Polymer Chemistry Overview

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Questions and Answers

Which property is NOT associated with polymers in dental applications?

Direct bonding to tooth structure (correct)

Ability to form light structures

High molecular weight

Good versatility

What is a significant disadvantage of using resin composites?

Release fluoride

Good aesthetic properties

Can be bonded to tooth structure

Technically sensitive (correct)

Which of the following is a characteristic of the initiation stage in addition polymerization?

Absence of free radicals

Degradation of polymers

Production of free radicals (correct)

Formation of smaller molecules

What factor does NOT control the properties of polymers?

Temperature of application Signup and view all the answers

Which component is NOT typically included in the powder phase of glass ionomer cements (GIC)?

Poly acrylic acid Signup and view all the answers

Which disadvantage is associated with glass ionomer cements?

Weaker bonding to tooth structure Signup and view all the answers

The elimination of a smaller molecule during a polymerization reaction is characteristic of which type of polymerization?

Condensation polymerization Signup and view all the answers

Which of the following represents a key advantage of resin composites over glass ionomer cements?

Better aesthetic appearance Signup and view all the answers

What is a reason for discoloration in resin composites over time?

Poor polymerization technique Signup and view all the answers

What is the primary role of the SA node in the heart?

It initiates the fastest depolarization in the heart. Signup and view all the answers

Which interval in an electrocardiogram represents the time of atrial excitation to ventricular excitation?

P-R interval Signup and view all the answers

How does increased preload affect stroke volume?

Increases stroke volume due to greater stretch of the heart muscle. Signup and view all the answers

What does the cardiac output formula represent?

The total amount of blood pumped out of the heart per minute. Signup and view all the answers

What is the primary factor influencing stroke volume?

Venous return Signup and view all the answers

Which segment of the cardiac cycle indicates that the ventricular myocardium is depolarized?

S-T segment Signup and view all the answers

What is a key disadvantage of using conventional dental amalgam?

Contains mercury Signup and view all the answers

Which characteristic is true for thermosetting plastics?

Are fixed into shape by an irreversible reaction Signup and view all the answers

Which polymer classification is formed through a condensation process?

Alginate Signup and view all the answers

What is the primary structure type of most synthetic polymers?

Cross-linked Signup and view all the answers

Which of the following is NOT a typical application of polymers in dentistry?

Thermal insulators Signup and view all the answers

What process is responsible for the joining of monomers in polymerisation?

Condensation or addition reactions Signup and view all the answers

What is a characteristic of thermoplastic polymers?

They can be remolded multiple times upon heating Signup and view all the answers

Which resin is commonly used for its good bonding properties in dental applications?

Bis-GMA Signup and view all the answers

Which of the following represents a false statement about polymer classification?

All synthetic polymers are thermoplastic. Signup and view all the answers

What is a significant advantage of resin composites over dental amalgam?

Bond directly to tooth structure Signup and view all the answers

What is the primary reason that surfaces have higher energy states compared to bulk molecules?

Surfaces are in a more unstable state due to fewer nearest neighbors. Signup and view all the answers

Which phenomenon describes the loose association of molecules at a surface without forming chemical bonds?

Physisorption Signup and view all the answers

How does surface contamination affect a solid's wettability?

It decreases the solid surface energy, reducing wettability. Signup and view all the answers

What are copolymers primarily formed from?

Two or more different types of monomers. Signup and view all the answers

What effect do crystal planes have on surface energy in metals?

Surface energy depends on the number of nearest neighbors removed. Signup and view all the answers

In resin copolymers, what role does a comonomer serve?

It is a minor component that can assist in cross-linking. Signup and view all the answers

Which of the following statements about surface energy and tension is correct?

Higher surface energy typically leads to better wetting. Signup and view all the answers

What is a key characteristic of block copolymers?

They have monomers clustered into distinct blocks. Signup and view all the answers

Which of these acrylate monomers is not typically used in dental resins?

Polyethylene glycol Signup and view all the answers

What happens to the wettability of a surface when it is cleaned?

Wettability improves as surface energy increases. Signup and view all the answers

What is a primary factor influencing the degree of crystallinity in polyethylene?

The average molar mass and degree of side branching Signup and view all the answers

What occurs to a resin copolymer when the temperature exceeds its glass transition temperature (Tg)?

It will soften and potentially deform Signup and view all the answers

Which statement accurately describes cardiac muscle cells?

They facilitate rapid transmission of action potentials through gap junctions Signup and view all the answers

What role do desmosomes play in cardiac muscle cells?

They anchor adjacent muscle cells together Signup and view all the answers

What initiates the electrical impulses in the conductive system of the heart?

The SA node Signup and view all the answers

What happens during Phase 2 of the cardiac muscle action potential?

Calcium channels open while potassium channels are still active Signup and view all the answers

Which condition accurately defines a functional syncytium in cardiac muscle?

Atria contract before the ventricles due to electrical isolation Signup and view all the answers

Which method is primarily used to synthesize low-density polyethylene (LDPE)?

Radical addition synthesis Signup and view all the answers

How does polymerization impact the glass transition temperature (Tg) of materials?

It can increase Tg beyond that of the monomer Signup and view all the answers

What is the main function of the gap junctions in cardiac muscle cells?

To facilitate electrical communication between cells Signup and view all the answers

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
- CO2 removal
- 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.