Magister Scientiae - MSc / The aim of this project was to compare the shear bond strengths of three light cure orthodontic adhesive resins with three different stainless steel molar brackets. / South Africa

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Self-etching dentine bonding agents are a recent addition to the choice of bonding agents which a clinician has available to bond resin restorations to tooth structure. The so-called ‘traditional’, total-etch fourth and fifth generation dentine bonding agents have proven their clinical abilities and the question now remains whether these ‘new’ self-etching dentine bonding agents will clinically perform as well as the ‘proven’ total-etch dentine bonding agents. For the purpose of this dissertation the author completed three research projects which were performed to evaluate the efficacy of a selection of dentine bonding agents and then used the results to compare some properties (shear bond strength, microleakage, and anti-bacterial properties) of total-etch dentine bonding agents with some self-etching dentine bonding agents. All discussions will focus on the three dentine bonding agent properties evaluated by the three research projects performed. The three specific aims of this study were: <ul> <li> To compare the dentine shear bond strength of a selection of self-etching dentine bonding agents with that of a total-etch dentine bonding agent control.</li> <li> To compare dentine and enamel microleakage values of a selection of self-etching bonding agents with that of a total-etch dentine bonding agent control.</li> <li> To evaluate the possible anti-bacterial properties of a selection of dentine bonding agents, with focus placed on the self-etching dentine bonding agent ABFb (Clearfil Protect Bond).</li></ul> The studies performed by the author achieved comparative/similar results to some studies described in the literature but it is clear from the literature that some studies provide conflicting results, especially leakage of enamel margins when using self-etching bonding agents. Taking into consideration the limitations of the three studies performed, it can be concluded that as far as the three evaluated properties of self-etching dentine bonding agents are concerned, they should prove to be acceptable clinical alternatives for use in place of total-etch dentine bonding agents. Copyright / Dissertation (MSc(Odont))--University of Pretoria, 2010. / Odontology / unrestricted

Please read the abstract in the section 00front of this document / Dissertation (MChD (Orthodontics))--University of Pretoria, 2007. / Orthodontics / unrestricted

Magister Scientiae Dentium - MSc(Dent) / The demand for posterior aesthetic restorations has dramatically increased in recent years. Several new materials have been developed with improved aesthetic, adhesive and mechanical properties. However, microleakage elimination, especially if the margins are on dentine or cementum, and attainment of optimum mechanical properties for posterior use, are still questionable. The aim of this study was to investigate microleakage and surface microhardness of a nanofilled, a nanohybrid and an ormocer based nano-ceramic composite restorative material. / South Africa

Magister Scientiae - MSc / Amalgam bonding agents have been shown to enhance retention of amalgam restorations by mechanical means. However, recent studies showed that the use o glass ionomer cements and resin cements as lining and bonding materials to amalgam restorations will increase the retentive strength of the amalgam restorations, hence reducing the micro leakage and secondary caries. The purpose of this study was to compare the relative retentive strength of conventional amalgam restorations and bonded amalgam restorations using resin adhesive, glass ionomer cements and resin cements. / South Africa

Although various organometallic carbene complexes have found use in industry or research, they still lack some fundamental footing in theory. These complexes have found significant use in catalysis. This is especially true for Schrock carbene complexes in olefination reactions. A few such titanium-based olefination catalyst examples are the Tebbe reagent, Petasis reagent and the Ziegler-Natta catalyst. The nature of organometallic carbene bonding is still not well defined theoretically. Schrock carbenes are expected to have a covalent bonding nature, but multiconfigurational studies have shown this to not be the best description of the bonding. Furthermore, expected Schrock carbenes have been shown to be Fischer carbenes due to the electronic structure. This work investigates the nature of the carbene bond in titanium Schrock carbene complexes by utilising DFT and further application of MO, NBO, QTAIM and FALDI methods. This allows for a modernised description of the nature of this bond as well as the identification of an important long-range ligand-ligand interaction that has not been reported on previously. The research aims to define the nature of titanium Schrock carbene bonding on a theoretical basis by the use of integrated cross-sections on the electron and orbital densities to determine the σ- and π-character of the interaction. These cross-sections provided the means to determine the major components of the bonding interaction. This is further investigated by defining FALDI fragment-based delocalisation indices which revealed the presence of long-range ligand-ligand interactions. The FALDI fragment approach also provided the means to quantify the inter-fragment delocalisation along with intra-fragment localisation and delocalisation which would prove useful for further investigation into the characteristics or various chemical interactions. The fragment-based description should prove to be more intuitive to the chemist than diatomic interactions between atoms where a chemical bond or interaction is not classically expected. This study was followed by a decomposition of the molecular orbitals into localised and delocalised components from atomic contributions which provides a novel approach to determining the bond order in compounds. This provided a quantitative means to describe which atoms contribute to the formation of each molecular orbital as well as providing a measure of the degree to which these atoms are contributing localised as well as delocalised electrons to the molecular orbital. / Dissertation (MSc)--University of Pretoria, 2020. / DST-CSIR Interbursary Support Program / Chemistry / MSc / Unrestricted

Philosophiae Doctor - PhD / Introduction: Biocompatibility of all kinds of dental materials is of paramount importance In order to prevent/limit irritation or degeneration of the surrounding tissues where it is applied. Some researchers suggested that dentine bonding agents may be used for pulpal protection, while pulpal inflammation and inhibition of pulpal repair following the use of dentine bonding agents were also reported. Objectives: The first part of this study compared the cytotoxicity of human pulp cell lines to a mouse 3T3 cell line to cytotoxic challenges from dentine bonding agents. The second part of the study compared the cytotoxicity of recent dentine bonding agents namely, Scotchbond 1, Prime & Bond NTand Xeno III through artificial membranes as well as thin dentine discs (after its reaction with apatite) and Clearfil Protect Bond (CPB)as such, as well as the primer part of CPBand the bond part of CPB separately. Methods and Materials: Near confluent human pulp cells and 3T3 cells were exposed to culture medium (DMEM)extractions from the various polymerized agents mentioned above and the cell viability (survival rate) was measured using the standard MTTassay and related to the non-exposed controls. Results: Two human pulp cells lines were more sensitive to 3T3 cell lines while the other human cell line was less sensitive to the 3T3 cell line. All bonding agents as such were found to be cytotoxic towards the 3T3 cells with Xeno III (25%survival rate) and CPB (35%)the most cytotoxic. Of the two parts from CPB the bond part was the least toxic (91% survival rate), but the primer part (containing the anti-bacterial pyridinium molecule) was very toxic (30% survival rate). ScotchBond 1 (59% survival rate) and Prime & Bond NT (62% survival rate) were not statistically different (Kruskal-Wallis Test, p>0.05). However,the survival rate of Xeno III (25% through membrane as well as dentine discs) and Clearfil Protect Bond (35%) were significantly lower than that of the other two bonding agents, with Xeno III significantly the most toxic (p<0.05 ) Conclusion: In general, all 4 dentine bonding agents were cytotoxic of which Xeno III was the most toxic even after its reaction with apatite (through dentine discs). The most toxic part of CPB was found to be the primer part containing the pyridinium linked molecule. If human pulp fibroblasts are used for cytotoxicity testing of dentine bonding agents many cell lines must be used.

OBJECTIVES: The aim of this in-vitro study is to evaluate the effect of different zirconia surface pretreatments, different cement types and the effect of accelerated aging on the adherence of bonding cements to zirconia. MATERIALS AND METHODS: 64 zirconia 3Y-TZP tapered rings were pressed from TZ-3YSB-E zirconia powder, pre-treated with different surface treatments, then cemented to titanium abutment pins using 8 different cements: Maxcem Elite chroma (Kerr), TheraCem (Bisco), RelyX Unicem2 (3M ESPE), Multilink Automix (Ivoclar Vivadent), Panavia SA Cement Plus (Kuraray), Ceramir C&B (Doxa), CemEZ Universal (Zest Dental), and Bifix SE (VOCO). The partitally sintered zirconia specimens were divided according to design of experment (DOE). Zirconia surface treatments: 1) control group with no surface treatment, 2) airborne particle abrasion of fully sintered zirconia ring (FS-APA50), 3) airborne particle abrasion of partially sintered zirconia (PS-APA50), 4) tribochemical silica coating of fully sintered zirconia (FS-CoJet30), 5) tribochemical silica coating of partial sintered zirconia (PS-CoJet30), and 6) nano-structured alumina coating of fully sintered zirconia (NanoAl). Zirconia rings were subjected to post-treatment:1) control 24h incubation after cementing proceedure, and 2) accelerated aging . The pull-out axial tensile retention load was tested using an Instron Model 5566A. Multi factorial linear regression model (JMP Pro 15) was used for data analysis (α=0.05). RESULTS: The retention force (N) of zirconia rings to titanium abutment pins was evaluated using a pull-out test. Four key factors were investigated in this study: zirconia surface pre-treatment, cement type, post-treatment and firing effect. There was a significant effect of zirconia surface pre-treatment on retention force (nano-structured alumina coating ≥ tribochemical abrasion = airborne-particle abrasion ≥ control). There was a significant effect of cement type on retention force [Multilink AM ≥ (Cem EZ = TheraCem = Panivia SA = RelyX Unicem2 = BiFix) ≥ Ceramir CB = Maxcem Elite]. There is a significant difference in retention strength to zirconia among post-treatment effect, with accelerated aging groups achieving slightly higher bond strength than 24h water storage groups. CONCLUSIONS: Significant different retention loads were found among tested groups. Nano-structured alumina coating surface pre-treatment has significantly higher bond strength than other treatments. Some cement systems with functional monomer had significant higher bond strengths.

Resin based composite is currently one of the most popular dental restoratives. Used as a direct restorative material, it displays many beneficial properties such as excellent micromechanical bonding to enamel, polishability and aesthetics. Despite many advances in dentine bonding agents, dentine bonding remains problematic with microleakage and recurrent caries, being frequent clinical sequelae. The open sandwich technique was developed to overcome two problems: deficient bonding of resin composites to dentine, and inadequate strength and fracture toughness of conventional glass-ionomers (GI). GI displayed excellent cavity sealing abilities by virtue of their chemical adhesion to tooth structure. Resin-modified glass-ionomers (RMGI) were developed to improve on the weaknesses of conventional GI during early setting i.e. setting rate, water sensitivity and strength. Recently literature has reported the use of ultrasonic activation to set conventional GI, opening the possibility of improving the initial properties of the material and suitability for use in the open sandwich technique. The aim of this study was to compare microleakage of Ketac Molar, Ketac Molar set by ultrasound (US), Vitremer and Ketac N100 used in the open sandwich technique, with the control of a resin based composite, Filtek Z250. Two hundred Class II cavities were prepared in a hundred caries free, human, molar teeth, with half of the cervical margins placed apical and the rest coronal to the cemento-enamel junction. For each material, twenty restorations were placed for each cervical position. The sandwich materials were placed to fill the interproximal box level with the pulpal floor, and a final two layers of resin composite was then placed to complete the restoration. Restored teeth were stored in a laboratory oven for 7 days at 37 °C; margins were then finished initially with a medium grit Sof-Lex disc and finally with a fine diamond drill. Material groups were separated into two halfs to commence microleakage testing or thermocycling. Thermocycling was conducted for 500 cycles between 5 °C and 55 °C, with a dwell time of 30 seconds. Restored teeth were then covered with nail varnish around the restoration margins, and immersed in 0.5% basic fuchsin solution for 24 hours. They were then cleaned, embedded in clear self-curing acrylic and sectioned 3 times with an Accutom-2 precision saw, at 2 mm intervals. Sections were evaluated using a light microscope under 4 time’s magnification and microleakage scores given as: 0 = no leakage; 1 = < ½; 2 = > ½ distance to the axial wall/pulpal floor; 3 = leakage up to axial wall/pulpal floor. Statistical analysis was undertaken using Analysis of Variance (ANOVA) for the cervical and occlusal microleakage scores; p-values <0.05 were considered significant. The cervical microleakage results of cavity margins in dentine showed that Ketac Molar (US) performed better than Ketac Molar, and Ketac N100 performed better than Vitremer. Results in enamel showed no significant differences. The use of the open sandwich technique effectively reduced microleakage of cervical cavity margins placed in dentine but failed to reduce occlusal microleakage of Filtek Z250. Copyright / Dissertation (MSc(Odont))--University of Pretoria, 2008. / Odontology / unrestricted