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Facial Bones X-Ray Positioning: Waters, Caldwell, Lateral, and SMV Views

Why Facial Bones Positioning Demands Precision

Facial bone radiography is one of the most common trauma examinations you'll perform in the emergency department — and one of the most frequently tested on the ARRT registry. Unlike extremity work where positioning errors are obvious, facial bone positioning demands millimeter accuracy because multiple bony structures (orbital floors, maxillary sinuses, zygomatic arches, and nasal bones) overlap in complex ways. A few degrees off on the Waters view, and you may miss a blow-out fracture or project the orbital floor over the maxillary sinus in a way that mimics pathology.

Every year, rad tech students struggle with the same questions: Is the Waters view 37° or 45°? Where does the CR exit? What's the difference between a standard Waters and a modified Waters? These aren't just trivia — they directly affect whether an orbital floor fracture is visible or hidden.

Whether you're a student preparing for clinical rotations or a working tech refreshing your facial bone positioning skills, this guide covers the six essential facial bone projections with Clark's-verified centering points, evaluation criteria, and ARRT exam tips you won't find in a standard textbook summary.

Anatomy of the Facial Skeleton: What You're Imaging

The facial skeleton consists of 14 bones (excluding the mandible, which is often radiographed separately):

Bone	Count	Key Landmark
Maxilla	2	Inferior orbital rim, maxillary sinuses, alveolar ridge
Zygomatic	2	Cheek prominence, zygomatic arch, lateral orbital wall
Nasal	2	Nasal bridge, nasal septum
Lacrimal	2	Medial orbital wall (smallest facial bones)
Palatine	2	Posterior hard palate
Inferior Nasal Conchae	2	Lateral nasal wall
Mandible	1	Jaw (often imaged separately)
Vomer	1	Nasal septum

On a clinical level, you're assessing the facial bones for fractures, displacement, sinus pathology, and foreign bodies. The three most common facial fracture patterns are:

• Le Fort I — Transverse maxillary fracture (floating palate)
• Le Fort II — Pyramidal fracture through maxilla, infraorbital rim, and nasal bridge
• Le Fort III — Craniofacial disjunction (floating face)

Key Landmarks and Baselines

Mastering facial bone positioning comes down to the same three anatomical lines used in skull radiography, plus a few specific facial landmarks:

Baseline / Landmark	Definition	Used For
Orbitomeatal Line (OML)	Outer canthus → center of EAM	Waters (37°), Caldwell, PA/AP skull
Infraorbitomeatal Line (IOML)	Infraorbital margin → upper margin of EAM	SMV, Towne variant
Acanthion	Junction of upper lip and nasal septum	Waters CR exit point
Nasion	Depression at bridge of nose	Caldwell CR exit point
Mental Point (Mentum)	Tip of chin	Lateral positioning reference
Glabella	Smooth prominence between eyebrows	SMV centering reference
Gonion	Angle of the mandible	Mandible oblique positioning

Projection 1: Waters — Parietoacanthial (Clark's, p208–210)

The Waters view (parietoacanthial projection) is the single most important facial bone projection and the one you'll perform most frequently. It demonstrates the maxillary sinuses, orbital floors, zygomatic arches, and nasal cavity in a single image. On the ARRT exam, this is the most-tested facial bone projection by a wide margin.

Patient Position

• Prone (preferred) or erect with the head against the bucky
• Neck hyperextended to bring the OML at 37° to the IR
• The acanthion (not the chin!) rests against the IR/bucky
• Midsagittal plane perpendicular to the IR
• Arms at sides for patient comfort

Baseline

• OML is 37° from the plane of the IR — this is the defining angle of the Waters view

Central Ray (Clark's, p208)

• Perpendicular (0°) to the IR
• Enters at the vertex (top of the skull)
• Exits at the acanthion (junction of upper lip and nose)

Technical Factors

• IR size: 24 × 30 cm (10 × 12 in), portrait
• SID: 100 cm (40 in)
• Grid: Yes
• Breathing: Suspend respiration

Evaluation Criteria

• The maxillary sinuses must be visualized below the petrous ridges — this is the most critical check. If the petrous ridges overlap the maxillary sinuses, the OML angle was too shallow (<37°)
• Orbital floors well demonstrated without superimposition
• Zygomatic arches visible
• Nasal septum centered (no rotation)
• Both zygomatic bones symmetric

Projection 2: Modified Waters — For Orbital Floor Evaluation (Clark's, p210)

The modified Waters uses a shallower angle to better demonstrate the orbital floor and infraorbital rim — the area most commonly involved in blow-out fractures. This is a high-yield ARRT topic.

Patient Position

• Same as the standard Waters (prone or erect, acanthion against IR)
• Neck hyperextended to bring the OML to 30° from the IR (instead of 37°)

Central Ray

• Perpendicular (0°) to the IR
• Exits at the acanthion (same as standard Waters)

Key Difference

The reduced angulation (30° vs 37°) shifts the petrous ridges further below the orbital floors without over-projecting the maxillary sinuses. This gives a clearer, unobstructed view of the orbital floor and inferior orbital rim.

Evaluation Criteria

• Orbital floor and infraorbital rim clearly demonstrated
• Petrous ridges projected well below the maxillary sinuses
• No rotation — symmetric orbital margins

Feature	Standard Waters (37°)	Modified Waters (30°)
CR to OML	37°	30°
Primary purpose	Facial bone survey, maxillary sinuses	Orbital floor, blow-out fractures
Petrous ridges	Below maxillary sinuses	Well below maxillary sinuses
Orbital clarity	Good	Excellent (orbital floor focus)

Projection 3: Caldwell — PA Axial (Clark's, p200)

The Caldwell view (PA axial) is used in facial bone imaging to evaluate the superior orbital fissures, frontal sinuses, ethmoid sinuses, and orbital margins. It's the same projection used in the skull series, but the interpretive focus shifts to the facial structures.

Patient Position

• Prone with forehead and nose against the IR/bucky
• Forehead resting on the IR — this is the key difference from the Waters (forehead, not acanthion)
• Midsagittal plane perpendicular to the IR

Baseline

• OML perpendicular to the IR

Central Ray (Clark's, p200)

• Angled 15° caudad
• Exits at the nasion

Evaluation Criteria

• Petrous ridges projected into the lower third of the orbits
• Superior orbital fissures clearly visible
• Frontal and ethmoid sinuses well demonstrated
• No rotation (symmetric orbital margins)

If the petrous ridges fill the lower two-thirds of the orbits, the angle is too shallow (closer to 0°). If they are below the orbits entirely, the angle is too steep (>15°). This petrous ridge logic is consistently tested across multiple projections on the ARRT exam.

Projection 4: Lateral Facial Bones (Clark's, p212)

The lateral facial bones projection provides a profile view of the entire facial skeleton. It is essential for assessing anterior-posterior displacement in facial trauma and for evaluating the overall alignment of the maxilla, mandible, and nasal bones.

Patient Position

• Erect or recumbent — same setup as the lateral skull
• Head in true lateral — midsagittal plane parallel to the IR
• Interpupillary line perpendicular to the IR
• Chin slightly elevated

Central Ray (Clark's, p212)

• Perpendicular to the IR
• Entering 2.5 cm (1 inch) superior and 2.5 cm (1 inch) anterior to the EAM — the same centering as the lateral skull

Technical Factors

• IR size: 24 × 30 cm (10 × 12 in), portrait
• SID: 100 cm (40 in)
• Grid: Yes

Evaluation Criteria

• Facial bones in profile — nasal bones, maxilla, mandible superimposed
• Orbital roofs superimposed (no tilt)
• Mandibular rami superimposed (no rotation)
• Sella turcica in profile

Projection 5: SMV — Submentovertex (Clark's, p204–206)

The SMV provides a bird's-eye view of the skull base and is the best projection for evaluating zygomatic arch fractures — one of the most common facial fractures seen in the ED. The zygomatic arch is often fractured as part of a "tripod" (zygomaticomaxillary complex) fracture.

Patient Position

• Supine (or erect in a wheelchair for patients with limited neck mobility)
• Hyperextend the neck until the IOML is parallel to the IR
• The vertex rests against the IR/bucky
• Shoulders supported with pillows

Central Ray (Clark's, p204)

• Perpendicular to the IOML
• Entering at the midpoint between the mental point and the EAM
• Passes approximately 1.5 cm (0.6 in) below the mandibular symphysis at the level of the sella turcica

Evaluation Criteria

• Zygomatic arches clearly demonstrated (no superimposition)
• Sphenoid sinuses and basal foramina visible
• Mandible superimposed on the petrous pyramids (no rotation)
• Symmetric basal anatomy

Safety Consideration

This is not a comfortable position — the SMV requires significant neck hyperextension and is contraindicated in patients with cervical spine injuries or severe arthritis. For these patients, consider a reverse Waters or tangential zygomatic arch view instead. Take your time explaining the position — patient cooperation is essential.

Projection 6: Nasal Bone — Lateral View

As the most prominent feature of the face, the nasal bones are the most frequently fractured facial bones. The lateral nasal bone view is one of the smallest and simplest projections but requires careful centering and low exposure factors.

Patient Position

• Lateral — head in true lateral (same as lateral facial bones position)
• The affected side is closest to the IR

Central Ray

• Perpendicular to the IR
• Entering at the nasion (bridge of the nose)

Technical Factors

• IR size: 8 × 10 in (18 × 24 cm), portrait
• SID: 100 cm (40 in)
• Grid: No (small part technique, although some departments use a grid)
• mAs: Low (nasal bones are thin and require low exposure to show detail)
• Breathing: Suspend respiration

Evaluation Criteria

• Nasal bones in profile — bridge, tip, and base of nose visible
• No rotation (the nasal septum should appear as a single vertical line)
• Soft tissue outline of the nose visible

Routine Facial Bones Series Summary

#	Projection	CR Angle	CR Entry	CR Exit	Primary Purpose
1	Waters (Parietoacanthial)	0° (perp) — OML at 37°	Vertex	Acanthion	Maxillary sinuses, orbital floors, zygomatic arches
2	Modified Waters	0° (perp) — OML at 30°	Vertex	Acanthion	Orbital floor (blow-out fractures)
3	Caldwell (PA Axial)	15° caudad	Posterior skull	Nasion	Superior orbital fissures, frontal/ethmoid sinuses
4	Lateral Facial Bones	0° (perp)	1" sup & ant to EAM	—	Displacement, profile, sella turcica
5	SMV (Submentovertex)	0° (perp to IOML)	Midpoint mental-EAM	—	Zygomatic arches, skull base, sphenoid sinuses
6	Nasal Bone Lateral	0° (perp)	Nasion	—	Nasal bone fracture evaluation

Note: A complete facial bone series varies by department protocol and clinical indication. A trauma series typically includes Waters, lateral, and Caldwell. Orbital trauma adds modified Waters. Zygomatic arch trauma adds SMV. Isolated nasal trauma may only require a lateral nasal bone. Always check your department's protocol card before starting.

Positioning Errors: Quick Reference

Error	Likely Cause	Correction
Petrous ridges overlap maxillary sinuses (Waters)	OML < 37° (too shallow)	Increase hyperextension — OML must reach 37°
Petrous ridges too low (Waters)	OML > 37° (too steep)	Reduce hyperextension — chin was used instead of acanthion
Blow-out fracture not visible	Standard Waters used instead of modified	Repeat with modified Waters (30°)
Asymmetric maxillary sinuses (Waters)	Rotation	Check midsagittal plane centered and perpendicular
Petrous ridges fill entire orbit (Caldwell)	Angle < 15°	Angle must be exactly 15° caudad
Orbital roofs not superimposed (Lateral)	Tilt	Check interpupillary line perpendicular to IR
Mandibular rami doubled (Lateral)	Rotation	Check midsagittal plane parallel to IR
Zygomatic arches not visible (SMV)	Insufficient hyperextension	Increase neck extension
Nasal bone blurred (Lateral Nasal)	Motion or high kVp	Use shorter exposure time; ensure breathing suspended
Excessive image density (Nasal Bone)	mAs too high for thin anatomy	Use low mAs settings — nasal bones require minimal exposure

ARRT Exam Prep: Facial Bones Quick Review

The ARRT registry examination typically includes 6–10 questions on facial bone and skull positioning. Here are the highest-yield facts to remember:

1. Waters = 37° to the OML with the CR exiting at the acanthion — this is the most tested facial bone fact on the registry
2. Modified Waters = 30° — for blow-out (orbital floor) fractures
3. Caldwell = 15° caudad — petrous ridges in the lower third of orbits
4. Lateral facial bones — same centering as lateral skull (1" superior and anterior to EAM)
5. SMV requires IOML parallel to IR — contraindicated in C-spine injuries
6. Le Fort classification: I = palate, II = maxilla + nose, III = entire face (craniofacial disjunction)
7. Tripod fracture (zygomaticomaxillary complex) best seen on SMV and Waters
8. Blow-out fracture (orbital floor) best seen on Modified Waters
9. The acanthion is the junction of the upper lip and nasal septum — do not confuse with the mental point (chin)
10. The OML is the primary baseline for most facial bone projections (not the IOML)

Clinical Pearls: Tips from the Techs

• Trauma patients first — In the ED, facial bone X-rays are often ordered after a trauma series (C-spine, chest, pelvis). Make sure the patient is stable and cleared for facial positioning before hyperextending the neck for the Waters or SMV views.
• Start with the Waters — The Waters view is the most informative single projection. If the patient is in significant pain or cannot cooperate fully, prioritize the Waters and lateral — they give you the most diagnostic information per exposure.
• Explain the breathing — For the Waters and modified Waters views, instruct the patient to breathe through their mouth while the nose is against the IR. This prevents the patient from feeling like they can't breathe and reduces the risk of motion artifact.
• Use the smallest IR possible — Collimate tightly to the facial bones. A 10×12" IR centered at the level of the acanthion covers all essential anatomy while reducing scatter and improving image contrast.
• Remove dentures and glasses — Both produce artifacts that can obscure or mimic fractures. This is especially critical for nasal bone and orbital views where even small artifacts can obscure subtle fracture lines.
• Palpate, don't guess — The difference between a diagnostic Waters view and a repeat is 3–5° of flexion. Palpate the OML, the acanthion, and the nasion before every exposure. A few extra seconds of palpation saves a retake.
• Low mAs for nasal bones — The nasal bones are paper-thin. Using standard facial bone technique will overexpose them. Drop your mAs to approximately half of what you'd use for the full facial series.