Browsing by Author "Oberholzer, Theunis"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    The effect of different reinforcements on the fracture toughness of materials for interim restorations
    (Elsevier, 2008) Geerts, Greta; Overturf, Jan-Hendrik; Oberholzer, Theunis
    STATEMENT OF PROBLEM. Fracture of an interim fixed partial denture (FPD) may jeopardize the success of the interim prosthodontic treatment phase and cause patient discomfort. PURPOSE. The purpose of this study was to compare the fracture toughness of a polymethyl methacrylate (PMMA) resin and a bis-acryl composite (BAC) resin reinforced with stainless steel wire, glass, and polyethylene fiber. MATERIAL AND METHODS. Four groups (n=13) of each of the 2 materials were prepared for the single-edge 3-point-bending test. Three groups had the different reinforcements, and the group without reinforcement served as control. Using a universal testing machine, peak load to fracture was recorded and fracture toughness (KIC) was calculated in MNm-1.5. Median KIC values were compared by means of nonparametric ANOVA (Kruskal-Wallis test, α=.05). RESULTs. For the controls, the fracture toughness for PMMA resin (KIC=27.9) was significantly lower (P<.01) than for BAC resin (KIC=31.2). Glass fibers and stainless steel wire reinforcements produced significantly higher fracture toughness for both PMMA (KIC=34.4, P<.01, and KIC=39.0, P<.001, respectively) and BAC resin (KIC=42.3, P<.001, and KIC=44.0, P<.001, respectively), but the polyethylene fibers did not (KIC=33.1, P>.10, for BAC resin and KIC=25.8, P>.10, for PMMA resin). There was no significant difference between the fracture toughness of the wire and glass fiber reinforcements for both interim materials (P>.10 in both instances). CONCLUSIONS. Of the 3 reinforcement methods evaluated, wire and glass fiber reinforced the PMMA and BAC resin materials best.
  • Thumbnail Image
    Item
    Effect of four over-the-counter tooth-whitening products on enamel microhardness
    (South African Dental Association, 2011) Majeed, Abdul; Grobler, Sias Renier; Moola, Mohamad H.; Oberholzer, Theunis
    OBJECTIVES: This in vitro study evaluated the effect of four over-the-counter tooth-whitening products on enamel microhardness. METHODS: Fifty enamel blocks were prepared from extracted human molar teeth. The enamel surfaces were polished up to 1200 grit fineness and the specimens randomly divided into five groups. Enamel blocks were exposed to: Rapid White (n=10); Absolute White (n=10); Speed White (n=10) and White Glo (n=10) whitening products, according to the manufacturers' instructions. As control, ten enamel blocks were kept in artificial saliva at 37 degrees C without any treatment. Microhardness values were obtained before exposure (baseline) and after 1, 7 and 14-day treatment periods using a digital hardness tester with a Vickers diamond indenter. Data were analysed using Wilcoxon Signed Rank Sum Test, one-way ANOVA and Tukey-Kramer Multiple Comparison Test (p<0.05). RESULTS: Both Rapid White and Absolute White reduced enamel microhardness. Speed White increased the microhardness of enamel, while White Glo and artificial saliva had no effect on hardness. CONCLUSIONS: Over-the-counter tooth-whitening products might decrease enamel microhardness depending on the type of product.
  • Thumbnail Image
    Item
    Insights into chitosan hydrogels on dentine bond strength and cytotoxicity
    (Scientific Research Publishing, 2013) Perchyonok, Tamara; Grobler, Sias Renier; Zhang, Shengmiao; Olivier, Annette; Oberholzer, Theunis
    Contemporary dental adhesives show favorable im- mediate results in terms of bonding effectiveness. However, the durability of resin-dentin bonds is their major problem. Materials and Methods: Preparation of 3 chitosan-antioxidant hydrogels was achieved us- ing modified hydrogel preparation method. Their effect on the bond strength to dentine both short term (after 24 hours) and long term (after 6 months) were evaluated using shear bond strength measurements using Instron Universal Testing Mascine). The SEM was used to study the surface of the hydrogels. The cell survival rate (cytotoxicity) of the antioxidants re- sveratrol, β-carotene and propolis towards Balb/c 3T3 mouse fibroblast cells was also assessed using the standard MTT assay. Results: It was found that chi- tosan-H treated dentine gives significantly (p < 0.05; Non-parametric ANOVA test) higher shear bond va- lues than dentine treated or not treated with phos- phoric acid. The anti-oxidants chitosan hydrogels improved the shear bond strength. Overall, there was a relapse in the shear bond strength after 6 months. The SEM study showed that the hydrogel formula- tions have a uniform distribution of drug content, homogenous texture and yellow color. The pH of the growth medium adjusted to relevant values had a highly significant influence (Tukey-Kramer Multiple- Comparison Test; p < 0.01) on the cell survival rate of Balb/c mouse 3T3 fibroblast cells and therefore most probably also to tooth pulp fibroblast cells. The lower the pH value the higher the negative influence. Fur- thermore, the sequence of survival rate was found to be: β-carotene (92%) > propolis (68%) > resveratrol (33%). Conclusion: the antioxidant-chitosan hydro- gels significantly improved bonding to dentine with or without phosphoric acid treatment. The pH of the growth medium had a high influence on the cell survival rate of Balb/c mouse 3T3 fibroblast cells. The release of the antioxidant β-carotene would not have an influence on the pulp cells. These materials might address the current perspectives for improving bond durability.