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Learning Objectives Chemical Properties of Direct Dental Materials Week 2 - pH, GIC Cements, Rheology Lecture 1 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS • Understand the pH scale and describe pH and pOH • Define the terms acid, base, buffers, amphoteric • Identify conjugate aci...

Learning Objectives Chemical Properties of Direct Dental Materials Week 2 - pH, GIC Cements, Rheology Lecture 1 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS • Understand the pH scale and describe pH and pOH • Define the terms acid, base, buffers, amphoteric • Identify conjugate acid-base pairs • Describe the difference(s) between strong acids/bases and weak acids/bases. • Describe the “strength” of an acid or base in terms of the extent to which its molecules donate (acids) or accept (bases) protons. • Write the equilibrium constant expression for the reaction of an acid (Ka) or a base (Kb) with water. https://essenciainmobiliaria.com/essencia-idea/ https://www.ic-network.com/tmd-ic-copcs-how-a-dental-condition-changed-the-future-of-ic-and-chronic-pain-research/ Content • Acids and Bases • pH Scale • Buffers • Amphoteric Amino Acids • Ionic Products of Water Kw • Conjugate Acid-Base Pairs • Acids Ex. Acid Etching • Percent Dissociation • Assumptions with Dissociation Constants • Henderson-Hasselbalch Equation • Bases Acids and Bases • H+ concentration relative to pure water • Acid: H+ concentration greater than 1x10-7M • increases the concentration of hydrogen ions (H+) in a solution • Donates H+ through dissociation • Base: H+ concentration less than 1x10-7M • raises pH by providing hydroxide (OH−) or another ion or molecule • pH = -log10 [H+] • pOH = -log10[OH-] https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRi-oGB1mfpjBDHUxcoDlWFUuuePY2RYYzwSuSvBKjOLzOz6AdhezHn2UszAJ9ckVQgAgM&usqp=CAU Acids and Bases pH Scale • pH Scale • Rank solutions based on acidity or basicity (alkalinity) • Logarithmic • 1 pH unit = 10 fold change in H+ • pH + pOH = 14 https://s3.studylib.net/store/data/009465038_1-44613fb67685d7c19551c4db2612526d.png https://cdn.kastatic.org/ka-perseus-images/7ca9aecccf7e9d5caaf1ea10d2835c81f4036708.png Buffers • Buffer: solution that resists changes in pH when small quantities of an acid or base are added to it • Conjugate acid-base pair: a pair differ from each other by the presence or absence of the transferable hydrogen ion Amphoteric Amino Acids • Acts as an acid in the presence of a base • Acts as a base in the presence of an acid • Amphoteric: substance acts as either an acid or a base https://alevelchemistry.co.uk/definition/amphoterism/ http://embracethebase.weebly.com/uploads/5/0/0/1/50010253/4179700.gif?372 Ionic Product of Water Kw Ionic Product of Water Kw • Water can act as an acid or base • At equilibrium • Simplified equation • Kw – equilibrium constant for water Summary Conjugate Acid –Base Pairs • Water can undergo autoionization to produce H3O+ and OH- ions • The equilibrium constant for the autoionization of water Kw is 10-14 at 25oC • A neutral solution: [H3O+] = [OH-] • An acidic solution: [H3O+] > [OH-] • A basic solution : [H3O+] < [OH-] • For aqueous solutions at 25oC • Acid: the molecule that loses the H • Base: The molecule that gains the H • Conjugate Base: the molecule “left behind” after the acid loses the H • Conjugate Acid: the molecule formed after the base gains a H https://j-tradition.com/acid.html Acids Acids • Strong/Weak vs Concentrated/Dilute • Strength – proportion has reacted with water to produce ions • Concentration – how much of acid is dissolved in solution • Weak Acid: an acid that does not fully ionize in water • Example • Strong Acid: an acid that is virtually 100% ionized in solution • Example • Strength of an acid depends on how much it dissociates • More dissociation = stronger acid • Acid Dissociation Constant (Ka) – equilibrium constant for acid dissociation reaction • quantify strength of acid • Simplified Form Acids • pH decreases as the concentration of the acid and/or Ka increases pKa = -log Ka Acids • What is the strongest acid listed in the table? • The lower the pKa value, the more acidic the solution http://saintssnrchem.weebly.com/ka-and-pka.html Percentage Dissociation Acid Etching • Percentage Dissociation of a weak acid • Roughens tooth surface • Dissolves enamel and dentine minerals • Controlled erosion • Creates tags and tunnels • Better absorption of bonding resin • 35-37% Phosphoric Acid for 15-30 seconds https://rickwilsondmd.typepad.com/rick_wilson_dmds_blog/2010/11/enamel-bonding-dentin-bonding.html • If nitrous acid (HNO2) has a Ka of 4.0 x 10-4 at 25oC, what is the percent dissociation of nitrous acid in a 0.400M solution? • Step 1: write a balanced chemical equation https://dentistry.co.uk/2018/07/02/delicate-art-etching/ Percentage Dissociation Percentage Dissociation 10-4 25oC, • If nitrous acid (HNO2) has a Ka of 4.0 x at what is the percent dissociation of nitrous acid in a 0.400M solution? • If nitrous acid (HNO2) has a Ka of 4.0 x 10-4 at 25oC, what is the percent dissociation of nitrous acid in a 0.400M solution? • Step 3: Find [H+] and [NO2-] at equilibrium • Step 2: Write the expression for Ka Simplified Expression: Percentage Dissociation 10-4 Percentage Dissociation 25oC, • If nitrous acid (HNO2) has a Ka of 4.0 x at what is the percent dissociation of nitrous acid in a 0.400M solution? • If nitrous acid (HNO2) has a Ka of 4.0 x 10-4 at 25oC, what is the percent dissociation of nitrous acid in a 0.400M solution? • Step 3: Find [H+] and [NO2-] at equilibrium • Step 3: Find [H+] and [NO2-] at equilibrium Simplified Expression: x = -0.004 ± √1.6 x 10-7 – 4 (1)(-1.6 x 10-4) We need: ax2 + bx + c = 0 2 (1) x2 = 4.0 x 10-4 (0.400 –x ) x2 = 1.6 x 10-4 – 4.0x 10-4 x = -0.0004 ± √0.00064 2 x2 + 4.0 x 10-4 – 1.6 x 10-4 = 0 x = -0.014645 or x = 0.012445 Percentage Dissociation 10-4 Simplified Expression: If you anticipate the value of x will be significantly smaller than Ka x2 = 4.0 x 10-4 x 0.400 x = √0.00016 x = 0.012M Assumptions with Dissociation Constants 25oC, • If nitrous acid (HNO2) has a Ka of 4.0 x at what is the percent dissociation of nitrous acid in a 0.400M solution? • Step 4: Calculate percentage dissociation % dissociation = [NO2-] [HNO2] X 100 = 0.012 M 0.400 M X 100 = 0.03 x 100 =3% • Weak acids and bases • Change in concentration is negligible compared to the initial concentration • Small Ka or Kb value (K < 10-3) • Change in concentration is equal to or less than 5% ! • % change = x 100 "#"$"%& '(#')#$*%$"(# Assumptions with Dissociation Constants Henderson-Hasselbalch Equation • Calculate the pH of bottled vinegar that is 0.667 M HC2H3O2. Ka = 1.8 x 10-5 • Relationship between pH and pKa or pOH and pKb Initial Change Equilibrium ! Ka = 0.667M -x 0.667 - x 0 +x +x $ &" pH = pKa + log10 ([A–]/[HA]) -., ./'!" ! [#"!#$" ] [!#"!#$"] 0 +x +x &" 1.8 x 10-5 = '.))*+& ≈ '.))* x = (1.8 x 10+, )(0.667) x = 3.5 x 10-3 M % change = '.))* = 0.5% x 100 • Used for weak acids and weak bases • Not used for strong acids and strong bases pH = -log(3.5 × 10-3) = 2.46 Henderson-Hasselbalch Equation Bases • Calculate the pH of bottled vinegar that is 0.667 M HC2H3O2. Ka = 1.8 x 10-5 • Strong Base: a base that is virtually 100% ionized in solution • pH between 10 - 14 • Weak Base: partially dissociates to give ions in solution • pH below 10 • Base Dissociation Constant (Kb) - equilibrium constant for basic dissociation reaction Initial Change Equilibrium 0.667M -x 0.667 - x 0 +x +x 0 +x +x pH = pKa + log10 ([A–]/[HA]) = -log(1.8 x 10-5) + log (3.5 x 10-3 M/ 0.667) = 2.46 • pKb = -log Kb Summary • For a generic monoprotic weak acid HA, with conjugate base equilibrium constant has the form: References A- the • The acid dissociation constant (Ka) quantifies the extent of dissociation of a weak acid. • The larger the value of Ka the stronger the acid • For a generic weak base B, with conjugate acid BH+ the equilibrium constant has the form: • The base dissociation constant (Kb) quantifies the extent of ionization of a weak base. • The larger the value Kb the stronger the base Textbook: Brown-Le May-Bursten-Murphy-Langford Sagatys “Chemistry The Central Science: A broad perspective 2e” (Pearson, 2014). • Acid and Base Theories - pages 527-529 • Conjugate Acid-Base Pairs - pages 529-530 • Acid and Base Strengths - pages 530-531 • The pH of Scale - pages 533-536 • Strong Acids and Bases - pages 536-538 • Weak Acids - pages 539-546 • Weak Bases - pages 547-549 • Buffers - pages 572 - 578 Learning Objectives Chemical Properties of Direct Dental Materials • Know the basic terminology associated with rheology • Understand salivary pH and the associated buffers • Be familiar with dental cements and local anaesthetics Week 2 - pH, GIC Cements, Rheology Lecture 2 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS https://essenciainmobiliaria.com/essencia-idea/ https://www.ic-network.com/tmd-ic-copcs-how-a-dental-condition-changed-the-future-of-ic-and-chronic-pain-research/ Content Rheology • Rheology • Wetting • pH • Body pH • Salivary pH • Dental Cements • Zinc Phosphate Cement • Local Anesthetic • Rheology is the study of flow of materials • Applied for solids and liquids • Viscosity • Resistance to flow • Working Time • Manipulation of materials • Setting Time: time taken for a material to reach its final set state Wetting Wetting • Used by bonding mechanisms • Wet adherent surface • Flow of adhesive to undercuts and over surface area • Contact angle • Measure of wetabillity • Low contact angle = good wetting • High contact angle = poor wetting • High surface energy reacts with surroundings to form a lower surface energy • Tooth surface has lower surface energy • Resin may not spread if surface energy of resin is higher than the surface energy of the tooth • Etch tooth surface • Increase in surface energy of tooth • Optimize chance for chemical bonding and mechanical interlocking https://justpaint.org/wp-content/uploads/2015/05/Page7_11.jpg Enamel before acid etching Enamel after acid etching https://analyticalsciencejournals.onlinelibrary.wiley.com/cms/asset/b8363ba2-b577-457f-afd5-472884d9eabd/jemt23333-fig-0001-m.jpg https://www.ultradent.com/products/categories/bond-etch/etchants/ultra-etch Body pH pH • Low blood pH = metabolic acidosis • High blood pressure • Kidney disease • Diabetes • Water can undergo autoionization to produce H3O+ and OH- ions • The equilibrium constant for the autoionization of water Kw is 10-14 at 25oC • A neutral solution: [H3O+] = [OH-] • An acidic solution: [H3O+] > [OH-] • A basic solution : [H3O+] < [OH-] • For aqueous solutions at 25oC • High blood pH = metabolic alkalosis • Adrenal disease • Alcohol abuse https://www.expii.com/t/ion-balance-regulation-homeostasis-10106 https://courses.lumenlearning.com/wmopen-nmbiology1/chapter/the-ph-scale/ Salivary pH Salivary pH • Ranges between 6.2 and 7.6 • Changed by • food and drink • Bacteria in mouth • Age • pH < 5.5 = demineralization • Enamel breakdown • Dentine exposure • Discomfort • Buffer – maintains approx pH when small amounts of acid or base are added • Resistant to changes in pH • 3 systems in saliva 1. Carbonic acid/bicarbonate buffer 2. Phosphate buffer 3. Protein buffer https://www.the-scientist.com/lab-tools/tools-for-drools-35231 https://courses.lumenlearning.com/wmopen-nmbiology1/chapter/the-ph-scale/ Salivary pH Salivary pH • 3 systems in saliva 1. Carbonic acid/Bicarbonate Buffer • Major buffer in stimulated saliva • Saliva flow rate increases, bicarbonate concentration increases • Carbonic acid → Carbon dioxide and water by carbonic anhydrase VI • Phase Buffering –CO2(l) to CO2(g) Carbonic 2. Phosphate Buffer anhydrase VI 3. Protein Buffer https://socratic.org/questions/what-is-the-carbonic-acid-bicarbonate-buffer-system-1 https://www.the-scientist.com/lab-tools/tools-for-drools-35231 • 3 systems in saliva 1. Carbonic acid/bicarbonate buffer 2. Phosphate buffer • Active in unstimulated saliva • pKA ranges 6.8-7.2 • Limited effect because of a low phosphate in the oral cavity during eating 3. Protein buffer http://edusanjalbiochemist.blogspot.com/2012/11/buffer-systems-and-their-roles-in.html https://www.the-scientist.com/lab-tools/tools-for-drools-35231 Salivary pH Salivary pH • 3 systems in saliva 1. Carbonic acid/bicarbonate buffer 2. Phosphate buffer 3. Protein buffer • Buffering below pH 5 • Amino acids have + amino group and – carboxyl group • Salivary proteome • Amylase, mucin, IgA and albumin suspected to be involved https://courses.lumenlearning.com/cuny-kbcc-ap2/chapter/acid-base-balance-no-content/ • Indications of unbalanced salivary pH • Persistent bad breath • Sensitivity to hold or cold foods/beverages • Tooth cavitation • Salivary dysfunction can be caused by • Salivary gland pathology • Head and neck radiation • Sjorgen’s syndrome • Diabetes https://www.the-scientist.com/lab-tools/tools-for-drools-35231 Dental Cements • Used for • Retention (luting) of restorations or ortho bands • Pulpal protection • Temporary or permanent restorations • Root canal sealers • Anticariogenic effects • Classified based on composition 1. Phosphates/Silicophosphate – Zinc phosphate 2. Phenolate – Zinc oxide-Eugenol 3. Polycarboxylate - Zinc polycarboxylate and glass-ionomer cements 4. Resin https://www.gcamerica.com/products/preventive/Saliva_Check_BUFFER/ Zinc Phosphate Cement • Hand-mixed powder-liquid system or capsule • Powder components (Base) • ZnO – main component • MgO – improves mechanical properties and colour stability • SiO2 or Al2O3 – improve mechanical properties and shade variety • SnF2 – anticariogenic effects • Liquid component (Acid) • H3PO4 – 45-64% • AlPO4 and/or ZnPO4 - (2-3%) buffer, stabilize pH and reduces the reaction rate • H2O – regulates ionization of the liquid, influences setting rate of the cement https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQYAlcVKa7EtlJqt5cJOU3zjR8izLRum1n56KPyBldv2PQ8OJPMemiu07O742ydIlSiKfQ&usqp=CAU https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQYAlcVKa7EtlJqt5cJOU3zjR8izLRum1n56KPyBldv2PQ8OJPMemiu07O742ydIlSiKfQ&usqp=CAU Zinc Phosphate Cement 3 ZnO + 2 H3PO4 Zn3(PO4)2 + 3 H2O powder liquid • Acid attacks and dissolves out later of ZnO • Release of Zn2+ • pH changes in cement • pH 1.6 after 2 minutes • pH 4.0 after 1 hour • pH 6.0-7.0 after 24 hours https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRZ4Bs9I5ElDdgTTAQCcR_N2HArD3AEDQC3gwtowRZpUlW8ci_xs17zYYEUTQJ4sjEx358&usqp=CAU Local Anesthetic • Interrupts neural conduction by inhibiting sodium ions • Hydrochloride salt • At time of injection • Molecules in quaternary, water soluble state • Can’t penetrate neuron • At time of onset, pH 7.4 • Molecules convert to tertiary, lipidsoluble structure https://healthjade.net/local-anesthesia/ Local Anesthetic • pKa • Predicts the proportion of molecules in lipid soluble and water-soluble forms • > 7.4 • Greater proportion of molecules exist in quaternary, water-soluble form • Infection creates an acidic environment • Favors quaternary, water-soluble form Local Anesthetic DS1102 Thank You SURFACE ENERGY VISCOSITY & RHEOLOGY Learning Objectives Have a question? • Role of intermolecular (interatomic) forces and physical properties, in particular surface energy and viscosity • Significance of the H bond – relevance in many dental materials • Origins of surface energy (surface tension) • Bring your questions to the lectures, labs or tutorials • Email: [email protected] • Schedule a time to meet one on one with me • Wetting and spreading of liquids on surfaces L10 / DS1102 INTERMOLECULAR FORCES DS1102 1 INTERMOLECULAR FORCES II Intermolecular bonding refers to weak (electrostatic) forces acting between molecules (typ solid and liquid phase). 3 types in order of increasing strength: Most dental materials (e.g. cements, etchants, composites, amalgams) are applied as liquids to surfaces so that flow, viscoscity and surface wetting are critical parameters to material performance Dispersion forces (London forces) –electrostatic attractions between fleeting instantaneous dipoles of atoms/molecules Only force in eg. He(l), N2(l), F2(l) Dipole-dipole forces – attractive and repulsive interactions of permanent molecular dipole Intermolecular forces affect viscosity and surface energy, affecting liquid flow and surface wetting H Cl Cl H Hydrogen bonding – a special form of dipole-dipole force involving O, N, or F lone pairs and a H bonded to N, O or F. L10 / 2 L10 / 3 THE NATURE OF THE H-BOND DS1102  An H-bond forms DS1102 DONOR H BONDING EXAMPLE ACCEPTOR  when an H atom covalently A H Y bonded to an appropriate X donor atom (N, O, F) is strong covalent bond weakly connected hydrogen bond through space to one (or more) other acceptor atoms (N, O, F). • The donor atom must act as an electronwithdrawing group. eg. X = F, O, N. • The acceptor atom must have an available lone pair on the acceptor atom. eg. A = F, O, N. L10 / QUESTIONS DS1102 DS1102 5 INTERMOLECULAR FORCES IV The forces between molecules (intermolecular)/atoms (interatomic) in liquids and solids has important consequences for physical properties and behaviour eg, bp, mp, vapour pressure, crystallisation Could you… • Define a hydrogen bond..? • Identify molecules that may partake in hydrogen bonding…? Of particular relevance to dentistry is surface energy (surface tension), surface wetting and rheology • Draw a molecule(s) and show how hydrogen bonding takes place? • Rank the relative strength of the intermolecular forces between molecules? L1 / DS1102 L1 / 4 6 INTERMOLECULAR FORCES II Surface energy (dental texts) and surface tension (physical science texts) are equivalent Rheology is the study of deformation and flow characteristics of matter (rheo – greek to flow) against variables such as temp, pressure, time and applied stresses. DS1102 L10 / 7 TYPICAL VISCOSITY Viscosity associated with molecule size and predominant intermolecular forces and relates to how easily molecules/atoms may move past each other Viscosity is a measure of a fluids resistance to flow It can be thought of as an “internal friction” Increased surface energy relates to loss of some of the stabilising intermolecular interactions at surface Falling ball viscometer is a quick and easy way to determine viscosity from terminal velocity of falling ball, densities of ball and fluid, ball radius and gravity (9.8 m/s2) Units of viscosity are centipoise (cP) 1 cP (centipoise) = 0.001 kg m-1 s-1= .001 N s m-2 Surface energy relates to the energy required to overcome intermolecular forces to create a new surface in a fluid L10 / Viscosity (cP) 0.326 .409 .542 .711 1.42 8 Increasing size Increasing dispersion forces (cP)Surface energy (mN m-1) 17.89 19.66 21.14 22.38 23.37 L10 / 9 SURFACE ENERGY DS1102 • Surface energy is a property of a liquid or solid surface • It arises because atoms/molecules at a surface are not attracted equally in all directions to other atoms/molecules around them • Molecules/atoms at surface are at a higher energy state (not as stable) as those below the surface DS1102 SURFACE ENERGY II Importantly, liquids can adjust their shape to minimise their surface energy but solids can’t. => falling liquid forms drops Surfaces are important to chemists because it is at the surface that physicoabsorption, chemisorption and catalysis can occur Surface energy affected by intermolecular forces, functional groups present and, for metals, crystal planes presenting at surface L10 / 10 CRYSTAL PLANES DS1102 100 plane L10 / 11 DS1102 SURFACE ENERGY VS SURFACE TENSION • Surface tension and surface energy often used interchangeably • Units: surface tension N/m  surface energy J/m2 Nm-1 = Nm m-2 = J/m2 1 Nm = 1 J work = force x distance F • because values are small, milli prefix often used mNm-1 Surface energy of a metal plane depends on number of stabilising nearest neighbours “removed” to form the surface eg, 4 for (100) plane ; 3 for (111) plane • Surface energy relates to work done by a force creating a new surface L10 / 12 DS1102 TYPICAL SURFACE ENERGY Surface Surface energy (mJ/m2) Enamel (“in situ”) Dentin (“in situ”) Gold alloy (“in situ”) 92 87 54 Au/Ag/Cu Alloy Al Mercury(25 ) Glass 1065 1160 486 310 Water (25 ) Saliva (37.5 ) Hydrogen Peroxide Ethanol Benzene 73 53 74 23 28 Note: for metals, presence of oxides/contaminants can change surface L10 / 14 energy considerably L10 / 13 DS1102 SURFACE TENSION Water has a high surface energy because it forms multiple intermolecular H-bonds. Considerable energy must be put in to increase the surface area of liquid H2O by breaking the Hbonds. •The ability of light objects (insects) to remain on the surface of water relies on the high surface energy of water. (or tension) •Mercury has even higher surface energy on account of multiple interatomic metallic bonds L10 / 15 SURFACE TENSION DS1102 Viscosity cP Surface Tension (mN m-1) 1.0 1.6 1.2 1.2 1490 0.3 73 486 74 22 76 18 Water Mercury H2O2 Ethanol Glycerol n-hexane H-bonding Metallic H-bonding H-bonding H-bonding dispersion TRENDS I DS1102 Trends surface energy Hg 486 Metallic H2O 73 H2O2 74 Hexane 18 mNm-1 H-bonding dispersion Metallic > H bonding > dipole > dispersion Maybe Hg will be most viscous??? L10 / 16 TRENDS II DS1102 Trends Viscosity L1 / 17 TRENDS III DS1102 Glycerol viscosity vs water? Hg 1.6 H2O 1.0 H2O2 1.2 486 73 74 hexane 0.3 cP 18 mNm-1 Glycerol Viscosity Surface Energy Viscosity 1490 Water 1.0 cP ??? Surface energy about the same.. L1 / 18 DS1102 QUESTIONS L1 / 19 DS1102 WETTING Effective wetting of surfaces is related to surface energy (or surface tension) of solid and liquid and the rheology of the liquid/suspension Could you… Provide a definition of surface energy? Relate magnitude of surface energy to intermolecular / interatomic forces? Define viscosity and explain simple trends in it? Wetting is critical in many dental procedures eg. acid etching, resin application etc, luting application, impressions Surfaces must wet satisfactorily to achieving optimal bond strength for instance L1 / 20 L10 / 21 WETTING II DS1102 WETTING III DS1102 • Generally, good wetting is achieved between a high surface energy solid and a lower surface energy liquid ( < 90) • poor wetting is achieved between a low surface energy solid and a higher surface energy liquid ( > 90) Wetting between liquids and solids is characterised by the contact angle,  Complete wetting  = 0 No wetting  = 180 High SE Low SE Low SE High SE L10 / 22 DS1102 • ADJUST SURFACE ENERGY • Surface contamination lowers solid surface energy, decreasing wettability. • Cleaning surface raises surface tension of solid, improving wettability eg cleaning biofilm (pellicle) off enamel raises surface energy and wettability • L10 / 23 DS1102 SURFACTANTS • Salts of fatty acids such as sodium stearate act as surfactants • SDS or sodium lauryl sulphate is another common surfactant • These have a hydrophilic head and hydrophobic tail • Surface active agents congregate and align at surface of liquid lowering surface tension with increasing concentration • Self assembly of Micelles occurs at a high enough concentration of surfactant Surfactants are molecules which lower surface tension in liquids – also known as surface active agents L10 / 24 DS1102 L10 / 25 QUESTIONS Could you?? Explain why some liquids will wet a solid surface well whilst others won’t … (e.g. water on glass, Hg on glass) Describe the significance of good and bad wetting in clinical applications. DS1102 Capillary action: the spontaneous rising of a liquid in a narrow tube which arises as a result of high cohesive (intermolecular) and high adhesive (liquid/wall) forces • In dentistry, capillary action of saliva •occurs in crevices around/between teeth • Explain what surfactants do? L1 / 26 CAPILLARY ACTION Denture retention assisted by adhesive action and capillary action • Application of liquids onto tooth structure assisted by capillarity into narrow crevices L10 / 27 CAPILLARITY DS1102 The high surface tension and high capillarity of water is due to Hydrogen bonding Glass surface H2O surface Mercury has a higher surface tension than H2O due to metalmetal bonds at the surface. It has a low capillarity due to weak Hg SiO2 interactions Chemical Properties of Direct Dental Materials Week 2 - pH, GIC Cements, Rheology Lecture 4 Dr. Alex Dancyger – B.Sc – Honours, M.Sc – Fellow, B.Ed. BDS Hg surface https://www.ic-network.com/tmd-ic-copcs-how-a-dental-condition-changed-the-future-of-ic-and-chronic-pain-research/ L10 / 28 Learning Objectives Content • Understand how spectroscopy is used in a dental context • Assess the relative strengths of acids and bases according to their ionization constants • Rationalize trends in acid–base strength in relation to molecular structure • Spectroscopy • Digital Shade Guide • Vein Mapping • Digital Scanners • Determining Acidity and Basicity • Electronegativity • Size of an atom • Resonance • Saliva Testing https://thed3group.org/tooth-fairies-and-science.html https://essenciainmobiliaria.com/essencia-idea/ https://asnanportal.com/index.php/dental-report/articles/cosmetics-restorative-prosthetic-dentistry/item/408increased-predictability Spectroscopy Spectroscopy • The Shade Guide • Tabs based on colour distribution of natural teeth • Basis for colour of restorative material • Visual shade matching • Most common technique • Disadvantages • Conditions of light • Experience • Age • Eye fatigue • Colour blindness • Spetrophotometer • Measures the colour of an observed object by reflection or transmission • Digital Shade Matching • Can have multiple spectrometers • 1 – monitors lamp output during calibration and measurements • 2 and 3 – analyzes scattered light by tooth structure • L value – measures lightness (0-100) • Chromaticity a value – measures redness – greenness • Chromaticity b value – measures yellowness to blueness • Measure cervical, body and incisal aspects https://www.vita-zahnfabrik.com/pdb_GG2G50G200_en,98478.html https://www.oralhealthgroup.com/features/totally-simplified-colour-matching-single-shade-direct-composite/ https://www.bremadent.co.uk/news/understanding-shade-taking-in-dentistry-basic-how-to-guide https://www.vita-zahnfabrik.com/pdb_GG2G50G200_en,98478.html Spectroscopy Spectroscopy • Vein Visualization (aka Vein Mapping) • Real-time “map” of veins • Arteries contain oxygenated hemoglobin • Absorb blue-green light, reflects red light • Veins contain deoxygenated hemoglobin • Absorb orange light, reflect blue light • Near Infrared Light (NIR) Spectroscopy • 2 lasers i) Infrared ii) visible light • Infrared light absorbed by hemoglobin, related to wavelength • Other tissues do not absorb light and reflect it back https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5822547/ • Intra Oral Scanners • Project light onto surface • Record individual image/video • Processed by software • Identifies points of interest (POI), stiches images together • Generates digital impression https://twitter.com/accuvein/status/1164598576783249412 https://phdentalinc.com/product/shining-3d-intraoral-scanner-aoralscan/ Determining Acidity and Basicity - Electronegativity Determining Acidity and Basicity • Determined by • Electronegativity • Size of an atom • Resonance • The Greater the Electronegativity, the More Acidic • Electronegative atom + H • Positive and negative charges • Polarized molecule • Hydrogen more likely to form H+ https://medictests.com/units/quick-and-dirty-guide-to-acid-base-balance https://groups.chem.ubc.ca/courseware/pH/section10/index.html Determining Acidity and Basicity - Size of an Atom Determining Acidity and Basicity - Electronegativity • The better an atom stabilizes a negative charge, the more stable the conjugate base is • The Larger the Atom, the More Acidic • Stronger acids have a stable conjugate base • Larger ions • Electrons more room to move around • Weaker bond strength • More likely to provide H+ • Acidity increases across a row https://chemistrytalk.org/periodic-trends-made-easy/ https://www.chemistrysteps.com/factors-determine-pka-acid-strength/ http://www.chemhelper.com/acidbase2.html Determining Acidity and Basicity - Size of an Atom Determining Acidity and Basicity - Size of an Atom • The shorter the bond length, the stronger the bond • The more stable the conjugate base, the stronger the acid • Larger ions have a negative charge that can spread out more https://kpu.pressbooks.pub/organicchemistry/chapter/3-4-structural-effects-on-acidity-and-basicity/ Determining Acidity and Basicity - Resonance https://chemistrytalk.org/periodic-trends-made-easy/ https://www.chemistrysteps.com/factors-determine-pka-acid-strength/ Intermittent Quiz • Which compound is most acidic? • Which is the least acidic? FCH2CO2H ClCH2CO2H BrCH2CO2H ICH2CO2H • Resonance • Multiple Lewis structures are used to represent molecule/polyatomic ion • Delocalization of electrons - Electrons present in various locations • Resonance of the conjugate base stabilizes the structure • Stronger acids have a stable conjugate base https://dentalchat.com/common-dental-question https://socratic.org/questions/599e7d077c01495b73b4ce23 Determining Acidity and Basicity Saliva Testing https://www.gcaustralasia.com/Upload/product/pdf/97/Brochure-Saliva-Check-BUFFER.pdf Saliva Testing Saliva Testing • Step 3 - Resting pH of unstimulated saliva • Low pH – oral environment is more acidic than normal • Can result in demineralization and mineral loss • Neural interference of salivary gland transmission • medications, recreations drugs, stress, depression, hormone imbalance • Saliva supply interference • Dehydration, smoking https://www.gcaustralasia.com/Upload/product/pdf/97/Brochure-Saliva-Check-BUFFER.pdf • Step 5. Stimulated flow - buffering capacity (quality) • Buffering capacity indicates saliva’s effectiveness at neutralizing acids • Acids come from diet, dental plaque, gastric reflux • Bicarbonate • Buffering system in saliva • More present in stimulate saliva versus unstimulated https://www.gcaustralasia.com/Upload/product/pdf/97/Brochure-Saliva-Check-BUFFER.pdf