DENTAL CEMENTS AS LUTING AGENTS

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DENTAL CEMENTS AS
LUTING AGENTS
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Numerous dental treatments necessitate
attachments of indirect restorations and
appliances to the teeth by means of a
cement. These include metal ,metalceramic, and ceramic restorations
provisional restorations, laminate veneers
for anterior teeth , orthodontic appliances,
pins and posts used for retention of
restorations .
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Characteristics of Abutment Prosthesis Interface
 When
two relatively flat surfaces brought
into contact, space exists on microscopic
scale, there are peaks and valleys
 There are only point contacts along the
peaks
 Main purpose of cement is to fill this space
completely
 If cement is not fluid enough voids can
develop around deep valleys
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Procedure for cementation of
prostheses

To be effective a Type-I cement must be fluid
and be able to flow into a continuous film of 25
um thick or less without fragmentation
 The cement paste should coat the entire inner
surface of the crown and extend slightly beyond
the margin. It should fill about half of interior
crown volume
 Moderate finger pressure should be used to
displace excess cement and to seat the crown
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 Variables
that can facilitate seating of
prosthesis include –
 Using a cement of lower viscosity
 Increasing the taper of preparation
 Decreasing the height of crown
preparation
 Vibration
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Removal of excess cement

Removal of excess cement depends on
properties of cement used –
 If cement sets to a brittle state and does not
adhere to surrounding surfaces,tooth and
prosthesis, it is best removed after it sets . This
applies to Zinc phosphate and ZOE cements
 For cements which are capable of adhering
chemically like GIC, polycarboxylate and resin
cement ,coat surrounding surface with
petroleum jelly and remove excess as soon as
seating is completeds
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Dislodgment of prosthesis
 Recurrent
caries may occur
 Disintegration of cement can result from
fracture or erosion of cement
 In oral environment , cement layer near
the margin can dissolve and erode leaving
a space. This space can be susceptible to
plaque accumulation and recurrent caries
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
Loss of cement at
marginal area
resulting from
exposure to oral fluid
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CHOICE OF LUTING AGENT
An ideal luting agent hasLong working time
Adheres well to both tooth structure and cast
alloys
Provides a good seal
Is nontoxic to the pulp
Has adequate strength properties
Has low viscosity and solubility
Exhibits good working and setting characteristics
Any excess can be easily removed
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ZINC PHOSPHATE CEMENT
 It
is the oldest of cementation agents
 It serves as standard by which newer
systems can be compared
 Zinc phosphate cement is still the luting
agent of choice for otherwise normal,
conservatively prepared teeth
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 Working
time- 5 min
 Setting time-5-9 min
 Manipulation-a cool mixing slab should
be employed ,cool slab prolongs the
working time
 Recommended powder:liquid ratio 1.4 gm
powder to 0.5ml liquid
 Mixing is initiated by addition of small
amount of powder with brisk spatulation
 A considerable area of mixing slab should
be used ,this reduces the amount of heat
generated.
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
Two mixes of cement
prepared with
identical powder liquid
ratio. Temp in A is 18
degree C. temp in
B is 29.5 degree C
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Physical properties –
 Compressive strength -104 MPa
 Modulus of elasticity -13 GPa
 It is quite stiff and resistant to elastic
deformation even when employed for
cementation of restorations that are
subjected to high masticatory stress
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Retention
 Primary bonding occurs by mechanical
interlocking at interfaces and not by chemical
interactions
Biologic properties
 The acidity of cement is quite high at the time
when prosthesis is placed on prepared tooth
 The pH then increases rapidly but still is only
about 5.5 at 24 hours
 Thus if underlying dentin is not protected against
infiltration of acid via dentinal tubules pulpal
injury may occur
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ZINC POLYCARBOXYLATE
CEMENT
It was the first cement system that
developed an adhesive bond to tooth
structure
This agent is recommended on retentive
preparartions when minimal pulp irritation
is important e.g. in children with large pulp
chambers
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 If
good bonding to tooth structure is to be
achieved ,the cement must be placed on
the tooth surface before it loses its glossy
appearance. The glossy appearance
indicates a sufficient number of free
carboxylic acid groups on the surface of
mixture that are vital for bonding to tooth
structure
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
Consistency of
polycarboxylate on
completion of 30 sec
mix
 Prolonged mixing or
mix is allowed to
remain on slab
cement becomes dull
and consistency
becomes s tacky
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time –much shorter than for zinc
phosphate ,2.5 min
 Setting time – ranges from 6-9 min
Manipulation P:L ratios - 1.5 parts of powder to 1 part
of liquid
 Cool the slab and powder but under no
circumstances should the liquid be cooled
 Powder is rapidly incorporated into liquid
in large quantities.30 sec mixing time is
adequate
 Working
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Properties –
 Compressive strength -55 MPa
 Modulus of elasticity - 5.1 GPa
 At manufacturers’ recommended powder:
liquid ratios ,mixed polycarboxylate
cement is very viscous .however
polycarboxylate have different rheological
or flow properties than zinc phosphate ,
exhibiting thinning with increased shear
rate .this means they are capable of
forming low film thicknesses despite their
viscous appearance
 Physical
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to tooth structure –it bonds
chemically to tooth structure ,the
polyacrylic acid is believed to react via the
carboxyl groups with calcium of
hydroxyapatite
 Bonding
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 Biologic
properties- The excellent
biocompatibility with the pulp is a major
factor in the popularity of this cement
system .this is due to larger size of
polyacrylic acid which may limit its
diffusion through the dentinal tubules
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GLASS IONOMER CEMENT
 Glass
ionomer is generic name of group of
materials that use silicate glass powder
and an aqueous solution of polyacrylic
acid . It is also referred to as
polyalkenoate cement
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TYPES OF GIC
Type-I Luting applications
Type-II Restorative material
Type-III Liner or Base
Type-IV Pit and Fissure Sealant
Type-V Orthodontic Bracket
Type-VI Core build up
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 Working
time-range is 3-5 min
 Setting time- 5-9 min
 Manipulation The powder is introduced into the liquid in
large increments and spatulated rapidly for
30 to 45 seconds
 Recommended P:L ratio is 1.25 to 1.5 g of
powder per 1ml of liquid
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 Physical
properties Compressive strength -86 MPa
 Modulus of elasticity-7.3 GPa
 A disadvantage is that during setting ,
glass ionomer appears particularly
susceptible to moisture contamination and
should be protected with a foil or resin
coat or by leaving a band of cement
undisturbed for 10 min
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 Biologic
Properties- the glass ionomer
cement bond adhesively to tooth structure
and they inhibit infiltration of oral fluids at
the cement tooth interface

In addition because it releases fluoride
it may have an anticariogenic effect
although this has not been documented
clinically
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ZINC OXIDE EUGENOL CEMENT
 ZOE
is extremely biocompatible and
provides an excellent seal .however its
physical properties are inferior to those of
other cements ,which limits its use
 Type-I
is used for temporary cementation
 Type-II is intended for permanent
cementation of restorations
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I ZOE Cements –it has a pH of 7 and
is biocompatible with pulp .
 It seals the cavity well against ingress of
oral fluids , hence irritation caused by
microleakage is minimized
 The strength of a temporary cement must
be low to permit removal of the restoration
without trauma to the teeth
 Type
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 Type-II
ZOE Cements- The 2-ethoxy
benzoic acid (EBA) modifier replaces a
portion of eugenol in conventional ZOE
cement ,it improves the strength ,but it
should be used only in restorations with
good inherent retention form where
emphasis is on biocompatibility and pulpal
protection
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RESIN CEMENTS
Composite resin cements with greatly
improved properties were developed for
resin retained prosthesis and are
extensively used for bonded ceramic
technique
 Resin cements are available with
adhesive properties i.e. they are capable
of bonding chemically to dentin

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 Bonding
is achieved with
organophosphonates , HEMA (hydroxy
ethyl methacrylate ) or 4-META (4methacrylethyl trimellitic anhydride )
 Resin based cements are irritating to pulp
especially if they are not fully polymerized
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RESIN MODIFIED GLASS
IONOMER
 They
were introduced in an attempt to
combine some of the desirable properties
of glass ionomer i.e. fluoride release and
adhesion with the higher strength and low
solubility of resins .
 These materials are less susceptible to
early moisture exposure than glass
ionomer
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 Currently
among the most popular luting
agents ,resin modified glass ionomer have
low solubility , adhesion and low
microleakage also perceived benefit of
reduced post cementation sensitivity
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 Resin
modified glass ionomers should be
avoided with all ceramic restorations
because they have been associated with
fracture which is probably due to their
water absorption and expansion
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THANKYOU
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