Dental Amalgam 11

Question 1

Definition:

Answer 1

mixing between
-LIQUID MERCURY +
-FILINGS= an alloy of Ag + Sn+Cu
=> definitive material,unaesthetic materia

Question 2

Composition:

Answer 2

Ag–causes setting expansion,increases the mechanical and corrosion strength

Sn(tin)–causes the shrinkage setting.Decreases the mechanical and corrosion strength

Cu–higher strength,more reduced corrosion,better marginal fitintime(reduced Cu=convention alamalgam, traditional)

Zn–expansion in contact with the saliva,reduces the oxidation of the other metals from the alloy (Zn›0,01%= amalgam with Zn,otherwise,amalgam without Zn).It seems that nowadays the dental amalgams with Zn have a longer clinical life

+/-otherelements:Au,Pd,In,evenHg

Question 3

Geometry of the particles:

Answer 3

a) chip particles(lathe-cut particles) –big and irregular particles; they are hardly mixed towards one another
b) spherical particles
c) mixed forms

Question 4

SPHERICAL PARTICLES

adv dsv

Answer 4

Advanges:

• smoother finished surface
• shorter setting time (1-1,5 hour)
• higher compression strength
• less Hg for the mixture

Disadvantages:
-higher shrinkage during setting time

Question 5

MIXED PARTICLES

adv dsv

Answer 5

Advantages:

• better interproximal contacts (more viscous)
• easier modeling –they keep their shape

Disadvantages:
-it needs higher force to be condensed

Question 6

Setting reaction.

Answer 6

• the particles of the alloy begin to dissolve inHg (like sugar into water)
• in the same time new formed compounds begin to form crystals (precipitation)
• crystallization continues and lead to the increase of the consistency of the dental amalgam
• completed setting before the dissolution of the whole original particles of the alloy. Their presence assures the mechanical and corrosion strength.
• after setting reaction is finished, the quantities of free Hg are very smaller, or absent, so Hgwon’t be released
• decreases the final quantity of compounds which containHg, so the dental amalgam will have better mechanical properties.

Question 7

γ1, γ2 –give weaker mechanical properties to the final amalgam
How can we prevent these?

Answer 7

a) reduce of the quantity of Hg within mixture
b) proper amalgamation
c) proper condensation of the dental amalgam within the cavity

Question 8

Packing/Delivery mode

Answer 8

• glasses with filing of alloy+glasses with mercury

- capsules 42% of mercury

Question 9

Properties:

1. Mechanical strength:

Answer 9

compression strength > than that of the enamel (the amalgams rich in Cu have the highest compression strength, the spherical amalgams reach it in shorter time) -proper abrasion strength -tensile strength amalgam is brittle in thin layers -higher marginal strength at non-gamma 2 amalgams (are less brittle) -the strength is influenced by the improper condensation – air bubbles -longer or shorter amalgamation changes the ratio between the unreacted γparticlesand those γ1 andη

Question 10

2. Dimensional changes:

Answer 10

• shrinkage setting –determined by the dissolution of the γ (Ag3Sn) particles -expansion –determined by the γ1,γ2andηphases’ formation -shrinkage+ expansion= zero dimensional changes(ideal) –improper handlingis associated with dimensional changes
• minimum: for the mixed non-gamma 2 amalgam
• higher: for conventional amalgam

Question 11

3. The creepof the amalgam (the plastic deformation):

Answer 11

• dimensional change of the amalgam fillings which is progressively produced in time, at their margins due to the occlusal loads
• the non-gamma 2 amalgam has a appearance of a ditch around the filling = “a demarcation line” of the amalgam

Question 12

4. Corrosion(oxidation):

Answer 12

Signs:

• increase of the porosity
• appearance change (dull appearance)
• it reduces the marginal integrity
• metalliccompoundsreleasedintotheenvironment–>this willfillthespaceswithmicroleakage+marginalblackness Causes: -the presence of 2 or more phases within the alloy(γcathod, γ2 andη-anods) -moist medium–saliva -more emphasized at the rough surfaces

Question 13

5.Tarnish:

Answer 13

-superficial appearance change
due to the chemical reactions between
the dental amalgam and saliva
at the filling’s surface≠corrosion

Question 14

6.Adhesion:

Answer 14

itdoesn’tadheretotheharddentaltissues=>itneedsa retentivecavitypreparation

• dentinaladhesivesforamalgam(basedon4-META)
• theyexclussivelyreducemicroleakage
• therearen’tproofsregardingtheincreaseoftheadhesion

Question 15

7. Biocompatibility:

Answer 15

-it transfers the thermal and electrical variations
-gingival inflammation-plaque accumulation -corrosion compounds
-Hgis potentially allergen(0,1%)and toxic
Acrylate-3% allergic potential
Ni-15-20% allergic potential for women
-PACIENT:
-during application–>vapours–it is needed good aspiration
-until the setting–extra Hg (predozed, good mixing method)
-after setting–1-2 µg / dayas a result ofmastication, (unimportant)
-amalgam removal –water jet andcontinuous suction
DENTISTANDMEDICALSTAFF:
-handling–avoid any contact (even with the gloves) with theamalgam orHg –predosedcapsules, amalgamcarrier
-duringapplication–>vapourswater jetandcontinuous suction+ mask
-floors which can be easily cleaned

Question 16

indications:

Answer 16

1.Class I and II cavities for lateral teeth
2.Class V cavities for latera teeth
3.Amalgam reinforced corebuild-ups in order to cover it with a crown
4.Cavities difficult to isolate
them correctly (still is sensitive to moisture,especially that
amalgam which contains Zn–late expansion–Zn+water
results gaseousH)

Question 17

Contraindications:

Answer 17

absolute cons:
-allergy to Hg o rto
the components of the Ag alloy

• relative cons:
• cavities on the anterior teeth
• cavities with very thin dental walls
• amalgam fillings in contact with Au prosthetic restorations=>a white layer on the Au restorations
• severe renal dysfunctions/pregnant women