Principles of Retentive Pins Placement in Dentistry

Retentive Pins:
These are Pins which are used to improve the retention of the restoration. Pins retain the restoration in position and and hold the restoration and prepared tooth structure together and they also the tooth by Cross-Splinting of Weakened Cusps.

Placing of Retentive pins should be planned and there are many factors to be considered in Retentive Pin placement in Amalgam Restorations, here we are going to list out the basic and must properties on which Number of Retentive pins, Retentive Pin Site, Orientation, Diameter, Size, Interpin distance and Depth are decided.

Number of Pins required: 

• One Pin per missing cusp or One pin per missing axial line angle of tooth

Site or Location of Pin to be placed depends on the following factors:

• Should be halfway between the pulp and dentinoenamel junction/external surface of the tooth
• There should be at least 1.0mm of sound dentin around the whole circumference of the pin
• Pin should be located no closer than 0.5mm to the dentino-enamel junction to avoid crazing of enamel
• Dentin thickness around each pin should be atleast 2.5 times the diameter of the pin hole
• Pin placement should be such that atleast 1 mm of Dentinal thickness is present between Pulp and the Pin

Pin Orientation depends on:

• Pin should be oriented parallel to the long axis of the tooth

Pin Diameter depends on:

• The amount of Dentin available
• Overall Size of the concerned Tooth
• Amount of Retention required

Pin Length depends on:

The Pin Length is seen separately in Dentin and in Restorative material.

• Cemented Pins: 3mm in Dentin and 2mm in Restorative material
• Friction locked Pins: 3mm in Dentin and 3mmin Restorative material
• Threaded Pins: 2mm in Dentin and 2mm in Restorative material

Inter Pin Distance depends on:

• Cemented Pins: 2mm
• Friction Locked Pins: 4mm
• Minikin threaded Pins: 3mm
• Minim threaded Pins: 5mm