All Ceramic Restorations PDF

All Ceramic Restorations Initially in dentistry casting was done using the lost wax technique → however it was not sustainable because each step might result in an error which can compound on itself growing larger and larger → eventually leads to shrinkage or expansion We can have poros...

All Ceramic Restorations Initially in dentistry casting was done using the lost wax technique → however it was not sustainable because each step might result in an error which can compound on itself growing larger and larger → eventually leads to shrinkage or expansion We can have porosity from the repeated cooling that prevents the complete filling of the mold Air bubbles can also be trapped within the investment material during the pouring process We started using metals → metals alone however provides no aesthetics (only provide strength and durability) → so we added porcelain → PFM crowns Most alloys contained (Ni) Nickel → however it is was not very biocompatible as it caused sensitivity → We made Nickel free alloys Metals are also not very biocompatible and are at a risk of corrosion → we started improving ceramics and porcelains Composition of Ceramics → Ceramics are Inorganic compounds → they are composed of metallic and non- metallic elements (which are oxides) → made by firing at a high temperature to achieve desirable properties Inorganic non-metallic (oxides) → are typically crystalline in nature Crystalline structures are highly ordered atomic structures where the atoms are arranged in repeating, regular pattern forming lattice While amorphous materials lack long-range order in their atomic arrangement → the atoms are arranged randomly or disordered Compounds formed between metallic and non-metallic elements Aluminum & Oxygen (Alumina - Al203) → most common Calcium & Oxygen (Calcia - CaO) Silicon & Nitrogen (Nitride - Si3N4) So we have metallic components that give non-metallic properties → the metallic compounds are mixed with non-metallic (oxides) → gives us the non-metallic properties The nonmetallic properties are important to avoid the high thermal conductivity and corrosion we find in metallic properties  So basically Ceramics are = Metallic Elements + Non-Metallic Elements (which are mainly oxides) → fired at a high temperature Ceramics = Silico (SiO2) & Feldspar + Crystalline (Al2O3, MgO, ZrO2) Dental Ceramics Mainly made up of nonmetallic, inorganic structures containing compounds of oxygen → added to one or more metallic (or semi-metallic) elements → like aluminum, calcium, lithium, magnesium, phosphorus, potassium, silicon, sodium, zirconium, OR titanium That being said Ceramics are mainly made up of → Silico (SiO2) & Feldspar → with small addition of crystalline (Al203, MgO, ZrO2) → with or without oxides Composites are made up of fillers within matrix Ceramics vs Porcelain Normal porcelain refers to a family of ceramic materials composed of → Kaolin, Quartz, & Feldspar → fired at high temperature Dental porcelain → the kaolin is almost omitted → becomes called Feldspathic porcelain → mainly composed of Feldspar and a little bit of quartz Kaolin is only 5% of the composition We also added Silica to add strength → Feldspar is added to increase translucency and aesthetics (reduces strength however) Ceramics ARE porcelain → Ceramics are simply porcelain with minimal amounts of Kaolin Ceramics = Feldspathic porcelain Characteristics of dental ceramics Excellent biocompatibility Is chemically inert in oral cavity However the metal is not biocompatible → causes corrosion and causes gingiva to become black Excellent aesthetics → Difficult to be stained Ceramics are dense structures → moreover their manufacturing process ensure minimal porosities are left in the final product → this minimizes the amount of pores the stain can settle in and stain the ceramic They are chemically stable Their smooth surface finish reduces the surface area available for the stain to stick Ceramics manufacturing process add a glassy layer on top → the glazed layer is less porous than ceramics → decrease chance of staining Strong but brittle If forces reaches elastic limit → material will fracture Their chemical bonds (ionic or covalent) create rigid material → but they do not allow for significant atomic movement → making it difficult for ceramics to undergo plastic deformation Their polycrystalline microstructure consist of many small grains separated by grain boundaries → the boundaries can impede movement of dislocations creating stress concentrations High compressive strength The maximum load a material can withstand while being compressed Low tensile strength Maximum stress material can withstand while being stretched Low shear strength Maximum stress material can withstand in shear before failure Low thermal diffusivity How quickly heat moves through a material Co-efficient of thermal expansion is almost close to natural tooth How much a material expands when heated High surface hardness Wear resistant → materials resistance to deformation or scratching Surface hardness helps prevent scratches → but if it is too high and patient has bruxism, it will cause antagonistic wear on the natural opposing teeth Expensive Due to technique and skills needed to create it Has a sensitive manipulation technique Abrasive to natural teeth Firing shrinkage → which is why initially the restorations are made a bit oversized During the initial stages of firing → water is driven off from the clay → leads to a reduction in volume of the clay As the temperature rises the clay particles begin to rearrange themselves and pack more closely together → the clay further shrinks Then at higher temperatures (>900C) some components of the ceramic (mainly Feldspar which has the lowest melting point) will begin to melt and form a glassy matrix that fills in spaces between solid particles → further reduction in volume Questionable durability Used to be only used on anterior teeth due to ease of fracture → However, nowadays it is used in posterior teeth  Zirconia has helped us to reach to acceptable durability → allows us to use them in long span bridges Applications Crowns and Bridges Veneers over metal substructures Inlays & Onlays Artificial denture teeth Posts Implants fixtures and Abutments Orthodontics brackets Ceramic burs → helps distinguish infected and affected dentine Composition Feldspar Feldspar is a naturally occurring mineral → Makes up 60-80% of composition of the ceramic → added to the composition by grinding it and mixing it with the other components Added to increase translucency They increase the translucency when the melt into the glassy matrix phase which is more translucent Has the lowest melting point → the first to melt on firing Composed of two forms Potash feldspar → potassium Potassium aluminum silicate (K2O-Al2O3-6SiO2) (Potassium-Oxide ; Alumina ; Silica) Is more commonly used than Soda Feldspar → mostly added to increase translucency of the ceramic → allows light to pass through with minimal reflection and deflection Soda feldspar → sodium Soda aluminum silicate (Na2O-Al2O3-6SiO2) (Sodium-Oxide ; Alumina ; Silica) Added to lower the fusing temperature → done to avoid stresses that can weaken the crown → indirectly increases the strength Quartz They are pure crystals of SiO2 (Silica) → makes up 15-25% of the composition Added to increase the strength of the composition  Has a high fusion temperature → Has the highest melting point of all components → very important point as thanks to its high melting point it provides the framework for the other components to stick to → its high melting point allows it to stay solid when the other components have melted → this allows the other components to stick to it Acts as a filler in porcelain restoration Kaolin It is a variety of clay → makes up 4% of composition Acts as a binder (or flux) to the Feldspar and Quartz → has a high fusion temperature allow glassy matrix to take shape → Its fusion temperature is higher than Quartz Increases the mouldability of unfired porcelain → makes the texture easier to form and less flowable by providing the necessary plasticity Has a disadvantage where it gives opacity → does this by limiting the amount of transparency of the ceramic, making it more opaque and less light able to pass through Materials added to achieve appropriate shade Opacifiers Zr (Zirconium); Ti (Titanium); Sn (Tin); Ce (Cerium); Oxides Important in forming appropriate opacity Pigments Provides the characteristic shade Glass modifiers Borax; Boric acid Lowers softening temperature → increases fluidity → acts as fluxers disrupting the silica network Flux Reduces viscosity of molten glass → lowers fusion and softening temperature of glass The fluxers break the bonds of the silica network reducing amount of energy needed to convert material from solid to liquid Binders Holds ceramic particles together prior to firing Conveys opacity to final product Kaolin Metallic oxides Conveys opalescence Provides color Cerium  Produces fluorescence → natural teeth have fluorescence → natural teeth “emit light” Uranium used to be used instead Manufacture of ceramic powder Ceramic is supplied as powder → done by grinding the materials with specific quantities to form fine powders The steps involve The various raw materials that make up the ceramic (alumina, silica, feldspar) are mixed creating the FRIT Then they are fired together in a high temperature furnace → the materials will undergo fusion (they are added together) forming molten mass Then it is rapidly cooled in cold water in a process called QUENCHING → where the molten frit is poured over water or air → leads to large internal stresses and cracking The cooled frit is then milled (ground down) to very fine powder with different colors The fine powder is then mixed with distilled water to form a creamy paste (by the technician in the lab → called SLURRY) → restoration is built up using special brushes The frit has an amorphous (glassy/vitreous) phase Feldspar → increases translucency making it more aesthetic but weaker This is a more weaker and soluble phase A pure amorphous phase is completely transparent like glass → as we increase crystalline phase → we get less translucency and more opacity Then it has a crystalline phase Like Quartz → provides framework but less translucency and aesthetics → i.e. increase in strength The ceramics are made in a way where no further chemical reaction is required → the addition of distilled water to create the restoration does not involve any chemical reaction → simply the water as a solvent allowing the particles of the ceramic to disperse creating the paste (the reaction is primarily physical) → moreover after the restoration is shaped and placed in the furnace we will see no melting → we only see fusion (a decrease in voids) → no change in composition → instead the particles of the ceramic powder will fuse when it is heated to just above glass transition temperature → called **sintering Sintering is the process of heating (firing) closely packed porcelain particles to a specified temperature (below the melting point of the main component) → helps to get densified (structure without any pores or voids) and to strengthen the structure → removes any voids adding more strength and translucency → we make oversized crowns to compensate the shrinkage caused by the condensing particles and eliminating voids Classification of dental ceramics Fusing temperature High-fusing ceramics (1315-1370C) Used for denture teeth to increase strength Medium-fusing ceramics (1090-1260C) Used for denture teeth to increase strength Also used for dental ceramics (metal + ceramics OR all ceramics)- Low-fusing ceramics (870-1065C) Used for dental ceramics (metal + ceramics OR all ceramics) Ultra-low fusing ceramics (100um) with a random distribution → helps in the low fracture resistance and abrasive properties relative to enamel Mostly used as veneer porcelain for metal-ceramic restorations Developed in powder/liquid → Vita VM 13 2.2 Subcategory High leucite-containing glass (approx. 50%)  Done by heat treatment so we get homogenous glass nucleates → grows crystals → the heat treatment helps grow the crystals The higher content will help improve mechanical and physical properties → increases fracture resistance, improves thermal shock resistance, and resistance to erosion The improvement depends on the interaction of the crystal and glass matrix → as well as on crystal size and amount Developed Powder/liquid Machinable Pressable → IPS empress (Ivoclar Vivadent) → example Can be used for Veneers Single crowns in limited force areas 2.3 Subcategory Lithium disilicate glass ceramic → Aluminosilicate glass has lithium oxide added to it → we are not adding Leucite here Introduced by Ivoclar as IPS empress II (now called IPS emax) → Contains larger crystals than empress I → can be created using pressable/machinable (CAT/CAM) Increased the crystal content to 70% with refined size Flexural strength is 360 MPa → three times more of IPS empress I Even with the high crystalline content → the material is still highly translucent due to the relatively low refractive index of lithium disilicate crystals → low refractive index means light will pass through it Can be used for Full contoured Veneered with flurapatite ceramic Full ceramic crown (ant-post) Anterior bridge (3 units max) → can’t be used for posterior bridge however This is due to the limited flexural strength Better alternatives (like zirconia) exist Category 3 (crystalline based systems with glass fillers) Interpenetrating - of the glass in between the crystals - phase ceramic → In here we have the opposite where we are using a full crystal base and then infusing it with glass particles Glass-infiltrated → partially sintered alumina  This system utilizes a sintered crystalline matrix of a high modulus material (comprises 85% of the volume) → in which there is a junction between the crystalline particles holding each other together → different than glass ceramic which does not have the junction Alumina is high modulus We see improved mechanical and physical properties This is owing to the geometrical and physical constraints the crack must follow to cause a fracture Examples include In-Ceram (Vita) → done by slip casting where we have a core material (mainly crystals) → which is then coated with glass In-Ceram SPINELL (350 MPa) In-Ceram ALUMINA (450 MPa) In-Ceram ZIRCONIA (650 MPa) Category 4 (polycrystalline solids) Solid sintered monophase ceramics → we have no glass here → mainly made up of alumina Formed by directly sintering crystals together without any intervening matrix to form a dense, air free, glass free polycrystalline structure In general all polycrystalline solids are prone to bulk fracture due to absence of glassy matrix → due to the grain boundaries that makes the material not very flexible Fabricated as either solid-sintered alumina or zirconia frameworks Examples include Procera AllCeram alumina (Nobel Biocare) (600 MPa) High purity alumina (99.5%) High hardness and strength Highest elastic modulus of all ceramic → objects ability to resist deformation elastically Leads to bulk fracture Lava Zirconia (3M ESPE) (900 to 1000 MPa) In order to cement a ceramics we need to be able to etch them first → ceramics that contain glassy phase are considered etchable → polycrystalline ceramics pose a problem here because they do not contain any glassy material The glassy phase is important because it allows the Hydroflouric acid to create porosities (micro-dentations) → the porosities allow the bonding agent to penetrate and adhere to these indentations → polycrystalline does not have the glassy phase and so etching is not effective  For ceramic material containing glassy phase → resin cement should always be used rather than GIC Dental Zirconia Is not pure zirconia → but is two times as strong and tough as alumina-based ceramics Is partially stabilized by addition of small amounts of other metal oxides Calcia (CaO) Magnesia (MgO) Yttria (yttrium oxide, Y2O3) → 3 wt% Yttria is the most common → Yttira plays an important role in stabilizing the zirconia in a certain phase (tetragonal or cubic) Ceria (Ceriumoxide; CeO2) Has the highest fracture toughness Used for multi-unit anterior and posterior fixed partial dentures We have low temperature degradation We have low rate of degradation of the material when exposed to moisture → degradation involves transformation from tetragonal to monoclinic → increasing Yttria concentration decrease temperature degradation We have three generations First generation → 3% most used → 3Y-TZP The best → because it has the largest tetragonal phase However not very translucent → can’t be used for anteriors unless as a core This is due to the more present tetragonal phase (and minimal cubic phase) → as the tetragonal phase scatters light more than the cubic phase (does not allow light to pass through) The monoclinic has the highest opacity → this is because its larger grain size and a less uniform structure → the tetragonal has smaller grain size and a more uniform structure → cubic has the highest uniformity and scatters light the least → cubic is the least opaque and most translucent Second generation → 5% → 5Y-TZP The increased Yttria concentration decreases densification of the crystals → increases translucency but decreases strength We have a decrease in strength because the zirconia is stabilized in the cubic phase which is weaker than the tetragonal phase → this is because the cubic phase cannot undergo transformation toughening Used for anterior crowns but not for posterior crowns or bridges Third generation → 4% → 4Y-TZP Is in between  Used for anterior bridges Pure zirconia found in three allotropic forms Monoclinic → stable up to 1170C → then transforms to Tetragonal → until 2370C → then transforms into Cubic The tetragonal to monoclinic transformation is accompanied by a shear strain and volume increase (4%) → this can close cracks leading to large increases in fracture toughness The tetragonal/cubic phase must be stabilized at room temperature to use the strengthening mechanism Dental zirconia is mostly Yttria-tetragonal zirconia polycrystals (Y-TZP) Strengthening mechanisms of zirconia - The mechanism works as follows → when a crack forms, energy from the impact interacts with the tetragonal phase of zirconia → during this transformation the crystal’s volume increases as it absorbs the energy → this create compressive stress which will compresses the crack and prevents it from propagating → this process is known as transformation toughening - The problem here is that zirconia alone used in the oral cavity is in the monoclinic phase means the process of transformation toughening is lost → It is solved however by adding Yttria which stabilizes the zirconia in the tetragonal phase - Moreover to preserve this stabilization of the zirconia any adjustments using burs must be minimal → in fact specialized burs are designed for zirconia adjustments are used → this is because the process of grinding the material with a bur creates small crack in the material → these cracks can permanently trigger the transformation from the tetragonal phase into monoclinic The more we increase Yttria concentration the more we move up the phases → 5% is in cubic phase (more translucent but less strength) → 3% tetragonal (more strength but less translucency) → 4% some tetragonal and some cubic Dental Zirconia is a non-etchable material → raises challenge to achieve its full strength as a restorative material when using resin cement as it is difficult for the resin cement to bond effectively to zirconia (Zirconia can be used with conventional cement but it only gives adequate strength 800-900 MPa → therefore it is better to cement with resin cement, with proper bonding technique, which gives better strength 1100 MPa) The main problem is that bonding to non-etchable Zirconia is unreliable → as the success of the restoration depends on the adhesion between restoration and tooth structure → which can’t be 100% if the restoration cannot be etched A better alternative in these cases is Lithium disilicate → which even though has lower strength, provides more reliable bonding → is a more optimal option for onlays  Some alternatives of zirconia alone have been created to overcome its non-etchable weakness Zirconia-toughened alumina (ZTA) → >50% wt AL → enhances bonding + optical properties Has a disadvantage of low temperature degradation (hypothermal degradation) where when water is combined with heat → phase transformation in zirconia occurs rapidly Alumina-toughened zirconia (ATZ) → >50% wt Zr → enhances bonding + optical properties This one resists low temperature degradation found above Has higher strength has two times higher fatigue resistance than Y-ZTP Graded Alumina Graded Zirconia Glass infiltration process is used → this is where glass is introduced/impeded into the zirconia → allows the zirconia to be etchable Can be used as a Framework Only used as a core Monolithic All the crown is made from the zirconia Also available as Monochromatic uniform material → can be stained by infiltration Polychromatic CAD/CAM blocks/disks (gradient Zirconia) → to imitate dentine and enamel With increasing translucency New ceramics like materials (hybrid ceramics) These are new alternative materials to zirconia → as doing any adjustments to zirconia is difficult and can lead to fractures, cracks, and failure These materials combine aesthetics + strength + ability to adjust them Resin matrix ceramics Resin matrix materials are highly filled with ceramics Organic phase (polymer) → surrounding inorganic phase (crystalline) Is specially designed for CAD/CAM milling Their advantages include  Softer nature → ideal for younger patients as it minimizes wear on opposing natural teeth More closely stimulates modulus elasticity of dentine Facilitate repair or modification with composite Subdivides into different families according to inorganic composition Resin Nanoceramic (Lava Ultimate) (Cerasmart GC) Glass ceramics in resin interpentrating matrix (Enamic Vita) → most common Zirconia-silica ceramic in resin interpentring matrix (MZ 100 block - 3M ESPE - Shofu Block HC) Strengthening of Dental Ceramics We strengthen by designing components that minimize stress concentration and tensile stress To minimize effect of stress raisers The design should avoid stress raisers in ceramics Abrupt changes in shape or thickness in ceramic contour All of these can act as stress raisers To minimize number of firing cycles An increase in Leucite crystals after multiple firing will increase thermal expansion coefficient → This creates a coefficient mismatch between porcelain and metal → Which will produce stress during the cooling process that can create immediate or delayed cracks in the porcelain Addition of residual compressive strength We introduce residual compressive stresses within the surface of the glass and ceramic objects in order to gain strength → the introduced stresses help neutralize the tensile strength developed during service → stops initiation of crack propagation This is significant in that compressive stress act in the opposite direction of tensile stress → so when we add residual compressive stress, they will equal and counter act the applied tensile stress (that comes from crack) → this means a higher magnitude of tensile stress is required to initiate a crack propagation Chemical Tampering (Ion Exchange) We create a thin surface layer of high-compressive stress → We do this by exchanging the smaller glass modifying ions (Na+) with larger ones (K+) → gets 35% larger → creates larger residual compressive stresses (700 MPa) Thermal Tampering  This involves the rapid cooling of the restorations surface from the molten state → this rapid cooling produces a skin of glass that surrounds the soft molten core → The skin will shrink during the solidification stage creating residual tensile stress in the core and residual compressive stress within the outer surface The strengthening occurs by inhibiting crack initiation instead of propagation The thermal tampering effect for porcelain reaches 150um depth Thermal Compatibility This applies for porcelain fused metal (PFM) → where we select the metal and porcelain that have a slight mismatch in their thermal contract coefficient → this causes the metal to shrink slightly more than the ceramic during cooling after the firing of the porcelain → results in development of residual compression in the ceramic surface Glazing This is the addition of surface glaze on the ceramic → We form a low-expansion surface layer at high temperature → upon cooling, the low expansion glaze will be placed on the surface of the ceramic and reduces the depth and width of surface flaws Not very useful in improving flexural strength of feldspathic dental porcelain Dispersion Strengthening This is the strengthening mechanism for Leucite-reinforced ceramics Crystalline improvement → where we add a second phase of crystal alumina to a glass material → causes dispersion strengthening The crystals will act as a roadblock to crack propagation → a crack spreading from a defect must go through or around the crystal → this takes some energy away from the propagating crack stopping it → called roadblock effect Moreover, the compressive stresses around the growing crystals may help in cracks and further enhance resistance Transformation Toughening This mechanism is specific for partially stabilized zirconia (PSZ) → partially stabilized with Yttria Stops crack propagation by transforming tetragonal crystals to larger monoclinic crystal Cementation process of all-ceramic It is very important step in the making of the restoration → Improves the longevity of the restoration Glass based ceramics These ceramics benefit from the addition of cements (adhesive luting agents) → as it increases their retention and fracture toughness However they requires surface treatment before cementation Acid etching with hydrofluoric acid (9%) → the etching will remove the glass particles from matrix and expose the crystal particles We then coat with a saline coupling agent (primer) to increase wettability And also acts as a bifunctional molecule → reacting with both the ceramic and copolymerizing with the resin Luting agents (cements) that involve acid-base setting reaction are not recommended here → Acid bases cements can degrade glass based ceramics → as silica are sensitive to acids Alumina based ceramics To etch We can abrade them with air particles OR treat them with tribiochemical silica coating The adhesive cements can increase the strength of the restoration Zirconia based ceramics They cannot be etched with acids or air particles (like in alumina) → lacks the silica layer Air abrasion can result in a premature phase transformation Both adhesive and conventional luting agents can be used to cement zirconia Best cementing agents For ultimate bonding strength → coupled with ease of use → RelyX Ultimate Adhesive Resin Cement with Scotchbond Universal adhesive For simplicity powered by performance → RelyX Unicem 2 Self Adhesive Resin Cement