FATIGUE OF RESIN-BONDED AMALGAM RESTORATIONS

Standardized MOD cavities were prepared in 80 human premolars, which w ere treated with either adhesive resin or copal varnish and then resto red with amalgam. Fracture resistance of these groups was compared aft er 24 hours of storage, 4 weeks of storage with thermocycling, and aft er 500 days of storage. The buccal cusps were loaded at an angle of 30 degrees to the tooth long axis until fracture occurred. Additionally, survival curves were compared for adhesive resin and copal varnish gr oups that had been repeatedly load cycled until fracture occurred. The 24-hour adhesive resin group was significantly stronger than the corr esponding copal varnish group (P < 0.05). However, no significant diff erences between adhesive resin and copal varnish were found for the ot her thermocycling, extended 500-day storage, or load cycling tests. In conclusion, the strengthening effect of an adhesive resin on teeth re stored with MOD amalgam restorations was transient.