CONTENTS 1. INTRODUCTION 2. RATIONALE FOR USE 3. INDICATIONS 4. CONTRAINDICATIONS 5. ADVANTAGES 6. DISADVANTAGES 7. CLASSIFICATION OF PINS 1.
Direct pins/non-parallel pins
2.
Indirect pins/parallel pins
8. MATERIALS USED FOR PINS 9. MECHANICAL ASPECTS OF PIN-RETAINED RESTORATIONS •
Pins and Tooth Structures 1. Stress capabilities of pins 2. Retention of pins in dentin 3. Microcracking and crazing
•
Pins and Restorative Materials
10. ANTOMICAL ASPECTS OF PIN-RETAINED RESTORATIOION 11. MECHANO-ANATOMICAL
ASPECTS
RESTORATIONS 12. CLINICAL TECHNIQUE Direct pins i) Cemented pins Technique Advantages of cemented pins Disadvantages ii) Friction locked pins Technique
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OF
PIN-RETAINED
Advantages Disadvantages iii. Threaded pins Pin Placement Factors and Techniques Advantages Disadvantages Cavity Preparations, Designs and Indications for Pin-Retained Restorations Class II Class III and IV Cavity Preparations Class V Tooth Preparations for Pinlay Cast Restorations •
Indications
•
Types 1. Wrought – Cast on, Soldered and Threaded. 2. Cast.
13. COMPLICATIONS DURING PIN PLACEMENT 14. AMALGAPINS Advantage Disadvantages 15. CONCLUSION 16. REFERENCES
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I. INTRODUCTION The classic cavity design for retention of plastic filling materials incorporates undercuts, usually in the form of boxes, grooves and slots. In the past, when severely damaged teeth lacked tooth structure to adequately retain a restoration, the options were frequently limited to extraction or endodontics followed by a post and core. Although these continue to be acceptable and necessary modalities, the use of pins in dentistry has offered an alternative that is often more practical, and more conservative. Before the development of original pin instrumentation, dentist were creative with the instruments that were available. E.g. tapered dental bur were forced or cemented into holes made into dentin. A portion of the bur heads remained protruding from the hole to be grasped by in amalgam restoration. Early texts suggested that auxillary retention could be gained by screwing wires into pits placed in dentin by a bi-bevel drill. Burgess was the first to consider pin retention from a scientific point of view and he published his findings in 1915. It was not until the application of precision twist drills by Dr Miles markly that the pin technique was widely applied. The key to dentist’s acceptance of the pin system was the predictability,
ease and
confidence in pin placement. Though recently, alternative techniques to some extent have overcome the dangers associated with pin placement, the use of pins cannot be totally eliminated. Definition Pin retained restorations may be defined as any restoration requiring the placement of one or more pin in the dentin to provide adequate resistance and retention forms. 2. RATIONALE FOR USE •
Help support the restorative material and resist their dislodgement in weakened teeth.
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Provide efficient and adequate retention to the restoration with least possible sacrifice of healthy tooth structure
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Limited cavity preparation, preserving esthetics and contours
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It should be emphasized that pins are auxillary aids of retention and should be used only after primary retentive features are not sufficient
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3. INDICATIONS 1. In badly broken down and mutilated teeth, large class II, class III, class IV and class V cavities. 2. For a transitional restoration in badly broken down teeth prior to endodontic orthodontic treatment these pin retained restorations act as build ups for rubber dam application or band attachment. 3. In foundations for partial or full veneer cast restorations or metal ceramic restorations. This will save a considerable amount of tooth structure by eliminating the need to remove undercuts for the cast fabrication. 4. In teeth with questionable prognoses endodontically or periodontally, pin retained restorations may be used as an economic provisional restoration until definitive prognoses is established after a specific waiting period. 5. Pins are also indicated for use as cross linkage mode between two bulky, sound parts of the remaining tooth structure, which are discontinued by abnormal tooth involvement or cracks. 6. As an auxillary or reciprocal retention mode for preparation containing principal retention modes which are insufficient to prevent restoration displacement in a given direction, and as an adjunct retentive mode with a post in endodontically treated teeth to prevent rotation of restoration around the post in the root canal. 4. CONTRAINDICATIONS 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. The complex amalgam restoration also may be contraindicated if area to be restored is esthetically important for the patient.
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5. 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 the 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 the amalgam restoration is a relatively inexpensive restorative procedure. 6. DISADVANTAGES 1. Dentinal microfractures: Preparing pin holes and placing pins may create craze lines or fractures, as way 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 restoration using cavity varnish microleakage around all types of pins has been demonstrated. 3. Decreased strength of amalgam: The tensile strength and horizontal strength of pinretained amalgam restoration are significantly decreased. 4. Resistance form: Resistance form is more difficult to develop than when preparing a tooth for a cusp capping onlay or a full crown. The complex amalgam restoration does not protect the tooth from fracture as well as an extracoronal restoration. However, amalgam restoration with cusp coverage significantly increase the fracture resistance of weakened teeth as compared to amalgam restorations without cusp coverage. 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 restoration.
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7. CLASSIFICATION OF PINS Pins can be classified as: 1.
Direct pins/non-parallel pins
2.
Indirect pins/parallel pins
1. Direct pins •
Are usually made of stainless steel, and inserted into dentin followed by the placement of a restorative material like silver amalgam, resin or cement directly over them.
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Other materials of which the pins can be made of, are silver, titanium, stainless steel with gold plating etc.
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These have also been referred to as the non-parallel pins since they can be inserted directly into the tooth structure and hence need not be parallel.
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Further, this category of pins includes cemented, friction locked and threaded pins of which the last category of pins is the most popular.
2. Indirect pins •
Are slightly undersized compared to their pinholes and are an integral part of a cast restoration.
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These are also known as the 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.
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The pins are held in the pinholes through cement.
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There are basically two types of pins used in the parallel pin technique. a) Cast gold pins, which have a relatively smooth surface. Restorations using these pins are fabricated by placing nylon bristles or plastic pins in the pinholes over which the rest of the restoration is built in the conventional form with a blue inlay wax. The whole assembly is invested and cast, with pins forming an inherent part of the cast restoration. b)
Wrought precious metal pins have surfaces that have been
deformed or roughened by means of threaded or knurled patterns.
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These pins are alloys of gold, platinum, palladium or platinumiridium. 8. MATERIALS USED FOR PINS Materials used for the construction of pins include stainless steel, titanium, silver, cast gold alloys, platinum-palladium, platinum iridium, plastic, aluminium, acrylic etc. •
Stainless steel, titanium and silver pins are commonly used for the direct/non-parallel pin technique, of which the stainless steel pins are used most frequently. Stainless steel pin is stronger than its gold and titanium counterparts but has the disadvantages of getting corroded and non-adherence to silver amalgam and composite restorative materials.
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Titanium pins have the advantages of being the least corrosive and most biocompatible of the metals but their strength and modulus of elasticity is less compared to that of stainless steel and high gold content alloys. Titanium pins also do not show any adherence to silver amalgam or composite restorative materials.
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Silver pins were introduced with the idea of achieving a true adhesive bond between the pin and silver amalgam material so as to render them an integral part of the restoration. An excellent bond does exist between silver pins and silver amalgam as shown by Moffa et al. (1972), but solid silver pins are soft and easily deformed.
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Pins constructed in cast gold, platinum-palladium or platinum-iridium are used with the indirect/ parallel pin technique. These pins are relatively corrosion resistant. Platinum-palladium or irido platinum pins are available as prefabricated pins and are cast directly to the overlying gold restoration.
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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.
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Aluminium pins are used for retaining a temporary restoration until the final restoration is fabricated and inserted.
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Acrylic pins have been tried for use with composite resins, but are not very popular.
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Silver plated and gold plated stainless steel pins have also been tried to achieve a true adhesive bond between steel and silver amalgam. However, these pins did not prove to be very successful.
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•
Microscopic observation revealed no difference in the interphase of silver plated pins and amalgam with that of the non-plated pins and amalgam (Moffa et al, 1972). It was speculated that there occurred a complete dissolution of the silver plate in the amalgam matrix resulting in voids and an irregular interphase. Bonding of amalgam to gold plated pins is also difficult to achieve because of the inability to maintain a gold surface free of contaminants especially under oral conditions. Gold plated pins are usually preferred under composite resins to reduce the 'shine through' of stainless steel pins.
9. MECHANICAL ASPECTS OF PIN-RETAINED RESTORATIONS Pins and Tooth Structures 4. Stress capabilities of pins 5. Retention of pins in dentin 6. Microcracking and crazing
1.Stressing capabilities of pins: •
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.
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These stresses might concentrate to a point exceeding the dentin's plastic limit, resulting in microscopic and/or macroscopic dentinal cracks, i.e., interrupted and/or continuous fractures of the dentin substance.
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Either can lead to pulpal, suface, and/or periodontal involvement with their sequelae (cracked tooth syndrome, gross fracture of the tooth or part of the tooth, loose restorations, etc.)
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There are many factors in pin techniques and materials that can increase or decrease these stresses: 8
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 dentin during insertion of the pin. Thus, in cemented pin techniques, there are little or no stresses. Maximum stresses are associated with the friction grip technique. The threaded pin technique introduces stresses intermediate to the other techniques. If the distance between threads is less, then the stresses induced are more. Blunts threads also increases the stress.
2. Diameter of pins: Greater the pin diameter to that of the pin hole more stresses. 3. Pin depth and dentinal engagement •
The greater the depth of a pin channel, greater are the stresses.
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This situation is most marked in threaded and friction grip pin techniques, which is due to the greater dentinal involvement.
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Modern pins have a lesser number of threads with a greater distance between these threads. Threads are designed to the self-tapping and sharp, extending very short distances laterally.
4. Bulk of dentin Greater bulk of dentin pulpally or towards the surface from the pins, less will be the 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 and toughness.
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The greater that the mineralization and dehydration of the dentin is, and the greater that the obliteratio of the dentinal tubules is, the less the dentin will be able to tolerate stresses without some eventual failure.
•
Sequence of stress tolerance of different types of dentin in decreasing order is -
Secondary dentin
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Sclerosed dentin
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Tertiary dentin
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Calcific barrier
Therefore it is a basic principle in pin technique to not use threaded or frictional grip pins in endodontically treated teeth and areas of dead tract formation in the dentin. 6. Inter pin distance -
Closer the pins are to each other more the stresses
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For small threaded pins a distance of not closer than 4mm should be maintained. For larger threaded pins the distance should be increased.
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For cemented pins the distance can be decreased.
7. Non – coinciding eccentricity in pins or pin channel circumferences -
Eccentricity is usually due to non-centrically running drills causing elliptical or irregularly shaped pin channel to occur that are not in conformance with the pin shape. 10
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The pin will contact the surrounding dentin at only one or two points, these by concentrating stresses that should be distributed evenly over all surrounding dentin.
8. Loose pins -
A loose pin within its pin channel could result in a pin retained restoration that is partially or completely mobile.
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The pin will move inside its channel with every movement of the restorations creating stresses within dentin.
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Stresses are directly proportional to the amount and the degree of pin movement within the dentin.
9. Wedge, chisel or irregularly shaped dentinal end of pins -
Irregularly shape pin ends can happen during pin manufacturing or pin adjustment prior to the insertion procedure.
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This situation will cause concentrations of stresses at small cross sections 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 ratio of dentinal engagement pin protrusion is 2:1.
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-
Although a ratio of 1:1 is tolerable, a lower ratio will make the dentinal portion of the pin the short side of a type one lever.
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 pins per unit volume of dentin.
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The fewest pins needed that will help retain a restoration should be used
12. Twist drill variability -
Blunt edged drills, vibrating drills or a twist drill used with laterally applied forces can magnify the stresses in the dentin to a greater level than will be consumed in the pin channel cutting. It will invite crack formation in the involved dentin.
13. Over threading or overdriving of pins into the channel: magnify and induce unnecessary stresses in dentin 14. Stress induced during shortening pins inside the cavity preparation. 15. Bending or aligning pins after dentinal engagement will lead to intolerabe stresses in dentin 16. Retentive features in the remaining portion of the cavity preparation. -
If the retentive features of the principal type are greater, less will be the displacing forces that will filter through the pins. Hence less stresses on the dentin. Hence should only be used as an auxillary means of retention
17. Inserting pins in a stress concentration area of a tooth -
In stress concentration areas, (e.g. the axial angle or incisal angle or the junction between clinical crown and clinical root), inserting pins will complicate pre-existing stress pattern, especially if the bulk of structure has already been reduced.
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2. Retention of pins in dentin The main objective of using pins in a restoration is to acquire or improve retention of the restoration in dentin. Such retention of pins in dentin is dictated by the following factors: 1. Type of pins -
self-threading pins will be 5-6 times more retentive than cemented pins.
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Friction grip pins will have 2-3 times the retention of a cemented pin.
2. Depth of pin engagement in dentin According to Moffa, a graph which plots the depth of pin engagement in dentin against tensile forces needed to create failure at the pin-cement-dentin complex will illustrate the following: o A linear relationship without a plateau exists in case of cemented pins. Failure usually occurs at the cement-dentin interface. o The plotting for friction grip pins shows no increase in the resistance to failure after 2 mm of dentinal engagement. Failure always occurs at the pin-dentin interface. o In the case of small threaded pins, there is no increase in the resistance to failure after 2 mm of dentinal engagement. Failures usually occur within pins themselves. o A plateau is formed after 1.5-2.0 mm of dentinal engagement in case of large threaded pins (regular). The failure usually occurs in the dentin itself. 3. Pin channel circumferential shape relative to that of the pin -
It stands to reason that the greater that the coincidence of these two shapes is, the better will be the retention.
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This will make for continuous contact between the pin and the dentin (cement), thereby increasing the frictional retention.
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4. Number of pins •
Pin proximity and location relative to displacing forces (not the total number of pins per tooth) affects the retention.
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Pins placed closer than 2 mm to each other in one tooth will result in a loss of pin retention in dentin, this may be caused by micocracks.
5. Type of cement •
In the case of cemented pins, copper-phosphate cement (which is only to be used in non-vital teeth) is the most retaining cement. This is followed by zinc phosphate cement, polycarboxylate cement, and ZOE, in that order.
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Using varnish with zinc phosphate cement will decrease its retaining power by almost 40%.
6. Type of involved dentin •
Young, resilient, primary dentin is the most retaining type of dentin, followed by tubular secondary dentin.
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Hypermineralization (sclerosis and calcification) and dehydration (nonvitality) of dentin will drastically decrease its pin-retaining power.
7. Surface roughness of the pins •
Pins with surface serrations or threading will have increased retention in dentin, especially in the case of the cemented pin technique.
8. The ratio of dentinal engagement of the pins to their protruding lengths in the cavity preparation •
The ideal ratio for the pin retention in dentin during function is 2:1. A higher ratio will increase the pin retention, while a lower ratio will definitely decrease the retention.
9. Mode of shortening the pins after insertion •
Ideally, pins should not be manipulated after insertion, but frequently it is necessary to shorten them after they are engaged within the dentin.
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•
The least disturbing method to the retention of the pin is to clip the excess with a cutting plier. In many cases, access will prevent using pliers, and rotary cutting is the only available way.
The following techniques will minimize the disturbance of pin retention in dentin when shortening pins with rotary instruments: -
Use the smallest carbide bur applicable, preferably a '/4 round or 699 bur.
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Apply pressure in a clockwise direction in the case of threaded pins, i.e., the direction of threading the pins.
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Hold the pin with a hemostat (plier or holding instrument) while applying the lateral cutting pressure.
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During all these acts use light intermittent pressure at the highest speed possible to minimize vibration that may disengage the pin from the dentin.
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Nick the pin at the designated level of shortening. Then bend the excess to fracture using a hemostat or pliers.
10. Bulk of dentin around the pin •
The greater that the cross-section of dentin separating the pins from the pulp, tooth, and root surface is, the greater will be its retention.
3. Microcracking and crazing •
Microcracking or mechanical separation of enamel components from each other can start at the surface or at the DEJ.
•
The most common crazing, and the least detrimental to the tooth, is: -
that originating at the surface. This type will encounter the gnarled enamel, decreasing the possibility of its propogation.
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Crazing starting
DEJ and appearing on the surface must
penetrate the gnarled enamel Unfortunately pins can cause the second type of crazing •
The following factors can dictate the occurrence, type, extent and number of crazing 1. Type of pins
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-
According to Moffa, cemented pins, even if they are located at the DEJ, do not create any crazing in the adjacent enamel.
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Friction lock pins create the maximum number and extent of crazings even at 1.5 mm from the DEJ.
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Threaded pins are intermediate etiologic agents especially when smaller sizes are used.
2. Proximity of pins to the DEJ -
It is considered that areas 0.5-1.0 mm from the DEJ are a safe location for cemented pins, 1.5-2.0 mm from DEJ is safe for threaded pins, and there is no practical safe location for friction grip pins.
3. Induced stresses in involved dentin -
One of the products of stress concentration in dentin is microcracks which can appear in enamel if the gnarled enamel is crossed.
4. Thickness of adjacent enamel -
The thinner that the adjacent enamel is, the greater with the possibility of crazing within it.
5. Type of dentin between the pin and adjacent enamel -
The greater that dehydration or mineralization in the intervening dentin is, the faster a crack will travel from pin site to the enamel, and the greater will be the possibility of crazing.
Pins and Restorative Materials
A. Effect of pins on the strength of amalgam and composite resins
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1. Pins will not increase the compressive strength of restorative material. They only help in retaining it mechanically. In fact, there will be a drop in the compressive strength of these restorations if: 1) The cavity end of the pin is chisel- or wedge-shaped or irregular in shape.
2) Pins are closer than 2 mm to each other. This situation will drastically affect the restorative material strength, possibly due to increased incidence of voids and decreased bulk of the material.
3) Pins protrude through or approximate the surface of the restoration. This situation leads to segmentation and separation of the restorative material with less bulk and more interfaces
4) Less than 1.5-2.0 mm exists between the pin surface and the restoration surface. In this circumstance, the restorative material bulk will be less than the minimum bulk for amalgam or composite resin to successfully resist mechanical failure under compression 5) There is non-adapatability of the restorative material to the pin due to improper wettability or voids. This will lead to movement of the restorative material independent of the pin. For this reason, the failure
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rate of composite resin restorations retained by pins is higher than the amalgam. 2. Tensile strength The same factors that affect the compressive strength of amalgam and composite resins also affect their tensile strengths. In addition: 1) There will be severe reduction (30-40%) in the tensile strength of the restorative material if the pins are placed at right angles to the direction of the tensile stresses induced during function. 2) A moderate reduction (10%) in tensile strength can be expected if the pins are placed at 45째 to the direction of the induced stresses in the restoration during function. 3) No reduction of tensile strength will occur if the pins are placed parallel to the direction of tensile stresses in the restoration. These three factors dictate the necessity to avoid the insertion of a gingival pin in isthmus portion of a cavity preparation, especially in cavities with shallow gingival floors. B. Retention of pins to restorative materials The following factors control pin retention to the restorative material: 1. Type of pins -
Friction grip pins are the least retentive for amalgam and composite resins due to their smooth surfaces.
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Cemented pins and threaded pins are four times more retentive than the friction grip, mainly due to the gnarled and threaded roughness of their surfaces.
2. Pin length in restorative material -
For friction grip pins, retention is directly proportional to the length of pin in the restorative material, without any plateau. Failure will almost always occur in the pin-restorative material interphase.
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For the cemented and small threaded pins, the retention in the restorative material is direct y proportional to the length of the pin in the restorative material up to a length of 2 mm where a plateau is reached. Failure will occur in the pins themselves.
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-
For large threading pins, the plateau for retention in the restorative material will occur at a pin length of 1.5 mm within the restorative material failure will always occur in the restorative material itself. There is no evidence that bending pins will increase retention of restorative materials to the pins.
3. Pin diameter -
There is a gradual increase in pin retention to restorative material with increasing pin diameter up to 0.035�.
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Any diameter larger than this will have no significant increase in retention.
4. Interpin distance -
Interpin distance of 2 mm will cause a definite reduction in pin retention within the restorative material.
5. Proximity of the restorative material to the pin surface -
The greater that the wetting ability of a restorative material to the pin surface is, the greater will be the adaptability and consequently the frictional retention components.
6. Surface material of the pins -
If the surface layer of the pin can chemically combine with the restorative material or one of its phases (mercury), and still be of sufficient thickness to leave a considerable part of it still adhering (cohering) to the pin bulk, an ideal retention mode will exist at this interphase.
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Unfortunately, gold or silver plating of SS pins is not as effective as would be expected.
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Amalgam mercury will combine with the silver veneering layer found in some pins, dissolving it and reacting with it completely.
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If pins are gold plated, gold must be pure and cleansed of any surface impurities for the mercury to react with it, a condition that cannot be attained inside a tooth preparation without endangering the tooth itself.
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All-silver pins are not effective retaining means because of their plasticity and affinity to mercury.
10. Anatomical Aspects of Pin-Retained Restorations To preserve the anatomical integrity of a tooth to receive a pin-retained restoration, one should confine the tooth retained part of the pin to dentin only. Of course,
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it is undesirable to approximate or perforate to the tooth surface, pulp chamber, root canal system, furcation or the cementum. 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, particularly in a spatial three-dimensional pattern, 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. It is a good habit to apply the drill on that adjacent surface, then move it 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 (during endodontic therapy) may enlarge the aforementioned space, decreasing the dimension of dentin.
E. Anatomical features -
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, etc., necessitates individual evaluation of the tooth involved to determine the best access, location, and angulation of pin channel.
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One of the most difficult teeth in which to insert a pin is an inclined tooth which has completely lost its crown
G. Cavity extent
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-
The more apically located that a gingival floor is, the higher will be the possibility of surface and pulp-root canal perforation.
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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.
12. Mechano-Anatomical Principles for Pin-Placement A. Maxillary central incisor •
This tooth has four pulp horns—three in the mesio-distal direction and one in the labio-lingual direction (cingulum). In a cross-section at the cervical margin, there is an average of 1.5-1.8 mm of dentin circumferentially gingivally, with more dentin labially than lingually.
•
Pin locations The ideal location is gingival, close to the proximo-labial and proximo-lingual corners. The second choice is the middle of a proximal gingival floor or the middle of a labial gingival floor and the third choice is incisal, where there is at least 2 mm or more of dentin between the labial and lingual enamel plates. Areas to be avoided include the middle of a 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, and incisal near a proximal pulp horn.
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Pin angulation Proximal and labial pins always should have a slight labial angulation in the labio-lingual direction. All gingival pins should have a very limited angulation (10-20%) with the longitudinal axis of the tooth in the mesio-distal direction. Incisal pins should be parallel to the incisal ridge.
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B. Maxillary lateral incisor •
These teeth have the same general anatomy of the pulp horn and chamber as central incisors. Circumferentially gingivally at the cervical line, there is an average of 1.21.5 mm of dentin.
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Pin location The ideal location and second choices are same as for the central incisors. The areas to be avoided are the middle of a lingual gingival floor and incisally.
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Pin angulation Pins should be angulated as in the central incisor except that all gingival pins should have slightly more angulation (15 20%) with the longitudinal axis of the tooth in the mesio-distal direction.
C. Maxillary cuspid •
In this tooth, the pulp chamber has only two pronounced surfacewise projections, incisally in the middle of the tooth and lingually (cingulum). At a cervical line crosssection, on the average there is from 2.5-3.5 mm of dentin circumferentially gingivally. There is more dentin labially than lingually.
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Pin location This tooth ranks second only to the 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. The 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 22
to be avoided include the middle of the lingual gingival floor, and gingival pins close to surface concavities or grooves, which can occur proximally. •
Pin angulation Gingival pins proximally and labially 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 20-35°. Incisal pins should be parallel to the adjacent proximal slope of the tooth.
D. Maxillary first bicuspid •
The pulp chamber in this tooth is narrower mesio-distally than bucco-lingually. There are two pulp horns, of which the buccal is the most pronounced. Always there is a pronounced concavity on the mesial surface of the tooth (canine fossa). Circumferentially gingivally at the cervical line, there is an average of 2 mm of dentin bucally and lingually, 1 mm mesially and 1.5 mm distally. There is more dentin lingually than bucally.
•
Pin location The ideal location is at or close to the proximo-facial and lingual corners of the tooth gingivally. The second choice is gingival between the corners of the tooth and the middle of the axial surfaces with the exception of the mesial surface. Areas to be avoided include the mesial gingival floor (canine fossa), the middle of the gingival floors bucally and lingually (because of the concavity of the pulp chamber, especially bucally), and the gingival floors, occlusal to furcations.
•
Pin angulation All gingival pins should be parallel to the longitudinal axis of the tooth.
E. Maxillary second premolar •
This tooth resembles the first premolar in its pulp anatomy, with more dentin circumferentially gingivally (on the average mesially and distally 1.5 mm, bucally and lingually 2.5 mm). There is no mesial surface concavity. There is more dentin lingually than bucally.
•
Pin location There is more freedom in using pins in the second bicuspid than in the first bicuspid. The ideal location is the same as for first premolars. The second choice
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is at gingival floors between the corner and their middle proximally, facially, and lingually. Areas to be avoided include the middle of the gingival floor facially and lingually (concavity of the pulp chamber), and areas of the gingival floor occlusal to furcation, if present. •
Pin angulation The same angulations apply to both first and second premolars.
F. Maxillary first molar •
The whole pulp chamber of the upper first molar is mesio-buccally deviated. Although there are four pulp horns, the mesio-buccal one is the most pronounced. Circumferentially gingivally at the cervical line, the dentin measures an average of 22.5 mm mesially and distally and 2.5-3.5 mm bucally and lingually. There is more dentin distally, especially disto-lingually, than mesially, especially mesio-buccaly. There are three furcations; one is located buccally, and each of the other two are located proximally. The closest furcation to the surface is the buccal, followed by the distal and the deepest furcation apically and inwardly is the mesial furcation.
•
Pin location o The ideal location is the gingival floor at or close to the disto-lingual corner. o The second choice is the gingival floor at or close to the disto-buccal and mesio-lingual corner of the tooth. o The third choice is the gingival floor lingually, mesially and distally if you can avoid the furcation and the isthmus portion of the future restoration. o
Areas to be avoided include the gingival floor or tables at the mesio-buccal corner of the tooth, any part of the gingival floor occlusal to a furcation (facially and proximally), its flutes, or a root concavity, and areas mesiobuccal to the cusp tips (pulp horns).
•
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.
G. Maxillary second molar
24
This tooth is very similar to the first molar in all aspects, except there may be less dentin circumferentially gingivally and the pulp horns are 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 quadritubercular, it can be similar to the first molar. If tri-tubercular, the anatomy will be very peculiar for each tooth.
•
Generally speaking, the pulp chamber can be expected to be more occlusally located, and its walls can be expected to converge more toward the cervical line following the slope of the tooth crown.
•
There is always a disto-buccal inclination of the crown, which can invite distal and buccal surface perforation, as well as mesial and lingual pulpal perforation.
•
To avoid unwanted perforation or encroachment during pin channel preparation in these teeth, they should be studied carefully and pin placement decided upon and executed carefully. To say the least, upper third molars are very poor candidates for pin-retained restorations.
I. Mandibular central incisor •
This tooth has a very peculiar pulp chamber, which is wider mesio-distally at its incisal half than labio-lingually; yet its gingival half or less is wider labio-lingually than mesio-distally. There are three pulp horns: two in the mesio-distal direction and one in the lingual direction (the most pronounced of the three). The pulp chamber is generally lingually deviated. Circumferentially gingivally the tooth has the least amount of dentin in a cross section, 0.8-1.7 mm on the average. There is more dentin labially than proximally or lingually.
•
Pin location There is no ideal place for pin location in this tooth. Pins are to be avoided as retention means for restoration this tooth. Pins may be used at the gingival floor proximally in an aged
•
Pin angulation As in the maxillary incisors, all gingival pins should be angulated slightly labially in the linguo-labial direction. Mesio-distally, pins could have an angulation of 30-
25
40° to the longitudinal axis of the tooth. Understandably, there is no place for incisal pins in this tooth. J. Mandibular lateral incisor •
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 of 1-2 mm dentin.
•
Pin location Pins should be located exactly as in the central incisors, with similar advice not to use pins except in aged teeth.
•
Pin angulation This tooth is similar to the central incisors, except in the mesio-distal direction, the angulation relative to the long axis of the tooth could be up to 50° to avoid perforation and encroachment.
K. Mandibular cuspid •
Surface, pulp chamber, and root canal system anatomy are very similar to those features of the upper cuspid. Circumferentially gingivally, the average amount of dentin in a cross-section is 2.2-3 mm, with more dentin labially than mesially, distally, and lingually.
•
Pin location and angulation are very similar to those of the upper cuspid.
L. Mandibular first bicuspid •
This tooth has the most predictable pulp chamber and root canal system anatomy. The pulp chamber is wider bucco-lingually than mesio-distally. The average thickness of dentin circumferentially gingivally at the CEJ is 2-2.5 mm. There is more dentin bucally and lingually than mesially and distally.
•
Pin location and angulation o The ideal location is close to or at the proximo-facial and proximo-lingual corners of a gingival floor or table. o The second choice is on the gingival floor between the mesial or distal corners and their centers, facially and lingually.
26
o The third choice is gingivally, anywhere between the two distal or mesial corners, avoiding the isthmus part of the restoration. o The areas to be avoided are the middle of the gingival floor, bucally and lingually. Pin angulation should always be parallel to the long axis of the tooth. M. Mandibular second premolar •
If this is a bicuspid premolar, its anatomy will be very similar to the first premolar, with the exception that it always has a lingual pulp horn and the pulp chamber is more rounded. If it is a tricuspid premolar, its pulp anatomy will be different, in that the pulp
chamber
will
be
mesio-bucally
deviated,
with
three
pulp
horns.
Circumferentially gingivally, the average thickness of dentin at the CEJ is 2-3 mm bucally and lingually, 2.3-2.6 mm mesially and distally. •
Pin location o 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. o The second choice is gingival floor of the other corners, except the mesiobuccal one. o
The third choice is the mesio-buccal corner gingival floor and in-between the four corners except areas to be avoided.
•
Pin angulation In bicuspid second premolars, angulation is exactly like first premolars. In tricuspid premolars, it should be like first lower molars.
27
N. Mandibular first molar •
This tooth usually has five pulp horns, the mesio-buccal being the most pronounced and closest to the surface. The whole pulp chamber is mesio-bucally deviated with more dentin distally, especially disto-lingually, than mesially, especially mesiobuccally. The floor of the pulp chamber is smaller than its roof. Circumferentially gingivally, the average thickness of dentin is 2-3 mm at the cervical line. There are two furcations between the mesial and distal roots: one in the buccal and another in the lingual.
•
Pin locations o The ideal location is the disto-lingual corner gingival floor. o 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. o Areas to be avoided include the mesio-buccal corner gingival floor, the middle of the buccal and lingual gingival floors (furcation), and mesio-buccal to any cusp tip (pulphorn).
•
Pin angulation
28
Mesially and distally, gingival pins should be parallel to the long axis of the tooth. Bucally and lingually, gingival pins should be approximately parallel to the occlusal two-thirds of the buccal surface. O. Mandibular second molar This tooth is very similar to the first molar, except that the pulp chamber has four pulp horns only, and less surrounding dentin bulk. P. Mandibular third molar o As in the upper third molars, there are infinite anatomical variations in these teeth. They can have some similarities to first molars if they have five cusps, yet, they can be similar to the second molar if they have four cusps. o As in the upper third molars the pulp chamber in the lower is very much deviated occlusally, with severe flaring of the pulp chamber apically. There is a great tendency for a mesio-lingual angulation of the tooth as a
o
whole, which increases the probability of mesial and lingual surface perforation. o As in the upper, every lower third molar should be studied carefully as an individual case. 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 the unpreditability of their anatomy.
13. CLINICAL TECHNIQUE Direct pins The three major categories of direct pins are cemented, friction locked and threaded pins.
29
Cemented
Friction locked
Self-threaded
i) Cemented pins •
Markley introduced this type of pin in early 1950's to achieve greater retention in a large silver amalgam restoration.
•
In this technique, the pins are 0.001"-0.002" smaller than their pin channels and the difference in diameter provides space for the cementing medium.
•
The pins can be of varying sizes - 0.018" to 0.030" and the corresponding pin channel sizes are then 0.020" to 0.032" respectively.
•
Cemented pins are generally indicated in cases where least crazing and stresses are desired in the remaining tooth structure e.g. endodontically treated teeth. It is the preferred technique for class IV preparations where the pins need to be bent in the form of U or L, or when crosslinking two parts of the same tooth is required.
Technique •
The method commonly utilizes pins in the form of stainless steel wires, which are serrated or threaded and cut to the required length.
• •
Pinholes extending 4-6 mm into dentin are prepared using twist drills. If the pin channel is directly accessible and visible and the operator has full control on the manipulation of the pin, the wire can be cut extraorally to the desired length with a wire cutter or a Dial-A-Pin cutter.
•
The length should be such that after seating the pin into the pin channel completely, the pin extends not more than 2-3mm above the base.
•
The pin is held in the locking tweezers or grooved haemostats and placed in the pinhole for checking its fit and length.
•
If necessary, the pins can be bent with contouring pliers to keep them within the contours of the restoration.
•
When access to the pin channel is difficult and there exists a possibility of losing or mislocating the pin during its try-in, the wire should not be cut completely but a groove made at the desired length. The rest of the wire serves as a handle during the try in and seating of the pin.
•
The pin channels are dried with precut endodontic paper points. For cementation purposes, zinc-oxyphosphate cement is mixed to a luting consistency on a cool glass slab. Other agents that can be used for cementation are polycarboxylates and light
30
cure glass ionomer cements. When Zinc phosphate cement is selected, the operator should consider applying a thin layer of copal varnish to the walls of the pin channel with endodontic paper points. •
The cement mix is introduced into the pin channel with a root canal file or/an explorer or a lentulo-spiral running at slow speeds of 1000 rpm or less.
Terminal end of lentulo-spiral cut •
The pin held in the forceps is also coated with the cement and inserted into the hole. An amalgam condenser is used to assure full seating of the pin. The pin is held in its position till it sets.
•
The excess cement is flicked off with an explorer point.
•
Any bending of the pin should be done prior to cementation to avoid loosening of the cement joint and introduction of stresses into dentin.
•
This technique was later modified using threaded stainless steel pins of the same size as the twist drill. Most commonly used size is the 0.027 inches.
•
The advantages offered by this technique are : close contact between the pin and channel and increased lateral stability. The pin is cut and modified by creating a longitudinal facet with a carborundum disc. This facet serves as a vent and is necessary to allow escape of excess cement especially when the pin and the channel diameters closely match.
Advantages of cemented pins 1. Cemented pins are approximately 0.001"-0.002" (0.025 mm-0.050 mm) smaller than their pinholes and hence are more likely to be seated to the full depth of the hole. 2. Since they are passively retained in the dentin, they virtually place no stress on the surrounding dentin during or after placement. 3. Because the cement seals the interface between the pin and the tooth, chances of microleakage are reduced.
31
4. These can be cut or bent to their final configuration before fixing them in the pin holes. Disadvantages •
They offer less retention compared to the friction locked and threaded pins.
•
It is often difficult to insert cement into the pinhole and later locate the hole after cement has been introduced.
•
At times, a poorly cemented pin is easily dislodged when the filling material is being inserted.
•
Greater time is required for the mixing and hardening of the cement.
ii) Friction locked pins •
With the idea to improve upon the disadvantages of cemented pins, Goldstein (1966) introduced the friction locked pins.
•
These pins are 0.001" larger than their pin channels and hence utilize the elasticity of dentin for retaining the tapped pins in a vise like grip e.g. a pin of size 0.022" is inserted into a pin hole of size 0.021".
•
Pin are tapped into place, retained by the resiliency of the dentin and are 2-3 times more retentive then cemented pins.
•
These pins are indicated in teeth that are vital and periodontally sound, and where direct access is possible so that the tapping force can be applied parallel to the long axis of the pin. The pins are indicated only when sufficient amount of dentin is available to surround the pin and in no way should they be placed closer than 1.5 mm to the dentino enamel junction.
Technique
32
•
A self-centering spiral drill mounted in a low speed handpiece is used to prepare the pin channel in dentin to a depth of 2-3 mm, 1.5 mm inside the dentino-enamel junction.
•
The channel must be kept dry until the pin is inserted. Friction locked retention pins are smooth surfaced and may be prefabricated from stainless steel wires with a cutting plier or carborundum disc.
•
The depth to which the pin channel has been drilled is marked on the pin with a permanent marker. The pin is inserted into a pin setter and carried to the pinhole.
•
A mallet is used to apply force parallel to the axis of the pin. Only moderate force similar to that used for condensing gold foil is applied to avoid any damage or discomfort.
•
Forces are applied until the established mark on the pin reaches the cavity floor.
•
Any excess length is then removed with a small round bur in an air rotor handpiece with adequate air water coolant.
•
If required, the pin is bent at a desirable angle with a contouring plier.
Advantages 1. Cement is not required. 2. Pins acquire stability from the moment they are inserted. 3. Better retention than the cemented pins. Disadvantages 1. The length of the pin is judged by trial and error. It cannot be removed from dentin for cutting to the desired length once inserted. 2. Bending or contouring of the pin after it has been inserted into the pinhole leads to further stresses. 3. Driving pins into their respective pinholes generates stresses in dentin in the form of cracks or craze lines. 4. Many a times, the pins do not reach the full depth of the channel because of gouging, and hence may lose some of their retentive capacity. 5. Microleakage is higher than for cemented pins, if the overlying restoration leaks. iii. Threaded pins
33
•
The use of threaded pins was described by Going in 1966. In this technique, the pins are 0.0015"-0.002" larger than their pin channels and like the friction locked pins they are also retained by the elasticity of dentin. The depth of the pinhole varies from 1.3 to 2mm depending on the diameter of the pin used.
•
Additionally, they actively engage the tooth structure through their threads similar to a screw inserted into a wooden block.
•
Currently, threaded pins are most popular amongst the three pin systems. The reasons for their rising popularity are ease and rapidity of insertion, and maximum retention offered.
•
However, the amount of stresses induced in dentin in the form of cracks and craze lines is also maximum with the threaded pins. These pins are indicated in vital teeth and where maximum retention is desired.
Pin Placement Factors and Techniques Pin size. •
Four sizes of pins are available each with a corresponding color-coded drill. Two determining factors for selecting the appropriate size pin are: 1. the amount of dentin available to safely receive the pin and 2. the amount of retention desired.
•
In the Thread Mate System, the pins of choice for severely involved posterior teeth are the Minikin (0.019 inch [0.48 mm]) and, occasionally, the Minim (0.024 inch [0.61 mm]).
•
The Minikin pins usually are selected to reduce the risk of dentin crazing, pulpal penetration, and potential perforation.
•
The Minim pins usually are used as a backup in cases where the pinhole for the Minikin was overprepared or the pin threads stripped the dentin during placement and the Minikin pin lacks retention. Dilts et al reported that the larger diameter pins have the greatest retention.
•
The Minuta (0.015 inch [0.38 mm]) pin is usually too small to provide adequate retention in posterior teeth.
•
The Regular (0.031 inch [0.78 mm]) or largest diameter pin is rarely used because a significant amount of stress and crazing, or cracking, in the tooth (dentin and enamel) may be created during its insertion.
34
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 pins safely, (3) the amount of retention required, and (4) the size of the pins.
•
As a rule, one pin per missing mini line angle should be used. Certain factors may cause the operator to alter this rule. The fewest pins possible should be used to achieve the desired retention for a given restoration.
•
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
Location. •
Several factors aid in determining pinhole locations: (1) knowledge of normal pulp anatomy and external tooth contours, (2) a current radiograph of the tooth, (3) a periodontal probe, and (4) the patient's age. Although the radiograph is only a twodimensional picture of the tooth, it can give an indication of the position of the pulp chamber, and the contour of the mesial and distal surfaces of the tooth. Occlusal clearance should be sufficient to provide 2 mm of amalgam over the pin.
A,Position relative to DEJ
B, Position relative to external surface
•
Several attempts have been made to identify the ideal location of the pinhole. Caputo and Standlee state that, ideally, pinholes should be located halfway between the pulp and the DEJ or external surface of the tooth root.
35
•
Standlee and others have shown that there should be at least 1 mm of sound dentin around the circumference of the pinhole. Such location ensures the proper stress distribution of occlusal forces.
•
Felton and associates-have demonstrated that pin placement providing at least 1 mm of remaining dentin thickness from the pulp elicits minimal pulpal inflammatory response.
•
Dilts and associates have reported that pinholes should be placed at 0.5 mm inside the DEJ.
•
In the cervical one third of molars and premolars (where most pins arc located), pinholes should be located near the line angles of the tooth, except as described later. The pinhole should be positioned) no closer than 0.5 to 1 mm to the DEJ or no closer than 1 to 1.5 mm to the external surface of the tooth whichever distance is greater.
•
Before the final decision is made about the location of the pinhole, the operator should carefully probe the gingival crevice to determine if any abnormal contours exist that would predispose the tooth to an external perforation.
•
As a rule, the pinhole should be parallel to the adjacent external surface of the tooth.
•
The position of a pinhole must not result in the pin being so close to a vertical wall of tooth structure that condensation of amalgam against the pin or wall is jeopardized. Therefore it may be necessary to prepare first a recess in the vertical wall with the No. 245 bur to permit proper pinhole preparation, as well as to provide a minimum of 0.5 mm clearance around the circumference of the pin for adequate condensation of amalgam.
•
If necessary, after a pin is inappropriately placed, the operator should provide clearance around the pin to provide sufficient space for the smallest condenser nib to ensure that amalgam can be condensed adequately around the pin. A No. 169L bur can be used, being careful not to damage, or weaken, the pin.
•
Pinholes 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," and a depthlimiting drill (discussed later) cannot prepare the hole as deeply as intended
•
Whenever three or more pinholes are placed, they should be located at different vertical levels on the tooth, if possible. This will reduce stresses resulting from pin placement in the same horizontal plane of the tooth.
36
•
Spacing between pins, or the interpin distance, must be considered when two or more pinholes are prepared. The optimal interpin distance depends on the size of pin to be used. The minimal interpin distance is 3 mm for the Minikin (0.019 inch [0.48 mm]) pin and 5 mm for the Minim (0.024 inch [0.61 mm]) pin. Maximal interpin distance results in lower levels of stress in dentin.
. Pinhole preparation. Three basic instruments are needed for pin channel preparations: 1. No.1,2, or 3 round burs 2. Measuring probes or depth gauge 3. The twist drill 1. Round burs
When the pinhole locations have been determined, a No. Âź 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 begun to rotate
2.Measuring probes or depth gauge To minimize guessing when using the standard twist drill, the Omni-Depth gauge can be used to measure accurately the pinhole depth.
37
3. The twist drill •
The Kodex drill (a twist drill) should be used for preparing pinholes. The drill is made of a high-speed tool steel that is swaged into an aluminum shank. The aluminum shank, which acts as a heat absorber, is color coded so that it can be easily matched with the appropriate pin size.
•
The drill shanks for the Minuta and Minikin pins are tapered to provide a built-in "wobble” when placed in a latch-type contra-angle handpiece. This wobble allows the drill to be "free floating" and thus to align itself as the pinhole is prepared to minimize dentinal crazing or breakage of the small drills.
•
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. Standard kodex drill
Depth Kodex limiting drill •
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.
•
With the drill in the latch-type contra-angle hand-piece place the drill in the gingival crevice beside the location for the pinhole, position it until it lies flat against the external surface of the tooth, and then, without changing the angulation
38
obtained from the crevice position, move the handpiece occlusally and place the drill in the previously prepared pilot hole .
•
With the drill tip in its proper position and with the handpiece rotating at very low speed (300 to 500 rpm), apply pressure to the drill, and prepare the pin hole in one or two movements until the depth limiting portion of the drill is reached, and remove the drill from the pin hole.
•
Although not usually recommended, a steady stream of air may be applied to the drill to dissipate heat.
•
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 molars and the lingual of maxillary molars are areas of potential problems because of the abrupt flaring of the roots just apical to the CEJ.
Pin design. For each of the four sizes of pins, several designs are available: 1. Standard, 2.
Self-shearing,
3. Two-in-one, 4.
Link Series, and
5. Link Plus.
39
The Link Series and Link Plus pins are recommended. TMS pins are available in titanium or stainless steel plated with gold. The Link Series pin is contained in a color-coded plastic sleeve that fits a latch-type contra-angle hand-piece or the specially designed plastic hand wrench. The pin is somewhat free floating in the plastic sleeve to allow it to align itself as it is threaded into the pinhole. 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. The Minuta, Minikin, Minim, and Regular pins are available in the Link Series. The Link Series pins are recommended because of their versatility, self-aligning ability, and retentiveness. The Link Plus pins are self-shearing and are available as a single or two-in-one pin contained in a color-coded This design has a sharper thread, a shoulder stop at 2 mm, and a tapered tip to more readily fit the bottom of the pinhole as prepared by the twist drill. It also provides a 2.7mm length of pin to extend out of the dentin, which usually needs to be shortened. Theoretically, and as suggested by Standlee et al these innovations should reduce the stress created in the surrounding dentin as the pin is inserted and reduce the apical stress at the bottom of the pinhole. Kelsey et al have demonstrated for the two-in-one Link Plus pin that both the first and second pins seat completely into the pinhole before shearing.
40
The standard pin is a full length pin i.e. 7mm long which can be cut to the required length after placement. It provides a flattened head for engagement with the hand wrench or the handpiece chuck. One advantage of the standard design pin is that 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. The self shearing single pin design is available in varying lengths depending upon the diameters. The pin is designed so that when it reaches the bottom of the pinhole, the head separates automatically at the shear line, leaving a portion of it to project from the dentin. Shearing occurs when there is marked resistance to turning i.e. pin insertion is torque limited. The flattened head on one end of pin is shaped to engage the slot in the hand wrench or the handpiece chuck. The two-in-one design is one in which two pins are connected to each other at a joint. This joint serves as a shear line for the peripheral pin. The two-in-one pin is approximately 8-9 mm in length and provides two pins of equal lengths. It has a flattened head to engage the slot of the hand wrench or the handpiece chuck. Out of the two pins, one which is released first is known as the pin A or the peripheral pin, where as the one which is released second is known as the pin B or the wrench attachment pin. As the name indicates, it is pin B which provides a head for attachment to chuck or wrench. After the first pin has been threaded to the floor of the pin channel, it shears off at the connecting joint leaving behind the second pin along with its attachment to be used in another pin channel. One major advantage with the two-in-one pin is that the handpiece need not be reloaded during two pin insertions. All of the above three designs may be manufactured with pre-attached wrenches, meant to be disposed off after the pins have been inserted. All of the pin designs can be inserted with an appropriate hand wrench. A conventional latch-type contra-angle handpiece with the appropriate chuck also can be used to insert any of the pins except the standard design. A 10:1 reduction gear contra-angle handpiece also is available to insert the pins. Selection of a particular pin design is influenced by the size of the pin being used, the amount of interarch space available, and operator preference.
41
•
The Minuta and Minikin pins are available only in the self-shearing and Link (also self-shearing) design.
•
With minimal interarch space, the two-in-one design is undesirable because of its length. Studies have shown that the two-in-one pin and the self-shearing pin may sometimes fail to reach the bottom of the pin-hole.
•
However, a study by May and Heymann found that 93% of Link Series and Link Plus two-in-one pins extended to the optimal depth of 2 mm.
•
Eames and Solly demonstrated no significant difference between the retention of the self-shearing pin and the standard design pin.
•
However, Newitter and Schlissel have shown that more force is required to dislodge the standard design pin than the self-shearing pin. COLOR
PIN
DRILL
TOTAL
Pin extending
NAME
CODE
DIAMETER
DIAMETER
PIN
from dentin
In / mm
LENGTH
Regular
Gold
0.031/0.78
0.027/0.68
7.1
5.1
Gold
0.031/0.78
0.027/0.68
8.2
3.2
(self-shearing) Regular Gold
0.031/0.78
0.027/0.68
9.5
2.8
In / mm
(standard) Regular
(2 in 1) Minim
silver
0.024/0.61
0.021/0.53
6.7
4.7
(standard) Minim
silver
0.024/0.61
0.021/0.53
9.5
2.8
Red
0.019/0.48
0.017/0.43
7.1
1.5
Pink
0.015/0.38
0.0135/0.34
6.2
1.0
(2 in 1) Minikin (self-shearing)
Minuta (self shearing)
Pin insertion. •
Two instruments for insertion of threaded pins are available: 1. Conventional latch-type contra-angle handpiece, and 2. Cable-drive pin setter for inaccessible pin insertion 3. TMS hand wrenches
42
The latch-type handpiece is recommended for the insertion of the Link Series and the Link Plus pins. The hand wrench is recommended for the insertion of standard 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.
•
For low-speed hand-pieces with a low gear, the low gear should be used. Using low gear 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.
Cable-drive pin setter (Loma Linda): for inaccessible pin insertion – permits the knob to be twisted forward and backward to screw the pin into or to back it out of the pinhole.
Hand wrench •
A standard design pin 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.
43
•
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.
Once the pins are placed, evaluate their length. Any length of pin greater than 2 mm should be removed. As described before, 2 mm of pin length into amalgam is optimal. Also, whenever possible, it is desirable to have at least 2 mm thickness of amalgam occlusal to the end of the pin to prevent unnecessary weakening of the restoration. To remove the excess length of pin, use a sharp No. 1/4,1/2 or 169L 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 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 hemostat or cotton pliers. After placement, the pin should be tight, immobile, and not easily withdrawn.
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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 . 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.
TMS Bending tool
Slotted excavator
Advantages 1. Ease of insertion 2. Maximum retention is offered. Summitt JB et al in a in vivo study compared the performance of complex amalgam restorations retained with self-trhreading pins or bonded with filled ,4META-based resin. The study concluded that at six years, there was no difference in the performance of pin-retained amalgam restorations and bonded amalgam restorations.( Operative Dentistry, 2004,29-3,261-268) Disadvantages 1. Excessive stresses in the form of cracks and craze lines are generated in the surrounding enamel and dentin, especially with the large sized pins. 2. Pins may need to be bent, cut or contoured after insertion, which places extra stress on the tooth or may loosen the pin.
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3. When the pin is forced into the channel, it may strip the sides of the dentin resulting in a loose fit. 4. Pins may fail to seat completely. 5. Microleakage is higher than the cemented pins if the overlying restoration leaks. L or T shaped threaded pins - Mattos (1973) introduced these pins to overcome the need for bending pins after their placement. The L or T shaped pins are well suited for class IV preparations as it devoids the need for a second pin at the incisal third. The transverse portion of the L is allowed to rest in a depression specially prepared in the dentin. These pins have either a square head or a flat extended head for attachment to the hand wrench. The extended head has a shallow groove at its junction with the pin at which it separates once the pin reaches the bottom of the pinhole. Cavity Preparations, Designs and Indications for Pin-Retained Restorations I. Class II •
Indications o In addition to the general indications, previously mentioned, pins are indicated for Class II cavity preparations in shallow and wide cavities where the contemplated axial wall of the preparation will be short or absent completely. o In posterior teeth with missing cusps where retention is not adequate in the rest of the cavity preparation, and o In a cavity preparation for a foundation, where many of the possible retention forms will be lost during the tooth preparation for a future cast restorations.
•
Design features
It must be emphasized that pins are auxiliary means of retention, i.e.. the cavity preparation should have principal means of retention before adding pins to augment this retention. All possible surrounding walls, especially opposing ones, boxes, and dove-tails should be prepared in the remaining parts of the tooth before placement of any pins is planned. The following are some design features in a Class II cavity preparation which have a pin as one of the retention means.
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1. As much as possible, pins should be put in the apically deepest and most peripheral parts of the cavity preparation. 2. Although most of the facio- and linguo-proximal corners of the tooth are choice locations for pins, they should be placed slightly mesial or distal and/or slightly facial or lingual to the actual axial angle there in order to avoid additional stresses in these critical locations. 3. The worst location for a pin is on a table replacing or capping a cusp, exactly under the tip of the cusp, for it will not be possible to achieve the minimum 2 mm restorative coverage for the pin without the possibility of impinging or involving the pulp horns. 4. An ideal arrangement is to have as many flat planes in the cavity preparation as possible, either surrounding to or it. 5. Reciprocation for the pin retention by another retentive form, i.e., another pin, groove, box, etc., at the other side and opposite to the pin is essential in any design for this kind of restoration. 6. Avoid putting pins in the gingival floor proximally, as it could be an isthmus area. If the gingival floor is deep apically, although the pin may not encounter the isthmus area, it may encounter the root canal or root concavities at its tooth end. 7. Establish external boxes (proximally, facially and/or lingually) adjacent to a pin, as this will immobilize the restoration, at least laterally, minimizing the stresses on the pin. 8. In locating pins for foundations, consider the future reduction for the cast restoration and estimate the minimum amalgam or composite resin coverage of pin. 9. Use the minimum number of pins possible, but strategically locate them. Remember, it is not the number of Pins that will enhance the retention, it is their location. 10. Analyze and estimate the direction of displacing forces on the contemplated restoration and try to place pins at the contemplated restoration, and try to locate pins at starting and the terminating points of these possible movements, rather than in between. 11. Use the minimum size (diameter) of pin possible, relative to the size of the restoration and remaining tooth structures.
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12. In case one side of the pin is close to a wall, usually the axial wall, enough space between the pin and this wall should be left (prepared) to accommodate a bulky amount of the restorative material for it to be self-resistant as well as to grip the pin. Remember, there should be at least 1.5-2 mm of restorative material lateral and occlusal to a pin. 13. All other features of the cavity preparation may be exactly similar to the different designs of Class II cavity preparations previously described. Class III and IV Cavity Preparations •
Indications o Since the introduction of enamel acid etching, pins in Class III and IV toothcolored restorations are rarely used. o
For a foundation that is to be subsequently covered with a permanent restoration or is to be used as a provisional restoration for an extended period of time.
o When the defect is much greater than the anticipated reduction for that permanent restoration. o If the Class III or IV cavity preparation involves two-thirds or more of the incisogingival length of the clinical crown or if the labial, incisal and lingual walls are either completely lost or have no dentin. o If the remaining tooth structure cannot accommodate retentive grooves or boxes compatible in bulk to the site of the foundation, without encroaching on vital pulp or roof canals. It is to be emphasized that direct tooth-colored materials are not ideal foundations for cast or cast-based restorations therefore, if esthetics is not of major concern, it is preferable to build the foundation in amalgam. o Sometimes pins are used for final restorations m Class III and IV lesions in situations where there is little or no remaining enamel on the tooth, or the restoration is going to be directly loaded in centric and excursive mandibular movements, or the available enamel to be etched cannot be strategically distributed around the defect to warrant adequate resistance and retention for the future restoration •
Design features
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Include the same principles applied in Class II situations, but in addition, there will be the following: 1. For Class III and IV cavity preparations, establish as pronounced a gingival floor in its two dimensions as possible. 2. Create labial and lingual walls even as little as 1 mm long. Sometimes it is necessary to extend the gingival floor apically, or the axial wall must be deepened to accommodate these walls. 3. If cavity margins approach the incisal angle, try to support it as much as possible by avoiding retention forms there.
4. Placement of only one pin per gingival floor is sufficient. 5. For unilateral Class IV's, the L-shaped cemented pin is the most efficient . It is to be emphasized that the short arm of the L will fit incisally, not in a pin channel, but within a ''step" which should not exceed 1 mm in depth. These L-shaped pins are used only when there is sufficient dentin bulk between the labial and lingual enamel plates. If the bulk is not sufficient, use a gingival pin only, as in Class III designs.
6. For bilateral Class IV the U-shaped cemented pin (staple) is ideal. The two ends of the U-pin will be located gingivally. 7. In the L-shaped and the U-shaped cemented pin techniques, sufficient space should be left between the vertical or horizontal arms of the pins and the internal
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parts of the cavity preparation to accommodate a bulky amount of the restorative material. 8. The bending of the pins in the L- or U-shaped cemented pin technique should be gradual and very rounded to avoid fracture and stress accumulation. 9. For esthetic purposes, pins should be located as internally as possible, away from direct observation, and covered with an opacifier if this is possible. Attin T, Hellwig E et al compared fracture toughness of pin retained class IV restorations [PCR pins (Brasseler) with bonding/opaquer coating and FO pins (Brasseler) without coating] and found that both pins reduce stress in dentin. Large class IV cavities should be restores with acid etch technique exclusively. (Operative Dentistry 1994) Class V •
Indications Seldom are pins used in Class V restorations, but they may be indicated in the following situations: 1. Both the mesial and distal walls of a Class V cavity preparation are lost. 2. Class V cavity preparations involve half or more of the facial or lingual surface of the tooth. 3. Remaining tooth structure cannot accommodate occlusal and gingival retention grooves large enough to be compatible with the size of the future restoration. 4. The gingival floor is lost due to fracture or furcation involvement.
•
Design features The same general principles to any class V are applicable In addition, observe the following: 1. Pins are placed axially, paralleling the adjacent proximal surface. In the mesio-distal direction, pins should be located between the axial angle and the pulp or root canal periphery. In the inciso- (occluso-) gingival direction, pins should be midway in the preparation, but as close to the gingival wall as possible.
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2. Pin protrusion within the cavity should be minimal (maximally 1 mm) to allow for restorative material bulk between the pin and restoration surface. 3. Place as many bulky and deep retentive grooves occlusally and/or gingivally as possible. . Tooth Preparations for Pinlay Cast Restorations •
Pin-retained cast restorations differ from pin-retained amalgam and direct toothcolored restorations in that the latter are a form of composite structure, in which pins are one of the phases and in which there are definite macroscopic interfaces between them and the restorative material, and with no adhesion between them.
•
In pin-retained cast restorations, on the other hand, the pins completely adhere to the cast material with no macroscopically evident interface. This feature alone prevents any possible failure at the juncture of the pin with the cast material.
•
Pin-retained cast restorations can be any type of a cast restoration which contains one or more pins for retention or other reasons.
•
It should again be emphasized, that pins are auxiliary means of retention. Under no circumstances should pins be the sole retention means.
A. Indications 1. For shallow and wide cavity (tooth) preparations, when it is impossible or con-traindicated to use surface extensions for retention purposes. 2. For short teeth occluso-gingivally (e.g., due to attrition, fracture or decay processes), necessitating the use of the root dentin to accommodate pin retention modes. 3. When there is incompatibility in length between two (or sets of two) opposing axial walls, e.g., one proximal preparation having very short surrounding walls opposed to another proximal preparation with very long surrounding walls occluso-gingivally. (assure proper reciprocation) 51
4. When proximal axial walls are unusually long in a proximo-occlusal preparation. 5. A tooth preparation with very tapered axial walls or surfaces negating or minimizing its retentive abilities, requires using pins in the restoration to immobilize it. 6. In teeth with completely lost cusp pins can be used in place of a cusp as a reciprocating measure opposite to another mode of retention. 7. In occluso-proximal cavity preparations where the occlusal outline form is not conducive to a dove-tail locking. 8. In proximo-occlusal or proximo-occluso-proximal preparations where the axial wall(s) is are not present or very short. 9. In cases of high pulp horns and or large pulp chambers limiting the depth and extent of the preparation, pins with their minimal tooth involvement can be used to retain a cast restoration without interfering with or endangering the PD organ 10. In thin and delicate teeth, e.g.. Anterior teeth, where bulky boxes and extensive cavity preparation can be detrimental. 11. Accidental or unavoidable loss of gingival floor, which can be detrimental to the resistance-retention form of a cavity preparation, can be compensated for by use of a pin. 12. In rounded preparations and lateral to a root canal post, pins act as antirotational devices, immobilizing the restoration laterally. 13. For esthetic reasons, especially in premolar and anterior teeth, pins can be used instead of surface tooth involvement in order to secure retention and resistance. 14. Pins can be used to seal venting orifices in a cast restoration after cementation. 15. Pins can be used to retain a repair type of restoration. marginal to an already serviceable cast restoration. B. Types - According to the modes incorporating them in a casting, pins for cast restorations can be classified into the following: 1. Wrought – Cast on, Soldered and Threaded. 52
2. Cast. - According to their relationship to the long axis of the tooth:
1. Wrought pins -
Can be made of iridio-platinum or rhodium-gold alloys to be used with cast gold alloy restorations. For silver-palladium or nickel-chromium cast alloy or cast moldable ceramic restorations, the same type of pins can be used. In addition, chromium based or stainless steel alloys can be used for pins in Class III, IV, and V cast material restorations.
-
Wrought metal pins are prefabricated, cold worked pins that come in different diameters and surface configurations.
-
They are cut to the desired length and engage the casting in one of three ways: 1.Cast on : It is fitted into the pin channel of the tooth and or its die followed by the wax pattern being built over it. It is then invested, and the cast material is cast on it (cast on pins). There will be true adhesion between the pin and the cast material of the restoration if these are properly handled. Of course, the melting point for the pin alloy should be higher than that of the casting material. 2. Soldered: The cast is fabricated without the pin. then, the pins are fitted in their pin channel on the tooth, keyed, and attached to the fabricated casting with a suitable agent (resin). The assembly is solder invested, and the pins are then soldered to the main restoration. (This is not indicated for ceramics.) The two above mentioned types are cemented pins, subject to all the principles and effects mentioned in the chapter on pin- and post-retained restorations. 3. Threaded in: The casting is fabricated without the pins, then pin holes are drilled into the casting to coincide with pin channels already prepared
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in the tooth dentin or both pin channels and holes are prepared together after the casting is fitted. Threaded pins, slightly larger in diameter than the pin hole and channel, are threaded in to hold the casting to the underlying tooth dentin. In some situations, the surface end of the pin is no different than any other cross-section of the pin. In others, the surface end of the pin will be bevel shaped to fit a bevel prepared with a special tool in the casting around its pin hole. To minimize marginal discrepancies in the latter, the length of the pin to be used must be predetermined, so the two bevels will coincide. The major advantages of wrought pins are their strength, which is much higher than that of cast pins, and the ability to adjust them directly in the cavity preparation before incorporating them in the casting. The major disadvantages include : •
Overheating during casting or during soldering of these pins to the main restoration. This may invite grain growth of the pin alloy, which will weaken it.
•
Secondly, overheating may lead to alloying between the metal components of the pin and the casting alloy, with unpredictable properties may occur,
•
Thirdly, the attachment of threaded pins to the casting is mainly mechanical, and. as such, it is subject to all the variables mentioned with pin- and post-retained restoration.
•
Fourthly, as a result of heating the pin and the casting alloy while in contact, the pins will share the nobility and passivity with that of the cast alloy, and vice versa.
2.Cast pins -
Can be fabricated as part of the restoration in an evaporating wax casting technique.
-
They have the major advantage of structural continuity between the restoration proper and the pin.
-
Parallel pins can be used parallel to the long axis of the tooth crown or at another angulation to that axis if the casting path necessitates it (Class IV and V).
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-
They are always the cemented type and either made with or attached to the casting before cementation.
-
Non-parallel pins are usually inserted into the casting and the tooth dentin after cementing the casting.
-
They can be wrought cemented or wrought threaded, though threaded types can be more mechanically advantageous.
The same principles and features of tooth pin channel preparation to receive a pin for casting, are applicable.
-
However for cast pins, the occlusal end (outer end) of the pin channel will he surrounded by a struss compartment or countersink to accommodate cast material bulk at this area of massive shear stress concentration.
-
For wrought pins it is not necessary to prepare such a compartment, as their strengths are very accommodating.
The armamentarium for pin channel preparation for cast alloy restoration is not too different from that described for the amalgam restoration. The only differences are: -
In the parallel pin technique, plain, unaided visual orientation of the twist drill, so as to prepare parallel pin channels, may be sufficient for a limited number of pins. With multiple pins, however, or if the pins must be parallel to numerous details in the same preparation, or if the pin must be parallel to pins and other details in adjacent preparations (so as to have a splint or bridge), a parallelometer is needed to insure parallelism
-
For cast restorations there are different sizes and types (final and temporary) of pins. To perfect the match between the diameter of the pin channel, their restoration's, pins, temporary restoration's pins, and burnishable pins for the wax pattern , color coding is used.
-
To prepare pin channel for threaded pins in the cast restoration, a special type of drill is used that can cut metal
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-
To prepare struss compartment around the outer end of the pin channel , a tapered fissure bur is adequate, followed by a monoangle chisel or a small hatchet
POSSIBLE PROBLEMS WITH PINS 1. Failures of Pin-retained Restorations: Failure might occur at any one of 5 locations: 1. Within the restoration (restoration fracture) 2. At the interface between pin and restoration 3. Pin fracture 4. At the pin dentin interface. 5. Within dentin.(Dentin fracture) Most common failure is at pin – dentin interface.
2. Broken Drills and Pins -
Occasionally, a twist drill will break if it is stressed laterally or allowed to stop rotating before being removal from the pin hole. Use of sharp twist drill 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.
-
Pins also may break during bending, if case is not exercised.
-
The treatment for both broken drills and broken pins is to choose an alternate location, at least 1.5mm remote from the broken item and prepare another pinhole.
-
Removal of an broken pin or drill is difficult, if not impossible and usually should not be attempted. 56
-
The best solution for these two problems is prevention.
3. Loose Pins: -
Self threading pins sometimes do not properly engage the dentin because the pin hole was inadvertently prepared too large or a self shearing pin failed to shear resulting in stripped out dentine.
-
The pin should be removal from the tooth and the pin hole prepared with the next largest size drill and the appropriate pin inserted.
-
Preparing another pinhole of the same size 1.5mm from the original pin hole is also acceptable.
-
If a pin becomes loose while shortening with a bur, remove the pin 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 of the same size and if still loose, redrill a larger hole and insert an appropriate pin.
4. 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 hemorrhage in the pin hole following removal of the drill. Also, if a standard or link series pin continues to thread into the tooth beyond the 2mm length depth of the pin hole, this is an indication of a penetration or perforation. - A pulpal penetration might be suspected if the patient is anesthetized and has had no sensitivity to tooth preparation until the pinhole is being completed. - Radiographs can verify that a pulpal penetration has not occurred if the view shows dentin between the pulp and the pin. In contrast , a radiograph showing a pin projecting out side the tooth confirms external perforation. •
In an asymptomatic tooth, a pulpal penetration is treated as any other small mechanical exposure.
•
If the exposure is discovered following preparation of the pin hole, control the hemorrhage, if any.
•
Then place a calcium hydroxide liner over the opening of the pin hole, and prepare another pin hole 1.5-2mm away.
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•
Although certain studies have shown that the pulp will tolerate pin penetration when placed in sterile environment, it is not recommended that pins remain in place.
If the pin were left in the pulp, •
The depth of the pin into pulp tissue would be difficult to determine.
•
Postoperative sensitivity might occur.
•
Pin location might complicate subsequent root canal therapy
The ideal treatment of a pulpal penetration for a compromised tooth generally id endodontic therapy. An external perforation might to occlusal or apical to gingival attachment. Careful probing and radiographic examination must accurately diagnose the location of a perforation. Three options are available for perforations that occur occlusal to gingival attachment: •
Pin can be cut off flush with the tooth surface with no further treatment.
•
Pin can be cut off flush with tooth surface and preparation for a cast restoration extended gingivally beyond the perforation.
•
Pin can be removed, external aspect of pinholes enlarged slightly and restored with amalgam.
For perforation apical to attachment •
Reflect the tissue surgically, remove bone if necessary, enlarge the pinhole and restore with amalgam.
•
Perform a crown lengthening procedure, place the margin of the cast restoration gingival to the perforation.
The patient should be informed about pulpal or external perforation, and the proposed treatment. Amalgapins. •
Seng and others tested circular chambers that they cut vertically into dentin to provide resistance and retention form for the restoration; they called these features amalgam inserts. Preparations for the inserts were made with a No. 35 inverted
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cone bur and were approximately 1.4 mm in diameter and depth. In their study, amalgam inserts provided resistance to displacement similar to that provided by self-threading pins. Shavell described a variation of the amalgam insert, which he termed the amalgapin . -
The amalgapin channel described by Shavell was prepared with a No. 1157 or No. 1156 bur and had a depth of 3.0 mm.
-
The margin of the channel entrance was beveled to decrease stress concentration in the amalgam.
-
Laboratory studies of the amalgapin have demonstrated that the resistance to displacement provided by amalgapins is similar to that provided by pins.
-
It has been demonstrated that a depth of 1.5 to 2.0 mm is adequate for amalgapins and that an amalgapin with a diameter of 0.8 mm provides resistance similar to that of an amalgapin with a diameter of 1.0 mm.
-
In addition to the burs advocated by Shavell (No. 1156 and No. 1157), others with similar diameters (such as the No. 330 and No. 56) also function well in creating amalgapin
Advantage: 1. No microleakage 2. no stress in dentin 3. no need of pins and pin system 4. pulp irritation is avoided. Disadvantages: 1. more tooth structure is removed 2. Shear strength of amalgam is less then that of pin amalgam
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Conclusion: The use of pins in conjugation with amalgam is useful for supporting the extensive restoration or core structure. The reinforcement from the pins should not reduce the strength of the material or tooth. The pin-retained restoration is an essential technique that can be used frequently to restore both vital and non-vital teeth. Though pins provide good retention, they should be the last resort, because their inadvertent use without good basic knowledge leads to numerous complications.
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References: 1. Theodore M Roberson, Harald O.Heymann and Edward J. Swift, Jr. Sturdevant’s Art and Science of Operative Dentistry. 4th edition. 2. M A Marzouk, A L Simonton and R D Gross. Operative dentistry. Modern theory and practice. 1st edition 3. Gilmore, Lund, Bales and Vernetti. Operative Dentistry. 4th edition 4. Gerald T. Charbeau. Principles and practice of Operative Dentistry. 3rd edition 5. Text book of Operative dentistry. Baum, Philips and Lund. 3rd edition. 6. James B Summitt. Fundamentals of operative dentistry. 2nd edition. 7. Summitt JB, Burgess JO, Berry TG, Robbins JW, Osborne JW, Haveman CW. Six-year clinical evaluation of bonded and pin-retained complex amalgam restorations. Oper Dent. 2004 May-Jun;29(3):261-8. 8. Attin T, Hellwig E, Hilgers RD, Zimmermann U. Fracture toughness of pinretained class 4 restorations. Oper Dent. 1994 May-Jun; 19(3):110-5.
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