ABO Cephalometric Analysis and Radiographic Interpretation 2 — Questions and Answers
Question 1: In Steiner cephalometric analysis, what is the normal value for the SNB angle?
- 74°
- 77°
- 80° (Correct answer)
- 83°
Correct answer: 80°
The normal SNB angle is 80° (±2°), representing the anteroposterior position of the mandible relative to the cranial base.
Question 2: The Wits appraisal is performed by measuring the distance between which two projected points?
- A and B points projected onto the Frankfort Horizontal
- A and B points projected perpendicularly onto the functional occlusal plane (Correct answer)
- SNA and SNB angular intersections
- Pogonion and Nasion on the mandibular plane
Correct answer: A and B points projected perpendicularly onto the functional occlusal plane
The Wits appraisal drops perpendiculars from A and B points to the functional occlusal plane, measuring the distance between those projected points (AO and BO).
Question 3: In Tweed's diagnostic triangle, what is the ideal value for the IMPA (Incisor-Mandibular Plane Angle)?
- 75°
- 82°
- 87° (Correct answer)
- 95°
Correct answer: 87°
Tweed's ideal IMPA is 87° (with FMA = 25° and FMIA = 68°), reflecting a slightly proclined lower incisor relative to the mandibular plane.
Question 4: In Downs' cephalometric analysis, what does the Y-axis (Sella-Gnathion to Frankfort Horizontal) primarily indicate?
- Transverse skeletal width discrepancy
- Direction and pattern of mandibular growth (Correct answer)
- Upper incisor anteroposterior position
- Total anterior facial height
Correct answer: Direction and pattern of mandibular growth
The Y-axis angle (normal ~59–66°) indicates the direction of mandibular growth, with lower values suggesting forward growth and higher values suggesting downward-backward growth.
Question 5: The cephalometric landmark A point (Subspinale) is defined as which point on the maxilla?
- Most anterior point of the maxillary alveolar process
- Most superior point of the nasal spine
- Deepest point on the curvature of the maxillary alveolar process between ANS and prosthion (Correct answer)
- Junction of the maxilla and the palatine bone
Correct answer: Deepest point on the curvature of the maxillary alveolar process between ANS and prosthion
A point is located at the deepest concavity on the anterior surface of the maxillary alveolar process, between the anterior nasal spine and the upper incisor.
Question 6: In Ricketts' cephalometric analysis, the E-plane (esthetic plane) is a line connecting which two landmarks?
- Orbital rim to soft tissue pogonion
- Tip of the nose to soft tissue pogonion (Correct answer)
- Subnasal point to upper lip
- Glabella to menton
Correct answer: Tip of the nose to soft tissue pogonion
Ricketts' E-plane connects the tip of the nose to soft tissue pogonion; normally the upper lip is 4 mm behind and the lower lip is 2 mm behind this line.
Question 7: What is the normal interincisal angle in standard cephalometric analysis?
- 105–115°
- 115–125°
- 130–135° (Correct answer)
- 145–155°
Correct answer: 130–135°
The normal interincisal angle is approximately 130–135°; values below this indicate bimaxillary proclination and values above indicate retroclined incisors.
ABO Cephalometric Analysis and Radiographic Interpretation 2
In Steiner cephalometric analysis, what is the normal value for the SNB angle?