Tooth #19 is in a buccal crossbite with its opponent. Which statement correctly describes the cusp relationship at this site?

Correct answer: B. The maxillary buccal cusp occludes in the mandibular central fossa and the mandibular lingual cusp occludes in the maxillary central fossa

• A. This describes a scissor bite (lingual crossbite), the opposite condition, in which the mandibular buccal cusps occlude LINGUAL to the maxillary lingual cusps and the teeth may bypass each other entirely with no functional contact.
• B. CORRECT. A buccal crossbite means the mandibular buccal cusps sit BUCCAL to the maxillary buccal cusps, which inverts the transverse relationship. The supporting (centric-holding) cusps swap roles: the maxillary BUCCAL cusp now drops into the mandibular central fossa, and the mandibular LINGUAL cusp now seats in the maxillary central fossa. Every subsequent piece of occlusal analysis at that site has to be re-reasoned from this inverted starting point — which inclines guide, which contacts are working and which are balancing, and where to adjust.
• C. This describes NORMAL transverse occlusion — the maxillary lingual (palatal) cusp seats in the mandibular central fossa and the mandibular buccal cusp seats in the maxillary central fossa. It is precisely this arrangement that a crossbite reverses.
• D. The defining feature of a crossbite is transverse, not vertical. The supporting cusps do change — that is the whole clinical significance of the finding.

Note: ⚑ The recall behind this item listed three occlusal-interference questions built on a #19 crossbite, but the writer did not record the answers, and the option text was captured only partially — so those specific items could not be keyed reliably. This question isolates the principle they all depend on. Two consequences worth carrying into the exam: standard mnemonics such as BULL assume a normal transverse relationship and are INVALID at a crossbitten tooth, and the non-working (balancing) contact at that site involves the buccal cusps rather than the lingual cusps, because the cusp that now sits in the fossa is the one on the opposite side from usual.