Pins In Dentistry : A Detailed Seminar

INTRODUCTION:

In 1897, Arthur described the use of anchor screws in the dentin to retain restorations. The pin-amalgam restoration became widely accepted after Markley popularized it in 1958. Large numbers of teeth have since been restored by skillful dentists who continue to praise the virtues of the pin-retained amalgam. However, there are others who point out that potential dangers lurk in this procedure such as pulp exposure, painful pulpitis, split roots, and cracked amalgam.In past, when severely damaged teeth lacked structure to adequately retain a restoration, the options were frequently limited to extraction. Use of pins in dentistry offered an alternative that is often more practical, less costly and more conservative. Before the development of organized pin instrumentations dentists forced dental bur heads into holes burred into dentin. A portion of the bur remained protruding from the hole to be grasped by an  amalgam. Pin foundations are used in extensive restorative problems such as in missing cusps and surfaces or for cores. The pin reinforces the properties of retention and resistances in the restoration.

DEFINITION:

·         A pin-retained restoration may be defined as any restoration requiring the placement of one or more pins in the dentin to provide adequate resistance and retention forms.

                                                                                                             Sturdevant

·         A pin is an extension of a restoration into a prepared hole or a metal rod secured in a hole drilled in dentin for the purpose of retaining a restoration in or on the tooth.

Atlas of Operative Dentistry

·         A pin is a small rod that fits into a channel drilled into dentin away from the pulp space. It is also referred as a dentinal pin or a parapulpal

                                                               Richard J, Shillingburg  D.C.N.A Vol 37(3) 1993.

INDICATIONS

1.    EXTENSIVE TEETH LOSS:

·         When large amounts of tooth structure are missing,

·         When one or more cusps need capping

·         Teeth with acute and severe caries.

·         When increased resistance and retention forms are needed.

2.      QUESTIONABLE PROGNOSIS: Control restorations in teeth that have a questionable pulpal and/or periodontal prognosis. In such teeth pin retained restorations may be placed as interim restorations, till the prognosis is established.

3.      AS FOUNDATIONS: Pin retained restorations may be employed for indirect restorations like onlays or crowns.

4.      ECONOMIC FACTOR: When cost is a major factor for the patient, pin-retained restorations may be a cheaper alternative in complex situations.

5.      AGE AND HEALTH OF PATIENT: For geriatric and debilitated patients, pin-amalgams are the preferred choice over cast restorations.

CONTRAINDICATIONS

The complex amalgam restoration may be contraindicated

1.      If the patient has significant occlusal problems.

2.      If the tooth cannot be properly restored with a direct restoration because of anatomic and/or functional considerations.

3.      If the area to be restored is esthetically important for the patient.

ADVANTAGES

1.      Conserves Tooth Structure:  The preparation for a complex amalgam restoration is usually more conservative than the preparation for an indirect restoration or a crown.

2.      Appointment Time: The complex restoration can be completed in one appointment. The cast restoration requires at least two appointments.

3.      Resistance and Retention Forms: Resistance and retention forms may be significantly increased by the use of pins, slots, and bonding.

4.      Economics: Compared to an indirect restoration, the amalgam restoration is a relatively inexpensive restorative procedure. When cost is a factor, the complex amalgam restoration may provide the patient with the only alternative to extraction of the severely broken-down tooth.

DISADVANTAGES

1.      Dentinal Microfractures: Preparing pinholes and placing pins may create craze lines or fractures, as well as internal stresses in the dentin. Such craze lines and internal stress may have little or no clinical significance, but they may be important when minimal dentin is present.

2.      Microleakage: In amalgam restorations using cavity varnish, microleakage around all types of pins has been demonstrated.

3.      Decreased Strength of Amalgam: The tensile strength and horizontal strength of pin-retained amalgam restorations are significantly decreased.

4.      Resistance Form: The complex amalgam restoration does not protect the tooth from fracture as well as an extracoronal restoration.

5.      Penetration and Perforation:  Pin retention increases the risk of penetrating into the pulp or perforating the external tooth surface.

6.      Tooth Anatomy: Proper contours and occlusal contacts, and/or anatomy, are sometimes difficult to achieve with large complex restorations.

CLASSIFICATION OF PINS

Pins can be classified as: 

a) Direct/Non-parallel   pins

b) Indirect pins/Parallel pins

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..

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 on which the rest of the restoration is built in the conventional form with blue inlay wax.  

·         The whole assembly in then invested and casted with pins jamming an inherent part of the cast restoration.

B.      Wrought precious metal pins  

·         They have surfaces that is deformed or roughed by means of threaded on Knurled patterns.

·         These pins are alloys of gold, platinum palladium or platinum indium.

·         The pins are placed in the pin holes 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:

n  Are usually made of stainless steel, titanium, or stainless steel with gold plating 

n   Inserted into dentin followed by placement of restorative materials like amalgam resin or cement directly over them.

n  They are also referred to as Non-parallel pins since they are directly inserted into the tooth structural and hence not parallel to each other.

n  This category of pins include cemented, friction locked and threaded pins.

TYPES OF DIRECT PINS

A.  CEMENTED PINS: Introduced  by DR. MILES MARKLEY in 1958

n  These are stainless steel pins with threads or serrations and the pin is retained with standard luting cements. Eg: ZnPO4/ zinc polycarboxylate.

n  Pins are cemented into pinholes prepared   .025-.05 mm larger than diameter of pins.

These come in two sizes:

PIN CHANNEL DIAMETER	PIN DIAMETER
0.027”	0.025”
0.021”	0.020”

INDICATIONS OF CEMENTED PIN TECHNIQUE:

Ideal for all pin–retained restorations, as it creates the least crazing and stresses in the remaining tooth enamel and dentin.

1.      Only technique to be used in endodontically treated teeth.

2.      Only technique to be used when the available location for the pin is very close to DEJ.

3.      Only technique to be used for U and L shaped pins in class 4 restorations and foundations.

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

5.      It is ideal technique for the sclerosed, tertiary, calicific barrier or any other highly mineralized or dehydrated dentin.

6.      It is the only technique for the cross-linkage of the two parts of the same tooth.

TECHNIQUE:

—  Cemented pins come in form of SS wires, which can be cut into specific required lengths prior to insertion with Dial-A-Pin cutter.

—  Pin holes extending 4.0 to 6.0 mm into dentin are prepared using twist drills.

—  Cutting a pin after cementation may break the cement bond and dislodge it.

—  The length of pin should be such that it should not exceed 2.0 to 3.0 mm above the base.

—  Pin hole is dried with endodontic paper points and coated with cement with help of endodontic file, explorer or lentulospiral.

—  The pin is held with forceps and coated with cement.

—  Pin is placed into pinhole where it is left undisturbed until cement hardens.

MODIFIED   TECHNIQUE:

—  This technique was later modified using threaded SS pins of the same size as twist drill.

—  Most commonly used size is 0.027 inches.

—  Advantages:

—  Increased lateral stability.

—  Close contact between pin and channel.

ADVANTAGES:

n  Ease of placement: Cemented pins are approximately 0.001 – 0.002” smaller than their pinholes and hence are more likely to be seated to the full length.

n  Since they are passively retained in the dentin they virtually place no internal stress on the surrounding dentin during or after placement.

n  Because cement seals the interface between pin and tooth, chances of microleakage are reduced.

DISADVANTAGES:

n  Least retentive: Offer less retention compared to the friction locked and threaded pins.

n  At times the poorly cemented pins gets dislodged

n  Greater time is required for mixing and hardening the cement

B.   FRICTIONAL GRIP, OR FRICTION LOCK, PINS : Introduced in 1966 By Dr. PHILIP GOLDSTEIN

The pin channel is .001 inch smaller than Pin diameter. These pins are tapped into the prepared channel with a mallet.

 These come in one size only:

PIN CHANNEL DIAMETER	PIN DIAMETER
0.021”	0.022”

n  Utilize the resiliency of dentin for retention. No need of cement.

n  2-3 times more retentive than cemented pins

n  Most difficult to insert and have not gained wide acceptance

INDICATIONS:

This is the least used of all pin techniques because of the following strict requirements:

1.      Used in vital teeth only.

2.      Very bulky dentin should be available to encompass the pin (at least 4 mm in three dimensions).

3.      Pins should be located at least 2.5 mm from the DEJ.

4.      Used only in the accessible areas of the mouth, so the seating force will be parallel to the pin axis.

This design comes in 4-5 mm pre-cut lengths, but they may come in the wire forms. If in the wire form, they can be cut and shaped the same way as the cemented pins.

TECHNIQUE:

—  A self centering spiral drill mounted in low speed handpiece is used to prepare pin channel in dentin to a depth of 2.0 to 3.0 mm, 1.5 mm inside the DEJ.

—  Desired length of pin is cut extraorally.

—  The depth to which pin channel has been drilled is marked on the pin.

—  The pin is inserted into a pin setter and carried to pin hole.

—  A mallet is then used to apply force parallel to the axis of the pin.

—  Forces are applied untill the established mark on the pin reaches the cavity floor.

—  Additionally sense of touch and sound can be used to check that pin has reached till bottom of pin hole or not.

ADVANTAGES:

·         Cement is not required so one does not to wait for the cement to set.

·         Pins acquire stability from moment they inserted.

·         Better retention than the cemented pins.

DIADVANTAGES:

·         Driving pins into  their respective pinholes generates stresses in dentin in the form of cracks or craze lines

·         Many a times, pins do not reach to the full length due to gauging, and hence loose their retentive properties.

·         Microleakage is higher than cemented pins of the overlying restoration leaks.

C.   THREADED PINS : Introduced By DR. GOING In 1966

·         Stainless steel/titanium with gold plated pins for increasing passivity.

·         The pin channel diameter is 0.015”-0.004” smaller than that of the pin.

·         These come in four sizes:

Pin channel diameter	Pin diameter
0.027”	0.031”
0.021”	0.023”
0.018”	0.020”
0.013”	0.015”

·         Placed by handwrench or contra-angle handpiece.

·         Pin is retained by the threads engaging the dentins as it is inserted.

·         Has got maximum Retention(5 to 6 times more than friction locked pins)        

·         Threads held in place by elasticity of dentin. The elasticity of the dentin allows insertion of a threaded pin into a hole of smaller diameter.

INDICATIONS:

This is the most applicable and feasible of all the techniques:

1.      It is used for the vital teeth.

2.      Dentin to engage the pin is primary or secondary dentin properly hydrated.

3.      Available pin location is at least 1.5 mm from the DEJ.

4.      A minimal number of pins is needed for restoration.

5.      Maximum retention of pin to the dentin and restoration is needed for one reason or another.

ADVANTAGES:

·         Wide range of pin sizes

·         Ease of Insertion

·         Maximum retention offered

·         Gold plated surface finish, which may eliminate the possibility of corrosion.

DISADVANTAGES:

·         Excessive stresses in the form and crack or craze lines are generated in the surrounding enamel and dentin, especially with large sized pins

·         Pins may need to bent, cut or contoured after insertion, which may place extra stresses on the tooth may loosen the pin.

·         Microleakage is higher than the cemented pins if the overlying restoration leaks

THREAD MATE SYSTEM (TMS): by Coltene Whaldent Inc Mahwah New Jersey

·         This is the most popular variety of self-threaded pins.

·         In this system the pins are made of stainless-steel or titanium plated with gold.

The self threading pins are available four sizes:

NAME	COLOUR CODE	PIN DIAMETER (IN/MM)	DRILL DIAMETER (IN/MM)	TOTAL PIN LENGTH (MM)	PIN LENGTH EXTENDING FROM DENTIN(MM)
Regular Standard	Gold	0.031/0.78	0.027/0.68	7.1	5.1
Regular Self-shearing	Gold	0.031/0.78	0.027/0.68	8.2	3.2
Regular Two-in-one	Gold	0.031/0.78	0.027/0.68	9.5	2.8
Minim Standard	silver	0.024/0.61	0.021/0.53	6.7	4.7
Minim Two-in-one	silver	0.024/0.61	0.021/0.53	9.5	2.8
Minikin Self-shearing	Red	0.019/0.48	0.017/0.43	7.1	1.5
Minuta Self-shearing	Pink	0.015/0.38	0.0135/0.34	6.2	1

REGULAR:

 These are the largest diameter pins. They cause considerable stress and maximum dentinal crazing during placement. Of the four pin sizes, the Regular pin caused the highest incidence of dentinal cracking that communicated with the pulp chamber. Due to these reasons regular pins are rarely used.

MINIM:

These are the next smaller diameter pins. They cause lesser stresses and dentinal crazing while providing good retention. The Minim pins usually are used as a backup in cases where the pinhole for the Minikin was over prepared or the pin threads stripped the dentin during placement and the Minikin pin lacks retention.

MINIKIN:

These pins cause very less risk of dentinal crazing. At the same time can afford good retention. The Minikin pins usually are selected to reduce the risk of dentin crazing, pulpal penetration, and potential perforation.

Minim and Minikin pins are pins of choice for severely involved posterior teeth and are commonly used sizes of TMS pins.

MINIUTA:

These are the smallest size of pins. They are too small to provide adequate retention. The Minuta pin is approximately half as retentive as the Minim and one third as retentive as the Minim pin. Hence, they are not used often.

Dilts et al reported that the larger diameter pins have the greatest retention.

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

·         LINK PLUS

The Link Series and Link Plus pins are recommended.

STANDARD:

·         It is approximately 7 mm 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.

·         This pin should be shortened after seating.

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.

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 handpiece check for threading into the pin hole.

·         The self shearing design automatically shears off at 4mm from the dentinal end, when this end comes in contact with pin channel floor, leaving a length of pin extending from the dentin.

·         Shearing occurs when there is marked resistance to turning i.e. pin insertion is torque limited.

TWO-IN ONE PIN:

·         It has actually two pins in one i.e. the two pins, with each one being shorter than the standard pin, are connected to each other at a joint which serves as the shear line for the peripheral pin.

·         The two-in-one pin in approximately 9.5 mm in length and provide two pins each about 4mm.

·         It has also flattered end that engages the wrench or the check of the hand piece that aids in threading it to the pinhole.

·         The wrench attachment part is on one end only.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 pinhole the pin shears approximately in half, leaving a length of  the pin extending from the dentin, with the other half remaining in the hand wrench or handpiece check.

·         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 handpiece need not to be reloaded during two pin insertions.

LINK SERIES:

·         Link series pin contained in a color coded plastic sleeve that fits into the latch type contra angle hand piece or specially designed plastic hand wrench.

·         These pins are also self-shearing. When the pin reaches the bottom of the hole, the top portion of the pin shears off, leaving a length of pin extending from the dentin. The plastic sleeve is then discarded.

·         This design is versatile and can align well into the pin channels.

Ø  The Minuta, Minikin, Minim and regular pin are available in the link series.

Ø  The Link Series pins are recommended because of their versatility, self-aligning ability, and retentiveness.

LINK PLUS DESIGN:

·         This design is similar to the link series design.

·         These pins are also self-shearing and may be available as single or two-in-one pins.

·         The major difference in the design is that the pins have sharper threads, a shoulder stop at 2 mm and a tapered tip in more readily fit the bottom of the pinhole as prepared by the twist drill in order to reduce dentinal stresses while seating.

·         It also provides a 2.7-mm length of pin to extend out of the dentin, which usually needs to be shortened.

ADVANTAGES OF THREAD MATE SYSTEM PINS:

1.      Versatile design.

2.      Wide range of pin sizes.

3.      Colour coding allows ease of use.

4.      Gold plating elimination corrosion.

5.      Good retention.

PIN MATERIALS:

STAINLESS STEEL PINS

·         Are most frequently used.

·         Advantage are stronger than its Titanium and gold counterparts

·         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 is less compared to that of stainless steels.

·         Also titanium pins show no adherence to the amalgam and composite restorations.

SILVER PINS

·         Have excellent bond with the silver amalgam restorative material but solid silver pins are soft and easily deformed.

ACRYLIC PINS and COMPOSITE RESIN PINS

·         Have been tried for use, with composite restoration for anterior restoration due to esthetic purposes.

PLASTIC PINS

—  These are used in indirect parallel pin technique, but do not serve part of final restoration.

—  These are meant for taking impressions of pin holes.

ALUMINIUM PINS

—  These are used for retaining a temporary restoration until a final restoration is fabricated and inserted.

Pin Placement- Factors And Techniques.

1.     PIN SIZE:

—  In TMS system, minikin and minim pins are usually the sizes selected for posterior teeth as they provide maximum retention without the risk of dentinal crazing.

2.     NUMBER OF PINS:

—  Factors that help to decide the number of pins for a given situation are:

—  Amount of missing tooth structure

—  Amount of dentin available

—  Size of the pin

—  Amount of retention needed.

—  Rule is to use one pin per missing axial line angle.

3. LOCATION OF PINS:

—  For proper placement of pins it is important to know the pulpal anatomy and external contours of the tooth to be treated.

—  Study the pre operative radiograph carefully.

—  Pin holes are usually placed in the cervical 1/3^rd of posteriors near the line angles of the teeth.

—  These holes should be 1 mm away from the DEJ or 1.5mm away from external surface of teeth.

—  Located atleast 0.5 mm from vertical wall of tooth to allow proper condensation of material.

—  Pin holes should be located on flat surface to prevent drill from slipping.

—  Inter pin distance should be 3-5 mm to lower stresses in the dentin.

—  Pin holes can be prepared at different levels to reduce stress concentration.        

TOOTH PREPARATION FOR PIN-RETAINED AMALGAM RESTORATIONS:

INITIAL TOOTH PREPARATION:

·         CAPPING CUSPS: When the facial or lingual extension exceeds two thirds the distance from a primary groove toward the cusp tip (or when the facial-lingual extension of the occlusal preparation exceeds two thirds the distance between the facial and lingual cusp tips), reduction of the cusp for amalgam is required for the development of adequate resistance form.

·         Reduction should be accomplished during initial tooth preparation because it improves access and visibility for subsequent steps.

·          If the cusp to be capped is located at the correct occlusal height before preparation, depth cuts should be made on the remaining occlusal surface of each cusp to be capped, using the side of a carbide fissure bur or a suitable diamond instrument.

·         The depth cuts:

o   2 mm deep minimum for functional cusps .

o   1.5 mm deep minimum for non-functional cusps.

If the unreduced cusp height is located less or more than the correct occlusal height, the depth cuts may be less or more deep respectively. The goal is to ensure that the final restoration has restored cusps with a minimal thickness of 2 mm of amalgam for functional cusps and 1.5 mm of amalgam for nonfunctional cusps, while developing an appropriate occlusal relationship.

·         Using the depth cuts as a guide, the reduction is completed to provide for a uniform reduction of tooth structure. The occlusal contour of the reduced cusp should be similar to the normal contour of the unreduced cusp.

·         Any sharp internal corners of the tooth preparation formed at the junction of prepared surfaces should be rounded to reduce stress concentration in the amalgam and thus improve its resistance to fracture from occlusal forces.

·         When reducing only one of two facial or lingual cusps, the cusp reduction should be extended just past the facial or lingual groove, creating a vertical wall against the adjacent unreduced cusp.

·         Extending the facial or lingual wall of a proximal box to include the entire cusp is indicated only when necessary to include carious or unsupported tooth structure or existing restorative material. When possible, opposing vertical walls should be formed to converge occlusally, to enhance primary retention form.

·          The pulpal and gingival walls should be relatively flat and perpendicular to the long axis of the tooth.

FINAL TOOTH PREPARATION:

·         Removal of any remaining infected carious dentin or removal of remaining old restorative material is accomplished.

·         A liner can be applied, if needed, and, if used, should not extend closer than 1 mm to a slot or a pin.

·         Coves and retention locks should be prepared, when possible. Coves are prepared in a horizontal plane and locks are prepared in a vertical plane. These locks and coves should be prepared before preparing pinholes and inserting pins.

·         When additional retention is indicated, Slots may be prepared along the gingival floor, axial to the dentino enamel junction (DEJ) instead of, or in addition to, pinholes.

PINHOLE PREPARATION:

Three basic instruments are needed for the pin channel preparations:

A.   TWIST DRILL

B.   NO. 1, 2, 3 ROUND BURS with which a leading hole is established, in the centre of which the pin channel drilling is started. This aids in avoiding any skidding of the twist drill.

C.   MEASURING PROBES OR DEPTH GAUZE:  Used to verify the depth of the pin channel.

·         The Kodex drill is used for preparing pinholes.

·         This is an end cutting revolving instrument with two blades, bibevelled in longitudinal section at precisely the same distance from the tool’s center. The sides of the drill are helix fluted allowing the escape of debris formed during end cutting.

·         The drill is made of high-speed tool steel that is swaged into an aluminium shank. The aluminium shank, which acts as a heat absorber, is colour coded so that it can be easily matched with the appropriate pin size. The drill is always made of steel, not carbide, so that there can be some slight plasticity in the drill substance.

There are 5 rules in using the drill:

1.      Should be used at ultralow speed (300-500 rpm) because the coolant cannot be used at such depths of dentin engagement. Also some tactile feeling is needed during cutting.

2.      Should be used in direct cutting acts, with forces applied at the parallel to the long axis of the drill. Lateral cutting acts will widen the pin channel and lead to drill fractures.

3.      The drill should be revolving while inside the pin channel. Inserting or withdrawing the drill from channel while it is not revolving will lead to drill or tooth structure fracture.

4.      Do not use pumping strokes (several up and down). This will widen the pin channel more than is required. Plan the cutting and use one stroke to the full designated depth, then one stroke out of the channel.

5.      Never use the drill in enamel. These drills will not cut enamel and will be dulled, even fractured by it.

Each drill is furnished in one of the three types or combination of types:

1.      Drill with cutting parts 4mm and more in length, without any self-limiting device.

2.      Drills with cutting parts ending in button or self limiting shoulder which can be adjustable or fixed, which is located at 2mm from the cutting edge of the drill.

3.      Drill for the parallelometer attachment, which fits loosely in the handpiece and has a sleeve to fit in the parallelometer. It is mainly used for the pins in cast restorations to assure parallelism of pin channels

DRILLING:

·         Because the optimal depth of the pinhole into the dentin is 2 mm (only 1.5 mm for the Minikin pin), a depth-limiting drill should be used to prepare the hole.

·         Only when this type of drill prepares a hole on a flat surface that is perpendicular to the drill will it prepare the pinhole to the correct depth.

·         When the location for starting a pinhole is neither flat nor perpendicular to the desired pinhole direction, either flatten the location area or use the standard twist drill, whose blades are 4 to 5 mm in length, to prepare a pinhole that has an effective depth.

·         To minimize guessing when using the standard twist drill, the Omni-Depth gauge can be used to measure accurately the pinhole depth.

·         With the drill in the latch-type contra-angle handpiece, place the drill in the gingival crevice beside the location for the pinhole, position it until it lies flat against external surface of the tooth, and then, without changing the angulation obtained from the crevice position, move the handpiece occlusally and place the drill in the previously prepared pilot hole.

·         Now, view the drill from a 90-degree angle to the previous viewing position to ascertain that the drill is also correctly angled in this plane.

·         With the drill tip in its proper position and with the handpiece rotating at very low speed (300 to 500rpm), apply pressure to the drill, and prepare the pinhole in one or two movements until the depth-limiting portion of the drill is reached, and remove the drill from the pinhole.

·         Using more than one or two movements, tilting handpiece during the drilling procedure, or allowing the drill to rotate more than very briefly at the bottom of the pinhole will result in a pinhole that is too large.

DRILL DULLING

Twist drills become dull in 2 ways from boring holes into teeth

Ø  Drilling against enamel surface

Ø  Dentin debris

 Standlee et al have demonstrated that a twist drill becomes too dull for use after cutting 20 pinholes or less, and the signal for discarding the drill is the need for increased pressure on the handpiece.

·         Dull drills used to prepare pinholes can cause increased frictional heat and cracks in the dentin. Although not usually recommended, a steady stream of air may be applied to the drill to dissipate heat.

·         Using a drill whose selflimiting shank shoulder has become rounded is contraindicated.

·         A worn and rounded shoulder may not properly limit pinhole depth and permit pins to be placed too deeply.

RESHARPENING OF DRILL

•         Can be done by carborundum disc on a hand piece at proper alignment.

•         As disc rotates one plane is momentarily held against the disc.

•         The drill is rotated 180 between one’s fingers and other side of the drill is re-defined.

•         A light touch is required.

•          Sharpening is accomplished by making the drill slightly shorter in all respects, So that the edges are in a position to shave away the dentin as a new drill.

PIN INSERTION

Two instruments for insertion of threaded pins are available:

·         Conventional latch-type contra-angle handpiece

·         TMS hand wrenches

HAND WRENCH:

•         Provides tactile sense during the threading of the pin into the dentin. This means screwing of the pin into position is best done with fingers than by motorized handpiece.

•         The hand wrench is recommended for the insertion of standard pins.

•         A Standard design pin is placed in the hand wrench and slowly threaded clockwise till definite resistance is felt when the pin reaches the bottom of the pin hole.

•         The pin should then be rotated one-quarter to one-half turn counterclockwise to reduce the dentinal stress created by the end of the pin pressing the dentin.

•         Carefully remove the hand wrench from the pin.

•         If the hand wrench is used without rubber dam isolation, a gauze throat shield must be in place, and a strand of dental tape approximately 12 to 15 inches (30 to 38 cm) in length should be securely tied to the end of the wrench.

•          These precautions will prevent the patient from swallowing or aspirating the hand wrench should it be dropped accidentally.

CONVENTIONAL LATCH TYPE CONTRA-ANGLE HANDPIECE:

•         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 increases the tactile sense of the operator.

•         It also reduces the risk of stripping the threads in the dentin once the pin in place.

•         The latch-type handpiece is recommended for the insertion of the Link Series and the Link Plus pins.

•         When using the latch-type handpiece, insert a Link Series or a Link Plus pin into the handpiece and place the pin in the pinhole. Activate the handpiece at low speed until the plastic sleeve shears from the pin. Then, remove the sleeve and discard it.

REMOVAL OF EXCESS OF PIN LENGTH:

·         Once the pins are placed, evaluate their length.

·         The optimum length of pin embedded within a restoration is 2 mm, and 2 mm of amalgam over the pin gives adequate strength to the alloy.

·         Some pins of the self-shearing variety are designed for placement without a subsequent need for shortening.

·         Frequently, however, the pin must be shortened because it is inherently too long or because it shears off before it screws all the way to the bottom of its pinhole.

·         To remove the excess length of pin, use a sharp No. 169L bur at high speed and oriented perpendicular to the pin.

·         If oriented otherwise, the rotation of bur may loosen pin by rotating it counter clockwise.

·         During removal of excess pin length, the assistant may apply a steady stream of air to the pin and have the evacuator tip positioned to remove the pin segment.

·         Also during removal, the pin may be stabilized with a small haemostat or cotton pliers.

·         After placement, the pin should be tight, immobile, and not easily withdrawn.

·         Using a mirror, view preparation from all directions (particularly from the occlusal) to determine if any pins need to be bent to position them within the anticipated contour of the final restoration and to provide adequate bulk of amalgam between the pin and the external surface of the final restoration.

BENDING TOOL:

·         A pin bending tool is a forked instrument that is useful for imparting a uniform curve to the pin, thus preventing fracture of the stiff pin material.

·         Pins are not to be bent to make them parallel or to increase their retentiveness. However, occasionally, bending a pin may be necessary to allow for condensation of amalgam occlusogingivally.

·         When pins require bending, the TMS bending tool must be used.

·         The bending tool should be placed on the pin where the pin is to be bent, and with 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 some point along the length of the exposed pin. Bending pins can be hazardous if the pins are not well supported by dentin and particularly if the dentin is weak or brittle. A Section of tooth could break away.

·         A hand instrument such as an amalgam condenser or Black spoon excavator should not be used to bend a pin because the location of the fulcrum will be at the orifice of the pinhole. These hand instruments may cause crazing or fracture of the dentin, and the abrupt or sharp bend that usually results, increases the chance of breaking the pin. Also, the operator has less control when pressure is applied with a hand instrument, and the chance of slipping is increased.

PINS, STRESSES AND TOOTH

·         Stresses are always associated with insertion of friction locked and threaded pins in dentin.

·         It is quite obvious that stresses will be generated as pins are inserted into channels.

·         Cemented pins are known to induce the least stresses, threaded pins induce intermediate while friction locked induce maximum stresses.

·         Impact forces introduced during insertion of friction locked pins are probably responsible for greatly magnifying the residual stresses in dentin.

Factors increasing the residual stresses in dentin are:-

·         Pin Morphology:

o   Large diameter of pins

o   Large difference between pin and channel diameter.

o   Blunt threads

o   Greater number of threads per unit distance

o   Inserting pins into channels not prepared with matching drills.

·         Placing pins close to each other

·         Increasing the number of pins per tooth.

·         If ratio of embedded pin to exposed pin is not proper.

·         Mismatch between pin and pin channel circumference increases stresses by concentrating stresses at point of contact rather than distributing evenly.

·         Pin which is loose in its channel induces stresses on dentin when the overlying restoration is stressed.

·         Attempt to over drive the pin into channel.

·         Bending or shortening pins after they have fully engaged in dentin.

·         Cutting channels with dull vibrating drills

·         Lesser the bulk of dentin surrounding the pin greater are the stresses per unit volume of dentin.

PINS, STRESSES AND RESTORATIVE MATERIAL

·         Originally pins were thought to reinforce the amalgam restoration as steel rods reinforce concrete.

·         But subsequent studies showed that pins did not strengthen or reinforce a restoration but assisted in retention form only.

·         Pins are likely to reduce the strength of amalgam and composite restorations because of absence of any chemical union between pin and restorative material at the interface.

Factors relating to pins that decrease the compressive and tensile strength of restoration are:-

·         Pin ends in restoration may be wedge shaped or irregular in shape serving as areas of stress concentration.

·         Pins are close to or protrude through the outer surface of the restoration.

o   Eg: silver is weeak if its not present in thicknes of 1.5-2.0 mm

·         Pins are closer than 2 mm to each other.

o   Increases possibility of voids

o   Insufficient bulk of material.

·         If pins are at right angle to direction of tensile stresses 30-40% reduction in tensile strength of material is seen.

ANATOMICAL ASPECTS OF PIN RETAINED RESTORATIONS

To preserve the anatomical integrity of a tooth to receive a pin retained restoration, the tooth retained part of the pin should be confined to dentin only. The following factors will assist the operator in acquiring the appropriate instrumentation for pin placement.

A.   Knowledge of anatomy

Full comprehension of the tooth anatomy, its invested and investing tissues is basic to the drilling of pin channels without perforation or encroaching on that essential anatomy.

B.   Radiographs

Although x-rays only illustrate the tooth in one plane, they are helpful in getting a basic idea about the dimensions of the dentin in this plane.

C.   Outer surface of the tooth

The outer surface of the tooth next to the contemplated location of the pin in the dentin is the ideal guiding landmark for the drilling location and angulation. The drill is applied on the adjacent surface, and then moved with the established inclination to the drilling location, so the resulting pin channel will be parallel to the adjacent surface.

D.   Amount of dentin

Factors which lead to obliteration of the pulp chamber or root canal spaces will increase the dimension of dentin. On the contrary, previous pathology or instrumentation may enlarge the aforementioned space, decreasing the dimension of dentin.

E.    Anatomical factors

Abnormal anatomy on tooth surfaces, in the form of grooves or concavities, approximating the planned pin location will increase the possibility of surface perforation

F.    Tooth alignment

Malalignment of teeth in the form of rotation or inclination necessitates individual evaluation of the tooth involved to determine the best access, location, and angulation of pin channel.

G.   Cavity extent

The more apically located 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 the taper of the tooth as one proceeds apically.

H.   Age or relative age

Aging decreases the size of the pulp chamber and root canal system and increases the dentin dimension.

MECHANO-ANATOMICAL PRINCIPLES FOR PIN PLACEMENT

MAXILLARY CENTRAL INCISOR

Pin locations:-

·         Ideal location is gingival floor, close to the proximo-labial and proximo-lingual corners.

·         Second choice is middle of a proximal gingival floor or middle of a labial gingival floor

·         Third choice is incisal, where there is at least 2mm or more of dentin between the labial and lingual enamel plates.

Areas to be avoided: the middle of a lingual gingival floor, incisal in absence of sufficient dentin.

Pin angulation:-  Proximal and labial pins always should have a slight labial angulation.

All gingival pins should have a very limited angulation in mesio-distal direction.

 Incisal pins should be parallel to the incisal ridge.

MAXILLARY LATERAL INCISOR

Pin location: The same as for the central incisors.

Areas to be avoided: Are same as central incisors.

Pin angulation:  Pin should be angulated as in the central incisor, except that all gingival pins should have slightly more angulation with the longitudinal axis of the tooth in the mesio-distal direction.

MAXILLARY CUSPID

Pin location: This tooth ranks second to upper first molar in freedom of pin insertion. The ideal location is at or close to the facio- and linguo-proximal corners of the tooth. Second choice is the middle of a proximal gingival floor and middle of a labial gingival floor. The third choice is incisal, close to the incisal angle.

Areas to be avoided: the middle of the lingual gingival floor, and gingival pins close to surface concavities or grooves.

Pin angulation: Gingival pins should have a slight labial angulation in the labio-lingual direction.

All gingival pins should form an angle with the long axis of the tooth in the mesio-distal direction, coinciding with the taper of the root. This angle can be between 20-35⁰. Incisal pins should be parallel to the adjacent proximal slope of the tooth.

MAXILLARY PREMOLARS:

Pin location: The ideal location is at or close to the proximo-facial and lingual corners of the tooth placed gingivally.

Areas to be avoided: the mesial gingival floor, the middle of the gingival floors buccally and lingually, and the gingival floors, occlusal to furcations.

Pin angulation: All gingival pins should be parallel to the long axis of the tooth.

MAXILLARY FIRST AND SECOND MOLAR

Pin location: The ideal location is the gingival floor at or close to the disto-lingual corner. The second choice is the gingival floor at or close to the disto-buccal and mesio-lingual corner of the tooth.

The third choice is the gingival floor lingually, mesially and distally if the furcation and isthmus can be avoided.

Areas to be avoided: the gingival floor at the mesio-buccal corner of the tooth, any part of the gingival floor occlusal to a furcation or a root concavity.

Pin angulation:-

Gingival pins facially and lingually should be approximately parallel to the occlusal two-thirds of the lingual surface.

Gingival pins mesially and distally should be parallel to the longitudinal axis of the tooth.

MAXILLARY THIRD MOLAR

 Pins are generally not placed because of variable anatomy of tooth. To avoid unwanted perforation, pin channel preparation and pin placement should be placed after radiographic evaluation.

MANDIBULAR CENTRAL INCISOR

Pin location:-

Pins are to be avoided as retention means for restorations as dentin thickness is less in this tooth. Pins may be used at the gingival floor proximally in an aged tooth where the pulp has receded appreciably.

Pins should be located exactly as in the central incisors.

MANDIBULAR CUSPID

Pin location and angulation similar to maxillary cuspid.

MANDIBULAR FIRST PREMOLAR

Pin location and angulation:-

The ideal location is close to or at the proximo-facial and proximo-lingual corners of a gingival floor. The second choice is on the gingival floor between the mesial or distal corners and their centres, facially and lingually. The third choice is gingivally, anywhere between two distal or mesial corners, avoiding the isthmus part of the restoration.

Areas to be avoided: are the middle of the gingival floor, buccally and lingually.

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

MANDIBULAR SECOND PREMOLAR

Pin location:-

In a bicuspid premolar pin location is exactly like the first premolar. In a tricuspid premolar, the ideal location is the disto-lingual corner on the gingival floor. The second choice is gingival floor of the other corners, except the mesio-buccal one. The third choice is the mesio-buccal corner gingival floor and in between the four corners except areas to be avoided. The latter include the area under the lingual groove (pulp horn), and the middle of the buccal gingival floor.

Pin angulation:-

In bicuspid second premolars, angulation is exactly like first premolars. In tricuspid premolars, it should be like first lower molars.

MANDIBULAR FIRST AND SECOND MOLAR

Pin location:-

The ideal location is the disto-lingual corner gingival floor. The second choice is the disto-buccal and mesio-lingual corner gingival floor, and the third choice is the gingival floor mesially or distally avoiding the isthmus portion of the future restoration.

Areas to be avoided: include the mesio-buccal corner gingival floor, the middle of the buccal and lingual gingival floors, and mesio-buccal (furcation) 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 pins should be approximately parallel to the occlusal two-thirds of the buccal surface.

MANDIBULAR THIRD MOLAR: Same as maxillary third molar

POSSIBLE PROBLEMS WITH PINS

A.   FAILURE OF PIN-RETAINED RESTORATIONS:

The failure of pin-retained restorations might occur at any of five different locations:

1.      Within the restoration (restoration fracture)

2.      At the interface between pin and the restorative material (pinrestoration separation)

3.      Within the pin (pin fracture)

4.      At the interface between the pin and the dentin (pindentin separation)

5.      Within the dentin (dentin fracture).

Failure occurs more at the pindentin interface than at the pin-restoration interface.

The operator must keep these areas of potential failure in mind at all times and apply the necessary principles to minimize the possibility of an inadequate restoration.

B.   BROKEN DRILLS AND BROKEN PINS:

·         Twist drill will break if it is 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 pinhole. Pins also may break during bending, if care is not exercised.

·         The treatment for both broken drills and broken pins is to choose an alternate location, at least 1.5 mm remote from the broken item, and prepare another pinhole.

·         Removal of a broken pin or drill is difficult, if not impossible, and usually should not be attempted.

·         The best solution for these two problems is prevention.

C.   LOOSE PINS:

·         Self-threading pins sometimes do not properly engage dentin because the pinhole was prepared too large or self-shearing pin failed to shear, resulting in stripped-out dentin. The pin should be removed from the tooth and the pinhole re-prepared with the next largest size drill, and the appropriate pin inserted. Preparing another pinhole of the same size 1.5 mm from the original pinhole also is acceptable.

·         Pin may get loosened while being shortened with a bur, if the bur is not held perpendicularly to the pin and the pin is stabilized.

·         If the pin is loose, remove it from the pinhole by holding a rotating bur parallel to the pin and lightly contacting the surface of the pin. This will cause the pin to rotate counterclockwise out of the pinhole.

·         Try to insert another pin of the same size. If the second pin fails to engage the dentin tightly, prepare a larger hole, and insert the appropriate pin. Preparing another pinhole of the same size 1.5 mm from the original pinhole also is acceptable.

D.     PENETRATION INTO THE PULP AND PERFORATION OF THE EXTERNAL TOOTH SURFACE:

·         Either penetration into the pulp or perforation of the external surface of the tooth is obvious if there is haemorrhage in the pinhole following removal of the drill.

·         Operator can sense penetration or perforation has occurred by an abrupt loss of resistance of the drill to hand pressure.

·         If a standard or Link Series pin continues to thread into the tooth beyond the 2 mm depth of the pinhole, this is an indication of a penetration or perforation.

·         Radiographs can verify that a pulpal penetration has not occurred if the view shows dentin between the pulp and the pin.

·         A radiograph projecting the pin in the same region as the pulp does not confirm a pulpal penetration because the pin and the pulp may be superimposed as a result of angulation.

·         In contrast, a radiograph showing a pin projecting outside the tooth confirms external perforation.

AMALGA PIN TECHNIQUE:

 SHAVELL in 1980 introduced the amalgapin technique for complex amalgam restorations.

·         In this amalgam itself as the retentive pin and vertical posts of amalgam are anchored in dentin.

·         The channel holes are prepared using a round ended bur # 33 ½ or no. 34 inverted cone bur on the gingival floor 0.5 mm within the DEJ to a depth of 1-2mm and width of 0.5 – 1mm.

·         The amalgam is then condensed into the holes and the remainder of the restoration is condensed and carved.

·         INDICATIONS: Weak gingival areas.

CONCLUSION:

While planning the restorative treatment of badly broken down teeth with vital pulps several factors have to be born in mind. The prognosis of the involved tooth and its role in the overall treatment plan help to decide the restoration to be placed. If the amalgam is selected as the restorative material to be placed, pins placed in the dentin improve the retention of the restoration. Pins have been extensively used in the past to restore such teeth. However studies are now leading to the conclusion that the deleterious effects of pins outweigh their benefits. Also availability of other treatment options are reducing the need to use pins. Clinical judgment should be the final factor in determining how and where they should be placed.

REFERENCES:

1.      Ramya Raghu, Raghu Srinivasan. Clinical Operative Dentistry. Principles And Practice. First edition. Page 253-266.

2.      Theodore M. Roberson, Haraldo. Heymann, Edward J. Swift: Sturdevant’s Art and Science of Operative Dentistry. Fifth edition, page no- 815-831.

3.      M.A. Marzouk, A.L. Simonton, R.D. Gross: Operative Dentistry- Modern Theory And Practice. First edition. Page No- 205-234.

4.      Joseph R. Evans, Jon H. Wetz. The pin-amalgam restoration. Part I. A review. The Journal of Prosthetic Dentistry, Volume 37, Issue 1, January 1977, Pages 37-41.

5.      R.L. Lambert, M.H. Goldfogel. Pin amalgam restoration and pin amalgam foundation.
The Journal of Prosthetic Dentistry, Volume 54, Issue 1, July 1985, Pages 10-12.