Clinical amalgam

Question 1

what are possible indications for amalgam use?

Answer 1

• direct restorations in moderate and large cavities in posterior teeth
• core build ups for an indirect cast restoration e.g. crown

Question 2

what are possible contra-indications for amalgam use?

Answer 2

• if aesthetics are important to a pt
• if the pt has a history of sensitivity to mercury or other components
• if loss of tooth substance is substantial so a retentive cavity cannot be produced
• where excessive removal of sound tooth tissue would be required to produce a retentive cavity

Question 3

what are the advantages of amalgam?

Answer 3

• durable
• good long term clinical performance
• long lasting
• long-term resistance to surface corrosion
• shorter placement time than composite
• corrosion products may seal the tooth restoration
• radiopaque
• colour contrast
• economical

Question 4

what are the disadvantages of amalgam?

Answer 4

• poor aesthetic properties
• does not bond easily to tooth
• high thermal diffusivity (can damage pulp)
• cavity prep can cause destruction of sound tooth tissue
• marginal breakdown
• long-term corrosion can lead to ditching around margins
• local sensitivity reactions
• lichenoid reactions
• galvanic response (battery response from two diff amalgams)
• possible mercury toxicity
• tooth discolouration (corrosion products migrate into tooth surfaces)
• amalgam tattoo (amalgam particles migrate into soft tissues)

Question 5

why do dentists use amalgam?

Answer 5

• quick and easy
• self-hardening
• can be used at load-bearing areas of mouth
• good bulk strength and wear resistance
• usually placed at one visit
• economical

Question 6

what is the restoration sequence when placing amalgam?

Answer 6

1. caries risk, assessment and diagnosis
2. likely material choice
3. informed consent
4. caries access and removal
5. cavity design
6. removal of deep caries
7. restoration process

Question 7

what is retention form in cavity design for amalgam restorations?

Answer 7

• features that** prevent the loss** of the restoration in any direction
• in an occlusal direction, significant undercut is not required and a parallel or minimal undercut is necessary

Question 8

what is resistance form in cavity design for amalgam restorations?

Answer 8

• features that prevent loss of the material due to distortion or fracture by masticatory forces
• ideally the cavity floor should be parallel to the occlusal surface with sufficient depth (1.5-2mm)
• the gingival floor of an interproximal box should be approx. 90 degrees to the axial wall

Question 9

what are the two cavity designs for occlusal caries in amalgam restorations?

Answer 9

• self-retentive box preparations (minimal preparation box)
• proximo-occlusal preparations

Question 10

what are the advantages of a self-retentive box preparation (minimal preparation box)?

3

Answer 10

• less tooth tissue removed than with proximo-occlusal preparation
• reduced amount of amalgam placed
• sound tooth tissue retained between proximal box and occlusal cavity

Question 11

what are the disadvantages of a self-retentive box preparation (minimal preparation box)?

2

Answer 11

• can be more technically demanding than proximo-occlusal preparations
• further treatment of pit and fissure caries may be required

Question 12

what are the advantages of proximo-occlusal preparations?

3

Answer 12

• very retentive
• treats caries in pits and fissures
• less or no opportunity for future caries in pits and fissures

Question 13

what are the disadvantages of proximo-oclusal preparations?

2

Answer 13

• destruction of tooth tissue for retention
• increased risk of weakening the tooth

Question 14

what are some mechanical ways to increase retention in cavity design for amalgam restorations?

Answer 14

• include grooves or dimples within the design
• pin placement to increase retention in large non-retentive cavities

Question 15

what are the problems with pins?

Answer 15

• causes stress around the pin
• can crack the dentine
• can cause sensitivity to tooth due to temperature transferrance
• can cause long term leaking but restoration does not fall out so secondary caries progresses because of pin

Question 16

how do you finish the amalgam cavity preparation?

Answer 16

• ensure all caries is removed
• smooth and round internal line angles
• check and finish cavo-surface line angles
• smooth cavity margins

Question 17

how does moisture contamination affect amalgam restorations?

Answer 17

• reduces strength
• increases creep and secondary caries
• increases corrosion
• increases porosity

Question 18

what is the use of matrices during restoration?

Answer 18

• essential for restoration of proximal areas
• recreate walls of the cavity
• allows adequate condensation
• confines amalgam to the cavity
• allows close adaption especially to cervical margin
• allows good contact with adjacent tooth (<0.05mm thick)

Question 19

how does the mixing time affect amalgam restorations?

Answer 19

• handling characteristics
• working time
• amalgam microstructure
• restoration longevity

Question 20

how do you condense amalgam? why does it need to be done?

Answer 20

• vertical and lateral pressure needed
• expels excess mercury and brings it to the surface so it can be removed
• adapts material to cavity walls
• reduces layering so restoration is homogenous
• eliminates voids

Question 21

what does inadequate condensation of amalgam restorations lead to?

Answer 21

• lack of adaption to cavity
• poor bonding between layers
• inadequate mercury expression and removal during carving
• inferior mechanical properties

Question 22

how can you remove excess material from amalgam restorations?

Answer 22

• carving
• burnishing (polish)

use high volume aspiration - airborne mercury

Question 23

what do you need to recreate when carving an amalgam restoration?

Answer 23

• marginal ridge
• inter-proximal contact areas
• fissure pattern
• cusps and cuspal inclines
• re-establishes occlusal contacts

Question 24

what is microleakage? what can cause it? what can it cause?

Answer 24

passage of fluid and bacteria in micro-gaps (10um) between the restoration and tooth caused by mechanical loading, thermal stresses or iatrogenic damage
* pulpal irritation and infection
* discolouration
* secondary caries

Question 25

what is corrosion? what can it cause? how is amalgam different now so less corrosion occurs?

Answer 25

**detrimental change in the character** of amalgam due to **reactions** in the mouth * *marginal breakdown* * *creep* * *ditching* associated with **gamma-2 phase** - most amalgam now is non-gamma-2 with **high copper** content so corrodes less

Question 26

what is creep? how is creep decreased? what is creep caused by? what can it cause?

Answer 26

**gradual internal stresses and deformation** of amalgam **under stress**, causing **weaker** amalgam * decreased by incorporating **copper** * caused by **internal corrosion, phase changes, or the stresses from mastication, thermal expansion, or continued setting expansion** * can cause **microleakage, marginal breakdown and restoration failure**

Question 27

what do you need when removing amalgam restorations?

Answer 27

* **dental dam** - protect patient from amalgam and swallowing restoration * **high volume aspiration** - airborne mercury * **minimal cutting** - don't remove more unnecessary tooth structure * **selective cutting** - cut filling into large chunks rather than one piece to reduce need to extensive cutting * **hand instruments** - excavator to flick filling out

Question 28

where can mercury from amalgam be absorbed in the body?

Answer 28

* vapour into the lungs * contact with the skin * gingivae and mucosa * GI tract

Question 29

what mercury protection is needed when working with amalgam? | 7

Answer 29

* usual PPE for dentist - mask, gloves, apron, visor * dental dam * high volume aspiration * amalgam separators * spillage kit * correct disposal of waste amalgam * correct disposal of unused amalgam

Question 30

when should amalgam not be used in patients?

Answer 30

* children under 15 * pregnant women * breastfeeding women * allergic reaction to amalgam constituents