Dental amalgam Flashcards
what is dental amalgam
an alloy of mercury mixed with metallic elements including silver, tin, copper, palladium, indium, and sometimes zinc
what is the purpose of dental amalgam in restoration
dental amalgam is used to create plastic mix that is applied to prepared cavity to restore the teeth structure and function
what is the role of mercury in amalgam
mercury liquefies and reacts with amalgam alloy to produce plastic mix that remains workable at room and body temp for reasonable period
improper handling of mercury can cause what
- systemic absorption through skin
-inhalation of mercury vapor
-inhalation of air borne particles
what are some mercury hygiene procedures in dental office
- avoid baseboard heaters
-avoid carpeting
-ensure proper ventilation
-regular monitoring of Hg vapor levels
what are mercury hygiene practices for dental personnel
-no touch technique when handling mercury
-wear a face mask
-regular urine analysis
-wear detection badages
what are important mercury hygiene techniques
- -regularly check amalgamator
- when removing old amalgam use water spray and suction
- store Hg in cool place
- store amalgam scrap in capped jars containing water with x-ray fixer
what are the affects of silver in dental amalgam alloy
increases : strength , resistance, to tarnish and corrosion and setting expansion
decreases : flow and creep, setting time
what are affects of tin in dental amalgam alloy
increases: flow and creep and setting time
decreases: setting expansion , strength
what are affects of zinc dental amalgam alloy
increases: strength, plasticity of mix
delays: expansion when contaminated with saliva
prevents oxidation of alloy constituents during manufacturing
decreases rate of marginal fracture under occlusal load
what are the types of dental amalgam alloy based on copper content
- low copper amalgam alloy ( convectional amalgam alloy): contains 2-5% copper
- high copper amalgam ( non gamma 2 amalgam alloy): contains 13-30% copper
what are the types of dental amalgam alloy based on zinc content
-zinc containing amalgam alloy
- zinc free amalgam alloy
how is the lathe cut prepared
by grinding an ingot of alloy on lathe
what are the characteristics of lathe
-particles are small they range from several micrometer to 200 micrometer in diameter
-irregular shape with sharp edges and rough surfaces
how is spherical alloy prepared
the ingot of alloy is melted and then sprayed through a nozzle
method of preparing known as water atomization
what are characteristics of spherical alloy
- particles have smooth surfaces and margins with a diameter of several micrometer to 100 micrometer
what is admired alloy
oldest type of high copper alloy
what is admired alloy composition
mixture of 2 alloys
1- high copper spherical particles( copper 20-40%)
2- low copper lathe cut particles
what is the total copper content of admired alloy
9-20%
what are the type of alloy particles based on size
micro cut
fine cut
coarse cut
what happens during setting reaction of low copper amalgam
tin reacts with mercury compound (y2)
reaction: silver tin y2 + mercury give us AgSn+ AgHg+ SnHg
y or y1 or y2 is the weakest phase and low strength phase of amalgam
y2
what is the weakness of low copper and amalgam
low strength: y is more than y1and y1 is more than y2
low corrosion resistance : y1 is more than y and y is more than y2
high creep
low marginal integrity
lowest melting point of all phases in set amalgam
what happens during setting reaction of high copper amalgam
Tin reacts with copper to form tin copper compounds( non y2 phase)
reaction: silver tin y + copper + mercury will give us AgSn y+ AgHg y1 + CuSn
in high copper amalgam reaction we don’t have y2 what does that mean
it leads to stronger and more resistant corrosion amalgam and high copper has 13% to 30% copper
what is the range of mercury content in dental amalgam and what factors influence it
the mercury content in dental amalgam is 40-50% influenced by shape , size and composition of alloy particles
why do irregular alloy particles require more mercury in amalgam
to fill spaces between them cuz of their uneven shape which create more voids that need to be filled
how does using spherical alloy particles affect mercury content in amalgam mixture
reduce the mercury portion to less than 50% cuz they fit together more efficiently leaving fewer gaps to be filled
which of these require more mercury due to their particles less efficient packing
A- high copper spherical alloys and mercury
B- low copper microfine lathecut alloys
B- low copper microfine lathecut alloys
the final mercury content in amalgam is influenced by
by the initial mercury content and clinical technique used during placement specially the force of condensation applied
how does condensation technique affect mercury in amalgam
it packs the core particles closer together and drives excess mercury to surface n that reduces the amount of mercury within amalgam mass
what happens if excess mercury is retained in amalgam matrix
can lead to loss of physical properties such as strength and durability making restoration less effective
what issues arise from a lack of dispensed mercury or faulty trituration
can create weak particle/ matrix interface which results in reduction of amalgam physical properties compromising its integrity
define corrosion in amalgam restoration
electrochemical destruction of metal by reacting with environment
types of corrosion
tarnish or surface corrosion
stress corrosion
galvanic corrosion
