OPTEC- Amalgam

Question 1

What is dental amalgam?

Answer 1

A dental material consisting of a mix of:

• powdered metals (silver/tin/copper & more)
• liquid non metal Mercury.

Question 2

What are the amalgam components and what are their functions?

Answer 2

Powder components:
Silver and tin- form compound (Ag₃Sn) that reacts with Hg to produce amalgam. -gamma phase

Copper- increases strength and hardness

Zinc- prevents oxidation of other metals

powdered Hg- to decrease reaction time.

Liquid components:

Mercury reacts with the metals.

Question 3

Compare the particle types used in amalgam?

Answer 3

Lathe cut- These are chippings produced by cutting a bar of metal (inglot) with a lathe

Spherical - Produced when droplets of metal are solidifed in an inert atmosphere.

Question 4

Describe the setting reaction of traditional amalgam?

Answer 4

Ag₃Sn reacts with mercury to form amalgam.

This produces the gamma phase:

gamma- provides good strength and corrosion resistance

gamma 1- provides good corrosion resistance.

gamma 2- makes amalagam weaker especially at the margins

Question 5

Compare the two types of amalgam?

Answer 5

We have traditional amalgam - which produces gamma 2 in the setting reaction.

Copper enriched amalgam- This does not produce gamma 2 and has extra copper to improve amalgam setting.

Question 6

Compare the two types of copper enriched alloy?

Answer 6

We have the dispersion modified amalgam which has two reactions before it sets.

Single composition amalgam which sets after one reaction

Question 7

Why is zinc not included in some amalgam?

Answer 7

As zinc reacts with blood or saliva to produce H₂ within the amalgam restoration.

This causes a build up of pressure.

& the restoration to expand downwards (pulpal pain) or Upwards (pushing up the restoration)

Question 8

Discuss the properties of amalgam?

Answer 8

Compressive strength is not great initially but improves

It has a high abrasion resistance (this is good for posterior teeth but not deciduous teeth)
Creep occurs (the amalgam does not maintain good contact with the surrounding tissue) this causes ditched margins.

Biocompatability concerns of amlagam being toxic

Thermal expansion of x3 of tooth tissue. (Bad)

High thermal conductivity (bad)

Retention is mechanical

Amalgam shrinks when it sets.

Question 9

Why is the gamma 2 removed in Copper enriched amalgam?

Answer 9

Gamma 2 phase is most likley to corrode. It weakens the amlagam material particularly at the margins.

Question 10

What are some advantages of amalgam?

Answer 10

• It is durable
• It has good bulk strength and wear resistance.
• Has a shorter placement time
• Long term resistance to surface corrosion
• Cheap

Question 11

What are the disadvantages of amalgam?

Answer 11

• Poor aesthetic qualities
• Does not bond easily to the dentinal surface
• Preparation of the retentive cavity requires damage to sound tissue.
• Galvanic response - acts like a battery in the mouth with other fillings
• marginal breakdown is common.

Question 12

What is shown in this image?

Answer 12

This is a lichenoid lesion which is a type 4 hypersensitivity reaction to the amalgam restoration in the mouth.

Question 13

How do we treat a lichenoid lesion?

Answer 13

Replace the amalgam restoration with a composite one.

Question 14

What is shown in this image?

Answer 14

This is tooth discolouring as a result of the corrosion products migrating into the porous material of the tooth.

Question 15

What is shown in this image?

Answer 15

This is an amalgam tattoo,

When the fine amalgam particles migrate into the soft tissue.

Do not assume, it could be cancerous and nothing to do with the amalgam. case by case.

Question 16

How do we design our amalgam cavity to prevent distortion or fracture?

Answer 16

• We have a cavity floor at 90° to the axial wall.
• a depth of 1.5mm to 2mm

Question 17

Compare a self retentive box preparation to a proximo-occlusal preparation?

Answer 17

Self- retentive box preparation removes less tissue & places less amalgam.

A proximo-occlusal preparation destroys tooth tissue for retention.

Question 18

What other ways are there of acheiving retention in an amalgam restoration?

Answer 18

• Adding grooves or dimples to the cavity design
• The placement of a pin in dentine around which amalgam is packed.
• Bonding amalgam into the booth.

Question 19

What are the problems with a pin?

Answer 19

• Pins cause stress around the tooth.
• Dentine could crack
• The Pin conducts heat which can make the tooth more sensitive.
• If the filling leaks, we will not know as the pin will prevent the filling from falling out. (allowing secondary caries to develop)

Question 20

What are the functions of the matrix?

Answer 20

Function of the matrix is:

• Allows close adaption at the cervical margin
• Allows good contact at the marginal ridge
• Allows adequate condensation of the amalgam.
• confines the amalgam to the cavity prep.
• Allows creation of the proximal form.

Question 21

What are the functions of the wedge?

Answer 21

• Seperate the teeth
• prevent excess amalgam at the gingiva
• hold the matrix band in place
• Aid the contour of the proximal wall.

Question 22

What is condensation?

Answer 22

How we adapt amalgam to the cavity walls.

This gets rid of excess mercury, bringing it to the surface so it can be scraped off.

Question 23

What happens if we have inadequate condensation?

Answer 23

Inadequate condensation causes:

• lack of adaptation to the cavity- the spaces around the edges allow plaque build-up)
• poor bonding between amalgam increments.
• inferior mechanical properties as the amalgam is full of holes.

Question 24

Why do we carve the amalgam restoration?

Answer 24

• In order to reproduce the occlusal anatomy
• To remove the amalgam at the surface which is the weakest amalgam.

Question 25

Compare corrosion to creep?

Answer 25

Corrosion is a change in the character of amalgam. This causes marginal breakdown and ditching.

Creep is the deformation of amalgam under repeated stress.

Question 26

Discuss mercury release as a result of amalgam restorations

Answer 26

The greatest amount of mercury is released during:

• insertion- the greater the surface area, the greater the mercury release
• removal- mercury vapour and particles are released.

Question 27

How can mercury be absorbed?

Answer 27

• Through vapour in the lungs
• Contact with the skin
• The Gastro-intestinal tract
• Gingiva and mucosa
• Dentine and pulp as metal ions.

Question 28

What safety measures are put in place for amalgam hygiene ?

Answer 28

• Dental dam
• High volume aspiration
• Amalgam Seperator in sinks
• Spillage kits
• Correct amalgam disposal.

Question 29

Discuss the guidelines for amalgam use?

Answer 29

• Amalgam should be encapsulated
• Use of amalgam should be minimsed
• All facilities should have an amalgam seperator
• Amalgam waste should be collected.

Amalgam should not be used on:

• Children under 15
• Pregnant woman
• Breastfeeding woman

Unless there is a justified dental reason (lack of co-operation or inadequate moisture control)

Question 30

Compare setting shrinkage to microleakage?

Answer 30

Microleakage is the passing of fluid and bacteira in micro-gaps between the restoration and the tooth.

Setting shrinkage is when the amalgam shrinks after it has set.