CDT Prosthodontic & Orthodontic Appliance Fabrication 3 — Questions and Answers
Question 1: What is the purpose of degassing (oxidizing) a metal coping before applying opaque porcelain in PFM crown fabrication?
- To harden the alloy surface
- To remove surface oxides and contaminants that would inhibit ceramic bonding (Correct answer)
- To increase the thickness of the metal
- To create a matte finish for esthetic purposes
Correct answer: To remove surface oxides and contaminants that would inhibit ceramic bonding
Degassing burns off surface contaminants and forms a controlled oxide layer that chemically bonds with the opaque porcelain for a durable metal-ceramic junction.
Question 2: Which articulator mounting technique is used to transfer the relationship of the maxillary arch to the temporomandibular joint using a face-bow?
- Centric relation mounting
- Arbitrary hinge mounting
- Kinematic hinge axis mounting
- Facebow transfer mounting (Correct answer)
Correct answer: Facebow transfer mounting
A facebow transfer records the spatial relationship between the maxillary teeth and the TMJ condyles, allowing the articulator to replicate this relationship when mounting the maxillary cast.
Question 3: During RPD framework fabrication, what is the function of a rest seat on an abutment tooth?
- To provide lateral bracing against horizontal forces
- To support the framework vertically and prevent tissue-ward movement (Correct answer)
- To engage the undercut for retention
- To guide the path of insertion of the denture
Correct answer: To support the framework vertically and prevent tissue-ward movement
Rest seats accept the occlusal, incisal, or cingulum rests that vertically support the RPD framework, preventing it from settling into soft tissue.
Question 4: A technician is pouring an irreversible hydrocolloid (alginate) impression. Which type of gypsum is most appropriate to produce a working cast?
- Type I impression plaster
- Type II laboratory plaster
- Type III dental stone (Correct answer)
- Type V high-strength die stone
Correct answer: Type III dental stone
Type III dental stone has sufficient strength for working casts poured from alginate impressions and is compatible with the moisture retained in hydrocolloid materials.
Question 5: In orthodontic appliance fabrication, what is the clinical indication for a tongue crib (tongue guard) appliance?
- To correct Class II skeletal discrepancy
- To deter tongue thrusting habits that contribute to anterior open bite (Correct answer)
- To expand the maxillary arch transversely
- To tip mandibular incisors lingually
Correct answer: To deter tongue thrusting habits that contribute to anterior open bite
A tongue crib creates a physical barrier that prevents the tongue from resting or thrusting between anterior teeth, helping to eliminate the habit causing an anterior open bite.
Question 6: When processing a complete denture in compression molding, at which stage is the flask opened to check for short pour (insufficient acrylic) before final curing?
- After bench cooling only
- During the trial pack (dough stage) prior to final closure (Correct answer)
- After 30 minutes in the curing bath
- Immediately after mixing monomer and polymer
Correct answer: During the trial pack (dough stage) prior to final closure
The trial pack at the dough stage allows the technician to check acrylic distribution and eliminate excess flash before final flask closure and curing.
Question 7: Which component of an RPD framework connects major connectors to clasps, rests, and indirect retainers?
- Minor connectors (Correct answer)
- Reciprocal arms
- Retentive lattice
- Stress-breaker
Correct answer: Minor connectors
Minor connectors are the rigid linking elements that join all minor components (clasps, rests, indirect retainers) to the major connector of the RPD framework.
CDT Prosthodontic & Orthodontic Appliance Fabrication 3
What is the purpose of degassing (oxidizing) a metal coping before applying opaque porcelain in PFM crown fabrication?