Matrices

MATRICES

The world matrix id derived from the Latin word ‘mater’ which means ‘Mother’. It was introduced in the year 1871 by Dr. Louis Jack .

The matrix is a device used to contour a restoration to simulate that of a tooth structure, which it is replacing.

IDEAL REQUIREMENTS OF A MATRIX

It should be inserted easily and should be sufficiently rigid to retain the contour given to it so that it can be transferred to the restorative material . It should not adhere or react with the restorative material . It should resist the condensation pressure. Should be easily removable after hardening of restorative material without compromising the created contact and contour or characteristics of the restorative material .

MATRICING

Matricing is the procedure, whereby a temporary wall is created opposite to axial walls and surrounding areas of tooth structure that were lost during preparation.

OBJECTIVES It must act as a temporary wall of resistance during introduction of the restorative material. It should provide shape to the restoration . It should confine the restoration within acceptable physiological limits . It must assist in isolating the gingiva and rubber dam during introduction of the restorative material. It must help in maintaining the dry operative field thereby preventing contamination of the restoration.

TYPE OF MATRICES

1. Matrices for Class I cavity preparations to receive a restorative material inserted in a plastic state :-

Double-banded Tofflemire for Class I, Designs 4,5,6,7, and 8 cavity preparations (fig. 26).

Procedure

Acquire a working understanding of the Tofflemire retainer (see next section)

Turn the large vice-moving knob until the slotted vice is about ¼ inch from the inner end of the retainer. Loosen the vice screw until its pointed end is clear of the slotted vice. Make a loop out of the universal band creating an edge with a narrow circumference and an edge with an wide circumference. The narrow circumference edge is placed gm givally and the wide circumference edge is places occlusally .Insert the occlusal edge of the universal matrix in to the slotted vice first. The free ends of the band are inserted in to the vice while the looped end of the band extends away from the retainer . (The band is inserted until it is in contact with the arched top of the vice slot.) Always be sure that the slotted end of the vice is facing gingivally. This will facilitate easy occlusal removal of the retainer .

Tighten the vice-screw to lock the band in the vice. Guide the looped end of the band gently over the tooth. The size of the loop may be increased or decreased by the turning the vice moving knob. With the band in position around the tooth, tighten the vice moving knob. Ideally, the retainer should be parallel and adjacent to the facial surfaces of the quadrant of teeth being operated on.

An additional small piece of matrix band material is them contoured to the facial or lingual axial configuration of the contemplated restoration and retained between the tooth and the previously positioned and retained matrix in the area of the facial or lingual extension of the cavity preparation. This piece of material should lap over the margins of the extension by about 1.5-2 mm circumferentially.

With a beaver-tail burnisher, create a separation between the two bands. Select a wedge that will create and maintain the proper separation between the two bands and thereby enable the formation of the proper contour facially and /or lingually . Cover the wedges with softened compound and insert it between the two bands and cool to harden .

Check the stability of each component of the matrix and be sure of its unyielding resistance to the insertion energy necessary for the restorative material .

2. Matrices for Class II cavity preparations to receive restorative material in a plastic state:-

a. Single-banded Tofflemire for Class II Designs 1,2,3,6,7,8 cavity preparations.

This is the most practical matrix for class II cavity preparations, making a very stable device against which restorative materials can be condensed . Its use is made universal by the easy application and removal of the band to and from its holder without disturbing the condensed material .Procedure .

Repeat the basic steps from the previously described double banded arrangement. Usually (especially in Designs, 1,2 and 3 cavity perparations) the band will go to its destination clear of the cavity margins and adjacent soft tissues. However in some cases of Designs 1,2,3and in most cases of Designs 6 ,7, and 8, the following modifications should be performed .

If the cavity preparation involves one proximal surface only and there is a substantial difference between the heights of the inteproximal gingiva on the mesial and distal sides of the tooth the matrix band should be trimmed so that it is narrower (occluco-apically) on the side where the interproximal gingiva is more occlusally located. It may also be possible to use matrix band with only one gingival projection, which should coincide with the proximal side where the interproximal gingiva is more apically located .

If the gingival extension of the proximal of the cavity preparation is more apically located than gingival lines facially and lingually, there is danger of cutting the gingival tissues facially and lingually in using a band with a straight gingival edge. In this situation it is necessary to either reduce the occluso-apical width of the band facially and lingually or to use a band with apical projections which coincide and cover the gingival extension of the proximal portion of the cavity preparation. The latter bands are supplied precut but they always need further trimming facially lingually or even proximally in order foe them top fit, exactly the outline of the proximal preparation without injuring gingival tissues.

In preparations with subgingival margins especially at the axial angles or any surface protrusion of the tooth the edges of the band occasionally encounter the gingival margin and became bent inward. Preventing for the seating of the band for this reason there should be unprepared. Exposed tooth surface apical to the gingival margin of the preparation to support the band in its apical path and to prevent its inward collapse or bending. This may necessitate gingival retraction or cutting. Also in these situations. The band edges should be guided in their apical path by placing a flat bladed. Blunt instrument between the band and the adjacent unprepared tooth surface apical to the gingival margin. This will enable the band to pass by the gingival margin without encountering it or the gingival floor.

Although it is preferable to put the retainer in the buccal vestibule. Parallel to the adjacent teeth. Sometimes due to shallow sulcus or sizable buccal involvement of the tooth in a cavity preparation. The retainer is placed on the lingual. This usually in necessitates a constringed retainer . However the retainer should never be located at a right angle to the facial or lingual surfaces of the teeth operated upon as this will drastically change the occluso-apical contour of the band .

The junction between the retainer and the band should always be located next to unprepared intact tooth surface to insure its stability and prevent unnecessary accumulation of excess restorative material at that location.

As soon as the band is in place and all cavity margins can be seen inside the matrix, a wedge, comparable to the dimensions of the future gingival embrasure, is chosen and tried (always from the opposite side of the retainer attachment ). The wedges should be trimmed using sharp knives. Plastic wedges could be trimmed with sand-paper discs and molded, after softening in warm water. Sometime the wood wedge is dipped in warmed compound and tried until it exactly fits the contemplated space for the future gingival embrasure.

Usually one wedge from the opposite side of the retainer is sufficient. However, more than one wedge could be necessary if the configuration of the gingival embrasure cannot be created by one wedge only. More than one wedge could also be necessaryin the fallowing situations: the gingival margins are located very apically, proximal preparations adjacent to a very exaggerated inter dental col, the margin is located in a proximal surface concavity or defect, more separation is needed than can be supplied by one wedge, or in extraordinarily large gingival embrasures resulting from extensive taper of the tooth or from gingival recession.

More than one wedge can be used, but usually two will suffice – one from the buccal and one from the lingual. Sometimes, more may be needed, and they should be inserted and located where they best fulfill their objectives. Each should be handled in the same manner as a single wedge. If more than one wedge is to be used, it is advisable to dip each in softened compound before the final insertion in order to assure their immobility

Using a ball burnisher from within the cavity preparation, shape the matrix band material to create the outline of the contact and contour of the future restoration. If the cavity has buccal or lingual extensions, repeat the modifying steps in the double-banded Tofflemire application. Check the stability and the details of the matrix before the insertion of the restorative material.

For all Tofflemire applications after the insertion and initial hardening and manipulation (carving- see chapter 4) of the restorative material the wedges and secondry band are removed. Then, the retainer is loosened and disengaged. The primary band is bent (reflected) against adacent tooth surfaces and removed from between the teeth in an occlusal direction while being pressed against the adjacent tooth (not on the restoration’s own proximal surface).

If the contact area is extremely tight and the band is resistant to removed, it is a good idea to cut the band on the opposite side of the retainer, remove the roughened portion of the band (formed by the holding screws of the retainer) and them to pull it bucco-lingually (or linguo- buccally) with pressure against the adjacent tooth. This creates some separation and reduces friction with the restoration.

In MOD restorations, after initial hardening and manipulation of the restorative material and removal of the retainer, slightly pull one side of the band away from the retainer side, stopping just short of the roughened terminal part formed by the retainer’s holding screw. This way there will be enough band material facially lingually to separately move the mesial or distal part of the band occlusally without moving the opposite proximal part of the band.

As soon as you release one side of tha band from the interproximal area, proceed with the other side as in a proximo-occlusal arrangement. If the contact is very tight, cut the band and drag each piece of the band faciolingually (or vice versa ) with positive pressure against the adjacent contacting teeth .

b. Ivory matrix No. I

The band encircles a posterior proximal surface so it is in dictated in unilateral class II cavities. The band is attached to the retainer via a wedge-shaped projection which engages with the tooth at the embrasures of the unprepared surface.

c. Ivory matrix No. 8

The band encircles the entire crown of the tooth. So it is indicated for bilateral Class II cavities. Both ivory matrices are remnants of old techniques, so their operating instruction are not presented here. They are indicated for Class II, Design 1,2 and 3.

d. Black’s matrices

Of all the different designs for matrices presented by black to the profession, only two will be described. Both are indicated for Class II, Designs 1,2 and 3 only.

i. Black’s matrix for simple cases (fig. 30) is recommended for the majority of small and medium size cavities .

Procedure

Cut a metallic band so that it will extend only slightly over the buccal and lingual surface of the tooth, beyond the buccal and lingual extremities of the cavity preparation. To prevent a warp around holding ligature (a wire or dental floss) from slipping off the band and the band sliding gingivally the corners of the gingival ends are turned up (occlusal) to hold the ligature.

ii. – Black matrix with a gingival extension (fig. 31) to cover the gingival margin of a subgingival cavity.

In this from, an extension is created in the occluso-gingival width of the band to cover the gingival margin of a subgingival cavity. The retaining procedures are the same as for the previous type of Blacks matrix. All matrix band should be trimmed smoothed and have corners rounded to prevent cutting of the ligatures and wounding of soft tissues.

The ligature should be securely tied with a surgical knot on the side, after wrapping it around the tooth. A wedge should be carefully adjusted to produce and maintain the proper separation and to hold the band tightly over the gingival margin of the restoration.

e. Soldered band or seamless copper band matrix (fig.32)

These are indicated for badly broken down teeth, especially those receiving pin-retained amalgam restorations, with large buccal and lingual extension i.e. in Class II, Designs 6, 7 and 8 cavity preparations .

A stainless steel band is cut according to the measured diameter of the crown of the tooth. Then the two ends are soldered together. Or a seamless copper band selected so that it barely clears the diameter of the tooth in the cervical area. Either band could be heated in a flame until it glows light red. It is them quenched in alcohol thus softening the band for easier handling .

With curved scissors, festoon the bands so its gingival periphery corresponds to the gingival curvature and the SJE. The band is than smoothed to removed rough edges cercically and occlusally. With contouring pliers, contour the band to reproduce the proper shape in the contact area as well as the buccal and lingual contours to be restored. Areas of the band in the contact area are reduced to a paper thinness using a coarse sand paper disc. They are then recontoured. Next the band is seated on the tooth and tightened at the cervical end by pinching up a “tuck” using a flat-bladed plier at the gingival edge in an area accessible to the plier.

To stabilize the band and prevent cervical flashes of amalgam wedges are placed gingival to the cervical margin of the preparation. Use the same procedures in choosing and adapting the wedges as described with the Tofflemire mitrix. The external portions of the matrix and the wedges are covered with compound to further stabilize the matrix in the same way as applied to the double-bow separator (embrasures and surrounding osslusal surfaces). A wire “staple” is inserted facio-lingually in the compound to further stabilize it.

Apply a heated ball burnisher from the inside of the cavity to the band, softening the external compound and insuring the proper contour, contacts, and embrasures. After condensation and initial carving, the compound is removed and the matrix is cut at the area of the tuck. The matrix band is opened and then slipped far enough occlusally to cut its edges with a crown scissors over each contact area.

With a plier or hemostat grip the band at either side of the scissor’s cut and tear through each thinned contact portion to remove the band without damaging the proximal region of the amalgam.

f. The anatomical matrix. (Fig. 33)

This is the most efficient means of reproducing contact and contour. It is entirely hand-made and contoured specifically for each individual requiring unique anatomy to be reproduced in the restoration. It is indicated for Class II, Designs 1,2,3,6,7,8 cavity preparations.

Procedure

A piece of 0.001-0.002 stainless steel matrix band 1/8” in width is drawn between the of a pair of festooning scissiors. This procedure facilitates the adaptation of the free ends of the matrix to the proximal surface of the tooth by curling the band.

The matrix is than cut to proper length. It must extend well beyond the cavity margins. To obtain the proper length, the centers of the proximo-buccal and proximo lingual cups are used as a guide. The matrix band is contoured with controuring pliers. Light pressure should be used and the process repeated until a suitable vertical as well as horizontal convexity is obtained. The band is than trimmed so that the matrix will extend well below the gingival margin of the cavity and at least 2mm beyond the buccal and lingual margins of the cavity.

A wedge is selected and shaped to conform to the gingival embrasures, and it is then placed in warm water to soften it slightly. This procedure facilitates adaptation of the wedges to any irregularities of the proximal surface of the tooth.

The wedges is forced in to position, to insure adequate gingival adaptation' as well as to provide adequate separation.

Two small cones of compound are warmed in hot water. The tips are heated in a flame to further soften them and make then adhesive. These compound cones are foced one at a time, using thumb and finger pressure, into the buccal and lingual embrasures. The pressure is maintained until the compound has flowed evenly over the entire buccal and lingual surface of the adjacent teeth.

A wire staple constructed from a metal paper clip, such that the length of the staple is slightly shortly shorter than the crown of the tooth. The staple is heated in a frame and forced in to the compound in the buccal and lingual embrasures. This adds to the stability of the matrix by locking together the two pieces of the blocking compound .

A warm ball burnisher is used to soften any compound that has been forced between the maatrix and the adjacent tooth. The matrix is burnished lightly against the contacting tooth. The matrix is now ready for condensation of the restorative material.

After initial hardening of the inserted restorative material the compound is cracket at its occlusal junctions using a sharp chisel or knife. Then the separated pieces are removed using the attached staple, if it is still present. The wedges are removed using a hemostat and the band is curled backwards against the adjacent tooth and withdrawn bucco-lingually (or vice versa) with pressure against the adjacent proximal surface.

g. Roll in band matrix (auto-matrix)

This is a recently introduced matrix in which the band is self-retained by holding one end of the band and rolling the other end over itself, decreasing the band length and conse quently , the matrix diameter until it fits tightly over the tooth and preparation. This rolling of one end of the band over itself is done with a hand-operated mechanical device. The matrix is supplied in different size to accommodate varieties of teeth. The matrix band comes with one end held in place and the other end pratially rolled on itself, ready to be applied and tightened.

h. S-shaped matrix band

This is used for Class II, Designs 4 and 5 and the facial or lingual extension part of the Class II, Design 7. the rest of the cavity preparation in Design 7 is done with any of the previous seven matrices after filling the very apically located extension with the S-shaped band matrix. Procedural instruction are exactly as described in class III cavity preparations.

i. T-shaped matrix band

These are premade T-shaped brass or stainless steel matrix bands. The long arm of the T is bent or encomani the tooth circumferentially and to overlap the short horizontal arms of T. This section is then bent over the long arm, loosely holding it in place. Wedges and stabilizing compound can be applied as in the anatomic matrix to add further stability .

3. Matrices for a cavity preparation for amalgam restorations on the distal of the cuspid :-

a. The S-shaped matrix for Class III cavity preparation on the distal of the cuspid, with either a labial or lingual access. The procedure for its construction is similar to that of the anatomic matrix.

Procedure

One half to one inch of regular strip matrix 0.001-0.002” in thickness is used. A mirror handle is used to produce the

S-shape in the strip. The band is contoured over the labial surface of the cuspid and the lingual surface of the adjacent bicuspid.

With contouring pliers, the strip is contoured in its middle part to create desired from for the restoration. It is then placed interproximally and wedged firmly apical to the gingival margin and covered with compound at its facial and lingual ends. The compound should lock into adjacent embrasures for stability.

If the lingual opening of the cavity preparation is blocked by this process, the compound can be removed with a warm instrument.(The previous arrangement is for lingual approach preparation. For a preparation with a labial approach, the exact reverse should be performed.) To insure proper contour of the band, a burnisher is heated, placed within the matrix and pushed towards the mesial surface of the bicuspid.

The remaining instruction are identical to those of the anatomic matrix. If this band is to be used for Class II, Designs 4,5,or 7, it should wrap around the operated tooth on its non-access side. At the access side the band should be away from the cavity and adapted on the adjacent tooth to the nearest embrasure.

b. For a cavity preparation with incisal access on the distal of the cuspid the regular Tofflemire could be used efficiently.

4.Matrix for Class III direct tooth-colored restorations

These are usually transparent plastic matrix strip. For silicate cements they are usually celluloid strip and for resins they are cellophane strips. Mylar strips may be used for either material .

a. Matrix for Class III preparation with teeth in normal alignment(Fig.37)

Procedure

The suitable plastic strip is burnished over the end of a steel instrument, e.g., handle of a tweezer, to produce a ‘’belly’’ in the strip. This will allow for a curvature which, if properly contoured and designed, will reproduce the natural proximal contour of the tooth.

The strip is cut to allow the belly to be placed where the contact is desired. In placing a plastic strip between the teeth, it should be cut as wide as the tooth is long. Bear in mind that the tooth is cone-shaped ,which will cause the apical corners of the strip to bend on the rubber dam, the gingival tissues or the palate. The corners of the strips should be trimmed therefore, to allow for better adaption to the tooth and to prevent any excess material from forming on and beyond the facial or lingual margins. The length of the strip should be just sufficient to cover the labial and lingual surfaces of the tooth . If the strip extends on to an adjacent tooth , it will bukcle and allow unnecessary excesses of restorative material to escape.

A wedge is trimmed and applied to hold the strip in place. This prevents the strip from slipping when it is brought over the inserted restorative material . The wedge also closes the avenue of escape for the material toward the gingival and helps create the separation necessary to produce approximate contact. Wedges are introduced from the side opposite to that of access. Any portion of the wedge protruding toward the access side should be trimmed, so that it will not interfere with the convenient insertion of the restorative material.

For a labial approach preparation , use the fingers of the left hand for holding the strip firmly against the lingual surface of the tooth while the material is being placed in the cavity . The reverse is true for a lingual approach preparation .

After insertion of the material , reflect the free end of the strip and hold the whole strip firmly against the setting restorative material using the thumb and first finger of the left hand(for a right-handed operator). Mechanical holding devices can also be used.

b. Matrix for Class III preparation in teeth with irregular alignment

Procedure

A suitable plastic strip is contoured and adapted as described previously, and then removed. For a labial approach preparation a compound impression is taken of the lingual surface. The compound is allowed to overlap the adjoining teeth.

It is cooled, then removed. The compound impression should show an imprint of the cavity preparation. This excess of the compound impression from within the cavity is trimmed off to produce a flat surface.

The compound impression is then warmed. The surface is softened without distorting the from of the entire impression. The is done by holding the impression close to a flame only for a moment .

The strip is then placed into position again, followed by the compound impression against the strip, assuring a perfect adaptation of the matrix to the cavity on the lingual surface. The material is then introduced from the labial. The reverse can be done for a lingual approach cavity preparation.

c. Matrix for two small proximal preparations in contact with each other (Fig.38)

An appropriate plastic strips folded with one end slightly longer than the other to facilitate their separation after the insertion of the strip between the teeth. A loop ½ ‘’in diameter is formed in the matrix strip. This loop is flattened and creased with a finger, making a ‘’T-shape’’ , and trimmed. The trimmed matrix is then placed between the teeth. For labial approach preparations the strip is held over the lingual surface with the fingers while the cavities are filled. After the insertion of the material each wing of the strip is folded over the setting restorative material and held with the thumb of the left hand. These instructions are for Class III cavities with a labial approach. For those with a lingual approach, reverse the position of the strip.

5.Matrices for Class lV preparations for direct tooth colored materials

a. The plastic strip for incisor-proximal cavities (Fig.39) procedure

A suitable plastic strip is folded at an angle into an

L-shape, then sealed with a plastic cement or any adhesive that does not react with the tooth-colored material. One side of the strip is cut so that it is as wide as the length of the tooth. The other side is cut so that it is wide as the width of the tooth. The strip, with a wedge in place, is adapted to the tooth. It is important that the angle formed by the fold of the strip approximates the normal corner of the tooth and supports the matrix on the lingual surface, which is held by the forefinger of the left hand. The cavity is then filled to a slight excess, and one end of the strip is bought across the proximal surface of the filled tooth. When this is completed ,the other end of the strip is folded over the incise edge. The matrix is held with the thumb of the left hand.

b. Aluminum foil incise corner matrix (Fig.40)

These are “stock’ metallic matrices shaped according to the proximo-incisal corner and surfaces of anterior teeth. They can be adapted to each specific case. These types of matrix cannot be used for light cured resin material.

Procedure

A corner matrix closest in size and shape of the lost area of tooth is selected .It is trimmed gingivally, so that it coincides with the gingival architecture and covers the gingival margin of the preparation. As it is readily deformable, hap it with the thumb and first finger until it fits the mesio-distal and labiolingual dimension of the tooth, with a sufficient overlap of unprepared surface areas. Loosely place the wedge, allowing space for the matrix band thickness. Partially fill the preparation and then the corner matrix, preferably after venting the corner

Apply the partially filled matrix over the partially filled tooth preparation at its predetermined location between the loosened wedge and the tooth. Tighten the wedge and wipe off excess material.

c. Ranceparent crown form matrices (Fig.41)

These are’ stock’’ plastic crowns which can be adapted to tooth anatomy. In bilateral Class lV preparation use the entire crown from, but in a unilateral Class lV cut the plastic crown inciso-gingivally into two halves and use only the side corresponding to the location of the preparation.

Procedure

Choose the crown form with the size and shape closest to the tooth to be restored . for a unilateral IV, after cutting the crown form inciso-gingivally, so that the correct incisal angle of the crown from matches the lost tooth incisal angle ,allow the lateral peripheries of the crown from to overlap the lateral extension of the preparation. If for bilateral Class lV ‘s , keep the crown as it is.

Trim the crown from (or its half) gingivally, so that it coincides with the gingival architecture and completely covers the gingival margin of the preparation . Then choose and trim a wedge and loosely fit it interproximally without the matrix in place .

Check the matrix to insure that it will recreate proper contact and contour ,and that it covers all margins of the preparation .Then remove the matrix and thin it at its contact area with a sand paper disc . It should also be incisal angle . completely fill the matrix with the restorative material and partially fill the crown form on the tooth in the desired location. The wedge is then tightened , excess material is wiped off the matrix peripheries and the material is allowed to set while it is under finger pressure .

  d. Anatomic matrix ( Fig . 42 )

Prior to preparing the teeth (tooth ) , study model for the affected tooth (teeth) together with at least one intact adjacent tooth on each side is made . it is preferable , especially in multiple involvement where the restoration (s) is (are ) part of the disclusion mechanism to make full arch study models and mount them in CO.

The defective area (s) is (are) restored on the study model in a fairly heat resistant material (Plaster acrylic resin blocking compound plasticine , (etc) to the appropriate configuration . A plastic template Is made for the restores tooth (teeth) on the model using a combination of heat ( to thermo plastically) soften the template material and suction ( vacuum ) consequently to draw the moldable material onto the study model . The template is trimmed gingivally to fit the tooth (teeth ) and adjacent periodontal architecture . It should seat on at least on unprepared tooth on each side . This is the matrix which should be vented by perforating the corners of its part corresponding to the future restoration . The restorative material is inserted into the preparation then the matrix is filled with the material and inserted over the prepared and partially filled tooth , ready for curing .

E . Modifield S-shaped band

A strip of dead metal (ametal with no elastic deformation malleable with no memory , usually copper, tin or aluminum foil) is cut 1/8’’ in length and made S-shaped with a mirror handle . Apply the band so that one arm will go over the labial surface of the contacting tooth operated upon. Contour and thin the part coinciding with the proximal surface of the lingual to fulfill all the objectives of wedging.

Flow softened compound on the lingual surface of the matrix and the adjacent tooth surfaces. While hardening , contour the band more for inside the cavity. By now we have a complete matrix with a labial opening but no incisal wall from which we can introduce our material . overfill toward the labial and incisal so we can contour the restoration after hardening .

6.Matrices for class v amalgam restorations Window matrix

This matrix if formed using either a Tofflemire matrix or copper band matrix (Fig.43)

Procedure for using the Tofflemire matrix

The contrangle retainer is applied at the side of the tooth that does not have the preparation. A window is cut in the band slightly smaller than the outline of the cavity (preformed windowed bands are available).Wedges are placed mesitly and distally to stabilize the band.

Procedure for using the copper band

A seamless copper band is selected that is just larger thanthe prepared tooth. Festoon and adjust the band to the tooth .A window is cut coinciding with the cavity, but smaller in diameter. The edges are smoothed. The band is positioned on the tooth, and wedges are placed.

b. The S-shaped matrix

This is usually indicated for a proximal extension of a buccal or lingual Class V preparation. It is done in the same manner as described for the Class III amalgam preparation with the exception that the buccal and lingual opening of the matrix is not excessively widened.

c. Other options in lieu of matrices in extremely wide Class V cavities

The cavity is prepared in two stages-a mesial half is prepared and filled with amalgam. After the amalgam hardens, the distal half is prepared and restored. If there are sufficient mesial and distal walls in the Class V cavity preparation con dence the mesial one- third of the amalgam mesio-axially and the distal one-third disto-axially, allow to partially harden, then condense the middle third axially with a flat-bladed instrument.

7. Matrices for Class V preparation for direct tooth-colored restoration

a. Anatomic matrix (Fig 44) for non-light cured, direct tooth colored materials

Procedure

The class v cavity may be preliminarily filled with inlay wax or gutta-percha and trimmed to the proper contour. The wax (gutta-percha) and the tooth are then cited with cocoa butter or Mylar strop and compound impression is taken of the tooth surface to be to be restored. Adjacent surfaces are to be included in the impression. After the compound has cooled, it is removed and the wax is removed from the cavity.

A mix of the restorative material is made and placed into the cavity, and the compound matrix is placed in to position and held securely in place under pressure until the material sets. In using resins ,the impression surface of the compound must be lined with a tin foil substitute, or Mylar strip.

b. aluminum or copper collars (fig.45) for non- light cured direct tooth colored restorations.

Aluminum or copper bands are reshaped according to the gingival third of the buckle and lingual surface . They can be adjusted to each specific case so that the band will cover 1-2 mm of the tooth surface circumferential in the cavity margins .They are then mounted on the tip of a softened stick of compound , which is used as a handle fill the cavity with restorative material and apply the adjusted collar onto the tooth .

C. Anatomic matrix for light and non-light cured, direct tooth colored materials

The same as anatomic matrix for class IV study models for the defected tooth (teeth) with at leasy one intact tooth on each side is made . after restoring the defacts on the model , a plastic template is made as described before . the template is cut mesio-distally, keeping its occusly (incisal) portion and the facial and lingual parts where the defects are. It is then trimmed gingivally and used as a matrix for applying pressure and keeping the restorative material while being cured.