A Technic for Direct Wax Patterns of Three-Quarter Crowns

A Technic for Direct Wax Patterns of Three-Quarter Crowns

A technic for direct wax patterns of three-quarter crowns August Bartelle, D.D.S., Pearl Harbor, T .H . if too much delay does not occur. Within twen...

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A technic for direct wax patterns of three-quarter crowns August Bartelle, D.D.S., Pearl Harbor, T .H .

if too much delay does not occur. Within twenty-four hours there will be a gingival constriction and obliteration of the crev­ ice, unless some mechanical means is provided to maintain it.

A cast gold three-quarter crown is only as accurate as the wax pattern from which it was reproduced, discounting the minute variables in casting procedures. It is essen­ tial, therefore, to produce a wax pattern that accurately fits the prepared tooth. This technic consists in the adaptation of the inlay casting wax to the three-quarter crown preparation with a contoured band in a matrix retainer, then removing the band and carving the wax with instru­ ments, sandpaper disks and burs to the proper anatomy and occlusion. These procedures can be used on conventional three-quarter crown preparations and modifications, such as gingival shoulder or pinledge preparations. Best results are obtained on preparations of anterior teeth and bicuspids. The armamentarium (Fig. 1) consists essentially of the following: Wagner ma­ trix retainer, steel matrix band material, crown and collar scissors, screw mandrel with inch coarse sandpaper disks, scalpel, Roach wax carver, Hollenback wax carver, long pointed explorer and round burs no. 2 to no. 9. It is best to make the wax pattern im­ mediately after completing the threequarter crown preparation. Reducing the gingival enamel will leave a temporary crevice between the prepared crown and the gingivae. In taking the wax pattern the wax will flow readily into this crevice,

PREPARATION OF T H E MATRIX BAND

Use steel matrix band material % inch wide. Cut off a strip about 2^4 inches long (Fig. 2 A ). Double this strip over and make a curved cut from the middle of the free ends to the margin of the loop. Open up the band and straighten out any kinks, round off the sharp corners, and file down the sharp edges (Fig. 2 B ). Loop the free ends of the band and at­ tach it to the Wagner matrix retainer with pliers (Fig. 2 C ). Carry the matrix retainer with the band attached to the prepared crown (Fig. 3 ). Check any im­ pingement on the gingivae and contour the band with crown and collar scissors as necessary. Return the attached band to the crown and tighten the matrix re­ tainer so that about 0.5 mm. of free space

Presented at the forty-seventh annual m eeting of the H a w aii T erritorial Dental Society, H onolulu, T. H., June 17, 1949. The opinions o r author a n d are not to b e construed as official or reflecting the view s o f the N a v y Departm ent or the N a v a l se rvice at large. C o m m a n d e r, DC , U.S. Navy.

assertions herein are those of the

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BARTELLE . . . V O L U M E 42, FEBR U A RY 1951 • 139

with cocoa butter or Vaseline. This pro­ cedure will prevent the inlay wax from adhering to the band. Fill the band with softened inlay wax. W ax softened in a wax annealer gives the best results. Do not heat the wax in the band. Use any hard wax which meets American Dental Association specifications. Carry the band filled with wax to posi­ tion on the prepared crown, force the wax into place, tighten the matrix retainer (Fig. 4 ) , and maintain pressure until the wax has congealed. Wash with tepid Fig. 1 • Arm am entarium for direct wax pat­ terns fo r a th ree-quarter crown

is observed between the crown and the band at the gingival margin. P L A C I N G T H E W A X I N P O S I T IO N ON T H E PR EPA R ED CRO W N

Remove the matrix retainer with the at­ tached band from the tooth; pass the band once through the flame to warm and then lubricate the inside immediately

Fig. 3 •Fitting matrix band to prepared crown

Fig. 2 • A : S teel matrix band material % inch wide. Cut strip about 2 l/\ inches long. B : Sharp edges are filed down and sharp corners are rounded off. C : F ree ends o f band are looped and attached to the W agner matrix retainer with pliers

water. Trim the excess wax around the band that has squeezed out at the gingival margin and at the top of the band (Fig. 5 left and right) and remove the matrix retainer. Then remove the matrix band carefully (Fig. 6). Examine the bulk of the wax. Insure that the wax has been forced under the free margin of the gin­ givae. If it has not been forced under the margin the band is either too tight around the tooth, or the wax too hard when forced on the crown. If the wax is not under the free margin of the gingivae, it is best to start over again by cleaning the band by passing it through a flame, lubricating it and using new wax.

140 • THE JO U R N A L O F THE A M ER IC A N DENTAL ASSOCIATION

Fig. 4 • Inlay w ax carried to place on the prepared crown

CARVING T H E W AX TO PROPER A N A TO M Y AND OCCLUSION

With two /s inch coarse sandpaper disks mounted back to back on a screw man­ drel, reduce the labial bulk of wax until the proximal and labial margins of the prepared crown are faintly visible through the wax (Fig. 7 left and right). Do not remove any more wax from the labial surface at this time. This wax will serve as an anchorage which will prevent dis­ placement and distortion while the re­ maining bulk of wax is being carved to

proper anatomy. With the coarse sand­ paper disks reduce the labial or occlusal wax to the proper dimension. Reduce the lingual bulk of wax with a scalpel cutting toward the gingival and reproducing the gross anatomy of the lingual surface of the tooth (Fig. 8). Heat a blunt longpointed explorer, and insert it through the wax into the pin retention hole on the lingual surface of the crown. (This pro­ cedure is disregarded if no provision has been made for a lingual pin retention hole in the three-quarter crown prepara­ tion.) The explorer will force the trapped air to the surface and carry wax to the floor of the pin hole. Include this pro­ cedure in modified pinledge preparations. Use light finger pressure over this region while the wax is congealing. Carefully carve the detailed anatomy of the lingual surface with round burs no. 2 to no. 9, whichever will reproduce the desired anatomy (Fig. 9 ). Check to see if the wax pattern is in occlusion. Make a paste of tin oxide or zinc oxide and water. Paint a thin layer of this paste on the labial or occlusal surfaces of the occluding teeth. Have the patient carefully close in centric occlusion until the teeth are in contact with the wax. A white mark will result where the wax pattern is high. Repeat this procedure for first right lateral and

Fig. 5 • L e ft: Labial view after excess wax is rem oved. R ig h t: Lingual view after excess wax is rem oved

BARTELLE

Fig. 6 • M atrix band rem oved

then left lateral occlusion. R edu ce this wax with a round bur or R o a ch wax carver. Repeat this procedure until the wax pattern is in proper occlusion. Sm ooth the lingual surface o f the wax pattern with a R oach wax carver or a discoid. Exam ine the proxim ogingival region and rem ove all the w ax that has been forced beyond the crow n into the undercut area. C ontour the proxim al surface to the proper anatomy with a H ollenback w ax carver, m aking sure there will be n o im pingem ent on the proxim ating tooth or teeth during re­

. V O L U M E 42, FEBRU ARY 1951 • 141

moval o f the wax pattern. H oldin g the wax pattern in position from the lingual aspect with the left index finger, care­ fully reduce the w ax on the labial surface with a H ollenback w ax carver to the proxim al and incisal margins. Examine the finished w ax pattern in position. Satisfy yourself that there are n o thin areas, that the wax is below the free margin o f the gingivae, and that the in­ cisal and proxim al w ax has been reduced to the form which is desired in the fin­ ished cast three-quarter crown. For direct w ax patterns fo r bicuspids, the matrix band is contoured and checked to be sure that it does not interfere with functional occlusion. A fter seating the band filled with softened inlay wax and tightening up on the matrix retainer, the patient is asked to close in centric, right and left lateral occlusions. Finish the wax pattern with the same instrumentation as for a three-quarter crow n w ax pattern o f an anterior tooth. T he wax on the lingual surface below the gingivae should n ot be touched. If the band was properly fitted, a sufficient thickness o f w ax will be reproduced at the linguogingival margin. A ny carving at the linguogingival m argin will distort the pattern and may produce hem or­

Fig. 7 • L e ft: R em oving labial wax with coarse sandpaper disk. R ig h t: Bulk o f labial wax rem oved, so that labial and proximal margins are faintly visible

142 • T H E J O U R N A L O F T H E A M E R IC A N D EN T A L A S S O C IA T IO N

Fig. 8 • R em oving lingual bulk o f wax with a scalpel

Fig. 9 • Carving lingual surface with round burs

Fig. 10 • L e ft: Labial view o f finished Y* crown wax pattern. R ig h t: Lingual view of finished 3/i crown wax pattern

rhage. The wax pattern is now ready to be sprued (Fig. 10 left and right). If, after spruing and removing the wax pat­ tern, it is discovered that the linguogin­ gival region is too thick, but that the wax pattern is otherwise satisfactory, invest, burn out, cast and reduce the gold to proper anatomy. C O N C L U S IO N

A technic, which consistently produces well-fitting three-quarter crowns for an­

terior and bicuspid teeth, has been pre­ sented. This technic is considered to be particularly advantageous for the follow­ ing reasons: (1) The wax pattern is inti­ mately and accurately adapted to the prepared crown. (2) Minimal hand carv­ ing is required for the production of normal anatomical form. (3) Distortion or displacement of the wax pattern dur­ ing carving is obviated. (4) Reproduction of accurate margins in the casting is ensured.