By Lee Ann Brady, DMD
There is only one thing that I miss about placing Class II and Class III amalgam restorations; I never worried about my matrix system. If amalgam expressed out beyond the preparation margins when I condensed it into the interproximal box, I had carving instruments that could easily take care of that, so the seal of the matrix against the tooth wasn’t critical. Amalgam was easy to condense, and I could create just enough force not to stress over the presence of a contact once the band was removed. As the popularity of posterior composites has increased, the conversations and frustrations about matrix systems have increased right alongside.
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Unlike amalgam, the difficulty of condensing composite presents us with the challenge, recreating a tight interproximal contact. Maybe more importantly, trimming composite that has been extruded beyond the preparation margin around an interproximal box is difficult, frustrating, and unpredictable. So in a quest to minimize the amount of trimming we need to do with high-speed instrumentation after the composite is cured, we search for a better matrix.
I was part of this search until a few years ago. While researching matrix systems for a presentation, I came across a list of criteria that define a successful matrix, and that powerfully shifted my perspective.
A matrix system must do the following three things:
- Recreate the natural tooth shape and interproximal contact
- Seal the proximal and gingival walls of the prep
- Overcome the thickness of the band
Pre-wedging Pre-wedging is an old concept, which I readopted in my practice about five years ago. I place a tight interproximal wedge after anesthesia and prior to the start of my preparation. Placing the wedge early allows time for the teeth to separate before placement of the composite. In addition, the wedge protects the interdental papilla, preventing the bur from cutting the tissue while creating clearance at the walls of the box. Lastly, it helps make it easier to avoid damaging the adjacent tooth during the prep by separating them. Once I am finished with the prep and ready to place a matrix, I remove this first wedge. Often I find that it is very loose now in the space between the teeth, and I will need to move to a larger wedge once my matrix is in place. When removing the wedge, the tissue may bleed; this is managed with the matrix and another wedge prior to placement of the restoration. Recreating the natural tooth shape and sealing the walls begins with the matrix. On the market today are both plastic and metal matrix bands. They are available in a variety of thicknesses and delivery systems that include sectional matrix bands, circumferential systems, and bands that require a holder. The band is simply a barrier between the tooth I am restoring and the adjacent tooth, so the thinner the better. The band prevents me from bonding the teeth together, and creates the appropriate shape. Sealing this band against the preparation walls is the job of the wedge and the separator ring system.
