7. Amalgam Restorations Flashcards
materials for direct restorations?
MERCURY + AMALGAMS
Definition of amalgam
MERCURY + AMALGAMS
- why is mercury a suitable metal to use in amalgams?
- is the only metal which is liquid a normal temperature and atmospheric
pressure and can dissolve other metals at room temperature - mercury is therefore used in manufacture of dental amalgams
can all metals dissolve in mercury (Hg)?
Amalgam history
key element required for a successful amalgam filling?
- key element of successful amalgam filling material was an adequate proportion of mercury with other alloys in the mix and in the mixing procedure itself
Dental amalgam composition is based on what system?
Why may we add other metals to dental amalgam?
what other metals may we add and how will they affect the amalgam?
CONVENTIONAL AMALGAM
1
what is conventional amalgam based on?
2
- what is the liquid part?
3
- what is the powder part
4
- what does the powder part form?
CONVENTIONAL AMALGAM
- powder / liquid system
1
why are other metals added by manufacturers
2
- function of mercury added?
3
- max amount of mercury added?
4
- what happens to the mercury after amalgamation?
1
- to change the properties of the final restorations
2
- pre amalgamation
3
- 3% max by weight
4
- during condensation phase and blemeshing phase of the restoration (after amalgamation), a significant portion of the mercury is removed from the amalgam
CONVENTIONAL AMALGAM
- powder / liquid system
1
- function of silver + tin?
3
- max % amount of silver and tin added by weight?
CONVENTIONAL AMALGAM
- powder / liquid system
1
why are other metals may be added by manufacturers
2
- function of the metals added added?
3
- max % amount of metals added by weight?
ALLOY MANUFACTURING
1
how is the gamma phase alloy used in dental amalgams manufactured?
2
what are problems you may face during this stage
3
how could you overcome this problem?
ALLOY PREPARATION
1
what form must the final alloy be so we can use it?
2
what are the 2 possible ways to grind the alloy into powder form?
- after the alloy has been produced, casted + cooled down, needs to be grinded down to powder to use for dental amalgams
ALLOY PREPARATION
1
what is a lathe cut?
2
How is a lathe cut done? (PICTURE)
3
what type/ shape of particles are produced?
1
cooling down and mechanically grinding alloy to powder form
2
3
irregular sized particles
ALLOY PREPARATION
1
what is a spherical manufacture?
2
How is a spherical manufacture done? (PICTURE)
3
what type/ shape of particles are produced?
1
- atomisation in an inert atmosphere to make alloy into powder form
2
3
- consistent sized particles
- spheroidal particles
PARTICLE MORPHOLOGY
1
in commercially available dental amalgams formulation, are lathe cut or spherical particles usually used?
2
why is this type used? (picture)
2
- many alloy powder are formulated by lathe-cut and spherical particles
(MIX OF BOTH)
PARTICLE MORPHOLOGY
Differences between lathe-cut and spherical alloys?
AMALGAMATION SETTING REACTION
1
initiated by?
2
Metals formed?
2
- metals are named gamma 1 and gamma 2 phases
SETTING REACTION
what happens during the setting reaction?
CARD 1
- INITIAL DISSOLUTION
SETTING REACTION
what happens during the setting reaction?
CARD 2
- FORMATION OF GAMMA 1
SETTING REACTION
what happens during the setting reaction?
CARD 3
- FORMATION OF GAMMA 2
SETTING REACTION
what happens during the setting reaction?
CARD 4
- SET AMALGAM
SETTING REACTION
electron microscope image
PROPERTIES: RELATIVE STRENGTH OF DIFFERENT PHASES?
1
what are the phases?
2
in terms of the mechanical properties of the different systems, different phases have different relative strength
phases tensile strength order? (what do we assume when having this order) (PICTURE)
1
- gamma
- gamma 1
- gamma 2
- amalgam
2
PROPERTIES: RELATIVE STRENGTH OF DIFFERENT PHASES?
1
what phase is relatively the weakest
2
what will reducing this phase do?
PROPERTIES: EVOLUTION OF STRENGTH WITH TIME
- amalgamation reaction develops slowly
- takes more than 24 hours to complete
- this is of clinical relevance as amalgam restorations remain weak during that time
- it usually good practice to recall the patient after 1 week of placing a restoration to refine the edges of the restoration + polish after the reaction is completely set
PROPERTIES: STRENGTH COMPARED WITH DENTAL TISSUES
- mechanical properties of amalgam restoration = similar to natural tooth substance
(NEED TO KNOW VALUES IN TABLE???? MAKE FCs FOR THESE??????)
PROPERTIES - DIMENSIONAL CHANGE
- what were some of the dimensional changes and why did some of these dimensional changes occur? (PICTURE)
- early composition of amalgam released in the market demonstrated significant dimensional changes upon preparation of the amalgam mix + then after the reaction had completely set
new ISO standards for contraction and expansion of amalgam?
- contraction should not exceed 0.1%
- expansion should not exceed 0.2%
THERMAL PROPERTIES
MAKE q’s
THERMAL PROPERTIES
Thermal diffusivity and thermal expansion coef. of
- Dentine
- Amalgam
(NEED TO KNOW VALUES???)
PROPERTIES: CORROSION
what happens when amalgam is placed in a wet environment?
CORROSION
PROPERTIES: CORROSION
what does corrosion of amalgam lead to
- can lead to the release of free mercury
PROPERTIES: CORROSION
what is a beneficial advantage of amalgam corrosion?
- corrosion at interface between amalgam restoration and tooth can be beneficial
- corrosion generates a less reactive species at the interface
- this can create a microseal
- this prevents microleakages
PROPERTIES: PLASTIC DEFORMATION (CREEP)
- amalgam is subject to
- what may cause higher creep?
- what does creep cause?
HIGH COPPER AMALGAM
- what does it eliminate?
- what does it do?
- how is copper added?
(- gamma 2 phase shows inferior mechanical properties)
DISPERSED PHASE
- EG of high copper amalgam where the final plan contains 2 additional dispersed phases
High copper amalgam Vs conventional amalgam?
- compressive strength
- reaction set speed
- creep
- corrosion
copper is…
KEY ASPECTS TO CONSIDER WHEN CREATING CAVITY FOR AMALGAM RESTORATION
Why are these important to do/ how’re they beneficial
- not leave any unsupported enamel structure under an amalgam restoration
- as upon load this can lead to chipping + infiltration
- lateral portion of cavity can be used to create a retentive structure like pit
- can help avoid creep of the amalgam + overhanging of the amalgam structures
- prep of corners of cavity not be wedge shaped, be more rounded
- as shown in diagram, chewing force may be concentrated at corner and this can lead to cracking of residual dental structure
- want a rounded corner of the cavity to have a more uniform stress pattern (stress of chewing would be dispersed over a large area + reduce risk of crack)
- support of residual enamel structure + away from the vicinity of the pulp
support of residual enamel structure + away from the vicinity of the pulp are KEY ASPECTS TO CONSIDER WHEN CREATING CAVITY FOR AMALGAM RESTORATION
In the diagrams which is the best and doing this and why?
C is the best
A- away from pulp so good in this sense BUT not good design for supporting residual enamel structure
B- residual enamel structure is well supported BUT too close to pulp
C- by exploiting a chamfer in the coronal part of the preparation, residual enamel is supported + is away from the pulp
How was proportioning previously done + how is it done now?
- PREVIOUSLY proportioning of powder + mercury of dental amalgam was done by dentist at dental chair
BUT
- NOW done done by manufacturer and delivers capsules containing pre weighted amount of powder + mercury and is triturated using machinery
MECHANICAL MIXING: TRITURATION
- why is correct trituration important?
- what is the correct trituration time dependent on?
- Under trituration causes…
- Over trituration causes…
1
- to ensure adequate properties of final amalgam mix
- hence in modern dent this is done automatically in machinery
- follow manufacturer instructions
CONDENSATION
1
why is this an important step?
2
objectives? (IMAGE)
1
- to ensure quality of amalgam restoration
CONDENSATION
1
when should it done
2
how should it be done
3
spherical Vs lathe cut amalgam condensation pressure?
CARVING + FINISHING
1
working time?
2
spherical vs lathe cut - which produces a better surface
3
why should you avoid using too much pressure
4
advantage of a smooth surface
Limitations of dental amalgams
Concerns about using mercury alloy?
Minimata treaty 2013
How safe is amalgam?
- some cases, mainly in incongruous amalgam restorations with sharp edges or particularly oxidised structures, can lead to mucositis + lesions in oral mucosa
- key result of minimata treaty of 2013, was phase down of use of dental amalgams in dental practise
REMOVAL OF DENTAL AMALGAM RESTORATIONS
what to consider?
- as many amalgam restorations have been placed some dentists may carry out amalgam restoration removal BUT this poses significant risk to operator and patient
BECAUSE - Hg levels during removal of amalgams exceed governments’ safety limits
REMOVAL OF DENTAL AMALGAM RESTORATIONS
Safety measures to minimise patient + operator exposure during removal?
1) (or slight incongruous ones)
2) (add for operator and team)
3) (+ possibly use more powerful aspiration system to minimise diffusion of microparticles in the environemtn)
OVERALL
1
use of amalgam is strongly discourage in
2
general
Minamata convention on mercury
http://www.mercuryconvention.org
Scientific Committee on Health and Environmental Risks (SCHER):
Opinion on the environmental risks and indirect health effects of mercury from
dental amalgam (update 2014)
https://ec.europa.eu/health/sites/health/files/scientific_committees/environmental_risks/docs/scher_o_165.pdf
Opinion on the safety of dental amalgam and alternative dental restoration
materials for patients and users
https://ec.europa.eu/health/scientific_committees/emerging/docs/scenihr_o_046.pdf
FURTHER READING APPENDIX 1 -
CONCERN ABOUT MERCURY IN AMALGAM
- why the concerns about mercury in amalgam?
- so some people have reactions to amalgam?
- if amalgam is safe, why does my dentist take precautions when handling it?
- should I have my amalgam fillings removed?
FURTHER READING APPENDIX 2 -
AMALGAM REMOVAL GUIDELINES
- international association for oral med + tech
FURTHER READING APPENDIX 3 -
POLICIES ON DENTAL AMALGAM
(BDA’s view)
CONT.
FURTHER READING APPENDIX 3 -
POLICIES ON DENTAL AMALGAM
