Clinical amalgam Flashcards
ILO 1.6c: have knowledge of the chemical and physical properties as well as the clinical uses of a range of dental materials
what are possible indications for amalgam use?
- direct restorations in moderate and large cavities in posterior teeth
- core build ups for an indirect cast restoration e.g. crown
what are possible contra-indications for amalgam use?
- 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
what are the advantages of amalgam?
- 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
what are the disadvantages of amalgam?
- 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)
why do dentists use amalgam?
- 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
what is the restoration sequence when placing amalgam?
- caries risk, assessment and diagnosis
- likely material choice
- informed consent
- caries access and removal
- cavity design
- removal of deep caries
- restoration process
what is retention form in cavity design for amalgam restorations?
- 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
what is resistance form in cavity design for amalgam restorations?
- 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
what are the two cavity designs for occlusal caries in amalgam restorations?
- self-retentive box preparations (minimal preparation box)
- proximo-occlusal preparations
what are the advantages of a self-retentive box preparation (minimal preparation box)?
3
- less tooth tissue removed than with proximo-occlusal preparation
- reduced amount of amalgam placed
- sound tooth tissue retained between proximal box and occlusal cavity
what are the disadvantages of a self-retentive box preparation (minimal preparation box)?
2
- can be more technically demanding than proximo-occlusal preparations
- further treatment of pit and fissure caries may be required
what are the advantages of proximo-occlusal preparations?
3
- very retentive
- treats caries in pits and fissures
- less or no opportunity for future caries in pits and fissures
what are the disadvantages of proximo-oclusal preparations?
2
- destruction of tooth tissue for retention
- increased risk of weakening the tooth
what are some mechanical ways to increase retention in cavity design for amalgam restorations?
- include grooves or dimples within the design
- pin placement to increase retention in large non-retentive cavities
what are the problems with pins?
- 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
how do you finish the amalgam cavity preparation?
- ensure all caries is removed
- smooth and round internal line angles
- check and finish cavo-surface line angles
- smooth cavity margins
how does moisture contamination affect amalgam restorations?
- reduces strength
- increases creep and secondary caries
- increases corrosion
- increases porosity
what is the use of matrices during restoration?
- 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)
how does the mixing time affect amalgam restorations?
- handling characteristics
- working time
- amalgam microstructure
- restoration longevity
how do you condense amalgam? why does it need to be done?
- 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
what does inadequate condensation of amalgam restorations lead to?
- lack of adaption to cavity
- poor bonding between layers
- inadequate mercury expression and removal during carving
- inferior mechanical properties
how can you remove excess material from amalgam restorations?
- carving
- burnishing (polish)
use high volume aspiration - airborne mercury
what do you need to recreate when carving an amalgam restoration?
- marginal ridge
- inter-proximal contact areas
- fissure pattern
- cusps and cuspal inclines
- re-establishes occlusal contacts
what is microleakage? what can cause it? what can it cause?
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
what is corrosion? what can it cause? how is amalgam different now so less corrosion occurs?
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
what is creep? how is creep decreased? what is creep caused by? what can it cause?
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
what do you need when removing amalgam restorations?
- 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
where can mercury from amalgam be absorbed in the body?
- vapour into the lungs
- contact with the skin
- gingivae and mucosa
- GI tract
what mercury protection is needed when working with amalgam?
7
- 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
when should amalgam not be used in patients?
- children under 15
- pregnant women
- breastfeeding women
- allergic reaction to amalgam constituents
