Week 1 Dental Biomaterials PDF

**[Week 1 ]** Dr Touraj- introduction to dental biomaterials Dental biomaterials is the science of (of materials used in dentistry): 1. Composition 2. Properties 3. Manipulation 4. Chemical reactions 5. Mechanism of action 6. Clinical application 7. Indication and contradiction **Ap...

**[Week 1 ]** Dr Touraj- introduction to dental biomaterials Dental biomaterials is the science of (of materials used in dentistry): 1. Composition 2. Properties 3. Manipulation 4. Chemical reactions 5. Mechanism of action 6. Clinical application 7. Indication and contradiction **Applications:** 1. Preventive and protective material (mouth guard). Generally made from polymers(resin) 2. Polymer composites (resin composites) 3. Orthodontics: 1. Polymers 2. Metal alloys 3. Polymer composites **Restorative materials:** 1. Direct 1. Metal alloys 2. Resin composites 3. Glass ionomers 2. Indirect: fixed and removable 1. Polymers 2. Metal alloys 3. Resin composites 4. Ceramics 5. Hybrid materials **Impression materials**-polymer composites **Dental model materials**-gypsum and polymers **Root canal materials**- metal alloys, polymers, polymer composites and mineral aggregates. **Surgical materials**- metal alloys, polymers, polymer composites, mineral aggregates and biological materials. **Implants**- metal alloys, polymers, polymer composites and ceramics **Direct restorative materials:** 1. **Resin composites**-chemical or light activated polymerization 2. **Glass ionomer materials (GIC)**- cross linking and gelation reaction 3. **Amalgam**- reaction when mercury and metal elements are mixed [Dr Liddell lecture 1- acids and bases] pH in dentistry- plays a key role in dental caries- critical pH and demineralization/ remineralization of hydroxyapatite. \ [*pH* =  − *log*\[*H*^+^\]]{.math.display}\ pH of blood- 7.35-7.45 pH affects drug absorption, activity and partitioning. pH describes the acidity of a solution on a scale from 0-14. Many dental cements use acid-base reaction. **Dental cements**- set intraorally to join a tooth and prosthesis (temporary fillings) Maybe classified in various ways including the principal setting reaction: 1. Polymerization 2. Acid-base cements Types of dental cements: zinc phosphate, zinc oxide eugenol, zinc polycarboxylate and GIC **Bronsted-Lowry definition**- the acid will act as a proton donor while the base acts are the proton acceptor. \ [*CH*3*COOH* + *H*2*O* → *CH*3*COO*^−^ + *H*3*O*^+^ ]{.math.display}\ Acid base properties of water: Water is amphiprotic which means it acts as a proton donor and acceptor Conjugate acid base pairs: **K~w~ pK~w~** Electrolyte classifications- the conductivity of a solute in solution determines the class of electrolyte of the solute. i. Strong electrolytes 1. Ionic compounds completely dissociate into ions and are good electrical conductors. 2. Covalent compounds have bonds between the atoms in which electrons are shared. ii. Weak electrolytes (Covalent compounds) 1. Partially dissociate into ions 2. Conduct electricity poorly iii. Non-electrolytes (covalent compounds) 1. Don't dissociate 2. Do not conduct electricity at all **Neutralization reaction-** formation of water (weak electrolyte) drives reaction forward.[ ]{.math.inline} \ [*acid* + *base* → *water* + *salt* ]{.math.display}\ Strong acids: HCl, HNO~3~, H~2~SO~4~, HClO~4~ Strong bases: NaOH, Ca(OH)~2~ Weak acids partially dissociate. **Weak acids in Dentistry** 1. Etchants in dentistry used to prepare surfaces for restorative bonding. Improvement in bond strength: - Enamel and dentine etchants - Ceramic etchants 2. Cements- (acid-base) **Kc Ka and pKa** \ **Kb and pKb**  Acid strength directly relates to Ka and pKa: - Large Ka or low pKa (property of a compound (can be -ve, 0-50)) =strong acid **Hydrofluoric acid (corrosive weak acid)** - pKa is 3.17 - most corrosive acid known and has an ability to dissolve organic and inorganic materials at moderate concentrations. - Important to keep calcium gluconate gel in first aid supplies in areas where HF is stored or used. - HF must be stored in Teflon or polyethylene **Phosphoric acid** - H~3~PO~4~ is routinely used for etching enamel and dentin. - Weak polyprotic acid. pKa= 2.1/7.2/12.3 - Corrosive acid. **Lecture 2- Buffers** Buffer- a solution which resists pH changes when a **small** amount of acid or base is added. "pH shock absorber" \ [*Buffer* = *weak* *acid* + *conjugate* *base*]{.math.display}\ - Normally made by taking a weak acid + salt of a weak acid + a strong base pH of a buffer solution is controlled by varying the relative concentrations of the weak acid and the conjugate base. - Buffer capacity- measure of the ability of the buffer to resist change in pH. 1. The more concentrated the components of the buffer, the greater the buffer capacity. - Buffer ratio- \[base\]/\[acid\] 1. Best buffering is achieved at a ratio of 1 2. The range 0.1-10 is effective. **The carbonic acid/bicarbonate buffer** - This buffer helps to maintain the blood plasma at pH 7.4 (7.35-7.45)- primary buffer system. - This buffer is also the primary buffer in stimulated saliva. **Phosphate buffer**  - The secondary buffer in saliva is the dihydrogen phosphate buffer, unstimulated. - Resting pH in the mouth is=6.3 and the pKa OF H2CO3 is 6.3. - Carbonate and phosphate buffers responsible for salivary buffering pH 5.1-8 **Protein buffers** - Proteins buffer cells and blood plasma through carboxylic acid and amine buffers. - The side chains of some amino acids are ionizable (e.g. lysine) - A 50kDa set of proteins is responsible for salivary buffering pH 3.4-5 **Organic acids** - To be an acid, an organic molecule **must** contain an acidic functional group. This means the molecule must contain either a carboxylic acid group (CO~2~H), a sulphonic acid group (SO~3~H), a phosphoric acid group (PO~3~H~2~) or a phenolic OH group (Ar-OH). **Acid Base equilibria and drugs** - A/B equilibria explain drug solubility vs pH - A/B equilibria explain drug stability vs pH stability pertains to acidic or basic attack on a drug molecule changing a functional group - A/B equilibiria helps understand the uptake mechanism for some drugs **Drugs and pH**  **Tooth enamel** - Enamel: 96% mineral by weight. The rest is 4% water and proteins amelogenin and enamelin. - Major mineral is calcium phosphate 1. Hydroxyapetite (Ca~10~(PO~4~)~6~(OH)~2~ **Demineralization/ Remineralization** - Dental caries is dynamic and the external structure of the enamel changes dynamically in response to the chemical/biochemical action going on around it. - Plaque buffer: 35% phosphate, 10% bicarbonate, 10% protein, 10% organic acid **Solubility product** The solubility product is a special equilibrium constant that is used to predict if an ionic compound will precipitate out from solution given known concentrations of the cation and anions in solution. - Defined for a saturated solution of the compound and the ions. - If the ion product (Q) exceeds Ksp the solid will precipitate out from solution. Degree of saturation- ratio of the ionic product of a substance in the solution to its ionic product at saturation (Ksp) - The tooth will dissolve when the pH of fluid phase is less than 4.5-5.5 at this point H+ removes PO~4~^3-^ - apatite mineral dissolves - Critical pH- pH at which a solution is just saturated WRT a particular mineral. - If solution pH \> critical pH and supersaturated- mineral precipitates. - If solution pH\< critical pH and undersaturated- mineral dissolves - Teeth don't usually dissolve as saliva and plaque contain Ca, P, OH, supersaturated- Q\>Ksp tooth enamel. **Fluoride** - One effect of fluoride is for F- to substitute for OH- in defect sites. 1. F- fills the vacancy and H-bonds with OH 1. Decreases crystal size 2. Strong attraction to Ca2+ 3. This stabilizes the lattice structure. 4. Improves the crystallinity 5. Lowers dissolution rate of the resultant FAP-like material a fluorhydroxyapatite. - Caries-reducing effect of fluoride is primarily achieved by its presence during active caries development at the plaque/enamel interface. **Fluoride mechanisms** - Plaque matrix concentrates F- from saliva. The -ve charges of F- in saliva matrix attract Ca2+. - The Ca2+ binds to F- to form CaF~2~ - CaF~2~ globules are F- reservoir that may provide F- for subsequent surface 'FAP-like' formation- bioavailable F released during acidification. **Fluoride vs Remineralization** Mechanisms of fluoride effect. 1. Inhibiting demineralization: a surface effect 1-50ppm reduces dissolution 2. Enhancing mineralization: Form a layer of FAP-like material on the crystal surface under CaF2 like globules. 1. Partially demineralized crystals= nucelators and F- adsorbs to the surface nucleators and attract Ca, P -\> FAP formation. The newly formed FAP-like veneer excludes carbonate and has a composition between HAP and FAP. 2. Inhibiting enolase **[L3- Bonding and Reactions]** **Intermolecular forces** - Most dental materials are applied as liquids so that flow, viscosity and surface wetting are critical variables to control material performance. - Intermolecular forces affect viscosity and surface energy, affecting liquid flow and surface wetting and capillary action Intermolecular bonding- happens due to weak forces (electrostatic) acting between molecules. **Polarity** Electronegativity- relative ability of an atom to attract shared e- in a covalent bond. Polarization indicates the charge distribution in a bond- the bond polarity Dipole moment is a numeric indicator of molecular polarity. Units are Debye (D) **Dipole moment** - Dipole moment correlates well with the strength of intermolecular forces. - Boiling point indicates the amount of energy required (as T input) to push molecules from liquid into the gas phase. **Hydrogen bonding** - A hydrogen bond is a special weak attractive force which exists through space between a hydrogen atom and the lone pair electrons on atoms such as oxygen and nitrogen **The nature of the H-bond** - A H-bond forms when an H atom covalently bonded to an appropriate donor atom (N, O) is weakly connected through space to one (or more) - The donor atom must act as an electron-withdrawing group to polarize H. HBD. - The acceptor atom must have an available lone pair **Strength of H-bond** - The strength of a H-bond is weak in contrast to covalent and ionic which are strong types of bonding **Solubility** - Of importance in solubilizing molecules in water is their ability to participate in H-bonds. - Acetic acid readily participates in intermolecular hydrogen bonds, hence acetic acid is very soluble in water. **Chemical reactions** - Chemical reactions proceed spontaneously on the basis of delta G but the driving forces differ. 1. Metathesis reactions a. No transfer of electrons b. Exchange of ions 2. Photochemical reactions- light curing reaction 3. Redox reactions **Metathesis reactions** Three types of driving forces exist for metathesis reactions. These forces remove ions, atoms or molecules from solution. 1. Formation of precipitate 2. Formation of a weak electrolyte 3. Acid/Base reactions **Photochemical reactions** 1. Involve the absorption by the reactants of light as a photon- usually in the UV-visible. 2. Temperature generally has very little effect on the overall rate of reaction 3. Photochemical reaction is regiospecific-activating part of a molecule. **Photochemistry** Overall Photochemical reaction- when a sample in solution is irradiated with light some may be absorbed. Primary reaction- these proceeds due to the absorption of radiation. Secondary reaction-these are thermal reactions which occurs subsequently Photo initiators- molecules that absorb photons and form reactive initiating species out of the excited state which subsequently initiate further reactions. The initiating species may be radicals, cations or anions. Primary photochemical process- Reactant S=ABC undergoes reactive decay and may undergo a range of primary photochemical processes. **Quantum yield** \` \` **[Dr Jennings L1- Thorax and heart anatomy]** Organization- Skeletal protection and muscular movement **Overview** - 3 internal compartments - Central mediastinum (and heart) - Left pleural cavity- smaller due to the heart taking up most of left side. - Right pleural cavity **Muscles of thoracic cage-** Similar to muscle layers in superficial abdominal wall. **Sternal angle-** on this angle, the trachea breaks into two bronchus, the aorta passes through it and the pulmonary trunk also passes through it. **Internal orientation** - Diaphragm movement changes thoracic volume - Creates basis for inspiration/expiration **Diaphragm** - Nerva supply is C3, C4, C5 - Inferior vena cava- T8 - posterior - Oesophagus +vagus- T10 - posterior - Aortic hiatus-T12 - posterior - Left and right phrenic nerve -- anterior - Vagus nerve- posterior travels through carotid sheeth. - Interior thoracic aortic central tendon -- anterior **Intercostal muscles** - External intercostal muscles- anterior and inferior (same as external oblique) - Internal intercostal muscles- posterior and inferior (same as internal oblique) - Innermost intercostal muscles- variable but largely follow direction of fibres of internal intercostal muscles. - Inside the rib, there is a costal groove and inside that groove runs the subsequent intercostal nerve, vein and artery. - Some more collateral branches on the interior groove of the intercostal muscles as well. **Pleura- (Simple squamous epithelium with some fluid)** - Two pleural cavities surround the lungs- one either side of the mediastinum - Parietal-innervated by branches of costal nerves. 1. Has somatic sensation. Good degree of localization. - Visceral- on the lungs 1. Innervated by visceral fibres which allow poor localization of pain. - Normally separately by a thin layer of serous fluid - Pleurae line the lung and the pulmonary cavities and is one continuous serous sac - Fluid aids movement and helps create surface tension which keeps the lung inflated. 1. There are internal negative pressures which aid this. - When negative pressures are disrupted, the lung will deflate (e.g. break a rib) **Right vs left lung** If a patient inhales a material, it is more likely to end up in the right lung due to the less acute angle of the right bronchus and the diameter and size of the bronchus. **Function of respiration** - Inspiration 1. Elevation of lateral aspect of ribs (bucket handle movement) 2. Superior and anterior movement of sternum (pump handle) 3. Sternum moves forward due to rib elevation 4. Diaphragm descends to increase thoracic capacity **Structure of a typical true rib** - Heads of most ribs articulate through two facts-one joins with the body of that same-numbered thoracic vertebra, whilst the other articulates with the superior vertebra. - The shaft of the rib extends to the costal cartilages- secure but flexible attachment to the sternum - The first pair of ribs are atypical- are flattened and are quite broad- support the blood vessels that serve the upper limbs - Ribs 1 and 10-12 only articulate with the vertebral body **Accessory muscles: inspiration** 1. Diaphragm (primary) 2. Scalene muscles 3. Sternocleidomastoid 4. External intercostals **Accessory muscles of Expiration (e.g. blowing up a balloon)** 1. Abdominal wall muscles 2. Internal intercostals 3. Passive recoil of lungs **Segmental supply** The primary artery is an aorta and descending aorta which runs through the aortic hiatus. Blood comes through the brachiocephalic veins into the superior vena cava. **Cardiovascular System** Organisation- Pulmonary circulation (lungs) and systematic circulation (around body). - 2 halves - 4 chambers - 2 atria - Collecting chambers - 2 ventricles - Pumping chambers **Where does the heart sit**- inferior aspect of mediastinum **Pericardium** - Heart sits in pericardial space - Pericardium covers the heart (visceral) and lines fibrous pericardial sac (parietal): pericardial cavity contains serous fluid - Parietal layer of pericardium is associated with the fibrous layer of the pericardium sac **Heart wall** - Epicardium -- epithelial + areolar tissue - Myocardium -- cardiac muscle tissue - Endocardium- areolar tissue and endothelium - Left ventricle wall is significantly thicker than right ventricle wall as blood is pumped systemically from left ventricle whereas it is pulmonary from right. **Atria** - Thin wall collecting chambres - Smooth walled area and ridged muscular area and septal area **Oval Foramen (Fossa ovalis)** - Flap which allows blood to go in one direction from right atrium to left atrium into the left ventricle to be pumped out of the aorta - Flap works in a way that only allows unidirectional flow **Papillary muscles** - Pull on the heart strings of chordae tendinae which will stop tri or bicuspid valves from blowing up **Adult orientation** Right border=right atrium Base= left and right atria Left border= left ventricle Apex (midclavicular line)= left ventricle **Heart Valves** - valves all lie behind body of sternum **Cuspid Valves** - cusps attach to chordae tendineae- papillary muscles **Semilunar valves** - as ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open - as ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close **Coronary arteries** **Right coronary artery**- right marginal branch of right coronary artery \- sinu- atrial nodal branch of right coronary artery \- right marginal branch of right coronary artery **Left coronary artery**- Left marginal branch of circumflex branch -anterior interventricular branch of left coronary artery -Diagonal branch of anterior interventricular branch -circumflex branch of left coronary artery All veins of coronary sinus drain into the right atrium **Superior mediastinum-** Right internal thoracic artery and left internal thoracic artery **Relations** - Right and left phrenic nerves (C3, C4, C5) pass anterior to lung root - Right and left vagus nerves pass posterior to lung root - Note the relationship of nerves to heart chambers **Thoracic duct (lymph)** - Begins at the upper aspect of the cisterna chyli, passing out of the abdomen through the aortic hiatus.