Week 2 Lectures: Introduction to Dental Biomaterials PDF

**[Week 2 lectures]** **Introduction to dental biomaterials 2- Dr Touraj** Resin Composites **Pro's Con's** 1. Good aesthetics 1. Technique sensitive 2. Good mechanical strength 2. Discoloration over time 3. Can be bonded to tooth structure 3. Polymerization shrinkage using a bonding a...

**[Week 2 lectures]** **Introduction to dental biomaterials 2- Dr Touraj** Resin Composites **Pro's Con's** 1. Good aesthetics 1. Technique sensitive 2. Good mechanical strength 2. Discoloration over time 3. Can be bonded to tooth structure 3. Polymerization shrinkage using a bonding agent 4. Doesn't bond directly **Polymers (High molecular weight)** - Distinct repeating group of atoms called monomer - Monomers can be gases or liquids which may be converted to a solid polymer after polymerization (bonded covalently) - Polymers are light, versatile, cheap and easily handled materials. **Addition polymerization**- happens when a reaction between two molecules produces a larger molecule without the elimination of a smaller molecule or by-product. - Activation- Process of producing free radicals (Light, heat or chemicals) - Initiation - Propagation - Termination **Free radical radiation**- Free radicals are provided by highly reactive chemicals (initiators) that have unpaired electron - Commonly used free radical producer is benzoyl peroxide (Initiator) **Activation**  **Initiation** **Propagation**  **Termination** A black background with white text Description automatically generated **Condensation polymerization-** happens when a reaction between two molecules produces a larger molecule with the elimination or production of a smaller molecule.  **What controls the properties of the polymers** - 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 the individual chains (Makes structure more rigid). GIC chemical structure **Powder**- Fluoro-alumino-silicate glass and Na-alumino-silicate glass and CaF. Also contains pigments **Liquid**- Poly (acrylic)+ (maleic) or (itaconic) acid, Tartaric acid and distilled water. **Pro's Con's** 1. Less technique and less moisture 1. Relatively poor mechanical strength. sensitive. 2. Weak bonding to tooth structure. 2. Bond directly to the tooth structure. 3. Not the best for aesthetics. 3. Release fluoride 4. Good clinical performance when used correctly. **GIC setting reaction Conventional dental amalgam**  **Amalgam Pro's Amalgam Con's** 1. High compressive strength. 1. Contains mercury. 2. Good clinical track record. 2. Does not bond to the tooth structure. 3. Less technique sensitive. 3. Has poor aesthetic.  Resin Composites are bonded using adhesives (bonding agents). GIC is bonded directly to tooth tissue **[Dr Liddell- L1 Polymers]** **Polymers in dentistry** Polymers find many applications including - Resin-based restorative composites - Impression materials - Dissolvable sutures - Prosthodontics **Polymerisation-** the chemical reactions which bring about joining of monomers. - All polymers consist of a large number of repeating monomeric units **Plastics** Term applied to polymers that can be formed into various shapes by the use of heat and/or pressure. - Thermoplastics are a plastic which 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 (e.g. Bis-GMA or Teg-DMA) - [Bis-GMA] [Teg-DMA]  **Polymer classification** 1. Classification based on origin i. Biopolymers (Carbs, proteins, DNA)- Most important biopolymers are formed by a condensation process eliminating H~2~O. a. Alginate is naturally derived biopolymer used in synthesis of dental impression materials b. Synthetic polymers (LDPE, PVC, nylon...) (2 synthetic roots are Condensation (nylon) and addition (LDPE) polymerization) **Polymer classification 2** 2. Classification from thermal behaviour: i. Thermoplastic (nylon, PMMA, LDPE) ii. Thermoset (BisGMA, TegDMA) Cannot be reshaped due to irreversible hardening/cross-linking upon curing. **Polymer classification 3** 3. Classification from structure of polymer: i. Linear ii. Branched iii. 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. 4. Classification of chemistry of monomer structural unit: Resin: a synthetic organic polymer system used in many plastics i. Acrylic resins (PMMA, bis-GMA) ii. Polyamide resins 5. Classification based on number of monomers involved in chemistry i. Homopolymer: only 1 monomer e.g. HDPE ii. Copolymers- 2 or more monomers **Synthetic polymer classifications** 1. Addition polymerization: the whole monomer becomes part of the polymer. 2. Condensation polymerization: the monomer is in with the loss of a small molecule such as H~2~O or HCl **Common synthetic polymers** **Chain growth**- monomers are added one at a time to the growing polymer **Step growth**- the polymer may grow from both ends. Growing polymer, monomers and oligomers (n\>10) may all react with each other. **Addition Polymers- chain growth** - Growing polymer has a reactive end group that only reacts with monomers. At each monomer, addition regeneration of a reactive end group occurs at the chain terminus. - Reaction proceeds as long as there are reactive end groups and monomers available. - No loss of atoms in polymerization Addition polymerization may take one of three mechanisms: 1. Radical chain growth polymerizations 2. Ionic chain growth 3. Ring opening polymerization: polar **Radical chain growth** 1. Radical chain growth polymerization Radical: a species with a single unpaired electron- they are highly reactive. Radical polymerization requires a source of radicals- initiation systems - Common initiators include: A. Benzoyl peroxide, CQ - Thermal production of radicals from initiator (benzoyl peroxide heat cure) - Visible light production of radicals from photo initiator system a. Camphorquinone (CQ, amine) light cure **Dental resin copolymers** Most dental composites combine a base acrylate monomer with another acrylate comonomer to form a copolymer. A structure of acrylate Description automatically generated  A structure of methanol Description automatically generated Radical chain growth Addition polymerisation of alkenes can occur via a radical mechanism.  **Polymer branching** During propagation, the active radical site may remain at the end as propagation proceeds, but not always. It is also possible for the active site on a growing polymer to transfer somewhere else on the chain, or to jump from one polymer to another and not necessarily to the end of the polymer. The latter is called chain transfer to polymer. Either route leads to branching. **Degree of branching** - Degree of branching is affected by steric hinderances, flexibility of polymer and synthesis conditions - Sometimes the active site in a growing polymer can transfer onto an unreacted initiator or other molecule. **Dead polymer-** when the polymer stops growing (termination is achieved) **Cross-linking** - A way of introducing stiffness into a polymer by bonding chains together. - Plasticizers are low molecular weight compounds added to a polymer to soften it - These molecules keep chains separate, inhibiting crystallinity. **Polycarbonate** **Polycarbonate crowns-** High impact and tensile strength Polycarbonate is now manufactured by condensation of bisphenol A and diphenyl carbonate avoiding use of the hazardous phosgene - Step growth polymer involving condensation of phenol which is removed by distillation. a. Some BPA may remain and there are toxicity concerns as a result. **Epoxy resin** Ring-opening polymerization- used as root canal sealers, ring opening mechanisms. **Condensation polymers** Synthesis is a step-growth polymerization where condensation happens. The polyamide is then processed by melting and spinning which orients the fibres and forms strong H-bonds **Lactomer polymers** - Lactomer sutures are biodegradable and adsorbable and do not need removal - Condensation polymerization reaction between glycolic acid and lactic acid yielding water. - Sutures dissolve as hydrolysis of ester linkages occurs- complete after 40 days + **[Dr Liddell L2- Rheology]** **Surface tension**- the energy required to increase the surface area of a liquid (J/m^2^) - Molecules at the surface are less stable and so the surface area is minimized - Water has a high surface tension as it forms multiple H-bonds. Considerable energy must be put in to increase the surface of liquid H~2~O. to break H-bond network. - The ability of objects to remain on the surface of water relies on high surface tension of water **Surfactants-** molecules which lower surface tension in liquids- also known as surface active agents - Surface active agents congregate and align at surface of liquid this lower surface tension with increasing concentration **Capillary action-** the spontaneous rising of a liquid in a narrow tube due to surface tension. Arises as a result of high cohesive (intermolecular) and high adhesive (liquid/wall) forces. - Adhesion pulling up, surface tension pulling in: creates an upward force, gravity determines the height of the column **Capillarity-** The high surface tension and high capillarity of water is due to hydrogen bonding. - Mercury has a higher surface tension than water due to metal-metal bonds at the surface. It has a low capillarity due to weak Hg-SiO~2~ interactions **Examples of Capillarity** Tear duct- capillary movement of tears through the lacrimal canals keep the eyes lubricated. A capillary drainage system. - Capillary action of saliva occurs in the crevices around and between teeth and around dental restorations. Marginal leakage caused by a thin film of saliva in a crevice is an aspect of capillary action. **Rheology/Viscosity** - Intermolecular and interatomic forces in liquids and solids have important consequences for physical properties and behaviour. - Key properties for dentistry- surface energy, surface wetting and rheology. (Nature of surface is key) Liquid: surface energy=surface tension Solid: surface energy Rheology- study of deformation and flow of matter against variables such as temperature, pressure, time and applied stresses. Viscosity- Measured to assess flow character of a liquid, semi-solid, gel - It is a measure of a fluid's resistance to flow (fluid internal friction) - Surface energy for solids is the energy difference between the surface molecules/atoms and the bulk. - For liquids it is the work/area done by the force required to overcome intermolecular forces and create a new surface - Units-J/m^2^ - As temperature increases, surface energy decreases **Surface tension/viscosity** - No easy relationship between viscosity and surface tension (static property) - Mercury has a high surface energy on account of multiple interatomic metallic bonds - Glycerol has a high viscosity on account of aggregation and hydrogen bonds. **Shear stress/viscosity** Viscosity- fluids normally more viscous at low temperatures and less viscous at high temperatures. Shear stress- force causes deformation by slippage along a plane parallel to an imposed stress- used to assess flow character such as viscosity Shear thinning- viscosity decreases under increased shear stress Thixotropy- time dependent shear thinning property (example) **Viscosity in Alkanes** - Viscosity is associated with molecule size and intermolecular forces. These relationships arise because of how easily molecules may move past each other. - Surface energy (tension) is increased in the alkane series which relates to an increase in dispersion forces **Surfaces** - 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- falling liquid drops. - 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 chmically bonded) (loose association van der waals) and chemisorption (chemically bonded)(bonded covalent or ionic) can occur. **Surface energy table**  **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 **[Dr Liddell L3- Dental Polymers 2]** **Copolymers** - Formed from 2 (or more) different types of monomer , A and B. - Block= each monomer clustered into blocks - Graft=linear back bone 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 a. 22% by weight polymer- comonomer viscosity diluent and cross-linking - Heraeus Kulzer Durafill- bisGMA/UDMA a. 40% by weight - 3M filtek P60 bisGMA/UDMA/bisEMA a. 27% by weight - Filtek A110- bisGMS/TEGDMA Copolymers are used to achieve a high degree of crosslinking and assist in making the uncured composites workable with respect to viscosity bisGMA intermolecular hydrogen bonding between hydroxyl H and lone pairs on oxygen (donar-acceptor): high viscosity TEGDMA- low molecular weight of TEGDMA H bond acceptors only: lower viscosity **Light Cure** - Light cure resin- photochemically activated - Single tube that includes monomers such as bisGMA and initiators - **Camphorquinone (CQ) + dimethylaminoethyl methacrylate (DMAEMA)** - Requires violet/blue around 440-480 nm to produce excitable state of CQ molecules, that reacts with DMAEMA- producing radicals **Degree of conversion** - Measure of percentage of carbon double bonds (in an acrylate resin) that have been converted to single bonds during polymerization - Unreacted monomer is reactive and often causes allergic reactions - DOC may be determined from the change in absorbance of IR radiation of the methacrylate double bonds between cured and uncured resin - Different functional groups absorb IR radiation at different frequencies or wavenumbers (cm^-1^) **DOC measurement** DOC equation for bis-GMA like monomers: A black line with text Description automatically generated **Characterising polymers** - Polymer architecture a. Most synthetic polymers from linear chains with varying lengths- average length - Synthetic polymers generally have extensive branching and cross linking **ATM and Polymers** Atomic force microscopy allows polymers to be directly imaged **Stereochemistry** - Polymer properties influenced by presence and orientation of groups on chiral centres - Isotactic polymers- synthesis promoted by certain catalysts **Degree of polymerization** - Average number of monomers per polymer  **Crystallinity** - Polymers are generally amorphous solids. - Usually with a mix of ordered domains (short range order) and disordered amorphous domains (no order). The relative amounts depend on the polymer, synthesis used and its conditions - Degree of crystallinity (by mass) may be approximated by:  **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 functional group e.g. comonomer - Crosslinking here increases the glass transition temperature- Tg **Resin Copolymers and Tg** - Polymerisation substantially increases the glass transition temperature, well above that of the monomer - Copolyermisation 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 **[Dr Simcock L1- Cardiovascular physiology]** The cardiovascular system consists of: - Blood vessels - Heart Conductive system: - Automatic - Initiate electrical impulses - Distribute throughout heart - Ensures all cells depolarize and muscles contract in a coordinated manner Transports blood around body for: - Oxygen diffusion - CO~2~ removal - Transport of waste - Immune function **Cardiac muscle** - Chamber muscles contract (changes blood volume) as one: functional syncytium Heart muscle has: - Unique cell structure- contractile muscle cells and excitatory and conductive cells. - Its own signal generator - Its own conducting system 1. Creates arithmetic pressures 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- splits 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 tiimes/min - SA node usually dominates (Pacemaker) - Sequence 1. SA node- fastest depolarization in heart 2. SA node is connected to adjacent myocardial cells which send impulse 3. AV node (delays impulse conduction from atria to ventricles) (slow) a. Pace set by AV is junctional rhythm 40-60 beats/min 4. AV bundle (bundle of His) (only electrical connection between at and ve) 5. Bundle branches 6. Endocardial network (Purkinje fibres) - Contraction: atria then ventricles **Pacemaker cell action potential** **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 **The cardiac cycle**- All events occurring from beginning of one heartbeat to the beginning of next **The normal sequence** P-R interval - Atrial excitation to ventricular excitation - Can 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* *outpout* = *stroke* *volume* *x* *heart* *rate*]{.math.display}\ - Cardiac output= venous return - cardiac output= arterial pressure/total peripheral resistance - the amount of blood pumped out depends on: 1. How many times the heart beats 2. How much blood is in the ventricles 3. How much pressure is developed in the ventricles 4. 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 - Venous return- quantity of blood flowing from veins into the right atrium each minute 1. Increased by: a. Exercise b. Increased ventricular filling time - High venous return, heart contracts forcefully, increases stroke volume **Contractility** - Contractile strength - Independent of stretch (Frank-Starling law) - More calcium ions enter cytoplasm from extracellular fluid and sarcoplasmic reticulum - Contractility goes up, blood ejected from heart goes up, stroke volume goes up - Sympathetic stimulation increases contractility - Sympathetic innervates SA node, AV node and heart muscle - Norepinephrine or epinephrine binding increases calcium ion entry and force of contraction **Afterload** - The pressure that the ventricles have to overcome to eject blood - Back pressure exerted by arterial blood on the aortic and pulmonary valves - Doesn't really affect stroke volume in healthy people **Regulation of heart rate** - Increase heart rate- positive chronotropic factors - Decrease heart rate- negative chronotropic factors **Autonomic nervous system regulation of Heart rate** - Emotional or physical stressors activate SNS - Norepinephrine release - Binds to beta 1 receptors in the heart - SA node fires more rapidly - Heart beats faster **Chemical regulation of heart rate** **Hormones** - Epinephrine - Thyroxine- increases metabolic rate and production of body heat (increase HR) **Ions** - Imbalance of intracellular and extracellular electrolytes can affect heart function **Nervous input** - Sympathetic simulation 1. Direct connections 2. Noradrenaline 3. Increases IC calcium and increases contraction of B1 4. Also increases heart rate of B1 5. Effects via cyclic AMP Parasympathetic stimulation - Via vagus - Slows heart M2 - Hyperpolarises cells - Little effect on contraction **Summary of cardiac output**  **Blood pressure** - Blood in vessels is flowing-creates pressure - Pressure=driving force for blood to move - Blood pressure=force blood applies blood vessels - Vessels create a resistance to flow - Need pressure to overcome resistance to get blood to flow **Diastolic pressure- (periods of relaxation in cardiac cycle)** - When the heart is not pumping blood: 1. Lowest pressure 2. Diameter of all arteries feeds back to pulmonary ateries and aorta 3. Total peripheral resistance **Systolic pressure- (periods of contraction in cardiac cycle)** - When heart is pumping blood: 1. systolic pressure 2. sum of diastolic and extra from heart - Difference between systolic and diastolic= pulse pressure **Typical flow** - Can redirect flow according to need - Variation is mostly skeletal muscle, skin, gut - Autonomics and local events **What controls overall blood pressure** - The body maintains a control of arterial blood pressure - Measured at baroreceptors - Feedback to the: 1. Cardioinhibitory 2. Cardioacceletory 3. Vasomotor centres - Moderated by higher brain centres **Ventricular filling- (passive ventricular filling Isovolumetric contraction** **and atrial contraction** - Mid/late diastole - Atria relaxed - Atria and ventricles fill - Ventricles contract - Pressure increasing slightly - Large pressure rise - Large volume increase in ventricles - No volume change in ventricles - AV valves open, SL valves closed - AV valves close, SL valves closed **Ventricular ejection Isovolumetric relaxation** - Ventricular systole - Early diastole (closing of valve)thy - Ventricles contracting - ventricles relax - SL valves open, AV closed - Large pressure change - Large volume change in ventricles - No volume change in ventricles - Rise then fall in pressure - 60% of volume is ejected from heart. **Response to low pressure Response to high pressure** **Cardiac muscle** - Striated - Contracts via sliding filament mechanism - Cells are short, branched and interconnected - One or two centrally located nuclei **Summary** - Contractile tissue - Contraction of muscle preceded by depolarization in the form of action potential - Sarcoplasmic reticulum releases calcium ions required for contraction - Cardiac cells electrically joined by gap junctions - No neural input required **Cardiac output** - Quantity of blood pumped into the aorta in one minute - Quantity of blood that flows through the circulation **Components of blood pressure** - Systolic pressure - Diastolic pressure - Pulse pressure - Mean arterial pressure **Mean arterial pressure** 1. =diastolic + pulse/3 2. = average overall 3. = takes out variability **Pressure changes in the vascular tree** - The heart pumps blood into the vessels - Pumping creates pressure to drive flow of blood through vessels - Flow is pulsatile, but smoothed out by arteries - Flow to capillaries is relatively constant **Typical flows from aorta to organs** - Can redirect flow according to need - Variation is mostly skeletal muscle, skin gut - Autonomics and local events **Varying blood flow** - Not enough blood to be everywhere - Redirected according to need - Pumped around faster if demand high - Pressure is 'relatively' constant - Flow is determined by resistance **Resistance in tissues** - Resistance in arterioles a. Sympathetic control 1. Noradrenaline- vasoconstriction - Renal control - Local control 1. Acetylcholine 2. Adrenaline 3. Local metabolites 4. Nitric oxide