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- Discussion:
    - to evaluate C1 (Jefferson), Dens, superior facets of C2;
    - for evaluating dens fractures, body of C2, & rotary C1-C2 dislocations;
    - mach lines - teeth, C1 arch;
    - open mouth view, along w/ lateral view, will reveal fractures of the dens ;
    - atlantoaxial articulation & integrity of dens and body of C2 are best seen on the odontoid view;
    - this is most technically most difficult film to obtain as it requires patient to open his mouth as wide as possible;
    - lateral masses of C1 should align over the lateral masses of C2;
    - lateral displacement of masses of C1 w/ respect to C2 may indicate Jefferson or burst fracture of the Atlas;
         - combined lateral mass displacement > 7 mm suggests that transverse ligament is torn;
    - children:
         - overlapping lateral masses can be a normal variant in children and therefore this view may not allos assessment of whether frx is
              stable or unstable;

- Normal Variants of Dens:  (see dens frx)
    - dens may be completely absent, hypoplastic, or incompletely fused to body of C2 (lesion called Os Odontoideum)
         - Os Odontoideum is smaller than normal dens & is fixed to anterior ring of C1: 2 move as a unit;
              - subluxation and instability are common;

- Assessment of RA Patient:
    - state of the odontoid peg and the lateral processes can be assessed by open mouth views, though disease of the tempomandibular 
         joint can make this difficult;
    - concomitant vertical subluxation may conceal amount of anteroposterior movement at the atlantoaxial level because broader base of 
           odontoid peg comes to lie opposite anterior arch of the Atlas;

- Technique:
    - the patient is positioned as for the supine AP;
    - central beam directed perpendicular to the midpoint of the open mouth;
    - patient should softly say 'ah' to depress the tongue to the floor of mouth during exposure

- Normal Case Examples: