Silver amalgam is undoubtedly the most commonly used restorative material. If amalgam is manipulated properly and used, it is still one of the best dental restorative material where its indicated The average life span of an amalgam restoration is upto 8-10 yrs if manipulated correctly. Howerver many amalgam restorations fail in function, mainly due to iatrogenic factors and can be avoided by careful attention to all the details during preparation and placement of amalgam restorations This presentation explains various reasons for the amalgam restoration to fail in the oral cavity

2. FAILURES IN
AMALGAM

3. INTRODUCTION
• Silver amalgam is undoubtedly the most commonly used restorative
material.
• The average life span of an amalgam restoration is upto 8-10 yrs if
manipulated correctly.
• Howerver many amalgam restorations fail in function, mainly due to
iatrogenic factors and can be avoided by careful attention to all the
details during preparation and placement of amalgam restorations.

4. What is a failure?
• A failure maybe defined as the
inability to meet the desired outcome.

5. • A failing amalgam filling can be defined as
a filling that has been a contributory cause
of secondary injury in the organ of the tooth
i.e, the tooth itself and its surrounding connective tissue. ( Knud
Dreyer Jorgensen, Amalgams in dentistry, Dental Materials Research: Proceedings
of the 50th Anniversary Symposium, Oct 6-8. 1969 Issue 354, By United States.
National Bureau of Standards, American Dental Association)

6. Types of Amalgam Failures
• At Visual Level:
Secondary caries
Marginal fractures
Bulk fractures
Tooth fractures
Dimensional change

7. • At Microstructural Level
Tarnish andCorrosion
Stresses associated with masticatory forces
Pain following restoration
Pulpal and periodontal involvement

8. Why?
Failures due to faulty cavity preparation
Failures due to poor matrix adaptation.
Due to faulty amalgam manipulation.
Due to improper condensation
Failures due to contamination
Improper finishing and polishing procedures

9. Postoperative pain.
Microleakage of amalgam.
Tarnish and corrosion
Role of creep
Role of faulty contacts

10. Faulty Cavity Preparation:
• Inadequate occlusal extension
• Inadequate extensions into pits and fissures increases the
chances of recurrent caries particularly in patients with high
caries index.
• Thus all susceptible pits and fissures should be included with
margins terminating in areas that can be finished.

12. • Inadequate extension of proximal box:
• Embrasures if not involved adequately
are not amneable to brushing and cleaning.
These result in secondary caries affecting the
life of the restoration.
• However radical extension of the proximal box will weaken
the tooth structure leading fracture of tooth and restoration.

13. Over extensions of cavity prepared walls:
• One fourth of inter-cuspal distance facio-lingually is the ideal
requirement for amalgam restoration to possess adequate
strength for functioning.
Caries involvement Suggested protocol
1. 1/4th of faciolingual distance
2. 1/2 of the faciolingual distance
3. 2/3rd of the faciolingual distance
1. Simple preparation
2. Consider cusp capping
3. Cuspal capping mandatory

14. • Cusp capping
• Functional cusps-2 mm
• Non-Functional cusps-1.5 mm
• If the thickness required is not
provided fractures result inadverently

15. • Improper resistance form
• It has been calculated that 1.5mm of minimal amalgam bulk
is necessary to resist fractures

16. • If pulpal floor is not smooth or is curved the restoration
causes a wedging effect and increases chances of fracture
of tooth.

17. Cavosurface angle
Butt joints are essential especially where occlusal stresses are
to be encountered. Thus the cavo-surface angle has been
suggested to be 90 or preferably 110
• More acute - Fractures of tooth margins
• More obtuse - Marginal amalgam fracture

18. Cavosurface Margin Acute margin Obtuse Margin

20. • Cavity margins are to be finished so as to remove
unsupported enamel rods susceptible to fractures and
resulting secondary caries
• Failure to round off axio pulpal line angle as well as internal
line-angles and point angles results in concentration of forces
at these places resulting in fractures of the material or worse
the tooth itself

21. Sharp internal line angle Rounded internal line angle
+ +
+ + + +

22. • Very narrow isthmus related to rest of the cavity preparation
and co-positioning of the isthmus and axio pulpal line angle
results in fracture of proximo-occlusal restoration
• Such phenomenon can also occur due to inadequate proximal
retention form. Undermining of mesial and distal walls of
preparations can result in fracture of mescal or distal marginal
ridge due to these areas being unsupported. Thus it is always
advised to keep mesial and distal walls straighter

23. Mesial Distal
Undermined Marginal ridges

25. • The retentive element of the cavity should be in dentine
without undermining enamel so as to give proper support to
the restoration.
• If pulpal floor is not flat there will be inability of the
restoration to resist forces directed along long axis of tooth.
This leads to stress concentration and as a real fracture of
restoration

26. Incomplete caries removal:
• Incomplete caries removal can lead to failures either by
1. Further involvement and pulpal insult.
2 Fracture of restoration due to unsupported material

27. • Poor Matrix Adaptation :
• Proper matrix selection is mandatory for a proximal
restoration to be successful.
• Also an extension of 0.5-1 mm beyond cavo-gingival line
angle of cavity and similarly above level of marginal ridge is
required for proper condensation of amalgam.

28. Excessive Correct
Correct
Insufficient gingivallty
Insufficient occlusally

29. • A Minimal thickness of 0.03-0.05mm is required for a matrix
to be burnishable and allow condensation of amalgam
without deformation
• Also, if band width is too large it will lead to creations of an
open contact or a contact too occlusally.
• If Band width is less it will allow amalgam to escape and
form an overhang resulting in tissue irritation & destruction
or incorporation of amalgan in tissues.

30. • Faulty Amalgam Manipulation
• Mercury -- Alloy Ratio :-
• Serious loss of structure was reported when residual mercury is in an
excess of 55% in a restoration
• Higher mercury content results in –
Decrease in crushing strength.
Increase in flow and increased susceptibility to tarnish and corrosion

31. • Mulling with bare hands causes incorporation of
contaminants moisture into the mix which is deleterious ;
especially in zinc containing alloys.
• Hardened set amalgam if not removed from the mortars will
act as points of weakness in the matrix of the mix, rendering
the restoration prone to failure as stress concentration occurs
at these points.

32. • Undertriturated and over triturated mixes and
their effects:
Under triturated mix Soft - powdery ,non coherent
mass
Over triturated mix May break already forming
matrix
 Effective removal of residual mercury is possible only
within 4 mins of trituration.

33. Proper mix Undertriturated mix Overtriturated mix

34. • Improper Condensation
• Improper condensation will lead to voids in the restoration
which will serve as areas of least strength which are
susceptible for fracture.
• Thus proper condensation in a stepping motion to drive away
any voids is recommended.

35. Contamination
• By moisture-
Bare hand mulling leads to decreased strength especially in
Zin containing alloys
Moisture contamination in oral cavity by saliva and blood-
leads to delayed expansion, resulting in marginal flaws,
tarnish, pitting corrosion and pain.

36. Delayed Expansion
• When a zinc-containing, low-copper or high-copper
amalgam is contaminated by moisture during trituration or
condensation, a large expansion can take place.
• This type of expansion is known as
delayed expansion or secondary expansion
Zn + H2O ZnO + H2

37. Improper carving finishing & polishing
• The main carving should be delayed until the surface offers
resistance to instrumentation.
• The correct time is indicated by a particular "Squeaking"
sound deviated from surface "Cry of tin".

38. • Overcarving: -
• Leads to decreased thickness of restoration with increased
chances of fracture.
• Undercarving:-
• Leads to production of high points causing increased forces
on tooth resulting in post operative pain and potential source
for fractures.

39. Polishing :-
• If rough surfaces exist they act as sources of plaque adhesion and
subsequent caries progression. If polishing temperature
increases more than 65o ,mercury is released from amalgam
leading to failure by rendering the matrix weak.
• Inadvertently this heat may also irritate the pulp
and cause deleterious effects.
• Polishing should not be initiated less than 24 hrs after
condensation and carving and should be done adequately and
sufficiently.

40. • Polishing should be done with a soft, unribbed, prophylactic
polishing cup and a fine, slightly moist prophylaxis paste.
• The cup should be tilted such that the edge rotates from
amalgam to tooth

41. Marginal degradation (Ditching)
• The Ditching around amalgam restorations is thought to be
due to amalgam contraction is mainly due to stress or
corrosion dependent effect occurring in areas subjected to
occlusal loading.
• Ditching is directly related to creep ; ie increased creep
results in increased ditching.

42. Ditched amalgam with marginal breakdown

43. Role of Creep
• Creep is defined as a time dependent plastic deformation.
• Creep of dental amalgam is a slow progressive permanent
deformation of set amalgam which occurs under constant stress
(static creep) or intermittent stress (dynamic creep).

44. • The higher the creep, the greater is the degree of marginal
deterioration .
According to ADA Sp. No. 1 creep should be below 3%.
• Low-copper lathe cut amalgam — 6%
• Low-copper spherical — 1.5%
• High-copper admixed amalgam — 0.5%
• High-copper unicompositional amalgam — 0.05 to 0.09%

45. Other factors responsible for marginal deterioration
1. Improper Marginal preparation
2. Improper Carving and finishing
3. Excess Mercury
4. Low copper amalgams
5. Amalgam expansion

46. Post operative pain
• Caused due to –
Hyperocclusion due to undercarving
Cracks in teeth
Galvanism
Delayed expansion

47. Amalgam blues and tattoos

48. Tarnish and corrosion

49. Tarnish
• Process by which a metal surface is dulled or discolored due to
reaction with a sulfide, oxide, chloride, or other chemical which
causes surface discoloration through formation of a thin oxidized film.
• It is the surface discoloration on a metal or even a slight loss or
alteration of the surface finish or lustre.
• Tarnish is often the forerunner of corrosion because the tarnish film
accumulates components that chemically attack the metallic surface

51. Corrosion
• Chemical or electrochemical process
in which a solid, usually a metal,
is attacked by an environmental agent,
resulting in partial or complete dissolution.
• It is not a surface discoloration but actual deterioration of a metal by
reaction with the environment.
• In due course it may lead to rapid mechanical failure of the structure.

53. Electromotive or Galvanic series
• Arrangement of metals by their
equilibrium values of electrode oxidation
potential.
• Used to judge the tendency of metals
and alloys to undergo electrochemical
(galvanic) corrosion
• Electrode potential-measure of
tendency to oxidise.

54. More positive electrode potential -more
resistant to tarnish and corrosion (cathode )
Eg- Noble metals
More negative electrode potential - more
prone to tarnish and corrosion ( anode)
Eg- Base metals
Eg of - Cu and Zn,
E.P of Cu : +0.47
E.P of Zn : -0.76
Zn (-0.76 ) Cu (+0.47 )
(Anode) ( Cathode )

55. Different factors responsible for corrosion
• Oxygen
• Chloride ions
• Sulfides like hydrogen sulfide or
ammonium sulfide.
• Various acids such as phosphoric,
acetic and lactic acid.
• Water

56. CLASSIFICATION OF CORROSION
• Dry / Chemical corrosion
• Wet /Electrochemical/ Galvanic corrosion
1. Due to Dissimilar metals
2. Heterogenous surface composition
3. Stress corrosion
4. Concentration cell corrosion

57. Chemical / Dry Corrosion
• Chemical corrosion is the direct combination of metallic and
nonmetallic elements to yield a chemical compound through
oxidation reactions.
Examples :
• Silver acts with Sulfur to form Silver sulfide
• Iron reacts with Oxygen to form Iron oxide

58. Wet corrosion / electrolytic corrosion / Galvanic
Corrosion
• This requires the presence of water or other fluid
electrolytes. There is formation of free electrons and
the electrolyte provides the pathway for the
transport of electrons
.

59. • Three essential components for electrochemical corrosion-
• Anode : Cations ( m+) are formed (oxidation)and production of free
electrons ( e-)
M M+ + e-
• Cathode : Metal ions are deposited ; consumes free e- produced on
anode.
M+ + e- M
Electrolyte : Carries away corrosion product from anode and supplies
ions to cathode surface

60. Due to dissimilar metals
• Galvanic corrosion occurs when dissimilar
metals lie in direct physical contact
with each other.
• If a gold restoration comes in contact with an
amalgam restoration, the amalgam forms the anode
and starts corroding.

61. Being said that, it is not necessary for two
dissimilar metals to be in direct contact

62. Galvanic Shock
• The electric couple
(500 millivolts) created when the
two restorations touch causes
sharp pain called ‘galvanic shock’

63. Heterogenous composition
• When an alloy containing two or more components is immersed in an
electrolyte the metallic grains with the lower electrode potential are
attacked and corrosion results.

64. • In metals or alloys the grain boundaries may act as anodes and the
interior of the grain as the cathode.
• Solder joints may also corrode due to the inhomogeneous
composition.
• Impurities in any alloy enhance corrosion.

65. Stress corrosion
• Stress application increases the internal energy of Alloy / Metal
• A metal which has been stressed by cold working, becomes more
reactive at the site of maximum stress.
• If stressed and unstressed metals are in contact in an electrolyte, the
stressed metal will become the anode of a galvanic cell and will
corrode.

67. Concetration cell corrosion/ crevice corrosion
• Electrolyte concentration cell - In a metallic restoration which is
partly covered by food debris, the composition of the electrolyte
under the debris will differ from that of saliva and this can contribute
to the corrosion of the restoration.

68. • Oxygen concentration cell - Differences in oxygen tension in between
parts of the same restoration causes corrosion of the restoration.
Greater corrosion occurs in the part of the restoration having a lower
concentration of oxygen.

71. Protection Against Corrosion
Passivation
Increasing noble metal content
Polishing
Other methods

72. Conclusion
If amalgam is manipulated properly and
used, it is still one of the best dental
restorative material where its indicated

73. References
• Marzouk operative dentistry modern theory and practice
• Sturdevant’s Art and Science of Operative Dentistry by 7th edition Andre V. Ritter
• Craig’s Restorative Dental Materials by Ronald L Sakaguchi
• Phillips Science of Dental Materials by Anusavice K.J., Shen C., Rawls H.R.
• Ramya Raghu Clinical Operative Dentistry Principles & Practice
• Basic Dental Materials by Manappallil John J. 3rd edition
• Healey HJ, Phillips RW. A clinical study of amalgam failures. Journal of dental research.
1949 Oct;28(5):439-46.
• Arola D, Huang MP, Sultan MB. The failure of amalgam dental restorations due to cyclic
fatigue crack growth. Journal of materials science: Materials in medicine. 1999
Jun;10(6):319-27.