Anterior retainer design for resin-bonded acid-etched fixed partial dentures

Electrolytically etched castings of varying designs were cemented to prepared enamel. The load required to displace these castings was compared with the load required to displace anterior and posterior three-quarter crowns cemented with zinc phosphate cement. Electrolytically etched castings with grooves, half grooves, pins, a labial wrap, and no additional resistance feature (lingual plate only) were cemented to properly etched enamel. All specimens were loaded in tension from the lingual surface with an Instron testing machine at a crosshead speed of 0.05 in/min. Specimens with proximal extensions (3/4 crowns, full grooves, or labial wrap) required significantly more load for displacement than the other groups. This study demonstrated the need for proximal extensions when designing retainers for the Maryland Bridge denture.