Pin retained restorations

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Presented by: Dr Ab h isek Gur ia
Dept. of Conservative Dentistry & Endodontics

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Contents
 Introduction
 Retentive features of a cavity
 Indications and contraindication
 Advantages and disadvantages
 Types of pins
1. Cemented pins
2. Friction locked pins
3. Self threaded pins –(TMS)
 Thread mate system
 Regular , minim, manikin, minuta
 Standard, self shearing, two in one, link series, link plus
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Pin retained restoration
 Factors involved
1. Mechanical aspect
2. Anatomical aspect
3. Mechano-anatomical principles
 Mechanical aspects of Pin-Retained restoration
Pins and tooth structure
1. Stressing capabilities of pins
2. Retention of pins in dentin
3. Microcracking and crazing
Pins and restorative materials
1. Effect of pins on strength of restorative materials
2. Retention of pins to restorative material
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 Anatomical aspects of Pin-Retained restoration
1. Knowledge of anatomy
2. Radiographs
3. Outer surface of tooth
4. Amount of dentin
5. Anatomical features
6. Tooth alignment
7. Extent of cavity
8. Age
 Mechano-anatomical principles for pin placement
Maxillary teeth
Mandibular teeth
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 Techniques for inserting pins
 Pin channel preparation
 Cemented pin technique
 Threaded pin technique
 Friction grip pin technique
 Cavity preparation design features (Class II, III, IV, V)
 The biologic form of pin restoration
 Effect of pin on pulp dentin organ
 Complications
† Failure of pin retained restoration
† Broken drills and broken pins
† Loose pins
† Perforation
 Conclusion
 References
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Introduction
 Used as auxiliary retentive means for restorations
 They may reduce property of restoratives

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Retentive features of a cavity
Primary means
a. Friction (opposing wall,
surface area)
b. Dove-tail
c. Undercuts
d. Elastic deformation of
dentin
Auxillary means
a. Slots
b. Grooves
c. Coves
d. Internal boxes
e. Etching of enamel
f. Pins
g. Posts
h. Amalgapins (Dr Shavell in 1980)

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Indications
1. Auxiliary retentive means for badly broken down teeth
2. Foundation for partial or full veneered cast restoration
3. As a provisional restoration before definitive restorations
4. As a cross-linkage mode between two remaining tooth
structure
5. As an adjunct retentive mode with a post in endodontically
treated teeth
(Marzouk)

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Contraindication
1. Significant occlusal problems
2. In esthetic areas
3. Difficult access

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Advantages
1. Conservative- less extensive than cast restoration
2. Single appointment
3. Increase retention
4. Economic

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Disadvantages
1. Dentinal microcracks
2. Lowered fractured resistance
3. Reduced transverse and tensile stress of amalgam

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Types of pins
1. Cemented pins
2. Friction locked pins
3. Self threaded pins

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Cemented pins
 Developed by Dr miles Markley in
1950
 Made of stainless steel
 Produce least stress
 Offer less resistance

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FRICTION LOCKED PINS
 Developed by Dr. Goldstein in 1966
 Made of stainless steel
 More retentive than cemented pins
 Used in vital teeth with good access and
ease of tapping/locked the pins
 Cause craze lines or cracks
 Retain by resilience of dentin

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SELF THREADED PINS
 Developed by Dr. Going in 1966
 Most popular type among all, the different types
and most extensively used pin.
 Made of stainless steel or gold plated titanium
pins
 Provide maximum retention among all types of pins
 Cause craze lines
 Used in vital teeth

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CEMENTED PINS FRICTION LOCKED PINS SELF THREADED PINS
Stainless steel with threads
or serrations
Stainless steel with threads
Stainless steel/Titanium
with gold plating
Pin channel [0.001” to 0.02”]
larger than pin size [0.020”
to 0.25”]
Pin channel is 0.001” smaller
than pin size
Pin channel is 0.002” to
0.004” smaller than pin size
Luted with standard luting
agents
Taped into place with mallet
Placed by hand wrench or
contra angle hand piece
Ease of placement Pin placement is difficult Pin placement is easy

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CEMENTED PINS FRICTION LOCKED PINS SELF THREADED PINS
Less internal stresses
Increased internal stress Increased internal stresses
Least retentive
2-3 times more retentive
than cemented pins
5-6 times more retentive
than friction locked pins

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SELF THREADED PINS – THREAD MATE SYSTEM (TMS)

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REGULAR MINIM MINIKIN MINUTA
•Largest diameter
pins
•Causes maximal
stress
•Causes maximum
dentinal crazing
•Rarely used
•Next smaller
diameter pins
•Lesser stress are
created
•Lesser dentinal
crazing
•Good retention
•Diameter is lesser
than minim pins
•Very less risk of
dentinal crazing
•Good retention
•Minim and minikin are
commonly used sizes
of tms system
•SMALLEST
SIZE of pins
•They are too
small to provide
adequate
retention
•Not widely used

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Pin designs
Standard
design
•7mm long
•They have flattened heads to fit into the hand wrench or handpiece
chuck
•After placement the pin is reversed 1/4th turn to reduce stresses on
dentin
•Pin height can be adjusted appropriately
Self
shearing
design
•Available in varying lengths
•They have flattened heads to fit into the hand wrench or handpiece
chuck
•During pin placement when the pin reaches the bottom of the pin hole,
the head automatically shears off, leaving a portion projecting from
dentin

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Two in one
design
 It consists of 2 pins connected by means of a joint which serves as a
shear line for peripheral pin
 Total length is 9mm and 2 pins are about 4mm each
 They have flattened heads to fit into the hand wrench or handpiece
chuck
 The handpiece need not be reloaded during insertion of more than 1
pin

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Link series
design
• They have a plastic sleeve that fits into the latch type contra angle
handpiece or a special plastic hand wrench
• Self shearing
• Pin engages the dentin and the plastic sleeve can be discarded
• Can align well into pin channels
Link plus
design
• Similar to link series design
• Self shearing
• Available as single or 2 in 1 pins
• The major difference in this pin design is that pins have sharper
threads and a tapered tip to decrease dentinal stresses while
seating

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ADVANTAGES OF TMS PINS
 Versatile design
 Wide range of pin sizes
 Color coding allows ease of use
 Gold plating eliminates corrosion
 Good retention

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Factors involved
1. Mechanical aspect
2. Anatomical aspect
3. Mechano-anatomical principles

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Mechanical aspects of Pin-Retained
restoration
Pins and tooth structure
2. Retention of pins in dentin
1. Effect of pins on strength of restorative materials
2. Retention of pins to restorative materials

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1. Type of pins
 Small diameter- less stress
concentration
 Friction grip has highest stress
 Blunt thread- more stress
 More distance b/w threads-
more concentration

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2. diameter of pins
 Greater diameter – more stress
3. pin depth and dentinal engagement
 More depth (laterally)- more stress
4. bulk of dentin
 Greater bulk pulpally- lesser stress
5. type of dentin
 Primary dentin of young tooth – least stress
 Decreasing order of stress tolerance
secondary > sclerosed > tertiary > calcific
barrier
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6. inter-pin distance
 Threaded pin- 4mm
 Cemented pin-3mm
7. non coinciding eccentricity in pin and pin
channel.
 loose pins
8. wedge, chisel or irregularly shaped
dentinal end of pin
 Causes stress concentration
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9. ratio of depth of pin
 Dentin engagement: pin protrusion= 2:1
10. number of pins
 Fewest no possible

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11. twist drill variability
 blunt., vibrating drill- more stress
12. over threading or over driving of pin in
pin channel
13. stressed induced during shortening of
pin inside cavity
14. bending or aligning pin after their
dentinal engagement
15. inserting pin in a stress concentration
area.
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2. Retention of pin in dentin
1. type of pin
 Self threading > friction grip > cemented
2. depth of engagement (Moffa)
 Cemented pin- linear relationship in graph. Failure- cement
dentin interface
 Friction grip – no increase after 2mm. Failure- pin dentin
interface
 Small threaded pin- no increase after 2mm. Failure within pin.

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3. pin channel circumferential shape relative to pin
4. number of pins
 If placed <2mm closer- cause crack
5. type of cement
 Copper-phosphate cement- for non vital tooth.
 Zn phosphate> polycarboxylate
6. type of involved dentin
 Young resilient dentin more retentive
7. surface roughness of pin
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 Can start at surface or at DEJ(least detrimental)
1. type of pin
 Friction lock > threaded > cemented
2. proximity of pin to DEJ
 0.5-1mm from DEJ
3. thickness of adjacent enamel

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1. Effect of pins on strength of restorative
materials
 Pin do not increase strength, it just retain restoration
 There will be drop of compressive strength if
a) Cavity end of the pin is wedge or chisel shaped
b) Pins are closer than 2mm
c) Pin protrude through the restoration
d) Non adaptability of restorative material to pin
There is reduction of tensile strength if placed at right angle
to stress

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2. Retention of pin to restorative material
1. Types of pin
 Friction grip is least retentive
2. Pin length and diameter in restorative material
3. Surface material of pin

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Anatomical aspects of Pin-Retained
restoration
1. Knowledge of anatomy
2. Radiographs
3. Outer surface of tooth
4. Amount of dentin

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5. Anatomical features
6. Tooth alignment
7. Extent of cavity
8. Age
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Mechano-anatomical principles for pin
placement

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Techniques for inserting pins

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1. Pin channel preparation
 Twist drill
1. Standard drill – length 4-5mm
2. Depth limiting drill – length 2mm
5 rules for use (Marzouk)
a) Speed 300-500rpm
b) Force applied parallel to long axis. No lateral cutting action
c) Drill should be always revolving inside pin channel.
d) Don’t use pumping stroke, use single stroke
e) Never use the drill in enamel

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2. Cemented pin technique
 Indications
1. Least crazing
2. Used when bulk of dentin is limited
3. Only technique to be used in endodontically treated tooth
4. Only technique for ‘’U’’ & ‘’L’’ shaped pin
5. Only technique for cross linkage of parts of tooth

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Procedure
 Cut proper length with dial-a-pin cutter
 Try in by a magnetized tweezer or hemostat.
 Any roughness should be smoothened with a carborundum disc.
 Apply cement by explorer
 Insert the pin and remove excess cement

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3. THREADED PIN TECHNIQUE
 Indication
1. Used in vital tooth
2. Minimum number of pin needed
3. If Maximum retention required

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procedure
 Engage the pin with its driving device.
 Threaded continuously until it offers
resistance initiated by touching pin channel
floor.
 Leads to self shearing or disengagement of
driving device
 Backup for quarter turn

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4. Friction grip pin technique
 Indication
1. Used in vital teeth only. Least used
2. Should be 2.5mm from DEJ
3. Can be used only in accessible area

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Procedure
 Prepare pin channel
 Mark channel depth on pin
 Pin is placed with a hemostat and hammered

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Cavity preparation design features

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Class II cavity
 Placed deepest and most peripheral part of cavity
 Placed slightly mesial/distal or facial/lingual to actual line angle
 Worst location- exactly below cusp tip
 Keep many flat planes in cavity
 Reciprocation for pin retention- another pin, groove etc
 Avoid at isthmus area
 Put external box to immobilize restoration
 analyze displacing forces to locate pin at starting and
terminating point of possible movement
 Use minimum size

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Class III and IV cavity
 Pronounced gingival floor
 Place one pin per gingival floor
 Unilateral class IV- ‘’L’’ shaped pin, short arm incisally
 Bilateral cavity – ‘’U’’ shaped cemented pin
 Bending of pin should be gradual and rounded
 Place more internally in esthetic cases

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Class V cavity
 Placed axially, paralleling adjacent proximal surface
 Pin protrusion minimal
 Place retentive grooves

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The biologic form
 Irritating ingredients for pulp dentin complex
1. Presence of cracks
2. Vibrations
3. Cement
4. Stress concentration
5. Conductivity
6. Irritants from restorative materials

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Effect on P-D organ
 No cracks present- healthy reparative reaction
 Pin induce crack- destructive reaction

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When there in accidental penetration of
pin into pulp chamber
 To enhance healing
1. Create sterile field, pin and armamentarium
2. Control bleeding using paper point
3. Place CaOH with paper point
4. Soak the tip of the pin with CaOH
5. Do not use cemented pin
6. Make sure pulpal end of pin is smooth

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Complications
1. Failure of pin retained restoration
 Within the restoration
 At pin / restoration interface
 Within the pin
 At pin/dentin interface
 Within the dentin

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2. Broken drills and broken pins
3. Loose pins
4. Perforation

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Conclusion
 Pins have been extensively used in past to restore badly broken
down teeth.
 However newer studies are leading to the conclusion that the
deleterious effect of pins outweigh their benefits.
 Availability of newer restorative materials and techniques are
reducing the need of Pin retained restoration.

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References
1. Operative dentistry- modern theory and practice – MA Marzouk
2. Clinical operative dentistry – Ramya Raghu
3. Sturdevant’s art and science of operative dentistry
4. Bharti R, Wadhwani KK, Tikku AP, Chandra A. Dental amalgam: An update.
J Conserv Dent 2010;13: 204-08
5. Garman TA, Binon PP, Averette D.B.S., Talman RG. Self-threading pin
penetration into dentin. J Prosthet Dent 1980; 43(3): 298-302.
6. Mondelli J, Vieira DF. The strength of Class II amalgam restorations with
and without pins. J Prosthet Dent 1972; 28: 179-88.

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