A

The coronal barrier has to be placed so its margin is protected from the oral environment; when the gingiva has receded, that protected zone is 1 mm apical to the recession line rather than the CEJ. Trimming gutta-percha to this level keeps the sealing material sub-gingival and has been shown to reduce micro-leakage once the intra-orifice barrier is placed [Yared et al., 1997, PMID 9594752; Abramovitz et al., 2001, PMID 11485271].