Objective: To assess the effects of ceramic opacity and thickness on delivered radiant exposure and degree of conversion and microhardness of the light-cured resin cement. Materials and Methods: IPS e-Max ceramic discs (Ivoclar Vivadent) were fabricated in 3 thicknesses (0.5, 1.0, and 1.5mm) and 4 opacities (HT, LT, MO, HO) (n=3/per group). Light-cured resin cement (Variolink Veneer Luting Cement - shade MVO, Ivoclar Vivadent) 50µm thick was cured through these ceramics disks using a quartz tungsten halogen curing light unit (Optilux 501, Kerr) with its radiant exposure measured by MARC from a fixed distance (1.5mm). Knoop microhardness was used to evaluate the bottom degree of cure and was correlated with the radiant exposure deliverd. Descriptive statistics were conducted. One- and two-way ANOVA with post-hoc Tukey's HSD test, Pearson correlation test, the simple linear regression analysis were used for the statistical analyses (alpha=0.05). Results: Significant interaction was found between ceramic thickness and opacity on radiant exposure (p=0.0078). Subsequent analyses demonstrated that there was a significant simple effect for opacity and for thickness on radiant exposure under different conditions of thickness and opacity. A significant relationship was found between resin cement microhardness and radiant exposure (p=0.0001) below 4.5 J/cm2. Moreover, the Pearson correlation coefficient of 0.93 indicated a strong correlation between the two variables below 4.5 J/cm2 of radiant exposure delivered. Conclusion: Ceramic opacity and thickness affect the polymerization of light-cured resin cements and need to be considered and compensated for when bonding indirect restorations. Based upon the findings of this preliminary study, the final study is ongoing.

No description available.

Master of Dental Surgery / The lack of adaptation between restorative materials and tooth structure has for many years been a major problem in Dentistry. Studies during this time have emphasized that the margins of restorations are not fixed, inert and impenetrable borders, but dynamic microcrevices which contain a busy traffic of ions and molecules (Going, 1972). The microleakage which results, has been defined as “the clinically undetectable passage of bacteria, fluids and molecules or ions between a cavity wall and the restorative materials applied to it” (Kidd, 1976, b). Microleakage has been implicated in a variety of clinical conditions, including recurrent caries, tooth discolouration, hyper-sensitivity, pulp pathology and hastened breakdown of restorative materials (Kidd, 1976, a and b; Torney et al, 1977). Buonocore (1955) was probably the first to bond resins to tooth structure, etched by the application of phosphoric acid to enamel surfaces. It was found that etching the enamel converted a previously hydrophobic, low energy surface to a more wettable high energy state possessing an increased surface area with numerous retentive sites for resin tag formation. Over the years, the acid-etch technique has been used in a number of dental procedures including fissure sealing, the repair of fractured incisal edges, the repair of hypoplastic and abraded areas, the placement of orthodontic brackets and the splinting of teeth. In recent years, studies have evaluated the ability of the acid-etch technique to improve both the adaptation and retention of composite resins to tooth structure and the marginal seal around composite restorations. However, much of the research examining adaptation of composite resins to tooth enamel has been limited to the study of the enamel tooth surface rather than the enamel of the cavity wall. In addition, previous studies have paid little attention to the effects, on the microleakage, of different etching times and different sizes of the inorganic filler particles and to the influence of aging the restorations on the microleakage. The review of the literature also indicated some controversy concerning the use and effectiveness of low viscosity resins. Since the early 1970’s acid-etching of the enamel has been used increasingly in the placement of composite resin restorations, to provide retention and to minimize marginal microleakage. It was the purpose of this investigation to examine the etched enamel cavity wall, to compare the ability of composite resins, of different particle size and viscosity, to adapt to this cavity wall, and to study the influence, in vitro, of these and other factors, on the microleakage occurring at the margins of restoration.

Master of Dental Surgery / This work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au

Master of Dental Surgery / This work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au

Thesis (M.D.S.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 89-114) Also available in print.

Thesis (M.D.S.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 189-208) Also available in print.

<p>The Aim of this study was to determine wheteher there are changes in the interdental arch widths and arch lengths of the madibular and maxillary arches during no-extraction and extraction orthodontic treatment. The records of 78 patients treated by one orthodontist were used for this study. Statistical data analysis included descriptive statistics of the data, analysis of the matrices, Wilcoxon Signed Rank tests and Kruskal-Wallis tests of the changes which occured during treatment. The study concluded that extraction treatment does not necessarily lead to the narrowing of the dental arches in the canine region.</p>

<p>&quot / Although facial aesthetics has always been a part of orthodontic diagnosis and treatment planning, the criteria for facial evaluation have been somewhat arbitrary. They are often based on parameters from the field of art or from evaluating faces chosen by orthodontists or other professionals. The aims and objectives of the study were to determine the soft-tissue profile preference of a group of lay persons and professionals / to compare the preferences of the male and female assessors (lay persons group) with regard to the preferred profiles for the maleand female patient respectively / to test similarities and differences in the professional's perceptions of the various profiles. This qualitative study was undertaken at the orthodontic clinic at UWC using post-treatment soft tissue profile photographs of patients who had attended the orthodontic clinic...&quot / </p>

Thesis (M.D.S.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 89-114).