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5. • An inlay
depends on
internal
retention to
hold it within
the
preparation
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6. • A crown depends
•
on external
retention to
resist removal
External
retention is
provided by
approximation of
the restoration to
the opposing
external axial
walls of the
preparation
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8. Biomechanical principles
of Tooth preparation
1. Preservation of tooth structure
2. Retention and resistance form
3. Structural durability of the
restoration
4. Marginal integrity
5. Preservation of the periodontium
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9. Preservation of tooth structure
Do not remove excess of tooth
structure , do not over taper
Tooth becomes weak
Pulp health gets jeopardised
Reduction must be adequate , less
reduction will lead to overcontoured
restoration
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14. • Retention is
enhanced by
restricting the paths
of insertion
• A—multiple paths of
insertion and
removal , decreased
retention
• B---additon of parallel
sided grooves limits
path of insertion to
one direction ,
increases retention
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15. • To produce an
optimal 6 degree
taper, each opposing
axial wall should have
an inclination of 3
degrees to the path
of insertion
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17. a functional cusp
bevel , in a
plane parallel to
the opposing
cusp , gives
adequate bulk
to the crown
without
sacrificing the
tooth structure
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18. if functional cusp
bevel is omitted ,
crown will be
too thin in this
stress bearing
area
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19. if crown thickness
is achieved by
overtapering the
axial wall ,
retention is
compromised .
• also health of the
pulp may be
jeopardised
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20. in absence of
functional cusp
bevel , the lab
(technician)
may overbulk
the crown .
this may lead
to
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occlusal
21. A. ---- adequate axial reduction
B. ---- inadequate axial reduction results in
crown with thin , weak walls
C. ---- bulky crown results in promoting plaque
accumulation , jeopardising the health of
periodontium
( niether flat nor fat )
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22. Thank you
For more details please visit
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www.indiandentalacademy.com