PA Mandible 0° View X-Ray: Positioning, Technique & Study Notes

PA Mandible 0° View-

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.

1. Clinical Indications & Contraindications

Detailed Indications:

• Mandibular Trauma & Fractures:
  • Assessment of medial or lateral displacement of fractures involving the mandibular body, angles (gonions), and lower rami.
  • Evaluation of parasymphyseal fractures and vertical cortical step-deformities.
• Neoplastic & Odontogenic Lesions:
  • Detection of bone lesions such as Ameloblastoma, odontogenic keratocysts (OKC), dentigerous cysts, and osteolytic metastases within the mandibular body and angle.
• Inflammatory & Infectious Conditions:
  • Evaluation of cortical destruction, sequestrum, and periosteal reaction in osteomyelitis of the mandible.
• Mandibular Asymmetry & Deformities:
  • Comparative assessment of mandibular body length, mandibular angle width, and facial asymmetry.
• Pre- & Post-Surgical Follow-up:
  • Verification of cortical reduction and alignment of titanium plates, reconstruction bars, or fixation screws along the body and basilar border.

Contraindications & Limitations:

• Unstable Cervical Spine Trauma: Absolute contraindication for turning the patient prone or flexing the head forward into the upright Bucky. An AP Mandible (0° or trauma-adapted AP Axial) must be performed supine with zero head/neck movement.
• Midline Symphysis Obscuration (Limitation): The dense cervical spine superimposes directly over the midline symphysis (mentum). A Mandibular Occlusal View, SMV, or Axiolateral Oblique (45°) is required to evaluate midline chin fractures.
• Condylar Neck Superimposition (Limitation): In the 0° PA position, the dense petrous pyramids and occipital base superimpose over the upper ascending rami and condylar processes (a 20⁰ to 25⁰ PA Axial Caldwell or Towne’s View is required to clear the condyles).

2. Technical Factors & Exposure Physics

3. Step-by-Step Patient & Part Positioning

                 [ Vertical Bucky Surface ]
                           ║
     (Lip Junction) ◄───── ║ ◄── Forehead & Nose touching Bucky
                           ║
                    /──────║──────\
                   │  OML  ║       │ ◄── OML strictly Perpendicular (90°) to IR
                   │ ──────║────── │
                   │  MSP  ║       │ ◄── Mid-Sagittal Plane Perpendicular to IR
                    \      ║      /
                           ║
                           ▲
                           │
                  [ Central Ray: 0° ]
                 (Exits at the Lips / Acanthion)

• Patient Preparation: Remove all radiopaque materials from the head, neck, and oral cavity (dentures, partial plates, earrings, necklaces, tongue piercings, hairpins, and glasses).
• Base Posture:
  • Erect (Preferred): Patient sits or stands erect facing the upright Bucky with shoulders relaxed and depressed equally.
  • Prone (Alternative): Patient lies prone on the radiographic table with arms resting near the head for stabilization.
• Alignment of Reference Lines & Points:
  1. Forehead & Nose Contact: Rest the patient’s forehead and the tip of the nose firmly against the surface of the Bucky board.
  2. Orbitomeatal Line (OML): Adjust head flexion/extension until the OML is strictly perpendicular (90⁰) to the plane of the image receptor.
  3. Mid-Sagittal Plane (MSP): Must remain strictly perpendicular to the midline of the vertical grid to ensure zero head rotation.
  4. Interpupillary Line (IPL): Must remain strictly parallel to the floor and receptor plane (ensuring zero lateral head tilt).

4. Central Ray (CR), Alignment & Collimation

• Central Ray (CR) Angle: Strictly 0⁰ (Perpendicular) to the image receptor.
• CR Exit Point: Directed horizontally (or vertically if prone) to exit at the junction of the lips (or midway between the acanthion and mental protuberance).
• Collimation: Four-sided collimation adjusted tightly:
  • Superiorly: Just above the TMJs and inferior orbital rims.
  • Inferiorly: Below the soft-tissue margin of the chin/submentum.
  • Laterally: To the outer skin margins of the mandibular angles (gonions) and cheeks.

5. Positioning Errors & Radiographic Signs

6. Comparison: 0° PA Mandible vs. 20°–25° PA Axial (Caldwell) Mandible

7. Radiographic Anatomy & Quality Evaluation Criteria

+───────────────────────────────────────────────────────────────────────────+
|                           [ Base of Skull / Petrous ]                     |
|                           (Overlying Upper Rami)                          |
|                                                                           |
|                  Condyles ──► [·]               [·] ◄── Condyles          |
|                                \                 /                        |
|                                 \  Mandibular   /                         |
|                                  \    Rami     /                          |
|                                   |           |                           |
|        Mandibular Angle ────────► /  Mandibular \ ◄──────── Mandibular    |
|           (Gonion)               /     Body      \             Angle      |
|                                 │ [#] [#] [#] [#] │                       |
|                                  \  (Mentum)   /                          |
|                                   \___________/                           |
|                            [ Superimposed C-Spine ]                       |
+───────────────────────────────────────────────────────────────────────────+

• Mandibular Body & Angles (Primary Hallmark):
  • Symmetrical, undistorted demonstration of the bilateral mandibular body, angles (gonions), and lower ascending rami.
• Rotational Symmetry:
  • Equal distance from the lateral margins of the cervical spine to the mandibular angles on both sides.
  • Symmetric cortical thickness and contour of the basilar border of the mandible.
• Superimposition Awareness:
  • Cervical spine is centered along the midline, superimposing over the mandibular symphysis.
• Bone Detail & Sharpness:
  • Distinct visualization of cortical borders, mandibular canal, and dental root relationships along the body with no motion blur.