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Questions and Answers
Which property is NOT associated with polymers in dental applications?
What is a significant disadvantage of using resin composites?
Which of the following is a characteristic of the initiation stage in addition polymerization?
What factor does NOT control the properties of polymers?
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Which component is NOT typically included in the powder phase of glass ionomer cements (GIC)?
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Which disadvantage is associated with glass ionomer cements?
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The elimination of a smaller molecule during a polymerization reaction is characteristic of which type of polymerization?
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Which of the following represents a key advantage of resin composites over glass ionomer cements?
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What is a reason for discoloration in resin composites over time?
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What is the primary role of the SA node in the heart?
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Which interval in an electrocardiogram represents the time of atrial excitation to ventricular excitation?
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How does increased preload affect stroke volume?
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What does the cardiac output formula represent?
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What is the primary factor influencing stroke volume?
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Which segment of the cardiac cycle indicates that the ventricular myocardium is depolarized?
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What is a key disadvantage of using conventional dental amalgam?
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Which characteristic is true for thermosetting plastics?
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Which polymer classification is formed through a condensation process?
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What is the primary structure type of most synthetic polymers?
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Which of the following is NOT a typical application of polymers in dentistry?
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What process is responsible for the joining of monomers in polymerisation?
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What is a characteristic of thermoplastic polymers?
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Which resin is commonly used for its good bonding properties in dental applications?
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Which of the following represents a false statement about polymer classification?
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What is a significant advantage of resin composites over dental amalgam?
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What is the primary reason that surfaces have higher energy states compared to bulk molecules?
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Which phenomenon describes the loose association of molecules at a surface without forming chemical bonds?
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How does surface contamination affect a solid's wettability?
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What are copolymers primarily formed from?
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What effect do crystal planes have on surface energy in metals?
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In resin copolymers, what role does a comonomer serve?
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Which of the following statements about surface energy and tension is correct?
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What is a key characteristic of block copolymers?
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Which of these acrylate monomers is not typically used in dental resins?
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What happens to the wettability of a surface when it is cleaned?
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What is a primary factor influencing the degree of crystallinity in polyethylene?
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What occurs to a resin copolymer when the temperature exceeds its glass transition temperature (Tg)?
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Which statement accurately describes cardiac muscle cells?
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What role do desmosomes play in cardiac muscle cells?
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What initiates the electrical impulses in the conductive system of the heart?
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What happens during Phase 2 of the cardiac muscle action potential?
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Which condition accurately defines a functional syncytium in cardiac muscle?
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Which method is primarily used to synthesize low-density polyethylene (LDPE)?
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How does polymerization impact the glass transition temperature (Tg) of materials?
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What is the main function of the gap junctions in cardiac muscle cells?
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Study Notes
Resin Composites
- Good aesthetics, mechanical strength, bonds to tooth structure using bonding agents.
- Technique sensitive, discoloration over time, polymerization shrinkage, does not bond directly to tooth structure.
Polymers
- Distinct repeating group of atoms called monomers.
- Monomers can be gases or liquids, converted to solid polymers after polymerization.
- Polymers are light, versatile, cheap and easy to handle materials.
Addition Polymerization
- Two molecules react to produce a larger molecule without the elimination of a smaller molecule or by-product.
- Activation: process of producing free radicals by light, heat or chemicals.
- Initiation, Propagation, Termination.
Free Radical Polymerization
- Free radicals are provided by highly reactive chemicals (initiators) with unpaired electrons.
- Benzoyl peroxide is a commonly used free radical producer (initiator).
Condensation Polymerization
- Two molecules react to produce a larger molecule with the elimination or production of a smaller molecule.
Factors Controlling Polymer Properties
- Molecular structure of repeating units.
- Molecular weight and chain length.
- Degree of chain branching.
- Cross linking.
- Filler or plasticizer.
Polymer Structure
- Crosslinked polymers form a three-dimensional network by joining individual chains (Makes structure more rigid).
Glass Ionomer Cement
- Powder: Fluoro-alumino-silicate glass and Na-alumino-silicate glass and CaF. Contains pigments.
- Liquid: Poly (acrylic)+ (maleic) or (itaconic) acid, Tartaric acid and distilled water.
- Less technique sensitive, bonds directly to tooth structure, releases fluoride, good clinical performance when used correctly.
- Relatively poor mechanical strength, weak bonding to tooth structure, not the best for aesthetics.
Conventional Dental Amalgam
- High compressive strength, good clinical track record, less technique sensitive.
- Contains mercury, does not bond to tooth structure, poor aesthetics.
Resin Composites & GIC Bonding
- Resin composites are bonded using adhesives (bonding agents).
- GIC is bonded directly to tooth tissue.
Polymers in Dentistry
- Resin-based restorative composites, impression materials, dissolvable sutures, prosthodontics.
Polymerization
- Chemical reaction joining monomers to form polymers.
- All polymers consist of a large number of repeating monomeric units.
Plastics
- Polymers that can be formed into various shapes by heat and/or pressure.
- Thermoplastics can be heated to a liquid and reshaped.
- Thermosetting plastic is fixed into shape by an irreversible reaction, heat drives the reaction or it may be exothermic.
- Polymers are substantially cross-linked covalently, often in 3-D networks.
Polymer Classification 1: Based on Origin
- Biopolymers (Carbs, proteins, DNA). Most important biopolymers are formed by a condensation process eliminating water.
- Alginate is a naturally derived biopolymer used in synthesis of dental impression materials.
- Synthetic polymers (LDPE, PVC, nylon...).
- Two synthetic methods are condensation (nylon) and addition (LDPE) polymerization.
Polymer Classification 2: Based on Thermal Behaviour
- Thermoplastic (nylon, PMMA, LDPE)
- Thermoset (BisGMA, TegDMA)
- Cannot be reshaped due to irreversible hardening/cross-linking upon curing.
Polymer Classification 3: Based on Structure
- Linear
- Branched
- Hyperbranched
- Polysaccharides built from glucose with different structures that relate to their physiological and biochemical functions.
- Most synthetic polymers have structures that are linked to function.
Polymer Classification 4: Based on Chemistry of Monomer Structural Unit
- Resin: a synthetic organic polymer system used in many plastics.
- Acrylic resins (PMMA, bis-GMA)
- Polyamide resins
Surface Energy
- Molecules/atoms at a surface are at a higher energy state (not as stable) as those below the surface (bulk).
- Liquids can adjust their shape to minimize their surface energy, but solids can't.
- Surface energy is affected by intermolecular forces, functional groups present and for metals, crystal planes presenting at surface.
Crystal Planes
- Surface energy of a metal plane depends on the number of stabilizing nearest neighbors "removed" to form the surface.
Surface-sorption
- Surfaces are important to dentistry. At the surface physisorption (not chemically bonded) (loose association van der waals) and chemisorption (chemically bonded) (bonded covalent or ionic) can occur.
Surface Wetting
- Effective wetting of surfaces is related to surface energy/ surface tension of solid/ liquid and rheology of liquid/suspension.
- Wetting is critical in many dental procedures.
- Surface contamination lowers solid surface energy, decreasing wettability.
- Cleaning a surface raises surface energy of solid, improving wettability.
Copolymers
- Formed from 2 (or more) different types of monomer, A and B.
- Block: each monomer clustered into blocks.
- Graft: linear backbone of one composition and randomly distributed branches of a different composition.
- Comonomer: a minor component in copolymer, bonds with the principal monomer e.g. cross-linking agent.
Acrylate Monomers
- Monomers with the acrylate functional group are common in many dental resins.
Resin Copolymers
- Heraeus Kulzer Charisma - bisGMA/TEGDMA - 22% polymer by weight. Contains comonomer viscosity diluent and cross-linking agent.
- Heraeus Kulzer Durafill - bisGMA/UDMA - 40% polymer by weight.
- 3M filtek P60 - bisGMA/UDMA/bisEMA.
- The relative amounts depend on the polymer, synthesis used and its conditions.
Polyethylene
- Polyethylene crystallinity shows a dependance on average molar mass and degree/length of side branching (LDPE M=10^4^ g/mol vs HDPE M=10^6^ g/mol).
- LDPE: radical addition synthesis (high P>1000 bar).
- HDPE: Ziegler-Natta catalyst (low P\1
Resin Copolymers and Tg
- Polymerisation substantially increases the glass transition temperature, well above that of the monomer.
- Copolymerisation may increase the Tg.
- Maximum oral cavity temperatures experienced with eating and drinking is (55-58 degrees Celsius).
- If the resin copolymer temperature exceeds Tg, it will soften and fall.
Cardiovascular System
- Consists of blood vessels and heart.
- Conductive system: automatic, initiates electrical impulses, distributes throughout heart, ensures all cells depolarize and muscles contract in a coordinated manner.
- Transports blood around body for:
- Oxygen diffusion
- CO
2removal - Transport of waste
- Immune function
Cardiac Muscle
- Chamber muscles contract (changes blood volume) as one: functional syncytium.
- Unique cell structure: contractile muscle cells and excitatory and conductive cells.
- Its own signal generator.
- Its own conducting system.
Contractile Muscle Cell Membrane
- Intercalated: each cell is interconnected, meaning one action potential is sent over multiple cells.
- Desmosomes: fuse cells together – prevention of separation of muscle cells.
- Gap junctions: share ions between cells.
Functional Syncytium
- Atrial and ventricular syncytium split in a way that electrically isolates the atria and ventricles.
- Allows atria to contract slightly before ventricles.
Cardiac Contractile Muscle Action Potential
- Phase 0: Na+ open.
- Phase 1: Na+ close, fast K+ open.
- Phase 2: Ca 2+.K+ open/close.
- Phase 3: Ca2+ close, slow K+ open.
- Phase 4: all closed.
Cardiac Pacemaker Cells
- Set rhythm of heart through impulses at approximately 60-100 times/min.
- SA node usually dominates (Pacemaker).
- Sequence:
- SA node: fastest depolarization in heart.
- SA node is connected to adjacent myocardial cells which send impulse.
- AV node: delays impulse conduction from atria to ventricles (slow).
- Pace set by AV is junctional rhythm 40-60 beats/min.
- AV bundle (bundle of His): only electrical connection between atria and ventricles.
- Bundle branches.
- Endocardial network (Purkinje fibres).
- Contraction: atria then ventricles.
Pacemaker Cell Action Potential
- Phase 4: slow inward Na+ current.
- Phase 0: fast inward Ca2+ current.
- Phase 3: outward K+ current.
Electrocardiograms
- Currents from detected with electrodes.
- Number of leads determines sensitivity of signal (minimum 3, standard 11-12).
- Normal heart rhythm has a distinct sequence.
- Abnormal sequence = heart problem.
Cardiac Cycle
- All events occurring from beginning of one heartbeat to the beginning of next.
Normal Sequence
- P-R interval: atrial excitation to ventricular excitation. Can also be P-Q interval.
- S-T segment: ventricular myocardium is depolarized.
- Q-T interval: ventricular depolarization to ventricular repolarization.
- R-R interval: ventricular cycle. Used for heart rate.
Cardiac Output
- Cardiac output = stroke volume x heart rate.
- Cardiac output = venous return.
- Cardiac output = arterial pressure/total peripheral resistance.
- The amount of blood pumped out depends on:
- How many times the heart beats.
- How much blood is in the ventricles.
- How much pressure is developed in the ventricles.
- How much pressure there is in the arteries.
Venous Return
- Most important factor in stroke volume.
- How much blood comes in through major veins (vena cava/pulmonary veins).
- Most blood in circulation is in veins.
Frank-Starling Law of the Heart (Pre-load)
- More blood in the heart means more stretch.
- More stretch = more contraction.
- Stronger contraction = more blood ejected.
Stroke Volume
- Amount of blood pumped out of the ventricle in 1 beat (50-120mL)
- Calculated from the end of diastolic volume - the end of systolic volume of the ventricle.
- Affecting factors include: preload, contractility and afterload.
Preload
- Preload up, stroke volume up.
- Quantity of blood flowing from veins into the right atrium each minute.
- Increased by: exercise and blood volume increase.
- Decreased by: dehydration, blood loss.
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Description
This quiz covers essential topics in polymer chemistry, including resin composites and various types of polymerization processes. Explore concepts such as free radical and condensation polymerization, and learn about the properties and applications of polymers. Test your understanding of how polymers are formed and their significance in material science.
