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

<p> Purpose: The purpose of this investigation was to evaluate the effect of aluminum oxide airborne particle abrasion, with and without subsequent steam cleaning on the surface free energy of alloys commonly used in dentistry, in an attempt to produce optimal surfaces for adhesion. Materials and Methods: Twelve samples, with dimensions 13 x 18 x 1 mm, of each: Type IV high noble gold alloy, metal ceramic gold-palladium high noble alloy, chrome-cobalt base metal alloy were cast and divested with glass bead airborne particle abrasion. Twelve samples, with dimensions 13 x 18 x 10 mm, of titanium alloy were milled using an Origin Proteus 5x Milling Machine. Samples were treated with 1) Steam cleaning only, 2) Aluminum oxide airborne particle abrasion and 3) Aluminum oxide airborne particle abrasion with subsequent steam cleaning. Contact angle measurements were recorded immediately after each treatment and at 1 and 12 hours, using a goniometer and the sessile drop method. Surface free energy was calculated using VCA Optima XE software. </p><p> Results: Steam cleaning treatment showed no significant changes in surface free energy (dynes/cm), compared to pretreatment values for the alloys investigated except Titanium alloy, which showed a modest increase in surface energy (p &lt; 0.05). Aluminum oxide airborne particle abrasion and aluminum oxide airborne particle abrasion with steam cleaning, resulted in an increase in surface free energy for all alloys investigated when compared to pretreatment and steam clean only values. Steam cleaning following airborne particle abrasion produced significantly lower (p&lt;0.001) surface free energy values compared to airborne particle abrasion alone for high noble gold alloy and metal ceramic gold-palladium high noble alloy. Exposure to ambient air following steam cleaning had minimal or non-enduring effects on surface free energy for all alloys investigated except Titanium alloy, which showed a significant decrease (p&lt;0.001) in surface free energy with time of ambient exposure. Exposure to ambient air following airborne particle abrasion with aluminum oxide resulted in a significant decrease (p&lt;0.001) in surface free energy for high noble gold alloy, metal ceramic gold-palladium high noble alloy and chrome-cobalt base metal alloy, however, Titanium alloy showed no ambient exposure effects. Ambient exposure following aluminum oxide airborne particle abrasion with steam cleaning resulted in a significant decrease (p&lt;0.001) in surface free energy for all alloys investigated. </p><p> Conclusions: Within the limitations of this study, it was found that aluminum oxide airborne particle abrasion, with and without subsequent steam cleaning, significantly increased the surface free energy of the dental alloys investigated. Steam cleaning following aluminum oxide airborne particle abrasion significantly reduced the surface free energy gain that the high noble alloys experienced with aluminum oxide airborne particle abrasion alone. And finally, exposure to ambient air following aluminum oxide airborne particle abrasion with and without subsequent steam cleaning resulted in a significant decrease in surface free energy for most alloys investigated.</p>

Doctor of Philosophy / The commercial introduction of glass infiltrated slip cast ceramic technology as a core dental ceramic for crowns and bridges began in 1990. The system known as Inceram® provided a metal free ceramic core with a flexural strength that was reported to be between 400 and 600 MPa. The first aim of this study was to investigate in vitro fractures for this type of crown that occurred from high localized occlusal loading. The second aim was to propose suitable guidelines for the construction of crowns that are more crack resistant when loaded by a spherical object such as an opposinc cusp. The review of the literature identified Young’s modulus (E) as an important aspect for the behaviour of a brittle solid when it is exposed to load. Young’s modulus is involved in the total energy of the solid, its free surface energy, its toughness, parameters involved in contact areas, stresses from indenters on those contact areas and at the interface between two materials with different moduli. This mismatch was to become more important when Finite Element Analysis was applied to the test results. A second physical property that has importance in bilaminar minerals is Poisson’s ratio. Less important than Young’s modulus, Poisson’s ratio still provides some of the answers to crack propagation at an interface, highlighted by the description of Dundurs parameters (Mencik 1996). The use of Weibull statistics provided information concerning reliability for different core to veneer thickness ratios in the experimental models and crown designs. The first experimental part was to establish a crown model suitable for investigation. The porcelain jacked crown restoration for an upper incisor was chosen because it provided the best opportunity to vary the construction parameters of the crown without sacrificing the aesthetics. The results from this initial in vitro study established thickness ranges for the standard design of these crowns, the loads that could be expected and the two types of fracture patterns that might occur when the bilaminar system is loaded via a hard steel ball indenter in the middle of the palatal surface. The data from chapter three were then compared with two basic bilaminar and monolithic disc designs to establish the relevance of the dimensions of the ISO standard test specimen design for flexural strength. The results of this chapter confirmed that the loads were in the same range for the bilaminate discs, and that the flexural strengths for the two component parts were in agreement with other known results. The use of Finite Element Analysis (FEA) was employed to provide an additional method for testing the model to establish areas when principal stresses might lie and how they were distributed. It was found that the ISO flexural strength test was not ideal for testing bilaminates because it did not account for the large mismatch in Young’s modulus between the two component materials. The FEA revealed an unexpected increase in tensile stress on the bottom surface of the In-Ceram when it was the bottom layer in the bilaminate. The FEA did confirm the difference between a flat punch and a ball indenter for stress intensities around the contact area with the ball indenter producing higher stresses for a given load…

Doctor of Philosophy / The commercial introduction of glass infiltrated slip cast ceramic technology as a core dental ceramic for crowns and bridges began in 1990. The system known as Inceram® provided a metal free ceramic core with a flexural strength that was reported to be between 400 and 600 MPa. The first aim of this study was to investigate in vitro fractures for this type of crown that occurred from high localized occlusal loading. The second aim was to propose suitable guidelines for the construction of crowns that are more crack resistant when loaded by a spherical object such as an opposinc cusp. The review of the literature identified Young’s modulus (E) as an important aspect for the behaviour of a brittle solid when it is exposed to load. Young’s modulus is involved in the total energy of the solid, its free surface energy, its toughness, parameters involved in contact areas, stresses from indenters on those contact areas and at the interface between two materials with different moduli. This mismatch was to become more important when Finite Element Analysis was applied to the test results. A second physical property that has importance in bilaminar minerals is Poisson’s ratio. Less important than Young’s modulus, Poisson’s ratio still provides some of the answers to crack propagation at an interface, highlighted by the description of Dundurs parameters (Mencik 1996). The use of Weibull statistics provided information concerning reliability for different core to veneer thickness ratios in the experimental models and crown designs. The first experimental part was to establish a crown model suitable for investigation. The porcelain jacked crown restoration for an upper incisor was chosen because it provided the best opportunity to vary the construction parameters of the crown without sacrificing the aesthetics. The results from this initial in vitro study established thickness ranges for the standard design of these crowns, the loads that could be expected and the two types of fracture patterns that might occur when the bilaminar system is loaded via a hard steel ball indenter in the middle of the palatal surface. The data from chapter three were then compared with two basic bilaminar and monolithic disc designs to establish the relevance of the dimensions of the ISO standard test specimen design for flexural strength. The results of this chapter confirmed that the loads were in the same range for the bilaminate discs, and that the flexural strengths for the two component parts were in agreement with other known results. The use of Finite Element Analysis (FEA) was employed to provide an additional method for testing the model to establish areas when principal stresses might lie and how they were distributed. It was found that the ISO flexural strength test was not ideal for testing bilaminates because it did not account for the large mismatch in Young’s modulus between the two component materials. The FEA revealed an unexpected increase in tensile stress on the bottom surface of the In-Ceram when it was the bottom layer in the bilaminate. The FEA did confirm the difference between a flat punch and a ball indenter for stress intensities around the contact area with the ball indenter producing higher stresses for a given load…