Dental Materials - Overview PDF

Dental materials Polymerization ​ Chemical reaction that joins many molecules together to form one large molecule ​ Mer is one molecule ​ Polymer is reaction to form one large molecule of high molecular weight Settings of polymers ​ Resins (acrylic) solidify when they polymerize ​ Add...

Dental materials Polymerization ​ Chemical reaction that joins many molecules together to form one large molecule ​ Mer is one molecule ​ Polymer is reaction to form one large molecule of high molecular weight Settings of polymers ​ Resins (acrylic) solidify when they polymerize ​ Addition polymerization ○​ Describes the formation of chains of linked molecules ○​ No byproducts ○​ I.e pvc acrylic ​ Condensation poly ○​ By product is formed such as water or alcohol ○​ Nylon polyester epoxies Steps ​ initiation - requires input of heat light or chemical energy to form free radicals ○​ Free radicals is a molecule with one or more unpaired electron on its outer shell ○​ High energy radicals are formed when there is an input of energy i.e mixing self cure ​ Propagation ○​ Polymer spends most of its time expanding its chain length ​ Termination can be achieved through direct coupling with another radical and monomer Oral environment ​ Biting forces ○​ Average biting force is 200 pounds ○​ 55 in anterior ○​ 247 in molars ○​ Must resist fracture ​ Temp changes ○​ Must keep low values of expansion and contraction ○​ Sudden change may fracture or crack surface of tooth\ ​ Acidity ○​ Ph balance in the oral cavity if ph 7 ○​ Can cause tarnish and corrosion Microleakage ​ Fluids and microorganisms and debris penetrate outer margins of restorations ​ May cause tooth to be sensitive ​ Marginal discolouration ​ Pulpal pathology ( inflammation of infection of the pulp) Galvanism ​ Conduction of electrical currents (galvanic currents) ​ Irritate the pulp and cause sharp pain ​ Opposing restorations plus saliva form a battery ​ Fixed ○​ Crown ○​ Bridge ○​ Implant ○​ Inlay ​ Removable ○​ Full denture ○​ Partial denture ○​ Ortho appliance ​ fixed/removable ○​ Over denture ○​ Fixed denture ○​ Ortho appliance ○​ Combination ○​ temps Solids ​ Can be described as crystalline ​ Atoms held in position by interatomic forces ​ Most crystalline materials used in dentistry form a cubic type of lattice ​ Crystalline structures are ridgid at all room temps below their melting point Amorphous solids ​ Isotropic- properties are the same in all direction because of the uniform distribution of atoms ​ No sharp melting point- do not have a distinct melting point, soften over a range of temperatures ​ Mechanical properties- tend to be less rigid and more flexible compared to crystalline solids Surface contact angle ​ Contact angle is formed at the interface where a liquid droplet meets a solid surface. It quantifies the wettability of the surface by liquid ​ Low contact angle (90) ○​ Indicates poor wettability ○​ the liquid beads up on the surface  ○​ Typical for hydrophobic surfaces ​ Amount of change (deformation) is the strain ​ Stress is measured in units of force per unit area ​ Strain is measured in deformation Types of stress ​ Tensile stress ○​ Results from a load that tends to elongate a structure such as a ortho wire. ○​ Tensile stress is accompanied by a tensile strain ​ Compressive stress ○​ Stress that opposes a load that compresses a structure. ​ Shear stress ○​ Deformed bu sliding one part parallel to another. ​ Elasticity ○​ Property of a body that can be deformed by an applied load and then assume its original shape when load is removed. ○​ Max stress that a structure can withstand being permanently deformed is known as the elastic limit ​ Proportional limit ○​ The structure does not return to its original shape when the external force is removed ○​ Occurs at the same time as the elastic limit, yield point or strength ​ Modules of elasticity ○​ The property that defines the rigidity of the material under stresses below the elastic limit Retention ​ Ability to maintain its position and resist displacement ​ Mechanical retention- undercuts ​ Chemical- glass ionomer cements Abrasion resistance ​ Material that can resist being worn away by rubbing or friction ​ Indicates how material can maintain its surface integrity and functionality over time ​ Factors affecting abrasion resistance ○​ Material hardness, harder materials have better resistance ○​ Surface finish, smoother surfaces have better resistance than rougher ○​ Composition, chemical and physical composition can influence its resistance Rheology ​ The science that deals with the flow and deformation of materials. ​ Thixotropic materials become less viscous over time when subjected to shear stress and return to original viscosity when stress is removed Enamel and dentin have low conductivity thus insulating the pulp against temperature changes Coefficient of thermal expansion (CTE) ​ Measure of how much a material expands or contracts when temp is changed ​ During heat transfer, energy is stored in the intermolecular bonds between atoms. ​ Stored energy can change the length of molecular bond aka expansion of the solid. ​ Linear thermal expansion ​ Area thermal expansion ​ Volumetric thermal expansion Light interaction with objects ​ Absorption and reflection ○​ Light hitting objects results in some wavelengths are absorbed and others reflected ○​ If object absorbs all light is results in black ​ Photoreceptors ○​ Retina in eyes have cones which are sensitive to wavelengths ​ Signal transmission ○​ Cones send signals to the brain which process the info and interprets as a colour ​ Lighting conditions ○​ Type and intensity of light can affect how colours appear. (natural vs artificial light) ​ Surrounding colours ○​ Colours can be influenced by adjacent colours due to contrasting effects ​ Individual differences ○​ People perceive colours differently from different processing and vision ○​ Called observer metamerism ​ Hue ○​ Colour of object (red green blue) ​ Value ○​ Brightness of colours ○​ Amount of grey in colours ​ Chroma​ ○​ Intensity of Hue ○​ Saturation of colour Vita shade guide ​ Invented by Vitat zahnfabrik ​ Designed to achieve consistent and accurate shade matching ​ 16 shades ○​ A1-A4 reddish brown shades ○​ B1-B4 reddish yellow shades ○​ C1-C4​ greyish shades ○​ D2-D4 reddish grey shades Zirconia (ZrO2) ​ White crystalline ​ Biocompatible ​ Corrosion resistant ​ Yttria is used to stabilize ZrO2 ​ 3Y-TZP is 3 mol% yttria 1200 MPa flexural strength ​ 4Y-TZP is 4 mol% yttria, more translucency 850 MPa flexural strength ​ 5Y-TZP is 5% yttria, even more translucency 650 MPa flexural strength ​ Zirconia powder is pressed into a die ○​ Uses 30,000 psi to create disc ​ Presses disc is partially sintered around 900-1000 c ​ Densification: ○​ The zirconia material, which starts as a porous, pre-sintered form, is heated to high temperatures (typically around 1,450°C to 1,600°C). This heat causes the particles to fuse together, reducing porosity and increasing density ​ Shrinkage: ○​ As the material densifies, it shrinks by about 20-25%. This shrinkage is accounted for during the design phase to ensure the final crown fits perfectly ​ Phase Transformation: ○​ The heat treatment stabilizes the zirconia in its tetragonal phase, which is crucial for its mechanical properties. This phase transformation contributes to the material's high strength and toughness ​ Improved Mechanical Properties: ○​ The fully sintered zirconia crown becomes much harder and stronger, with enhanced resistance to wear and fracture. This makes it suitable for the demanding environment of the mouth ​ Aesthetic Enhancement: ○​ Sintering also improves the translucency and overall aesthetic appearance of the zirconia, making it look more like natural teeth Metal ​ Fixed freezing and melting points ​ Wrought (rolled bent and stretched) ​ Crystalline (reg arrangement of atoms) ​ Grain metal crystalline ○​ Formed by cooling of the nuclei, smaller grain ○​ Harder more brittle ​ Pure metal have melting point ​ Alloy have melting range ​ Solidus- highest temp at which alloy is complete solid, marks beginning of melting ​ Liquidus - highest temp at which Heat treating  ​ Heating metal to specific temp ​ Below red hot ​ Increases hardness Annealing ​ Softening metal by healing ​ Red hot Hardening ​ For gold (840 f/450c) ​ Cool to 400f for 15 mins ​ Quench High noble ​ 90% or more noble metal Medium noble ​ 70% or more Low noble ​ Less than 70% Base metal ​ No noble metals Silver ​ Increases strength and hardness ​ Lowers melting range ​ Increases tarnish ability ​ Can discolor porcelain Copper ​ Lowers and shortens melting range ​ Forms oxides ​ Lowers density Platinum (pt) and palladium (pd) ​ Increase strength ​ Broadens melting range ​ Increase hardness ​ Increase tarnish resistant, price and density ​ Gives white colour Base metal ​ Chrome ​ Beryllium ○​ Improves casting but its toxic ​ Cobalt and nickel ​ Used in partials- stronger lighter less dense and expensive Additive CAM ​ SLA (stereolithography) ○​ Uses lasers to etch DLP ( digital light processing) ​ Cures whole layer with light Photopolymer resin ​ Acrylste monomers ​ Form solid polymers ​ Photoinitators ​ Dyes pigments and fillers ○​ Added to control optical properties and modify characteristics