A case of mucous cyst of the floor of the mouth associated with thumb sucking in an infant with polydactylia

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We describe an infant with polydactylia who presented with a mucous cyst of the floor of the mouth that was associated with thumb sucking.A 8 -month-old boy with a ventricular septal defect, pulmonary atresia, and polydactylia was referred to us because of a cystic swelling in the right side of the floor of the mouth. There was no history of trauma, but thumb sucking became frequent before the swelling had occurred. When the infant sucked this thumb, his left thumb and radial duplicated thumb were placed in the oral cavity. His thumb was put between the maxilla and the tongue, but a small radial thumb was placed on the right side of the floor of the mouth. This manner of thumb sucking, with the duplicated thumb rubbing against the floor of the mouth, apparently caused the mucous cyst of the floor of the mouth.