Revisiting amalgam: a comparative study between bonded amalgam restoration and amalgam retained with undercuts

To compare the retention of amalgam restorations in bonded amalgam restoration and restorations with undercuts.

With improvement in adhesive technology problem associated with conventional preparation for amalgam restorations mainly compromised resistance form of tooth structure have been largely overcome.

Forty caries free extracted molars were used. A basic box preparation was done proximally with buccoproximal and linguoproximal walls diverging at 45° angle and the axial wall is 1.3 mm in dentin. The teeth were randomly divided into 4 groups of 10 each. Group 1 - Teeth with basic box preparation. Group 2 - Teeth with box preparation for bonded amalgam. Group 3 - Teeth with box preparation and proximal retention grooves. Group 4 - Teeth with box preparation and occlusal dovetail. Group 1, 3 and 4 were restored with silver amalgam and group 2 restored with resin-bonded amalgam. All samples were subjected to simulated occlusal load against marginal ridge using a blunt stainless steel point in an Instron testing machine. The force in kilogram required to dislodge the restorations as well as the type and location of failure were recorded.

The main force required to dislodge the restoration was least in group 1 and 3 and maximum in group 2.

The in vitro study showed that the amalgam bonding technique, using an adhesive resin liner in proximal box form preparation, was more effective than either box form with proximal grooves or dovetails or proximal box only in providing resistance to displacement.

Amalgam bonding eliminates the unnecessary removal of sound tooth structure during cavity preparations.