review of the literature (Crispen, 1991), that the most objective form of testing colour at the time of the study, was the use of a reflectance spectrophotometer. This form of testing had been proved to be cost effective and was consequently used in this investigation. III ThesurveItem The performance of base metal ceramic alloy restorations with reference to variances in thickness in metal and porcelain in order to establish optimal thickness ratios to maxize strength and aesthetic characteristics(2000) Le Roux, Andre Rayne; Coertze, Dirk J.; Somers, GrantThe greatest problem in maximizing strength and aesthetic characteristics of metal ceramic restorations arises when there is a lack of available space to allow sufficient thickness of metal alloy and porcelain. This generally results in the metal alloy being reduced to its minimum to allow adequate porcelain thickness. The minimum thickness to which noble metal alloys can safely be reduced, is generally accepted to be 0.3 mm due to previous clinical time-dependent trial and error. Agreement regarding the minimum thickness to which base metal alloys can safely be reduced is still under dispute possibly because base metal alloys have not had the same duration of clinical exposure. The objectives of the present study were: 1. To determine the influence thickness variations of the base metal alloy would have on strength characteristics of metal ceramic restorations and thereby establishing the minimum thickness to which base metal alloys can safely be reduced. 2. To determine the influence thickness variations of porcelain would have on strength and aesthetic characteristics of metal ceramic restorations and thereby establish the minimum thickness to which the porcelain thickness can safely be reduced. 3. To determine which base metal alloy to porcelain thickness ratios would be most suited in order to maximize strength and aesthetic characteristics in metal ceramic restorations where the amounts of available space for the alloy and porcelain are varied. For objective (1) Tensile strength tests to determine and compare the ability of various alloy thickness to resist porcelain fracture were performed in Newtons. For objective (2) Tensile tests to determine and compare the ability of various porcelain thickness to resist porcelain fracture were performed in Newtons.Item 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, KrishnanPumice 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.Item 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, NirushaGlobally 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.Item Design and evaluation of alumina/feldspar resin infiltrated dental composite materials(2008) Le Roux, Andre Rayne; Lachman, Nirusha; Walker, Mark; Botha, C. TheoIntroduction: Incorporating a feldspar chemical bond between alumina filler particles is expected to increase the wear resistant and flexural strength properties, while reducing flexibility of dental composites. Aims and Objectives: An investigation was carried out to evaluate the influence of the feldspar chemical bonding between alumina filler particles on wear, flexural strength and flexibility of experimental alumina/feldspar dental composites. It was hypothesized that wear resistance and flexural strength would be significantly increased with increased feldspar mass, while flexibility was expected to decrease. Methods: Alumina was chemically sintered and bonded with 30%, 40%, 50% and 60% feldspar mass, silanized and infiltrated with UDMA resin to prepare the dental restorative composite material specimens. Results and conclusions: Significantly higher wear resistant characteristics resulted with increased feldspar mass (p<0.5). Improvements in flexural strength characteristics as the feldspar mass was increased was not statistically different (p>0.5). Flexibility characteristics as the feldspar mass was increased was not statistically different (p>0.5). The alumina/feldspar specimens showed lower flexibility (mm displacement) than SR ADORO (p<0.05). Feldspar chemical bonding between the alumina particles may improve on the wear resistance and Flexibility of alumina/feldspar composites when compared to SR ADORO. This study evaluated the influence of a chemical feldspar bond between alumina filler particles.Item An in vitro investigation of the effects of surface corrosion on the metal element content and tensile strength of orthodontic silver brazed stainless steel joints arising from varying exposure periods in Fusayama's artificial saliva(2004) Vahed, AnisaGlobally in the field of Dental Technology, brazing continues to be the prevailing joining technique for removable orthodontic appliances. However, the strength of the brazed joint is a growing concern to dental technicians since the commonly employed silver solder brazing material undergoes changes in brazed joint composition (microstructure) thereby enhancing corrosion susceptibility. This ultimately influences the success of orthodontic appliances intra-orally. The objective of this in vitro investigation was therefore to determine the effects of corrosion on the composition and tensile strength of orthodontic silver brazed stainless steel joints after varying exposure periods in Fusayama’s artificial saliva.