Flashcards
Year 2 Biomaterials 1
Cards in this deck (200)
- 1Define 'biomaterial'A nonviable material used in a medical device, intended to interact with biological systems
- 2What is the difference between 1st generation, 2nd generation, and 3rd generation biomaterials?1st generation - bioinert
2nd generation - bioactive
3rd generation - regenerative - 3Why are biomaterials needed in Dentistry?Need for functional biomaterials to repair injury caused by caries, periodontal disease, peri-implantitis, and oral cancer
- 4The development of adhesive dentistry has brought many advantages. List some of the advantages.- Better aesthetics
- Conservation of tooth tissue
- Reinforcement of weakened tooth structure
- Reduced marginal leakage
- Reduced potential for pulp sensitivity
- Wide range of techniques
- Provides a high bond to enamel and dentine - 5What is the hybrid layer?Essential to adhesive dentistry, it is where the dental adhesive system creates a micromechanical bond with dentinal collagen
- 6What is the hybrid layer formed by?Bonding agents
- 7What is there formation of in the hybrid layer?Strong long-lived bonds between the rein and dentine
- 8What is the effect of the formation of the hybrid layer?To lock dissimilar substances together on a molecular level
- 9What types of bonds are involved in the hybrid layer?Ionic bonds
Hydrogen bonds
van der Waals forces - 10What are direct procedures using biomaterials?They are placed in unset conditions into cavities and usually only require one session
They harden in situ
E.g. amalgam, tooth coloured composite, root canal treatment - 11What are indirect procedures using biomaterials?Require external laboratory fabrication
Usually require multiple sessions
E.g. inlays, crowns, bridges, acrylic dentures, CoCr partial dentures, ortho appliances, maxillo-facial appliances - 12How might the choice of filling material guide treatment?It will likely influence the design of the cavity preparation (e.g. with amalgam, you will need macromechanical retention so might create undercuts or retention grooves, compared to composite where you can conserve more tooth structure)
- 13What property of an impression material is needed to capture finer details?Low viscosity
- 14How else, other than as direct or indirect, can biomaterials be classified?Based on composition
- 15What are the two main classes of biomaterials based on composition?Synthetic
Natural - 16Polymers, metals, ceramics and composites all come under what composition class of biomaterial?Synthetic
- 17Proteins and polysaccharides come under what composition class of biomaterial?Natural
- 18What are polymers?Large molecules of many repeating chemical groups
- 19What are the typical properties of metal biomaterials?Usually hard and lustrous with good thermal and electrical conductivity
- 20What are ceramics?Compounds of metals and non-metals
- 21What are composites?Mixture of polymers and ceramics/metals
- 22What are some examples of natural protein-based biomaterials?Collagen
Silk - 23What are some examples of natural polysaccharide-based biomaterials?Hyaluronic acid
Chitosan - 24Name some examples of dental materials that fall into the following group: PolymersPolymethylmethacrylate - denture base material
Bis-GMA - filling material and sealants
TEGDMA - diluent monomer - 25Name some examples of dental materials that fall into the following group: MetalsGold, titanium - pure metals
Cobalt chrome - alloy
Stainless steel - 26Name some examples of dental materials that fall into the following group: CeramicsAluminous porcelain
Zirconia porcelain
Silicates - 27Biomaterials can also be classified according to their usage. What are the classes they can be divided into?Short-term (minutes to hours) - tissue conditioners, impression materials, fluoride rinses, surgical guides
Temporary (days to weeks) - provisional crown, temporary dressing
Permanent (months to years) - implants, scaffolds, resin composite - 28Biomaterials can also be classified according to their activity. What are the classes they can be divided into?Bioinert
Bioactive
Bioresorbable - 29Explain what each of the following terms mean: 1) Bioinert 2) Bioactive 3) Bioresorbable1 - has minimal interaction with tissue
2 - interacts with surrounding tissue
3 - slowly dissolves and is replaced by tissue - 30Define 'biocompatability'The ability of a material to perform with an appropriate host response in a specific application
- 31What properties should any dental materials used in the oral cavity have?Should be harmless to the surround oral tissue - gingiva, mucosa, pulp, and bone
Should contain no toxic, leachable, or diffusible substance that can be absorbed into the circulatory system, causing systemic toxic responses/toxicity (including teratogenic or carcinogenic effects)
Should be free of agents that could elicit sensitisation or an allergic response in a sensitised patient - 32What stages generally occur when we implant a biomaterial into the body?1. Implantation
2. Tissue trauma/ injury
3. Blood-material interaction
4. Acute inflammation
5. Fibrous capsule (body trying to reject it)
6. Regeneration (fibrous capsule regenerated) - 33What happens immediately after implantation of a biomaterial, with regard to proteins?Coating of the material with proteins (protein conditioning)
The proteins attach - adsorb, unfold, change formation, detach and allow attachment of different proteins
It is the attachment of proteins that allows cells that are interacting with the material to start the host reposnse - 34Cells of which system are the ones predominantly involved in the host response to a biomaterial?Innate immune system
- 35What is the purpose of the immune system?To provide defence against pathogens, removal of debris, and identification and destruction of mutant cells
- 36Describe the differences between the innate and adaptive immune systems.Innate:
- First and fast
- Unspecific
- Unmodified by evolution
- Cellular response and supported by cytokines, complement system, lysozymes
Adaptive:
- Slow
- Evolved from innate
- Increased antigen specificity and memory
- Orchestrates action of antigen presenting cells, B cells, CD4, CD8 positive T cells, antibodies - 37Name the 2 main cells involved in the initial host response to a biomaterial.Macrophages - monocytes accumulate and turn into macrophages which try and engulf the foreign body
Neutrophils - first cells to site to remove debris/pathogens and recruit other cells - 38Describe what happens in the acute inflammation stage following implantation of a biomaterial.Exudation of fluid, plasma and proteins - some of these are serum factors (e.g. IgG, complement activate fragment C3B) which adsorb to biomaterials
Neutrophils and macrophages have receptors for these proteins
Increase of neutrophils first, then monocytes that differentiate into macrophages
Activation of neutrophils and macrophages involves recognition, attachment, engulfment, and degradation
Due to large size of biomaterial, macrophages release further enzymes (reactive oxygen and nitrogen species, proteinases, cytokines and chemokines) in an attempt to degrade the biomaterial - 39What are the main serum factors that elicit an immune response following implantation of a biomaterial?Immunoglobulin G (IgG)
Complement activate fragment C3B - 40What do macrophages have to do as a result of the large size of biomaterials?They release further enzymes (reactive oxygen and nitrogen species, proteinases, cytokines, chemokines) in an attempt to degrade the biomaterial
- 41What is the name of the process used by a macrophage to engulf a foreign body?Phagocytosis
- 42What is generally the maximum size of a foreign body that can be engulfed by a macrophage via phagocytosis?< 10 microns
- 43How does a macrophage deal with a slightly larger foreign body (10-100 µm), such as small fragments that break off the biomaterial?Macrophages fuse to form a foreign body giant cell, which is then big enough to engulf the foreign body and digest it
- 44How does macrophage deal with something like a large restoration in direct contact with dental pulp or a dental implant?It is far too big for the cells to be able to engulf and degrade it
Inability to degrade the material results in further recruitment of immune cells 0 macrophages merge to form a foreign body giant cell, which still fails to degrade the biomaterial
Fibroblasts form a dense collagen tissue around the foreign body (fibrous capsule) in an attempt to separate the material from the body
Fibrous capsule is not remodelled - 45What cells produce the fibrous capsule that surrounds the foreign body?Fibroblasts
- 46What are some of the problems associated with overactive host response/ fibrous capsule formation?Rejection, pain, inflammation
Poor tissue integration (e.g. implants)
Contraction of material
Alter drug release
Sensor malfunction (e.g. glucose sensor) - 47What are some material factors that can affect the host response to a biomaterial?Bulk properties - chemical composition, structure, purity, presence of leachables
Surface properties - roughness, hydrophilicity, geometry, surface charge, surface biochemistry
Mechanical properties - match properties of component being replaced and stability and fixation
Long-term structure integrity - fatigue, fracture, wear, corrosion and creep resistance - 48What are some patient/ surgeon factors that can affect the host response to a biomaterial?Age and health status
Immunological/ metabolic status
Surgery - minimise tissue damage, contamination, correct implantation - 49For an implanted material, put the following in the correct order: 1) Arrival of neutrophils 2) Protein adsorption 3) Tissue trauma 4) Foreign body giant cell 5) Arrival of macrophages 6) Fibrous capsule formation3, 2, 1, 5, 4, 6
- 50What are some of the possible reactions we can get from biomaterials in Dentistry?Post-operative sensitivity - pulpal reaction (methacrylates in adhesive restorative materials, mercury in amalgam)
Toxicity - mercury
Corrosion - discolouration (amalgam and composites)
Hypersensitivity/allergy - metals (mercury, nickel, titanium/ cobalt) and polymers (acrylic (PMMA) monomer, impression materials (zinc oxide eugenol) - 51What component of adhesive restorative materials tend to cause a pulpal reaction resulting in post-operative sensitivity? What component of amalgam tends to cause a pulpal reaction resulting in post-operative sensitivity?Adhesive restorative materials - methacrylates
Amalgam - mercury - 52Name some of the types of adverse reactions that can occur in response to biomaterials.Toxic reactions - cytotoxicity (cell death) and carcinogenicity (causes cancer)
Contact dermatitis/stomatitis - allergic contact dermatitis/stomatitis or irritant contact dermatitis/stomatitis
Contact urticaria
Oral lichenoid reactions
Anaphylactic reactions
Biomaterial-associated infections - 53What is allergic contact dermatitis/stomatitis?A form of dermatitis triggered by a reaction to a substance (allergen) contacting the skin/mucosa
Takes hours to days to appear and can be long-lived
Memory response - 54How can the risk of allergic contact dermatitis/stomatitis be reduced?Patient medical history
Food or medicine allergies
Safety data sheet/ manufacturing instructions
Monitoring during treatment
Personal protective equipment for clinician
Patch test - 55What are some of the risk reduction procedures that should be taken with regard to mercury hygiene?Personnel should be familiar with the hazards
Environment - ventilation, monitoring, work surfaces, spillage
Handling - single-use pre-capsulated alloys preferred
Removal - copious cooling under water, rubber dam
Disposal - filters to water drainage, sealed bottles with sulphide solution - 56What type of reaction is irritant contact dermatitis/stomatitis not?It is not an immune response
It is non-immune chemical or physical changes - 57How is the risk of irritant contact dermatitis/stomatitis reduced?Packaging
Non-contact operative techniques/ isolation
PPE for clinician
Ready safety data sheet - 58Describe contact urticaria.Immediate and short-lived
Localised swelling with red, raised, itchy bumps
Can be immunological or non-immunological - 59How can the risk of contact urticaria be reduced?Patient medical history
Food or medicine allergies
Monitoring during treatment
Patch test
Using alternatives to latex (i.e. nitrile) - 60How do oral lichenoid lesions tend to present?Lichenoid/white or red erosive lesions in the oral mucosa reported in direct contact with dental amalgam, composite and other restorative materials
- 61What are anaphylaxis reactions?Severe, potentially life-threatening generalised allergic reactions, characterised by rapidly developing symptoms and signs
- 62Name some of the characteristic signs and symptoms of an anaphylactic reaction.- Skin changes (redness, itching)
- Mucosal changes (swelling below skin surface)
- Swallowing and breathing difficulties (due to swollen mouth, throat, tongue)
- Wheezing
- Tachypnoea
- Tachycardia
- Hypotension - 63What is tachypnoea?Quick, shallow breathing
- 64What is the used to treat anaphylactic reactions?Adrenaline 0.5 mg IM
(repeat after 5 mins if no response) - 65What are some of the components of composite resins that can affect biological tissues if the composite is not cured sufficiently?Organic matrix (bis-GMA)
Silane coupling agent
Initiator/ accelerator - 66What is the major aetiological factor in denture stomatitis?Colonisation by Candida albicans
- 67What is denture stomatitis also known as?Chronic atrophic candidosis
- 68What surface of an upper denture acts a reservoir of Candida albicans in denture stomatitis?Fitting surface
- 69Why are implants susceptible to peri-implantitis?Metal surfaces are prone to bacterial colonisation and biofilm formation
Bacterial virulence factors induce inflammation and bone resorption - 70What is the ISO?International Organization for Standardization
- 71Tests based on which guidelines would need to be performed to ensure a biomaterial for patients is safe?ISO 10993 guidelines
- 72What is the difference between in vitro testing and in vivo testing?In vitro - cell culture
In vivo - implantation into animals - 73What is the MHRA?Medicines and Healthcare products Regulatory Agency
- 74Name some mechanical properties that dental materials can have.Strength - tensile, compressive, shear, creep, yield, flexural, stress rupture
Formability - percentage elongation and reduction
Durability - hardness, wear resistance, fatigue strength
Rigidity- modulus of elasticity, flexural modulus
Toughness - impact strength, notch sensitivity, critical stress intensity factor - 75Name some chemical properties that dental materials can have.Adhesion
Water sorption
Corrosion - 76Name some physical properties that dental materials can have.Rheology - viscosity
Thermal properties - coefficient of expansion and contraction
Optical properties - colour - 77What 2 factors should be considered when measuring forces between teeth?Magnitude of the force in Newtons (N)
Duration of the force - 78What have biting forces been measured to be during the process of the mastication of food?50-250 N
- 79Where are the strongest muscle forces of the jaw exerted?Close to the hinge - the force diminishes as the distance from the fulcrum increases
- 80Why do we need strong anterior stops on the incisors/anterior teeth?To protect the posterior teeth which are facing the strongest forces due to being closes to the hinge of the jaw
- 81What are centric stops?Point contacts between the mandible and maxilla
- 82Where are the point contacts/centric stops located?Maxillary posterior teeth - palatal cusp tips
Maxillary anteriors - palatal
Mandibular posterior teeth - buccal cusp tips
Mandibular anteriors - incisals
Marginal ridges of posterior teeth - 83Define 'stress'A measure of the force in a component relative to the cross-sectional area over which the force is applied
Stress = force per unit area - 84What is the formula for calculating stress?σ = F/A
Units: N/m2 or Pa (pascals) - 85What are the ways in which a material may be stressed?Compression
Tension
Torsion
Shear
Flexure - 86Name the 2 types of stress that occur as a result of axial forces applied to a material.Tensile stress (from elongation)
Compressive stress (from shrinkage) - 87What type of stress occurs as a result of sliding forces on a material?Shear stress
- 88What type of stress occurs as a result of twisting forces on a material?Torsional stress
- 89What type of stress occurs as a result of bending forces on a material?Bending stress
- 90What does the same amount of force applied to a different size of area do to the intensity of the force?Changes the intensity (e.g. same force over smaller area = higher intensity)
- 91Define 'strain'A measure of deformation, either elastic or plastic (i.e. how much the material is going to change in shape or length)
- 92What is the calculation for strain?Strain = change in length per unit original length
ε = ΔL / L0
(Unitless because m/m, mm/mm) - 93Define 'deformation'The cumulative effect of the strains in a component
- 94What are the 2 types of deformation?Elastic deformation
Plastic deformation - 95What is the difference between elastic deformation and plastic deformation?Elastic deformation - component returns to its original shape upon removal of the forces
Plastic deformation - component permanently deforms - 96What is elastic deformation associated with at a molecular/atomic level?Associated with stretching but not breaking of the chemical bonds between atoms in a solid
- 97What is plastic deformation associated with at a molecular/atomic level?Atoms change neighbours, returning to a stable configuration with new neighbours after the dislocation has passed
- 98What type diagram is this?Stress-strain curve
- 99What does the elastic region of the stress-strain curve show?If we were to apply a stress to the material, it would gradually change in shape (strain)
If we were to remove the stress from the material while it is still within the linear part, it would go straight back to its original shape - 100What does the plastic region of the stress-strain curve show?If we keep applying a stress until it enters the plastic region, the material will not return to its original shape but will instead go to a point along the strain axis
- 101What happens if we continue to apply stress to a material beyond the plastic region?It will fracture
- 102What is the proportional limit?The point where the stress is no longer proportional to the strain - where we shift from elastic deformation to plastic deformation
- 103What is another name for the modulus of elasticity?Young's modulus
Stiffness - 104How do we work out Young's modulus/ modulus of elasticity?Divide stress by strain for the linear (elastic) region
- 105What does the Young's modulus/ modulus of elasticity tell us?How the material is going to respond to a stress
- 106How would the Young's modulus/ modulus of elasticity of a stiff metal compare to that of alginate?Stiff metal - will not change much in shape, slope of the curve is more vertical
Alginate - will change a lot in shape, slope of the curve is more horizontal - 107What is the meant by the rapid onset of necking?A type of deformation that occurs when a material's cross-sectional area decreases in a localised area under tensile load (high stress)
- 108What does stress-strain testing provide?Basic information on the stiffness (modulus of elasticity/ Young's modulus), strength and how the material deforms under certain stresses
- 109What does the shape of the stress-strain curve tell us about?The characteristics of the material
- 110What does the area under the stress-strain curve tell us?The energy required to deform or break the material
- 111What is the clinical significance of the stress-strain curve?When load is applied to a tooth, this load is transmitted through the material, giving rise to stresses and strains. If these stresses and strains exceed the maximum value the material can withstand, fracture is the most likely outcome
- 112In what manner do materials that fracture without very much plastic deformation behave?In a brittle manner
- 113Give some examples of materials that behave in a brittle manner.Glass, stone
Acrylic resin (denture base materials) - 114In what manner do materials that are capable of sustaining large amounts of plastic deformation behave?In a ductile manner
- 115Give some examples of materials that behave in a ductile manner.Metals - copper, lead
Polymers - polyethylene
Mouthguard materials - PVAc-PE - 116What is the difference between brittle and ductile materials?Brittle materials fracture without very much plastic deformation
Ductile materials are capable of sustaining large amounts of plastic deformation - 117What must stress not exceed?The strength of the material (ultimate load) - otherwise we will get failure
- 118Define 'hardness'The ability of a material to resist indentation (resist scratching, wear)
- 119Why is the hardness of a material clinically relevant?We do not want to mismatch materials. If we have a very hard material rubbing against a softer material, the softer one is going to wear much more rapidly.
It is also the reason why we use hard dental instruments and burs - otherwise they would wear down faster than the enamel we are working on does. - 120What equipment is used to measure the hardness of a material?Microhardness tester (Knoop or Vickers)
- harder material will have a smaller indentation than a softer material - 121What is impact strength used to measure?A material's ability to withstand shock or impact loading
- 122Define 'impact strength'The energy required to fracture a given volume of material - measured in J or J/m3
(= area under stress-strain curve) - 123What 2 tests are used to measure impact strength?Drop-weight test
Pendulum swing test - 124Define 'fatigue'A form of failure that occurs due to fluctuating stresses. If often occurs as stresses much lower than the maximum stress of the material.
- 125What are some causes of failure that need to be considered?Stresses are often present and act in more than one direction
Stresses may be repeatedly applied and removed, or the direction of stress may be repeatedly reversed
Stresses may be applied for long periods of time (e.g. ortho)
Dental components may contain flaws or even cracks - 126What is stress concentration?Localised high stresses in specific areas even though the average stress in the structure is low - this can result in failure
- 127What is the main cause of stress concentration?Microscopic flaws or micro-structural defects on the surface or within the internal structure
- 128What are the 3 stages of fatigue failure.1. Crack initiation
2. Crack growth/propagation
3. Final failure - 129Fatigue failure can generally be associated with defects. Where do the defects come from?Materials themselves
Manufacturing - finish, design
Clinical application (e.g. incorporating a lot of air when mixing the material) - 130What failure mechanism is responsible for around 90% of dental restoration failures?Fatigue
- 131What is bonding achieved through?Chemical adhesions and/or mechanical attachment
- 132Define 'adhesion'The force that binds two dissimilar materials together when they are brought into intimate contact
- 133Define 'cohesion'The attraction between similar atoms or molecules within one substance
- 134What are the advantages of adhesive techniques in Dentistry?- More retention and stability
- Reduce microleakage (thus reducing post-op sensitivity, marginal staining, recurrent caries, pulp pathology)
- De-sensitisation (seal dentinal tubules)
- Expands the range of materials that can be used for aesthetic restorative dentistry
- Better transmission and distribution of functional forces (potential to reinforce weakened tooth structure and promote material strength)
- More conservative (minimal loss of tooth tissue) - 135Adhesive techniques have an advantage of reducing microleakage. What does this subsequently reduce?Post-operative sensitivity
Marginal staining
Recurrent caries
Pulp pathology - 136What criteria need to be considered for adhesion?Wettability of the substrate by the adhesive
Viscosity of the adhesive
Morphology or surface roughness of the substrate - 137Define 'wettability'The ability of a liquid to maintain contact with a solid surface
- 138What is meant by good wetting?The ability of a liquid to cover the surface of the substrate completely
- 139Solid surfaces with contact angles > 90° are considered what?Hydrophobic - poor wetting
- 140Solid surfaces with contact angles < 90° are considered what?Hydrophilic - good wetting
- 141Why are resin composite materials designed to be very hydrophilic in nature before curing, and hydrophobic in nature after curing?Dentine is very hydrophilic so we get a lot of spreading and interaction between the uncured resin composite and dentine. Then, when the material is cured and polymerisation reaction takes place, we get the hydrophobic nature.
- 142Name the 4 mechanisms of adhesion.Micromechanical
Physical
Chemical
Molecular entanglement - 143What are these 4 things examples of: micromechanical, physical, chemical, molecular entanglement?Mechanisms of adhesion
- 144How is micromechanical adhesion predominantly achieved? Give an example.Through micromechanical retention
Examples:
Phosphoric acid etched enamel - enamel prisms are exposed, creating regions for the resin to penetrate into and create a mechanical retention
Resin tags - if we are able to clean the surface of the dentinal tubules and penetrate it with our resin, we can get micromechanical retention - 145How is chemical adhesion achieved?Use of a conditioner to strip away the minerals in dentine - after washing off the conditioner, the dentine is now demineralised which exposes the collagen fibrils. The mineralised tissue is then replaced by the resin - molecular entanglement with the collagen.
- 146What does conditioning/etching do?1. Remove the smear layer
2. Exposes the dentinal tubules
3. Demineralises the dentine
4. Collagen network collapses after drying - 147Once the conditioner/etch causes the collagen network to collapse, what is applied?Primer
- 148What does the primer act as?An interface between the resin composite and dentine
- 149What does the primer do?Penetrates the collapsed collagen network and intertwines with the collagen to give us the hybrid layer
- 150What does the primer penetrating the collapsed collagen network and intertwining with the collagen give us?The hybrid layer
- 151What step follows the primer?Bonding
- 152What does the bonding stage involve?Bonding the restoration/material to the primer to get the hybrid layer
- 153What is polymerisation shrinkage?The decrease in volume that occurs when a liquid or resin is converted into a solid during the polymerisation process - due to replacement of van der Waals forces with covalent bonds
- 154How can polymerisation shrinkage lead to microleakage?When polymerisation shrinkage occurs, the overall volume of the polymer shrinks. If we do not have good adhesion to the natural tooth structure, the material will pull away from the sides, creating a gap leading to microleakage.
- 155When looking at the adhesive approach, what do we have to make sure about the bond strength of the material being used?That the bond strength exceeds the polymerisation stress (13-18 MPa) (i.e. the shrinking of the material)
- 156Name some of the clinical challenges associated with high shrinkage and polymerisation stress.Microleakage, leadig to:
Secondary caries
Post-operative sensitivity
Debonding
Marginal staining - 157What is microleakage?The movement of bacteria, fluids, molecules, or ions between a tooth's natural structure and a dental restoration, such as a filling or crown
- 158Define 'corrosion'A chemical or electrochemical process through which a metal is attacked by natural agents such as air and water, resulting in partial or complete dissolution, deterioration, or weakening of any solid substance
- 159Name some of the types of corrosion.Crevice corrosion
Galvanic corrosion
Pitting corrosion
Stress corrosion
Tarnish
Concentration cell - 160What are all of the following types of: crevice, galvanic, pitting, stress, tarnish, concentration cell?Corrosion
- 161What is crevice corrosion?Corrosion in narrow spaces caused by localised electrochemical process and chemistry changes such as acidification and depletion of oxygen content
E.g. microleakage in dental restorations - 162Fill in the blanks: Crevice corrosion is corrosion in [1] spaces caused by localised electrochemical process and chemistry changes such as [2] and depletion of [3] content. An example of this is [4] in dental restorations.1 - narrow
2 - acidification
3 - oxygen
4 - microleakage - 163What is a common example of crevice corrosion in Dentistry?Microleakage in dental restorations
- 164What is galvanic corrosion?Corrosion on a less noble metal when electrochemically dissimilar metals are in electrical contact in presence of a corrosive liquid environment
- 165Fill in the blanks: Galvanic corrosion is corrosion on a less [1] metal when electrochemically [2] metals are in electrical contact in the presence of a corrosive [3] environment.1 - noble
2 - dissimilar
3 - liquid - 166What is pitting corrosion?Sharply localised corrosion in base metals like iron, nickel, and chromium (which are naturally protected by a thin film of oxide) in the presence of chlorides in the environment. The film locally breaks down causing dissolving of the metal underneath in the form of pits.
- 167Fill in the blanks: Pitting corrosion is a sharply [1] corrosion in [2] metals like iron, nickel, and chromium (which are naturally protected by a thin film of [3]) in the presence of [4] in the environment. The film locally breaks down causing dissolving of the metal underneath in the forms of pits.1 - localised
2 - base
3 - oxide
4 - chlorides - 168What are base metals like iron, nickel and chromium naturally protected by?A thin film of oxide
- 169What is stress corrosion?Degradation by the combined effects of mechanical stress and a corrosive environment, usually in the form of cracking
- 170Fill in the blanks: Stress corrosion is degradation by the combined effects of [1] stress and a [2] environment, usually in the form of [3].1 - mechanical
2 - corrosive
3 - cracking - 171What is tarnish?A process by which a metal surface is dulled in brightness or discoloured through the formation of a chemical film, such as a sulphide or an oxide
- 172Fill in the blanks: Tarnish is a process by which a [1] surface is dulled in brightness or [2] through the formation of a chemical film, such as a [3] or an [4].1 - metal
2 - discoloured
3 - sulphide
4 - oxide - 173What is a concentration cell?An electrochemical corrosion cell, in which the potential difference is associated with the difference in the concentration of solutions, causing corrosion at different parts of the metal surface
- 174Fill in the blanks: A concentration cell is an electrochemical corrosion cell, in which the potential difference is associated with the difference in the [1] of solutions, causing [2] at different parts of the metal surface.1 - concentration
2 - corrosion - 175What does the following describe: A chemical or electrochemical process through which a metal is attacked by natural agents such as air and water, resulting in partial or complete dissolution, deterioration, or weakening of any solid substance.Corrosion
- 176What are some of the natural causes of corrosion and tarnish?Formation of hard (calculus) and soft (plaque and films composed of microorganisms) deposits on the surface of the restoration
Formation of thin films of oxides, sulphides and chlorides on a metal causing surface discolouration
Corrosion results from surfaces under stress or with irregular impurities on the metal
Moisture, atmosphere, acid or alkaline solutions and certain chemicals
Extra-orally, it is important that metal devices to be sterilised or cleaned should not corrode (e.g. burs, forceps, endodontic files, reamers, face-bows) - 177What would happen if a patient with an amalgam restoration were to bite on foil?It will cause pain
The foil acts as an anode, the filling as a cathode and saliva as the electrolyte. The O2 is reduced to water, creating a current which can conduct to dental pulp. - 178What might happen if a gold inlay on one tooth is in contact with an amalgam restoration on another, especially in an acidic environment like with acidic saliva?You get huge amounts of electrons flowing which can result in corrosion of the gold inlay and deterioration of the amalgam
- 179What are some of the extrinsic factors that can affect the corrosion of dental restorations?Diet - acidic environment
Drugs - saliva flow reduction
Smoking - changes pH of mouth
Bacterial activity
Oral hygiene and habits - 180Why can smoking affect corrosion?It can alter the pH of the mouth (more acidic)
- 181Define 'rheology'The science of deformation and flow
- 182What does the following describe: The science of deformation and flow?Rheology
- 183Define 'viscosity'Resistance to flow
A liquid with high viscosity is thick and has high resistance to flow - 184Define 'viscoelastic'Describes a material that exhibits characteristics of both a viscous liquid and an elastic solid
- 185How do we define the modulus in terms of rheology?Modulus = shear stress (pushing force) / strain (amount it moves)
The tougher the material is, the more resistance to move. The weaker the material is, the lower the resistance to move. - 186What are 2 methods of measuring viscosity?Rheometer
Shark fin test - 187What type of fluid would exhibit a linear relationship between stress and strain?Newtonian material
E.g. water - 188What type of material becomes thicker/harder to change in shape as more shear stress is applied?Dilatant material
- 189What type of material becomes more liquid as more shear stress is applied?Pseudoplastic material
- 190Give an example of each of the following: 1) Newtonian material 2) Dilatant material (shear-thickening) 3) Pseudoplastic material (shear-thinning) 4) Thixotropic material1 - water
2 - conventional composites, corn starch
3) polycarboxylate cements, whipped cream
4) prophy paste, toothpaste, ketchup - 191What is meant by thixotropic?A term applied to a shear-thinning liquid that recovers to the original viscosity when the shear is removed
E.g. prophy paste, toothpaste, ketchup - 192What are some thermal properties materials have?Thermal conductivity
Specific heat
Thermal diffusivity
Thermal expansion - 193What is thermal conductivity? What unit is it quantified using?How well heat travels through the material
Kelvin (K) - 194What is specific heat?How fast a material heats up
- 195What is thermal diffusivity?How fast your material will heat up at one point if heated at another point
- 196What is thermal expansion?How much a material changes in volume when heated/cooled
- 197What do each of the following definitions describe: 1) How well heat travels through the material 2) How fast a material heats up 3) How fast your material will heat up at one point if heated at another point 4) How much a material changes in volume when heated/cooled1 - thermal conductivity
2 - specific heat
3 - thermal diffusivity
4 - thermal expansion - 198What is it important to know about the different parameters of thermal properties?Mismatch of thermal expansion coefficients can result in material pulling away from tooth structures, leading to microleakage and its various consequences
Thermal conductivity, diffusivity, and specific heat are important to prevent pulpal sensitivity - 199What are some of the optical properties of materials?Colour
Translucency
Surface texture - 200What are the optical properties of materials important for?Aesthetics
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- Undergraduate Restorative Dentistry (Dental Materials) Flashcards on Year 2 Biomaterials 1, created by Riya X on 11/12/2024.
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- Riya X
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