Clinical amalgam Flashcards
what is amalgam
“ An alloy of mercury with
another metal or metals”
what are direct restorative materials
- Amalgam
- Composite Resin
- Glass Ionomer & RMGI
what are indirect restorative materials
- Gold
- Other metals
- Ceramic
- Composite Resin - Ceromeric
When would you use amalgam
A direct restoration in moderate and large sized cavities in posterior teeth.
Core build ups when the definitive restoration will be an indirect cast restoration such as a crown or bridge retainer
Why might you not use amalgam
If aesthetics are paramount to patient
The patient has a history of sensitivity to mercury
or other amalgam components
Where the loss of tooth substance is such that a retentive cavity cannot be produced
Where excessive removal of sound tooth substance would be required to produce a retentive cavity.
Advantages of amalgam
- Durable
- Good long term clinical performance
- Long lasting if placed under ideal conditions (median survival 12 – 15 years)
- Long-term resistance to surface corrosion
- Shorter placement time than composite
- Corrosion products may seal the tooth restoration interface
- Radiopaque
- Colour Contrast
- Economical
Disadvantages of amalgam
- Poor aesthetic qualities
- Does not bond easily to tooth substance
- Thermal diffusivity high (1.7cm2 /sec vs 0.0026cm2 /sec for dentine)
- Cavity preparation may require destruction of sound tooth tissue
- Marginal breakdown
- Long-term corrosion at tooth restoration interface may result in “ditching” leading to replacement or repair
- Local sensitivity reactions
- Lichenoid lesions (type IV hypersensitivity reaction)
- Galvanic response can occur (Battery effect from 2 different amalgams or more likely amalgam and a cast metal restoration)
- Tooth discolouration (Corrosion products migrate into tooth surfaces which is porous –>Darkened tooth)
- Amalgam Tattoo (fine amalgam particles migrate into soft tissues, differential diagnosis is the main problem- is it a tattoo or is is a melanoma?)
- concern about possible mercury toxicity
Why has it been used for over 100 years?
Quick and Easy
Self-hardening at mouth temperature
Can be used in load-bearing areas of the mouth
Good bulk strength and wear resistance
Usually placed at one visit
Economical (time of patient rather than the price of the material)
vs gold (historically)
vs composite or indirect restorations
What is retention and how much of an undercut do you need
Features that prevent the loss of the restoration in any direction
In an occlusal direction significant undercut is not required, parallel or minimal undercut is all that is necessary.
What is resistance and how do you achieve that, what happens if you don’t achieve it
Features that prevent loss of the material due to distortion or fracture by masticatory forces
Ideally the cavity floor should be approximately parallel to the occlusal surface with sufficient depth of the cavity to give adequate mechanical strength (approx 1.5 – 2mm)
The gingival floor of an interproximal box should be approximately 90o to the axial wall. If it is greater this –> a sloping inclined plane which makes the filling liable to slide out of the cavity.
should amalgam be your restoration material of choice
With improved composite and glass ionomer technology and evidence of success clinically, for pit and small fissure caries, amalgam restorations should not be regarded as the restoration of choice.
What are the different approaches to cavity design to treat interproximal caries
Self-retentive box preparation (minimal preparation box)
Proximo-occlusal preparation
Advantages of the self retentive box preparation for interproximal caries
• Less tooth tissue removed than with a proximo-
occlusal preparation
• Reduced amount of amalgam placed
• Sound tooth tissue retained between proximal box and
any occlusal cavity
Disadvantages of the self retentive box preparation for interproximal caries
• Can be more technically demanding than proximo-
occlusal preparation
• Further treatment of any pit and fissure caries may be
required
Advantages of the proximo-occlusal preparation for interproximal caries
(Should be) Very retentive
Also treats any caries in pits and fissures
Less or no opportunity for future caries in pits and fissures
Disadvantages of proximo-occlusal preparation of interproximal caries
Destruction of tooth tissue for retention
Increased risk of weakening of the tooth
What is additional retention
Include grooves or dimples within the cavity design (mechanical)
How can you incorporate additional retention
Pin placement (controversial)
Adhesive technology
How are pins used
to increase retention in large non-retentive cavities
Pins are self tapping screws
Place pin into dentine in the greatest bulk of the tooth.
Never in enamel or at the ADJ (dentine will bend when enamel will break)
Avoid the pulp and periodontal ligament
Pack amalgam around the pin
What are the disadvantages of using pins
Initial
Stress in tooth around the pin.
Cracking of dentine,
Sensitivity of tooth due to temperature transference
Long term
filling can leak but will not fall out because of the pin –> secondary caries which can progress further into the tooth because of the pin
Never use pins with composite resins
What are some examples of adhesive technology that can be used as additional retention
Sealing + bonding restorations
- scotchbond
- prime and bone
Bonding-Resin cement
e.g. PANAVIA21
Resin modified GIC
e.g. vitrebond
Do bonded amalgams have better survival than non-bonded amalgams
no evidence for this
How do you finish the preparation
- Ensure all caries is removed
- Smooth and round internal line angles
- Check and finish cavo-surface angles
- Smooth cavity margins
Why should the preparations be kept dry if possible
Moisture:
Reduces Strength
Increases creep
Increases corrosion
Increases porosity
Critical but not as critical as in bonded composite restorations
How is dentine sealed
- Cavity Varnishes
- Normally with RMGIC
• Can use DBA but this
complicates the process
• ? Bonding
what is microleakage
Passage of fluid and bacteria in micro gaps (10 microns) between restoration and tooth
what can microleakage cause
• Pulpal irritation and infection
• Discolouration
• Secondary Caries
Over time; mechanical loading and thermal stresses may lead to microleakage (not worse than composite though)
functions of a matrix
- Recreate wall(s) of the cavity
- Allows creation of proximal form
- Allows adequate condensation
- Confines amalgam to the cavity
characteristics of a matrix
- Should be < 0.05mm thick
- Smooth and strong
- Allow close adaptation especially at the cervical margin
- Allow good contact with adjacent tooth
Functions of a wedge
Essential to produce adaptation of the matrix at the cervical margin (Buccal or lingual approach)
- Temporary tooth separation
- Prevents excess amalgam gingivally
- Aids proximal wall contour
- Prevents movement of matrix band
what does mixing time affect
- Handling characteristics
- Working time
- Amalgam microstructure
- Restoration longevity
Why is condensation so important
- Expels excess mercury bringing it to the surface where it will be carved off (weakest part of amalgam on surface which you then carve off)
- Adapts material to cavity walls
- Reduces layering (homogenous)
- Eliminates voids
How do you achieve optimal condensation
Require correct size of instruments
Easier to control initial increment with a large plugger
- Smear into the cavity
- Smaller plugger
- Overlapping axial strokes
Lateral as well as axial condensation
Spherical alloys require less force for condensation
what happens if you have inadequate condensation
- Lack of adaptation to cavity
- Poor bonding between layers
- Inadequate mercury expression and consequently removal during carving
- Inferior mechanical properties
You need to overfill a cavity with amalgam, why?
Higher mercury content in surface amalgam which needs removal by :
Carving
Burnishing ?
Using high volume
aspiration
How do you carve amalgam
- Marginal Ridge
- Inter-proximal contact areas
- Fissure Pattern
- Cusps and cuspal inclines
- Re-establishes occlusal contacts
Is finishing essential
Only if required to adjust anatomical contour after amalgam has set
polishing is considered unnecessary
why might finishing not be done
- adverse effects of heat
- mercury risk?
what is corrosion
detrimental change in the character of amalgam due to reactions in the mouth
what is corrosion associated with
with gamma 2 phase
(Most amalgam is now non-gamma 2, high copper, so less of a problem).
what does corrosion do to amalgam
• Can cause marginal breakdown
with creep and ditching
• Expansion of amalgam during corrosive process may assist in the development of a marginal seal
what is creep
“slow internal stressing and deformation of
amalgam under stress”
what is incorporated into amalgam to reduce creep
copper (Ag-Sn-Cu) phase stronger
what does creep cause
reduced marginal integrity
what is essential to prevent creep
a correct cavo-surface angle
why might you need to remove amalgam restorations
- Secondary caries
- Bulk fracture
- Removal of an amalgam core within an extracoronal restoration
How do you go about removing amalgam
- Dental dam
- High volume aspiration
- Minimal cutting
- Selective cutting
- Hand instruments
- operator and assistant protection
when is mercury release a particular problem
The greatest amount of mercury is released during the insertion and removal of amalgam restorations
During Insertion
• Amount is proportional to the restorations’ free surface area
During removal
• Vapour + particles
How is mercury absorbed
- Vapour into lungs
- Contact with skin
- Gastro-intestinal tract
- Gingiva and mucosa
- Dentine and Pulp as metal ions?
How much mercury is absorbed from a filling
Inorganic mercury vapour is released very slowly from an amalgam (about 0.5 microgrammes/surface/day).
Organic Mercury in food is absorbed much more easily (About 90% of that
ingested) E.g tuna
What is required for safe use of mercury
Dental dam
High Volume aspiration
Amalgam traps – separators
Spillage Kit
Correct disposal of waste amalgam
Correct disposal of unused amalgam
Where does a lot of the mercury in the environment come from
natural sources
- ocean evaporation
- geothermal activity
- rock erosion
What toxic effects can mercury cause through amalgam
Dental Amalgam Can produce delayed hypersensitivity contact reactions on the skin and mucous membrane
- Neuro-toxicity
- Kidney dysfunction
- Reduced immunocompetence
- Effects on the oral and intestinal bacterial flora
- Effects on general health
- Foetal and birth effects
What is the minamata convention on mercury
a global treaty to protect human health and the environment from the adverse effects of mercury (2013).
Governs use of all mercury containing products.
By 2032 there will be no mining for mercury
how is amalgam affected by the minamata convention on mercury
subject to a phase down as opposed to a phase out
What does the minamata convention mean for dentistry in the UK
Encapsulated Amalgam
- From January 2019
- Already in use in the majority of practices in uk
Amalgam Separation
- Amalgam separation mandatory from 2021
- All amalgam separators installed from June 2017 must retain at least 95% of amalgam particles
All amalgam waste must be collected by an authorised waste management establishment
From July 2018 Silver amalgam should not be used in:
Children under 15
Pregnant Women
Breastfeeding Women
What is the SDCEP guidance on amalgam use
Acknowledges that there is no justification on health grounds for not placing amalgam restorations.
There is no justification for removal of sound amalgam restorations except in patients with a proven allergic reaction to constituents of the material.
Limited itself just to Article 10(2)
From July 2018 Silver amalgam should not be used in:
Children under 15
Pregnant Women
Breastfeeding Women
Unless there is a specific medical reason for it’s use.
what are the main limitations for placement of an amalgam alternative
- lack of cooperation
- inadequate moisture control
(It doesn’t matter how good you are at doing composite restorations. If it’s not dry, they don’t work)
What is the blacks cavity classification (now modified)
- Class I: Pit and fissure caries
- Class II: Approximal caries (posterior teeth)
- Class III: Approximal caries (anterior teeth)
- Class IV: Approximal caries involving incisal angle
- Class V: Caries affecting cervical surfaces
- Class VI: Caries affecting cusp tips
Arranged as how common they are
