Retention and resistance features for complex amalgam restorations.

Although not absolute, there are indications for each of the retention and resistance features described. Amalgapins and circumferential slots have their greatest indication in teeth with short clinical crowns and in cusps that have been reduced 2-3 mm for coverage with amalgam. In these situations, slots provide more resistance than amalgapins and amalgam inserts. When amalgapins or slots are used as the only retention and resistance features, the restoration is susceptible to early fracture during matrix removal. When the technical requirements for placement of vertical pins can be met, they provide excellent retention and resistance form. Vertical pins should be placed at least 0.5 mm inside the dentinoenamel junction, at a depth of approximately 2 mm, and should protrude from the tooth approximately 2 mm. However, there are inherent risks involved with pin placement; these include crazing of tooth structure, perforation into the pulp or periodontium, and weakening of the amalgam restoration over the pins. The use of both vertical and horizontal pins may be limited by inadequate access; in these cases, alternate devices should be used. When a cusp has been reduced and increased resistance is needed, a ledge or peripheral step may be indicated. It must be remembered that this feature will result in a greater display of amalgam and may be esthetically unacceptable on a facial cusp. If esthetic appearance is a factor, horizontal pins may be used to reinforce a remaining facial cusp. Horizontal pins may also be used to splint or tie a remaining cusp to the restoration.(ABSTRACT TRUNCATED AT 250 WORDS)