COMPONENTS:
Silver - increases strength, expansion and reactivity, decreases creep; corrosion products are AgCl and
AgS
Tin - increases reactivity and corrosion; decreases strength and hardness; corrosion products are SnO, SnCl
and SnS
Copper - increases strength, expansion and hardness; decreases creep; corrosion products are CuO and
CuS
Zinc - increases plasticity, strength and the Hg/alloy ratio; decreases creep; causes secondary expansion;
corrosion products are ZnCl and ZnO
Mercury - wets the alloy particles; decreases strength if in excess amounts; implicated in toxic and allergic rx
Mercury and amalgam
Chemical forms of mercury: elemental, inorganic and organic
TLV: threshold limit value for elemental mercury vapor set by NIOSH and is a time-weighted average for an 8 hour day; equal to 50mg/m3
Mercury hypersensitivity
incidence in the general population and only 0.6% show clinical manifestations
usually presents as a contact dermatitis and is treated locally with antihistamines or corticosteroids most allergic reactions subside in 1-2 days
TYPES OF AMALGAM
1. Spherical AgSnCu + Hg ® AgHg + CuSn +AgSnCu (Ex. Tytin, Valiant)
2. Lathe cut AgSn + Hg ® AgHg + SnHg + AgSn (Ex. Tytin FC)
3. Admixed AgSn + AgCu + Hg ® AgHg + Ag Sn + CuSn ( Dispersalloy, Valiant PhD)
(No gamma 2 if copper >12%)
Phases: Gamma - AgSn
Gamma 1 - AgHg
Gamma 2 - SnHg
Epsilon - CuSn
Eta - CuSn
Beta - AgSn
Beta 1 - AgHg
Amalgam thickness
cuspal coverage- 2mm over cusp
pin coverage - 1-2 mm (Burgess)
Amalgapins
Shavel recommends using 2.5 mm amalgapins
Roddy claims that 1 mm amalgapins are just as retentive as 3mm pins
Clinical advantages of using "pinless" retention techniques when preparing teeth for extensive restorations:
1. Occlusal clearance can be minimal; less than the 4mm needed for retentive pins
2. Passive in nature and does not rely on elasticity of dentin
3. Can be used when replacing a fractured drill or pin without consideration for 3-5mm spacing
Condensation
-incremental placement helps
-be methodical to ensure intimate adaptation of alloy to all features of the preparation
-maximum density to try to eliminate air voids
-lower residual mercury by incremental build-up and carve- back of excess
OPER DENT 19: 53-58, 1994. This study measured the fracture resistance of complex amalgam restorations when pins or amalgapins were either distributed around the preparation or concentrated in one area of the preparation. Either 4 TMS stainless steel Regular pins or four amalgapins were used. The pins were either concentrated at two line angles, or distributed at the four line angles. Distributed pins provided more resistance than amalgapins or clustered pins.
Trituration
-overtrituration
working time - decreases for all alloys
compressive and tensile strengths
lathe cut alloys -both compressive and tensile strengths are increased
spherical and admixed alloys-over trituration reduces compressive and tensile strengths
increases creep- for all alloys
-undertrituration - lowers creep
Clinically differentiating between over and under trituration
undertrituration - mass is difficult to manage crumbles and not convenient to manipulate during
insertion; undertrituration of spherical and admixed high-copper alloys reduce compressive and
tensile strength
overtrituration - mass often sticks to mixing capsule and is difficult to handle due to its short working
time
Decreasing trituration time gives you a wetter mix, and increased working time; if mix is too dry, decrease
the trituration time
Amalgamator Maintenance and Calibration (2 techniques)
run your amalgamator to warm it up before using; calibrate every 6 months to RPM 3600 +/- 200
Rupp Technique
-select the speed specified by the manufacturer
-set the amalgam time 6 sec less than that recommended by the manufacturer
-triturate and observe the resultant mixture
-when the 1st plastic mixture is obtained increase the time by 2 sec and this will become the setting
for your amalgamator
Asgar Technique
-select the speed recommended by the manufacturer
-select a time 5 sec. greater than that specified by the manufacturer
-triturate and observe the resultant mixture
-reduce the time until the mix is no longer shiny and sticky (falls out of capsule after a light tap)
Life expectancy of Amalgams
Class I amalgam lasts 19.5 years
Half life complex amalgam 11.5 years
Mean age of replacement of amalgams of all classes was 11 years
Reasons for replacement
secondary caries
residual caries not removed
inadequate condensation
inadequate retention
insufficient bulk for strength, isthmus fracture, etc.
failure to remove unsupported enamel
Criteria for selection of an amalgam
Composition
Cu > 12%
eliminates gamma 2 phase
strength over low Cu alloys; < susceptible to marginal corrosion, deterioration and creep
less susceptible to manipulative and operator variables
restorations of superior longevity
The ADA classifies "high copper" amalgams as those having a copper content of 9% or higher. However for the complete elimination of Gamma-2 phase, there must sufficient copper to combine with the tin liberated during amalgamation. Copper content must be at least 12% to eliminate all of the Gamma-2.
Ref.: Dental Materials Syllabus, CAPT J.C. Meiers.
Zinc
more plasticity
low oxidation
in high copper alloys, decreased marginal breakdown
particle size: want variety to increase packing fraction
Galvanism
Galvanic corrosion is an electrochemical reaction between dissimilar metals that have the potential to
cause unpleasant and even painful biologic effects intraorally. The highest current density of
electromotive force between materials commonly used intraorally occurs between silver amalgam
restorations and type III gold. The first method of treatment is to place a rubber separator between
the dissimilar restorations. Other barriers used to separate the teeth include silver nitrate on the
surface of the new restoration, coating the entire surface of the restoration with unfilled composite
resin and curing, and replacing the contact area with resin. Galvanism can occur between a
temporary aluminum crown and a gold crown.
Spherical vs. admixed - clinical trials
Spherical
-contains spheres of various sizes, each of which contains silver, tin and copper.
-need 10% less Hg to amalgamate due to less surface area.
-higher strength 15 min after condensation than admixed.
-less condensation force but voids easier to occur
-greater capsule-capsule consistency
-smaller particles-smoother surface
-excellent corrosion resistance
Spherical alloys amalgamate very readily (due to increased surface area). Therefore, amalgamation can be accomplished with smaller amounts of mercury than is generally required for many lathe-cut alloys. . . The condensation pressures are less. . . Forcing the band against the opposing tooth to develop a positive contact becomes more of a problem with spherical alloys. . . Spherical alloys have greater compressive strength at 15 minutes and 1 hour. Ref.: Baum L, Textbook of Operative Dentistry. W.B. Saunders, 1995.
Admixed
-more resistance to condensation
-contain both spherical and irregularly shaped particles
-easier adaptation to cavity walls and better contacts
-medium to high strength
-very good corrosion resistance
-handling characteristics
-setting time: personal choice, range 3-20 mins.
-condensability: spherical easier than lathe-cut or admixed, however, contacts harder to achieve
with spherical
-carvability
-tensile strength of spherical improved over pure lathe cut
-early compressive strengths (15min.-1hr.) are higher for spherical than those for lathe-cut alloys-
good for cores or large buildups
Delivery system/cost
-pre-encapsulated- for mercury hygiene
-variety of spill sizes- saves material
-presence of diaphragm in mixed alloy
-budgetary constraints
Osborne's clinical assessment (June 1990)- after 3 years amalgam restorations were evaluated for surface
luster and marginal fracture
-least marginal failure- Dispersalloy, Indiloy, Cluster, and Unison
-highest surface luster- Unison and Tytin
-greatest factor in long term success of restoration is the size
Conservative amalgam preparation
Degree cavo-surface angle
B-L dimension of occlusal preparation no more than 1/4 intercuspal width
Depth 0.5mm into dentin
Reverse "s" curve
Independent surface retention
Proximal outline just below proximal contact
No longer advocate GV Black’s “extension for prevention” into all groves
Slot preps for class 2 preparations; if occlusal extensions less than 1.2 mm wide, augment retention of
approximal box with retention locks on facial/lingual walls
Butt cavosurface margin
Gives bulk of amalgam at margin and resists fx.
Restoration of endodontically treated teeth/Build-ups, posts & pins
Factors to consider when deciding to restore a tooth with a core build-up
Extent of the carious involvement
Restoration/remaining tooth structure
Success of endodontic treatment
Periodontal health status
Occlusion/function requirements
Restoring endo teeth with amalgam
To resist fracture restorative techniques should conserve as much dentin as possible and also provide
cuspal protection
Reagan concluded that a properly completed amalgam restoration with cuspal coverage has the same
resistance to fracture as an unrestored tooth
Composite and glass ionomer lack the physical and mechanical properties necessary to function as
cusp coverage restorations and load bearing restorations in posterior teeth; however, excellent
results have been obtained in using composite to restore root canal treated teeth with minimal
access preparation and most coronal tooth structure remaining
Cuspal coverage restorations of endodontically treated posterior teeth can be either a core material followed by
a casting; or an amalgam core combination amalgam crown
Adequate retention can be achieved from the pulp chamber alone if its height is 4mm or greater
Condensing amalgam into canals, slots, amalgapins, and boxes improves retention
Self threaded pins are an option to increase retention but have inherent risks of crazing and cracking of
the dentin or perforation into the PDL
Premolar teeth require post retention more often due to the smaller pulp chamber and dentin available
for other internal retentive features
When a post is indicated, the following guidelines should be used for the best results:
Posts should be at least as long as the crown, longer if possible, and still leave 3-5 mm of gutta percha for
an apical seal
Increased post length increases retention; they should be the smallest diameter that will adapt to
the minimally prepared canal; tapered posts increase the risk of fracture of the tooth; there
should be at least a 1mm ferrule affect no matter what type of post and core is utilized
Antirotational devices should be incorporated into the core if the post is cylindrical
Core material should have good compressive and tensile strength and be dimensionally stable
Glass ionomer cores have the advantage of direct placement, fluoride release, dimensional
stability and bonding to dentin but have a low tensile strength
Composite core advantages are direct placement and lack of corrosion, but has the inherent
disadvantage of low tensile strength and dimensional instability due to water sorption
Amalgam and cast alloys have the advantage of better strength and dimensional stability than
other core materials and are usually the appropriate materials
The tooth with less than four complete coronal dentin walls may require a cemented post and
additional internal retentive features for adequate retention of the final restoration; clinical
assessment of remaining tooth structure will determine the combination of retentive features
used by the clinician
Pins
Types
cemented
friction-lock
self-threading
Advantages
more conservative and less time involved than castings
enhances retention form (adds walls) and is an economical alternative to castings
Disadvantages
can cause dentin crazing
microleakage can occur at pin channel
pins weaken amalgam alloy
Number of pins
one per cusp or marginal ridge may be excessive
3-5 mm between pins
0.05 to 1.0 mm inside dentinoenamel junction
sizes of pins in inches
Self threading (TMS) drill size pin diameter
regular 0.027 0.031
minum 0.021 0.024
minikin 0.017 0.019
minutia 0.0135 0.015
When pins are placed nearer the occlusal surface, as in cuspal coverage areas, the pins should project only
minimally into the restorative material; long pins near an area of occlusal loading will significantly
weaken the amalgam; additionally, the purpose of the pin in cuspal coverage areas is to bind the cusp
to the restoration and to resist lateral displacement with occlusal function; should have 2 mm of amalgam thickness above pin
Retention vs. resistance form
-retention form resists displacement through tipping or lifting forces
-resistance form enables tooth to withstand stress on restoration and remaining tooth during function
-the effectiveness of pins, slots, box-forms (ledges), or amalgapins can be maximized when used in
combination and properly distributed
Cuspal coverage
cover cusps not because of drying but because of weakness created due to access opening, existing restoration, etc.
1/4 intercuspal distance = to intact tooth
1/3 intercuspal distance 1/3-2/3 as strong
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