• 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.

ADVANTAGES

• Conservation of tooth structure
• Save time compared with cast restoration.
• Greater resistance and retention form
• Economics

DISADVANTAGES

• Dentinal micro fractures or crazing
• Lowered fractured resistance
• Strength of amalgam restoration is reduced
• Micro leakage around pin
• Perforations of pulp or ext. tooth structure.
• Difficulty to achieve proper contours

INDICATIONS

• Badly 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

CONTRAINDICATIONS

• Occlusal problems
• Esthetics-Rarely used in anterior teeth (Bonding Technique).
• Access difficulties-In class V horizontal groove in the gingival & occlusal aspect etc.

TYPES OF PINS

• Cemented pins
• Friction locked pins
• Self-threaded pins

SELF THREADED PINS – THREAD MATE SYSTEM

PIN DESIGNS

ADVANTAGES OF TMS PINS

• Versatile design
• Wide range of pin sizes
• Color coding allows ease of use
• Gold plating eliminates corrosion
• Good retention

FACTORS AFFECTING THE RETENTION OF THE 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

• ↑ diameter of pin – ↑ retention

↑ No:, diameter, depth – danger of perforation on pulp or external tooth surface
Interfere with condensation of amalgams and adaptations to the pins.
↓ Amount of dentin available
↓ Amalgam strength

• Extension into dentin & amalgam

Retention is not increased when depth of the pin increases in 2mm in depth – fracture of dentin
If 2mm increase in amalgam-fracture of amalgam.

TECHNIQUES FOR INSERTING PINS

• Pin channel preparations
• Cemented pin technique
• Threaded pin technique
• Friction grip pin technique

Failure of the pin retained restorations

• If the failure is within the restoration, the restoration can fracture.
• If the failure is at the interface between the pin and the restorative material, the pin can pull out of the restorative material.
• If the failure is within the pin, the pin can fracture when stressed beyond its ultimate tensile strength.
• If the failure is at the interface between the pins and the dentin, the pin can pull out of the dentin.
• Within the dentin, the dentin can fracture.