ORE Part 1 Dental Anatomy & Occlusion 5 — Questions and Answers
Question 1: What anatomical structure separates the anterior and posterior cranial fossae?
- The lesser wing of the sphenoid and the petrous part of the temporal bone (forming the floor boundaries) (Correct answer)
- The cribriform plate of the ethmoid
- The occipital bone
- The frontal ridge
Correct answer: The lesser wing of the sphenoid and the petrous part of the temporal bone (forming the floor boundaries)
The boundary between the anterior and middle cranial fossae is formed by the lesser wing of the sphenoid and the anterior clinoid processes. This is relevant in dental anatomy when understanding skull base relationships.
Question 2: What is the 'leeway space' in mixed dentition?
- The size difference between primary canine and molars versus their permanent successors (premolars and canine) — typically 1.5 mm in maxilla and 2.5 mm in mandible (Correct answer)
- The space between erupting permanent teeth
- The overjet and overbite combined
- The space created by caries in primary teeth
Correct answer: The size difference between primary canine and molars versus their permanent successors (premolars and canine) — typically 1.5 mm in maxilla and 2.5 mm in mandible
Leeway space is the additional space from the fact that primary canines and molars are wider mesiodistally than their permanent successors (canine + premolars). It is used to accommodate the permanent canines and correct minor crowding.
Question 3: Which movement of the TMJ is described as the 'hinge movement'?
- Pure rotation of the condyle around a transverse axis in the lower joint compartment (inferior joint space) (Correct answer)
- Translation of the condyle down the articular eminence
- Lateral pterygoid protrusion
- Combined Bennett and rotation movement
Correct answer: Pure rotation of the condyle around a transverse axis in the lower joint compartment (inferior joint space)
The hinge (rotational) movement of the mandible occurs in the inferior compartment of the TMJ, with the condyle rotating around a transverse axis. Pure rotation allows approximately 20–25 mm of mouth opening.
Question 4: What is the 'Frankfort plane' and what is it used for in orthodontic assessment?
- A horizontal reference plane from the inferior margin of the orbit (orbitale) to the tragus/superior margin of the external auditory meatus — used as a standard reference in cephalometric analysis (Correct answer)
- The occlusal plane
- The palatal plane
- The mandibular plane
Correct answer: A horizontal reference plane from the inferior margin of the orbit (orbitale) to the tragus/superior margin of the external auditory meatus — used as a standard reference in cephalometric analysis
The Frankfort Horizontal plane is defined by the infraorbital rim and porion (external auditory meatus). It represents the natural head position and is a key reference plane in lateral cephalometric radiograph analysis.
Question 5: What is the average root length of the maxillary central incisor?
- Approximately 13 mm (Correct answer)
- 5 mm
- 20 mm
- 8 mm
Correct answer: Approximately 13 mm
The maxillary central incisor has a crown length of approximately 10–11 mm and a root length of approximately 13 mm, giving a total tooth length of approximately 23 mm on average.
ORE Part 1 Dental Anatomy & Occlusion 5
What anatomical structure separates the anterior and posterior cranial fossae?