CDT Orthodontic Appliance Construction 2 — Questions and Answers
Question 1: Which wire alloy is preferred for fabricating Adams clasps on removable orthodontic appliances due to its springiness and formability?
- Gold alloy
- Stainless steel 0.7mm hard wire (Correct answer)
- Nickel-titanium wire
- Cobalt-chromium wire
Correct answer: Stainless steel 0.7mm hard wire
Hard stainless steel wire (0.7mm) provides the ideal combination of stiffness and springiness needed for Adams clasps to engage undercuts effectively.
Question 2: When constructing a Hawley retainer, the labial bow should contact the anterior teeth at which third of the crown?
- Gingival third
- Middle third (Correct answer)
- Incisal third
- Equally at all thirds
Correct answer: Middle third
The labial bow of a Hawley retainer is positioned at the middle third of the anterior crowns to maintain tooth position without impinging on the gingiva.
Question 3: A palatal expander that uses a jackscrew mechanism and is cemented to molar bands is best described as which appliance type?
- Hawley retainer
- Rapid Palatal Expander (RPE) (Correct answer)
- Bionator
- Frankel appliance
Correct answer: Rapid Palatal Expander (RPE)
A Rapid Palatal Expander (RPE) uses a midline jackscrew bonded or banded to the molars to apply heavy orthopaedic forces that open the mid-palatal suture.
Question 4: What is the primary purpose of incorporating ball clasps (bullet clasps) into a removable orthodontic appliance?
- To apply tipping forces on teeth
- To provide retention by engaging embrasures between teeth (Correct answer)
- To act as bite registration stops
- To serve as attachment points for elastics
Correct answer: To provide retention by engaging embrasures between teeth
Ball clasps engage the interproximal embrasure between adjacent teeth, providing passive retention for the appliance without wrapping around individual teeth.
Question 5: During acrylic processing of a removable orthodontic appliance, what defect results from too-rapid polymerization caused by excessive heat?
- Voids and porosity (Correct answer)
- Increased transverse strength
- Improved surface hardness
- Better color stability
Correct answer: Voids and porosity
Excessively rapid polymerization generates heat faster than it can dissipate, causing boiling of the monomer and leaving voids and porosity within the acrylic.
Question 6: Which functional appliance is designed with separate upper and lower acrylic portions connected by guide planes that posture the mandible forward?
- Twin Block appliance (Correct answer)
- Activator
- Herbst appliance
- Face mask (reverse-pull headgear)
Correct answer: Twin Block appliance
The Twin Block uses interlocking upper and lower acrylic blocks with inclined guide planes that hold the mandible in a forward and downward position during function.
Question 7: When trimming a stone model for construction of a removable orthodontic appliance, the posterior extent of the baseplate should end where?
- At the distal of the first molars
- At the junction of the hard and soft palate (Correct answer)
- At the distal of the second molars
- At the level of the tuberosities
Correct answer: At the junction of the hard and soft palate
The posterior border of the baseplate should terminate at the hard-soft palate junction to avoid impinging on movable soft tissue while maximizing palatal coverage for retention.
CDT Orthodontic Appliance Construction 2
Which wire alloy is preferred for fabricating Adams clasps on removable orthodontic appliances due to its springiness and formability?