PINS IN

RESTORATIVE DENTISTRY

Pins retained restorations

HISTORY

Dr. Miles Markley in 1958 cemented threaded

stainless steel wires, reporting as “pin reinforcement and retention”

Later studies showed that pins increased retention in amalgams, but decreased strength

Pin Retained RestorationDefinition: One or more pins may be required to supplement inadequate retention in a cavity for retention.

> Extension of cavity into holes or channels

> Channels are placed in dentine , pins are placed in channel.

Hence called dentine's pins

Pin Retained Restorations

Retentive Features of a Cavity

Two Types: 1. Primary or Principal means 2. Auxiliary means

1. primary or Principal means: i. Friction : a. Opposing walls b. Parallel walls c. Surface area of opposing walls d. Proximity or packing ii. Dove-tail :iii. Undercuts or inverted cones :iv. Elastic deformation of dentine

Retentive Features of a Cavity

2. Auxiliary means : i. Grooves ii. Internal boxes iii. Etching of enamel iv. Pins v. Posts etc.

IndicationsIndications 1. Mutilated / badly brocken down tooth : > For rubber dam application > For bands-attachment > For restoration of tooth2. Foundation : > For crowns > To conserve tooth-structure 3. Questionable prognosis : > Endodontically > Periododontically4. Cross linkage mode : To connect two bulky parts abnormal tooth removal5. Adjunct retention mode : To resist post rotation6. Economical :Than crowns7. Auxiliary / reciprocal retentive mode for a restoration.

Indication of pinIndication of pini. Grossly carious

teeth

2. Foundation :

> For crowns

> To conserve tooth-structure

Indications of pinIndications of pin

Indications of pinIndications of pin3. Questionable prognosis :

> Endodontically

>

Periododontically

Indications of pinIndications of pinv. Adjunct retentive mode : The presence of pins in case of post retained restoration , help in prevention of rotation of restoration

Indications of pinIndications of pin

4. Cross linkage mode :To connect two bulky parts abnormal tooth

removal.

6. Economical

than crowns

Indications of Indications of pinpin

Advantages of pins

i. Conserve cutting of tooth : offer retention without the need for extensive preparation of tooth structureii. Resistance : may increase resistance form of the preparation to some extent e.g. in case of cross-linkageiii. Less time consuming : need single visitiv. Less expensive : than cast-restorations

Disadvantage of pins Do not increase the strength of restorative materials Even decrease the strength of restorative materials-Reasons:

i.Induce stresses in dentine maycause : a. cracks / crazes in tooth b. micro-leakage c. pulpal damage

External or pulpal perforation Chance of micro-leakage around the pins- dentine interface

Pin Retained RestorationTypes of pins:

Four kinds of pin systems

are currently available :

1. Cemented pins

2. Friction-locked pins

3. Self-threading pins

4. Cyanoacrylate pins

1. Cemented pins :

Sizes of pins: a. 0.020''

b. 0.025''

Cemented pin

2. Friction grip / friction lock pins :

Sizes of pin : 0.0021'' or 0.022''

3. Threaded pins:- >Thread made system >Stabilock system Sizes of pins: a. Regular ( 0.031” ) b. Minim ( 0.024” ) c. Minikin ( 0.019” ) d. Minuta ( 0.015” )

Compare sizes of the channels with that of

different pins :Type of pins Pin channel diameter Pin diameter

Difference

1. Cemented pins 0.027 “ 0.025 “ 0.002

0.021 “ 0.020 “ 0.001

2. Friction grip pins 0.021 " 0.022 “ 0.001

3. Threaded pins 0.027 “ 0.031 “ 0.004

0.022 “ 0.024 “ 0.002

0.017 " 0.019 “ 0.002

0.013 “ 0.015 “ 0.002

TYPES OF PINS

☻Cemented – pin is 0,002’ smaller than the channel

☻Friction-locked – pin is 0.001’ larger than the channel

☻Self-threading (TMS) – pin is 0.001-0.004 ’

larger than the channel

Pin channel

Compare sizes of the channels with that of different pins :

Successful Pin PlacementThis depends upon following factors :

1. Stresses induced by pins insertion in the dentine

2. Retention of pin in the dentine

3. Effect of pins on restorative materials.

4. Knowledge of tooth anatomy ( External & Internal )

5. Knowledge of radiographic findings.

6. Proper techniques of placement of pins in dentin in cavity.

Stresses induced by pins in dentinFactors related to dentine :1. types of dentine : - elasticity of dentin stress tolerance - Decreasing order of tolerance Primary dentin > secondary dent > sclerosed dentine > tertiary dentin > caleific barrier

2. bulk of dentin ∞ stress toleranceFactors related to pins :Types of pins : diameter surface texture techniqueOther factors : Inter pin distance loose pins pin depth wedge end of pinNo of pin pin handling dentinal depth : protrusi Avoid stress ideal 1:1 bearing areas acceptable 2:1 Using drill correctly

Factors related to dentine1.Types of dentine : – Elasticity of dentin ∞ stress tolerance

- Decreasing order of tolerance Primary dentin > secondary dentine > sclerosed dentine > tertiary dentin > caleific barrier

2. Bulk of dentin ∞ stress tolerance

Factors related to pins :Types of pins depending on: ●diameter ● surface texture ● techniqueOther factors : ●Inter pin distance ●loose pins ● pin depth ● wedge end of pin ● pin handling ● no. Of pins ● Using drill correctly ● dentinal depth : protrusion To avoid stress ≈ ideal 1:1 Stress bearing areas ≈ acceptable 2:1

Stresses induced by pins in dentin

Stresses are denoted by a symbol ~~

Stresses induced by friction grip pin in dentin

are greater than threaded pins & cement pins.

Stresses induced by threaded pins > that of

cemented pins.

Retention of pins in dentine :Factors related to dentine ; 1. Types of dentine : - elasticity of dentine ∞ retention 2. Bulk of dentin ∞ RetentionFactors related to pins : 1. Types of pins : Diameter Surface texture Technique 2. Other factors : pin channel no of pins circumference < ( cutting )( bending )( orientation ) pin depth pin handling inter pin dentinod depth : protrusion distance ideal 2:1 acceptable 1:1Type of cement : decreasing order of retention copper phosphate cement > z p c > p.c.c > Z no E

Retention of pins in dentine : Factors related to dentine1. Types of dentine :

- elasticity of dentine ∞ retention

2. Bulk of dentin ∞ Retention

Retention of pins in dentine :Factors related to pins : 1. Types of pins with : ▪Diameter ▪ Surface texture ▪ Technique

2. Other factors : ◊ Pin channel circumference ◊ no. Of pins ◊pin handling Ξ ( cutting )( bending )( orientation ) ◊pin depth ◊inter pin distance ◊dentinal depth : protrusion ideal 2:1 acceptable 1:1 ◊type of cement : decreasing order of retention:

copper phosphate cement > z. p. c. > p.c.c. > zinc-o-eug

Pins and restorative material

See the effect : strength wise & retention wise Pins increase retention of restorative material Pins decrease strength of restorative material

Following factors & retention: Pins factors : i. Types of pins : a. diameter b. surface texture ii. Other factors : a. orientation b. pin length on restorative material c. interpin distance d. no. of pins iii. Proximity of restorative material to pins

Stresses and pins in restorative material

i. Chiesel / wedge end of pin in restorative materi

ii. Inter pin distances iii. Bulk of restorative material over the cavity end of pin iv. Adaptability of rest material around the pin

Knowledge of tooth anatomy

1. Pulp chamber 2. Tooth morphology [surface contours] 3. Tooth alignment 4. Cavity extentsion 5. Age of patient

PULP CHAMBERKnowledge of co-relation of

normal pulp chamber anatomy and

external tooth surface contour

Symbol >< shows the region of avoidence

of placement of pins in teeth.

Proper and successful pin placementTwo factors : (i) Factors {Proper & successful pin placement depend (ii) Technique {on the factor and techniquesFactors for proper placement of pins : i. Pin size : Selection of pin size depend on : a. Amount of dentin pin size b. Retention required pin size ii. no. of pins : Depends on: a. Amount of lost tooth structure. b. Amount of dentine. c. Retention required. d. Size of pins. iii. Depth of pin in dentin : Maximum depth : 2-4mm. iv. Inter pin distance : Optimum distance : 3-5mm. v. Length or Height of pin in cavity : * Maximum height : 2mm. * 1-5 or 2mm minimum amalgam should be present above the cavity end of pin.

Proper & successful pin placement

depend on two fields :

(i) Factors (ii) Technique

Factors for proper placement of pins :

i. Pin size depends on : a. Amount of dentin pin size b. Retention required pin size

ii. No. of pins depends on: a. Amount of lost tooth structure. b. Amount of dentine. c. Retention required. d. Size of pins.

iii. Depth of pin in dentin : Maximum depth : 2-4mm. iv. Inter pin distance : Optimum distance : 3-5mm. v. Length or Height of pin in cavity : * Maximum height : 2mm. * 1-5 or 2mm minimum amalgam should be

present above the cavity end of pin.

Proper & successful placement of pinFactors of proper & successful placement of pin : (vi). Location or distribution of pins : a. The pin should always be placed midway between the pulp and tooth surface b. Place at cervical 1-3 rd of molars & premolars. c. Where greatest bulk of amalgam can be placed

(minimum 1.5mm) d. As close as possible to the line angles e. Where the greatest bulk of dentin is present f. 0.5mm away from DEJ g. 0.5mm away from axial or vertical wall cavity h. Always on flate surface / even the different levels i. Use one pin her cusp for TMS (regular) Two or more

for TMS (minimum), friction lock or cemented pins j. Limited no. Of pins should be used

General Principles

◘ Pins must be stable.

◘ Pins must not perforate into the pulp or periodontal membrane.

◘Tips of pins will be covered with at least 2mm of

amalgam.

◘Pins will clear matrix brand laterally.

General Principles

◘ Pins will not predispose to caring or fracture of tooth structure.

◘Place so pin is surrounded by 0.5mm-1.0mm of dentin .) Larger pins or non-vital teeth require 1.0mm(

General Principles

If pin is close to the DEJ, or if tooth is non-vital

Use smaller pins : regular Minim minikin -

minuta

Use hand wrench to prevent over-torquing

Monitor torque and seat pin completelyBack off pin ¼ turn

General Principles

If pin is close to the DEJ, or if tooth is non-vital

Use cemented pins

Cut groove in pin and “tap”threads in dentin

General Principles

Must provide flat seat and space around the pin

Allows more complete seating of drill

Allows maximum depth of pin channel

Allows amalgam to flow around the grasp pin

Choose pinhole direction parallel to external surface of tooth, not parallel to long axis of tooth or crown

Factors of proper & successful placement of pin :

(vi). Location or distribution of pins :

General Principles

Choose proper location for pins

Place in area of greatest bulk of dentin

Place 0.5-1.0mm from the dej to prevent crazing

Place halfway between pulp and external surface of

root if gingival margin is in cementum

Avoid furcations and depressions on roots

a.

The pin should always be placed midway between the pulp and tooth surface

b.

Place at cervical 1-3 rd of

molars & premolars.

c. Where greatest bulk of

amalgam can be placed (minimum

1.5mm)

d. As close as possible to the line angles

e. Where the greatest bulk of dentin is present f. 0.5mm away from DEJ g. 0.5mm away from axial or vertical wall cavity h. Always on flate surface / even the different levels i. Use one pin her cusp for TMS (regular) Two or more

for TMS (minimum), friction lock or cemented pins j. Limited no. Of pins should be used

Proper & successful placement of pinFactors : (vii) Direction of pins : a. Pin is placed always midway between pulp chamber and tooth surface. b. Always place the pins at the line angles of the tooth.

( C ) The following areas should be avoided : i. Pulp-chamber {areas of pulp-proximity} ii. Isthmus area iii. Bi and Tri furcation areas iv. Concavities or flutings on the outer surfaces of tooth v. Where amount of dentine is too less yo place pin e.g. Mesiofacial corners of molar teeth vi. Too close enamel or DEJ