Prosthodontics & Occlusion · patient case question
During try-in of the crown for #30, which material is used to identify interferences on the internal surface of the restoration?
Patient case: The Crown That Keeps Falling Off
Patient: 32-year-old female
Chief Complaint: “The crown on my front tooth has fallen off three times this year.”
Background: Healthy, no medications. Reports jaw soreness on waking and has been told she grinds her teeth. Non-smoker.
Medications: None
Vital Signs: BP 112/70 mmHg · HR 68 bpm · RR 14 · T 98.4°F
Findings: Deep overbite of approximately 80% with minimal overjet. Wear facets on the incisal edges of the mandibular anteriors. Bilateral masseter hypertrophy. Tooth #8 carries a ceramic crown with an adequate 2 mm ferrule and a healthy periodontium: 2–3 mm probing depths, 4 mm of attached gingiva, no recession. A separate new crown for #30 is being tried in at this appointment.
Show answer and explanation
Correct answer: B. Fit-checking vinyl polyether silicone
- A. Incorrect. Zinc oxide-eugenol paste is used for final impressions on edentulous ridges and as a bite registration medium. It sets too rigidly and thickly for this purpose.
- B. Correct. Fit-checking materials are formulated as very thin, low-viscosity films that record contact points on the intaglio surface. Where the film is displaced or perforated, an interference exists and can be relieved precisely.
- C. Incorrect. Irreversible hydrocolloid is a preliminary impression material with poor dimensional stability and no capacity for the fine detail this application requires.
- D. Incorrect. Heavy-body impression material is far too viscous to record fine internal contacts. It is designed to carry a tray, not to detect microscopic interference.
Note: Two different materials for two different jobs: fit-checking silicone or disclosing wax evaluates the internal surface, while articulating paper or shimstock evaluates the occlusal surface.
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