Zirconia, Endo, Post & Core Flashcards
2024 Cesar Shang Recent Advances in Zirconia
1. What happens during zirconia sintering? What happens the longer you sinter?
2. What are some advantages of short sintering?
3. What are downsides?
- Densification via reduction of the porosity and junction of the powder particles. Longer you sinter, the bigger the grain sizes.
- One study found higher flexural strength (, shorter time
- Reduced translucency due to isolated tiny pores (light scatter)
What are heatless stones made out of?
Silicon carbide
At what temps does zirconia exist in its different phases?
Below 1170˚C: Monoclinic
1170-2370˚C: Tetragonal
Above 2370˚C: Cubic
How much vol % change when Zirconia changes phase from tetragonal to monoclinic?
5%
Noble metals do not oxidize easily. What elements are added to alloys in order to facilitate the oxide layer formation for ceramic veneering?
What can cause some alloys to become green?
Easily oxidized elements, like indium and tin.
Green: Silver
Per Sorensen and Engelman 1990, ferrule effect improve the structural integrity of the purples tooth by counteracting what three forces?
Counteracts
- Functional lever forces
- Wedging effect of tapered dowel
- Lateral forces exerted during insertion of dowel
What were Sorenson and Engelmann’s four conclusions?
- 1 mm of coronal dentin above shoulder significanty increased the failure threshold
- Coronal walls should be parallel for max resistance
- Contrabevel design did not improve failure threshold
- Axial width of tooth at crown margin didn’t improve fracture resistance
Who originally published on the amalgam coronal-radicular technique?
Nayyar 1980
What did Aquilano and Caplan find in regards to Endodontically treated teeth and survival rates?
Endodontically treated teeth not crowned after obturation were lost at a 6.0 times greater rate than teeth crowned after obturation
Goodacre 1994 - Why no post in the anterior endo treated tooth?
What two author’s 1985 article discussed this?
We know that the purpose of posts is to retain the cores. The tooth had adequate tooth structure and ferrule to retain a crown if I just did a composite filling that I felt no need to prepare for a post. I thought that would further weaken the tooth and its longterm prognosis.
Sorenson and Martinoff 1985 - Posts decreased success of single crowns
2023 Meta-Analysis Systematic Review on Zirconia speed sintering
- What was the only reported difference?
Speed-sintering only affected CIELab-baed translucency.
Didn’t affect CIEDE2000-based translucency, three-point flexural strength, biaxial strength, or fracture toughness of YSZ
Increasing yttrium content of zirconia to 4 or 5 mol % increases cubic phase to what percentage volume?
4 and 5 mol% zirconia increases zirconia to 30% to 50% cubic. More esthetic, less low temperature degradation. Transformation toughening does not occur.
What causes the mother of pearl effect in zirconia crowns?
Result of light interaction with the microscopic surface irregularities and high refractive index of zirconia, leading to light interference and the perception of iridescence.
What are criticisms of zirconia bonding? (4)
- Difficult to rough or chemically modify zirconia
- Lack of silane coupling
- When you do roughen the surface, it’s not to same level as acid etching on porcelain
- Long-term stability of MDP is questioned
What is low temperature degradation of zirconia?
Water infiltrates micro cracks, inducing tetragonal to more stable monoclinic. Can be mitigated by aluminum oxide.
Also mitigated by incorporation of cubic phase zirconia, since that cannot phase transform.
How does yttrium stabilize tetragonal phase zirconia?
Yttrium stabilizes by dissolving into the zirconia crystal lattice, replacing some Zr ions. Oxygen vacancy also occurs. This lowers the free energy and allows tetragonal phase to exist; it’s less favorable for the tetragonal phase to rearrange into monoclinic.
