Mounting & Anatomical Landmarks
Orientation and Identification for the RHS Exam
🎯 Learning Objectives
- Distinguish between Labial and Lingual mounting.
- Identify the “Identification Dot” and its role in orientation.
- Recognize primary Radiopaque and Radiolucent landmarks.
- Master the “Curve of Spee” for bitewing mounting.
1. The Golden Rule of Mounting
The DANB RHS exam focuses almost exclusively on Labial Mounting (the ADA-recommended method). In this method, radiographs are viewed as if you are standing outside the patient, looking in.
The Identification Dot: Every film has a small raised bump. In labial mounting, the “Dot is UP” (convex/facing you). This means the patient’s left is on your right, and vice versa—just like shaking hands with the patient.
2. Radiopaque vs. Radiolucent
You must categorize landmarks by how they appear on the X-ray:
- Radiopaque (White/Light): Dense structures that resist the X-ray beam (e.g., Enamel, Bone, Fillings).
- Radiolucent (Black/Dark): Less dense structures that allow the beam to pass through (e.g., Pulp, Sinuses, Foramina, Decay).
3. Key Landmarks for Orientation
If you see these, you know exactly where you are in the mount:
| Landmark | Appearance | Location |
|---|---|---|
| Maxillary Sinus | Radiolucent (Dark) area | Above Maxillary Molars |
| Mental Foramen | Small Radiolucent circle | Near Mandibular Premolars |
| Incisive Foramen | Ovoid Radiolucency | Between Maxillary Centrals |
| Genial Tubercles | Radiopaque (White) ring | Below Mandibular Centrals |
🚨 DANB EXAM ALERT: The Curve of Spee
When mounting bitewings, look for the Curve of Spee. The occlusal plane should curve upward toward the distal (like a smile). If the curve is “frowning” or curving downward, the X-rays are mounted upside down or on the wrong side.