Sectional Matrix Contact Failure on a Mandibular Molar
A 34-year-old patient returns two weeks after a MOD composite on tooth #30 with food impaction between #30 and #29. Tooth #29 has a full-coverage lithium disilicate crown; #31 has a large amalgam. A bitewing shows a 0.15 mm interproximal gap at the gingival third and an open contact. The original restoration used a sectional matrix with a contoured ring and a small wooden wedge placed from the lingual. The clinical note says the ring slipped during curing and was repositioned before the final cure. The patient reports no pain, but floss catches and shreds between #30 and #29. The dentist asks you to prepare for a replacement restoration and to recommend a matrix and wedge strategy that will produce a verifiable contact. You have sectional matrices in two curvatures, a dead-soft metal matrix, several ring sizes, and wooden and plastic wedges.
1. What is the most likely reason the contact remained open, and what matrix and wedge plan would you propose for the replacement? Explain how each choice addresses the failure.
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The most likely cause is loss of matrix adaptation when the ring slipped. The small lingual wedge did not create enough separation or stabilize the matrix against #29, so the composite was placed without a stable proximal seal. For the replacement, I would pre-wedge from the lingual with a wedge that fills the embrasure and produces slight separation, then place a sectional matrix whose curvature matches #30 and seat a ring sized so its tines engage the buccal and lingual undercuts without tipping. I would burnish the matrix toward #29, confirm the wedge is not displacing the matrix, and place composite in increments, curing after each. The reasoning is that a proximal contact depends on matrix adaptation, separation, and ring stability, not on bulk alone. If the contact is still open, I would use a more contoured matrix or add a small amount of composite at the proximal ridge and re-verify before curing.
2. How would you verify proximal contact and contour before light-curing, and what would you do if the contact is tight but the gingival margin is overhanging?
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Before curing, I would pass floss from the occlusal with light resistance and confirm it snaps through rather than passing freely; I would also use shimstock to check that the contact holds the strip. A radiograph can show the proximal contour and any ledge. If the contact is tight but the gingival margin is overhanging, I would not cure and then grind blindly. I would reseat the wedge deeper to lift the matrix, check that the matrix is not torn, and re-adapt the ring. If the overhang persists, I would remove the uncured or partially cured material, re-place the matrix, and rebuild. Adjusting after cure risks opening the contact and damaging the adjacent crown, so the correction belongs before final cure.