Standardized sequence for carving and finishing amalgam restorations

Standardized sequence for carving amalgam restorations Roger A. Solow, University

and finishing

D. D. S. *

of the Pacific, School of Dentistry,

San Francisco, Calif.

1

here has been much research on the formulation and physical properties of silver amalgam in recent years. This has promoted amalgam from it’s initial use to an excellent restorative material. However, there has been less attention directed toward the actual carving and finishing technique. The specific objective of this article is to present a technique allowing (1) reproduction of tooth morphology by correct cusp and groove placement, in harmony with the occlusion, and (2) maintenance of strong and imperceptible margins.

CARVING

TECHNIQUE

A sequence of steps is described for carving amalgam preparations of conventional isthmus width. After the preparation is condensed with hand instruments or mechanically, the cavosurface margin is concealed beneath the overfill of amalgam. Removal of the overfill may eliminate excess mercury brought to the surface by condensation. To clear the margins at this stage risks ditching due to guessing the margin location and cutting through amalgam that has little resistance. If the margins are cleared by a straight or convex-bladed instrument with a sharp edge, the resulting shape of amalgam will be straight or concave at the cavosurface angle (Fig. 1). Such feathering of amalgam near the margin decreases edge strength and resistance to the sharp carving blade, thus increasing the possibility of ditching. Acorn burnisher Select an acorn burnisher that will be wide enough to ride along the isthmus without entering the preparation (Fig. 2). After condensation, introduce the acorn burnisher into the overfill and apply heavy pressure, carrying the instrument throughout the

*Clinical

Instructor,

0022-3913/81/110519

Department

of Operative

+ C6$00.60/00

1981 The

Dentistry.

C. V. Mosby

Co.

Fig. 1. Cross-section through isthmus of molar amalgam restoration. Left side illustrates feathered, concave shape produced by half Hollenback instrument drawn along cavosurface margin. Right side illustrates convex architecture with good edge strength. length of the central and developmental grooves. This action will create a central groove midway between the buccal and lingual cavosurface margins (Fig. 3). With this pressure, amalgam will course out of the preparation and against the internal walls, ensuring good wetting and adaptation at the margins. Since the acorn burnisher is smooth and has no sharp cutting edge on the sides where it contacts the enamel, a slight excess of amalgam will remain over the cavosurface margin. The margins are thus pro tected from ditching while the bulk of excess amalgam is readily removed. The acorn burnisher produces the initial carving step only.

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Fig. 4. Rotation amalgam.

of discoid

cleoid

about

margin

into

Fig. 2. Small and large tips of acorn burnisher.

Fig. 5. Placement of explorer create occlusal embrasure. Fig. 3. Central and developmental grooves produced by acorn burnisher. Note that bulk of excess peels out, and slight amount of amalgam remains covering margins.

Carving Instead of sweeping a sharp instrument blade across the margins to remove the small amount of amalgam still overlying the margin, place a discoid cleoid in each supplemental and developmental groove of the enamel and rotate into the amalgam. The instrument never leaves its point of rotation at the margin, precluding any chance of ditching (Fig. 4).

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to clear matrix band and

At this point, all desired groove locations for the definition of triangular ridges have heen placed. To create the marginal ridge of a Class II restoration, the occlusal embrasure is initiated by clearing the band at the proximal with a Suter No. 2 curved explorer (Suter Dental Mfg. Co., Chico, Calif.) angled toward the preparation, not perpendicular to the occlusal table (Fig. 5). Place two grooves with the discoid cleoid, one from the buccal and one from the with the rotational motion previously lingual, described (Fig. 6). By placing these grooves parallel to the proximal surface, a strong yet discrete ridge approximately 1 mm wide is formed, allowing room

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Fig. 6. Orientation proximal surface.

AMALGAM

of marginal

Fig. 7. Incorrect orientation define marginal ridge.

RESTORATIONS

ridge grooves parallel

to Fig. 8. Exposure of cavosurface margin by carrying discoid cleoid from enamel supplemental groove onto amalgam.

of supplemental

grooves to

for a mesial or distal fossa area. One common error is defining the marginal ridge by making grooves that converge toward the center of the tooth (Fig. 7). This results in a pit and a ramp of amalgam inclined toward the height of the marginal ridge, with no room for the opposing cusp to fit into a fossa area. The amalgam is now gaining resistance. Remove the matrix band by rotating it toward the buccal or lingual. Clear the proximal and gingival margins with the curved explorer, and level the height of the marginal ridge by resting the discoid on the adjacent ridge and planing buccolingually. At this point, the amalgam is near initial set and should offer firm resistance to the discoid cleoid

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Fig. 9. Orientation of discoid cleoid blade to clear cavosurface margin and burnish carving.

during carving. When a silver-colored streak is produced by gently moving the cleoid. in a groove, the amalgam should be burnished. Introduce the sharp tip of the cleoid into each supplemental groove and gently carry it across the cavosurface margin onto the amalgam. The course of the cleoid should define a curve in the amalgam that is continuous with the supplemental groove of the enamel. By using greater pressure in the supplemental groove as the cleoid approaches the central groove, the natural convex contour of t.he triangular ridge may be emphasized. In scribing the supple-

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Fig. 10. Small round finishing grooves to initiate polishing.

bur carried

through

all

Fig. 1 2.2. Thin flame-shaped finishing bur carried into finish gmgival gingival and proximal margins. emb bra.sures to tuush cleoid at a low over amalgam (Fig. 9).

rake the

angle entire

to remove the excess cavosurface margin

Burnishing

Fig. II. Small pear-shaped finishing bur carried around triangular ridges and over cavosurface margin. mental groove from enamel to amalgam, the flash is removed and the occlusal margin is exposed for the first time (Fig. 8). Because amalgam left in the enamel grooves is difficult to remove after it has set, it should be removed with an explorer at this time. With a light brushing motion, use the discoid

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Use the discoid cleoid to redefine all grooves, smooth all ridges, and burnish the entire surface. Cotton is too soft to smooth amalgam that has achieved initial set. Rounded burnishers are not recommended as they will be unable to reach the depth of the pits and grooves and will tend to form concave architecture unless used very lightly. They are also inefficient since a sphere on a flat surface has only a point contact whereas a discoid cleoid can contact a curved plane over the area of the blade. Use the discoid cleoid with the blade at a low rake angle as in clearing the cavosurface margins, allowing the weight of the instrument to lightly move back and forth over all ridges. This will result in a smooth, satiny finish that progresses to a high shine. Use the cleoid tip to burnish all grooves.

Occlusion Remove ribbon to absence of contact on

the rubber dam, and use articulating ensure a light centric contact and the excursive prematurities. Maintain centric the marginal ridge or in the fossa area

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AMALGAM

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designed to accept the opposing cusp. Remove any protrusive prematurities occurring on uneven marginal ridges.

POLISHING Polishing of smooth amalgam can be accomplished quickly with few instruments. Run a small, round 12-fluted finishing bur through all grooves to polish and slightly round them (Fig. 10). Then, rest a small pear-shaped carbide finishing bur in the polished grooves and carry it around the triangular ridges and over the cavosurface margin until a smooth, bright finish is obtained (Fig. 11). Use a light brushing motion with slow rotation of the bur to prevent scratches and waves in the final finish. Carry a thm flame-shaped finishing bur into the occlusal and gingival embrasures to finish the proximal and gingival margins. -Disks are difficult to apply in the embrasure without lacerating the gingiva and are not recommended. Use a fine grit rubber abrasive point (Shofu Super-greenie point, Shofu Dental Corp., Menlo Park, Calif.) over the entire carving to bring up the final mirror-like luster (Fig. 12). Use firmer pressure at slow rotation of the point and a direct air spray to prevent overheating and disperse the rubber debris. Do not use coarser points as they dull the finish achieved by the finishing burs and flatten the anatomy.

Fig. 13. Fine grit rubber sequence.

point used to firtish polishing

DISCUSSION For the ultraconservative restoration there is little room to define anatomy or manipulate instruments. Since centric contacts will rest solely upon enamel, we are concerned with obtaining a dense amalgam with imperceptible margins. After condensation, a small acorn burnisher was chosen and used as in a conventional preparation. As much flash as possible was expressed by carrying the burnisher along the isthmus with firm pressure. When the amalgam gained resistance, the point of an explorer was ;sed to remove amalgam from the enamel grooves and expose the cavosurface margin. The curve of the explorer was then placed on the enamel, and a light brushing motion was used to carry the explorer toward the central groove and clear the margin. For cusp onlays and preparations with wide isthmuses the sequence was similar to the one for conventional size carvings. The largest acorn burnisher was chosen and used to delineate the central and developmental grooves. Often the isthmus was

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Fig. 14. Finished Class II amalgam. wider than the largest burnisher tip available, but this was not a problem since the resistance of the amalgam increased with bulk and the large burnisher tip is flat and wide, precluding ingress into the amalgam. A discoid cleoid was then used to carve the cusps as previously described, without the guide of the supplemental grooves in the enamel. Burnishing of conservative and large carved amalgam restorations is identical to that of conventional sized restorations. Burnishing some amalgams reduces marginal leakage.‘, ” In this sequence, emphasis was

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SOLOW

placed on obtaining a smooth finish to expedite polishing. Carving, smoothing, and burnishing used the same discoid cleoid at different stages of amalgam set so that less amalgam is displaced at each step until only the top microlayer is refined. A small pear-shaped finishing bur was used to polish the ultraconservative carving, followed by a rubber point. For large amalgams and cusp onlays, large pear-shaped finishing burs and rubber abrasive fine grit cups were used to give a uniform surface without creating ripples in the finish.

SUMMARY This method of amalgam carving and finishing, described in a step-by-step sequence, is fast and effective. The initial step of using the acorn burnisher eliminates the great bulk of excess amalgam and contours the restoration. A simple armamentarium is all that is required for carving, burnishing, and

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polishing. A general scheme for reestablishing original or ideal occlusal morphology has been discussed, emphasizing distinct triangular and marginal ridges and convex contour. Attention was focused on the prevention of ditching at the cavosurface margin, thus ensuring full benefit of the improved physical properties of silver amalgam. REFERENCES 1,

2.

Reprint

Kanai, S.: Structural studies on amalgam II-The effect of burnishing on margins of occlusal amalgam fillings. Acta Odontol &and 24:47, 1966. Matyas, J., Caputo, A. A., and Cowie, A.: Burnishing and its effectiveness in sealing margins of amalgam restorations-A laboratory study. Oper Dent 3:3, 1978. requests

to:

Dx ROGER A. SOLOW UNIVERSITY OF THE PACIFIC SCHOOL OF DENTISTRY SAN FRANCISCO, CA 94115

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1981

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