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Thesis (M.S.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 49-58). Also available via World Wide Web.

In a limited screen of monokaryons and dikaryons of various strains of Trametes versicolor, the monokaryons generally bleached hardwood and softwood kraft pulps more extensively than dikaryons, although there was great variation among both groups. A monokaryotic strain (52J) derived from a Paprican dikaryon (52P) by regenerating mycelium-derived protoplasts had better pulp bleaching ability than its dikaryotic parent. Unusually low extracellular laccase and manganese peroxidase activity levels were associated with reduced pulp bleaching. Mutants of strain 52J were isolated with various manganese peroxidase and laccase activities. Those with markedly reduced laccase and manganese peroxidase activity had impaired abilities to bleach, delignify, and produce methanol from hardwood kraft pulp, mineralize $ sp{14}$C-labelled synthetic lignins, reduce the colour of kraft mill bleach plant effluent, or had lost these abilities altogether. Dechlorination of kraft bleach plant effluent organochlorines was only slightly less in the mutants tried than in 52J. When purified manganese peroxidase was added back to mutant M49 of 52J, significant pulp bleaching was restored. Effluent decolorization also improved with added manganese peroxidase.

The extracellular culture supernatants of the white rot fungus Trametes versicolor can bleach and delignify unbleached kraft pulps, however the process is too slow for commercial application. Though at least two oxidative enzymes, laccase and manganese peroxidase (MnP) produced by this organism can catalyze a partial delignification of kraft pulp, the effect observed is small relative to that obtained with the complete fungal system. To develop a synthetic (cell-free) delignification system, other protentially important components of the culture supernatant were identified and their contributions to biobleaching and delignification were evaluated. The presence of pulp did not significantly affect the overall carbon balance of the fungus, but a number of non-volatile metabolites (oxalic, fumaric, glyoxylic and phenyllactic acids) induced by the presence of pulp were identified. In T. versicolor 52J, the secretion of manganese peroxidase (MnP), and cellobiose:quinone oxidoreductase (CBQase) enzymes were inducible by pulp whereas cellulase and laccase were not. Several low molecular weight metabolites secreted by T. versicolor functioned as effective Mn(III) complexing agents at their physiological concentrations and promoted MnP activity. / Two distinct CBQase proteins are secreted by T. versicolor 52J, CBQase 4.2 a a 113kDa homodimer containing both heme and flavin cofactors and CBQase 6.4, a 48 kDa monomer with a flavin cofactor only. Superficially, these enzymes appear very similar to the cellobiose oxidase (CBO) and CBQase reported in Phanerochaete chrysosporium. CBQase 4.2 was shown to reduce insoluble manganese dioxide to its soluble Mn(II) and Mn(III) forms with the concommitant oxidation of cellobiose. The sugar acids formed by CBQase could function as effective complexing agents for Mn(III),and complement the Mn(II) to Mn(III) oxidation activity of MnP. / It is proposed that a redox cycling of lignin molecules by certain fungal oxidative and reductive enzymes occurs during delignification and that this cycling ultimately promotes net lignin degradation. A redox cycle wa established between T. versicolor CBQase and laccase which allowed the O$ sb2$ comsumption rate of laccase to remain at a constant level and the total O$ sb2$ consumption by the enzyme was much treater than if the substrate were incubated with laccase alone. A new assay for CBQase based on the ability of this enzyme to reduce the radical intermediates formed during laccase-mediated chlorpromazine oxidation was developed. A redox cycle for these two enzymes was established using both model substrates like CPZ, and with a kraft lignin preparation. CBQase inhibited the formation of polymeric material by laccase; however no evidence was found indicating that cycling with these two enzymes favors depolymerization of kraft lignin. However, the alkali extractability of residual lignin in kraft pulp was increased by a sequential treatment with MnP followed by CBQase.

<p>The aim of this laboratory based study is to assess the efficiency of a tooth bleaching agent by measuring the degree of color change with a spectrophotometer (Konica Minolta, CM 2600d) and not by the usual subjective visual guide methods. Objectives of the study are: To determine tooth shade with a spectrophotometer prior to staining the tooth (baseline). To determine which insult causes the most discoloration numerically. To measure the efficiency of the bleaching agent used in the study with periodic color change pectrophotometer readings.&nbsp / To assess if the baseline tooth shade can be regained by the bleaching agent.</p>

<p>The aim of this study was to determine whether tooth bleaching agents alter the colour of stained direct composite resins.</p>

The work described in this dissertation was aimed at obtaining an understanding of / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007

Objective: To evaluate the effect of an in-office plus at-home bleaching protocol on shear bond strength of orthodontic buttons when using a fluoride-releasing sealant. Methods and Materials: One hundred and sixty extracted human molars were randomly divided into bleached (N=80) and unbleached groups (N=80). The bleached group was treated with 45% carbamide peroxide for half an hour, followed with five applications of 20% carbamide peroxide at 24 hour intervals. After two weeks, lingual buttons were bonded on the teeth in both groups using either Transbond XT primer or Pro Seal sealant. The teeth were then stored in artificial saliva and subjected to shear testings at 24 hours and 3 months using a Zwick Universal Test Machine. Results: The ANOVA analysis of the 24-hour results indicated a significant difference between the four subgroups (p<.0011). Further simple t-tests indicated that the differences were significant only between bleached and unbleached subgroups (p<.0011). The 3-month results showed the mean shear bond strengths of the unbleached group using Pro Seal sealant was statistically significantly lower than the others although still greater than clinically minimal suggested bond strengths. Interestingly, 15% of the bleached teeth exhibited enamel fracture at the 3-month testing. Conclusion: At 24 hours, both Pro Seal sealant and Transbond XT primer appear to be a reliable choice on both bleached and unbleached teeth. However, at the 3-month period, Pro Seal sealant yielded significantly lower shear bond strength on unbleached teeth, nevertheless well within the range of values considered to be "clinically acceptable".

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