Recurrent Caries and Sensitivity at a Deep Composite Margin
A 45-year-old man has a large MOD composite restoration on tooth 46 placed three years ago. He now has recurrent caries at the gingival margin, marginal staining, and cold sensitivity. His medical history includes hypertension treated with a thiazide-like diuretic, and he reports dry mouth. He drinks two sugar-sweetened sodas daily and has not used fluoride toothpaste consistently. The original restoration was placed in one 4 mm bulk increment, the universal adhesive was used in self-etch mode, and the composite was cured for 20 s from the occlusal surface only. The gingival margin was 1 mm below the cementoenamel junction, and isolation was poor because of limited mouth opening. The patient wants 'a stronger filling that will not break again.' The dentist must decide what failed, what material and technique to use, and how to address the sensitivity and caries risk.
1. Identify the likely causes of failure and explain why a single 4 mm bulk increment with occlusal-only curing is a poor choice in this cavity.
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The failure is at the interface, not a sudden material fracture. A 4 mm bulk increment in a large MOD has a high C-factor: the composite bonds to many walls, so polymerization shrinkage cannot be relieved by flow and instead pulls on the adhesive. Occlusal-only curing leaves the gingival floor far from the light and shadowed by the matrix, so the composite and adhesive there may be undercured. Self-etch adhesive on sclerotic dentin and moisture contamination further reduce bond strength. The gingival margin 1 mm below the CEJ is difficult to isolate and enamel is absent, so the bond depends on dentin. Recurrent caries and marginal staining indicate leakage. The high sugar intake and dry mouth create a cariogenic environment that overwhelms the restoration. The patient's request for a 'stronger filling' misses the point: the material did not break; the seal failed.
2. What material and technique would you choose for the replacement, and why? Consider isolation, margin location, and caries risk.
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First address caries risk: reduce sugar-sweetened soda, use high-fluoride toothpaste, manage xerostomia, and schedule short recall. For the restoration, the choice depends on isolation. If a dry field and matrix/wedge can be achieved, a composite placed in 2 mm increments, cured from occlusal and gingival directions, with a proven adhesive and selective enamel etch, is reasonable. If the gingival margin remains subgingival and moisture control is poor, a resin-modified glass ionomer or a glass ionomer base at the gingival seal is more forgiving and releases fluoride, though it is weaker and less wear-resistant. A large cavity may be better treated with an indirect onlay. Avoid a single bulk fill unless it is a dedicated bulk-fill material with documented depth and adequate light. No material choice substitutes for controlling caries.
3. Explain the cold sensitivity and outline how you would diagnose and manage it.
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Cold sensitivity can come from marginal leakage and fluid movement in dentinal tubules, from recurrent caries, or from irreversible pulpitis. Test vitality, percussion, palpation, bite, and take a radiograph for caries and the restoration margin. If the pulp is reversible and the problem is a marginal gap, remove the restoration, excavate caries, reseal the dentin with an adhesive or liner, and restore with proper isolation and increments. If there is spontaneous pain, lingering cold, or periapical change, treat the pulp. Do not simply prescribe desensitizing toothpaste without checking the margin. After resealing, sensitivity often resolves, but the patient should be reviewed because the high caries risk remains.