DMD Orthodontics 1 — Questions and Answers
Question 1: According to Angle's classification, which occlusal relationship is present when the mesiobuccal cusp of the maxillary first molar occludes in the buccal groove of the mandibular first molar?
- Class I (Correct answer)
- Class II Division 1
- Class II Division 2
- Class III
Correct answer: Class I
Class I is defined by the mesiobuccal cusp of the upper first molar occluding in the buccal groove of the lower first molar, representing the ideal molar relationship.
Question 2: Which cephalometric landmark is defined as the most anteroinferior point on the contour of the mandibular symphysis?
- Pogonion (Pog)
- Gnathion (Gn) (Correct answer)
- Menton (Me)
- B point
Correct answer: Gnathion (Gn)
Gnathion (Gn) is the most anteroinferior point on the mandibular symphysis, located midway between Pogonion and Menton on the bony chin.
Question 3: Which type of orthodontic force is most effective for producing physiologic tooth movement without causing hyalinization of the periodontal ligament?
- Heavy intermittent forces exceeding capillary pressure
- Light continuous forces within the range of capillary blood pressure (Correct answer)
- Heavy continuous forces applied over long periods
- Alternating heavy and no-force cycles
Correct answer: Light continuous forces within the range of capillary blood pressure
Light continuous forces (approximately 20–26 g/cm²) maintain capillary blood flow in the PDL, allowing steady osteoblast and osteoclast activity without necrosis or hyalinization.
Question 4: The 'leeway space' (E-space) in the dental arch refers to the difference in mesiodistal width between which tooth groups?
- Primary incisors and permanent incisors
- Primary canines/molars and permanent canines/premolars (Correct answer)
- Primary first molars and permanent first premolars only
- All primary teeth and their permanent successors
Correct answer: Primary canines/molars and permanent canines/premolars
Leeway space is the difference between the combined mesiodistal widths of the primary canine, first molar, and second molar versus the permanent canine, first premolar, and second premolar — averaging about 1.5 mm per side in the mandible.
Question 5: Which orthodontic wire alloy exhibits the highest springback (range of action) and is most commonly used during the initial alignment phase of fixed appliance therapy?
- Stainless steel
- Beta-titanium (TMA)
- Nickel-titanium (NiTi) (Correct answer)
- Cobalt-chromium (Elgiloy)
Correct answer: Nickel-titanium (NiTi)
Nickel-titanium (NiTi) wires have the highest springback due to their superelastic or thermoelastic properties, delivering light, continuous forces ideal for initial leveling and alignment.
Question 6: The Frankfort horizontal plane used in cephalometric analysis is constructed by connecting which two landmarks?
- Nasion and Sella
- Porion and Orbitale (Correct answer)
- Anterior nasal spine (ANS) and posterior nasal spine (PNS)
- Gonion and Menton
Correct answer: Porion and Orbitale
The Frankfort horizontal plane connects Porion (top of the external auditory meatus) and Orbitale (lowest point of the bony orbit), approximating the natural head position.
Question 7: In lateral cephalometric analysis, the SNA angle measures the anteroposterior position of which structure relative to the cranial base?
- Mandible relative to the cranial base
- Maxilla relative to the cranial base (Correct answer)
- Maxilla relative to the mandible
- Upper incisor inclination relative to the cranial base
Correct answer: Maxilla relative to the cranial base
The SNA angle measures the anteroposterior position of the maxilla (A point) relative to the cranial base (SN plane); the norm is approximately 82°.
DMD Orthodontics 1
According to Angle's classification, which occlusal relationship is present when the mesiobuccal cusp of the maxillary first molar occludes in the buccal groove of the mandibular first molar?