The PA Projection of the Mandible (0° Central Ray) is the primary baseline view designed to evaluate the mandibular body, bilateral gonions (angles), and lower ascending rami in true anatomical symmetry.
Unlike the PA Axial (Caldwell) view which angles the tube to elongate the rami and condyles, the 0° PA view directs the beam perpendicular to the image receptor with the forehead and nose touching the board. This minimizes perspective distortion of the mandibular body and provides an accurate, un-distorted view of the lower half of the mandible.
Detailed Indications:
Contraindications & Limitations:
| Parameter | Recommended Specification | Radiographic Rationale |
| Patient Posture | Erect (Preferred) or Prone | Erect seated/standing prevents torso rotation and maximizes patient stability |
| Image Receptor (IR) | 18 × 24 cm or 24 x30 cm (Portrait) | Tight vertical coverage from TMJs down to the submentum |
| SID | 100 to 115 cm ( 40 to 44 inches) | Standard focal distance balances spatial resolution and beam divergence |
| Grid Ratio | 8: 1 to 12: 1 focusedgrid | Essential to absorb high Compton scatter from the occiput and cervical spine |
| Tube Potential (kVp) | 75 – 85 kVp | Adequate penetration through the cervical spine and dense mandibular cortical bone |
| mAs Range | 20 – 30 mAs | Calibrated for dense bone trabeculae (Center AEC cell active) |
| Focal Spot | Small (0.6 mm) | High spatial sharpness needed for hairline fracture lines and cortical margins |
| Breathing | Suspended respiration | Eliminates respiratory and swallowing motion artifacts |
Both forehead and nose rest against the Bucky to secure head position and minimize subject-to-image distance.
Maintains the OML at 90° to the IR to superimpose the petrous ridges over the maxillary sinuses, clearing the rami.
Mid-sagittal plane is centered perpendicular to prevent asymmetrical foreshortening of bilateral mandibular rami.
Perpendicular beam exits through the junction of the lips (acanthion level) to project mandibular rami symmetrically.
| Error Type | Radiographic Sign on Film | Clinical Impact | Correction |
| Over-Flexion (Tucking chin too far down) | Petrous temporal bones project inferiorly into the mandibular body. | Obscures the mandibular body and molar teeth. | Raise chin slightly until the OML is strictly perpendicular. |
| Under-Flexion (Head tilted backward) | Maxilla and teeth superimpose heavily over the lower mandibular body. | Obscures bone trabeculae and mandibular canal. | Lower forehead/nose until OML is perpendicular. |
| Head Rotation (MSP not 90°) | Asymmetric width of bilateral mandibular bodies; one side appears widened, the other narrowed. | Mimics displaced cortical fracture or asymmetry. | Realign the Mid-Sagittal Plane (MSP) perpendicular to the IR. |
| Head Tilt (IPL not parallel) | Bilateral mandibular angles (gonions) lie at unequal vertical heights. | Creates artificial slant and asymmetry of the basilar border. | Realign the Interpupillary Line (IPL) parallel to the floor. |
| Feature | 0° PA Mandible | 20°–25° PA Axial Mandible (Caldwell) |
| Tube Angle | 0⁰ (Perpendicular) | 20⁰ to 25⁰ Cephalad |
| Primary Region of Interest | Mandibular Body & Angles (Gonions) | Mandibular Rami & Condylar Necks |
| Petrous Ridge Location | Superimposed over upper rami / condyles | Projected superiorly away from rami |
| Condylar Visualization | Partially obscured by cranial base | Clearly elongated and visualized |
| Distortion of Body | Minimal / True anatomical length | Mild vertical elongation / foreshortening |
Mandibular rami and angles (gonion) are projected equidistantly from the cervical spine without rotation.
Anterior arch and symphysis menti are centered, though partially superimposed over the cervical spine.
Subcondylar regions and coronoid processes are visualized lateral to the petrous temporal overlap.
Petrous ridges superimpose the maxillary regions, clearing the mid-to-lower thirds of the mandibular rami.