NATIONAL BOARD DENTAL EXAMINATION PART I
DENTAL ANATOMY & OCCLUSION - DECEMBER 1988
9. On a mandibular first molar, the distofacial
groove serves as an escapeway for the
mesiolingual cusp of the maxillary first molar
during which of the following mandibular
movements?
1. Protrusive
2. Centric slide
3. Working (laterotrusion)
4. Non-working (mediotrusion or balancing)
Kaplan explanation:
9. The correct answer is choice 4. When you place the maxillary and mandibular teeth in intercuspal position and slide the
mandible lingually. you will notice that the mesiolingual cusp of the maxillary first molar passes through the distofacial groove of the
mandibular first molar. This movement of the mandible more lingually would be a balancing or nonworking movement. On the
other side of the head. the mandible would be moving more buccally and the maxillary and mandibular teeth would slide in a grinding
action. This lateral movement on the opposite side of the head would be a working movement. Choice 1. a protrusive movement, is
a movement of the mandible forward and the mesiolingual cusp of the maxillary first molar would move backwards relative to the
mandibular teeth. not sideways. Choice 2 is incorrect. The centric slide refers to a short motion between centric occlusion or
maxillary intercuspation and centric relation or retruded contact position. So the correct answer to question 9 is choice 4.
Dental Decks II 2007-2008
PROSTHODONTICS Occlusion
During non-working, excursive movements, the permanent maxillary first molar's
mesiolingual cusp escapes through:
The lingual groove of the mandibular first molar
The mesiobuccal groove of the mandibular first molar
The buccal groove of the mandibular second molar
The distobuccal groove of the mandibular first molar
The space between the mesiobuccal and distobuccal cusps of the mandibular first
molar
on the back of the card:
The dlstobuccal groove of the mandibular first molar
Examples:
1. The mesiolingual cusp of the mandibular first molar opposes the lingual
embrasure between the maxillary first molar and second premolar.
2. The mesiolingual cusp of the mandibular second molar opposes the lingual
embrasure between the maxillary second molar and first molar.
Note: The distolingual cusp of the mandibular first molar fits into (opposes) the
lingual groove of the maxillary first molar.
Remember: The lingual cusp of permanent mandibular first premolars does not occlude
with anything.
Important: During mandibular movements (working, non-working, etc.) the outer aspects
of the lingual cusps of the mandibular molars will not contact their maxillary antagonists.
All other areas of buccal and lingual cusps may contact during mandibular movements
(this is assuming that all occlusal relationships are normal).
Note: In unilateral balanced occlusion, contact between mandibular buccal cusps and
maxillary buccal cusps, along with simultaneous contact between mandibular lingual
cusps and maxillary cusps will most likely occur in laterotrusive movements.
