Cephalometric Analysis

Historical Background

• 1922: Paccini published the first paper on cephalometric analysis.
• 1931: Broadbent (USA) and Hofrath (Germany) introduced and popularized it.
• 1948: Clinical application was done by **Down’s**.

Equipment / Apparatus

• Head holding device or Cephalostat (Head holder)
• X-ray source
• Cassette holder

Types of Cephalostat

• Broadbent Type:
  • Has 2 X-ray sources and 2 holders.
  • Allows for **lateral and posterior-anterior X-rays without moving the subject**, making it more **precise**.
  • Disadvantage: Occupies more space and is expensive.
• Highley Type:
  • Has **1 X-ray source and 1 holder**.
  • The **subject needs to move** for different views.

Anatomical Landmarks

• Anatomic landmarks (True anatomical points):
  • Example: **Anterior Nasal Spine (ANS), Nasion (Na)**.
• Implants:
  • Artificially inserted **radiopaque markers**.
• Derived landmarks: These can be of three types:
  • External points
  • Intersections of edges of regression
  • Intersections of constructed lines
• Unilateral (Anatomically):
  • Examples: **Anterior Nasal Spine, Gnathion, Menton, etc.**
• Bilateral (Anatomically):
  • Examples: **Orbitale, Pterygomaxillary Fissure, etc.**

Anatomic Landmarks	Derived Landmarks
• Nasion	• Articulare
• Anterior nasal spine (ANS)	• Pterygomaxillary fissure
• Subspinale (Point ‘A’)	• Gonion
• Supramentale (Point ‘B’)	• Gnathion
• Superior and Inferior prosthion	• Orbitale
• Pogonion, Menton, Condylion	• Sella
• Basion	• Key ridge
• Porion

Unilateral landmarks (present in the midline)	Bilateral landmarks
Nasion	Gonion
Menton	Porion
Gnathion	Articulare
Basion	Mastoid
Pogonion

→ All anatomic landmarks except condylion are unilateral. Condylion is bilateral in nature.

→ Most of derived landmarks are bilateral in nature, except pterygomaxillary fissure which is a unilateral landmark.

Cephalometric Landmarks

Xi-Point and Ramus Landmarks

Xi-Point

Location of Xi-Point

Xi is **keyed geometrically** to **PO-OR (Frankfort Horizontal Plane – FH)** and perpendicular through **PT (Pterygoid Vertical – PTV)** following these steps:

• Step 1: Construction of **planes perpendicular** to **FH** and **PTV**.
• Step 2: These constructed planes are **tangents** to points (**R1, R2, R3, R4**) on the **borders of the ramus**.
• Step 3: The **constructed planes form a rectangle enclosing the ramus**.
• Step 4: **Xi is located at the center** of the rectangle at the **intersection of diagonals**.

Ramus Landmarks

R1 – Mandible

• R1 is the **deepest point on the curve of the anterior border of the ramus**.
• It is located **halfway between the inferior and superior curves**.

R2 – Mandible

• R2 is located on the **posterior border of the ramus of the mandible**.

R3 – Mandible

• R3 is located at the **center and most inferior aspect of the sigmoid notch** of the ramus.

R4 – Mandible

• R4 is a **point on the border of the mandible** directly **inferior to the center of the sigmoid notch** of the ramus.

Cephalometric Planes and Analyses

Horizontal Planes

• FH Plane (Frankfurt Horizontal Plane): Drawn from Porion to Orbitale. Named in the Frankfurt Conference on Anthropology in the late 19th century.
• SN Plane (Sella-Nasion Plane): Represents the anterior cranial base and remains stable after age 6-7 years. However, endpoint drift can cause errors.
• Palatal or Maxillary Plane: Parallels the floor of the nose, passing through ANS and PNS.
• Occlusal Plane: Passes midway between the cusp tips of the upper and lower first permanent molars and a point bisecting the overbite anteriorly.
• Mandibular Plane: Constructed as a tangent to the lower border or as a plane joining Gonion and Menton or Gonion and Gnathion.
• Basion-Nasion Plane: Used in Ricketts analysis.
• Bolton-Nasion Plane: Joins Bolton and Nasion.

Vertical Planes

• Facial Plane: Joins Nasion and Pogonion.
• Ramal Plane: Joins Articulare to Gonion.

Various Cephalometric Analyses

• Steiner Analysis: Uses SN plane as the reference plane. Developed by Cecil Steiner in 1950.
• Down’s Analysis: Uses FH plane as the reference plane. Identifies whether dysplasia is in the facial skeleton, dentition, or both.
• Tweed Analysis: Uses three planes:
  • FH Plane
  • Mandibular Plane
  • Long Axis of Lower Incisor
  Tweed’s findings:
  • FMA = 25°
  • FMIA = 65°
  • IMPA = 90°
• Sassouni Analysis: Emphasizes vertical and horizontal proportion using:
  • SN Plane
  • FH Plane
  • Palatal Plane
  • Occlusal Plane
  • Mandibular Plane
  If these planes are nearly parallel, they converge far behind the face.
• Wits Analysis: Based on the projection of point A and point B to the Occlusal Plane.
  • Class II: Point A is in front of Point B.
  • Class III: Point A is behind Point B.
• Ricketts Analysis
• McNamara’s Analysis

Dental Assessments

Upper Incisor Assessment

• Upper 1/1 to SN Plane
• Upper 1/1 to FH Plane
• Upper 1/1 to Maxillary Plane
• Upper 1/1 to NA Plane
• Upper 1/1 to NA Plane (Linear Measurement)

Interpretation:

• If values are average → Average position
• If values increase → Proclined incisor in relation to the plane
• If values decrease → Retroclined incisor in relation to the plane

Lower Incisor Assessment

• Lower 1/1 to Mandibular Plane
• Lower 1/1 to Occlusal Plane
• Lower 1/1 to NB Plane
• Lower 1/1 to NB Plane (Linear Measurement)

Interpretation:

• If values are average → Average position
• If values increase → Proclined incisor in relation to the plane
• If values decrease → Retroclined incisor in relation to the plane

Registration Point

Importance of Cephalometry

1. Study of Growth and Development

• Serial radiographs taken with a standardized head position enable the study of jaw and dentition growth.

2. Diagnosis

• To assess the resting lip posture, position of the tongue, soft palate, and posterior pharyngeal wall.
• To assess the relation of the lower lip to the upper lip.
• To assess the adequacy of the dental base to accommodate all teeth.
• To assess the presence, position, and angulations of any unerupted teeth.
• To assess any pathology or abnormality of teeth, bone, and soft tissue.
• To assess the length of incisors and their inclination.
• To assess the skeletal pattern.

3. Treatment Planning, Growth Prediction, and Prognosis Assessment

• Assessment of changes in upper and lower angulations and position needed to achieve normal overbite and overjet.
• Assessment of the extent of overbite correction possible.
• For deciding on extractions, disimpactions, etc.
• To assess whether distal movement of buccal teeth is possible.
• Accurate planning before surgical correction.
• Assessment of future growth (V.T.O – Visualized Treatment Objective).

4. Analysis of Tooth Movement, Anchorage Control, and Prognosis of Treatment

5. Final Assessment of the Case

Cephalometric Angles

SNA Angle

Definition: Angle formed by the intersection of the SN plane and a line joining Nasion and Point A.

Importance: Indicates the relative antero-posterior position of the maxilla in relation to the anterior cranial base.

Mean Value: 82°

The Angle May Be:

• Normal – Average position of the maxilla in relation to the anterior cranial base.
• Increased – Maxilla prognathic (as in Class II).
• Decreased – Maxilla retrognathic (as in Class III).

SNB Angle

Definition: Angle between the SN plane and a line joining Nasion to Point B.

Importance: Indicates the antero-posterior positioning of the mandible in relation to the anterior cranial base.

Mean Value: 80°

The Angle May Be:

• Normal – Average position of the mandible in relation to the cranial base.
• Increased – Mandible prognathic (Class III).
• Decreased – Mandible retrognathic (Class II).

ANB Angle

Definition: Angle formed by the intersection of lines joining Nasion to Point A and Nasion to Point B.

Importance: Denotes the relative position of the maxilla and mandible to each other on skeletal bases.

Mean Value:

• SK Class I – Angle is 2-4°
• SK Class II – Greater than 4°
• SK Class III – Less than 2°

The Angle May Be:

• Average.
• Increased.
• Decreased.

Inter Incisal Angle

Definition: Angle formed between the long axis of the upper and lower incisors.

Average Value: 130° to 150.5°

Importance: Helps to assess the inter-incisal relationship.

The Angle May Be:

• Average Angle – Indicates average inclination of incisors.
• Increased Angle – Indicates retruded incisors (Class II Div 2 case).
• Decreased Angle – Indicates protruded incisors (Class I bimaxillary protrusion, Class II Div 1 case).

Parameter	MH	Mean
SNA	83°	81° ± 3°
SNB	77°	78° ± 3°
ANB	6°	3° ± 2°
UIInc to MxPl	103°	109° ± 6°
LIInc to MnPl	96°	93° ± 6°
MMPA	20°	27° ± 4°
LIInc to APog	-0.7 mm	1 mm ± 2 mm
LAFP	53.3%	55% ± 2%