Dental Amalgam 11 Flashcards Preview

Dental Materials 2 > Dental Amalgam 11 > Flashcards

Flashcards in Dental Amalgam 11 Deck (17):
1

Definition:

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

2

Composition:

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

3

Geometry of the particles:

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

4

SPHERICAL PARTICLES
adv dsv

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

5

MIXED PARTICLES
adv dsv

Advantages:
-better interproximal contacts (more viscous)
-easier modeling –they keep their shape

Disadvantages:
-it needs higher force to be condensed

6

Setting reaction.




-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.

7

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

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

8

Packing/Delivery mode

-glasses with filing of alloy+glasses with mercury
-capsules 42% of mercury

9

Properties:
1. Mechanical strength:

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

10

2. Dimensional changes:

-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

11

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

-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

12

4. Corrosion(oxidation):

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

13

5.Tarnish:

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

14

6.Adhesion:

itdoesn’tadheretotheharddentaltissues=>itneedsa retentivecavitypreparation
-dentinaladhesivesforamalgam(basedon4-META)
-theyexclussivelyreducemicroleakage
-therearen’tproofsregardingtheincreaseoftheadhesion

15

7. Biocompatibility:

-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

16

indications:

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)

17

Contraindications:

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