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,

titanium, stainless steel with gold plating, silver, cast gold alloys, platinum-

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palladium, platinum iridium, plastic aluminium, acrylic, composite resin. Stainless

steel, titanium and silver pins are commonly used for the direct or non-parallel pin

techniques.

Stainless steel pins or stainless steel pins coated with gold are most

frequently used. Stainless steel are stronger than its Titanium and gold

counterparts but has disadvantage of getting corroded and non-adherence to silver

amalgam and composite restorative material.

Titanium pins have the advantage of non-corrosive and most biocompatible

of all metals but their strength and modulus of elasticity is less compared to that of

stainless steel. Also titanium pins show no adherence to the amalgam and

composite restorations.

Silver pins have excellent bond with the silver amalgam restorative material

as shown by Moffa et al. (1975), but solid silver pins are soft and easily deformed.

Pins constructed in cast gold, platinum-palladium or platinum iridium are

used with indirect/ parallel pin technique. These pins are relatively corrosion

resistant.

Plastic pins are used in the indirect parallel pin technique but not to serve as

a part of the final restoration. They are meant for taking impressions of the

pinholes for fabricating a cast gold alloy restoration.

Aluminium pin are used for manufacturing a temporary restoration until the

final restoration is fabricated and inserted.

Acrylic pins and composite resin pins have been tried for use with

composite restoration for anterior restoration due to esthetic purposes.

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Devices for Pin Insertion:

The pins can be inserted into the dentin in various ways.

1) Hand wrench:

Hand wrench which provides tactile sense during the threading of the pin

into the dentin. Different designs of hand wrenches available for the different

TMS pins.

If the hand wrench is used without rubber dam isolation, a gauze throat

shield must be placed in the place and strand of dental tape approximately 12 to 15

inches (30 to 38 cm) in length should be securely tied to the end of wrench. This

will prevent the accidental swallowing or aspiration of the wrench. Hand wrench

are mainly recommended for the insertion of the standard pins.

A standard design pin placed in the hand wrench and slowly threaded

clockwise till definite resistance is felt when the pin reaches the bottom of the

pinholes. The pin than should be rotated counterclockwise ¼ to ½ turn to reduce

the dentinal stresses.

In most instances tactile sense is advantageous in seating pins. This means

screwing of the pin into position is best done with fingers than by motorized hand

piece.

b) Conventional latch type contra-angle hand piece:-

This is mainly recommended for the insertion of link series and link plus

series. A 10 : 1 reduction gear contra angle hand piece is available to insert the

pins. During the insertion of the pins the low speed hand piece is with low gear

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increases the torque and increases the tactile sense of the operator. It also reduces

the risk of stripping the threads in the dentin once the pin is in place.

c) Acrylic wrench:-

The acrylic wrench can be fabricated by quick-curing acrylic. Using a metal

bur shank a ball of the acrylic about the size of the pea is molded over the end.

After curing it can be removed and can be used as a in wrench to screw the pin in

and out of the pin hole.

d) Cable drive pin setter:

For pin placement in posterior areas that are inaccessible, the cable drive in

setter is quite effective. It provides essential tactile sense. The knob is twisted

forward and backward to screw the pin into or to back it out of the pin hole.

The Twist Drill:

Success with the pin technique requires a working knowledge of three

things: the dull, the pin and the dentin.

Pin holes are prepared using a device called ‘twist drills’. This is an end

cutting, revolving instrument with two blades bibeveled in longitudinal section at

precisely the same distance from the tool’s center.

As one compares its shape to that of dental bur, a marked difference is

apparent. The twist dull cuts only on the end, a dental bur which is a router, cuts

on the sides as well.

The two cutting blades of the drill tip are sloped so that they will cut only

when the drill is turning a clockwise direction. The sides of the drill are helix

fluted allowing the escape of debris formed during end cutting.

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Twist drills may be either made one piece or two piece. One piece twist

drills is made of steel, is less expensive and more likely to fracture. Two piece

drill is made of steel that is swaged onto an aluminium shank, is more expensive

stronger and less likely to fracture.

The aluminum shank, which act as the heat absorber, is color coded so that

it can be easily matched with appropriate pin size.

The drill is always made of steel, not carbide so that there can be some

slight plasticity in the drill substance. Carbide is not used for construction of the

drill as they are brittle.

For cutting the dentin the right one is preferred because flutes are less likely

to become clogged with dentin, the one on the left is designed for cutting metal

and to withstand strong torquing forces, which are not encountered when cutting

dentin.

Two type:-

A) Kodex twist drills

a. Standard

b. Depth enlarged

Rules for using the twist drills:

1) It should be used at ultra low speed (300-500 rpm) because coolant cannot be

used at such depths of dentin engagement. Also some tactile feeling is needed

during cutting. Time is also needed to allow debris to travel out of the channel.

2) Be sure the drill is sharp.

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3) It should be used in direct cutting acts, with force applied parallel to the long

axis of the drill, lateral cutting acts widen the pin channel and lead to drill

fractures.

4) The drill should be revolving while inserting or withdrawing the drill from the

pin channel otherwise lead to drill or tooth structure fracture.

5) Do not use pumping strokes (several up and down strokes). This will widen the

pin channel more than is required.

6) Never use to drill in enamel. These drills will not cut enamel and will be drilled

even fracture by it.

The four basic designs of twist drills are:-

1) Regular twist drill:- They have their cutting part about 4mm or more in length

without limiting shoulder/ stop.

2) Limited depth twisted drill:- They have their cutting part of about 2mm in

length with the limiting shoulder / stop. The limiting shoulder are either

preferred or adjustable.

3) Miniature twist drills:- They are same as regular or limited depth type but their

cutting blade length is smaller i.e. 17mm.

4) Twist drills with parallelometer attachment:- These are regular or limited type

of drills designed to function with the paralleling instrument. They have

narrow shanks that penetrate freely in the bur sleeve of the hand piece and a

sleeve to fit in the parallelometer.

The drill shanks for the link series and link plus pins are tapered to provide

a built in “Wobble” when placed in a latch type contra angle hand piece. This

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wobble allows the drill to be “free-floating” and thus to align itself as pinhole is

prepared to minimize dentinal crazing or breakage of small drills.

Because the optimal depth of the pinhole into the dentin is 2mm (only

1.5mm for minikin pin), a depth limiting drill should be used to prepare the hole.

The pinhole to the correct depth can only be prepared when the drill prepare

or hole on flat surface that is perpendicular to the drill.

Thus drilling of the pin hole should be done against the flat surface.

Drilling against a sloping surface makes calculation of pinhole depth difficult.

Also to restricts the placement of a deeper hole depth-limiting shoulder on

the drills should be given. Omni-depth gauze can also be used to measure the

depth of the hole.

Sharpening of twist drills:

Dull drills used to prepare pinholes can cause increased frictional heat and

cracks in the dentin. Studies have demonstrated that twist drills becomes too dull

for use after cutting 20 pinholes or less and signal for discarding is the need for

increased pressure on the hand piece.

Use of a drill whose self limiting shank shoulder has become rounded is

contraindicated.

Sharpening a dental twist drill is accomplished by making the drill slightly

shorter in all respects so that the leading edges are again longer. Sharpening must

be done with the help of carborundrum disk mounted on a straight hand piece.

Each carborundrum disk has a coarse and a smooth side. The smooth side should

face the hand piece.

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Additional tilting is then done so the disk slopes away fro the cutting edge.

Principles of pin placement:

The placement of pins whether any size and shape utilizing any technique

should follow certain principles for the success of the restoration. The principles

are as follows:

1) Pin size: Diameter:- The selection for the diameter of pin depends upon.

a) Amount of the dentin available to safely receive the pin.

b) Size of concerned tooth.

c) Amount of retention desired

It is difficult is specify a particular size of pin that is appropriate for the

particular tooth. Increasing in the diameter of the pin offers increased retention,

but large sized pins are also associated with the heavy concentration of stress in

dentin.

In thread mate system pins for choice for severely involved posterior teeth

are – manikin (0.019 inch) and occasionally minim (0.024 inch).

Minikin is selected to reduce the risk of the dentin crazing pulpal penetration and

potential perforation.

Minim pin are used as a backup in cases where the pinhole for the manikin

was over prepared or pin threads stripped the dentin and manikin pin lack

retention.

Studies have shown that larger diameter pins have greater retention. Pins

shows ½ retention than minim and 1/3rd as retentive as manikin pin.

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Either minim or minikin can be used in a given tooth depending on the

dentin available in the area where the pins are to be inserted. The regular 0.031”

(0.78mm) are rarely used because of the significant amount of crazing, cracking in

the tooth during the insertion.

2) Number of pins:-

Several factors must be considered when deciding how many pins are

required.

1) the amount of missing tooth structure

2) the amount of dentin available to receive pin safely

3) the size of the pins

As a rule, one pin per missing axial line angle should be used. Certain

factors may cause the operator to alter this rule.

When only 2 to 3 mm of the occlusogingival height of a cusp has been

removed, no pin is required because enough tooth structure remains to use

conventional retention features.

Increasing the number of pins increases the chances of increased stresses,

pulpal damage and or perforation. Hence aim should be maximum retention with

minimum number of pins. The fewest pins possible should be used to achieve the

desired retention for a given restoration.

3) Pin length:-

The ideal ratio of the dentinal engagement pin protrusion is 2:1. although a

ratio of 1 : 1 is tolerable. A lower ratio will make the dentinal portion of the pin

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the short side of a type of a level. This causes the movement of the cavity end of

the pin during the loading of the restoration.

The ratio also varies with the different types of pin for cemented it is 3mm

and 2mm for friction locked pins it is 3mm and 3mm for threaded pins it is 2mm

and 2mm. preferably the length of the pin inside the dentin and in the cavity

should be equal.

4) Pin orientation:-

Pin should be oriented parallel to the long axis of the tooth. However in

excessively cervically placed areas towards the cemento-enamel junction where

sharp constructions are likely to present and dentin thickness is reduced, it is

mandatory to direct the pin parallel to the closest external surface of the tooth then

bend it slightly as needed.

This will prevent the perforation and the external surface or the penetration

of the pulp. To determine the abnormal contours place a probe adjacent to the

surface close to the intended location and examine its direction.

5) Inter pin distance:-

Spacing between the pins or the interpin distance must be considered when

two or more pinholes are prepared. The distance between the two pins should

allow space for insertion of restorative material and should prevent the excessive

concentration of residual stresses in dentin.

The optimal interpin distance depends on the type and size of the pin used.

The minimal interpin distance for cemented pin is 2mm for friction locked pin is

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4mm and for manikin (0.010 inch) threaded pins is 3mm and for minim threaded

(0.024 inch) pin is 5mm.

Pin location:

Several factors aid in determining pinhole location.

1) Knowledge of normal pulp anatomy and external tooth contours.

2) Current radiograph of the tooth

3) Periodontal condition

4) Patients age with aging the size of the pulp chamber reduces and increase in

the dentin dimension.

Consideration also must be given to the placement of pins in areas where

the greatest bulk of amalgam will occur to minimize the weakening effect of the

pins to the tooth structure.

Area of the occlusal contacts must be anticipated because a pin oriented

vertically and positioned directly below an occlusal load weakens the amalgam

significantly. Occlusal clearance should be sufficient to provide 2mm of amalgam

over the pin.

5) Cavity extent:- The more apically located that a gingival floor is, the higher

will be the possibility of surface and pulp root canal perforation in trying to

prepare a pin channel. This is due to decrease in dentin bulk, root surface

concavities and grooves and taper of the tooth as one proceeds apically.

6) Tooth alignment:- Malalignment of the teeth in the form of rotation,

inclination etc. necessitates individual evaluation of tooth involved to

determine the best access, location and angulation of pin channel.

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MECHANO-ANATOMICAL PRINCIPLES OF PIN PLACEMENT:

A) Maxillary central incisor:

The tooth has four pulp horns. Three in M-D direction and one labio-

lingual direction (cingulum). The cingulum pulp horn is most pronounced. The

lateral horns are close to the incisal angles and whole pulp chamber is lingually

deviated.

In cross section cervical margin there is an average of 1.5 – 1.8mm of

dentin circumferentially gignivally with more dentin labially than lingually.

Pin Location:

Ideal location:- Close to proximo labial and proximolingual corners.

Second choice:- Middle of proximal gingival floor or middle of labial gingival

floor.

Third choice:- Incisal where there is at least 2mm or more of dentin between labial

and lingual enamel.

Areas avoided:- Middle of lingual gingival floor. Incisal when the dentin between

the labial and lingual enamel plates is not bulky enough to stand pin insertion

without possible failure. Incisal near the proximal horn.

Pin angulation:-

Proximal and labial pins always should have slight labial angulation in

labio-lingual direction. In mesiodistal direction they have a very limited

angulatiion of about 10-20% with the longitudinal axis of the tooth.

26

B) Maxillary lateral incisors:

Same general anatomy of the pulp horn and chamber as central incisors.

Circumferentially gingivally at the cervical line an average of 1.2 – 1.5mm of

dentinal thickness is there.

Pin location:-

Ideal location and second choice is same as that of the central incisors.

Areas avoided:- The areas to be avoided are the middle of lingual gingival floor

and incisally.

Pin angulation:-

- Pin should be labially directed in labiolingual direction.

- In mesiodirection gingival pins should have more angulation (15-20%) with

the longitudinal axis of the tooth.

C) Maxillary Cuspid:

The pulp chamber has only two pronounced surface wise projections,

incisally and middle of the tooth and lignually (cingulum). The pulp chamber is

lingually deviated. At cervical line in cross section, on the average there is from

2.5 – 3.5mm of dentin circumferentially gingivally. There is more dentin labially

than lingually.

Pin location:-

The tooth ranks second only to the upper first molar in freedom of pin

insertion.

Ideal location choice is at or close to facio-linguo proximal corner.

Second choice:- Middle of proximal gingival floor. Middle of labial gingival floor.

27

Third choice:- Close to incisal angle

Areas to be avoided:- Middle of lingual gingival floor, gingival pins close to

surface concavities or grooves which can occur proximally.

Pin angulation:-

- Gingival pins proximally and labially should have slight labial angulation in

labiolingual direction.

- All gingival pins should form an angle with long axis of the tooth in

mesiodistal direction, coinciding with the taper of the root. This angle can be

between 20 - 35.

- Incisal pins should be parallel to the adjacent proximal slope of the tooth in the

mesiodistal direction, coinciding with the taper of the root.

D) Maxillary First Bicuspid:

- The pulp chamber is narrower mesiodistally than buccolingually.

- Mesial distal walls of pulp chamber are flat and buccal and lingual walls are

concave from inside.

- Two pulp horns are there of which buccal is pronounced.

- Always there is a pronounced concavity on the mesial surface of the tooth

(canine fossa).

- Circumferentially gingivally at he cervical line an average of 2mm of dentin

buccally and lingually, 1mm mesially and 1.5mm distally. There is more dentin

lingually than buccally.

Pin location:-

Ideal location:- Close to proximofacial and lingual corners of the tooth gingivally.

28

Second choice:- Between the corners and the middle of axial surfaces with the

exception of the mesial surface.

Areas to be avoided:- Mesial gingival floor (canine fossa). Middle of the gingival

floors buccally and lingually (because of concavity of the pulp chamber especially

buccally). Gingival floor occlusal to furcation.

Pin angulation:-

All gingival pins should be angulated to the longitudinal axis.

E) Maxillary second premolar:

The tooth resembles the first premolar in its pulp anatomy with more dentin

circumferentially gingivally (on the average mesially and distally 1.5mm, buccally

and lingually 2.5mm).

There is no mesial surface concavity. There is more dentin thickness

lingually than buccally.

Pin location:-

There is more freedom in using pins in 2mm bicuspid than first bicuspid.

Ideal location:- Same as that of first premolars.

Second choice:- Gingival floor between the corner and their middle proximally,

facially and lingually.

Areas to be avoided:-

Middle of gingival floor facially and lingually (concavity of the pulp

chamber). Areas of gingival floor occlusal to the furcation.

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F) Maxillary First Molar:

The whole pulp chamber on the upper first molar is mesiobuccally

deviated. Four pulp horns, the mesiobuccal is one of the most pronounced. Walls

of pulp chamber is almost convex inwardly. Circumferentially gingivally at the

cervical line, the dentin measures an average of 2-2.5 mm mesially and distally

and 2.5 – 3.5mm buccally and lingually.

There is more dentin distally i.e. distolingually and less dentin mesially i.e.

mesio-buccally. There are three furcations: one is located buccally and each of the

other two are located proximally.

The proximal furcations are deviated lingually and inwardly. The closed

furcation to the surface is buccal followed by distal and followed by mesial which

is deepest apically and inwardly.

Pin location:-

Ideal location:- Gingival floor at or close to distolingual corner.

Second choice:- Distobuccal or the mesiolingual corners of the tooth.

Third choice:- Gingival floor lingually, mesially and distally. At this point the

furcation and isthmus portion of the future restoration should be taken care.

Areas to be avoided:-

- Corners of the tooth

- Any part of the gingival floor occlusal to the furcation (facially and

proximally) its flutes, or a root concavity and mesiobuccal to the cusp tips.

Pin angulation:-

Gingival pin facially and lingually should be approximately parallel to the

occlusal 2/3rd of the lingual surface.

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Gingival pins mesially and distally should be parallel to the longitudinal

axis of the tooth.

G) Maxillary second molar:

The tooth is very similar to the first molar in all respects except there may

be less dentin circumferentially gingivally and the pulp horn is less pronounced.

H) Maxillary third molar:

This is the youngest upper tooth and unfortunately, there are numerous

varieties in its morphology and pulp anatomy.

If quadric-tubercular, it can be similar to the first molar.

If tritubercular the anatomy is very peculiar for each tooth.

Generally speaking pulp chamber can be expected to be more occlusally

located and its walls can be expected to coverage more toward the cervical line.

There is always distobuccal inclination of the tooth causing more chances

of buccal distal surface perforation as well as mesial and lingual pulpal

perforations.

To say the upper 3rd molars are the poor candidates for pin retained

restorations.

A) Mandibular Central Incisor:

This tooth has peculiar pulp chamber which is wider mesio-distally at its

incisal half than labiolingually, yet its cervical half is under mesiodistally than

labiolingually.

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There are three pulp horns: two in mesiodistal direction and one in lingual

direction. Circumferentially gingivally in a cross-section one on average there is

0.8 – 1.7 mm thick dentin. There is more dentin labially than proximally and

lingually.

Pin location:-

Ideal location:- No ideal location in this tooth. In fact the pins should be avoided

as the retentive feature for restorations in thin tooth. Pins may be used at the

gingival floor proximally in tooth where the pulp has receded appreciably.

Second choice:- Proximolabial and proximolingual corners.

Third choice:- Gingival middle of proximal and labial surface.

Areas to be avoided:-

Gingivally lingual surface incisal.

Pin angulation:-

All gingival pin should be angulated slightly labially in labiolingual

direction.

Mesiodistally to prevent perforation of the root surface or involving the

mesiodistal widening of pulp chamber in incisal half, pins could have angulation

and the 30-40 to the longitudinal axis of the tooth in the mesiodistal direction.

B) Mandibular lateral incisors:-

The morphology and pulp chamber anatomy of this tooth are very similar to

those of central incisors. The tooth and pulp chamber are more fan-shaped inciso-

apically.

Circumferentially gingivally in cross-section the tooth has an average and

1-2 mm dentin.

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Pin location:-

Pin should be located exactly at the central incisors.

With similar advise not to use pins except in aged patients.

Pin angulation:-

The tooth is similar to the central incisors, except in the mesiodistal

direction, the angulation relative to the long axis of the tooth could be 50 to avoid

perforation and encroachment.

C) Mandibular cuspid:

Surface, pulp chamber and root canal anatomy are very similar to those

features of upper cuspid. Aside from the fact that pulp chamber is slightly

compared mesio-distally, the pulp horns are little bit blunt in this tooth and there is

a distant possibility of two root canals.

Circumferentially gingivally, the average amount of dentin in cross-section

is 2 – 2.3mm with more dentin labially than mesially, lingually and distally.

Pin location:-

Similar to upper cuspid

Ideal choice:- Proximolabial and proximolingual corner of gingival floor.

Second choice:- Gingival middle of the facial floor mesial and distal surfaces.

Third choice:- Incisal

Areas to be avoided:-

Gingival lingual surface (as the dentinal thickness is very less).

Pin angulation:-

Similar to upper cuspid

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D) Mandibular First Bicuspid:

- Most predictable pulp chamber and root canal anatomy

- Pronounced buccal pulp with the blunt lingual pulp.

- Pulp chamber is in shape cervically

- Pulp chamber is wider bucco-lingually than mesiodistally

- Circumferentially gingivally the average thickness at the cervical line is 2 –

2.5mm.

- There is more dentin buccally and lingually than mesially and distally.

Pin location:-

Ideal location:- Proximolabial and proximolingual corners of the gingival surface.

Second choice:- Gingival floor between the mesial and distal corners and their

centers.

Third choice:- Anywhere between the two distal or mesial corners avoiding the

isthmus part of one restoration.

Areas to be avoided:-

Middle of the gingival floor, buccally and lingually.

Pin angulation:- Should be always parallel to the long axis of the tooth.

D) Mandibular second premolar:

If this is a bicuspid then its anatomy is similar to the first premolar with the

exception that it always has lingual pulp and pulp chamber is more rounded. If it is

tricuspid premolar – pulp chamber will be mesiobuccally deviated and it has three

pulp horns.

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Circumferentially gingivally the average thickness of dentin at the CEJ is 2-

3mm buccally and lingually, 2.3 – 2.6mm mesially and distally.

Pin location:-

In a bicuspid premolar pin location is exactly like first molar.

In tricuspid premolar

Ideal location:- Distolingual corner of the gingival floor.

Second choice:- Other corners of the gingival floor except the mesiobuccal one.

Third choice:- Mesiobuccal corner and in between the four corners except the

areas which are to be avoided.

Areas to be avoided:- Area under the lingual groove. Middle of buccal gingival

floor (maximum concavity of the pulp chamber and pulp horn).

Pin angulation:-

If bicuspid then the pin angulation is similar to that of the first premolar.

If tricuspid it should be similar to the first lower premolar.

E) Mandibular First Molar:

The tooth has usually five pulp horns: the mesiobuccal being the most

pronounced and closest to the surface. The whole pulp chamber is mesiobuccally

deviated with more dentin distally, especially distolingually with more dentin. The

floor of the pulp chamber is smaller than its roof.

The side walls of pulp chambers are flat to concave inwardly.

Circumferentially gingivally, the average thickness of dentin is 2-3mm at the

cervical line.

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Pin locations:-

Ideal choice:- Distolingual corner of gingival floor

2nd choice:- Distobuccal and mesiolingual corner of gingival floor.

3rd choice:- Gingival floor mesially or distally avoided the isthmus portion of

future restoration.

Areas to be avoided:- Mesiobuccal corner of the gingival floor (furcation) and

mesiobuccal to any cusp tip (pulp horn).

Pin angulation:-

Mesially and distally, gingival pins should be parallel to the long axis of the

tooth. Buccally and lingually, gingival pin should be approximately parallel to the

occlusal 2/3rd of buccal surface.

F) Mandibular Second Molar:

The tooth is very similar to first molar, except that the pulp chamber has

four pulp horns only, and less surrounding dentin bulk.

G) Mandibular Third Molar:

As in the upper third molars, there is infinite anatomical variations in these

teeth. They can have some similarities to first molar if they have five cusp and to

second molar if they have four cusp. There is a great tendency of the mesiolingual

angulation of tooth as a whole, which increases the probability of mesial and

lingual surface perforation together with distal and buccal pulpal perforation.

Whatever approach is used, it should be executed very cautiously, with an

understanding that pins are the last resort for retaining restorations in these teeth

because of unpredictability of their anatomy.

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Several attempts have been made to identify the ideal location of the

pinhole. Caputo and Sandlee state that ideal pinhole position is half way between

the pulp and the DEJ or external surface of the tooth root.

Standlee and others have shown that there should be about at least 1mm of

the dentin around the circumference of the pinhole. Such locations ensure the

proper stress distribution of occlusal forces.

Felton associates have demonstrated that pin placement providing at least

1mm of remaining dentin thickness from the pulp elicits minimal pulpal

inflammatory responses.

Delts and associates have reported the pinholes should be placed at 0.5mm

inside the DEJ.

As a rule: In the cervical 1/3rd of molar and premolars (where most pins are

located) pinholes should be placed near the line angles of the tooth. At line angles

dentinal thickness is the maximum. The pin hole should be positioned no closer

than 0.5 to 1.0mm to DEJ or no closer than 1 to 1.5mm to the external surface of

the tooth, whichever distance is greater.

As a rule pinhole should be parallel to the adjacent external surface of the

tooth. The position of a pinhole must not result in the in being close to vertical

wall of tooth structure that condensation of amalgam against the pin or wall is

jeopardize. Therefore it is necessary to prepare on a recess in the vertical wall with

no.245 bur to permit proper pin hole preparation as well as to provide a minimum

of 0.5mm clearance around the circumference of the pin for adequate condensation

of the amalgam.

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The distance between the axial wall/ vertical wall and the pin should be

such that it should provide sufficient space for the smallest condenser to ensure

that amalgam can be condensed adequately around the pin.

Pinhole should be prepared on a flat surface that is perpendicular to the

proposed direction of the pinhole. Otherwise the drill tip may slip or crawl.

Whenever three or more holes are present they should be located at

different vertical levels on the tooth if possible. This will reduce the stresses

resulting from pin placement in the same horizontal plane of the tooth.

When the pinhole locations have been determined, a no ¼ bur is first used

to prepare a pilot hole (dimple) approximately one half the diameter of the bur at

each location. The purpose of this hole is to permit more accurate placement of the

twist drill and to prevent the drill from “crawling” once it has begum to rotate.

PINHOLE PREPARATION/ CHANNEL PREPARATION:

1) A rubber dam should be placed when pin channels are prepared to protect the

patient from accidental aspiration of pin and to prevent contamination by

saliva in case there is pulpal perforation.

2) The tips of drills tend to move when the rotating tip placed against dentin, it is

usually helpful to place an indentation or starting point in the dentin at the

desired location for the initiation of pin channel.

3) The pilot point may be placed with a small bur such as no. ¼ or no. 1/8 bur.

4) Appropriate twist drill is selected mainly the depth limiting drill with shoulder

is selected.

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5) To avoid perforation of the pulp and the external pulp on surface the location

of pin channel is critical.

6) The channel should be usually parallel to the nearest external tooth surface.

7) With the drill in the latch type contrangle hand piece place the drill in gingival

crevice beside the location of the pin hole.

8) Position it until it lies against the external surface of the tooth. For alignment,

the twist drill is placed against the external tooth surface and the angulation of

this is changed until the drill separates from the margin of the preparation. It is

then rotated back until it just contacts the margins.

9) Without changing the angulation obtained from the crevice position, more the

hand piece occlusally and place the drill in the previously prepared pinhole.

10) Now view the drill from 90 angle to the previous viewing position to

ascertain that the drill is correctly angled in this plane.

11) Should the proximity of an adjacent tooth interfere with the placement of the

drill into the gingival crevice, place a flat, thin bladed hand instrument into the

crevice and against the external surface of the tooth to indicate the proper

angulation for the drill.

12) With the drill tip in its proper position and with the hand piece rotating at very

low speed (300 to 500 rpm) apply the apically directed pressure to the drill

and prepare a pinhole in one or two thrusts until depth-limiting position of the

drill is reached.

13) Using more than two movements, tilting the hand piece during the drilling

procedure, or allowing the drill to rotate more than very briefly at the bottom

of pinhole will result in pinhole that is too large.

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14) Although not usually recommended the air of stream is used to dissipate the

heat of the drill.

15) The drill should never stop rotating (from insertion to removal from the

pinhole) to prevent the drill from breaking while in the pinhole.

Certain clinical locations require extra care in determining pinhole

angulation:-

The distal of mandibular molar and lingual of maxillary molar. They are

area of problem due to abrupt flaring of root just apical to the CEJ.

Mandibular posterior teeth (with their lingual tilt), teeth that are rotated in

the arch, and teeth that are abnormally tilted in arch deserve careful attention.

For mandibular second molar with mesial tilt, the extra caution should be

taken to prevent the external perforation on the mesial surface and pulpal

penetration on the distal surface.

Pin Insertion:

A) Cemented pin technique:-

Indications:-

This technique is ideal for all pin retained restorations as it creates the least

crazing and stresses in remaining tooth enamel and dentin.

It is only technique used for the endodontically treated teeth.

It is used when the available location for the pin is very close to DEJ.

It is only technique to be used for U and L shaped pins in class IV

restorations and foundations.

It is used when the bulk of dentin to accommodate a pin is limited.

40

It is ideal technique for a sclerosed, tertiary, calcific barrier or any other

highly mineralized or dehydrated dentin.

Technique for cross linkage of two parts of same tooth.

Procedure:-

The procedure was advocated by Dr. Markley with subsequent

modifications.

Prepare the pin channel as mentioned

If the area of the pin channel is easily and readily accessible, cut a piece of

wire to the designated length using a wire cutter or preferably a dial-a-pin

cutter.

Slightly round the end of the pin with the carborundum disk if they are not

smooth.

Place pins in the tooth and evaluate need for bending

Hold pin with tooth pair of pliers and blend if necessary.

Allow setting zinc phosphate cement, polycarboxylate cement in case of

endodontically treated teeth, copper phosphate cement is mixed and

introduced slightly in the pin channels using a root canal perio-explorer tip

or lentulo spiral at low speed.

Using a haemostat, or a magnetized forcep / tweezer, the pin is held firmly

at its cavity end, dipping the pin channel end into the cement and seating it

firmly into the pin channel.

A large amalgam plugger is required for the complete seating of the pin.

41

If the pin with same diameter as the pin channel is used as advocated by

Courtade, the same procedure is followed except that a lateral facet is

placed on the side of the pin using a carborundum disc to create a escape

way for cement during cementation and reduce friction during seating into

pin channel.

In case of class IV restoration foundation, where it may be necessary to

bend pins to confirm with the incisal angles, bending should be done prior

to cementation. Bending a pin while it is in the tooth will loosen the cement

joint and it may stresses the surrounding dentin beyond recovery.

B) Friction grip pin technique:

Indications:-

Used in vital teeth only

Very bulky dentin should be available to encompass the pin (at least 4mm

in three dimensions)

Pin should be located at least 2.5mm from the DEJ

Use only inaccessible areas of the mouth, so the sealing force will be

parallel to the pin axis.

Procedure:-

Pin channel is prepared to the designated depth.

A counter sink is prepared at the pin orifice to the depth 0.5mm using a 168

bur.

The correct length of the bur is then cut from the supplied wire or precut

pins using cutting pliers or carborundum disk. Both the ends are squared up

and smoothed.

42

The pins are held by haemostat or magnetized tweezer or lockup tweezer at

its cavity end.

Put a mark on the pin with color marker to show the exact depth of the pin

channel as prepared.

The pin is then seated at the pin channel orifice.

While the pin being held there, a specially made seater with concave head

is firmly applied on pin head, being sure that its axis is parallel to that of

the pin in three dimensions.

With the hammer, apply light strokes to the seater, parallel to its

longitudinal axis, until the established mark on the pin comes to cavity

floor.

Check the cavity floor, walls and surrounding tooth surface for any cracks

chipped piece, or grass fractures.

THREADED PIN TECHNIQUE:

Indications:

It is used for vital teeth

Dentin engage the pin is primary or secondary dentin properly hydrated

Available pin location is at least 1.5mm from DEJ

Maximum retention of pin to dentin and restoration is needed for one

reason or another.

43

Procedure:-

Two instruments are available for insertion of threaded pins – 1)

conventional latch-type contrangle hand piece and 2) TMS hand wrench.

The conventional latch type hand piece is recommended for the insertion of

link series and link plus pins. The hand wrench is recommended for

insertion of standard pins.

When using the latch type hand piece, insert a link series or a link plus into

the hand piece and place it in pin hole. Activate the hand piece in the slow

speed until the plastic sleeve shears from the pin. Then remove the pin and

discard it.

For low speed hand piece, low gear is used. Low gear increases the torque

and increases the tactile sensation. It also reduces the stripping the threads

in the dentin once the pin is in place.

A standard design is placed in the appropriate wrench and slowly threaded

clockwise into the pinhole until a definite resistance is felt. When the pin

reaches the bottom of the hole. The pin should then be rotated one quarter

or half turn counterclockwise to reduce the dentinal stresses at the end of

the pin pressing the dentin.

If the hand wrench is used without rubber dam, a gauze throat shield is

placed and a strand of dental tape approximately 12 to 15 inch (30 to 50cm)

in length should be securely tied to the end of the wrench. This will reduce

the chances of accidental swallowing or aspiration of the hand wrench.

Once the pins are placed their length is evaluated. Any length of pin greater

than 2mm should be removed. Also it is desirable to have at least 2mm

44

thickness of amalgam occlusal to the end of pin to prevent unnecessary

weakening of the restoration.

To remove excess length of the pin use a sharp No. 1/4, ½ or 196L bur at

high speed and oriented perpendicular to the pin. If oriented otherwise, the

rotation of the bur may loosen the pin by rotating it counterclockwise.

During the removal of the excess pin the assistant should constantly apply a

steady stream of air and have a evacuator tip positioned to remove the pin

segment. Also during the removal of the pin stabilize the pin with the

hemostat or cotton pliers.

Using a mirror determine if any pin need to be bent to position them with

the anticipated contour of the final restoration and to provide adequate bulk

of amalgam between the pin and external surface.

Pins are not to be bent to make them parallel or to increase their

retentiveness. Bending a pin may be necessary to allow for condensation of

amalgam occlusogingival.

When pin require bending TMS bending tool must be used. The bending

tool should be placed on the pin where the pin is to be bent, and firm

controlled pressure, the bending tool should be rotated until the desired

amount of bend is achieved.

Use of the bending tool allows placement of the fulcrum at the same point

along the length of the exposed pin. A hand instrument such as Black spoon

excavator should not be used to bend pin because the location of the

fulcrum will be at the orifice of the pin hole.

45

These hand instruments may cause crazing or fracture of the dentin and the

abrupt or sharp bend that usually result, increase the chance of breaking the

pin. Also the operator has less control when pressure is applied with hand

instrument, and chance of slipping is increased.

A slotted discoid / cleoid, or large excavator which are prepared with the

help of corborundum disk can be used for the bending of pins.

FACTORS AFFECTING RETENTION OF PIN IN DENTIN:

Retention of pins in dentin indicated by the following factors:-

1) Type of pins:- Provided pins are of equal diameter and depth of dentinal

engagement, self threading pins will be 5-6 times more retentive than cemented

pins. Friction grip pin will be 2-3 times relative than cemented pins.

2) Depth of pin engagement in dentin:- According to Moffa a graph is plotted

between the depth of the dentinal engagement in dentin and tensile forces

needed to create a failure at the pin-cement-dentin complex.

a. For cemented pins:- A linear relationship without a plateau exists.

Failure occurs at cement dentin junction.

b. For friction grip: No increase in resistance to failure after 2 mm of

dentinal engagement. Failure occurs at pin dentin interface.

c. For small threaded pins: There is no resistance to failure after 2mm of

the dentinal engagement. Failure occur within pin themselves.

d. For large threaded pins:- A plateau occurs after the 1.5 – 2.0 m of

dentinal engagement. The failure occurs usually in dentin itself.

46

3) Pin channel circumferential shape relative to that of pin:- It stands to a reason

that the greater the no difference of these two shapes is, the better will be the

retention. The ideal arrangement can be obtained by truly centrically rotating

drill that will provide a rounded pin channel circumference to accommodate a

pin with a circular cross section. This will make for continuous contact

between the pin and dentin thereby increasing the frictional retention.

4) Number of pins:- Pin proximity and location relative to displacing forces

affects the retention. The number of the pins per tooth don’t much affects the

retention. Pins placed closer than 2mm to each other in one tooth will result in

loss of pin retention in dentin. This may be caused by micro cracks occurring

during placement of pins, which then become continuous with each other prior

to or as a result of functioning.

5) Type of cement:- In case of cemented pins, copper phosphate cement (which is

only used in non-vital teeth) is the most retaining cement. This is followed by

ZnPO4, polycarboxylate and ZoE in that order. Using varnish with zinc

phosphate cement reduces its retention up to 40%.

6) Type of involved dentin:- Young resilient, primary dentin is most retaining

type of dentin followed by tubular secondary dentin. Hyper mineralization

(sclerosis and calcification) and dehydration (non-vitality) of dentin will

drastically reduce the pin-retaining power.

7) Surface roughness of the pins:- Pins with surface serrations or threading will

have increased retention in dentin, especially in case of cemented pin

technique.

47

8) The ratio of dentinal engagement of the pin to their protruding lengths in cavity

preparation. The ideal ratio for the pin retention in dentin during furction is 2 :

1. A higher ratio will increase the pin retention and lower ratio will decrease

the retention.

9) Mode of shortening the pins after insertion:- Ideally pin should not be

manipulated after insertion, but frequently it is necessary to shorten them after

they are engaged within the dentin. The least distributing method to retention

of pin is to clip the excess with the cutting pliers. In many cases access will

prevent using pliers, then rotary instruments are used for cutting the excess pin.

a. Use the smallest carbide bur applicable preferably a ¼ round or 699 bur.

b. Apply pressure in a clockwise direction in case of threaded pin i.e.

direction of threading pins.

c. Hold the pin with a haemostat (plier or holding instrument) while

applying the lateral cutting pressure.

d. During all these acts use light intermittent pressure at the highest speed

possible to minimize vibration that may disengage the pin from the

dentin.

e. Nick the pin at the designated level of shortening.

10)Bulk of dentin around the pin:- The greater that the cross-section of dentin

separately the pins from the pulp, tooth and root surface is greater will be its

retention.

PINS AND RESTORATIVE MATERIALS:

A) Effect of pins on the strength of amalgam and composite resins:

Pins effect the compressive and tensile strength of restorative materials.

48

Compressive strength:- Pins do not increase the compressive strength of

restorative material. They only help in retaining it mechanically. In fact there will

be drop in the compressive strength of these restorations if,

a) The cavity end of the pin is chisel or wedge shaped or irregularly shaped.

This situation will lead to creation of shear lines enhancing fatigue failure

of restoration under compression.

b) Pins are closer than 2mm to each other. This situation will drastically affect

the restorative material strength due to increased chances of voids and

decreased bulk between the pins. The pins will actually segment the

restorative material.

c) Pin protrudes through or approximates the surface of the restoration. This

situation leads to segmentation and separation of the restorative material

with less bulk and more interfaces.

d) Less than 1.5 mm to 2.00 mm exists between the pin surface and restoration

surface. In this circumstances restorative material bulk will be less than the

minimum bulk for amalgam or composite.

e) There is non-adaptability of restorative material to the pin due to improper

wetability. This increase in the number of voids lead to movement of the

restorative material independent of the pin induce intolerable stresses

within the restorative material.

For this reasons failure rate of composite is more than amalgam in pin

restoration because amalgam offers less voids and more adaptability around pins

than composite resin do.

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Tensile strength:

The same factors which reduce the compressive strength of the restorative

reduces the tensile strength of the restorative materials. In addition,

a) There will be severe reduction (30-40%) of tensile strength of the

restorative material if the pin is placed at right angles to the direction of

tensile stresses induced during function.

b) A moderate reduction (10%) of tensile strength can be expected if the pins

are placed at 45% to the direction of the induced stresses in the restoration

during function.

c) No reduction of the tensile strength if pins are placed parallel to the

direction of the tensile stresses of the restoration.

Factors affecting retention of pins in restorative materials:

The following factors control pin retention to the restorative material:-

1) Type of pin:- Friction grip pins are least retentive for amalgam and

composite resin due to their smooth surfaces. Cemented pins and threaded

pins are four times more retentive than friction grip, mainly due to threaded

roughness of their surfaces.

2) Pin length in restorative materials:-

- For friction grip retention is directly proportional to length of pin in

restorative material without any plateau.

- Failure will almost occur in pin restorative material interface.

- For cemented and small threaded pins, the retention of the restoration

material is directly proportional to the length of the pin in the material

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up to the length of 2mm whereas plateau is reached. Usually failure

occurs in the pin itself.

- For large threading pins, the plateau for retention in the restorative

material will occur at pin length of 1.5mm within the restorative

material. Failure occur in the restorative material itself.

3) Pin diameter:- There is a gradual increase in the pin retention to restorative

material with increasing pin diameter up to 0.035”. Any diameter layer than

this will not have significant increase in retention.

4) Interpin distance:- Bridging pins closer to each other will increase retention

up to a distance of 2mm. Interpin distance closer this will cause definite

reduction in the pin retention.

5) Proximity of restorative material to pin surface:- The greater that will be the

wetting ability of the restorative material to pin surface is, the greater will

be the adaptability and consequently the frictional retention component.

6) Surface material of pins:- If the surface layer of the pin can chemically

combine with the restorative material or one of its phase, an ideal mode of

retention will exist at this phase.

Unfortunately the gold and silver plating of stainless steel pins is not as

effective as would be expected. Amalgam mercury will combine with the silver

veneering layer found in some pins, dissolving it and reacting it with some pins. If

the pins are gold plated it is not possible.

PINS AND TOOTH STRUCTURE:

A) Stressing Capabilities of Pins:-

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Stresses are always induced in dentin substance as a result of pin insertion.

If these stresses exceed the elastic limit of the dentin permanent plastic

deformation will occur.

These stresses might concentrate to a point exceeding the dentin’s limit,

resulting in macroscopic /or microscopic dentinal cracks i.e. interrupted and

continuous fractures of the dentin substance.

Either can lead to pulpal, surface and a periodontal involvement with their

sequelae (cracked tooth syndrome) gross fracture of the tooth or part of the tooth,

loose restoration etc.). There are many factors in pin techniques and materials that

can increase or decrease these stresses.

1) Type of pins:-

The smaller that the diameter of the pin is relative to that of the pin channel,

the less will be the amount and concentration of stresses in the dentin during the

insertion of the pin. There is cemented pin techniques, there are little or no

stresses.

Maximum stresses are associated with the friction locked pins where in

addition to the relative diameter of pin and pin channel, the impact forces

introduced during insertion can magnify these stresses. The threaded pin technique

introduces stresses intermediate to other techniques.

The threading acts dissipate and consume some of the insertion energy by

cutting part of the pin channel in dentin walls. In threaded pin-technique greater

than differences between the pin diameter and pin channel diameter, the greater

will be the stresses. Also the blunter threads produces more dentinal stresses. Also

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the less distance between the threads produced more concentration of stresses.

This is because the intervening dentin will be of lesser dimensions, while the

number of shearing threads per pin increases.

2) Diameter of pins:-

The greater that the diameter of a pin is, the greater will be induced

stresses.

3) Pin depth and dentinal engagement:-

The greater that the depth of the pin channel is, the greater will be the

stresses. This situation is most marked in threaded and friction grip pin techniques

which is due to greater dentinal involvement.

With threaded pins, the deeper that the engagement of the pin is into the

surrounding dentin, the more will be the stresses. Thus to reduce stresses the

modern pins have a lesser number of the threads with the greater distance between

these threads.

The threads are designed to be self-tapping and sharp extending very short

distance laterally. Pin diameter themselves have been scaled down.

4) Bulk of dentin:-

The greater that the bulk of dentin pulpally or toward the surface from the

pin is, the greater will be amount of stresses per unit volume of dentin.

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5) Type of dentin:-

Regular, primary dentin of young teeth is the least affected by stresses

induced by pin techniques because of its high elastic and plastic limit i.e. the

modulus of resilience. The greater that the mineralization and dehydration of the

dentin is, the greater that the obliteration of the dentinal tubules is, the less the

dentin will be able to tolerate stress without some eventual microfracture.

Accordingly the sequence of different types of dentin in decreasing order is,

secondary dentin > sclerosed dentin > tertiary dentin > calcific barrier. Therefore,

it is a basic principle not to use threaded pins in the endodontically treated teeth.

6) Interpin distance:-

The closer that the pins are inserted to each other, the greater will be the

possibility of stress concentration beyond the tolerable limits of the dentin. It is

advisable to not insert pins closer than 4mm when using the threaded pins. For

cemented pins the interpin distance is 2mm.

7) Non-coinciding eccentricity in pins or pin channel circumferences:-

Eccentricity is due to non-centrically running drills causing the elliptical or

irregularly shaped pin channels to occur that are not in conformance with the pin

shape. The pin will be contacting the surrounding dentin at only one or two points,

there bay concentrating stresses that should be distributed evenly over the dentin.

8) Loose pin:-

A loose pin within its pin channel could result in pin retained restoration

that is partially or completely mobile. Consequently the pin will definitely more

54

inside its pin channel with every movement of the restoration. The stresses will be

directly proportional to the amount and degree of pin movement within the dentin.

9) Wedge, chisel or irregularly shaped dentinal and of pins:-

Irregularly shaped pin-ends can happen during pin manufacturing, or pin

adjustments prior to the insertion procedure. This situation can invite

concentration of stresses at small cross-section of dentin which may result in

stresses beyond its tolerance.

10) Ratio of depth of the pin in dentin to that protruding into the cavity

preparation:-

The ideal dentinal engagement, pin protrusion is 2 : 1. Although 1 : 1 is

tolerable, a lower ratio will make the dentinal portion of the pin.

11) Number of pins in one tooth:-

It is not only the number of pins per tooth that will dictate the type and

amount of induced stresses, but also the number of volume of dentin.

12) Twist drill variability:-

Blunt edged drills vibrating drills or a twist drill used with laterally applied

forces can magnify the induced stresses in the dentin to a greater level than will be

consumed in pin channel cutting.

13) Over threading or over driving of pins into the pin channel:-

These situations can magnify and induce unnecessary stresses in the

underlying of involved dentin.

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14) Stresses induced during shortening pins inside the cavity preparation:-

After the dentinal engagement, any energy not consumed in cutting the pin

can induce intolerable stresses in the involved dentin.

15) Bending or aligning pins after their dentinal engagement and induce

intolerable stresses.

16) Retentive features in the remaining portion of the cavity. Pins should be used

only as the auxillary means of retention.

17) Inserting pins in a stress concentration area of the tooth:-

In stress concentration areas (e.g. the axial angle or incisal angle the

junction between the clinical crown and clinical root) inserting pins will

complicate pre-existing stress patterns, if the bulk of the tooth has been already

reduces.

POSSIBLE PROBLEMS WITH PINS:

A) Failure of pin-retained restorations:- The failure of pin retained restorations

might occur at any five different locations. Failure can occur (i) within the

restoration (ii) at the interface between pin and restorative material, (iii) within

the pin, (iv) within the dentin.

B) Broken drills and broken pins:- Sometimes a twist drill will break if it stressed

laterally or allowed to stop rotating before being removed from the pinhole.

Use of sharp twist drills helps eliminate the possibility of drill breakage. The

standard pin usually breaks if turned more than needed to reach the bottom of

the pin hole. Puss may also break during the bending, if care is not exercised.

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Treatment of both broken drill and pin is to choose an alternate location, at

least 1.5mm remote from the problem item and prepare another hole.

C) Loose pins:- Self threading pin sometimes does not properly engage the dentin

because the pin hole was inadvertently prepared to large or a self shearing pin

failed to shear, resulting in stripped out dentin. The pin should be removed and

pin with the next larger size is inserted.

D) Penetration into the pulp and perforation of external tooth surface:- When

penetration or perforation has occurred there is an abrupt loss of resistance of

the drill to hand pressure. Also if a standard or link series pin continue to threat

into the tooth beyond the 2mm depth of the pin hole, this is an indication of a

penetration or perforation.

Radiographs are not very helpful in detecting the pulpal penetration as there

can be chances of superimposition of the pulp and pin. But they are helpful in

detecting the external surface exposure.

If the pulpal penetration occurs in asymptomatic teeth the treatment is same

as any other small mechanical exposure. If mechanical exposure has occurred

control the haemorrhage and place Ca(OH)2 in the hole and prepare a hole 1.5 to

2mm away from the previous pinhole.

An external perforation might be suspected if an unanaesthetized patient

senses pain when pinhole is being prepared or a pin being placed in tooth that has

had endodontic therapy. Perforation can occur occlusal or apical to gingival

attachment.

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Three options if perforation occurs above the epithelial attachment:-

Pin can be out of and flush off with the tooth surface and no further treatment.

Pin can be cut off flush with the tooth surface and preparation for cast

restoration extended gingivally beyond the perforation.

Pin can be removed and external aspect of the pin hole can be restored with the

amalgam.

Two options available if perforation occurs apical to the attachment:-

1) Reflect the tissue surgically, remove the necessary bone, the pinhole slightly

and restore it with amalgam.

2) Perform a crown lengthening procedure and then place the cast metal

restoration of margins below the perforation.

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