CIT CIT Prosthetics & Restoration 5 — Questions and Answers
Question 1: A laboratory technician must verify the fit of an implant framework before veneering. Which test best confirms passive fit at the bench?
- Sheffield test (single-screw test) with tactile assessment at non-tightened joints (Correct answer)
- Spectrophotometric color measurement at each abutment interface
- Radiographic evaluation of all contacts simultaneously with all screws tightened
- Bite registration verification against the opposing cast
Correct answer: Sheffield test (single-screw test) with tactile assessment at non-tightened joints
The Sheffield (single-screw) test isolates discrepancies by tightening one screw and checking for movement or gaps at others.
Question 2: When fabricating an implant-supported overdenture with a ball attachment system, the housing is picked up in the denture intraorally. What material is placed around the ball before pick-up?
- Blockout resin to prevent retention of excess acrylic
- Metal primer to bond the housing to the denture base
- Activating resin (auto-polymerizing acrylic) to capture the housing in situ (Correct answer)
- Silicone relief material to protect the tissue during polymerization
Correct answer: Activating resin (auto-polymerizing acrylic) to capture the housing in situ
Auto-polymerizing acrylic flows around the ball housing and polymerizes in place, securing the attachment within the denture base.
Question 3: Which condition would most indicate converting a patient from a tooth-borne to an implant-supported prosthesis?
- Excessive residual ridge resorption causing instability (Correct answer)
- Patient preference for a removable appliance
- Existing anterior cross-bite requiring orthodontic correction
- Presence of bruxism with normal ridge anatomy
Correct answer: Excessive residual ridge resorption causing instability
Severe ridge resorption leads to denture instability and function loss, making implant retention clinically necessary.
Question 4: A CAD/CAM zirconia abutment is milled from a pre-sintered puck and then sintered. Approximately how much does zirconia shrink during sintering?
- 2–4%
- 10–15%
- 20–25% (Correct answer)
- 30–35%
Correct answer: 20–25%
Pre-sintered zirconia blanks are milled oversized by approximately 20–25% to compensate for sintering shrinkage.
Question 5: In an implant-retained mandibular overdenture retained by two locator attachments, what is the primary stress distribution mechanism compared to a conventional complete denture?
- Load transfers entirely to the implants with no ridge involvement
- Implants resist dislodging forces while the ridge still bears compressive occlusal loads (Correct answer)
- Palatal coverage is required to distribute forces adequately
- Posterior cantilever extensions bear all masticatory force
Correct answer: Implants resist dislodging forces while the ridge still bears compressive occlusal loads
Locator attachments resist vertical dislodgement and horizontal rotation, but the mucosa and ridge still share compressive loading.
Question 6: During the try-in of a metal-ceramic implant crown, the patient reports the bite feels high. Adjustment should begin by:
- Reducing the porcelain until articulating paper marks are eliminated entirely
- Checking implant stability with resonance frequency analysis before adjusting occlusion
- Marking occlusal contacts with articulating paper and reducing only heavy marks systematically (Correct answer)
- Re-cementing the crown with a thinner cement film to lower the vertical dimension
Correct answer: Marking occlusal contacts with articulating paper and reducing only heavy marks systematically
Systematic identification and selective reduction of heavy contacts prevents over-reduction and maintains proper occlusal relationships.
Question 7: Which measurement guides the selection of emergence profile diameter when designing a custom implant abutment?
- The implant platform diameter at the bone level
- The mesiodistal tooth width at the cementoenamel junction of the natural contralateral tooth (Correct answer)
- The soft tissue thickness measured by transgingival probing
- The inter-arch distance from implant shoulder to opposing occlusal surface
Correct answer: The mesiodistal tooth width at the cementoenamel junction of the natural contralateral tooth
The CEJ width of the contralateral natural tooth provides the target crown diameter that guides abutment emergence design.
CIT CIT Prosthetics & Restoration 5
A laboratory technician must verify the fit of an implant framework before veneering.
Which test best confirms passive fit at the bench?