Properties of Dental Materials PDF 2024-25

Properties of DENTAL MATERIALS Dr Alex Cresswell-Boyes [email protected] Key Clinical question. If you see this icon a question related to the clinical aspect of the topic will be asked. Clinical consideration. If you see this icon some key clinical considerations to b...

Properties of DENTAL MATERIALS Dr Alex Cresswell-Boyes [email protected] Key Clinical question. If you see this icon a question related to the clinical aspect of the topic will be asked. Clinical consideration. If you see this icon some key clinical considerations to be made aware of regarding the topic. Materials question. If you see this icon a question related to the materials aspect of the topic will be asked. Learning Objectives ▪ Demonstrate a clear understanding of key terminology related to dental materials, including terms such as hardness, elasticity, and viscosity. ▪ Analyse and describe the physical properties of dental materials, including but not limited to hardness, density, thermal conductivity, and coefficient of thermal expansion. ▪ Assess and compare the mechanical properties of dental materials, such as strength, toughness, and fatigue resistance, and their relevance to clinical applications. ▪ Explain the optical characteristics of dental materials, including colour, translucency, and opacity, and their impact on aesthetics in restorative dentistry. ▪ Examine the chemical composition of dental materials and their interaction with oral environments, including corrosion, degradation, and chemical bonding. ▪ Apply acquired knowledge of dental material properties to make informed decisions in material selection for various clinical applications. Outline ▪ Mechanical properties. ▪ Physical properties. MCQs – Question 1 A dental material's ability to resist fracture under squeezing forces is known as: A. Tensile Strength B. Flexural Strength C. Compressive Strength D. Shear Strength E. Fatigue Resistance MCQs – Question 2 The capacity of a material to be stretched into a wire without breaking is referred to as: A. Malleability B. Ductility C. Brittleness D. Hardness E. Toughness MCQs – Question 3 Which property measures a material's resistance to the propagation of cracks, indicating its ability to absorb energy before fracturing? A. Hardness B. Elastic Modulus C. Fracture Toughness D. Yield Strength E. Creep MCQs – Question 4 Which property indicates a material's resistance to indentation or surface scratching? A. Hardness B. Toughness C. Elastic Modulus D. Flexibility E. Resilience MCQs – Question 5 A material's ability to withstand repeated cycles of stress without failing is referred to as: A. Fatigue Resistance B. Impact Strength C. Shear Strength D. Elastic Limit E. Malleability MCQs – Answers 1. C. Compressive Strength. Compressive strength is the maximum compressive stress a material can withstand without failure, crucial for materials bearing biting forces. 2. B. Ductility. Ductility describes a material's ability to undergo significant plastic deformation before rupture, allowing it to be drawn into wires. 3. C. Fracture Toughness. Fracture toughness assesses how well a material can resist crack growth, reflecting its capacity to absorb energy during fracture. 4. A. Hardness. Hardness measures how resistant a material is to localised plastic deformation, such as scratching or indentation. 5. A. Fatigue Resistance. Fatigue resistance is crucial for materials subjected to cyclic loading, preventing failure over time. Mechanical Properties ▪ The success of dental restorations depends heavily on the mechanical properties of the materials used. ▪ Understanding these properties ensures optimal performance and longevity. ▪ Mechanical properties dictate how materials respond to forces Photo: © Collins 2024 in the oral environment. ▪ Fundamental principles include stress, strain, elasticity, and strength. Stress & Strain ▪ Stress (σ): ▪ The internal force per unit area within a material that arises due to externally applied forces. ▪ Measured in Pascals (Pa) or megapascals (MPa). ▪ Think of it as the pressure pushing or pulling on something. ▪ Strain (ε): ▪ The deformation or change in dimension per unit original length resulting from applied stress. Photo: © Plastometrex 2020 ▪ A dimensionless quantity (ratio). ▪ Simply put, it's how much something What is the fundamental relationship between stretches or compresses under force. stress and strain? Stress causes strain; their relationship is characterised by material properties like elastic modulus. Elastic Modulus (Young's Modulus) ▪ Definition: ▪ A measure of a material's stiffness or rigidity. ▪ It is the ratio of stress (force per unit area) to strain (deformation) in the elastic region of the stress- strain curve. ▪ How bendy or stiff a material is. ▪ Measurement: ▪ Determined using a tensile or compressive test. ▪ Calculated from the slope of the linear portion of the stress-strain curve. ▪ Importance: ▪ Indicates how much a material will deform under load. ▪ Critical for matching the flexibility of restorative materials to that of tooth structures. Photo: © McGuinness-Hickey 2023 ▪ Clinical Significance: ▪ Materials with similar elastic moduli to tooth structure reduce stress at the interface. ▪ Prevents debonding and failure of restorations. Why is matching the elastic modulus of restorative materials to tooth structure important? It reduces stress at the restoration-tooth interface, preventing debonding and fractures. Compressive Strength ▪ Definition: ▪ The maximum compressive stress a material can withstand before failure. ▪ How much squeezing a material can handle before it gets crushed. ▪ Measurement: ▪ Conducted using a compressive strength test where a sample is compressed until it fractures. ▪ Importance: ▪ Essential for materials used in areas Photo: © SPI 2024 subject to high biting forces. ▪ Clinical Significance: ▪ Ensures that restorations can Why is compressive strength vital for withstand masticatory forces without posterior restorations? crushing or deforming. Because posterior teeth endure high biting forces; materials must resist crushing. Tensile Strength ▪ Definition: ▪ The maximum tensile stress a material can withstand while being stretched or pulled before necking. ▪ How much pulling a material can take before it snaps. ▪ Measurement: ▪ Determined using a tensile test where a sample is pulled until it breaks. ▪ Importance: ▪ Critical for materials that experience pulling forces. ▪ Clinical Significance: ▪ Important for bonding agents and Photo: © Velling 2020 materials used in situations where tensile forces are present. Flexural Strength (Bending Strength) ▪ Definition: ▪ The stress at which a material fractures in a flexure (bending) test. ▪ How much bending a material can withstand before breaking. ▪ Measurement: ▪ Measured using three-point or four- point bending tests. ▪ Importance: ▪ Reflects a material's ability to resist deformation under load in bending. ▪ Clinical Significance: Photo: © Rutland Plastics 2024 ▪ Relevant for bridges and dentures where materials span gaps and are subject to bending forces. Fracture Toughness ▪ Definition: ▪ The ability of a material containing a crack to resist fracture. ▪ How hard it is to make a crack in a material grow and cause it to break. ▪ Measurement: ▪ Determined using fracture mechanics tests like the single-edge notched beam test. ▪ Importance: ▪ Indicates resistance to crack propagation. ▪ Clinical Significance: Photo: © Williams 2019 ▪ Materials with high fracture toughness reduce the risk of catastrophic failure in restorations. Why is fracture toughness critical in materials with existing flaws? It determines the material's ability to resist catastrophic failure from cracks. Hardness ▪ Definition: ▪ The resistance of a material to indentation or scratching. ▪ How resistant a material is to being scratched or dented. ▪ Measurement: ▪ Measured using tests like Vickers, Knoop, or Brinell hardness tests. ▪ Importance: ▪ Correlates with wear resistance. ▪ Clinical Significance: Photo: © Anton Paar 2024 ▪ Harder materials resist abrasion and wear but may cause wear on Should materials with high hardness opposing teeth. always be chosen for restorations? Not necessarily; balance hardness to avoid wear on opposing teeth. Ductility ▪ Definition: ▪ The ability of a material to undergo significant plastic deformation before rupture. ▪ How much a material can be stretched into a wire without breaking. ▪ Measurement: ▪ Quantified by the percentage elongation or area reduction in a tensile test. ▪ Importance: ▪ Indicates how a material can be shaped or drawn without breaking. ▪ Clinical Significance: Photo: © Gabrian 2020 ▪ Ductile materials are useful for intricate restorations that require shaping. Why is ductility important in orthodontic wires? Allows wires to be shaped and adjusted without breaking. Fatigue Resistance ▪ Definition: ▪ The ability of a material to withstand repeated cycles of stress without failure. ▪ How well a material withstands repeated use without breaking. ▪ Measurement: ▪ Determined through fatigue testing where samples are subjected to cyclic loading. ▪ Importance: Photo: © ARCCA 2016 ▪ Materials may fail at stresses lower than their tensile strength when subjected to repeated loading. ▪ Clinical Significance: ▪ Critical for endodontic files and What factors affect a material's fatigue orthodontic wires that undergo cyclic resistance? loading. Material defects, microstructure, and environmental conditions. Creep ▪ Definition: ▪ The time-dependent plastic deformation of a material under constant load or stress. ▪ Slow, continuous deformation of a material under constant stress. ▪ Measurement: ▪ Evaluated by applying a constant stress at a constant temperature and measuring deformation over time. Photo: © Torres et al. 2019 ▪ Importance: ▪ Can lead to dimensional changes in restorations over time. ▪ Clinical Significance: ▪ Excessive creep can cause restorations to protrude or margins to break down. What properties of a material influence its creep behaviour? Temperature, applied stress, and material composition. Wear Resistance ▪ Definition: ▪ The ability to resist loss of material due to mechanical action such as friction or abrasion. ▪ How well a material resists being worn away by friction. ▪ Measurement: ▪ Assessed using wear testing machines that simulate mastication. ▪ Importance: ▪ Affects the longevity and functionality of restorations. ▪ Clinical Significance: Photo: © Arc1977 2011 ▪ Materials must balance wear resistance to avoid excessive wear of opposing teeth while maintaining durability. Should materials with very high wear resistance always be used? Not always; overly hard materials may wear opposing teeth. Brittleness ▪ Definition: ▪ The tendency of a material to fracture without significant plastic deformation. ▪ How easily a material breaks without bending much. ▪ Measurement: ▪ Assessed qualitatively; brittle materials have low toughness. ▪ Importance: ▪ Brittle materials fail suddenly, which can be catastrophic in clinical applications. ▪ Clinical Significance: ▪ Design considerations must minimise stress concentrators in restorations Photo: © Glossary Live 2024 made of brittle materials. Viscoelasticity ▪ Definition: ▪ Property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. ▪ When a material behaves both like a thick fluid and a stretchy solid. ▪ Measurement: ▪ Assessed using dynamic mechanical analysis (DMA). ▪ Importance: Photo: © Jones 2024 ▪ Viscoelastic materials have time- dependent strain. ▪ Clinical Significance: ▪ Affects the accuracy of impressions and the timing of their use. How does viscoelasticity affect impression accuracy? Time-dependent deformation can distort impressions if not handled properly.  Comparison Property Definition Importance Examples Indicates how much a material will deform Enamel (high modulus), Dentine (lower Elastic Modulus Measure of a material's stiffness or rigidity under load modulus) Maximum stress a material can withstand Essential for materials in areas subject to Compressive Strength Dental amalgam, Composite resins under compression biting forces Maximum stress a material can withstand Metals (high tensile strength), Ceramics (low Tensile Strength Important for materials under tensile loads when stretched tensile strength) Stress at which a material fractures in Reflects ability to resist deformation under Flexural Strength Ceramics, Fiber-reinforced composites bending bending Indicates resistance to fracture in presence of Zirconia ceramics (high toughness), Glass Fracture Toughness Ability to resist crack propagation flaws ceramics (lower toughness) Enamel (high hardness), Dentine (lower Hardness Resistance to indentation or scratching Correlates with wear resistance hardness) Ability to be stretched into a wire without Influences material manipulation during Gold alloys (high ductility), Ceramics (not Ductility breaking fabrication ductile) Ability to withstand repeated loading without Fatigue Resistance Prevents failure under repeated stress Nickel-titanium alloys failure Time-dependent permanent deformation Creep Can lead to dimensional changes over time Dental amalgam under constant stress Ability to resist material loss due to Affects longevity and functionality of Ceramics (high wear resistance), Some Wear Resistance mechanical action restorations polymers (lower) Tendency to fracture without significant Brittleness Brittle materials fail suddenly Ceramics, Glass ionomer cements deformation Exhibiting both viscous and elastic behavior Viscoelasticity Affects deformation over time and recovery Alginate impression materials when deformed Physical Properties ▪ Physical properties influence how materials interact with their environment. ▪ Understanding these properties is crucial for predicting material behaviour in the oral cavity. ▪ Properties include thermal conductivity, thermal expansion, optical properties, and more. Thermal Conductivity ▪ Definition: ▪ The ability of a material to conduct heat. ▪ Importance: ▪ Influences the transfer of temperature changes to tooth structures. ▪ Clinical Significance: Photo: © KYYOCERA 2024 ▪ Materials with high thermal conductivity can cause thermal sensitivity. ▪ Insulating materials or liners may Why is thermal conductivity important in be needed under metal restorative materials near pulp tissue? restorations. High thermal conductivity can transmit temperature changes to the pulp, causing sensitivity or pain. Coefficient of Thermal Expansion ▪ Definition: ▪ The rate at which a material expands or contracts with temperature changes. ▪ Importance: ▪ Mismatch between materials and tooth structure can lead to gaps or stress. ▪ Clinical Significance: ▪ Matching coefficients reduces the Photo: © KYYOCERA 2024 risk of microleakage and secondary caries. ▪ Important for the long-term seal Should materials matching the tooth's and integrity of restorations. thermal expansion be selected? Yes, to ensure the restoration expands and contracts similarly to tooth structure. Solubility ▪ Definition: ▪ The degree to which a material can dissolve in a solvent, typically water or saliva. ▪ Importance: ▪ Affects longevity and stability of dental materials. ▪ Clinical Significance: Photo: © ZabMilenko 2020 ▪ High solubility can lead to material loss and restoration failure. Why is low solubility important for dental ▪ Selecting materials with low cements in restorations? High solubility leads to material dissolution, compromising solubility enhances durability. seal and increasing risk of secondary caries. Water Sorption ▪ Definition: ▪ The ability of a material to absorb moisture. ▪ Importance: ▪ Can lead to dimensional changes and affect mechanical properties. ▪ Clinical Significance: ▪ Excessive water sorption may compromise the fit and strength of restorations. ▪ Important to choose materials with Photo: © dixcyn 2014 minimal water uptake. Viscosity ▪ Definition: ▪ A measure of a fluid's resistance to flow. ▪ How thick/flowable a substance is. ▪ Importance: ▪ Affects handling characteristics of materials like cements and impression materials. ▪ Clinical Significance: Photo: © Anton Paar 2024 ▪ Appropriate viscosity ensures proper adaptation and ease of use. ▪ Influences the accuracy of How does temperature influence the viscosity of impressions and restorations. dental materials? Higher temperatures generally decrease viscosity, affecting handling characteristics. Radiopacity ▪ Definition: ▪ The ability of a material to absorb X-rays and appear opaque on radiographs. ▪ Importance: ▪ Allows for detection and assessment of restorations on radiographs. ▪ Clinical Significance: ▪ Radiopaque materials help in identifying restorations and detecting recurrent decay. Photo: © Iwaki et al. 2024 ▪ Important for diagnostic purposes. Corrosion ▪ Definition: ▪ The gradual degradation or deterioration of metals and alloys caused by a chemical or electrochemical reaction with their environment. ▪ Mechanism: ▪ Occurs when metals react with substances like oxygen, moisture, acids, or other chemicals. ▪ Electrochemical processes lead to the formation of corrosion products (e.g., rust). ▪ Importance: ▪ Affects the durability and longevity of dental restorations and appliances. ▪ Can compromise mechanical strength and aesthetic appearance. ▪ Clinical Significance: Photo: © Sild 2024 ▪ Corrosion can lead to weakening and failure of restorations. ▪ Release of metal ions may cause allergic reactions or toxicity. ▪ Discoloration and tarnishing affect the appearance What factors accelerate corrosion in dental of restorations. alloys? Saliva composition, pH changes, and galvanic interactions with other metals.  Comparison Property Definition Importance Examples Influences heat transfer to tooth Metals (high conductivity), Ceramics and Thermal Conductivity Ability of a material to conduct heat structures Polymers (low conductivity) Coefficient of Thermal Rate at which a material expands or Mismatch can lead to gaps or stress at Tooth Structure (~11 μm/m·K), Amalgam Expansion contracts with temperature changes restoration margins (similar), Composites (higher coefficient) Degree to which a material dissolves in a Affects longevity and stability of dental Glass Ionomer Cements (some solubility), Solubility solvent, typically saliva materials Ceramics and Metals (low solubility) Can cause dimensional changes affecting Resin-based Materials (can absorb Water Sorption Ability of a material to absorb moisture fit and strength water), Acrylic Resins Affects handling and adaptation of Flowable Composites (low viscosity), Viscosity Resistance of a fluid to flow materials Impression Materials (varying viscosity) Ability of a material to absorb X-rays and Allows detection and assessment of Metals (high radiopacity), Radiopaque Radiopacity appear opaque on radiographs restorations on X-rays Composites Degradation of metals due to chemical or Affects durability, aesthetics, and Amalgam (tarnish and corrosion), Base Corrosion electrochemical reactions with the biocompatibility Metal Alloys environment Summary ▪ Materials with appropriate mechanical properties can withstand biting forces, resist wear, and maintain integrity over time. ▪ Physical properties like thermal expansion and conductivity affect the longevity and performance of restorations. ▪ Accounting for properties like fatigue resistance, creep, and corrosion prevents long-term issues. ▪ Materials that properly mimic the properties of natural teeth contribute to better chewing efficiency and overall oral function. ▪ Knowledge of these properties drives the development of new and improved dental materials. References ▪ Callister, W. D., & Rethwisch, D. G. (2018). Materials Science and Engineering: An Introduction (10th ed.). Wiley. ▪ Askeland, D. R., & Wright, W. J. (2015). The Science and Engineering of Materials (7th ed.). Cengage Learning. ▪ Craig, R. G., & Powers, J. M. (2012). Restorative Dental Materials (12th ed.). Elsevier. ▪ Sakaguchi, R. L., & Powers, J. M. (2012). "Mechanical Properties of Dental Materials". Journal of Dentistry, 40(1), 123-131. ▪ Ferracane, J. L. (2011). "Resin Composite—State of the Art". Dental Materials, 27(1), 29-38. MCQs – Question 6 Which property measures a material's stiffness and is calculated from the slope of its stress-strain curve in the elastic region? A. Hardness B. Elastic Modulus C. Ductility D. Toughness E. Malleability MCQs – Question 7 The ability of a material to resist deformation under bending stress is termed: A. Tensile Strength B. Compressive Strength C. Flexural Strength D. Shear Strength E. Yield Strength MCQs – Question 8 Which property describes the slow, continuous deformation of a material under constant stress over time? A. Fatigue B. Creep C. Elastic Deformation D. Plastic Deformation E. Viscoelasticity MCQs – Question 9 The rate at which a material expands or contracts with temperature changes is known as: A. Thermal Conductivity B. Coefficient of Thermal Expansion C. Specific Heat Capacity D. Thermal Diffusivity E. Thermal Emissivity MCQs – Question 10 The tendency of a material to break or shatter without significant deformation is known as: A. Ductility B. Malleability C. Toughness D. Brittleness E. Resilience MCQs – Answers 6. B. Elastic Modulus. Elastic modulus quantifies how much a material deforms under stress within the elastic limit, indicating its stiffness. 7. C. Flexural Strength. Flexural strength measures resistance to bending forces, important for materials like bridges. 8. B. Creep. Creep occurs under sustained stress below the yield strength, leading to permanent deformation. 9. B. Coefficient of Thermal Expansion. This coefficient measures dimensional changes due to temperature variations, critical for matching materials. 10. D. Brittleness. Brittle materials fracture with minimal plastic deformation, lacking flexibility. Feedback – YourVoice We are continuously improving your learning experience through plenaries and their delivery. We would appreciate your feedback on what you found effective and what could be improved. Please scan the QR code below or click on the yellow icon to visit the YourVoice site.