Orthodontic Appliance Construction Flashcards
7 cards from real CDT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Orthodontic Appliance Construction flashcards as text
When fabricating a removable orthodontic appliance on a plaster model, why is a separating medium (such as sodium alginate solution) applied to the model before adding acrylic?
Answer: To prevent the acrylic from bonding permanently to the plaster model
A separating medium creates a barrier that prevents the acrylic monomer from chemically bonding to the plaster, allowing the finished appliance to be removed cleanly.
A coffin spring incorporated into the midline of a removable upper appliance is designed to produce which type of arch development?
Answer: Transverse (lateral) expansion of the maxillary arch
The coffin spring is a large omega-shaped wire loop placed at the midline of the baseplate that, when activated, pushes the two halves of the appliance apart to widen the upper arch.
In fixed orthodontic appliances, which bracket slot dimension is used most commonly in the Roth and MBT straight-wire systems?
Answer: .022 × .025 inch
The .022 × .025 inch slot is the standard dimension in Roth and MBT straight-wire systems, offering adequate torque expression while accommodating a range of archwire sizes.
What is the purpose of incorporating a posterior bite plane into an upper removable orthodontic appliance?
Answer: To disarticulate the posterior teeth and allow anterior deep bite correction
A posterior bite plane lifts the posterior teeth out of occlusion, removing their vertical support and allowing the anterior teeth to erupt or the deep bite to reduce via relative eruption mechanics.
Which characteristic of beta-titanium (TMA) archwires makes them suitable for the finishing stages of orthodontic treatment?
Answer: Intermediate stiffness with easy formability for custom bends
TMA wires have stiffness about half that of stainless steel, making them easy to bend for finishing details while still delivering adequate force for precise tooth positioning.
When a removable orthodontic appliance is returned from a patient with a fractured acrylic baseplate, which repair method is most appropriate for a laboratory repair?
Answer: Re-invest on the original model, stabilize fragments with sticky wax, and add new self-cure acrylic across the fracture line
Stabilizing fragments on the original model and adding fresh self-cure acrylic ensures accurate repositioning and a strong chemical bond across the fracture without distorting the appliance.
The inner bow of a face-bow (cervical-pull headgear) is adjusted to contact the maxillary first molars at which location of the molar tubes?
Answer: Entering the headgear tube passively in a straight line at the occlusal plane
The inner bow should insert passively and straight into the headgear tubes without any intrusive or extrusive activation to ensure force is directed along the intended vector.