Basically there are two main types of matrix; the circumferential (e.g. Ivory No. 8, Bonnalie and Tofflemire) and the unilateral (e.g. the Ash No. IX) (figure 16.1). The former are intended for use on both M.O.D. and MO or DO cavities and the latter are solely for MO and DO cavities. In the first category, the Ivory No. 9 and the Tofflemire are to be recommended because of the facility with which the retainer may be disconnected in the mouth. There are short and long bands for use on molars and premolars. They are curved in such a way that, when the ends are approximated, a conical form is produced. Thus when the band is tightened on the tooth, it flares out from the gingival margin, giving better adaptation gingivally. The bands have either one or two convexities which are positioned over the gingival margins of two- or three-surface cavities. The matrix is threaded through the space provided in the retainer and held firmly in place by a locking bar at the end of a knurled knob, which is screwed up until it is tight.
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© J. J. Messing and G. E. Ray 1982