Dental Ceramics Flashcards

Question

leucite forms

Answer 1

around the glass phase of ceramic

Answer 2

forms around the glass phase of the ceramic gives a powder of known physical and thermal properties no further chemical reaction is required during fabrication of the restoration

Answer 3

* The powder is mixed with distilled water and built up into the restoration (wet sand) * Feldspathic ceramics form **leucite** when heated to 1150-1500^oC * Leucite is potassium aluminium silicate * This forms around the glass phase of the ceramic. * Gives a powder of known physical and thermal properties. * No further chemical reaction is required during fabrication of the restoration * The powder melts together to form the crown

Answer 4

* Ceramic powder is mixed with water and applied to the die with a brush * The crown is built up using different porcelains for dentine and enamel * These are not tooth coloured * The crown is heated in a furnace to coalesce the powder into ceramic * Heating leads to **SINTERING** * This occurs just above the glass transition temperature * It is when the ceramic particles begin to fuse into a single mass. * During sintering the glass phase softens and will coalesce * Over time there is controlled diffusion and a solid ceramic mass is formed * During sintering the material contracts by about 20% * Considerable skill required by technician to judge the contraction in 3D

Answer 5

heating leads to sintering (crown in furnance to coalesce the powder) * This occurs just above the glass transition temperature It is when the ceramic particles begin to fuse into a single mass.

Answer 6

* Aesthetics * Chemical Stability * Biocompatibility * Thermal Properties * Dimensional Stability * Mechanical Properties

Answer 7

* Ceramics have the best aesthetic properties of any dental restorative material * Colour Stable * Very smooth surface * Retain their surface better than other materials  less staining long term * Optical properties * Reflectance * Translucency * Opacity * Transparency * Opalescence

Answer 8

* Chemically very stable * Generally unaffected by the wide pH range found in the mouth * Do not take up stain from food/drink * Good BIOCOMPATIBILITY minimal adverse effects on biological tissues

Answer 9

* Similar to tooth substance * Coefficient of thermal expansion is similar to dentine * Results in low stresses to the restoration in the mouth during use * Thermal diffusivity is low * Protective of the remaining tooth.

Answer 10

* Once fully fired the material is very stable * During fabrication shrinkage is a problem and must be accommodated for by the technician * Shrinkage of 20% during firing is normal for a conventional feldspathic ceramic crown

Answer 11

* High compressive strength * High hardness * Can lead to abrasion of opposing teeth especially if not glazed * Tensile strength – very low * Flexural strength – very low * Fracture toughness – very low * All lead to failure during loading * Static Fatigue * Time dependant decrease in strength even in the absence of any applied load. * Probably due to hydrolysis of Si-O groups within the material, over time in an aqueous environment. (small principle) * Surface micro-cracks * Can occur during manufacture, finishing or due to occlusal wear. * These are areas where fractures can initiate – potential to get bigger and fail * Slow crack growth * Cyclic fatigue under occlusal forces in a wet environment over time * All of these problems mean that conventional feldspathic ceramics can only be used in low stress areas. * Only anterior crowns. * Not in all patients * Too brittle for use elsewhere

Answer 12

* Aesthetics are good but they need to be stronger * Produce a strong coping, resistant to fracture, and cover in conventional porcelain * Cast or press a block of harder ceramic * Mill a laboratory prepared block of ceramic

Answer 13

* Metal coping * See DMS Porcelain-fused-alloys * Alumina core * Zirconia core

Answer 14

* Alumina reinforced feldspathic core ceramics since 1960s * This type of core was used as the first choice crown for anterior teeth for decades * It is not strong enough for posterior use * Aesthetics could be excellent but enough room was required for aluminous core and feldspathic layers above. * Possibly more palatal reduction required than in a metal ceramic crown, but less labial reduction required.

Answer 15

Flex strength double that of feldspathic porcelain \>120Mpa * Alumina particles act as crack stoppers preventing cracks propagating through the material and causing fracture * Aluminous porcelain is opaque and can only be used as a core material 1st choice for anterior teeth not strong enough for posterior use

Answer 16

Aesthetics could be excellent but enough room was required for aluminous core and feldspathic layers above. * Possibly more palatal reduction required than in a metal ceramic crown, but less labial reduction required. Relatively cheap to make * No specialist equipment required, just a furnace Conventional Aluminous cores are a maximum of 50% alumina * Increased alumina content increases the strength leading to new techniques * INCERAM * PROCERA

Answer 17

50% increased alumina content increases the strength leading to new techniques * INCERAM * PROCERA

Answer 18

INCERAM PROCERA

Answer 19

PJC anterior teeth 1st choice not strong enough for posterior

Answer 20

* Core material has an alumina content of around 85% * Complicated technique (Slip Casting) In-Ceram-Spinel has Spinel (MgAl2O4) rather than alumina as its core material * Better aesthetics but lower flex strength In-Ceram-Zirconia has 33% Zirconia replacing Alumina in core * Higher strength but poorer aesthetics

Answer 21

The ceramic core is formed onto a refractory model A fine slurry of alumina is applied to the model It is heated to 1120^oC for 10 hrs This is below the glass transition temperature for alumina Partial sintering occurs A porous core is produced Core is infiltrated with lanthanum glass at 1100^oC HIGH STRENGTH CERAMIC \>400 MPA flexural strength

Answer 22

* has Spinel (MgAl2O4) rather than alumina as its core material * Better aesthetics but lower flex strength

Answer 23

* has 33% Zirconia replacing Alumina in core * Higher strength but poorer aesthetics

Answer 24

* Pure Alumina core \>99% pure * Even more complicated * Core is made centrally not in every lab * A fully densified alumina core is produced at around 1700^oC * High flexural strength \> 700MPA * Possibly better translucency than glass infiltrated core.

Answer 25

in-ceram procera

Answer 26

with conventional feldspathic porcelain to produce the final crown

Answer 27

single posterior crowns not used often as bridge material

Answer 28

* Probably the most popular ceramic core material. Zirconia (Zirconium Dioxide) is a naturally occurring mineral * It occurs in different forms at different temperatures Very hard * Zirconia powder does not sinter unless heated to over 1600^oC * Pure zirconia can crack on cooling

Answer 29

used extensively in jewellery - imitation diamonds Until CAD-CAM was introduced the use of Zirconia as a core material would not have been possible * The Zirconia used in dentistry is Yttria-stabilised zirconia

Answer 30

used in dentistry Very small amounts of Yttria is present in the material \<1% * Normal Zirconia is a monoclinic crystal at room temperature * Yttria is a tetragonal crystal structure If a crack begins when the stress at the crack tip reaches a critical level the crystal structure transforms to the monoclinic structure * This causes a slight expansion of the material and closes up the crack tip This ability leads to a material which is very * Hard * Strong (1000MPA flexural strength) * Tough * Strong enough to use as a Bridge Framework

Answer 31

Hard Strong (1000MPA flexural strength) Tough Strong enough to use as a Bridge Framework

Answer 32

Yttria is a tetragonal crystal structure * Normal Zirconia is a monoclinic crystal at room temperature If a crack begins when the stress at the crack tip reaches a critical level the crystal structure transforms to the monoclinic structure * This causes a slight expansion of the material and closes up the crack tip

Answer 33

* Impression is taken of the preparation and sent to the lab * A model is cast and then scanned digitally * Software Unit Creates a bridge substructure on virtual preparations * Minimum thicknesses of connectors are determined and fabricated * Raw Zirconia block is selected for milling * A presintered block is much easier to mill * Milling for a three unit bridge will take around an hour * The cut framework is then heat treated at around 850^oC to achieve its final physical properties * This causes a 20% shrinkage but the computer softwear deals with this during the milling process. * The framework is also stained to an appropriate colour * The Zirconia core is then veneered with feldspathic porcelain to produce the final restoration

Answer 34

* Most manufacturers have their own Zirconia system * LAVA from 3M is probably the best known * IPS e.max Zir CAD * Opalite * Zerion

Answer 35

* Expensive equipment required * Potential for veneering porcelain to debond from core * Zirconia core is opaque ? Are aesthetics much better than metal ceramic * Inert fitting surface, cannot etch or bond

Answer 36

Once you have the equipment they are cheaper to make * Cost of metal is increasing Fit is generally excellent

Answer 37

* Zirconia * Lithium Disilicate * Precious metal * Non-precious metal * Titanium

Answer 38

for better aesthetics

Answer 39

For the same material a **milled crown will be stronger than a built up or pressed crown.** * The block will have been subjected to the ideal heat treatments to maximise it’s properties and all blocks will be consistent As aesthetics of ‘blocks’ of ceramic improve these will become the most commonly used crown*. (darker cervically, more translucent at top – decide where in the block going to cut the crown; hand layered crowns better than milled but can dye milled to improve)* * Probably already acceptable in posterior teeth

Answer 40

* Cast goes into scanner * Scanned image of cast * Lower cast is scanned and ‘articulated’ * Select crown margin * adjust crown margins * select crown type and place on ‘model’ * Adjust shape and size of selected crown * Save file * Send to milling machine * Can be anywhere in the world * *GDH mainly go to Spain* * 30 – 40 minutes you have your crown *In GDH return from Spain takes 48hrs* * Still requires final finishing * *In GDH this is still done on a plaster model*

Answer 41

can dispense with models and impressions. * Scan in the mouth * Design on CAD machine * Mill * Polish * Cement

Answer 42

Trios scanner in GDH * Used mainly by postgraduates * Digital Dentistry SSM * Limited but increasing undergraduate use Dentsply Sirona CAD-CAM

Answer 43

A different technique more like casting a metal restoration * The restoration is waxed-up, as you would for a metal restoration * Invested * Cast from a heated ingot of ceramic (1100^oC) * No sintering occurs the ceramic ingot is already fully condensed prior to firing. * Once devested and cleaned the restoration is heated to improve its crystal structure producing crack inhibiting crystals. * This process is called CERAMING * The cast crown can be stained * More often it is cut back labially and veneered with appropriate feldspathic porcelains

Answer 44

called glass-ceramics * Lithium Disilicate Glass * Leucite Reinforced Glass

Answer 45

Two stage process * Stage 1 crystal formation maximum number of crystal nuclei are formed * Stage 2 crystal growth to maximise the physical properties Crystal phase of the ceramic can approach 100%

Answer 46

Strong materials have small crystal size and high volume fraction of crystals

Answer 47

Lithium disilicate glasses have a unique needle-like crystals * This makes crack propagation through this material very difficult so good flexural strength * possibility to use this material for bridgework ? * can look better than block zirconia but may not be as strong

Answer 48

* Any silica containing ceramic can be etched with hydrofluoric acid to produce a retentive surface * This etched surface can be bonded to, using a silane coupling agent and in turn bonded to the tooth using an appropriate bonding agent * Zirconia cored crowns do not contain silica and are not affected by acid * They are strong enough to be self supporting and can be luted with a conventional dental cement – doesn’t need to rely on support of underlying tooth

Answer 49

Any silica containing ceramic can be etched with hydrofluoric acid to produce a retentive surface * This etched surface can be bonded to, using a silane coupling agent and in turn bonded to the tooth using an appropriate bonding agent Zirconia cored crowns do not contain silica and are not affected by acid * doesn’t need to rely on support of underlying tooth

Answer 50

produced by or subjected to sintering (the process of coalescing a powdered material into a solid or porous mass by means of heating without liquefaction).

Answer 51

come together to form one mass or whole.

Answer 52

reduced to fine particles by grinding in a mill.

Dental Ceramics Flashcards

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