[Changes in retention strength of luting cements by repeated loading].

The retention of crowns cemented on abutment tooth model was examined for three types of luting cements when compressive loads of 2.5 to 10.0 kg were repeatedly applied to the occlusal plane. The chamfer type Ni-Cr alloy crown and abutment tooth model were prepared, and their surfaces to be cemented were sandblasted with glass beads. Loads were applied 7,200 times a day for 1, 3, or 7-day period after cementing. The polycarboxylate and zinc phosphate cements showed higher crown retentions than glass ionomer cements. Although retention strength of glass ionomer cements was significantly increased by storing the cemented specimen in water for 7 days, repeated loading tended to decrease retention. In polycarboxylate cements and one brand of zinc phosphate cement employed, retention strengths were decreased when stored in water over 3 days. However, their highest levels were maintained or even positively impacted by repeated loading for 7 days.