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Week 5 Intro to Restorative Dental Materials Mechanical and Physical Properties Lecture 1 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS Learning Objectives • Describe and define the various terms used to measure the physical and mechanical properties of dental materials. • Understan...

Week 5 Intro to Restorative Dental Materials Mechanical and Physical Properties Lecture 1 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS Learning Objectives • Describe and define the various terms used to measure the physical and mechanical properties of dental materials. • Understand the concept of stress and strain. • Given a stress-strain diagram, identify the following: elastic modulus, proportional limit, elastic limit, yield stress, ultimate strength, fracture strength, ductility, resilience and toughness. • Relate the physical and mechanical properties of materials to their use in dentistry and explain their clinical significance. https://splan.in/1-identifying-and-assessing-the-idea/ Content • Mechanical Properties • Force • Occlusal Force • Forces on Restorations • Stress • Strain • Stress-Strain Curve • Proportional Limit • Yield Strength • Ultimate Strength • Fracture Strength • Strain Hardening • Necking • Elastic Modulus • Ductility • Resilience • Toughness https://creativemarket.com/introwiz1/4545293-Restorative-Dentistry-Icons Mechanical Properties • Oral cavity is a hostile environment with fluctuations in : • pH • Salivary flow • Mechanical loading • Temperature • Look at several properties, conduct standardized lab and clinical tests • Success of restoration depends on • Physical qualities of restoration • Qualities of supporting tissues https://smart.servier.com/smart_image/oral-cavity/ Week 5 Intro to Restorative Dental Materials Mechanical and Physical Properties Lecture 3 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS Learning Objectives • Demonstrate a fundamental understanding of the principles of abrasion, finishing and polishing • Define and describe the terms abrasion, finishing, polishing and explain how they differ • Be familiar with various types of abrasives, prophylaxis, polishing and dentifrices. • Summarize why tooth structures and restorations are polished and the factors which influence the rate and efficiency of abrasion. • Have a clear understanding of how the factors of abrasion, polishing and prophylaxis are used in dentistry and affect patient care. https://splan.in/1-identifying-and-assessing-the-idea/ Content • Finishing and Polishing • Types of Abrasives • Factors Affecting Finishing • The Polishing Process • Prophylaxis paste • Dentifrices https://creativemarket.com/introwiz1/4545293Restorative-Dentistry-Icons Finishing and Polishing • Finish and polish • Restorations • Intraoral appliances • Tooth structures • Removal excess material, smooth roughened surfaces • Improve aesthetics • Minimize trauma to hard and soft tissues • Improve tissue health • Increase longevity of restorative material https://www.youtube.com/watch?v=BzJtk5m5ftY https://j-ips.org/article.asp?issn=09724052;year=2007;volume=7;issue=2;spage=95;epage=101;aulast=Srinivasan;type=3 https://www.intensiv.ch/caso-clinico/final-polishing-of-composite-restoration-with-intensiv-uniglosspaste-simonagiani-varese-italy/ Finishing and Polishing • Cleaning – use agents that do not contain abrasive particles • The surface if not altered or abraded • Finishing and Polishing – use abrading agents that are harder than the surface being abraded/polished • Microscopically alter the tooth/restoration surface • Selection varies depending on surface and material • Select an agent that will not cause detrimental effects • Non-smooth surfaces • Cause patient irritation • Gingival irritation and inflammation • Poor appearance, not aesthetically pleasing • Food debris and plaque trap • Unhygienic http://topnotchdentalclinic.com/blog/what-is-air-polishing-how-is-it-different-from-regular-professional-cleaning/ Finishing and Polishing • Abrasion: wearing away of a surface by rubbing, cutting or scraping • Abrasive: the object that does the abrading • Finishing: contouring to remove excess material and produce a smooth surface • Final shape and contour • Make a restoration acceptable to fit occlusion and contour • Remove material by abrasion • Polishing: final removal of material results in a smooth, highly reflective surface that doesn’t contain scratches • Follows finishing • Polished surface most resembles natural oral cavity surfaces • Minimal removal of material, no further change in contour https://www.raymondsheridandds.com/keep-your-smile-healthy-and-sparkly/ Types of Abrasives • Diamonds • Made of C • Hardest substance – does not wear down or lose sharpness easily • Natural or synthetic chips • Bonded to metal shank for use in handpiece • Mixed with glycerin + water to make a polishing paste • Used with water to prevent heat build up or debris clogging • Carbide • Si carbide, B carbide • Pressed onto discs or wheels • Tungsten (W) carbide • Burs for highspeed handpieces to cut tooth structure https://blog.dentalsky.com/a-guide-to-burs/ Types of Abrasives • Emery (aka Corundum) • Oxides of Al • Looks like sand • Can be bonded to paper strips or discs • Aluminum Oxide (Al2O3) • Very abrasive, replaced Emery • Can be bonded to paper strips or discs • Al2O3 + diamond ingredients in polishing paste for restorations – acrylics and composites • Cuttle (SiO2) • Fine grade of quartz • Can be bonded to paper strips or discs https://pocketdentistry.com/polishing-materials-and-abrasion/ Types of Abrasives • Tin Oxide (SnO2) • Powder or paste • Mixed with water, glycerin or alcohol • Used to polish metallic restorations (amalgams) and enamel • Garnet • Contains silicates of Mn, Mg, Fe, Co, Al • Used to polish acrylic appliances, amalgams and composites • Pumice • Glass rich in SiO2 • Used to polish acrylic appliances, amalgams and enamel https://www.whipmix.com/products/pumice-preppies-unit-dose-flour-of-pumice-paste / Factors Affecting Finishing • Hardness • Abrasive particles must be harder than the surface being abraded • Moh scale – ranks materials in terms of being scratched • Shape • An irregular object digs into the surface • Cutting efficiency is enhanced by having sharp edges • Repeated use dulls instrument, clogs with debris https://pocketdentistry.com/polishing-materials-and-abrasion/ Factors Affecting Finishing • Size • Roughness of finished surface is proportional to size of abrasive particles • Larger particles cut deeper grooves into surface, abrade more rapidly • Smaller particle abrasive efficiency increases with force • Not always desirable • Grit – size of the abrasive particles • Measured in micrometers (µm) • Gradual reduction in size of abrasive particles • Scratches from previous abrasive are replaced by smaller and shallower scratches https://www.kerrdental.com/en-fi/dental-restoration-products/optidisc-finishing-and-polishing https://debargold.com/dental-clinic/ https://johnsonpromident.com/diamond-burs/ Factors Affecting Finishing • Pressure • Greater force, more rapid removal of material, deep cuts into surface • May increase temperature which can lead to distortion or physical changes • Concern of over abrading around restoration margins • Over contouring affects occlusion and margin adaptation • Speed • Speed affects cutting efficiency • Faster speed, faster cutting • Higher speeds generate heat, may cause over cutting • Lubrication • Cooling effect - carries heat away from surface • Carries away debris • May obscure cutting surface https://misieco.com/product/dental-high-speed-with-led-light/ The Polishing Process 1. Decrease adhesion • Prevent plaque adhesion • Stains and calculus less likely to adhere 2. Feel of a smooth surface • Unsmooth surface can irritate patient 3. Increase aesthetics • Want a shiny and smooth filling 4. Corrosion resistance • Reduce formation of tarnish and corrosion of metal restorations https://www.dentist-manila.com/glossary/oral-prophylaxis/ The Polishing Process • Remove surface stains • Do not damage or roughen underlying structure • Moderately abrasive materials Ex. Pumice • Aggressive abrasion may cause damage • Avoid excessive polishing • May alter anatomy • Leave roughness • Makes fine and shallow scratches • High polish and low abrasion https://www.dentist-manila.com/glossary/oral-prophylaxis/ Dentifrices • • • • • Effective abrasive Promote oral hygiene Toothbrush bristles not very abrasive Abrasive agent needed for pellicle and stains Contain • Water • Humectant glycerin – prevents drying out • Detergent sodium lauryl sulphate – foaming • Binders alginates, synthetic cellulose – prevents solid and liquid from separating • Coloring and flavoring peppermint, spearmint, wintergreen https://www.healthline.com/health/dental-and-oral-health/how-to-brush-your-teeth • Therapeutic fluoride – prevents dental caries https://www.schoolmum.net/parenting/parenting-tips/3-great-ideas-make-brushing-teeth-fun-kids/ Dentifrices • 3 major abrasives 1. Phosphates • Dicalcium phosphate dihydrate (DCPD) and calcium pyrophosphate (CalPyro) • Looking whiter and feeling clean 2. Carbonates • Fresh smelling and abrasive properties • Sodium bicarbonate (baking soda) • Calcium carbonate (chalk) 3. Silicas • Chemically inactive • Available in difference sizes and characteristics • Can mechanically clean teeth • Can thicken toothpaste https://www.stlawrencedentistry.com/blog/dental-tips/10-most-trusted-toothpaste-brands/ References • Reynolds EC. Contents of toothpaste - safety implications. Aust Prescr 1994;17:49-51. • McCabe JF, Walls A. Applied Dental Materials. 9th ed. / John F. McCabe, Angus W.G. Walls. Blackwell Pub.; 2008. • Darvell BW. Materials Science for Dentistry . 8th ed. B.W. Darvell; 2006. • Dental materials [Internet]. Pocket Dentistry. 2021 [cited 10 August 2021]. Available from: https://pocketdentistry.com/14-dental-materials/ • Gladwin M, Bagby M. Clinical Aspects of Dental Materials : Theory, Practice, and Cases . 3rd ed. Wolters Kluwer Health/Lippincott Williams & Wilkins; 2009. • Jack L. Ferracane (1995). Materials in dentistry principles and applications. Philadelphia J.B. Lippincott Week 5 Introduction to Restorative Dental Materials Mechanical and Physical Properties Lecture 2 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS Learning Objectives • Describe and define the various terms used to measure the properties of dental materials including compressive strength, flexural strength and fatigue strength • Understand the concepts of hardness, fatigue, creep and fracture toughness • Define the coefficient of thermal expansion and give examples of their importance to clinical dentistry. • Be familiar with the various hardness tests used to evaluate dental materials • Relate the surface mechanical properties of materials to their use in dentistry and explain their clinical significance. https://splan.in/1-identifying-and-assessing-the-idea/ Content • Compressive Strength • Flexural Strength • Fatigue Strength • Fracture Toughness • Creep • Coefficient of Thermal Expansion • Hardness • Brinell Hardness Test • Knoop Hardness Test • Vickers Hardness Test https://creativemarket.com/introwiz1/4545293-Restorative-Dentistry-Icons Part 1 • Compressive Strength • Flexural Strength • Fatigue Strength • Fracture Toughness • Creep • Coefficient of Thermal Expansion What Do We Already Know • The outstanding clinic performance of amalgam restorations is due to a) Compressive strength b) Tensile strength c) Corrosion d) Creep https://www.adansw.com.au/CPD/Courses/Complex-Amalgam-Restorations-and-Update-on-Amalgam?eventid=C426 http://edelweisspublications.com/keyword/30/127/Dental-Materials What Do We Already Know Your patient has the same things for lunch every day – hot homemade soup and drinks a cola with ice. She is complaining of tooth sensitivity and when you look at the 36 occlusal composite resin restoration you notice signs of secondary caries. Why has this occurred? https://www.adansw.com.au/CPD/Courses/Complex-Amalgam-Restorations-and-Update-on-Amalgam?eventid=C426 http://edelweisspublications.com/keyword/30/127/Dental-Materials Compressive Strength • Complex stresses result • Compressive stress (SC) • Shear stress (SS) • Tensile stress (ST) • Used for comparing brittle materials and weak in tension https://pocketdentistry.com/5-testing-of-dental-materials-and-biomechanics/ Flexure Strength • Determined strength of material and amount of distortion expected • Single cantilever Flexure Test – material is fixed at one end, force applied at a fixed distance from the fixed end • Dual Cantilever Flexure Test – material is fixed at both ends, lead is placed in the centre • Three-point Flexure Test – material is supported and a load is applied in the middle • Four-point Flexure Test – material is supported and 2 loading elements are applied • Flexure strength: the maximum stress measured while testing Flexure Strength https://pocketdentistry.com/mechanical-properties-of-dental-materials-2/#f0015 Fatigue Strength • Fatigue: progressive fracture under repeated loading • Fatigue test • Subject a material to stresses below the yield strength until facture occurs • Fatigue Strength: stress at which a material fails under repeated loading • S-N Curve – stress or strain (S) to number of loading cycles (N) • Endurance Limit: a stress that can be loaded an infinite number of times without failing • Dental materials subjected to many moderate stresses • Design is important • Avoid areas of stress concentration, surface defects, notches • Role of environment • Ex. mastication cycles https://pocketdentistry.com/5-testing-of-dental-materials-and-biomechanics/ Fatigue Strength https://www.sciencedirect.com/science/article/abs/pii/S1751616118307562 • The _____ of a material can be defined as its ability to resist a fluctuating or repetitive stress. Intermittent Quiz a) Compressive strength b) Fatigue strength c) Impact strength d) Tensile strength https://www.managers.org.uk/knowledge-and-insights/listicle/10-tips-for-getting-your-team-to-think-more-creatively/ Fracture Toughness • Fracture Toughness: the energy required to resist the propagation of an existing crack or flaw • High fracture toughness indicates a good resistance to cracking • Dental porcelain – low fracture toughness • Metals – high fracture toughness • Differs from Toughness • Toughness – the ability of a material to absorb energy so that a fracture is delayed • Fracture Toughness – ability of a material with cracks to resist fracture by absorbing energy Creep • Creep: time-dependent deformation of an object subjected to a constant stress • Small change in shape • Observed over a long period of time • Most materials undergo creep at temperatures are close to melting point • Ceramics and most metals do not undergo creep • Amalgam and composite resin restorations creep • Seen as ditching and marginal breakdown https://www.brisbanesmileboutique.com.au/news/amalgam-fillings Coefficient of Thermal Expansion • Coefficient of Thermal Expansion (∝): fractional increase in length of a material for each degree oC increase in temperature • Thermal expansion of restoration and tooth may not match • Differential expansion • Leakage of oral fluids between restoration and tooth • Can irritate dental pulp and cause recurrent decay https://www.researchgate.net/publication/41163257_Dental_Glass_Ionomer_Cements_as_Permanent_Filling_Materials_-_Properties_Limitations_and_Future_Trends/figures?lo=1 https://pocketdentistry.com/18-biomaterials/ What Do We Know Now • The outstanding clinic performance of amalgam restorations is due to a) Compressive strength b) Tensile strength c) Corrosion d) Creep https://www.adansw.com.au/CPD/Courses/Complex-Amalgam-Restorations-and-Update-on-Amalgam?eventid=C426 http://edelweisspublications.com/keyword/30/127/Dental-Materials What Do We Know Now Your patient has the same things for lunch every day – hot homemade soup and drinks a cola with ice. She is complaining of tooth sensitivity and when you look at the 36 occlusal composite resin restoration you notice signs of secondary caries. Why has this occurred? https://www.adansw.com.au/CPD/Courses/Complex-Amalgam-Restorations-and-Update-on-Amalgam?eventid=C426 http://edelweisspublications.com/keyword/30/127/Dental-Materials Part 2 • Hardness • Brinell Hardness Test • Knoop Hardness Test • Vickers Hardness Test What Do We Already Know • Your patient has a very heavy bite and has ben identified to have Bruxism • The treatment plan indicates the need for dental crowns on the posterior teeth • Your patient wants an aesthetic material and is asking about porcelain fused to meta (PFM) crowns and zirconia crowns • Based on just hardness, which type of crown would be better suited for your patient and why? http://edelweisspublications.com/keyword/30/127/Dental-Materials https://www.shutterstock.com/search/metal+ceramic+crown Hardness • Hardness: resistance to permanent surface indentation • Resistance to plastic deformation • Force per unit area of indentation • Important in dentistry • Ease of cutting materials • Finishing and polishing • Resistance to scratching while in use • Various tests to measure hardness • Similar – small object pushing into surface of material • Differ – type of material to be tested, the range of hardness, degree of localization https://www.tecquipment.com/materials-testing-and-properties/hardness-testing-industrial Hardness • Hardness Test • Fixed load applied with a standardized symmetrical indenter • Dimensions of the indentation measured • Inversely proportional to the material’s resistance to penetration • Low values of hardness = softer material • Higher values of hardness = harder material • Harder materials • Difficult to scratch • Difficult to polish • More resistant to wear https://www.tecquipment.com/materials-testing-and-properties/hardness-testing-industrial Brinell Hardness Test • • • • • • • • Macrohardness test Indenter: Steel or tungsten carbide ball 1.6mm diameter Load: 35N Indenter remains in contact with test material for 30 seconds Indentation diameter measured Small indentation, harder the material, larger test value Advantage: Used for determining the average hardness values Disadvantage: poor at determining localized values https://www.gordonengland.co.uk/hardness/brinell.htm Knoop Hardness Test • Microhardness Test • Indenter: Diamond in the shape of a pyramid, up to a depth of 19mm • Load: Less than 35N • Applied load is varied • Indentation varies based on the applied load and the nature of the test material • Advantage: range of hardness can be tested • Disadvantage: test surfaces need to be flat and highly polished https://niom.no/hardness-testing-of-dental-materials-and-tooth-substance/ Vickers Hardness Test • • • • • • Microhardness Test Indenter: Square-based diamond, up to a depth of 19mm Load: Definite load, ranges from 9.8N Load is applied for 10-15 seconds Square indentation produced, diagonals are measured Advantage: suitable for brittle materials • Used for testing small specimen • Can be used for soft and hard materials because the test load can be varied https://www.gordonengland.co.uk/hardness/vickers.htm • What is the shape of the indenter used for a Vickers hardness test? Intermittent Quiz a) Steel ball b) Diamond ball c) Diamond square pyramid d) Tungsten carbide ball https://www.managers.org.uk/knowledge-and-insights/listicle/10-tips-for-getting-your-team-to-think-more-creatively/ What Do We Know Now • Your patient has a very heavy bite and has ben identified to have Bruxism • The treatment plan indicates the need for dental crowns on the posterior teeth • Your patient wants an aesthetic material and is asking about porcelain fused to meta (PFM) crowns and zirconia crowns • Based on just hardness, which type of crown would be better suited for your patient and why? http://edelweisspublications.com/keyword/30/127/Dental-Materials https://www.shutterstock.com/search/metal+ceramic+crown References • Sakaguchi RL, Powers JM. Craig’s Restorative Dental Materials. Elsevier; 2011. • McCabe JF, Walls A. Applied Dental Materials. 9th ed. / John F. McCabe, Angus W.G. Walls. Blackwell Pub.; 2008. • Darvell BW. Materials Science for Dentistry . 8th ed. B.W. Darvell; 2006. • Dental materials [Internet]. Pocket Dentistry. 2021 [cited 10 August 2021]. Available from: https://pocketdentistry.com/14-dental-materials/ • Gladwin M, Bagby M. Clinical Aspects of Dental Materials : Theory, Practice, and Cases . 3rd ed. Wolters Kluwer Health/Lippincott Williams & Wilkins; 2009. • Jack L. Ferracane (1995). Materials in dentistry principles and applications. Philadelphia J.B. Lippincott Force • Force: one body interacting with another generates force • Applied through contact of bodies or at a distance • 3 defining characteristics: • Point of application • Magnitude – lbs, Kg, N • Line of action • System of Units (SI) – Newtons • 1 pound of force = 4.4 Newtons https://leverageedu.com/blog/pu/force-and-laws-of-motion/ https://thefactfactor.com/facts/pure_science/physics/forces/4200/ Occlusal Forces • Occlusal forces • Range: 200-3500N • Highest in posterior region at mandibular hinge axis • Decrease from molars to incisors • 1st and 2nd molars: 400-800 N • Premolars: 300 N • Canine: 200 N • Incisors: 150 N • Increase in force as children grow – average of 22N/year https://www.williamsburgdentalllc.com/blog/2015/11/4-reasons-youre-clenching-teeth-stop/ Forces on Restorations • Occlusal forces with dental prostheses is lower than natural dentition • Removable partial dentures: 65-235 N • Complete dentures: Molars/Premolars 100N and Incisors 40N • Age and gender variations • Facial form and muscle definition are good predictors of occlusal force • High mandibular angle = Lower occlusal force • Lower mandibular angle = higher occlusal force • When designing and selecting dental materials consider • Location • Opposing dentition • Force generating capacity of patient • Look at success of other restorations in the patient’s mouth https://www.lakeviewdentalfl.com/post-36-my-dentures-are-loose/ Stress • Stress (S or σ): is the force per unit cross-sectional area that is acting on a material. • The applied force is distributed over the area of the body • Stress = F/A • F: applied force • A: cross-sectional area • SI Unit: Pascal = N/m2 Stress https://pocketdentistry.com/4-fundamentals-of-materials-science/ Strain • Strain (ɛ): is the fractional change in the dimensions caused by the force • Strain (ɛ) = Change in length (∆L = L – Lo) Original length (Lo) • Dimensionless • Recoverable – material returns to original length after the removal of applied force • Non-recoverable – material remains deformed after removal of the applied force • Time-dependent recovery Stress-Strain Curve Proportional Limit • Proportional Limit: the highest point on the stress- strain curve where stress is linearly proportional to strain (Point A) • Below the proportional limit • No permanent deformation • When force is removed, the object returns to original dimensions Stress-Strain Curve Proportional Limit • Proportional Limit: the highest stress point on the stress- strain curve where stress is linearly proportional to strain (Point A) • Below the proportional limit • No permanent deformation • When force is removed, the object returns to original dimensions • Elastic region: The region of the stress-strain curve before the proportional limit, reversible strain • Plastic Region: the region of the stress-strain curve beyond the proportional limit, irreversible strain • Elastic Limit: max stress a material can withstand without permanent deformation Stress-Strain Curve Yield Strength • Yield Strength: The stress beyond which a material is permanently deformed when a force is applied (Point B) • Used when the Proportional limit cannot be determined with accuracy • Permanent strain • Arbitrarily chosen at percent offset • Draw a line parallel to linear portion of stress-strain curve, point of intersection Stress-Strain Curve - Yield Strength • Yield Strength https://www.ozident.com/tag/amalgam/ https://dentistryandoralcare.wordpress.com/2017/03/25/evaluation-of-fatigue-resistance-of-acetal-resin-andcobalt-chromium-removable-partial-denture-clasps-an-in-vitro-study-part-1/ Stress Stress-Strain Curve Ultimate Strength • Ultimate Strength • The limit of applied force a material can withstand • Maximum stress • Characterizes the strength of a material Ultimate tensile strength/stress Ultimate compressive strength/stress • Maximum load in tension (or compression) Cross-sectional area of material • For safety the ultimate strength should not be reached during normal function Stress Stress-Strain Curve Fracture Strength • Fracture Strength • The stress at which a brittle material fractures • May not occur at max stress • Ultimate and Fracture strengths similar for dental alloys and ceramics Stress Stress-Strain Curve Strain Hardening • Strain Hardening (Cold Working, Work Hardening) • Between Yield Strength (B) and Ultimate Strength (C) • Hardness and strength increase at the area of deformation • Plastic deformation becomes more difficult at the grain boundary Stress Stress-Strain Curve Necking • Necking • For Tensile forces • Between Ultimate Strength (C) and Facture (D) • Reduction in cross-sectional area • Material can no longer withstand the maximum stress, strain increases • Leads to fracture Stress-Strain Curve – Elastic Modulus • Elastic Modulus (aka Modulus of Elasticity, Young’s Modulus) (E) • A measure of the rigidity of a material, • defined by the ratio of stress to strain (below elastic limit) • Hooke’s Law (Law of Elasticity) • The displacement or size of the deformation is directly proportional to the deforming force or load • the object returns to its original shape and size upon removal of the load https://www.bio-meca.com/en/glomeca-3-hookes-law/ Stress-Strain Curve – Elastic Modulus • Elastic Modulus (aka Modulus of Elasticity, Young’s Modulus) (E) • Dependent on attractive forces of material • Slope of stress-strain curve in the elastic portion • Steep slope = high E = rigid material • Shallow slope = low E = flexible material https://www.bio-meca.com/en/glomeca-3-hookes-law/ Stress-Strain Curve – Elastic Modulus https://pocketdentistry.com/mechanical-properties-of-dental-materials-2/ https://www.drummoynedentalpractice.com.au/news/abfraction https://friscokidsdds.com/teenage-academic-stress-and-teeth-grinding/ Stress-Strain Curve – Ductility • Ductility: ability to be drawn and shaped into wires by tension • Permanent deformation • A reduction in area of the material + elongation = ductile metal or alloy • Metals are ductile, ceramics are brittle Stress-Strain Curve – Resilience • Resilience: the resistance of a material to permanent deformation • Areas under the stress-strain curve to the elastic limit https://www.apsed.in/toughness-and-resilience https://www.wise-geek.com/what-are-orthodontic-wires.htm Stress-Strain Curve – Toughness • Toughness: the amount of energy required to stress a material to the point of fracture • Total area under the stress-strain curve • Elastic + plastic • Tough material – able to absorb large quantities of energy • Brittle material – little plastic deformation before fracture • Facture Toughness (KIc): the ability to plastically deform when a fracture is present https://www.apsed.in/toughness-and-resilience Stress-Strain Curve – Toughness https://www.dentistrytoday.com/restorative/9775-efficient-and-economical-composite-resin-placement-a-fasttrack-technique-for-posterior-restorations https://www.juniordentist.com/zirconia-crowns-advantages-indications-cost.html Summary • Stress (σ )= F/A • Strain (ε) = ∆L/Lo • Elastic behaviour: the material will return to its original shape when the load is removed. • Plastic behaviour - the material will permanently deform • Proportional Limit - the maximum point of stress when stress is directly proportional to strain • Elastic Limit – the maximum point of stress when the material will return to its original shape when the applied load is removed • Yield Strength – the material deforms permanently with no/little increase in the stress • Ultimate Strength - the maximum stress that a material can bear before it fails Summary • Elastic Modulus (E) = Stress (σ ) / Strain (ε) • Poisson’s Ratio (v) = ε lateral / ε longitudinal • Ductility – the material can easily deform without breaking under tensile stress (drawn into wires) • Malleability – the material can easily deform without breaking under compressive stress (hammered into sheets) • Resilience - the ability of the material to absorb energy within an elastic range • Toughness - the ability of the material to absorb energy within both the elastic and the plastic range Summary References • Powers JM, Ferracane J, Sakaguchi RL. Craig’s Restorative Dental Materials. Mosby; 2018. • McCabe JF (John F., Walls A. Applied Dental Materials. 9th ed. / John F. McCabe, Angus W.G. Walls. Blackwell Pub.; 2008. • 14 Dental materials [Internet]. Pocket Dentistry. 2021 [cited 10 August 2021]. Available from: https://pocketdentistry.com/14-dental-materials/ • Gladwin M, Bagby M. Clinical Aspects of Dental Materials : Theory, Practice, and Cases . 3rd ed. Wolters Kluwer Health/Lippincott Williams & Wilkins; 2009. • Sarode GS, Sarode SC. Abfraction: A review. J Oral Maxillofac Pathol. 2013;17(2):222-227. doi:10.4103/0973-029X.119788