Browsing by Author "Geerts, Gavm"

Now showing 1 - 4 of 4
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    The effect of dentine-bonding agents on the microleakage of provisional crowns
    (University of the Western Cape, 2005) Moosa, Rustim; Geerts, Gavm; Dept. of Prosthodontics; Faculty of Dentistry
    The use of provisional acrylic crowns is common practice with prosthodontic treatment. Provisional crowns are prone to marginal leakage and poor retention due to weak interim cements. The aim of this study was to assess the effect of the application of two different dentine-bonding agents on the microleakage of provisional crowns.
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    The effect of temperature on the linear dimensional stability of elastomers
    (University of the Western Cape, 2012) Muller, Susan Sanette; Geerts, Gavm
    Sometimes, dental impressions need to be transported to distant laboratories. It has been reported that the temperature in a vehicle can reach up to 66C when the outdoor temperature is 38C. These temperatures may be reached during South African summers. The objective of this in vitro study was to investigate the effect of temperature and time on the dimensional stability of two elastomeric impression materials. Methodology: Specimens consisted of impressions made of an ISO-specified test-block featuring a pattern of grooves. Materials used were polyether (Impregum Penta) and polyvinylsiloxane (Affinis Precious regular body). Using an SLR camera and standardized technique, the specimens were photographed at 2 different temperatures (21°C and 66°C) and 3 time intervals (30min, 8hrs and 14 days). This resulted in a total of 12 groups (n=10) to be compared. Digital images of the impressions were calibrated and measured using digital analyzing software. These distances were used to evaluate the mean % dimensional change (%DC) for each group. VEPAC module of Statistica 10 was used for the statistical analysis. To analyze exactly where the differences lied, a Fisher LSD correction was applied to correct for multiple pair wise comparisons. Results: Comparing polyether with silicone, there was no difference in the mean %DC for specimens kept at 21°C for 8hrs (polyether=0.364; silicone=0.237). Neither was there a difference between polyether and silicone when heated to 66°C, cooled off, and measured after 8hrs (polyether=0.306; silicone=0.297) or after 14 days (polyether=-0.272; silicone=-0.093). For both polyether and silicone, the mean %DC of the groups exposed to 66°C, cooled off and measured after 8hrs (polyether=0.306; silicone=0.297) differed significantly when compared to the group measured after 14 days (polyether=-0.2723; silicone=-0.092) (P<0.0001 and P=0.0029 resp). For both polyether and silicone, the mean %DC of the groups exposed to 66°C, cooled off and measured after 8hrs (polyether=0.306; silicone=0.297) did not differ when compared to the 21°C (polyether=0.364; silicone=0.237). Conclusions: Within limitations of this study, both materials were heat-sensitive. It is recommended that materials return to 21°C before casting. Despite statistical differences, all results were within ISO specifications of maximum 1.5%DC.
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    Mechanical and handling properties of light-cured acrylic resin custom tray material
    (University of the Western Cape, 2007) Khan, Saadika B.; Geerts, Gavm; Dept. of Restorative Dentistry; Faculty of Dentistry
    Both light-cured (LC) and chemically-cured (CC) acrylic resin custom tray materials are used at the Oral Health Centre, Faculty of Dentistry, University of the Western Cape. At present, the CC acrylic is the standard for formal undergraduate teaching and training. The LC material is not part of routine didactic teaching as little evidence-based scientific information is available with regards to its properties and its usage in the clinical environment. Negative effects have caused researchers to focus on alternatives and to research for other materials with more advantageous properties. The objectives of this study was to determine the linear dimensional shrinkage and fracture toughness of light-cured acrylic custom tray materials and compare it to the chemically-cured type. Also to evaluate the acceptance of light-cured acrylic resin custom trays by undergraduate students.
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    Photoelastic stress patterns produced by the angled distal implants in the All-on-Four concept
    (University of the Western Cape, 2006) Begg, Tasneem; Geerts, Gavm; Gryzagoridis, J.; Dept. of Restorative Dentistry; Faculty of Dentistry
    The purpose of this study was to investigate the stress produced around the angled distal implants under simulated occlusal loading in the All-on-Fourª concept by means of two-dimensional photoelastic stress models.