13,14 - Ceramics (slides 1-46) Flashcards
what is a ceramic
any product made form nonmetallic inorganic material that is usually processed by firing at a high temperature
what is porcelain?
a type of ceramic materials originally made by mixing Kaolin, quartz, feldspar and firing them at high temperatures
what are porcelains used for
metal-ceramic and ceramic dental restorations
how do we classify ceramics? (3)
by application
by fabrication method
by crystalline phase
classifying by application: what are three applciations for ceramics?
metal ceramic crowns and fixed partial dentures
all ceramic crowns
miscellaneous: ceramic orthodontic brackets, dental implant abutments, ceramic denture teeth
callsification by fabrication: what are ways that ceramics are made?
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
regardless of the fabrication technique, ceramics are made of what?
a glassy or vitreous phase and one or more ctystalline phases with various amounts of porosity
what causes the wide variation in mechanical and optical properties of porcelain?
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.
Materials for all ceramic restorations have increased what?
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.
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.
ceramics are the best material for
matching the aesthetics of a complex human tooth.
what are some general applications of ceramics in dentistry
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
Ceramic is widely used as the veneering material in what?
in metal ceramic crowns and fixed partial dentures.
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)?
it enhances the porcelain-metal bond, keeping the porcelain in a state of compression and lessening the chance of fracture.
With regard to metal ceramic restorations, what is good about them?
are they still widely used?
how good is their survival rate?
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.
what is the approx survival rate of a zirconia based all ceramic system?
about 5 years, remember that zirconia is the really strong stuff
give me a bit of history on cermics?
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
what are some pro’s and con’s of ceramic inlays and onlays?
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.
what is a ceramic veneer?
how are they made?
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
What is done to adhere the ceramic veneer to the tooth?
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
How does the flexural strength compare for different types of porcelains?
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.
How does the fracture toughness (the resistance to brittle fracture when a crack is present) compare for different types of porcelains?
How does the modulus of elasticity compare for different types of porcelains?
is shrinkage a problem for all ceramic matierials?
yes, with the exception of machined ceramics from fully sintered blocks and heat pressed ceramics
shrinkage of the veneering ceramics applied on all ceramic cores has to be ________ during the porcelain buildup
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
what is the density of ceramic materials
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
what are two optical problems affecting appearance in dental ceramics?
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.
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?
the use of a translucent resin luting agent. this improves the optical properties. they are available in different shades.
_______ is a very importnt optical property
translucency.
The translucency of opaque, dentin (body), and enamel (incisal) porcelains differs considerably.
______ have very low translucency, allowing them to mask metal substructure surfaces
opaque porcelains
Tin oxide (SnO2) and titanium oxide (TiO2) are important opacifying oxides
_________ have the highest translucencies, ranging between 45-50%
enamel porcelains
how does the translucency and opacity of alumina and zirconia compare?
