Dental Materials Past Paper Fall 2024 PDF

General Guidelines Final - D150 -- Dental Materials -- Fall 2024 1\. Review the content from ALL lectures (online and live during class) 2\. Exam is cumulative. Check previous guidelines for midterm 2\. Recommended to read the book pages recommended in the syllabus 3\. Recommended to check the "...

General Guidelines Final - D150 -- Dental Materials -- Fall 2024 1\. Review the content from ALL lectures (online and live during class) 2\. Exam is cumulative. Check previous guidelines for midterm 2\. Recommended to read the book pages recommended in the syllabus 3\. Recommended to check the "Self-Test Questions" at the end of each chapter of the book Adhesion and Bonding Understand types of bonds found in dentistry (mechanical and chemical) Mechanical interlocking with rough surfaces portion of one material fills surfaces and causes retentive interlocking to bind, Chemical (true) adhesion use chemistry in one material to form chemical bond with other material. Can use mechanical interlocking and chemical bonding at the same time. Understand acid etching, compounds used for etching and objective of etching Etching done for removal or modification of smear layer Can use 37% phosphoric acid, EDTA to remove the smear layer without demineralizing the surface dentin layer, or functional monomers (for self-etching systems) such as 10-MDP, 4-META, and phenyl-P. Identify names of compounds use for bonding agents, primers and resin composites Primers -- examples are HEMA and 4-META. Solution of resin monomers, organic solvent, water, and stabilizers. Bond collagen with hydrophilic end and resin with hydrophobic end. Bonding agents -- examples are Bis-GMA\< UDMA\< and TEGDMA. These are unfilled or lightly filled monomers. Understand differences between bonding strategies (etch and rinse, self-etch and universal), and the number of steps/bottles Etch and rinse always uses acid etch step. Etch and rinse is oldest strategy. Always uses acid etching. Can be 2 or 3 step process. Two step is etching + primer + bonding. 3 step is etching + primer/bonding. This utilizes a wet bonding technique and the primary adhesion mechanism is mechanical locking. Self-etch strategy no acid etch or blue syringe step. Primer contains functional monomer and there is partial demineralization. Has 2 or 1 step process. 2 steps is acid/primer + adhesive and this is the gold standard. 1 step is acid/primer/adhesive. Self etch has astringer bond If lower pH is used. Uses mechanical locking and chemical bonding. Universal is most simple to use adhesive. Is versatile. Can be used in ER mode with acid etching + universal bottle or SE mode with universal bottle all included. Can be used for a wide range of clinical applications. Understand challenges of bonding to dentin Retention can be an issue. Need to keep bond for duration of service with no leaks or bacteria penetrating interface. If no retention, then sensitivity, failure, staining, 2^nd^ caries, and inflammation could occur. Challenges for retention are degradation of biomaterials. Technique with proper preparation and use of biomaterials, and handling with materials and lamp calibration. Understand wet bonding in dentin The presence of water and organic components lower surface energy of dentin. Water keeps collagen expanded and retains spaces for resin infiltration. Do not went dry collagen as it collapses and obstructs resin from reaching dentin. Also, the higher the tubule density, the lower the bond strength values of dentin adhesives so need the pulp, tubule density is higher so harder to bond there. Chlorohexidine used to clean/disinfect before bonding. Glume used as a collagen crosslinking agent. Metals - Amalgam Amalgam composition and chemical reaction (amalgamation) o Identify gamma phases (1, 2) Dental amalgam made of silver alloy + mercury + small quantities of zinc and palladium. Amalgamation involves copper, silver, and tin dissolving into the mercury. Reaction forms amalgam matrix. Once amalgamation reaction is complete, little or no mercury remains. When high copper alloy particles contact mercury, dissolution of Cu, Ag, Sn and other elements in the ally occurs. The crystallization of new products continues until all the liquid mercury is consumed. For low copper amalgamation, there are three gamma phases. Gamma phase is silver-tin alloy. This is unreacted alloy and provides strength. Gamma 1 Y1 phase is silver-merucy compound. This is primary matrix phase that forms during amalgamation. It is strong and somehow corrositon resistant. Main contributor to final strength of amalgam. Gamma 2 Y2 phase is tin-mercury compound. Forms as secondary phase during amalgamation. Undesreble due to weakness, prone to creep, and susceptible to corrosion. Modenr high copper amaglms reduce or eliminat this phase bu reacting tin with copper instead. Y2 phase disappears for high copper amalgam as compared to low copper. Silver powder composition, types, influences on properties Silver powder omposition within dental amalgam has silver + tin + copper. Amount of copper changes properties of amalgam. Differences high copper and low copper High copper alloys have hgher strength, less corrosion, less creep, better longevity at the margins, reduced corrosion. Low copper alloy has zinc which causes long term expansion due to moisture. Is being replaced by high copper which is stronger and doesn't expand as much. Differences silver alloy shape (irregular,., admixed) and influence over Properties Shape of silver alloy particles influence properties of amalgam. There is ireegular, spherical, and compination amalgam shape. Spherical shape has higher compressive strength than admixed. Irregular shape has higher surface area, increased mechanical interlocking, and lower flowability. Spherical shape has smooth surfaces so lower surface area, improvd flowability because particles pack more efficiently, lower porosity, and iniformity in how they fit together. Admixed shape allow enhanced bonding strength and improved flowability and packing density all in one. Understand basic properties of amalgam (creep, mechanical, dimensional change) Amalgam is a brittle material. For amalgam, stenght changes with time after restoration palcements so the risk for fracture and fiauulre is higher for the first few days. During setting, dimenstional changes occur for amalgam. Contraction occurs during alloy dissolution. Expansiron occurs during impingement of reaction product crystals. Material first contracts then it expands. Creep is associated with breakdown at the margins of restoration overtime as it is being subjected to constant stress. Creep depends on the type of amalgam. Corrositon is progressive destruction of metal by chemical or electrochemical reaction with its environments. Limit exposure to mercury because it is toxic. Slow elimination from body. Amalgam generates a minimal amount of merucy vapor. Trying to phase down use of amalgam. Pages 58-71 Read Self-Test questions page 70 Metals - Casting Alloys and Titanium Identify different noble and base metals Noble metals include gold, palladium, and platinum. Base metals include nickel, copper, silver, cobalt, zinc, and titanium. Understand and identify differences between high-noble, noble and predominately base Metals Noble metals defined by their high resistance to corrosion. Base metals have a high tendancy to easily corrode in oral environment. Gold is best known of dental metals, excellent resisant to corrosion, good malleability, and low melting point. Palladium has excellend corrosion, medium melting point, and much harder than gold. Can add palladium to gold to increase hardness, increase melting temperature, and whiten the color. Platinum has a high melting point, is harder than palladium, but is low dental use tue to mixing and price. Nobility of metals is sum of weight percentages of notble metals in alloy. High noble metal is classified if greater than 40% gold content and greater than 60% noble metal content. Noble metal does not havet o have any gold but must have greater than 25% noble metal content. Predoimnantly bse metals do not have to ave any gold but must have less than 25% noble metal content. High noble alloys are expensive, have high densitives, often have copper and silver added to increase hardness or strength. Addition of Pt or Pd are ofthn used. Have excellent corrostion reistnace. Do not have high moduli and are flexible for large restorations. Have low melting point. Noble alloys most compositionally diverse of casting alloys. Moderate densities. Strength or hardness greater or equal than high noble allowys due to Pd content. Lowerr cost than high noble. Au based noble alloys relativelt low melting so not be used for ceramic-alloy restorations. Predominantly base metal alloys. Have minor amounts of noble elemnts. Most complex and contain six to eight elements. Extremetly high yeile dstrengths and hardness, difficult ot ploisj, relatively low desnisites, difficult to cast, least expensive. Nickel and cobalt based controversial because relatively high corrostion and questionable biocompatibility. Base metal alloys used for crowns and fixed partial dentures, removable partial dentures, or dental implants. Understand relevant properties of casting alloys (strength, melting range, density) Melting range allpowys don't melt at single temperature but have melting range. Liquidus si temperature at which all alloy melts (uppr range). Solidus istemeprature at which all alloy freezes (lower rnage). Modulus and strength relevant for clinical success and prevention of restoration failure (bear occlusal forces). High modulus is required to resist occlusal forces. Strength must be suffieicnt to prevent permanent deformation or failure. Hardness indication of how easy alloy is t indent or polish. High yield strength = high ahrdness = difficult to polish. Hardness ca be icreased twith heat treatment. All metals expand on deating and shrink on cooling. Alloys with little solidification and cooling shrinkage able to produce more accurate casting (dimenstional change is low). Alloys with higher shrinkage reates require special support. Density important for metal alloys. If alloys have higher densities are easier to cast. Cost is higher for alloys with higher densities. Color important only for esthetics not physical property. Identify the different titanium (cp-TI and Ti6Al4V), and differences in properties Cp-Ti and Ti-6Al-4V are two maine types of titanium. The amount of titanium in cp-Ti is 99%. Amount of oxugen determines grade of alloy with lower oxygen conetn being grade 1 and higher being grade 4. Higher qquantities of oxygen means higher strength alloy. Ti6Al4V has 90% titanium, 6% aluminum, and 4% vanadium. Has excellent corrosion resistance, is extensively used as implant biomaterial due to suitable biocompatitbility, mechnanical properties, and ossseointegration. Improved strength, similar modulus compared tocp-Ti. Understand why Ti-alloys are biocompatible Ti-biocompatibility/ corrosion protection because oxide layer: titanium spontaneously forms oxide surface on exposure to air or physiologic saline environment. Self-healing layer, inhibits low-charge transfer (biocompatibility), and prevents corrosion (good osteointegration). Dnetal titanium implants implant surfaces coated for bioccitivyt. Have antibacterial properties like silver copper, and flouride, improve osteointegration from calcium phosphates, and have antibiotic proterites like chlorhexidine on them. Pages: 138-149 Read Self-Test questions page 153 Cements Identify different types of cements (composition, reaction, main properties and differences (GIC, RMGI, ZOE, Calcium hydroxide) There are 3 types of dental cements. Type I: luting agents for permantn and temporary tooth structure. Type II for restorative mateirals. Type III for liners or bases placd within the cavity preparation. Within luting cements are water-based (glass ionomer cements), oil-based (zinc oxide eugonol ZOE), and resin-based cements (resin modified glass ionomer RMGI). High strength resin bases used mor for foundation. Low strength resin bases more for liners. It is improtnat to consider that bases are generally strnger than cememnts. Rovide mechanical support for a restoration. Thermal protection for the pulp. Because metal thermal conducvitity is high. High strength includes glass ionomer, resin modified glass ionomer, zinc phosphate. Low strength bases functon as a barrier to irritating chemicals and provide a therapeutic benefit to the pulp and are made of calcium hydroxide and zin oxide eugonol. Often clled liners. Different applications of cements including: retain restoarationns such as alloy or ceramic crowns and bridges, inlays, onlays, and veneers. Cements can be used as temporary filing matierals. Cements can be used as base to protect pulp from irritants. Can be sued as used for pulp-capping agent. Gass ionomer cements are also called water-based. Can be usedas restorative material, as luting material (luting material provides the retention of indirect restorations by providing mechanical interlocking, chemical bonding or both of them) and as base. Resin modified glass ionmers bring the benefits of glass ionomers such as floride release and adhesion with composite resin benefits such as strength and aesthetics toegtehr into same materials. Try and reduce hydrations ensitivity, delayed set, poor early strength in glass ionomer and reduce polymerization shrinkage, micro-leaskge, and recurren caries in composite resin. Water-soluble mathacyrlate-abased monomers used to replace part of liquid component of conventional glass ionomer cements. Includes power ad liquid with methacrylate and HEMA and tartaric acid to help with viscocity. Understand chemical reaction GIC GICs used as restorative matierla, luting material, and base. Composition of GICs includes liquid with polymeric -wataer soluble acid, power glasses and watr. Reaction forms cross-linked gel amatrix that surrounds the partially reacted powder particles. Acid starts to dissolve glass, releasing calcum, aluminum, sodium, and fluorine ions. Fourine ions dispersed in matrix. The glass (powder) compositions includes silica, calcium, alumina, and fluoride. The ratio of amunina to silica is key to their reactivity with polyacrylic acid. Fillers in glass powedr control release of ions, setting characteristics, solubiity, release of fluoride. Larger particle sizes for restorative and finerd sizers for cementing. Identify different types of ZOE Type I ZOE forms an amorphous chelate of zinc eugenolate. Type II ZOE is ethoxybenzoic acid (EBA)-alumina reinforced. EBA in liquid forms a stronger crystalline matrix. Water and heat accelerate eh setting reaction of these cements. Basic qualities for each type GICs - Glass ionomers chemically can bond to tooth structure by chelation of the carboxyl groups with the calcium in apaitie of enamel and dentin. Mechanical response relatively low for GICs. Retention of glass onomer cements primarily micromechanical but some chemical bonding. Considered superior to many types f cements bc it is adherent and translucent. GICs release fluoride for anticarcinogenic effects.Inhibits demineralization of enamel and dentin. Not all clinical studies confirm he ability of GIC to prevent secondary caries. ZOE - Zinc oxide-eugenol are oil based cements and have sedative effect on pulp. Commonly used for luting and intermediate restorations Used for short term cementation. Weak and easily cleaned for casting. Resin based cements -- low -viscocity versions of restorative composites. There ae one or two paste systems for resin-based cements. Curing can be light or chemical. Temporary resin cements are easy to mix and clean up, low to medium compressive strength, low bond strength so easy to remove. Relyx veneer cement example of resin based cement. Composition is BisGMA, and TEGDMA. Also fillers such as zirconia/silica. Pages: 84-94 Read Self-Test questions p. 94 Ceramics Identify the composition, phases (crystal and glass) of dental ceramics Glassy ceramic used mostly for esthetics such as veneers. Low strength but good for appearance. Glass-dominated ceramics have good esthetic (translucency) and better strength than glassy ceramics. Crystalline-dominated ceramics have improved strength, but are more opaque so not as good for esthetics as glassy ceramic. Often used for cores for anterior posterior crowns and some inlay/onlay.. Crystalline ceramics are strongest type but are opaque so cant control mush with esthetics. Used for any dental restoration (crowns/bridges). Crystal base for ceramic includes materials such as leucite, fluorapatite, spinel, zirconia, alumina, lithium disilicate, and lithium silicate. Glassy phase usessilica (quartz, silicone oxide). Identify different manufacturing methods for ceramics Different methods for manufacturing ceramics includes stacking, pressing, milling, additive manufacturing, and slip casting. Glassy ceramic use stacked manufacturing. Glass dominated use stacked, pressed and machined. Hot pressing used and is plastic molding. Crystalline dominated use infused, pressed, and machined. Glass infusion is a way to infuse glass into crystalline dominated ceramics. Crystalline used machined. Example of machine milling is CAD/CAM with digital impression or CNC milling where burrs cut based on shape you scanned. Additive manufacturing is 3D printing. Slip casting is ceramic forming technique fitting ceramic into certain shape. Sintering uses high heat to form materials. Stacking material on top of each other. Understand different properties of ceramics (mechanical, thermal) Mechanical properties of ceramics. Have high compressive strengths and moduli so can withstand a lot of pressure before fracture. Have low tensile strengths and elongation because brittle so cannot elongate. Stiff and brittle relatively to alloys and polymer. Ceramics can compress but can't expand much. Hardness of most glassy or glass dominated crystalline ceramic is substantially higher than enamel. Enamel may wear first. Wear can be minimized if restoation surface is smooth. Coefficient of thermal expansion is a measure of how much a material expands per unit length if heated 1 degree Celsius. Changes in amterial temperature results in dimensional changes (expansion/cameration) Understand implications of CTE difference on debonding The coefficient of thermal expansion or CTE is important when a ceramic is bonded to another madeira since it can cause failure. When CTE of the alloy or ceramic material supporting the veneer is less than CTE of the veneer, the veneer is in tension and the ceramic will break. Veneer in compression will be fine when the CTE of the ceramic material is greater than the CTE of the veneer. Proper CTE matching required between bonded materials to prevent failure. Tall alloys are compatible with all ceramics. Understand bio integration of ceramics Ceramics are biocompatible if minimal adverse effects on biological tissue. Some loss of mass occurs (corrosn during service) but don't want too much. Understand the use of ceramics on restorations (PFM and All ceramic) Ceramics in restorations include all ceramic crowns, porcelain fused to gold crown, and porcelain fused to metal crown. Porcelain fused metal can have opaque porcelain that masks the darkness of oxidized metal framework. Overlap of ceramic gives natural tooth color and final buildup of dentin/enamel porcelain. Alloys formulated to have an oxide layer. Bond is result of chemistries by difficusion btween surface oxide layer on allow and ceramic (covalent bond). Roughen f of surface interface also increases bond strength. Increases wetting area for porcelain and micromechanical retention. Failure of ceramic-alloy bonding if inadequate oxide layer or high thermal residual strength (large difference in thermal expansion coefficient between cermai can d alloy. Majority of retreatments use to biological failures. All ceramic alloy restorations advantage is potential for better esthetics. No dark oxide color to mask from alloy. Crown made entirely of glaasss dominated ceramics. All ceramic restorations where core replaces alloy are high strength, crystalline dominated, opaque tdue to crystallinity. Made by pressing or matching. Veneering ceramics are glassy or glassy dominated and are greater estehtic naturetranslucent. Made by stacking. All ceramics relatively brittle and could fracture more often thatn ceramic-alloy restorations. Greater thickness required, complex cementation comared to PFM. High hardness, and lack of clinical evidence on the success. Pages 213-192 Impression Materials Identify different types of impression materials (alginates, elastomeric) and basic Compounds Types of impression materials include hydrocolloids and elastomeric. Alginate hydrocolloids are a dissolving solid (solute) is dispersed into liquids (solvent). Depending on quantity of water could result in different states such as gel (jelly-like) or sol (viscous liquid). Colloid particles are hydrophilic polymers dispersed in water. Elastomeric includes addition silicones and polyether. Elastomeric known as silicone rubbers. Are flexible cross-linked polymers when set. Compared to alginates elastomeric have greater accuracy, dimensional stability with time, excellent record of details and tear strength. Addition silicon supplied as 2 paste system with base and catalyst. No generation of volatile by-products (water-alcohol). Addition silicones are hydrophilic. Have low, medium, and high viscosity. Addition silicones have small dimensional change, elastic revoery after mouth removal, working time is short, tear strength is mid-low, available also as paste and relies on shear thinning behavior for dispensing. Polyether impression materials like addition silicones, good hydrophilicity, limited dimensional stability over time, shelf life greater than 2 years. Uses base + catalyst system. Form a cross linked high molecular weight elastomer. Haas medium-viscosity consistency, dimensional change greater than addition silicones, should iota be stored in water (absorbs), and supplied in two mixing systems. Can use motorized mixers. CAD/CAM technologies for digital impressions. Digital scanners to get impressions. Also, in office scan and mill to make croons same day. Use coordinates for scanning. Understand chemical reaction for alginates Chain of reactions for alginate. Cross linking of alginate chain by replacement of Na ions with Ca ions. Sodium phosphate controls setting time for alginates. Working time is the time to actually mix and work with the material. Setting time is the time required for chemical reaction to be completed, and material solidify. Temperature, proptortion of water to powder and mixing modifies setting and working time. Increase in temperature, shorten setting and working times. Thinner mixes increase setting time so changes in water/powder also influences strength. Under mixing ad over mixing are detrimental to strength. Understand differences effects of amount of compression, time under compression, consistency of the mix on permanent deformation Elastic recovery -- perament deforation increases when the time before testing decreases, when the amount of deformation increases during removal, when the time that is help under compression increases, whcen thinner mixes are used. Thinner mixes are more water and have lower mechanical strength compared to thicker mixes. How fast you load alginate affects the strength. Fast loading. = high mechanical properties. Dimensional change and alginate. Alginate loses accuracy with incisded time of storage. Sored in air? Water evaporates, alginate shrinks. Stored in water? Water is absorbed, alginate expands. Type of stone affects the reproduction detail of alginate. Alginates advantages are ease of mixing and manipulation, minimum equipment, flexibility, accuracy if handled properly, and low cost. Alginate disadvantages are low tear strength, limited elasticity, limited surface detail, storage dimnestional stability. Understand different relevant properties of impression materials (dimensional chance, tear strength, recovery, detail reproduction - wettability, viscoelastic, strain rate dependence) Impression materials behave as viscoelastic materials. Have creep and stress relaxation qualities. Strain rate dependence -- mechanical response of dental materials depend on how fast they are loaded. Higher strain rates = higher values of modulus. Elastic revovery -- ability to recover to the original shape after stress. Doesn't fully recover for impression materials there is some permanent deformation. Elastic recovery important for removal of impression material from mouth. Tear strength - ability for impression material to resist tearing in thin sections. Spaces in mouth that are thin and when you remove impression, need to try and prevent tear strength from causing ruptures. Working and setting times/ dispensing- working time is time to work with material. Can mix and fluid behaves with low viscosity. Setting time is how time you have to set and cure. Viscosity gets higher during setting. Dimensional stability -- ability to retain its absolute dimensional size over time. change of dimesnions of material. Surface resolution. Is surface hydrophilic where theta is less than 90 and there is a high degree of surface detail and surface gets wet or hydrophobic where theta is less than 90 and low degree of surface detail and surface does not get wet. Understand Strain rate definition Strain rate dependence -- mechanical response of dental materials depend on how fast they are loaded. Higher strain rates = higher values of modulus. If stiffness is high, stress is higher, higher mechanical properties in terms of stiffness and yield if fast removal. Slow removal means stiffness is low and stress is low. Pages: 98-113 Read Self-Test questions (page 112) Dental Stones (Model & Die, Investments) Identify different types of dental stones (differences?) 1. Impression plaster -- type I. To mount casts in articulator 2. Dental plaster -- type II. for typical study models, diagnostics, art portion. It is a weak cast 3. Dental stone -- type III. Called dental stone. For full/partial denture model. Less water and stronger than type II. Hydrocal. 4. High strength/low-expansion dental stone. Type IV. Also called die stone. For dies, which require high strength/high abrasion resistance. Densite. 5. High strength/high-expansion dental stone. Type V. High expansion to compensate shrinkage of casting alloys. Type V dental stone has the strongest compressive strength. Type I dental stone has the weakest compressive strength. Understand and identify different stone phases (dihydrate, hemihydrate) Gypsum which is a mineral from the earth is calcium sulfate dihydrate. Dental stone is a powder product one buys for dental labs and includes model plaster, dental stone, and die stone is calcium sulfate hemihydrate. Cast/die final product is calcium sulfate dihydrate again. To get from dihydrate earth form to hemihydrate powder form is a process called calcination. Stone goes from hemihydrate in the dental office to dihydrate by addition water. This is an exothermic reaction so crystal expansion and interlocking. Identify different types of crystal shapes/forms/porosity Size and porosity of the crystals require different amount of excess of water to produce workable mass. Porosity of plaster \> dental stone \> die stone. Effect of accelerators and retarders Accelerators - increase the rate of setting. Faster setting time. Accelerators increase the number of crystal nuclei available for growth. Examples of accelerators are potassium sulfate or sodium chloride (but increases expansion). Retarders -- decreases rate of setting. Slower setting time. Make hemihydrate powder slightly less soluble than dihydrate. Example of retarders are borax or sodium citrate. Understand relevant properties of stones (W/P, hygroscopic, working-setting time, dimensional accuracy) The water-powder ratio is the amount of water added to 100 grams of powder. Powder is fixed at 100g and water is variable. As W/P increases which means that more water is used, setting time increases, strength of gypsum product decreases, and setting expansion increases. Excessive water increases setting time, increases porosity, and decreases strength (voids after evaporation). Larger crystal size (die stone) the less water needed. Increase in temperature = increase in setting time. Higher temperature = slower setting tme. Lower temperature = faster setting time. Spatulation -- increase in speed and time, shortens setting time. Humidity: gypsum materials are hygroscopic (absorb water from abient). Xposed power (hemihydrate) will be dihydrate. During mixing, increased setting time. The higher the W/P, the lower the mechanical properties. The lower the W/P the higher the mechanical properties. Gympsum materials expand on setting. Depends on the type of stone. Higher setting expansion, lower accuracy becase crystals grow and more water causes more expansion. Worst for expansion is plaster \> dental stone \> high strength stone. Hygroscopic expansion after initial mixing is where water is added to surface or humidity. Expansion not uniform in every direction. There are hardening solutions which can harden the gypsum and also increase its abrasion resistance. Relevant for dies, in which high accuracy and high abrasion resistance are required. The liquid-poweder ratios maight be different because agents reduce excess of water needed to wet hemihydrate. Gypsum products are compatible with agar, alginate, condensation silicones, addition silicones, polysulfides, and polyethers. As hardness increases, contact with alginate decreases hardness. Dry harder than wet. Colloidal silica hardening solution. Some disinfectants decrease hardness. Reproduction of detail important for dental stones. Good wetting between water based couples (alginate and gypsum). Addition silicone (non water absed) and gypsum limited reproduction. Materials such as agar have small contact agnle which means good wettability and good surface detail. Pages: 118-129 Read Self-Test questions page 129 Dental Waxes Identify different types of dental waxes (natural/synthetic) The differet types of dental waxes are natural and synthetic. In natural, there are animal based, plant based, and mineral based waxes. Animal based are bee wax for example. Synthetic wax includes things such as polyethylene wax, polystyrene wax, and castor wax. Effect of temperature/force/time on flow properties Temperature - Waxes exhibit a sharp change in flow properties around their melting point. Below this temperature, they are typically solid with limited flow. As temperature increases past the melting point, the wax transitions to a liquid state, significantly reducing viscosity. Force - Many waxes exhibit non-Newtonian behavior, particularly shear-thinning. Under applied shear or pressure, molecular alignment occurs, reducing resistance to flow and thus decreasing viscosity. Time -- Under constant force, waxes may exhibit time-dependent deformation. This is particularly relevant in semi-solid or soft waxes, where long-term stress leads to flow or deformation. Can have stress relaxation over time. Identify important/relevant properties of waxes (melt range, flow, residual stress, thermal expansion) Waxes don't melt at the same / single temperature due to variation in composition. There is a melting range for wax. Flow is the change in shape under an applied force. Waxes should exhibit considerable flow at time of preparing wax pattern. Waxes should exhibit little or no flow at mouth or room temperature. Waxes have low compressive strength, low modulus of elasticity (waxes are not stiff), waxes are flexible (low young's modulus), depends on the type of wax. Residual stress is stress remaining in a wax as a result of manipulation during heating, cooling, bending, carving, or other manipulation. Stresses are released as temperature of the wax increases, and the wax molecules can move more freely. Flow depends on temperature, time, and applied force. Waxes have highest coefficient of thermal expansion of any dental material. Pattern waxes vs processing waxes. Pattern waxes include inlay, casting waxes, and base plate waxes. Inlay waxes generally used for wax patterns, crowns, inlyas, or bridges. Casting (RPD) wax used to form wax pattern of metallic framework of removable partial dentures. Copy well and are not brittle. Base plate waxes are used to build the contours of denture and hold the position of the denture teeth before the denture is processed in acrylic. Type I (soft): used for contouring dentures and veneers. Type II (medium): used for patterns that will be placed into the mouth in a temperate climate. Type III (hard) used for mouth use in tropical climates. Processing waxes boxing, beading, utility, sticky waxes. Boxing waxes primarily used in taking and pouring impressions. Have a slight tackiness which allows them to be attached to each other. Can be melted easily to seal them to surfaces. Think of wax that makes a box around material. Utility waxes think utility so easy to work with and is adhesive. High flow. Used to alter stock tray extension and rim the tray to prevent irritation/height adjustment. Sticky wax is hard and brittle at room temperature. After heated, it is sticky and will adhere tenaciously to dry stone or other dental materials. Commonly used to assemble metallic or rein pieces temporarily in position. Bite-registration wax used for accurate articulation of certain models of opposing arches. Identify types of waxes Pages: 131-136 Read Self-Test questions (page 136)