13,14 - Ceramics (slides 1-46)

Question 1

what is a ceramic

Answer 1

any product made form nonmetallic inorganic material that is usually processed by firing at a high temperature

Question 2

what is porcelain?

Answer 2

a type of ceramic materials originally made by mixing Kaolin, quartz, feldspar and firing them at high temperatures

Question 3

what are porcelains used for

Answer 3

metal-ceramic and ceramic dental restorations

Question 4

how do we classify ceramics? (3)

Answer 4

by application

by fabrication method

by crystalline phase

Question 5

classifying by application: what are three applciations for ceramics?

Answer 5

metal ceramic crowns and fixed partial dentures

all ceramic crowns

miscellaneous: ceramic orthodontic brackets, dental implant abutments, ceramic denture teeth

Question 6

callsification by fabrication: what are ways that ceramics are made?

Answer 6

sintering - the most common method for metal ceramic restorations (sintering is the process of firing the compaced ceramic powder at high temp. It reduces pores and binds particles together increasing the final density (see image of firing in a vaccum, also increses density).

slip casting

heat pressing

CAD/CAM machining

combinations of the above

Question 7

regardless of the fabrication technique, ceramics are made of what?

Answer 7

a glassy or vitreous phase and one or more ctystalline phases with various amounts of porosity

Question 8

what causes the wide variation in mechanical and optical properties of porcelain?

Answer 8

variations in the nature of the crystalline phase and the degree of porosity. Increasing crystalline component can improve resistance to fracturing but can also decrease translucency.

Question 9

Materials for all ceramic restorations have increased what?

Answer 9

amount of crystalline phase. They have more crystalline phase than ceramo-metal restorations to make up for the lost strength of metal, but they are usually more opaque than porcelains used in ceramo-metal restorations with lower crystallinity.

Question 10

Slides 13-21, I don’t think we need to know, so i don’t include them… These are those charts with the yellow headings that talk about different ceramic materials and who manufactures them and their crystalline phase. look over them if you want.

Question 11

ceramics are the best material for

Answer 11

matching the aesthetics of a complex human tooth.

Question 12

what are some general applications of ceramics in dentistry

Answer 12

single and multi unit metal ceramic restorations

all ceramic systems:

inlays, onlays, veneers, crowns

zirconia based (super strong) systems: dental implant abutments, fixed partials

but be careful, they can be brittle, quality is essential

Question 13

Ceramic is widely used as the veneering material in what?

Answer 13

in metal ceramic crowns and fixed partial dentures.

Question 14

when porcelain and metal are used together, why is there an intentional sleight mismatch of coefficients of therml expansion (of the porcelain and the metal)?

Answer 14

it enhances the porcelain-metal bond, keeping the porcelain in a state of compression and lessening the chance of fracture.

Question 15

With regard to metal ceramic restorations, what is good about them?

are they still widely used?

how good is their survival rate?

Answer 15

good: the finished restoration is color stable, tissue friendly, biologically inert, and chemically durable

yes they are

a metal ceramic crown lasts a similar amount of time compared to an all ceramic crown, but the survival rate of a multiunit all ceramic fixed partial prosthesis lasts less time than a metal ceramic one.

Question 16

what is the approx survival rate of a zirconia based all ceramic system?

Answer 16

about 5 years, remember that zirconia is the really strong stuff

Question 17

give me a bit of history on cermics?

Answer 17

ceramics have been used to make jacket crowns since the early 1900’s

they used felspathic porcelain

alumina reinforced ceramics introduced in 60’s

many improvements in the last 30+ years such as:

heat pressed ceramics, slip cast ceramics, machined all ceramic materials

Question 18

what are some pro’s and con’s of ceramic inlays and onlays?

Answer 18

pro’s: better abraision resistance than posterior composites. so, more durable

con’s: occlusal adjustments more difficult, wear opposing natural dentition, marginal gap not as good as gold but improving with technology.

Question 19

what is a ceramic veneer?

how are they made?

Answer 19

a laminate veneer, a layer of ceramic bonded to the facial surface of a prepared tooth to cover an unsightly area.

It is custom made in a dental lab, made by heat pressing or machining using either a leucite reinforced lithium dislocate ceramic

Question 20

What is done to adhere the ceramic veneer to the tooth?

Answer 20

tooth enamel is etched with phosphoric acid and the bonding asurface of teh ceramic is etched with 5-9% hydrofluoric acid gel and treated with a silane coupling agent

or, resin compisites specifically made for bonding to ceramic can be used as the adhesive

Question 21

How does the flexural strength compare for different types of porcelains?

Answer 21

feldspathic porcelains for metal ceramic restorations have a mean flexual strength between 60 and 80 MPa. this is lower than all ceramic materials. But, metal ceramic restorations are supported by a metal framework so their long term survival usually higher. For the other flexural strengths see picture.

Question 22

How does the fracture toughness (the resistance to brittle fracture when a crack is present) compare for different types of porcelains?

Answer 22

Question 23

How does the modulus of elasticity compare for different types of porcelains?

Answer 23

Question 24

is shrinkage a problem for all ceramic matierials?

Answer 24

yes, with the exception of machined ceramics from fully sintered blocks and heat pressed ceramics

Question 25

shrinkage of the veneering ceramics applied on all ceramic cores has to be ________ during the porcelain buildup

Answer 25

very carefully compensated for.

the large shrinkage of machined zirconia restorations during the subsequent sintering at very high temperatures (about 25%) is compensated for at the design stage by enlargement of the restorations

Question 26

what is the density of ceramic materials

Answer 26

density varies with porosity and the amount and nature of the crystalline phase that is present. feldspathic percelain is about 2.45 and zirconia about 6.08

Question 27

what are two optical problems affecting appearance in dental ceramics?

Answer 27

shade matching. light absorption and scattering is different between the dentin/enamel complex and porcelain.

cementing medium also affects the appearance. due to it’s higher opacity, aluminous all ceramic restorations may be cemented with a wider range of luting agents.

Question 28

More translucent all-ceramic restorations such as

leucite-reinforced heat-pressed or machined inlays,

crowns or veneers, or a machined inlay or veneer,

usually require what?

Answer 28

the use of a translucent resin luting agent. this improves the optical properties. they are available in different shades.

Question 29

_______ is a very importnt optical property

Answer 29

translucency.

The translucency of opaque, dentin (body), and enamel (incisal) porcelains differs considerably.

Question 30

______ have very low translucency, allowing them to mask metal substructure surfaces

Answer 30

opaque porcelains

Tin oxide (SnO2) and titanium oxide (TiO2) are important opacifying oxides

Question 31

_________ have the highest translucencies, ranging between 45-50%

Answer 31

enamel porcelains

Question 32

how does the translucency and opacity of alumina and zirconia compare?

Answer 32