Seating single or multiple crowns is one of the most basic skills for a dentist. If the interproximal contacts are excessively tight, complete seating of a single crown may not be possible. If the crown is slightly too large for the space it should occupy, the crown may not seat completely, and open margins may result. Open margins produced by improperly seated restorations on the maxillary right first molar and second premolar are shown in Figure 1. The clinician used floss to evaluate the interproximal contacts. Open margins are difficult to clean, can lead to inflammation of the gingival tissues, and may result in recurrent dental caries. 1 A contact that is too tight also may produce patient discomfort because of pressure exerted on the adjacent teeth. Therefore, it is important to ensure the complete seating of crowns. Difficulties arise when either a radiograph or an explorer are used to evaluate subgingival crown margins. Assif et al 2 recommended the use of impression materials when crown