Prosthodontics & Occlusion · patient case question
A NON-WORKING (mediotrusive) interference classically occurs between which two cusps?
Patient case: Posterior crossbite — occlusal interferences
Scenario: Clinical photo of a patient with a posterior crossbite on the LEFT side. Three questions ask about interference between the opposing cusp ridges of #14 and #19. (In the exam image #18 was missing and #13 occluded normally with the lower arch.)
Show answer and explanation
Correct answer: D. Lingual cusp of the maxillary tooth and buccal cusp of the mandibular tooth
- A. Maxillary buccal against mandibular lingual is not a physiologic contact relationship in a normal occlusion.
- B. Buccal-to-buccal contact is a working-side relationship, not a balancing interference.
- C. Lingual-to-lingual contact is a working-side relationship on the palatal aspect.
- D. Correct. The non-working (balancing) interference is the classic contact between the INNER INCLINE OF THE MAXILLARY LINGUAL CUSP and the INNER INCLINE OF THE MANDIBULAR BUCCAL CUSP. These are the most destructive interferences because the contact is far from the fulcrum and the elevator muscles are at a mechanical advantage.
Note: The recall wrote this question as 'same side non working interference LLBU', which is internally contradictory — non-working is by definition the CONTRALATERAL side. Learn the standard rule as written here.
Practice Prosthodontics & Occlusion questions Prosthodontics & Occlusion study notes