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JULY 1953 V O L U M E 47 N U M BE R 1

O F T f f A M F J U C A i V D E N T A I A S S O C IA N O #

Methodical jacket crown preparation

Charles B. Walton, D.D.S., Pittsburgh

The preparation of a vital tooth for a jacket crown is the most radical operationthat a tooth must undergo and yet remain vital. At best it is a traumatic experience for the tooth and for the patient.

Th e purpose of this paper is to suggestsome details that will reduce the physicaltrauma to the tooth and the psychological

trauma to the patient. Its aim, also, is toaid the dentist; to suggest ways to increase his skill and efficiency, to reducehis operating time, and thus to minimizehis fatigue.

Preliminary treatment of the patientis important. A clinical examination, withaccurate roentgenograms and study casts,should precede any mouth rehabilitation.Before reconstruction, if there is any evi

dence of gingival inflammation, athorough prophylaxis is necessary, andparticular care must be taken to removeserumal calculus. It is imperative to produce normal gingival tissue tone and topromote the proper position of this tissuefor the margins of the completed jacketcrown.

Careful attention during this prophylactic treatment will help the operator toappraise the patients emotional and painreactions.

Examination of the patients occlusionand, if necessary, grinding in the occlusion in order to coordinate it to the hinge-axis relation of the mandible are essential

before any preparation of teeth is begun.1 The prophylactic treatment and occlusalequilibration will establish the confidenceof the patient and convince him of thedentists interest in his oral health. Hewill then be better prepared emotionallyto accept more radical operations.

If gross malalignment of anterior teethmust be corrected, it will be useful to cutpreparations on a duplicate study cast of

the mouth and make wax patterns of

Presented before the Section on Partial Prosthodon-tics, ninety-third annual session, American Dental Association, St. Louis, September 9, 1952.

Associate professor, head of ceramics department,Dental School, University of Pittsburgh.

I. Lauritzen, A. G . Function, prime object of restorative dentistry. J.A.D.A. 42:523 May 1951.

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2 TH E J O U R N A L O F T H E A M E R I C A N D E N TA L A S S O C I AT I O N

proposed crowns. The study cast enablesthe operator to develop a method for thepreparatory work on the individual teethand he also can visualize how the mouthmay be expected to look when the work iscompleted. In addition, this cast may beshown to the patient so that he can betterunderstand the proposed treatment. Figure 1 shows an example of a congenitallymissing upper lateral incisor and hypoplastic enamel of the central incisors.Slightly narrow jackets are made for the

central incisors so that a normal widthlateral incisor may be supplied. Thesecentral incisors are cut for jackets on astudy cast so that three teeth may be positioned normally.

METHODICAL TEC HNIC

It is most important to establish a wellorganized method for jacket crown

preparation. Such a preparation shouldbe viewed as a surgical operation and bepatterned after the surgeons operatingroutine as much as possible. The equipment and instruments should be preparedand laid out beforehand and a step bystep plan should be followed. Each cuton the tooth should be made in itsplanned sequence and each instrumentshould be used to complete a cut before

it is discarded. I f this idea is followed,certain benefits will accrue:

1. Needless pain and discomfort willbe eliminated.

2. The pulp and gingiva will undergoless trauma.

3. A better preparation will result.4. Operating time will be saved.If the dentist follows an organized

plan, his habits of work will be benefitedand the patient will be impressed by thesureness and confidence of the operator.

PREPARATION OF TEETH

The excellent treatise by H. Conod2 hasbeen used as a guide to the preparation ofteeth for jacket crowns. In his article

Conod clearly illustrates the mechanicalprinciples that are significant in the development of a proper tooth form so thatthe porcelain crown may be well supported by the preparation. He illustrateshow the preparation can be made so thatthe porcelain will be subjected to compressive forces rather than to destructivetensile forces during mastication.

Enough time must be allotted to the

patient so that the preparation may becompleted, the impressions taken and thetemporary crown placed at one appointment. Brecker3 suggests that all preparatory cutting be done on any one tooth atthe same appointment. This is soundpractice because it prevents repeatedirritation to the pulp and the periodontaltissues, and it certainly is much less ob

jectionable to the patient. Usually one

and a half hours is sufficient for the

2. Conod, H. Etude sur la statique de la couronneaquette. Actualit Odontostomatologique, no. 14, 1951.

3. Brecker, S. C. The porcelain jacket crown. St.Louis, C. V. Mosby Co., 1951, p. 22.

Fig. 1 Cast. Left: Preoperative labial view. Center: Teeth prepared. Right: Wax patterns of pr op os ed resto rations

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completion of the afore-mentioned stepson a single tooth. Much less time, proportionately, will be required for the twoadjoining teeth.

Routine presedation of the patient witha barbiturate of short duration, such assecobarbital sodium, ^4 grain or 1 f i grains, will reduce apprehension andmake the patient more cooperative. Thedepth of local anesthesia also will beenhanced.

The assistant should have the armamentarium and materials prepared beforehand so that they may be availablequickly and without confusion. Her cooperation is important here and is invaluable during operating procedure.

Effective local anesthesia for so longa procedure may be obtained by the useof 4 per cent procaine hydrochloride withphenylephrine 1:2,500, or by 2 per centlidocaine hydrochloride with epinephrine1:100,000. Our experience has been satisfactory with these more potent anesthetics.

IN STRUMENTATION

Th e following method is- suggested forthe preparation of an upper incisor toothin normal alignment.

Diamond disks and wheels are used toreduce the major bulk of the tooth. Tepid

water is kept running over the instrument.

1. The outline of mesial and distalslices are pencilled. These are cut witha true-running % inch or /g inch flatdiamond disk. Proximal shoulders areestablished with this instrument and theshoulders are carried through to thelingual angles.

2. The incisal angle is reduced with

a /% inch narrow diamond wheel, onehalf being reduced at a time. I f the incisor is thin, it is not cut to the full depthuntil after the labial and lingual enamelis removed.

3. The important cuts are those whichreduce the four proximal line angles andthose which establish the shoulders at the

proximolabial and proximolingual anglesof the tooth. When there are two ad

joining sound teeth, these cuts are madeby a % inch or % inch cup-shaped truediamond or vulcarbo disk. Considerablewater is poured over it. The inner edgeof the disk is used, beginning at the incisal edge and gradually cutting to theshoulder area, so that the proximal lineangle of enamel may be removed easilywithout touching the approximatingtooth. When use of this disk is mastered,these difficult line angles may be cuteasily and the cutting of the shouldersat the angles begun. For use on theseangles, the cup-shaped disk is preferableto the small diameter, cylinder cutterwhich is inefficient and which createsheat. Figure 2 illustrates the use of thecup-shaped disk. The object is to reducethe enamel with as large an abrasive instrument as can be used safely and onewhich can, at the same time, be used tobegin the shoulders in these difficult areas.

This means, naturally, that the fingerrests and guards for teeth, lips and tonguemust be especially good.

4. Next the shoulder is established(but not finished) around the entiretooth. A thin diamond wheel of about2.5 mm. diameter cuts the labial shoulderto the dentin from the mesial to distal

angles. Then it is used to make the lingualshoulder.5. This same wheel is used to cut a

median groove in the labial enamel tothe incisal edge in order to establish thedepth of labial enamel to be removed.

6. One half of the labial enamel isremoved at a time with inch or %inch diameter diamond wheel (Fig. 3,left). The cutting edge is held parallel

to the axis of the tooth. This is followedby a inch diamond wheel held inthe opposite direction (Fig. 3, right) toremove the remaining collar of enamelincisal to the shoulder groove.

7. Th e lingual enamel is removed bythe 54 inch diamond wheel, following thecontour of the surface. This is finished

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with a small barrel-shaped carborundumwheel to prevent the formation of sharpangles.

8. A Bastian shoulder cutting wheel isused ( right-angle style held in the straighthandpiece) to raise the shoulder beneaththe free gingiva on the labial side.

9. A thin tapered cylinder mountedpoint with square end, preferably an extremely fine grit, is now used to hone allthe axial walls, to reduce sharp axialangles and to straighten the shoulder.

10. A no. 600 plain fissure bur isthen used to sharpen the shoulder afterwhich it is filed with end-cutting Bastianfiles.

11. The preparation is polished withlubricated fine-grit paper disks.

IMPRESSION METHOD

On completion, the prepared toothshould be isolated and scrubbed carefullywith some mild antiseptic and obtundent.

The formula may be the one preferredby the University of Michigan (phenol,1 part; creosote, 2 parts; eugenol, 3parts), or it may be Blacks 1-2-3 solution. The dentin is dried with cotton andtwo or three thin coats of copal varnishare applied. Desiccating agents such as

alcohol or other volatile irritants shouldnot be used for drying.

It has been found that while the toothis free of saliva, the operator can fit thecopper bands for the tube impressionsmost satisfactorily. Fairly tight, well annealed copper seamless bands are used.

The bands are not selected for size untilafter the preparation because they arealways found to be too large if selected

before the shoulder cutting is complete.I f the band is contoured to the gingivalsection of the tooth and is carried underthe lingual shoulder first and graduallyrotated forward, it will conform to theproximal surfaces easily. Scribing can bedone in order to trim it to fit uniformlybeneath the gingival tissue.

Th e festooned band is beveled on itsouter gingival edge. The tube impressionis taken in graphite-impregnated wax foran electro-formed copper die. This waxhas a low fusing point and may besoftened thoroughly in the band. Theband is pressed to position with a minimum of pressure on the open end. Justenough pressure is created while seatingthe band so that it will hold the wax inthe band. After the band is placed in itsproper position, it may be held at that

level by the fingers, and as cool water isdropped on it, heavier pressure is appliedagainst the open end. The object is notto force the edges deeply into the periodontal attachment and to prevent excessimpression material from extruding atthe gingival edge. In this way, minimumirritation occurs.

For the transfer, or master impression,it is best to take a duplicate tube im

pression in low-fusing inlay wax and pinchthe band so that the contacts of the ad joining teeth are established against theband. Plaster is the material preferredfor the transfer impression so that theduplicate tube impression may be exactlypositioned and the die may be pressedinto it without fear of forcing it out ofposition.

TEM PO RAR Y PR OT EC TION

OF THE TOOTH

After impressions are complete, thetooth is again isolated and the sedativesolution applied. A moderately stiff mixof zinc oxide and eugenol cement isspatulated into a small string of cottonfibers for a gingival pack. After the toothis lubricated with petroleum jelly, this

little rope is packed into the shoulderarea against the gingival third of the cutdentin. Silicate that has been mixed ona cold slab is then molded over this totooth form with plastic instruments. Thesilicate must not impinge against thegingival tissue and any existing impingement must be removed. In this manner

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W AL TO N . . . V O LU M E 47, JU LY 1953 5

Fig . 2 Red uction of

prox im al angles . L e ft : Labial

view of cup-shaped disk cutting labioproximal angle.

R ig ht: Incisal view of disk

Fig. 3 Red uct io n of labial surfa ce. La rge whee l used to reduce bulk. Right: Smaller wheel used to remove remaining collar of enamel

the tooth is carefully protected and noirritating edges are forced against thegingiva to injure it.

It is usual to allow several days toelapse before the jacket crown is

cemented. This will help the pulp to recover from operative shock and thegingiva to be less irritated.

SUMMARY

During diagnosis and prophylactic treatment it is possible to estimate thetemperament of the patient and to establish his confidence.

When repositioning of teeth is required,it is helpful to prepare the teeth on aduplicate study cast and build a mock-up in wax. This will clarify the methodof procedure. The dentist then may cutthe preparations with a definite andmethodical plan in mind, working precisely and without confusion.

Th e larger abrasive instruments areused for the major enamel cutting. Eachcut requiring a particular instrument

should be completed before the next cutis begun. The use of concave disks toreduce the proximal angles and to cutthe shoulders in these difficult angles willexpedite and simplify the whole prepara

tion. This also will eliminate the heatand trauma that can be produced soeasily when cutting with small cylindricalinstruments. The reduction of theshoulder subgingivally is done principallywith wheel-shaped instruments, and theshoulder is merely sharpened and finishedwith steel burs. Sharp . line angles andcorners should be eliminated from theaxial surfaces so that internal tensions

are reduced in the porcelain crown.Proper care of the cut dentin with a

sedative cement pack and a temporarycrown that does not impinge on thegingiva and is not in traumatic occlusionwill eliminate most postoperative painand sensitivity. The gingiva will be keptas nearly normal as possible so thatcementation of the permanent jacketcrown will be accomplished without theinterference of serum or hemorrhage.