Prosthodontics & Occlusion · patient case question
On the contralateral radiograph, a radiopaque box-and-key interface is visible between a retainer and the adjacent unit. What does this represent?
Patient case: Attachment-Retained Partial Denture
Patient: 47-year-old female
Chief Complaint: “I don’t want a metal clasp showing when I smile.”
Background: Missing #18, #19, and #20 on the left with a dentate right side — a mandibular Kennedy Class II arch. Generalized moderate chronic periodontitis, currently stable after non-surgical therapy: probing depths 3–5 mm, no bleeding on probing, grade I mobility on the abutments.
Medications: None
Vital Signs: BP 118/74 mmHg · HR 70 bpm · RR 16 · T 98.6°F
Findings: An attachment-retained removable partial denture is planned, using an intracoronal (precision) attachment within a splinted crown on #21 rather than an extracoronal clasp. A radiograph of an existing prosthesis on the contralateral side shows a radiopaque box-and-key interface between a retainer and an adjacent unit.
Show answer and explanation
Correct answer: C. A non-rigid connector
- A. Incorrect. A retained root tip is a discrete fragment of root with a periodontal ligament space and lamina dura, located within bone.
- B. Incorrect. A cast post and core is a tapered radiopaque structure occupying the canal space within a root, not an interface between two prosthetic units.
- C. Correct. A non-rigid connector appears radiographically as a distinct rectangular keyway in one retainer with a matching key on the adjoining unit, producing a visible interface line within an otherwise continuous prosthesis.
- D. Incorrect. An implant abutment screw is a threaded component within the implant body, showing the characteristic screw thread pattern along its length.
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