Matrix Systems for Restorative Dentistry
Celluloid (SEL-yoo-loid) strip Clear plastic strip used to provide a temporary interproximal wall for the restoration of an anterior tooth surface.
When a tooth is prepared for a class II, III, or IV restoration, at least one interproximal wall of the tooth has been removed. A matrix system creates a temporary interproximal wall for the amalgam, composite resin, or intermediate restorative material to be placed against (Fig. 49-1). (The plural term for matrix is matrices.) Besides acting as a temporary wall, the matrix system has additional functions such as the following:
Placement and removal of the matrix system may be a legal expanded function in the state in which you are practicing. Pay special attention to the type of tooth preparation, the type of matrix system to be prepared and placed, and the techniques of placement and removal.
Posterior Matrix Systems
The matrix system most commonly used today for the class II restoration is the universal retainer and matrix band. To avoid unnecessary delays in a procedure, the assistant will have the retainer and band assembled at the beginning of the procedure.
The universal retainer, also referred to as the Tofflemire retainer, is a mechanical device that holds the matrix band snugly in position. This type of retainer is positioned from the buccal surface of the tooth that is being restored.
If during tooth preparation, the interproximal wall extends onto the buccal surface, a contra-angle retainer has been designed with a slight bend in the body to accommodate positioning from the lingual surface.
The matrix band is made of a thin flexible stainless steel material. The two designs of the matrix band most commonly used are the universal band and the extension band (Fig. 49-2). The universal band is selected for the class II preparation when the proximal “box” is prepared to a minimum depth and width and the cusps are intact. The extension band is selected for the deeper class II preparation requiring gingival extensions to compensate for the loss of a cusp, because insufficient height of a universal band will not exceed the height of the occlusal surface of the tooth as required.
The matrix band is designed in such a way that when the ends of the band are brought together, the band will form a circle. One side of the circumference (perimeter or outside edge) of the circle will be smaller than the other side. The circumference guides you in placing the band as follows:
In preparation for use, the center of the matrix band should be contoured (shaped) in the proximal contact area, so the final restoration will have proper contact with the adjacent tooth. To contour the band, place the band on a paper pad. Using a burnisher or an end of the mirror handle, rub against the inner surface of the band until the ends begin to curl (Fig. 49-3).
See Procedure 49-1.