The current invention relates to an adjustable mandibular advancement device with a unique combination of resilient hinging, dentition engagement and adjustability, to prevent or reduce Snoring and/or Obstructive Sleep Apnea Syndrome. The adjustability is described by means of two concepts of adjustability for the relative enlargement or diminution of the members of the device, incremental and successive advancement mechanisms, in either combination or separately. By use of thermoplastic materials the device can be used in the outmost variability of the human dentition.