PIN RETAINED RESTORATIONS

Dr Rakesh Kumar Yadav

INTRODUCTIONMost of the teeth can be restored with

amalgam and composite but if large crown portion lost due to caries or some other reasons, the remaining tooth structure is decrease and difficult to obtained resistance and retention form so prepare dentine lock and slot but when these retention features are insufficient to provide desired retention then pin supported restorations are used.

TRETMENT OF BADLY BROKEN TOOTH First-Evaluate biologically and mechanicallyStatus of pulp and periodontium should be

evaluated.Involvement of pulp or not Restorative design planning if pulp is not involve-pin,inlay,onlayPulp involvement- pulpotomy ,pulpectomy,

pin,full coverage-Tooth anterior or posterior

HISTORYIn 1958, Dr. Miles Markley introduced a

practical instrumentation for the use of a stainless steel cemented pin that resulted in the extensive use of cemented pins in dentistry

DEFINITION Defined as any restoration which requires the

placement of one or more pins in dentin to provide to adequate resistance and retention form to the restoration.

It has a greater retention than those using boxes or bonding system.

INDICATIONSBadly broken down or mutilated teeth. Questionable prognosis-Controlled

restoration in tooth with questionable pulp or periodontal prognosis

As a foundation under fixed restoration(core)

Economics Age and health of the patient

CONTRAINDICATIONSOcclusal problemsEsthetics-Rarelly used in anterior

teeth(Bonding Technique).Access difficulties-In class V horizontal

groove in the gingival & occlusal aspect etc.

ADVANTAGESConservation of tooth structuresave time compared with cast restoration.Greater resistance and retention formEconomics

DISADVANTAGESDentinal micro fractures or crazingLowered fractured resistanceStrength of amalgam restoration is reducedMicro leakage around pin Perforations of pulp or ext. tooth structure.Difficulty to achieve proper contours

TYPES OF PINS1. Cemented pins2. Friction locked pins3. Self threaded pins

FRICTION LOCKED PINSDeveloped by Dr. Goldstein

in 1966Made of stainless steel More retentive than

cemented pinsUsed in vital teeth with good

access and ease of tapping/locked the pins

Cause craze lines or cracksRetain by resilience of dentin

SELF THREADED PINSDeveloped by Dr. Going in

1966Most 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 linesUsed in vital teeth

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 [0.020” to 0.32”] larger than pin size [0.018” to 0.30”]

Pin channel is 0.001” smaller than pin size

Pin channel is 0.015” 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

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

SELF THREADED PINS – THREAD MATE SYSTEM

SELF THREADED PINS – THREAD MATE SYSTEM

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

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

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

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

ADVANTAGES OF TMS PINSVersatile designWide range of pin

sizesColor coding allows

ease of useGold plating

eliminates corrosionGood retention

FACTORS AFFECTING THE RETENTION OFTHE PIN IN DENTIN AND AMALGAM

Orientation, number and diameter -Non-parallel pin - ↑ retention -Bending of pin – not desirable Interfere with condensation of amalgam Weaker pin, fractured dentin

↑ no. of pin - ↑ retention ↑ crazing & fracture ↓ amount of dentin available ↓ amalgam strength

PIN PLACEMENT

1. MECHANICAL ASPECTS2. ANATOMICAL ASPECTS3. MECHANO – ANATOMICAL ASPECTS

MECHANICAL ASPECTSA] STRESSING CAPABILITIES OF PINSB] RETENTION OF PINS IN DENTINC] MICROCRACKING AND CRAZING

MECHANICAL ASPECTS

[PINS AND TOOTH STRUCTURE]

A] Stressing capabilities of pins

Type of pins Diameter of pins Pin depth and dentinal

engagement Bulk of dentin Type of dentin

Shape of pin channels

Loose pinsIrregularly shaped

dentinal end of pins

Ratio of dentinal engagement : pin protrusion [ideal 2:1]

Number of pins in one tooth

Drill – its use and functionStresses induced during shortening pinsRetentive featuresInserting pins in stress concentration area of

tooth

B] RETENTION OF PINS IN DENTIN

Type of pinPin depth and dentinal

engagementPin channel

circumferential shape relative to that of pin

Inter pin distance

Type of cementRatio of dentinal engagement : pin protrusion

[ideal 2:1]Type of involved dentinSurface roughness of the pinsMode of shortening of pins after insertion of

pinsBulk of dentin around the pin

C] MICROCRACKING AND CRAZING

Type of pinProximity of pin to DEJInduced stresses in involved dentinType of dentin

ANATOMICAL ASPECTS

Knowledge of anatomy

RadiographOuter surface of

toothAmount of dentin

MECHANO ANATOMICAL ASPECTS FOR PIN PLACEMENTAnatomical featuresTooth alignmentCavity extentEffect of age or relative age on the pulp

chamber

TECHNIQUES FOR INSERTING PINS

Pin channel preparationsCemented pin techniqueThreaded pin techniqueFriction grip pin technique

PIN CHANNEL PREPARATION

Twist drill-By using twist drill latch type or depth limiting drill at low speed ( 300-500) RPM

No. 1/4 round burs- first make pilote hole with round bur to localize position of the pin the complete the hole in one or two thrust( movement)

Apply intermittent pressure

CEMENTED PIN TECHNIQUE

INDICATIONS

Ideal techniqueOnly technique for endodontically

treated toothOnly technique to be used when

avaliable location of the pin is close to DEJ

Ideal technique for a sclerotized / tertiary / calcific barrier / highly demineralized / dehydrated dentin

For class IV restorationsWhen there is limited bulk of dentin

PROCEDUREPreparation of pin channelChecking the surface irregularities of pinsSlow setting phosphate / polycarboxylate

introduced by perio explorer tip or lenticulo spiral at slow speed

Placement of pin using lock in or magnetised tweezer or hemostat

Large amalgam plugger is needed to check the complete seating of the pin

In case of class IV restorations, bending of the pins is to be done before cementation of the pin channel

THREADED PIN TECHNIQUE

INDICATIONSVital teethDentin to engage the pin is either

primary or secondaryMinimum avaliable location is 1.5mm

from DEJIf minimum pins are needed for the

restoration

PROCEDUREPreparation of pin channelPin is engaged to a driving device and pin is

continuously threaded into the pin channel until it offer resistance initiated by the pin channel floor

Desired length of the pin can be cut using small bur and high speed handpiece in the direction of threading and with light intermittent touches

Surface irregularities are correctedNo bending should be performed

FRICTION GRIP PIN TECHNIQUE

INDICATIONSFor vital teethWhen bulk of dentin is present [min 4mm

in all 3 dimensions]Only in the accessible areas

PROCEDUREPin channel is preparedChecking the surface irregularities of

pinsPut a colored mark on the pin to indicate

the exact depth of the pin channel using a measuring probe

Pin is held in its place at the entrance of the cavity

Concave headed seater is placed on the pin

With the hammer light strokes are given until that colored mark

Remove all the holding devicesCheck for cracks, chipped pieces or grossed

fractures

CAVITY PREPARATIONRemove all carious and weakened tooth

structureInitial cavity is prepared with dovetails,

boxes, grooves etcFacial and lingual walls are kept parallel

wherever possibleMargins are placed supra-gingivally

Areas to receive pins should be flat and perpendicular to long axis of the tooth.

There must be enough dentin for pin placement

Weakened cusps should be reduced and occlusal contour should follow the normal contour of the unreduced tooth

PULP PROTECTION

CLASS II DESIGNPins should be put in apically deepest and

most peripheral parts of the cavityPin should not be placed below the cuspDecreasing the stress concentration on the

pinUse of minimum number of pins with less

diameterPlacement of the pin should be such that

theres enough restorative material around it

CLASS V DESIGNPins are placed axially

parallel to the adjacent proximal surface

Pin protrusion should be minimal

Deep retentive grooves are placed

Pins should be placed midway in the preparation but as close to gingival wall as possible

RESTORATION

COMPLICATIONSDrill breakagePin breakageLoose pinsHeat generationDentinal cracksPerforation into pulpal space or external

tooth surface

FAILURES

EFFECT OF PINS ON PULPGenerally it responds positively and accepts

its presence without any adverse effectsHistologic evaluation reveals inflammatory

response, necrotic tissue encapsulation, fibrous tissue regeneration and formation of pre dentin by odontoblasts

Inflammatory reactions have been observed under all kinds of pins

CONCLUSIONThe prognosis of the involved tooth and its

role in overall treatment plan helps to decide the restoration to be placed

If amalgam is selected as the restorative material to be placed, pins placed in dentin improve the retention of the restoration

Pins have been extensively used in the past to restore such badly broken tooth