Prosthodontics & Occlusion · patient case question
Wear facets on the LINGUAL inclines of the maxillary buccal cusps on the right side are produced during which movement?
Patient case: A Premolar Missing Its Lingual Cusp
Patient: 51-year-old male
Chief Complaint: “Half the tooth broke off while I was eating.”
Background: Heavy clencher. Multiple worn restorations. Root canal treatment on this tooth was completed last week.
Medications: None
Vital Signs: BP 126/80 mmHg · HR 72 bpm · RR 16 · T 98.4°F
Findings: Maxillary right first premolar with a fractured and missing LINGUAL cusp. Remaining buccal wall is sound but thin. Access cavity present and root filled. Wear facets are present on the lingual inclines of the maxillary buccal cusps on the right side.
Show answer and explanation
Correct answer: C. Right lateral excursion — the working side
- A. Retrusion is a very small movement of a few tenths of a millimetre from maximum intercuspation to centric relation and does not generate significant wear facets.
- B. Non-working (balancing) interferences occur between the maxillary LINGUAL cusp and the mandibular BUCCAL cusp on the side away from the movement — a different pair of inclines entirely.
- C. CORRECT. This is the BULL relationship — Buccal Upper, Lingual Lower. On the WORKING side (the side toward which the mandible moves), the mandibular buccal cusp slides up the LINGUAL INCLINE of the maxillary buccal cusp. Facets in that location on the right therefore record right lateral, working-side contact.
- D. Protrusive contacts are recorded on the incisal edges and palatal surfaces of the maxillary anterior teeth, and posteriorly on the distal inclines of maxillary cusps against the mesial inclines of mandibular cusps.
Note: The maxillary first premolar's lingual cusp is small and NON-functional, which is exactly why it fractures: it is unsupported, thin, and loaded obliquely by excursive contacts. Reduce interferences before restoring, or the new restoration fails the same way.
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