[Dental-radicular cysts invading the maxillary sinus]

The authors report three cases of radicular cyst developing into the maxillary sinus which was partially or completely obscured. Looking for a thin rim of cortical bone should be undertaken in case of opacity of maxillary sinus. This rim correspond to the floor of the sinus, which is lifted up by the cyst. If the attenuation value of the intrasinusal process is near of that of water, the diagnosis of radicular cyst invading the maxillary sinus is very likely and may indicate intraoral surgical approach.