2 Occlusal forces Average occlusal forces for fully dentate patients : 150 Newton in the anterior region to 500N in posterior regionMaximum occlusal forces: different reports in the literature up to 3500N.The occlusal forces for edentulous patients 15% of dentate patients.
4 Stress Stress: Internal resistance to applied external force. Force per unit area; a force exerted on one bodythat presses on, pulls on, pushes against, or tends to invest,compress another body; the deformation caused in a body by such a force;an internal force that resists an externally applied load orforce. It is normally defined in terms of mechanical stress, whichis the force divided by the perpendicular cross sectional area overwhich the force is applied.GPT 2005, J Prosthetic DentistryStress: Internal resistance to applied external force.Stress= Force/Area
13 B:Yield strength(YS)The stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain* YS indicates a degree of permanent deformation (usually 0.2%)YS indicates a functional failure!!!
14 Elastic modulusIs a measure of elasticity of the material: how stiff the material is in the elastic rangeElastic modulus= Stress/StrainThe slope of the curveABStress (Pa)StrainResilience
15 Poisson’s ratioRatio of lateral to axial strain within the elastic range
16 Ductility and malleability Ductility: The ability of a material to be plastically deformed.Malleability: The ability of a material to be hammered or rolled into thin sheets without fractureing.
18 C: Ultimate strength Tensile or Compressive. The Ultimate strength: The maximum that a material can withstand before failure (tension or compressive).it does give an indication of the needed thickness (cross section) of the restorations before failure.
19 D: fracture strengthThe stress at which the material fractures.
20 Toughness The resistance of a material to fracture So what does yellow area under curve represent?
21 Fracture toughnessThe amount of energy required for fracture.
22 Bond strength:the bond strength between two dental materials.Either tensile or shearFatigue bond strength?
23 Bending and torsionEndodontic files and reamers
24 Transverse strength Modulus of rupture or flexural strength 3- point bending test
25 Fatigue strength Fatigue: Progressive fracture under repeated loading The importance of endurance limit?Stress (Pa)StrainCyclesStress
26 Fluid behaviour and Viscosity Viscosity: the resistance of a fluid to flowViscosity= Shear stress/shear strain rate.
27 Viscous fluids The importance of thixotropic impression materials Shear stressNewtonianStress (Pa)StrainShear ratePseduplasticDilatantThe importance of thixotropic impression materials
28 Creep and stress relaxation Creep is the increase in strain in a material under constant pressure.Creep test is used for study of new amalgam materials
45 MetamerismWhen two colour samples match when viewed under one light source but not another.Any significance in dentistry?
46 FlouresenceThe emission of luminous energy by a material when a beam of light is shown on it.What impact does this have in anterior restorations.
47 Thermal properties Heat of fusion: melting or freezing heat. Coefficient of thermal expansion: of paramount importance in clinical dentistry, why???Glass transition temperature??? For non metallic structures; glasses and polymers