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_5_ Amalgam Restoration I

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					                         Amalgam Restoration I

Notes: - the mid-term practical exam is out of 15 (10 marks for cavity
preparation and 5 marks for amalgam restoration)
   - The mid-term theoretical exam is out of 15 (online exam, not written)
   - The mid-term theoretical exam will include 6 lectures:
   1- introduction lecture
   2- instrumentation
   3- principle of cavity preparation I
   4- principle of cavity preparation II
   5- amalgam restoration I (today’s lecture)
   6- amalgam restoration II (next lecture)

This lecture is divided into two parts:
First part: about classification of dental amalgam and some properties
related to the uses of amalgam.
Second part: will be about the principles of cavity preparation related to
amalgam that we have taken in the labs, so this part is repetition ,but we
should remember it to be included in the theoretical exam, and we will be
asked about them
First part:

Amalgam = Tin-silver amalgam alloy+ mercury
So Tin-silver alloy mixed with mercury to form dental amalgam, we use the
amalgamator to mix them together.
Previously, the process of mixing was made manually, where there is to
bottle one contain powder (the alloy), and the other contain the mercury,
they mix them together to get dental amalgam, but the disadvantage was the
spilling of mercury which is a heavy metal.

Now we use capsules, so we don’t touch the mercury at all, these capsules
contain mercury and alloy separated by a sheet, to get the amalgam we put a
capsule in the amalgamator, this sheet will broken so the mercury mixed
with the alloy to form dental amalgam.
Classification of dental amalgam:
Dental amalgam can be classified according to copper content into:
   1- Conventional amalgam alloy (low copper alloy)
   2- High copper alloy
 Or according to particle size and shape into:
  1- lathe-cut alloy
  2- spherical
  3- admixed



Copper content:
- The amalgam alloy consists of silver, tin, copper, zinc.
- The conventional alloy contain 0-6% by weight, while
- High copper alloy 12-30% by weight.
- All what we use mow in the clinic is high copper alloy, bcz all the physical
properties increase as the copper contents increase.

Conventional Vs High Copper Amalgam Alloy:
High copper amalgam alloy have superior resistance to discoloration,
corrosion, marginal breakdown, and creep compared to conventional
amalgam.
So all the physical properties is improved with increase the amount of
copper in the alloy.

Particle size and shape:
  1- lathe-cut alloy: during the processing of the amalgam they shape it in
      different shapes one of them lathe-cut alloy which has sharp angles
      and irregular shape.
  2- Spherical alloy: balls in shape.
  3- Admixed: mixture of the two, so it has properties intermediate btw the
      two.


Spherical Vs Lathe-cut:
● Spherical alloy particles require less condensation pressure than lathe-cut
fillings.
Why?
Bcz the irregular shape of the particles in lathe-cut require more pressure
during condensation to condense the particles together, so as the shape is
irregular this means that we need more pressure during condensation to
bring them together.

● spherical alloy particles have less mercury content since less mercury is
needed to coat the particles during amalgamation (amalgam mixing),
comparing to lathe-cut alloy which has irregular particles (it is better to get
less mercury)

● spherical alloy require greater care in condensation than admixed or lathe-
cut alloy to obtain good adaptation and tight contact.
Imagine that the spherical alloy as a room full with balls, if you press from
one side the balls will escape to the other side. The same for the spherical if
you press (condense) it, the particles will escape up and to the margins, so
the spherical alloy requires care in condensation to get good contact.

● so we need larger size condenser with the spherical alloy.

●spherical high copper amalgam is the fastest in setting.
It is important to know which has faster setting time, bcz the setting time
affects the working time, so if we have small cavity like class I we can use
the one with short working time, but if we have cusp building or MOD we
have to use the one with longer working time to be able to condense and
carve it.


Advantages of amalgam:
  1- strong: here we talk about direct restoration (direct restorations: which
     we use directly in the clinic e.g. amalgam, composite, GIC… indirect
     restorations: the one which need impression and lab e.g. inlay, onlay,
     crown), so amalgam relatively to other direct restoration is the
     strongest.
  2- Durable: last for long period of time.
  3- Relatively easy to use.
  4- Low-technique sensitivity.

   5- Marginal sealing with time: amalgam is the only material that cause
      marginal sealing with time.
      You should know that always there is a gap btw the restorative
      material and the tooth structure; we call this gap “micro-gap”. No
      material what ever this material can fill this gap. And also what ever
      you do in adaptation to fill this gap it will remain. But the only
      material that will seal with time is amalgam. This sealing occur bcz of
      a process called “corrosion” to amalgam, where the corrosion results
      will seal this micro-gap with time. (Although this process considered
      as a disadvantage, it can be useful here).

   6-Antibacterial properties: the bacterial growth is less near amalgam.

   7-Wears at rate similar to that to of tooth structure:
   wearing: is the deterioration or loss of tooth structure as a result of
   contact with a other thing. Now if two teeth come in contact for long
   period of time they will take from each other in the same amount bcz
   they are the same material, what happen if we do a restoration to the
   opposing tooth? The rate will differ bcz the relation become tooth-
   restoration. But if this restoration is amalgam the rat will be similar to
   that if we have tooth.                                                     If
   we compare it with porcelain, porcelain will wear the opposing tooth
   structure more. So this is an advantage to amalgam.

   8-Least time consuming and has the lowest cost.

Disadvantages of amalgam:
   1- not tooth colored (silver in color)
   2- susceptible to corrosion and galvanism
   3- does not bond to tooth structure
   4- contain mercury

Indications:
Where we use amalgam.
   1- we use it in stress bearing area. (E.g. class I, II, V ) restoration in
      posterior teeth, we cant use it for anterior teeth bcz it isn’t teeth
      colored.
   2- Base build-up prior to crown preparation. This is beyond you ,but this
      when we have a broken tooth and we need to crown this tooth, so we
      need to build up this tooth first (bcz we don’t make crown on a broken
      tooth) using amalgam, then we do the crown.
Properties:
● Adaptation:
1- We said that there is a micro-gap btw amalgam and restorative material
that cause microleakage. (this is in any material, but the sealing occur with
time in case of amalgam, but initially this gap is found)
2- condensation of amalgam in the cavity should be done efficiently and
promptly to minimize this micro-gap. As minimum as possible.
3- amalgam does not strengthen the remaining tooth structure, as more tooth
structure is lost the possibility of fracture increases.
In comparison to composite it strengthen the remaining tooth structure bcz it
binds to tooth structure.
According to that, if we have undermined enamel we should remove it with
amalgam restoration, bcz there is a possibility later on to fracture in this
undermined enamel.
But in composite sometime I leave it bcz composite bind to tooth structure
so it is strengthen these undermined enamel.

● Amalgam bonding:
 There is attempts have been made to bond amalgam with adhesive resin
liners (means make amalgam like composite )
Some of the studies found good result n increase retention and strength of
amalgam but most of them are laboratory studies.
And still we need to make the mechanical retention features such as
convergent wall, retention grooves…

● setting dimensional changes:
1- there is a number of dimensional changes during setting of amalgam
(expansion & contraction)

2- most of this dimensional changes occur in the first 6 to 8 hours after
mixing. We have initial set: this is when the working time finish, after that
we cant work with it any more. But the final set actually after that bcz still
there is a dimensional changes occur (expansion & contraction)

3- factors that contribute to expansion are: undermixing, excess mercury &
moisture contamination.

4- factors contribute to contraction are: overmixing, increased condensation
forces & the use of smaller particles alloy.
5-high copper amalgam have less setting dimensional change than
conventional amalgam. (remember; all the properties is better for high
copper amalgam than low copper (conventional)

● Strength:
1- Amalgam tensile strength (tensile force when we tense two thing from
each other) is lower than its compressive strength (compressive force is the
force on the long axis of the tooth) so the fracture of amalgam occurs due to
tensile forces.

2- so amalgam should have sufficient bulk to compensate for this weakness.
Sufficient bulk obtained by 1.5 mm thickness by making the depth of the
cavity 1.5mm.

   3-all margins should be90 to minimize marginal fracture .which is the
   cavosurface margins of amalgam to give enough thickness at the margins
   so prevent fracture of the amalgam at the margins.

  4-Factors that contribute to increased strength of the amalgam is:
     a- Removal of excess mercury during condensation
       ( by the way if we do good condensation all the excess mercury
comes to the surface and then removed by burnishing the amalgam)
       b- increase condensation force to eliminate voids
       (if we have voids in the amalgam this means the thickness of the
amalgam is less that affect the strength of the amalgam.)

5- decrease strength will result from undermixing or contamination during
placement

● setting speed:
1- the fastest setting time is the high-copper spherical.

 2-the high copper admixture & the low copper spherical have intermediate
setting time (but we don’t use the low copper alloy any more)

3- the low copper lathe-cut amalgam is the slowest in setting. (if we have
large cavity it is better to choose high copper lath-cut amalgam, high bcz we
don’t use low any more)
 4-the working time is related to the setting speed. The more setting time
speed the less the working time.

5- manufacturer’s classification:
  - fast-set: usually it is high copper spherical
  - regular-set: it is admixed high copper
  - slow-set: it is high copper lathe-cut
6-alloy should be selected that has appropriate working time.


● Creep:
It is deformation due cyclic load( force). As you know the forces inside the
patina’s mouth is cyclic ( repeated for long period of time)

1- The permanent deformation of set amalgam when it is subjected to mild,
continuous or cyclic forces.

2- can result in marginal or proximal extrusion of amalgam restorations. So
these margins may subjected to break to produce open restoration.

3- high copper amalgam alloy have lower creep than conventional amalgam
alloy.

4- creep of conventional amalgam is influenced by
  - increasing mercury
  - incorrect mixing time and
  - decreased condensation to a greater degree than is the creep of high
copper amalgam.

● Corrosion:
  1-it is the slow deterioration of amalgam in the oral environment.

2-it isn’t good bcz initially can result in pitting and discoloration of the
surface of amalgam.

3-and if proceeds it can weaken & cause fracture to the amalgam.

4- one advantage of amalgam corrosion is the filling of the marginal gap
with the corrosion products.
5-two types of corrosion chemical and electrochemical.

               By this we finished the first part of the lecture




Second part:
Cavity preparation for amalgam:

●Outline form:
  1- the cavosurface outline should be continuous curved, line, especially
      on occlusal surface. It is difficult to condense ,carve & burnish
      amalgam in to sharp angles.
  2- The outline should be kept as conservative in width as possible(and as
      small as possible), removing only carious & potential carious pit &
      grooves.
  3- The cavosurface margins on the proximal surface should not touch the
      adjacent teeth or restorations from all direction bucaal, lingual &
      gingival.

●Resistance form:
  1- the pulpal &axial walls should be in dentin. And the cavity should be
     box in shape with 1.5 mm depth and should be in the DEJ

   2- the pulpal floor should be flat & smooth. The axial walls should be
      convex &follow the contour of the surface of the tooth.

   3- Cavity depth and width should be enough to create sufficient bulk to
      the restoration.

   4-The opposing walls of the cavity preparation should be parallel or
   slightly convergent toward the surface of the tooth.

   5-All cavosurface angles (the angle btw the prepared and the unprepared
   tooth surface) should be approximately 90◦ ,so the thickness of amalgam
   at the margins should be good enough to prevent fracture of the amalgam
   at the margins.        While in composite it is more than 90◦
●Retention form:
  1- sufficient retention is obtained by resistance form. In large
     preparation, auxiliary retention features can be added.
  2- Retention grooves are routinely placed in the buccal and lingual
     proximal walls of class II preparation.

●Convenience form:
  1- wide enough for instrumentation of the cavity & condensation of
     amalgam.
  2- In proximal lesions, the access should whenever possible avoid
     extension beyond what is necessarily to access the proximal lesion
     &the adequate retention form.
  3- If occlusal lesion is present it should be treated separately whenever
     possible.

-Removal of carious dentin.
-Finishing the enamel , and all the enamel margins should be 90.
-Cleaning the cavity.




Class I with buccal pit amalgam:
●Outline:
When we did the buccal pit in the lab ,we made it round, bcz we assumed
that the carious was round shape. But we have different shapes of the caries
in this area:
    1- triangular outline so we should make a cavity triangular with 1.5mm
       width
    2- if the caries extended more all over the fissure we call it capsular
       outline, with 1 mm width and 1.5mm depth.
    3- If the caries was rounded we will carve in round shape.(as we did in
       the lab)
 So the outline reflects the caries.

● resistance form:
1- mesial and distal walls are parallel or slightly divergent toward buccal
wall
2- occlusal & gingival walls are parallel or slightly divergent toward the
buccal surface.

3- the axial wall depth is 1.5mm or just inside the DEJ

4-the axial wall follow the external contour of the buccal surface of the
tooth.

● retention form:
1- in ideal size buccal pit, no need for additional retention.
2- in large size preparations, retention grooves can placed in mesial, distal or
gingival walls. We make it by small round bur and pass it in the pulpoaxial
line angle.



Class I occlusal amalgam:
   ●outline form:
   1- include mesial and distal pits, central, buccal, lingual grooves.
   2- Free flowing outline form with no sharp corners.
   3- All faciolingual width should be 1.5-2 mm expect at the intersection
      of grooves.

When we have 2 separate occlusal cavities ,we should treat them separately
such as:
- mandibular first premolars
- maxillary molars
If you remember what we did in the lab on lower 6, we did 2 cavities
separately bcz the presence of the oblique ridge .
But actually there is two situation where we remove it:
    1- if there is undermined enamel under the oblique ridge
    2- if we remove a lot of the oblique ridge that the remaining part of it
       only 0.5mm ,in these two situation we should remove the oblique
       ridge and make one restoration.

   ●resistance & retention forms:
   1- pulpal floor should be at right angle to the long axis of the tooth.
   2- Except of the mabdibular first premolar (angled lingually)
   3- Pulpal depth :1.5-2 mm
   4- B & L walls are parallel or slightly convergent occlusally.
   5- M & D walls diverge occlusaly.(shouldn’t de undermined with
      enamel)



Class I with buccal extension:
   ●outline:
   1- same as class I
   2- B groove is extended to include buccal pit
   3- Depth puloully: 1.5-2 mm
   4- Depth axially: 1.25 mm

   ●resistance & retention form:
   1- pulpal floor should be at right angle to the long axis of the tooth.
   2- B & L walls are parallel or slightly convergent
   3- M & D walls: on occlusal diverge occlusaly. Those on facial
      extension are parallel
   4- Retention grooves: grooves in M & D walls


Class I with lingual extension:
   ●outline:
   1- mesial: central pit, mesial pi, ½ of buccal groove.
   2- Distal: “ L” shaped preparation, include distal pit and lingual grove.
   3- Pulpal depth :1.5-2 mm
   4- Axiall depth :1.25 -2 mm

   ●resistance & retention form:
   1- B & L walls :parallel or slightly convergent
   2- M & D walls: mesial diverges. Distal wall is vertical
   3- M & D walls of the extension: parallel
   4- Retention grooves in the lingual box. In M, D walls ,from gingival to
      pulpoaxial line angle.


                                   The End
                                                     Done by: Alaa Al-sarhan

				
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posted:10/20/2011
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