clinical amalgam Flashcards
what is amalgam
an alloy of mercury with another metal or metals
what are the 2 types of restorative materials
> direct
> indirect
name direct restorative materials
amalgam
composite resin
glass ionomer
RMGIC
name indirect restorative materials
gold
other metals
ceramic
composite resin - ceromeric
what are the possible indications for amalgam to be the restorative material for a filling
> direct restoration
moderate and large sized cavities
posterior teeth
core build ups (when the definitive restoration will be an indirect cast restoration such as a crown or bridge retainer)
what are the situations when amalgam should not be used
> when aesthetics are important to the patient
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
what are the advantages of amalgam
> durable
good long term clinical performance / long lasting when placed under ideal conditions
long term resistance to surface corrosion
faster placement than composite
corrosion products may seal the tooth restoration interface
radiopaque
colour contract
economical (cheaper than composite as it takes less time to place)
what are the disadvantages of amalgam
> poor aesthetically > does not bond easily to tooth substance > thermal diffusivity high > cavity preparation may require destruction of sound tooth tissue > marginal break done > long term corrosion at tooth restoration interface may result in ditching leading to replacement or repair > local sensitivity reaction > lichenoid lesions > galvanic response can occur > tooth discolouration > amalgam tattoo > concern about mercury toxicity
what is the thermal diffusivity of amalgam and dentine and what problems does this cause
amalgam = 1.7 cm2 per second dentine = 0.0026 cm2 per sec
need a lining placed under amalgam to protect the tooth
may cause patient to have discomfort when having ice cream or coffee otherwise
what are lichenoid lesions and how are they treated
occur with type IV hypersensitivity reaction
remove the amalgam and replace with another restoration material and the lesion will go away
how does a galvanic response occur
battery effect from 2 different amalgams or more likely an amalgam and a cast metal restoration
causes a tingly feeling in the mouth
pretty rare
how does tooth discolouration occur with amalgam
corrosion products migrate into tooth substances which is porous which will darken the tooth
stains the dentine so there will be a dark line where the amalgam previously was when you go to place a tooth coloured replacement
what is an amalgam tattoo
when fine amalgam particles migrate into soft tissues
need a differential diagnosis using a biopsy or x ray (although this is seldom helpful)
if it suddenly appear in the last 6 months you have to ask is that definitely an amalgam tatto or could it be something more sinister
why has amalgam been used for so many 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 in one visit
economical
what is the restoration sequence for amalgam
- caries risk, assessment and diagnosis
- likely material choice (in this example = amalgam)
- informed consent
- caries access and removal
- cavity design
- removal of deep caries
- cavity toilet
- restoration placment
what 2 things should be considered in a cavity design of amalgam
- retention form
- resistance form
what does retention form mean
- features that prevent the loss of the restoration in any direction
- in an occlusal direct a significant undercut is not required
- parallel or minimal undercut is all that is needed
- usually an undercut is created in caries removal (more caries in dentine than enamel so it is wider deeper in the cavity than that at the surface)
what does resistance form mean
- features that prevent the 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
- not bonded to tooth surface so restoration can move
- the gingival floor of an inter proximal box should be approximately 90 degrees to the axial wall
- if it is greater than this then a sloping inclined plane is created which making the filling liable to slide out of the cavity and the material may gradually creep
what type of caries restoration should amalgam not be the material of choice in
pit and small fissure caries restorations
what are the 2 cavity designs to treat interproximal caries for amalgam
- self retentive box preparation (minimal preparation box)
- proximo-occlusal preparation
what are the advantages of a self retentive box preparation
> 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 (leaves more tooth behind)
what are the disadvantages of self retentive box preparation
- can be more technically demanding than proximo-occlusal preparation
- more difficult
- further treatment of any pit and fissure caries may be required
- doesnt treat caries elsewhere on the tooth (occlusally)
what are the advantages of proximo-occlusal preparation
> should be very retentive (wont fall out)
also treats caries in occlusal surface
less or no opportunity for future caries in pits and fissures
what are the disadvantages of proximo-occlusal preparation
> destruction of tooth tissue for retention so it removes more tooth tissue
increased risk of weakening of the tooth
name mechanical additional retention for amalgam restorations
- include grooves / dimples within the cavity design
- pin placement
how would you place a pin for additional retention in an amalgam filling
self tapping screws in tooth
place hole in dentine (in greatest bulk of tooth) using a bur that is the same size or smaller than the pin in diameter
place pin (half goes in half sticks out - must be parallel to the long axis of the tooth)
pack amalgam around the pin
what are pins made from
titanium / stainless steel
why should a pin never be placed in enamel
dentine will bend slightly when the pin is placed
placing a pin in enamel will just cause it to break
when would you use a pin?
to increase retention in large non-retentive cavities
works well in large restorations and for cores beneath crowns
it is controversial to use a pin now as they are considered old fashion
what are the initial problems with pins
- causes stress in tooth around where the pin is placed
- can crack the dentine
- sensitivity of tooth due to temperature transference
what are the long term problems with pins
filling can leak but will not fall out because of the pin so secondary caries can progress further into the tooth because of the pin but the patient won’t know this as they will feel no pain
what adhesive technology can be used for additional retention in amalgam restorations
- sealing and bonding restorations (resin)
> scotchbond(TM)
> prime&bond(R)NT
must be a dual curing bonding agent - bonding
> resin cement = PANAVIA(R)21 - resin modified GIC
> gives a bond strength of similar value = vitrebond
what is an advantage of amalgam that is lost when using adhesive technology as an additional retention method
you can use amalgam where it is wet but these adhesive technologies need complete dryness so you can no longer place the amalgam where it is wet
is there evidence to refute or claim a difference in survival between bonded and non-bonded amalgam restorations
no
what should be done in the finishing of the cavity preparation for amalgam restorations
- ensure all caries are removed
- smooth and round internal line angles
- check and finish cavo-sruface angles
- smooth cavity margins
what does moisture contamination do to the restoration
> reduces strength
increases creep
increase corrosion
increases porosity
critical but not as critical as in bonded composite restorations
amalgam gives better results when in a dry field
how can you seal the dentine?
> cavity varnishes
= normally with RMGIC
> dentine bonding agents
this complicates the process
> bonding
but whats the point
define micro-leakage
passage of fluid and bacteria in micro gaps (10 microns) between restoration and tooth
what problems does micro-leakage cause
- pulpal irritation
- discolouration
- secondary caries
can can cause microleakage in amalgam restorations
over time mechanical loading and thermal stresses
name 2 matrices for amalgam restorations
> KerrHawe Matrices
> omni-matrix
what are matrices used for in amalgam restorations
- recreate walls of the cavity
- allows creation of proximal form (want nice smooth margins joining the tooth and it is impossible to clean the material between the teeth if there is no matrix band)
- allows adequate condensation (need to use significant pressure when placing amalgam)
- confines amalgam to the cavity
what should a matrix band be like / do for an amalgam restoration
- should be less than 0.05mm thick
- should be smooth and strong
- allow close adaptation especially at the cervical margin
- allow good contact with adjacent tooth
what are wedges needed
essential to produce adaptation of the matrix at the cervical margin
name 2 types of wedges
- wizard wedges
- anatomical wedges
can use a buccal or lingual approach
what are wedges used to do
- separate the teeth temporarily
- prevent excess amalgam gingivally
- aid proximal wall contour
- prevent movement of the matrix band
what does the mixing time affect
- handling characteristics
- working time
- amalgam microstructure
- restoration longevity
why are condensation forces (vertical and lateral pressure) needed
- expels excess mercury bringing it to the surface where it can be carved off
- adapts material to cavity walls
- reduces layering (homogenous)
- eliminates voids
how can you achieve optimal condensation
- need the correct size of instrument
= easier to control initial increment with a larger plugger as the material will stick around a smaller plugger meaning it is more difficult to insert - use overlapping axial strokes
- lateral as well as axial condensation
what type of alloys requires less force for condensation
spherical alloys
what does inadequate condensation lead to
- lack of adaptation to cavity (leaves spaces around the edges, may lead to secondary caries)
- poor bonding between layers
- inadequate mercury expression and consequently removal during carving
- inferior mechanical properties = weaker material
why should you always overfill the cavity
higher mercury content in surface amalgam which needs to be removed by
- carving
- burnishing (polish by rubbing)
- using high volume aspiration
weakest amalgam at the top with the highest amount of mercury
what does carving do
recreate anatomical contour
what features should be created with carving
- marginal ridge
- inter-proximal contact areas
- fissure pattern
- cusps and cuspal inclines
- re-establishes occlusal contacts
when do you finish / polish an amalgam restoration
only if required to adjust the anatomical contour after amalgam has set
(goes in and out of fashion)
can be seen as unnecessary unless adjusting the occlusion as you are just freeing up amalgam in the patient’s mouth that they may swallow
how do you polish / finish an amalgam restoration
- amalgam finishing burs with water spray
- aspiration
define corrosion
detrimental change in the character of amalgam due to reactions in the mouth
associated with gamma 2 phase
what does corrosion cause
- marginal breakdown with creep and ditching
- expansion of amalgam during corrosive process may assist in the development of a marginal seal
why is corrosion not as big of a problem now a days
as most amalgam is non-gamma 2, high copper
define creep
slow internal stressing and deformation of amalgam under stress
the greater the amount of creep the weaker the amalgam
what is incorporated to decrease creep
copper
reduced creep should maintain the marginal integrity (correct cavo-surface angle is essential)
why would you need to remove an amalgam restoration
> secondary caries
bulk fracture
removal of an amalgam core within an extra coronal restoration
what do you need to remove an amalgam restoration
- dental dam
- high volume aspiration
- minimal cutting
- selective cutting
= cut mesial to distal
= parts should pop out - hand instruments
- operator and assistant protection
why is colour contrast an advantage in an amalgam restoration removal
you can easily see the difference between the tooth and the restoration
composite can be more difficult to remove as you can’t see the difference easily between tooth and restoration
when is the greatest amount of mercury released
during the insertion and removal of amalgam restorations
- insertion = amount is proportional to the restorations free surface area
- removal = vapour and particles
how can mercury be absorbed
- vapour into lungs
- contact with skin
- gastro-intestinal tract
- gingiva and mucosa
- dentine and pulp as metal ions
how inorganic mercury vapour is released from an amalgam filling
released very slowly
about 0.5mg per surface per day
would need 490 amalgam surfaces in the mouth to reach the exposure dose limit set by the WHO
Only about 15% of the mercury released is absorbed (0.08mg) from the lungs and GI tract
difficult to absorb inorganic mercury
what is essential for mercury hygiene
- usual protection for dental personnel
- dental dam
- high volume aspiration
- amalgam trays - separators
- spillage kit
- correct disposal of waste amalgam
- correct disposal of unused amalgam
define mercury toxicity
dental amalgam can produce delayed hypersensitivity contact reactions on the skin and mucous membrane
what can high levels of mercury toxicity cause
> 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
global treaty to protect human health and the environment from adverse effects (anthropogenic emissions and releases) of mercury and mercury compounds
what is dental amalgam subject to with regards to the minamata convention
subject to a phase down
does not say a phase out
what is being done in dentistry to phase down dental amalgam
- promote dental caries prevention and health promotion = less need for dental restoration
- minimise use of amalgam
- promote mercury alternatives for restorations
- promote research and development of quality mercury free materials for dental restoration
- educate and train professionals and students to use mercury alternatives
- discourage insurance policies and programmes that favour dental amalgam use over mercury free dental restorations
- encourage insurance policies and programmes that favour amalgam alternatives
- restrict the use of dental amalgam to its encapsulated form
- promote the use of best environmental practises in dental facilities to reduce releases of mercury and mercury compounds to water and land
who can dental amalgam not be used on
children under 15 years, on primary teeth, on pregnant or breastfeeding women
how is dentistry in the UK following what was raised in the minamata convention
- use of encapsulated amalgam
- amalgam separation
- all amalgam must be collected in an authorised waste management establishment
- amalgam is not used on children under 15, pregnant or breastfeeding women unless there is an appropriate reason for its use
what is blacks cavity classification
- class I
> pits and fissures caries
> occlusal
- class II > approximal caries (posterior)
- class III > approximal caries (anterior)
- class IV > approximal caries involving the incisal edge
- class V > caries affecting cervical surfaces
- class VI
- caries affecting cusp tips
what is included in the SDCEP guidance for amalgam
- no justification on health grounds for not placing amalgam restorations
- no justification for removal of sound amalgam restorations (except in patients with proven allergic reaction to constituents of the material)
- main limitations for placement of an amalgam alternative will be
> lack of cooperation
> inadequate moisture control
