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Restorative & Materials · patient case with 2 questions

Food impaction between two restored premolars

Patient: Adult who recently received Class II restorations

Chief complaint: “Food keeps getting stuck between my back teeth.”

Background: Mesial and distal restorations were recently placed in the premolar region.

Current findings: Bitewing radiograph shows an open contact between teeth #20 and #21.

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Question 1

What is the cause of the open contact?

  1. Poor contour and adaptation of the matrix band
  2. The matrix band was too thick
  3. A normal self-cleaning mechanism
  4. Excessive condensation of the restorative material
Show answer and explanation

Correct answer: A. Poor contour and adaptation of the matrix band

  • A. CORRECT. The proximal contour and contact of a Class II restoration are determined entirely by the matrix. If the band is not properly contoured, wedged and burnished against the adjacent tooth, the restoration is built flat and the contact is left open or deficient. This is the commonest technical cause of post-restorative food impaction.
  • B. Band thickness contributes, and thinner sectional bands are preferred precisely for this reason, but the governing failure is contour and adaptation.
  • C. 'Self-cleaning' is not a real explanation for an open contact; food impaction is pathological and causes papillary inflammation and interproximal caries.
  • D. Over-condensation is a concern for amalgam marginal ridge fracture, not for open contacts.

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Question 2

What is the principal advantage of a sectional matrix system over a circumferential band?

  1. It reproduces a more anatomic proximal contour and a tighter contact
  2. It eliminates the need for a wedge
  3. It is faster to place
  4. It permits a deeper increment of composite to be cured
Show answer and explanation

Correct answer: A. It reproduces a more anatomic proximal contour and a tighter contact

  • A. CORRECT. A sectional matrix, used with a separating ring, is pre-contoured to the natural proximal anatomy and actively separates the teeth to compensate for band thickness. The result is a properly contoured contact at the correct height and a markedly lower incidence of open contacts than a flat circumferential band produces.
  • B. A wedge is still required, to seal the gingival margin and aid separation.
  • C. Speed is not the advantage, and sectional systems can take longer to place correctly.
  • D. Cure depth is a property of the material and light, and is unrelated to the matrix.

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