A NON-WORKING (balancing) interference is most commonly found on which surface?

Correct answer: B. The buccal incline of the lingual cusp of a mandibular posterior tooth

• A. The lingual incline of the mandibular BUCCAL cusp opposes the buccal incline of the maxillary buccal cusp — these are WORKING-side contacts, on the side toward which the mandible has moved.
• B. CORRECT. On the NON-WORKING (balancing) side, the mandible swings medially and the mandibular LINGUAL cusps travel up against the maxillary LINGUAL cusps. The contacting surfaces are therefore the BUCCAL INCLINE of the mandibular LINGUAL cusp against the LINGUAL INCLINE of the maxillary LINGUAL cusp. These are the classic balancing interferences, and they are considered the most damaging occlusal contacts because the load is delivered obliquely, far from the working side, with the elevator muscles at a mechanical advantage.
• C. The buccal incline of the maxillary buccal cusp faces the cheek and does not contact an opposing tooth in normal function.
• D. The lingual incline of the mandibular lingual cusp faces the tongue and has no opposing contact.

Note: Memory device — 'BULL' identifies the WORKING contacts: Buccal cusps of Upper teeth contact the Lingual inclines of the buccal cusps of lower teeth. Whatever is left over on the lingual cusps in a mediotrusive movement is the NON-WORKING contact. Non-working interferences should be eliminated in a natural dentition; balanced bilateral contact is a goal only in complete dentures.