ABO ABO Growth and Development 1 — Questions and Answers
Question 1: The primary site of mandibular growth that contributes most to mandibular lengthening in adolescents is:
- Mental symphysis
- Condylar cartilage (endochondral growth at the condyle) (Correct answer)
- Coronoid process
- Gonial angle region
Correct answer: Condylar cartilage (endochondral growth at the condyle)
The condylar cartilage undergoes endochondral ossification, adding new bone to the posterior-superior condyle and lengthening the mandible.
Question 2: Normal primary (deciduous) dentition eruption begins with which tooth?
- Upper central incisor
- Lower central incisor (Correct answer)
- Upper first molar
- Lower first molar
Correct answer: Lower central incisor
The mandibular central incisors are typically the first primary teeth to erupt, at approximately 6–10 months of age.
Question 3: The 'ugly duckling stage' of dental development is characterized by:
- Crowding of all four lower incisors
- Spacing and flaring of upper central incisors due to erupting lateral incisor and canine crowns (Correct answer)
- Anterior open bite from finger sucking
- Retained primary canines in the mixed dentition
Correct answer: Spacing and flaring of upper central incisors due to erupting lateral incisor and canine crowns
As the maxillary lateral incisors and canines erupt, their follicles push the central incisor roots together, causing temporary crown flaring and midline diastema.
Question 4: Which of the following is a normal finding in the early mixed dentition that does NOT require orthodontic intervention?
- Posterior crossbite with mandibular shift
- Mild crowding due to tooth-size/arch-size discrepancy that may self-correct (Correct answer)
- Anterior crossbite of a permanent incisor
- Severe Class III skeletal pattern
Correct answer: Mild crowding due to tooth-size/arch-size discrepancy that may self-correct
Mild crowding in the early mixed dentition can resolve naturally as the leeway space is utilized during the transition to permanent teeth.
Question 5: The 'leeway space' in the mixed dentition refers to the size difference between:
- Upper and lower first molars
- The combined primary canine and molars versus the combined permanent canine and premolars (Correct answer)
- Upper and lower incisors
- Primary central and lateral incisors
Correct answer: The combined primary canine and molars versus the combined permanent canine and premolars
Leeway space is the difference in combined mesiodistal widths of primary canines/first/second molars minus permanent canines/first/second premolars (approximately 1.5 mm upper, 2.5 mm lower per side).
Question 6: Eruption of the permanent first molars into a flush terminal plane primary dentition most commonly results in which permanent molar relationship?
- Class III molar relationship
- Class I molar relationship after mesial step develops
- Class II molar relationship
- End-to-end permanent molar relationship initially, typically resolving to Class I (Correct answer)
Correct answer: End-to-end permanent molar relationship initially, typically resolving to Class I
A flush terminal plane leads to end-to-end first molar eruption; Class I is then achieved through differential leeway space utilization (lower more than upper) and late mesial shift.
ABO ABO Growth and Development 1
The primary site of mandibular growth that contributes most to mandibular lengthening in adolescents is: