Matrix Systems for Restorative Dentistry Chapter 49 Matrix Systems for Restorative Dentistry Copyright 2003, Elsevier Science (USA). All rights reserved. No part of this product may be reproduced or transmitted in any form or by any means, electronic or mechanical, including input into or storage in any information system, without permission in writing from the publisher. PowerPoint® presentation slides may be displayed and may be reproduced in print form for instructional purposes only, provided a proper copyright notice appears on the last page of each print-out. Produced in the United States of America ISBN 0-7216-9770-4

Introduction A matrix system provides and takes the place of the proximal tooth surface that was removed to restore the proximal contours and contact to their normal shape and function.

Posterior Matrix System Universal retainer Also referred to as the Tofflemire retainer. This device holds the matrix band in position. The retainer is positioned most commonly from the buccal surface of the tooth being restored.

Components of a Universal Retainer

Posterior Matrix System- cont’d Matrix bands Matrix bands are made of flexible stainless steel and are available in premolar, molar, and universal sizes and thicknesses. The larger circumference of the band is the occlusal edge and is always placed toward the occlusal surface. The smaller circumference of the band is the gingival edge and it is always placed toward the gingiva.

Fig. 49-2 Types of matrix bands.

Wedges A wedge is either triangular or round and made of wood or plastic. The wedge is inserted into the lingual embrasure to position the matrix band firmly against the gingival margin of the preparation.

Fig. 49-6 A wedge correctly positioned.

Automatrix System The automatrix system is an alternative to a universal retainer. There is no retainer used to hold the band in place. Bands are already formed into a circle and are available in assorted sizes in both metal and plastic. Each band has a coil like autolock loop. A tightening wrench is inserted into the coil and turned clockwise to tighten the band. When finished, the tightening wrench is inserted into the coil and turned counterclockwise to loosen the band. Removing pliers are used to cut the band.

Matrix Systems for Primary Teeth The T-band is a T-shaped copper band. When formed, the top portion of the T allows the straight portion to adjust and fit the circumference of the primary molar.

Fig. 49-7 Example of copper T-band used for primary molars.

Preparing the T-Band Matrix The wings of the T-band are bent to form a U-shaped trough. The free end of the band is slipped loosely through the U formation. The wings are closed, and the free end is pulled to make a small circle of the band. Holding the free end toward the facial surface, place the band on the tooth to be prepared.

Additional Matrix Systems for Primary Teeth A spot-welded band is a form-fitted band placed around a prepared tooth, then removed and placed in a smaller form of a welder that fuses the metal together to make a custom band.

Fig. 49-8 Spot-welded band.

Preparing a Spot-Welded Matrix Band Measure ¾ to 1 inch of stainless steel matrix material. Fit the matrix materials around the prepared tooth. Adapt the band, making sure the ends of the matrix material is at the facial surface for visibility and control. Holding the ends tightly, remove the band in an occlusal direction. Place the band in the spot welder. Spot-weld the matrix at three positions.

Matrices for Composite Restorations A plastic matrix, also referred to as a celluloid matrix or mylar strip, is used for class III and IV restorations in which the proximal wall of an anterior tooth is missing.

The Use of a Clear Matrix The matrix is placed interproximally before the etching and priming of a tooth. This protects adjacent teeth from these materials. After placement of composite material, a matrix is pulled tightly around the tooth to help reconstruct its natural contour. The clear plastic matrix allows the curing light to penetrate the material and complete the curing process.

Sectional Matrices A thin polished palodent-type band and a tension ring produce a tight anatomic contact for composite resin materials for class II restorations.

Fig. 49-10 Sectional matrices.