As per Anderson and D'Alonzo classification the most dangerous type of odontoid fracture is

Anderson and D'Alonzo classification for odontoid fracture  Type I : Avulsion of tip . Type II : Fracture at junction of odontoid process and axis. Type III : Fracture through the body of axis. Treatment according to classification  Type I : Conservatively Type II : Most dangerous type, treated with screw fixation Type III : Conservatively