The Occlusal Matrix Technique
This nugget is submitted from Dr. James Crawford Hamilton. Dr. Hamilton was formerly the Director of Technical Services at Kerr. He is now on staff at the University of Michigan Dental school.
I am using fewer instruments to place composite, and the type of instrument is not as important as it use to be. A NEW technique, the custom matrix technique will save any dentist who uses light cured composite 5 to 10 minutes on every light cured composite that they do. SOUNDS IMPOSSIBLE? Read on:
This was written before Transbite was available. I currently recommend PolySil Transbite for the following technique because it sets faster and is initally stronger and harder, probably related to the slower set time of Memosil.
What follows is a technique that can save you a lot of time on your next composite: a technique that reduces finishing time of posterior composites from 15 minutes to 2 minutes or less.
This technique, which is called the Occlusal Matrix, can also be used on other classes (Class III, IV and V) of light cured composites. The first step after anesthetizing the patient is to take an impression of the occlusal surface of the tooth to be restored. This impression is taken with a translucent bite registration material called Memosil, which is sold by Miles, a subsidiary of Bayer. A non translucent bite registration material can be used, such as Stat BR, but as explained later, you lose some of the benefits of the technique. This impression is about the size of dime and should be 4-5 millimeters thick to give it body This matrix is put aside, and the operative procedure is completed as usual.
The posterior composite preparation is etched and bonded as usual, and the composite placed and cured in layers. The only difference is that when the last layer of composite is placed, instead of shaping and curing, the occlusal matrix is forced into the uncured composite. This gives the restoration the same anatomy that the tooth had when the patient came into the clinic. The curing tip of the light wand is then placed with pressure on the occlusal matrix and the composite is cured through the matrix. After removing the matrix, the composite is cured again, since the matrix reduced the light energy that initially cured the composite. The advantages are:
- The occlusal surface of the composite is hard and not air inhibited, and does not need to be polished. It has the same smoothness as the original tooth.
- The occlusal surface has the anatomy that the patient was comfortable with. It needs minimal, if any, occlusal adjustment.
- With practice the amount of flash at the margins is minimal. You do want to have a small amount of flash.
The disadvantage is:
- Time and cost of materials to make an occlusal matrix.
If you do not use a translucent bite registration material, you will need to place a small amount of bonding resin on the part of the matrix that touches the composite. This keeps the composite from sticking to the matrix when you have to remove the matrix in order to cure the composite. The surface of the composite will be air inhibited and need some polishing.
If the occlusal surface is not acceptable, then the defects (most likely due to marginal breakdown of the amalgam) are filled in with wax. This actually does not take very long. Sticky wax is heated and smeared onto the occlusal surface and the excess scraped off. What about Class II preparations? You have to place your matrix band and retainer prior to making the occlusal form so it will fit within the matrix band. The retainer and band are taken off prior, to prepping the tooth. The Occlusal Matrix Technique can also be used on anterior composites. It is unnecessary to use the technique when restoring small Class III restorations, but it can save much time when the area to be restored is large. Most likely this will be the replacement of large Class IV and V restorations. The reason for this is that these classes of restorations are often replaced due to discoloration or staining at the margins.
The following references may be helpful.
Liebenberg, WH: Occlusal index-assisted restitution of esthetic and functional anatomy in direct tooth-colored restoration. Quintessence Int 27(2):1-8, 1996
Using PolySil Transbite vps material to create a custom matrix by SciCan (applying new technologies) (1996) Dent Prod Rpt 30:5 62-63.