ceramics review Flashcards
what are the contraindications for all ceramic crowns?
• Parafunctional Activity
• Insufficient support from tooth
preparation
• Insufficient porcelain thickness in lingual aspect (0.8mm)
• Opposing teeth that occlude with cervical fifth of crown
• Short clinical crowns
what are the advantages of all ceramic crowns?
• Best esthetics
• Best color stability
• Some all-ceramic crown systems can be bonded to natural tooth structure
what causes catastrophic failure of all ceramic crowns?
weak strength and the brittle nature of ceramics
name the silica based ceramics
- Feldspathic Porcelains
- Hot-pressed Glass Ceramics
- Leucite reinforced glass ceramics
- Lithium disilicate reinforced glass ceramics
name the non-silica based ceramics
• Slip-cast, Glass Infiltrated Ceramics
- Alumina, alumina/zirconia and magnesium alumina
• Polycrystalline “Densely Sintered” Alumina and Zirconia
T/F: silica based ceramics are difficult to bond
false- silica ceramics can, and must, bond with resin cement to improve strength
which type of ceramics are more translucent? more opaque?
silica based- more translucent
non-silica based- more opaque
what type of ceramics have the highest strength?
non-silica based
strong, but opaque, and you cannot bond them
what is “Feldspar”?
potassium and sodium aluminosilicates
T/F: dental feldspar ceramics are mostly opaque, and have a small amount of leucite crystal (min 12%)
False:
they are GLOSSY, and have small amount of leucite crystal
_______ crystal has a much higher thermal expansion than glass
leucite
what factor determines the size of leucite crystals?
temperature
Leucite is needed to make bonding to _____ possible
metal
Leucite has a _______ coefficient of thermal expansion (CTE) than the surrounding glass.
higher
Ceramic materials are susceptible to _____ fracture
brittle
T/F: Ceramics are weaker when in tension and stronger when under compression
true
how does feldspar reinforce the ceramic? (crystalline reinforcement)
crystalline reinforcement strengthens the ceramic by resisting crack propagation via deflection of the advancing crack.
how does the coefficient of thermal expansion of Feldspar crystals enhance the strength of the glass around it?
it results in a layer of glass under compression immediately adjacent to the crystal.
This stronger layer within the glassy matrix deflects the advancing crack.
what are the characteristics of “opaque” dental porcelain?
high concentration of ceramic and metal oxides
block out metal substructure
(0.1mm thick)
what do porcelain laminate veneers require?
Requires silination and resin bonding for strength
modern feldspathic glass contains at least ____% leucite
20%
why is modern feldspathic ceramic weaker than other forms of ceramics?
Relatively low strength (60 – 80 MPa) due to lower crystalline phase (high glass content for esthetics)
______________ has the Highest Translucency (Superior Esthetics) of any dental ceramic
dental feldspathic porcelain
what are the disadvantages of feldspathic porcelain?
- Low strength
- Translucency prevents masking of discolored teeth
ceramic fractures usually start from the ______ surface
internal
why do ceramics fail?
• Brittle fracture – (Griffiths flaws) • Initiated from internal surface • Cyclic fatigue – Low loads – Many cycles • Stress corrosion
what are the 2 development strategies for dental ceramics?
– Develop stronger materials to substitute for metal and veneer with feldspathic porcelain
– Develop higher strength translucent materials that can be used in full thickness or minimal reduction
do “dicor like” (monolithic) or “Metal-ceramic like” (layered substructure) porcelain crowns use more feldspathic porcelain?
metal-ceramic like
what are Griffith’s slips?
dislocation slips in the ceramic
-cause brittle fractures
in what situations would feldspathic porcelain be indicated for use?
- Layering porcelain for metal and all ceramic crowns
- Feldspathic porcelain veneers
(any time you need aesthetics, but not a lot of strength)
