all ceramic materials part 2 Flashcards
what do flaws in ceramics lead to
Stress concentrations (magnifiers)
strength of ceramics
strong theoretical strength
weak actual strength due to flaws
why do ceramics have more flaws than metals
Cuz they cant reform cracks
where does stress appear when placing glass on a complicent surface
tensile strength on the bottom side of the glass
how does chemical strengthing work
add larger attoms that press the crack togethre to create compressive strength
where is the sorse of stress in an anterior crown
directly under contact
what is the source of hoop stress
due to tooth squat leading to expansion on the base of the crown
what teeth are likely to have hoop stress
posterior crowns
what does polishing and glazing due for a crown
removal of flaws from the surface
does glass normally react with water
no
how does water lead to cracking
Comes in and forms hydrogen bonds breaking the glass bonds
steps of crack propogation with water
functional load applied stress on the bottom of the crown existing cracks strained water enters crack extends
the most common way to strengthen a ceramic
Crystalline reinforcement
what is dental porcelain made of
Noncrystalline/amorphous silica based glass
minor components of crystalline silicates (quartz or crystobilite, leucite (NOT lucite)
how does crystalline reinforcement work
deflects cracks
examples of crystalline reinforcement
Leucity-reinforced glass ceramics
Lithium disilicate glass ceramic
Characteristics of glass ceramics
Moderate strength Good translucency used in full thickness restorations formed by pressing, machining or sintered powders no shrinkage/good fit
Characteristics of crystalline reinforced ceramics (85%) alumia)- glass inflitrated alumina
High strength
Poor translucency
no shrinkage
can be fabricated without special equipment
downside of crystalline reinforcement( greater crystallines)
Poor translucency
characteristics of crystalline reinforced ceramics (100% alumina)- dense sintered alumina
high sttrength
low translucency (core only)
need special quiment (CAD and high temp ovens)
characteristics of Dense sintered zirconia (100 zirconia)
high strength
Variable translucency
core and full thickness restorations
Special equipent (CAD and high temp ovens)
ranking of ceramic strengths(weakest first)
silicate glasses: Porcelain LRGC LDS Non-silicate ceramic: Inceram AlO ZrO
stregnth of zirconia crowns
1200 – 1400mPa
how does zirconia do transformation toughening
Crack causes local crystals to go from cubic to tetragonal to monoclinic shape filling the void not allowing water in(phase transformation)
What is LDP (aging)
the spontaneous t-m transformation occurring over time at low temperatures, when the t-m transformation is not triggered by local stress from an advantage
problem with LDP (aging)
may lead to long term weakness?
ways to make a All-ceramic crowns
MEtalceramic like (high strength opaque substructure) minimal curback (porcelain only in critial esthetic areas) monolithiic (moderate strength translucent ceramics)
benifit of full contour crowns with surface strains
Less labor intense (less expensive)
good outcome
full contour strength of material
characteristics of minimal cutback with layered porcelain
Labor intense (expensive)
excellent outcome
full contour strenth in high stress areas
characteristics of full cutback with layered porcellain
most labor intense (expensive)
excelled outcome
strength reduced due to increased thinness
what crown type cannot be pressed
zirconia(must be milled)
how does one get zirconia
isostatically pressed powders like strong chalk to be machined
heat processed at 1500 c
what does heat processing zirconia do to it
20% shrinkage
what have zirconia developments done
make the structure translucent (at the expense of stength with less stable tetragonal zirconia)
