During right lateral excursion, the patient has a cusp-to-cusp contact between the upper right second premolar (#4) and lower right second premolar (#29) on the LEFT side. What type of occlusal interference is this?

Correct answer: B. Non-working (balancing) side interference

• A. Protrusive interference occurs during anterior movement (protrusion), not lateral excursion.
• B. CORRECT. During right lateral excursion, the RIGHT side is the working side and the LEFT side is the NON-WORKING (balancing) side. Tooth contact on the non-working (left) side during right lateral excursion is a NON-WORKING side interference. This is the most damaging type of lateral interference as it prevents canine or group function guidance on the working side.
• C. Anterior guidance involves the anterior teeth guiding the mandible during excursion — this is a posterior interference on the non-working side.
• D. Working side contact occurs on the RIGHT during right lateral excursion. The contact described is on the left side — non-working.