Wednesday, September 27, 2017

Why Sectional Matrices Are *So* Important

point caontact.jpg
The image above is a classic example of a point contact on tooth #12 (FDI 24).  In this clinical situation, a MO composite was placed using a traditional Tofflemire matrix system.
The problem here is not that the Tofflemire does not do its job, no the problem is the restorative material.  The Tofflemire system was designed to be used with amalgam.  Because of that fact, the band was built with some “give” in it that bowed it out slightly in the middle (in a cervical-occlusal direction).  When condensing amalgam, the physical consistency of the material meant that a lot of pressure could be applied.  This caused the Tofflemire to give slightly which resulted in a restoration that recreated the correct anatomical curvature of the tooth in all directions.
When dentistry transitioned to the current restorative philosophy, many practitioners transitioned away from amalgam and began to use composite exclusively.  What happened next is a fairly predictable result when dealing with the metrics of human learning and understanding.  Basically what I mean is that doctors changed materials but continued to perform as they were trained and where their comfort level resided without consideration for a change in the physical properties of the new restorative materials.
Since composite is much less dense in its uncured state, it is difficult, if not impossible, to apply proper pressure during condensation that would cause the band to create the same contours as when using amalgam.  Due to this, what happened with many interproximal restorations is what happened in the radiograph above.  The band was burnished against the adjacent tooth, but due to the consistency of composite the contact ended up at the marginal ridge and not in the middle third which would be anatomically correct.
Fortunately, this problem hadn’t presented itself for very long before some smart minds began to spin up with ideas of how to correct this problem.  Companies such as Garrison and Triodent (just to name a couple) hit the market with systems designed to create anatomical contacts while allowing doctors to work with composite.  The concept became known as a Sectional Matrix System and rapidly changed to way the majority of dentists perform composite restorations.
These systems consist of a C-shaped matrix band, flexible wedges, and a “ring” that provides pressure to separate the teeth slightly and hold the band in place.  When the ring is removed the teeth return to their original contact which closes the slight separation the ring created.  The result is a properly contoured restoration that has the correct contact and anatomical shape.
Triodent 1.jpgGarrison 1.jpg

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