Congenital fusion of the maxillary alveolar process and mandible is a very rare entity. A one day old male newborn was referred to our clinic with a diagnosis of a 'absence of oral cavity'. Physical examination revealed that there was no mouth opening bilaterally in the posterior region due to maxillary and mandibular bone fusion; and in the front there was only 1 mm of mouth opening. Examination of the intraoral space could not be achieved. No other congenital anomaly was detected on general examination. The infant, who was fed via a nasogastric tube for 1 month, was operated on. An intra-oral device which separated maxillary and mandibular alveolar arches from each other was designed and used for 8 weeks to avoid recurrence of the fusion. An adequate mouth opening was obtained and the infant could be fed orally.