Key to the long-term success of a posterior composite is the marginal seal and integrity. The margins are the area most likely to break down, evidenced by leakage, staining or recurrent decay. Interproximal margins are perhaps more subject to these issues than the margins we see easily on the occlusal surface. So how do we assure proper seal that will last over time. In the prior post of posterior composites I mentioned convenience form. I think this is a critical step in marginal integrity. Having adequate convenience form allows us to see, feel and finish the margins interproximally. In this way we can be certain the day of placement we have created sealed the margins.
Sealing the margins takes multiple steps. First is proper placement of the matrix band to ensure we seal the composite against the preparation. With this accomplished we now have to make certain the composite is adequately condensed. Many practitioners will use a first step of flowable along the exterior margins. This layer is placed into the depth of the box, and teased along the margin line with a perio probe. It can be left uncured during placement of the first increment of composite or cured first.
Some of our newer bulk fill composites are designed to increase the ability to properly fill a box form and seal the margins. Regardless of the material used we need to place the composite and than make certain it either flows or is condensed into the preparation to eliminate voids and create marginal seal. When using a layering technique, place increments less than 1.5mm in thickness and condense. Using instruments designed to minimize stick of the composite, materials with low stickiness and the addition of a small amount of dentin adhesive to the condenser will reduce pull back. Layering and the use of composites that have been shown to have low shrinkage stress will also reduce the strain at the margins that can result in breakdown after the final cure is complete.