MFDS Part 1 - Membership of Faculty of Dental Surgery Orthodontics and Dentofacial Development Questions and Answers — Questions and Answers
Question 1: A 13-year-old patient presents for an orthodontic assessment. The clinical examination reveals a Class II division 1 incisor relationship with an overjet of 7mm. All other occlusal features are within normal limits. According to the Index of Orthodontic Treatment Need (IOTN), what is the Dental Health Component (DHC) grade for this patient?
- 3a
- 4a (Correct answer)
- 4d
- 5a
Correct answer: 4a
The IOTN DHC is used in the UK to assess the need for orthodontic treatment on dental health grounds. Grade 4 indicates a 'great' need for treatment, which typically qualifies for NHS funding. An overjet greater than 6mm but less than or equal to 9mm is specifically classified as grade 4a.
Question 2: Which structure of the cranial base completes its growth earliest and is therefore commonly used as a stable reference structure for superimposition in longitudinal cephalometric analysis?
- Spheno-occipital synchondrosis
- Mandibular symphysis
- Anterior cranial base (Sella-Nasion line) (Correct answer)
- Maxilla
Correct answer: Anterior cranial base (Sella-Nasion line)
The anterior cranial base, represented cephalometrically by the Sella-Nasion (S-N) line, completes its growth relatively early (around age 7). Its stability makes it an invaluable reference plane for superimposing serial cephalometric radiographs to assess treatment changes and subsequent facial growth. The spheno-occipital synchondrosis is a major growth centre that fuses in the late teens, while the maxilla and mandible undergo significant growth throughout puberty.
Question 3: An Upper Removable Appliance (URA) has been constructed to correct a unilateral posterior crossbite affecting the maxillary first premolars and molars. Which component is essential for providing the force required to achieve the desired buccopalatal expansion?
- Z-spring
- Adams clasp
- Southend clasp
- Midline expansion screw (Correct answer)
Correct answer: Midline expansion screw
A midline expansion screw is an active component specifically designed to generate transverse forces to widen the maxillary arch. When activated, it separates the two halves of the appliance, pushing the posterior teeth buccally to correct the crossbite. Adams and Southend clasps provide retention, while a Z-spring is typically used to move a single anterior tooth labially.
Question 4: A 10-year-old patient is reviewed for a routine dental examination. The maxillary right deciduous canine is still present and firm, and the permanent canine is not palpable in the buccal sulcus. A parallax radiographic assessment confirms the permanent canine is palatally displaced. According to UK orthodontic guidelines, what is the most appropriate initial management?
- Extract the deciduous canine and review eruption in 6-12 months. (Correct answer)
- Immediately refer for surgical exposure and bonding of the ectopic canine.
- Place a fixed appliance to create space for the canine.
- Monitor without intervention until the patient is 13 years old.
Correct answer: Extract the deciduous canine and review eruption in 6-12 months.
For a palatally displaced maxillary canine in a 10-13 year old with sufficient arch space, the extraction of the deciduous canine is the recommended interceptive measure. This intervention has been shown to have a significant chance of encouraging the permanent canine to improve its position and erupt successfully without further intervention. Surgical exposure is considered only if this interceptive extraction fails.
Question 5: The Twin Block appliance is a widely used functional appliance in the UK for the correction of Class II division 1 malocclusions. What is its primary mode of action in correcting the skeletal and dental relationship?
- By applying extra-oral force to restrain maxillary growth.
- By encouraging mandibular growth and causing dentoalveolar changes. (Correct answer)
- By causing proclination of the lower incisors only.
- By expanding the maxilla and distalising the maxillary molars.
Correct answer: By encouraging mandibular growth and causing dentoalveolar changes.
The Twin Block appliance holds the mandible in a protruded position. This posture is thought to stimulate condylar growth, encouraging the mandible to grow to its full potential. Concurrently, it produces significant dentoalveolar changes, including retroclination of upper incisors and proclination of lower incisors, which contribute to overjet reduction. The overall effect is a combination of skeletal and dental modifications.
Question 6: Following the completion of comprehensive fixed appliance therapy, which factor is considered a primary contributor to long-term post-treatment relapse, such as late lower incisor crowding?
- Contraction of the supracrestal gingival fibres.
- Unfavourable continued facial growth. (Correct answer)
- Persistent soft tissue pressures (e.g., tongue thrust).
- Inherent memory of the periodontal ligament fibres.
Correct answer: Unfavourable continued facial growth.
While all listed factors can contribute to relapse, unfavourable continued facial growth is a primary reason for long-term occlusal changes, particularly late lower incisor crowding. Even after orthodontic treatment, the face and jaws continue to mature, with late mandibular growth often leading to changes in the incisor relationship. This understanding underpins the modern UK orthodontic consensus that retention should be considered a lifelong commitment.
MFDS Part 1 - Membership of Faculty of Dental Surgery Orthodontics and Dentofacial Development Questions and Answers
A 13-year-old patient presents for an orthodontic assessment.
The clinical examination reveals a Class II division 1 incisor relationship with an overjet of 7mm.
All other occlusal features are within normal limits.
According to the Index of Orthodontic Treatment Need (IOTN), what is the Dental Health Component (DHC) grade for this patient?