Sir, in the paper presented by Motamedi and Talesh (BDJ 2005; 198: 203–206), about handling large dentigerous cysts, the authors say that the fluid content was helpful for establishing the diagnosis of cyst instead of an odontogenic tumour. We would like to remember that ameloblastomas can also present a fluid similar to cysts, including solid variants. In Brazil, ultrasonography is performed for evaluating the content of intra-osseous maxillo-mandibular lesions, helping the differential diagnosis between odontogenic keratocyst and solid or cystic ameloblastomas. In the case of cystic ameloblastomas, this procedure is crucial for determining the area of an incisional biopsy, because part of the tumoral wall presents an epithelial lining very similar to dentigerous cysts, which can lead to a misdiagnosis, if the biopsy is performed in a non-representative area.