Chipping Fracture Resistance Of Dental CAD-CAM Restorative Materials.pptx

1. Chipping Fracture Resistance Of
Dental CAD/CAM Restorative
Materials

2. Introduction
• New methods of materials
processing (ex: grinding and milling)
• Machinability is broadly understood
as the ease with which a material is
cut
• Potential for generation of machining
damage that could reduce the life
time of the restoration.

3. Introduction
• Chipping is a common failure mode in
many dental restorations made of brittle materials.
• Edge chipping arising from CAD/CAM machining of dental
restoration materials is a major concern.
• Defects can get more prominent if a more conservative
tooth reduction is attempted by preparation of bevelled
margins especially with specific materials.
• The microstructure of the material play a very strong role in
determining chip sizes in 90◦ edges prepared by CAD/CAM
milling

4. Dental CAD/CAM Materials
• Lithium disilicate (Empress II ®)
• Glass infiltrated alumina (In-Ceram Alumina®)
• Glass infiltrated alumina with partially stabilized
zirconia (In-Ceram Zirconia®)
• Densely sintered high-purity alumina (Procera®)
• Yttria-stabilized tetragonal zirconia polycrystal
materials (Cercon®, DCS Precident®, Lava®)

5. Quinn G.D., Giuseppetti A.A., Hoffman K.H. Chipping fracture resistance of dental CAD/CAM restorative materials: Part I –
Procedures and results. Dental Materials 30 (2014) e99–e111.

6. Definition
• Chipping fracture resistance:
– Resistance of brittle materials to flaking near an edge.

7. Importance
• Chipping is a common failure mode in
many dental restorations made of
brittle materials.
• "Edge toughness" is a parameter to
obtain information about the edges of
materials rather than the bulk or
surface characteristics.
• Define the machinability of a material.
• Determine the level of integrity of the
restoration margins.

8. Edge chipping is a multistep process that entails:
a. Formation of a small indentation
b. Formation of short, stable radial cracks (unless the indenter
is blunt, in which case cone cracks form in some materials).
c. Propagation of some of the radial cracks downward and
parallel to the side surface.
d. Unstable crack propagation towards the side surface
causing a flake to pop off.

9. Parameter Equation Reference
Brittleness Index B=H/KIc (Lawn & Marshall 1979)
Brittleness of glasses B = γP-2/4 [C/α]3/2 (Sehgal & Ito 1995)
Edge toughness Te = F/d
McCormick & Almond 1990;
J. Quinn 2000
Edge chip power law F = A dn J. Quinn 2001
Edge strength
The force necessary to create a chip at
an arbitrary distance of 0.5 mm
(Watts et al. 2008)
Edge chip resistance European prestandard 2009
Chipping factor CF = [L/P] x 100 (Tsitrou et al. 2007)
How to Assess

10. Brittleness Index
• Concept of brittleness is not so well defined.
• Brittleness is a measure of the relative
susceptibility of a material to deformation and
fracture.
• Brittleness index provides a relationship
between the hardness (H), which quantifies the
resistance to deformation, and the toughness
(kIc), which quantifies the resistance to fracture.
A typical indent produced with
the Vickers tester. The top
dashed line represents the crack
length C and the bottom dashed
line the contact diagonal α.
γ equals to 2.39 N1/4/mm1/2
P = Load
C = crack length
α = contact diagonal

11. Chipping Factor
• Steps to Calculate:
– Edge of crown is divided in eight sections so that when
the distance between two points is observed axially
would be a straight line
– A top view image of the margins of the crown is taken
to measure the circumference
– Each image was calibrated with a steel rule adjacent to
the crown surface.
– The length (L) of the chipped margins and the
perimeter (P) of the crowns were measured and the
chipping factor (CF) calculated. L = length of chipped margins
P = length of circumference
• Definition:
– ratio of overall marginal chipping over the total marginal circumference of the
restoration multiplied by 100 to give the percentage of chipping.

12. Correlation analysis gave a perfect positive correlation relationship
between BI and CF (Spearman’s r correlation coefficient = 1)
Table 1 Average CF with standard deviations (SD) and brittleness index BI. The
statistically significant different groups are indicated with a different background
color (materials in the same background colour group showed no statistically
significant differences).
Correlation between Brittleness Index and Chipping Factor

13. Chipping fracture resistance of dental CAD/CAM
restorative materials: Part I – Procedures and results
• Edge toughness
Te = F/d
• Edge chip power law
A = F/dn
• Edge chip power law curve fits
more accurate with data points
than the linear edge toughness
curve.
• Especially as distance increase.
Edge Toughness Vs Edge Chip Power Law
Edge chip results for the lithium disilicate glass
ceramic with a 120◦sharp conical indenter.

14. In materials with high mechanical
properties as zirconia the curves
of edge toughness and edge chip
power law are close when a sharp
indenter is used.
Chipping fracture resistance of dental CAD/CAM
restorative materials: Part I – Procedures and results
Edge Toughness Vs Edge Chip Power Law
Results for the 3Y-TZP zirconia.

15. Indenters
• original Rockwell C diamond indenters
(rounded tip with a 200 µm radius),
• Knoop and Vickers pyramidal indenters,
• sharp-tip diamond 120◦ conical indenter

16. Effect of Indenter
Results on one batch of
feldspathic porcelain material,
but with different sharp conical
indenters. The dashed vertical
line at d = 0.5 mm and the
intercepts with the trend lines
correspond to the “edge
strengths” .
Edge strength decrease when
indenter become sharper.
Quinn G.D., Giuseppetti A.A., Hoffman K.H. Chipping fracture resistance of dental CAD/CAM restorative materials: Part 2.
Phenomenological model and the effect of indenter type. Dental Materials 30 (2014) e112–e123.

17. Materials Comparison
Comparative power law trends for (a) the sharp conical 120◦indenter, and (b)
for the Vickers indenter
Quinn G.D., Giuseppetti A.A., Hoffman K.H. Chipping fracture resistance of dental CAD/CAM restorative materials: Part I –
Procedures and results. Dental Materials 30 (2014) e99–e111.

18. Thank You

19. References
• Quinn G.D., Giuseppetti A.A., Hoffman K.H. Chipping fracture resistance of dental CAD/CAM
restorative materials: Part I – Procedures and results. Dental Materials 30 (2014) e99–e111.
• Quinn G.D., Giuseppetti A.A., Hoffman K.H. Chipping fracture resistance of dental CAD/CAM
restorative materials: Part 2. Phenomenological model and the effect of indenter type.
Dental Materials 30 (2014) e112–e123.
• Tsitrou, E.A., Northeast, S.E. and van Noort, R. Brittleness index of machinable dental
materials and its relation to the marginal chipping factor. Journal of Dentistry (2007);35
(12), 897 - 902.
• Zhang Y., Chai H., W. Lee J.J., Lawn B.R. Chipping Resistance of Graded Zirconia Ceramics for
Dental Crowns. J DENT RES 2012 91: 311

20. Top modes of fracture
1- top-surface chipping
2- subsurface flexural fracture
Resistance to one mode does not necessarily
imply resistance to the other