PINRETAINED RESTORATIONS EXTENSIVELY DAMAGED TEETH Extensively damaged teeth
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PIN-RETAINED RESTORATIONS
EXTENSIVELY DAMAGED TEETH Extensively damaged teeth are routinely encountered Damage may be because Caries Fracture Loss of ½ or more than ½ of tooth structure Remaining tooth structure not enough to retain a restoration Pins used for retention
WHAT IS A PIN RETAINED RESTORATION? DEFINITION: A pin retained restoration is defined as any restoration that requires the placement of one or more pins in the dentin so as to provide adequate resistance and retention form to the restoration.
Dimension & nature of the destruction: Occluso – apical destruction – more resistance problems BL & MD destructions – both resistance & retention problems Restoration design – no additional stresses Immobilizing modes in stress concentration areas – decrease micromovements
Partial / complete loss of a cusp: Evaluate …. Functional / non – functional cusp? Working / balancing incline planes involved? Width of destruction relative to intercuspal distance?
BL partial loss of the cusp from occlusal direction – resistance – retention problems MD partial loss without BL loss – resistance problems Occluso – apical loss – retention problems Length of remaining part of cusp relative to width Incomplete loss of cusp – resistance – retention problems
PIN RETAINED RESTORATIONS Auxiliary methods of retention Do not reinforce the restoration But improves retention and reduces the strength
INDICATIONS • Auxiliary aids of retention in badly broken down or mutilated teeth • Large Class II, Class IV Cavity preparations • Endodontically & Periodontically treated teeth with guarded prognosis • Foundations for full crown restorations • To facilitate Rubber Dam application
CONTRAINDICATIONS • Occlusal problems • Esthetic areas • Access difficulties
ADVANTAGES • Conservation of tooth structure • Single appointment procedure • Resistance and retention forms • Economical
DISADVANTAGES • Dentinal microfractures • Lowered fracture resistance than cast restorations • Pins lower transverse and tensile strengths of amalgam • Microleakage • Perforations • Difficult to achieve proper contour
GUIDELINES 1 • Knowledge of anatomy of the tooth and supporting tissues • Radiographs • Tooth alignment • Age of the patient
GUIDELINES 2 • PIN DIAMETER Maximum retention by 0. 035 inch pin • INTER PIN DISTANCE Pins closer than 2 mm reduces retention • RATIO OF PIN INTO DENTIN Ideal 2 : 1 • BULK OF DENTIN More bulk better retention • MANIPULATION OF PINS After insertion reduces retention
Pinholes and pins: Are probably the only retention features that do not require existing vertical supragingival tooth structures for their placement. They can be used in 2 ways. Pinholes parallel to path of insertion where the pins are an integral part of the cast restoration. These pins aid in enhancing retention of over tapered preparations Non-parallel pinholes and pins aid in retaining a core of amalgam / composite over which a cast restoration is fabricated.
TYPES OF PINS There are 3 types of pins : Cemented Threaded Friction lock Regardless of the type of pin which is used, it should be surrounded by 1. 5 mm of dentin. Hence, it is contraindicated in small, thin teeth.
Some general rules to be followed while placing pins are: • Place them as close to the line angles as possible within 1. 5 mm from DEJ and 1. 5 mm from axial wall. This allows for sufficient dentin bulk for stress distribution, adequate space for amalgam condensation and prevention of crazing or fracture of enamel.
• Threaded pins need to be placed at a depth of only 2 mm while cemented need about 4 mm. Both should extend 2 mm into the restorations. • Place them as far from the fulcrum of the anticipated tipping motion. • Safest locations are the line angles and tooth corners while the least desirable is in the middle of the tooth especially over furcation and external concavities.
Always examine radiographs carefully before starting pinhole preparation. A drill can also be placed in the gingival sulcus in the estimated direction of the hole to get an idea of the outer surface in area of pinhole.
Procedure • Involves making a pilot hole or a dimple with a no. ¼ bur • A depth limiting twist drill to drill a channel up to 2 mm. • A slightly larger diameter self- threading pin is then twisted into this channel using a hand wrench / latch type HP. • The excess length of pin is removed with a 169 L bur placed perpendicular to the pin, in a brushing motion to prevent unscrewing the pin. • Self shearing pins are also available. If they need to be bent, it should be done with a pin bending tool.
RETENTION OF PIN IN DENTIN • TYPE OF PIN TMS pins 5 to 6 times more retentive than cemented Friction lock 2 to 3 times than cemented pins Cemented pins least retentive • PIN CHANNEL CIRCUMFERENCE Round gives more retention • NUMBER OF PINS Pins closer than 2 mm reduces retention • TYPE OF CEMENT USED Adhesive cements give more retention • SURFACE ROUGHNESS OF PINS Serrated pins give more retention
STRESSES INDUCED INDENTIN • TYPE OF PIN USED Cemented pins less stress Friction lock pins maximum stresses as they are tapped into position • DIAMETER OF THE PIN Greater the diameter greater the stresses • TYPE OF DENTIN Young permanent tooth dentin has higher elasticity and hence least affected
CLASSFICATION OF PINS • CEMENTED PINS Markley 1958. Pin channel more than the pin Available in various sizes – 0. 018” to 0. 30” Pin channels are 0. 0 o 1” to 0. 002” larger than the pin
• FRICTION LOCK PINS Goldstein 1966 Pin channel is narrower than pin size 0. 022 inch pin channel diameter 0. 021 inch
THREADED PINS Introduced by Going 1966 Also called as Thread Mate System or TMS pins Pin channel diameter smaller than the pin 4 sizes • REGULAR 0. 030”, 0. 031” • MINIM 0. 024”, 0. 021” • MINIKIN 0. 19”, 0. 20” • MINUTA 0. 14”, 0. 15”
PIN CHANNEL PREPARATION Basically requires the following • Twist drill • Round burs • # 1/4 , ½, 1 Depth gauge or measuring probe
TWIST DRILL End cutting rotating instrument with 2 steel blades helix fluted , allows easy removal of debris. Twist drill is an instrument which should be used with the utmost care in the tooth surface.
GUIDELINES FOR TWIST DRILL USE • Speed 300 to 500 only as coolants not used in deep areas and tactile sensation only in slow speed • Should be used in direct cutting with forces parallel to the long axis of the drill. Lateral cutting widens the pin channel. • The drill should b rotating when in contact with tooth • Do not use pumping stroke. ( widens channel ) • Never use the twist drill in enamel.
CEMENTED PIN TECHNIQUE INDICATIONS • • • Endo treated tooth should have only cemented pins When available dentin is close to pulp. Insufficient bulk of dentin. Class 4 cavities where shape of the pin is L or U. Ideal in Sclerosed , dehydrated dentin. Cemented pins are the only technique of cross linkage between two parts of the same tooth. • Cemented pins are always safer.
PIN PLACEMENT Required length of the pin is cut from the wire form. Inserted in to the channel , tip of the pin is smoothened Poly carboxylate , zinc phosphate or GIC can be used. A lentulo spiral can be used for cement aplication. With a haemostat the pin can be held in position
FRICTION LOCK PINS INDICATIONS • • Use only in resilient dentin. Bulky dentin should be available. Pin should be located 2 to 2. 5 mm in to d e j. Should be tried only in accessible areas where the seating forces can be given parallel to pin axis. Friction lock pins are available in 4 to 5 mm precut
PIN PLACEMENT Pin channel is prepared. The required length of pin is selected. The ends are smoothened. Pin placed in position. Using a small hammer pin is forced in place.
T M S PINS INDICATIONS • Only in vital tooth • Available pin locations should be at least 1. 5 mm from d e j • When minimum number of pins are to be used. • When maximum retention is to be achieved.
TYPES OF PINS • Standard pin 7 mm long • Self shearing pin 4 mm long • Two in one pin 2 shearing areas are provided at 4 mm difference • Link series with plastic heads for the pins
PIN PLACEMENT Pin channel is prepared Selected pin is introduced in the channel. Using the wrench the pin is driven into dentin. Sheared of with a high speed cutting bur The balance of he pin can be used for another channel. Bending of the pin should be avoided.
COMPLICATIONS FAILURE OF RESTORATION Restoration Fracture Restoration pulls away from the Pin Fracture Pin pulls out along with the Restoration Dentinal fracture BROKEN DRILLS & BROKEN PINS LOOSE PINS PERFORATIONS
THANK YOU
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