Failure of composite and amalgam Flashcards
Time dependent change in the form of amalgam under constant loads and temperature
creep
how to overcome creep in amalgam
High copper amalgam shows lower creep values
breakage of a thin edge of a restoration creating an irregular
V-shaped crevice.
Marginal degradation ( ditching, Fracture, Crevicing )
one of the causes of Marginal degradation is depletion of support at margins , it may be due to ?
Excessive expansion resulted from:
-Under trituration —Excess mercury. -Moisture contamination (causes delayed expansion)
one of the causes of Marginal degradation is insufficient bulk at margins , it may be due to ?
l. Beveling of CSA.
2. Over carving.
3. Leaving thin marginal flashes.
one of the causes of Marginal degradation is voids, it may be due to ?
l. Inadequate condensation force. 2. Too dry amalgam mix.
3. Moisture contamination of zinc containing amalgam.
4. Corrosion.
one of the causes of Marginal degradation is excess mercury
, it may be due to ?
1.Wrong proportioning of alloy / mercury ratio.
2. under trituration and squeezing.
3. Inadequate condensation force.
Isthmus outline especially … wall of …….. are more common sites for marginal ditching?
buccal wall of lower first molars
walls should be made in the form of reverse curve to provide CSA 90 ° to avoid what
marginal ditching
treatment of Very small ditching
Resurfacing with finishing bur.
treatment of moderate ditching
repair with amalgam
treatment of gross ditching
Total replacement of the restoration is indicated.
the narrowest junction between
the principle portion (occlusal) and the auxiliary portion (buccal, lingual or proximal).
Isthmus
A fracture of compound
amalgam restoration at the junction between the principle portion and the auxiliary portion of the cavity.
Isthmus fracture
The causes or factors contributed to isthmus fracture may be:
- Factors that decrease flexural strength
- Factors that increase flexural stresses
one of the Factors that increase flexural stresses is Incorrect-resistance and inadequate retention to avoid it we should have?
1.Flat pulpal floor and gingival floor perpendicular to the
direction of force.
2.Walls parallel to the direction of masticatory force.
3. CSA 90°.
one of the Factors that increase flexural stresses is Excessive occlusal forces it may be duo to?
1) Presence of premature contact due to:
A. Under carving of the marginal ridge.
B. Misplacement of marginal ridge.
C. Sudden biting on a hard object. D. Presence of protruded or over erupted opposing plunger-
cusp.
2) Biting on amalgam before sufficient setting.
one of the Factors that increase flexural stresses is Surface and structural discontinuities it may be duo to?
1) Poor polishing leaving the surface rough and full of
pits and scratches.
2) Over carving into deep grooves not only creates
stresses, but also weakens the restoration by decreasing
its bulk.
3) Presence of internal voids due to corrosion ,moisture
contamination ,too dry amalgam mix and lack of forceful condensation.
one of the Factors that decrease flexural strength is insufficient bulk of the amalgam it may be duo to?
Over carving,
decreased cavity depth.
one of the Factors that decrease flexural strength is excess mercury , what dose it cause?
lowers the strength of amalgam
one of the Factors that decrease flexural strength structural discontinuities: it may be duo to?
Corrosion,
moisture contamination,
dry mix,
lack of condensation forces.
Formation of a surface film of discoloring oxides and
sulfides
tarnish-loss of surface luster-
tarnish is due to
Excess Hg, under trituration,
improper condensation, Lack of finishing, moisture
contamination, and bad oral hygiene.
Actual disintegration of the bulk of amalgam.
Corrosion-rough pitted amalgam surface-
Chemical corrosion is due to
lack of polishing
The amalgam shown through
enamel.
amalgam blue-dark bluish discoloration-
amalgam blue is due to
-Thin or undermined enamel that shows dark blue discoloration of amalgam.
-Penetration of metallic ions and corrosive products of amalgam through the dentinal tubules.
how to fix tarnish
re-polishing
how to fix corrosion
may require removal of old restoration
how to fix amalgam blue
may require removal of old restoration
marginal discoloration is due to ?
1.Gross marginal leakage of environmental fluids and stains
- Poor application of bonding systems.
- Moisture contamination.
- Excessive thinning out of margins, premature polishing
may cause crevicing - Softening of composite due to hydrolytic instability, and
degradation increases their tendency to marginal
discoloration- especially- at the gingival margins where
local acidity tends to increase.
surface discoloration is due to
The rougher the surface the more dull it appears and the greater is its tendency to retain food and stains and get discolored
bulk discoloration can cause?
Excessive porosity is a most common attribute for bulk discoloration thus, trapped air voids , cause unfavorable changes of optical characteristics.
treatment of surface discoloration?
polishing
treatment of slight marginal discoloration?
if not complicated by any caries recurrence may be repaired in the same shade composite
treatment of bulk discoloration
replacement of the restoration
