COMPLEX AMALGAM RESTORATIONS Amalgam: Restorations are customarily anchored by small undercuts within the dentin, when a large portion of crown is missing because of caries or for other reasons such as fracture. It is difficult to obtain this anchorage. There are many features that provide resistance and retention form to the amalgam such as pins, locks, cores, slots etc. Bonding also provide anchorage of restorative materials to the dentin. It has been seen that the mutilated teeth are successfully restored with the use of pins. These are called the complex amalgam restorations. Thus are the restorations which involve more than two surfaces of the tooth with or without cusp capping. These complex amalgam restorations are used occasionally as an alternative to indirect restorations. Indications: 1
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COMPLEX AMALGAM RESTORATIONS
Amalgam:
Restorations are customarily anchored by small undercuts within the dentin,
when a large portion of crown is missing because of caries or for other reasons
such as fracture. It is difficult to obtain this anchorage. There are many features
that provide resistance and retention form to the amalgam such as pins, locks,
cores, slots etc. Bonding also provide anchorage of restorative materials to the
dentin. It has been seen that the mutilated teeth are successfully restored with the
use of pins. These are called the complex amalgam restorations. Thus are the
restorations which involve more than two surfaces of the tooth with or without
cusp capping. These complex amalgam restorations are used occasionally as an
alternative to indirect restorations.
Indications:
Complex amalgam restorations are indicated.
1) When large amounts of tooth structure are missing.
2) When one or more cusps need capping.
3) When increased retention and resistance form is required.
Uses:
Complex amalgam restorations may be used as,
1) Control restorations in teeth with questionable pulpal and periodontal
prognosis.
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2) Control restorations in teeth with acute and severe causes. A control
restoration helps,
a. To protect the pulp from oral cavity
b. Provides anatomic contour against which the gingival tissue may be
healthier
c. Facilitates control of caries and plaque
d. Provides some resistance against tooth fracture or propagation of an
existing feature.
3) Definitive final restoration
4) Foundations
5) Abutment teeth for fixed prosthesis may utilize a complex restoration as a
foundation
6) In patients for periodontal and orthodontic treatment, the complex
restoration may be the restoration of choice until final phase of treatment
when cast restoration may be preferred.
Contraindications:
If patient has significant occlusal problems.
If the tooth cannot be properly restored with direct restoration because of
anatomic and functional considerations.
If the areas to be restored in the esthetic region.
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Advantages:
Conserves tooth structure: The preparation for a complex amalgam
restorations is usually more conservative than the preparation for indirect
restoration or a crown.
Appointment time:- The complex restoration can be completed in one
appointment. The cast restoration require at least two appointments.
Resistance and retention form: Resistance and retention form is
significantly increased by pins, slots and bonding.
Economics:- Compared to an indirect restoration, the amalgam restoration
is relatively inexpensive restoration procedure. When cost is the factor the
complex amalgam restorations provides the patient with only extraction of
severely broken down teeth.
Martin and Bader have published the 72% of the 4 to 5 surfaced complex
amalgam restoration are of successful at five years compared with 84% of both
gold and porcelain crowns.
In another study it is reported that 72% of amalgam restorations survived
for 15 yrs including those of cusp coverage.
Disadvantages:
1) Dentinal micro fractures:- Preparing pinholes and placing pins may create
craze lines or fractures, as well as internal stresses in the dentin. Craze line
and internal stresses have little or no clinical significance but they may be
very important when minimum dentin is present.
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2) Micro leakage:- In amalgam restoration using cavity varnish micro leakage
around all types of pins has been demonstrated. Amalgam bonding has
reduced the incidence of micro leakage.
3) Decreased strength of amalgam: The tensile and compressive strength of
pin amalgam restorations are significantly reduced.
4) Resistance:- Resistance form is more difficult to develop when preparing a
tooth for cusp covering onlay. However amalgam restorations with cusp
coverage significantly increases the fracture resistance than amalgam
restoration without the cusp coverage.
5) Tooth anatomy: Proper contours and occlusal contacts and/or anatomy are
sometimes difficult to achieve with large complex restorations.
The various features that provide resistance and retention to the complex
restorations:
1) Slots
2) Pins
3) Bonding
1) Slot Retained Complex Amalgam Restorations:
For complex restoration, a slot is a retention groove in dentin whose length
is in horizontal plane. Slot retention may be used with the pin retention or as an
alternative to it. Slots are prepared with No. 33 ½ bur approximately 0.6mm deep
and 0.5 to 1mm inside the dentino enamel junction.
Another retentive feature that provides additional retention form is cores.
Cores are prepared with No ¼ bur. Depth = 0.25mm.
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Another retentive feature that provides the retention is proximal locks
placed in proximal bone and in other locations where sufficient vertical tooth
preparation permits.
Operators use slot retention and pin retention interchangeably. Slot
retention is used in preparation with vertical walls that allow retention locks to
oppose one another. Pin retention is used for frequently in preparation with few or
no vertical walls.
Slots are particularly indicated in short clinical crowns and in cusps that
have been reduced 2 to 3 for amalgam.
The amount of tooth structure removed in slots is more as compared to the
pins. However slots are less likely to create micro fractures in dentin and to
perforate the tooth or penetrate into the pulp.
Studies have shown that slots placed within 0.5mm of the pulp do not show
any inflammatory response but the medium sized self threading pins do show.
Studies whether in vitro or in vivo have shown that the retention provided
by slots and pins are quite similar. But Pashley and associates reported that the
shear strength of pin retention was significantly stronger than slot retention.
Pin retained amalgam restorations:
A pin retained restoration may be defined as any restoration requiring the
placement of the one or more pins to provide adequate resistance and retention
form.
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Pins are used whenever adequate resistance and retention form cannot be
established with slots, locks or undercuts. Pin retained amalgam is an important
adjunct in the restoration of teeth with caries or fracture.
Armamentarium:
Successful pin placement does not require large number of specialty items.
Basic list include:-
1) Contra angle hand piece (slow speed) latch type
2) Drill and matching pins
3) Finger wrench for accessible areas
4) Cable drive pin setter for inaccessible areas
5) Bending tool
6) Sharp fissure bur (e.g. no. 557) for cutting of the pins
Optional list include:-
1) Autoclutch hand piece
2) Altered comborundum disk to make a self-tapping pins
3) Haemostat forceps (needle holder)
4) Magnifying glasses
Cable-drive pin setter available as the Loma Linda alloy.
Classification of Pins:
Pins can be classified as –
a) Direct / Nonparallel pins
b) Indirect pins/ parallel pins
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A) Direct Pins:-
Are usually made of stainless steel, titanium or stainless steel with gold
plating etc. and inserted into dentin followed by placement of restorative materials
like amalgam, resin or cement directly over them.
They are also referred to as non-parallel pins since they are directly inserted
into the tooth structure and hence not parallel to each other. These category pins
include cemented, friction locked and threaded pins.
B Indirect pins:-
They are slightly undersized to their pinholes and are the integral part of the
cast restoration. These are known as parallel pins as the method necessitates
placement of pins parallel to each other as well as parallel to the path of insertion
of the restoration. Retention of parallel pins are less than the non-parallel pins.
There are basically two types of pin used in parallel pin technique.
a) Cast gold pins:-
They have relatively smooth surface. Restorations using these pins are
fabricated by keeping the nylon bristles or plastic pins in the pinholes over which
the rest of the restoration is built in the conventional form with blue inlay wax.
The whole assembly is then invested and casted with pins forming an inherent part
of the cast restoration.
b) Wrought precious metal pins:-
They have surfaces that is deformed or roughened by means of threaded or
knurled patterns. These pins are alloys of gold, platinum, palladium or platinum
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indium. The pins are placed in the pinhole and are included in the wax pattern.
Their high melting point and tarnish resistance enable them to be incorporated into
the final gold casting. These are 20-30% more retentive than smooth cast pins.
Direct pins:
The three major categories of direct pins are:-
a) Cemented
b) Friction locked
c) Threaded pins
A) Cemented Pins:-
Markley introduced this type of pin in 1958. These pins are cemented into
the pinholes prepared 0.001 to 0.002” (0.025 to 0.05mm) larger than diameter of
the pin. The difference in the diameter provides space for luting cement.
Cemented pins comes in two sizes
Pin diameter Pin channel diameter
0.025” 0.027”
0.020” 0.021”
Indication of cemented pins:
Cemented pins are generally indicated in cases where least crazing and
stresses are desired in the remaining tooth structure e.g. Endodontically treated
teeth, where there is no other choice but to place a pin near the dentino-enamel
junction, where bulk of dentin to accommodate the pin is limited or where dentin
has lost its elasticity because of sclerosis or dehydration.
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Advantages of cemented pins:-
Cemented pins are approximately 0.001” – 0.002” smaller than their
pinholes and hence are more likely to be seated to the full length.
Since they are passively relined in the dentin, they virtually place no stress
on the surrounding dentin during or after placement.
Because the cement seals the interface between pin and tooth, chances of
micro leakage are reduced.
These can be cut or bent to their final configuration before fixing them in
the pinholes.
Disadvantages of the cemented pins:-
They offer less retention compared to the friction locked and threaded pins.
If it is often difficult to insert cement into the pinholes and later locate the
hole after cement has been introduced.
At times the poorly cemented pins get dislodged when filling material is
being inserted.
Greater time is required for mixing and hardening the cement.
B) Friction locked pins:-
These were introduced by Goldstein in 1966. The diameter of the prepared
pinhole is 0.001” (0.025 mm) smaller than the diameter of the pin. The pins are
tapped into place and retained by the resiliency of the dentin. The pins are 2 to 3
times retentive than the cemented pins. These pins come in only one size i.e.
Pin diameter Pin hole diameter
0.022” 0.021”
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Indications for friction locked pins:-
Teeth that are vital and periodontally sound and where direct access can be
obtained so that tapping force can be applied parallel to the long axis of the
pin.
Sufficient amount of dentin is available to surround the pin and no way
should they be placed closer than 1.5mm to the dentino enamel junction.
Advantages of friction locked pins:-
Cement is not required so one does not have to wait for the cement to set
and other related problems.
Pins acquire stability from moment they are inserted.
Better retention than the cemented pins.
Disadvantages of friction locked pins:-
The length of the pin is judged by trial and error. It cannot be removed from
dentin for cutting to the desire length once inserted.
Bending or contouring of the pin after it has been inserted into pinhole
leads to further stresses.
Driving pins into their respective pinholes generates stresses in dentin in
the form of cracks or craze lines.
Many a times, pin do not reach to the full length due to gauging, and hence
loose their retentive properties.
Microleakage is higher than cemented pins if the overlying restoration
leaks.
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C) Threaded pins/ self threaded pins:
The most frequently used pin type is small self threading pins. Friction
locked and cemented pins although are still available are rarely used. The pin
retained amalgam restoration using the self threading pins was originally described
by Going in 1966.
The diameter of the prepared pin hole is 0.0015” to 0.0014” smaller than
the diameter of the pin. The threads engate the dentin as it is inserted, retaining the
pins. The resiliency of the dentin permits insertion of a threaded pin into a hole of
smaller diameter.
Although the threads of the self-threading pins do not engage the dentin for
their entire width, the self-threading pins are the most retentive of the three types
of the pins being three to six times more retentive than the cemented pins.
Vertical and horizontal stresses are generated when the self-threading pins are
inserted into the dentin. The self threading pins are available in four diameter in thread
mate system (TMS) by cotton/ Whaldent Inc Mahwah, New Jersy.
Type Color Pin diameter in/mm
Pin hole diameter (in/mm)
Regular (Standard)
Regular (self shearing)
Regular (Two in one)
Gold 0.031” / 0.78 0.027 / 0.68
Minimum (standard)
Minimum (two in one)
Silver 0.024 / 0.61 0.021 / 0.53
Minikin (self shearing) Red 0.019 / 0.048 0.017/ 0.43
Minuta (self shearing) Pink 0.015 / 0.38 0.0135 / 0.34
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Dutts et al. have reported that insertion of 0.031” self threading pins
produce more dentinal craze lines than insertion of either 0.021” self-threading
pins or 0.022” friction lock pins.
However other studies done by Pameijar and Saltard et al. have shown that
self-threading pins do not create dentinal crazing and the crazing demonstrated in
some studies may be caused by the technique for the preparation of the specimen.
Pulpal stresses in maximum when the self-threading pin is inserted
perpendicular to the pulp. The depth of the pin hole in the dentin varies between
1.3 to 2mm depending upon the diameter of the pin used.
Indications for self-threading pins:-
Indicated in vital teeth where maximum retention is desired.
Pins should be given when sufficient amount of dentin is available to
surround the pin.
Advantages of self-threading pins:-
Versatility
Wide range of pin sizes
Color coding system of thread mate system
Ease of insertion
Maximum retention offered
Gold plated surface finish, which may eliminate the possibility of
corrosion.
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Disadvantages of self-threading pins:-
Excessive stresses in the form of cracks or craze lines are generated in the
surrounding enamel and dentin, especially with large seized pins.
Pins may need to bent, cut or contoured after insertion, which may place
extra stresses or the tooth may loosen the pin.
When the pin is forced into the channel it may strip the sides of the dentin
resulting in a loose fit.
Pin may fail to seat completely.
Micro leakage is higher than the cemented pins if the overlying restoration
leaks.
Different pin designs of threaded pins:-
For each of the four sizes of pins several designs are available: Standard,
self-shearing, two-in-one, link series and link plus.
The link series and link plus pins are recommended.
a) Standard:- It is approximately 7mm long with the flattened head to engage the
hard wrench or the appropriate hand piece chuck and is threaded to place until
it reaches the bottom of pinhole as judged by tactile sense.
Advantage of standard design: it can be reversed one-quarter to one half turn
following insertion to full depth to reduce stress created at the apical end of the
pinhole.
b) Self-shearing pin:- It has a total length that varies according to the diameter of
the pin. It also consists of flattened head to engage the hand wrench or the
appropriate hand piece chuck for threading into the pin hole. When the pin
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approaches the bottom of the pinhole, the head of the pin shears off, leaving a
length of the extending from the dentin. Shearing occurs when there is marked
resistance to turning i.e. pin insertion is torque limited.
c) Two-in-one pin:- It has actually two pins in one i.e. the two pins are connected
to each other at a joint. The joint act as the shear time for the two pins. The
joint act as the shear time for the two pins. The two-in-one pin is
approximately 9.5 mm in length. It has also flattened end that engages the
wrench or the chuck of the hand piece that aids in threading it to the pinhole.
Out of the two pins which is released first is known as pin A or peripheral pin
whereas the one which is released second is called Pin B or wrench attachment
pin.
When the pin reaches the bottom of the pin hole the pin shear approximately in
half, leaving a length of the in extending form the dentin, with the other half
remaining in the hand wrench or hand piece chuck. This second pin may be
then positioned in another pinhole and threaded to place in the same manner as
the standard pin.
Advantage of two-in-one design is that hand piece need not to be reloaded
during two pin insertions.
d) Link Series:-
Link series pin contained in a color coded plastic sleeve that fits to the latch
type contra angle hand piece or specially designed hand wrench. The pin is free
floating in the plastic sleeve to allow it to align it self as ti is threaded into the
pinhole.
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When the pin reaches the bottom of the hole, the top portion of the pin
shears off leaving a length of the pin extending from the dentin. The plastic sleeve
is then discarded. The minuta, minikin are minimum and regular pin are available
in the link series.
Advantage:- The link series pins are versatile,
- Self-aligning ability
- Retentiveness
e) Link Plus Pins:-
Are self shearing and are available as a single or two in one pin contained
in a color coded plastic sleeve. The design has a sharper thread, a shoulder stop at
2mm and tapered tip to more readily fit the bottom of the pinhole as prepared by
twist drill.
It also provides 2.7 mm length of pin to extend out of the dentin which
usually needs shortening. Minimum sizes are available in these. Theoretically and
as suggested by Standlee these innovations should reduce the stress created in the
surrounding dentin as the pin is inserted an reduce the apical stress at the bottom
of pin hole.
L or T-shaped threaded pins:-
Mattos (1973) introduced these pins to overcome the need for bending after
their placement. The L and T shaped threaded pins are well suited for class IV
prepared as it devoids the need for second pin at the incisal third.
Pin Materials:
Materials used for construction of pins which include stainless steel,