RESUMEN
AIM: To assess whether several try-in attempts change the circumference of preformed metal crowns (PMCs). METHODS: This in vitro, experimental study was performed on 68 PMCs of maxillary and mandibular molars that required crimping. First, a photograph was obtained of the gingival margin of each crown using a digital camera (fixed at a specific distance). Crown margins were then crimped using 114 pliers. The second photograph was obtained under the same conditions as the first one. After crimping, the crowns were removed using an excavator to assess the amount of crimping. This was repeated for the second time and a photograph was obtained after each time of PMC removal. The crown was crimped again and tried on the tooth and a photograph was obtained after completion of each phase. Photographs were saved in a computer and the circumference of the crowns was calculated using AutoCAD software. RESULTS: The reduction in circumference of the crowns following the first crimping was greater for the primary second molars than for the primary first molars and was on average 0.87%. After trying the crowns on teeth, the circumference of the crowns increased on average by 0.33%. This increase was 0.53% after trying the crowns for the second time. The reduction in circumference after the second crimping was 0.51%. There was an increase in circumference after re-trying of 0.35%. Changes in circumference of the crowns after the first (p = 0.037) and second (p = 0.00) try-in attempts were statistically significant. CONCLUSIONS: Re-crimping is necessary after trying the crown on tooth and prior to cementation.