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What is the place of the full crown in restorative dentistry?
WHAT
IS THE PLACE OF THE FULL IN RESTOR,ATIVE DENTISTRY?
GILBERT
P.
SMITH,
D.D.S.,”
NEW
YORK,
CROWN
N.
Y.
T
HE full gold crown is one of the oldest devices used in restorat,ive dentistry and through its evolution has served the profession and the public well Although gold crowns were found in tombs of ancient Italy and the Easi Tndies,t the first dentist credited with using them was C. Mouton in 1740 In 1873, J. H. Beers patented a gold-banded crown with swaged cusps; in 1907, Taggart’s casting process was introduced into dentistry and it was soon applied to the full crown. The succeeding years brought refinements to the techniques of the full crown until now it is possible to fabricate one that meets t,he requirements of modern restorative dentistry. Throughout its history the full crown has had its champions and its opponents. We are all familiar with the poorly fitting, overextended, carelessly contoured crowns seen in so many mouths, and their common associatesinflamed, proliferated, and infected tissues. Ready-made crowns carelessly fitted over insufficiently prepared stumps have taken their toll in the loss of countless teeth. Is it any wonder that in many minds the full crown has fallen into disrepute; that many physicians immediately question any gold seen in the mouth? We all, however, have seen well-contoured crowns with accurate marginal fit that, have served for years, the tooth and surrounding tissue in a state of health. To many, the full crown is a “means of last resort” rather than an “instrument of choice.” What is the place of the full crown? Is it a restoration A disto be avoided if possible or is it the’ answer to many of our problems? cussion of it.s advantages, disadvantages, and use should help to answer these questions. The full veneer crown has a number of advantages over any other individual tooth restoration. One advantage is that no other restoration is as complete a protection to t,he tooth from the inroads of caries as is the full crown. By virtue of its complete coverage and a tight peripheral fit beneath the free gum margin, it seals off the tooth as effectively as is possible and prevents caries from recurring at any point but below the gingival margin, an area rarely susceptible. The cavosurface margin has been reduced to the shortest possible length in proportion to the surface covered. In the case of multiple Presented
lumbia The
*l?mfeSSor
before of
University. ?Tylman, S. D.: C. V. Mosby Co.,
the Bronx-Northern Dentistry, School Theory pp. 1-14.
and
of
Practice
Dental Society, Dental and Oral of 471
Crown
and
March Surgery,
20, 1947. Faculty
Bridge
Prosthesis,
of St.
Medicine,
Co-
Louis,
1940,
472
Gilbert
P. Smith
cavities in an ipdividual tooth, many operators go to great lengths to place separate fillings whose total eavosurface margins are several times greater in length and are in more susceptible areas than that of the full crown. How much more simple it would be to fit a full crown and how much more permanent a restoration it would be ! Another marked advantage of the full crown is its retentive properties. Its complete coverage of the tooth in conjunction with close adaptation to closely paralleled walls of the preparation gives it a degree of retention unequaled by any other restoration. By completely enveloping the tooth, the crown holds together the portions weakened by the inroads of caries to form the strongest possible abutment for a bridge. The inlay, on the other hand, depends upon the strength of remaining portions of the tooth to resist fracture for its retention. The three-quarter crown derives it,s retention from a partial envelopment of the tooth. The margins of inlays, particularly the indirect slice type, and of three-quarter crowns are susceptible to spreading upon application of excessive stresses. The breaking down of cement that accompanies the opening of these margins leads to development of caries, loosening and failure of the bridge. The full crown is immune from this type of distortion and cement beneath it is free from fracture. A third advantage is that no other type of tooth restoration affords the opportunity to improve existing undesirable contours and ocelusal relations as does the full crown. The importance of these factors is well recognized in modern restorative dentistry. The individual tooth is no longer an entity in itself but must be considered in the light of its relation to the mouth as a whole. By virtue of its envelopment, the full crown provides a new contour for the tooth-a form completely subject to the manipulation of the operator. Tipped, tilted, or rotated teeth can rarely be brought into harmonious relation with their neighbors by means of partial restorations. A fourth advantage of the full crown is that its preparation, fabrication, and placement are relatively simple routine procedures. Tooth preparation has been reduced to a definite technique. Accurate impressioning results in a completely indirect method for construction and inaccuracies in the process of fitting and setting are reduced to the minimum. A fifth advantage is pulp protection and preservation of tooth structure, important attributes of the full crown. Adequate cement lining within a full crown provides excellent thermal insulation to the pulp. Tooth crowns weakened structurally by caries to the extent that fillings could no longer be retained can often be crowned and preserved as healthy units. In discussing the disadvantages of the full gold veneer, the first is the excessive display of metal. This is a problem on all anterior teeth and the upper bicuspids and first molars. On the average lower posteriors, the occlusal is the only portion visible in the normal range of lip movements-an area where the metallic display of the full crown varies little from that of the large inlay or three-quarter crown. In teeth where appearance is a factor, the recent innovation of the acrylic veneer facing incorporated in the metal makes an aesthetic restoration comparable with the three-quarter crown.
Full
Crown in Itestorative
Dentistry
The second disadvantage is the excessive reduction of sound tooth structure necessary to permit extension of the margin into the gingival crevice and accurate gingival fit. In this case, the full crown should be used only where other type restorations fail to meet the requirements and the full crown is the only one that is adequate. The third disadvantage of the full crown is that it prevents the use of the electric pulp tester. Since other restorations leave a portion of the tooth surface exposed, it is usually possible to apply the electrode to them in a manner suitable for testing. The full crown must be removed to make such a test. The fourth disadvantage of the full crown often cited is gingival irritation. This is not a just criticism. The carefully fitted crown is no more irritating to the gingival tissues than is the carefully fitted inlay. To further consider the place of the full crown in restorative dentistry it would be, well to consider its many uses. The first and most universal is as a simple restoration for missing tooth structure. The second common use of the full gold crown is as a bridge abutment. It provides the strongest retention of any type of abutment available and in many respects is the most satisfactory. Dr. E. T. Tinker,* though the leading exponent and father of the modern three-quarter crown, stated that the full crown was the ideal fixed bridge abutment and that the more he saw of bridgework the more he used it. This has been echoed by a number’of competent prosthodontists, A third use for the full crown is in conjunction with removable partial dentures. The abutment teeth for a partial denture should be prepared for the reception of stabilizers and retainers. Occlusal rests are more efficient and distribute stresses more advantageously when they are recessed within the contours of the tooth to which they are applied. The normal axial contours of abutment t,eeth often present surfaces unfavorable for retention by clasp arms and for stabilizing contacts. Full crowns present an ideal medium for providing for the recessed rests, for recontouring axial surfaces, and for providing surfaces for denture contact not subject to dental caries. A fourth use of the full crown is in large occlusal reconstruction and mouth rehabilitation cases. The full crown is the best individual tooth restoration for meeting the demands of occlusion, caries prevention, and tooth support. A fifth use of the full crown is as a splinting medium. Very often the demands of occlusion combined with weakened alveolar support require that teeth be tied together for mutual st,rength. The difficulties of fitting, finishing, and cementing multiple inlays are more hazardous than those of multiple crowns. Two or more full crowns soldered together are an efficient and practical means of splinting teeth where required. To further evaluate the full crown, it is well to consider its requisites. What should an acceptable full crown do 8 First, it. should restore missing tooth structure. Caries and all questionable fillings should be completely removed and replaced with suitable base *Personal
communication.
474
Gilbert
P. Smith
material. The crown should cover and extend gingivally beyond all cavity margins into contact with sound tooth structure. Second, a good full crown should restore the tooth to proper occlusion. By reshaping teeth with crowns in indicated cases, faulty occlusal relations can be brought into harmony with the general occlusal pattern of the mouth. Where the occlusion is heavy and the imbedded-root-to-exposed-tooth ratio is disproportionate, the occlusal surface may be reduced in buccolingual width, thus preventing the overloading of the periodontal tissues. Marginal ridges should be re-established in conformity with those of the neighboring teeth. Third, the crown should provide harmonious axial contours. Proximal surfaces should be so shaped as to form interproximal embrasures large enough so that impingement on the interseptal tissues is eliminated. The occlusal sluiceways should blend into the proximolingual and buccal surfaces to provide pathways for the escape of food particles during chewing, reduce occlusal stresses, and thus maintain the health of the septal tissues. Buccal and lingual surfaces should blend into the occlusal contours to produce normal tooth form as closely as possible. Crowns are often placed on teeth when pronounced recession has taken place and they must be extended below the existing free gum margin. This results in a crown longer than the original anatomical crown. The contour of the crown near the gingival tissue is important. Normally, the form of the tooth serves as a protection to the free gingivae. The curvature is greatest on the buccal of lower posteriors but is characteristic of most axial surfaces. On the buccal of lower mola.rs the height, of contour is relatively low and the convergence below this region is fairly marked. This results in a form that is protective to the gingival cuff in that it causes food passing by this point to be diverted off on the buccal side. If this contour is excessive, the gum tissue is not benefited by the detergent action of food and results in an inflammation. If there is insufficient contour, the gum cuff is poorly protected and food particles produce irritation and possible stripping of the gingival tissue resulting in gingival recession. It is important that optimum contour of the crown be established in proper relation to the existing gingival margin. The remainder of the axial surface should blend from this region to the occlusa1 surface. Fourth, properly placed contact, which is positive, should be established with adjoining teeth. We are all familiar with the conditions resultant from inccrrectly placed light contacts. Food impaction, periodontal pockets, mobile teeth and cavities are all too common sequelae. Fifth, accurate marginal gingival fit is essential for all full crowns. It is as important for the margin of a crown to fit properly as it is for any other tooth restoration. Margins placed under the gingivae should be explored for accuracy as carefulIy as those placed above the gingivae, regardless of the type of restoration. What is a proper and accurate margina. fit for a full crown? It should extend into the gingival crevice-experience has taught us that this is an area relatively free from caries and that the gum cuff renders a certain amount of protection. A crown should cover a11 cut tooth surface and should not be
Pull
Crown in Restoratilqe Dentistry
short of the preparation. Ground tooth surfaces present irregularities that invite t)he occurrence of caries and are irritating to gingival tissue. The margin of the crown should be in close contact with the gingival surface of the tooth and no overhang should exist. This does not mean that the margin is undetectable to the explorer; if the previously ment,ioned concept of contour is accepted, a change in contour at the junction of the crown and tooth is inevitable in many instances, It does mean that the explorer point should not be able to go under the crown. The margin of the crown should be even, finished to a knife edge, polished and protected by the gingivae. Sixth, a full crown should provide adequate pulp protection. Overheating of the tooth during grinding must be zealously avoided. Constant application of a stream of tepid water should be routine. Between appointments prepared teeth should be given the protection of temporary caps filled wit,h a sedative paste and the final cementation should be made with a nonirritating mixture of cement preceded by a careful toilet of the prepared stump. When the prepared surface is sensitive to heat and cold, the interior of the crown above the gingival margin may be relieved to provide room for an insulating layer of cement. Seventh, a full crown should provide adequat,e retention. Approximate parallelism of the surfaces of the preparation provides a.mple retention in most cases. Occasionally extremely short or conical teeth present problems in retention but these may be met by preparing parallel axial grooves in the preparation or by the use of ocelusal boxes or pins. In general, the full crown’s retentive powers are ample to meet any demands placed upon it. In discussing the full crown, some reference should probably be made to operative procedures. The first step, the preparation of the tooth for the reception of the crown, can be reduced to a simple routine-mesial and distal slices, buccal and lingual surface reduction, rounding of the line angles, and occlusal clearance. Each step, if executed precisely and completely, results in a preparation being made quickly without waste motion. The surfaces should be smooth, the gingival margin regular and even, and no undercuts should be allowed to remain on the a,xial contours. A carefully finished preparation is the first step in developing a successful crown. The full cast crown is superior to other types which depend upon the adaptation of wrought metal for gingival fit ; namely, the banded cast contour or the swaged crown. This use of wrought metal is usually a direct procedure and permits only limited adaptation. If done indirectly, where swaging is possible, it presents no advantages over the casting process. The full cast crown has been developed to the point where it now is used almost universally when a full gold crown is indicated. The fabrication of a full cast crown is an indirect procedure having the inherent benefits of reducing chair time for the operation and inconvenience for the patient, The fabrication of a direct full crown wax pattern is a difficult procedure fraught with the danger of incorrectable disfortion. Combinations of the direct and indirect procedures introduce unnecessary possibilities for error and negate the advantages of fitting and finishing tipon,:a
476
Gilbert
P. Smith
die. A completely indirect procedure permits more accurate control of crown form and fit. The second step in the development of the full crown is the impressioning of the preparation. The accuracy of the fit of the crown depends upon the impression. No other step in construction has more effect on the success of the restoration or is more critical. Perfection in the procedure is mandatory to completion of a satisfactory crown. Probably no step offers more opportunities for advancement than does the taking of an accurate abutment impression. It is a trying procedure and taxes one’s ingenuity. In no other step is misinterpretation so probable. What a boon it would be to have a simple, easy, accurate method for obtaining the impression of a tooth. The impression procedure currently used by the writer uses a low-heat, fine-grained compound confined in a carefully adapted copper band. Meticulous fitting, shaping, and trimming of the band are essential. ’ Step No. 1.-A band is selected that fits fairly snugly on the preparation but does not bind-undersize is preferable to oversize, for the band can be stretched. In trying the band and in taking the impression the band is always inserted and held with its long axis coinciding with that of the preparation. Fitting the band in one inclination and then taking the impression with the band held in another inclination defeats the usefulness of the fitting. Step No. 2.-The band is reshaped from a round cross-sectional form to that of the cross-sectional form of the gingival portion of the preparation. This is most easily done with a fully annealed band. Step No. 3.-The gingival margin of the band is festooned by trimming it until it contacts the gingival tissue in its entire circumference simultaneously when the band is inserted parallel to the axis of the preparation. At this stage the band should slide to place easily on the tooth without binding and with a slight space between it and the gingival periphery of the preparation. It should slip between the free gum margin and the tooth. If it is too snug, it may be stretched; if it stands away at points, these portions may be crimped closer to the tooth. Step No. 4.-A small layer of compound is seared to the inside of the gingival end of the band and seated on the tooth for a trial impression of the gingival margin. It is chilled slightly, removed, and examined. An imprint of the gingival margin should be visible. If it is not and the band was seated properly, it most likely indicates that the festooning of the band is incorrect. To correct the festooning further, the band is reduced at all edges where the impression of the margin of the tooth preparation is visible ; do not trim where the margin cannot be seen. The impressioning and trimming is repeated until the complete tooth margin is visible in the trial impression. Step No. 5.-The band is filled with evenly softened compound and seated on the tooth. This step requires skill that can be developed only by experience. Seating of the band parallel to the axis of the preparation, control of excess compound by forcing it out ahead of the band, relief of pressure and excess material from the occlusal end of the band, avoidance of folds or wrinkles,
Full
Crown in Restorative
Dentistry
477
and complete seating of the band are all to be accomplished in one continuous deft movement. Step No. 6.-The impression is cooled in place under pressure and without movement once the insertion stroke is completed. Sufficient time is allowed to ensure dissipation of heat from throughout the body of compound in the impression. Xtep No. 7.-Removal of the impression must be by direct pull in line with the axis of the preparation. Any rocking, twisting, or tilting in withdrawing the impression will result in its distortion and a misfit crown. The impression when completed should be carefully checked for inaccuracies in preparation, such as complete marginal registration, wrinkles, fractures, drawn surfaces, evidence of calculus remaining on the tooth, and gingival tissue trapped within the band. Rarely is it impossible to distinguish the limits of a preparation. Cut or ground surfaces can be discerned from uncut surfaces in an accurate impression even though in the same plane. If the impression is incomplete it should be discarded and another taken without hesitation. Once an accurate impression has been obtained, care must be taken to preserve the accuracy throughout the fabrication of the crown. Careless handling of the die, wax pattern, or casting may invalidate all effort expended in developing the accurate impression. The copper-plat,ed die has proved superior to other types of dies. It requires less time to make than does the amalgam die and is less susceptible to loss of detail during handling. The cutting of a groove on the die 0.5 mm. below the margin of the preparation and 0.5 mm. deep facilitates trimming of the margin in both the wax pattern and the casting. A large inverted cone bur (No. 39 or 40), pointed toward the gingival margin, may be used to cut this groove on the base of the die, The tendency for beginners using this technique is to cut too close to the margin and to try to work too accurately. The groove acts as a guide for the blade in trimming the gingival margin of the wax pattern and greatly simplifies this step. After the casting is seated on the die, the groove is again used to finish the gingival margin. By reversing the direction of approach of the bur, so that it points toward the base of the die, both casting and die are carefully cut back to the exact margin of the preparation. This gives a perfection of fit to the margin limited only by the accuracy of the contributing steps. Disks, rubber wheels, and polishing agents are then used to finish the contour of the crown in harmony with the tenets out,lined earlier in this paper. Full crowns constructed along these lines are tolerated well by mouth tissues and provide t,he safest possible protection for the tooth from dental caries. SUMMARY
What is the place of the full crown in restorative dentistry? It is the foundation of good fixed bridgework. It is a restoration which, when properly used, completely restores a tooth by providing ideal oeclusal, proximal, and
478
Gilbert
P. Xmith
gingival relations, and the acme of protection to the tooth from caries. It has the greatest margin of tolerance of any restoration-full crowns constructed with the same degree of skill are less susceptible to failure than are threequarter crowns or inlays. It is not the wish of the essayist to convey the opinion that the full crown should supersede all other types of retainers or individual tooth restorations. It is rather to indicate a more intelligent approach to the use of the full crown. A full appreciation of its merits and limitations by dentists and public alike will allay the misapprehensions so commonly encountered. The familiar allusion to infection commonly associated with crowns may be dispelled by adhering to the concept,s of pulpal and gingival health. The complete protection afforded by the full crown is the safest and surest foundation upon which large and involved dental restorations may be built. Neither patient nor dentist should risk extensive replacements on inlays or three-quarter crowns in mouths where the caries frequency is high. The well-executed full crown is a restoration worthy of the confidence of both patient and dentist.
IS THE PLACE OF THE FULL IN RESTOR,ATIVE DENTISTRY?
GILBERT
P.
SMITH,
D.D.S.,”
NEW
YORK,
CROWN
N.
Y.
T
HE full gold crown is one of the oldest devices used in restorat,ive dentistry and through its evolution has served the profession and the public well Although gold crowns were found in tombs of ancient Italy and the Easi Tndies,t the first dentist credited with using them was C. Mouton in 1740 In 1873, J. H. Beers patented a gold-banded crown with swaged cusps; in 1907, Taggart’s casting process was introduced into dentistry and it was soon applied to the full crown. The succeeding years brought refinements to the techniques of the full crown until now it is possible to fabricate one that meets t,he requirements of modern restorative dentistry. Throughout its history the full crown has had its champions and its opponents. We are all familiar with the poorly fitting, overextended, carelessly contoured crowns seen in so many mouths, and their common associatesinflamed, proliferated, and infected tissues. Ready-made crowns carelessly fitted over insufficiently prepared stumps have taken their toll in the loss of countless teeth. Is it any wonder that in many minds the full crown has fallen into disrepute; that many physicians immediately question any gold seen in the mouth? We all, however, have seen well-contoured crowns with accurate marginal fit that, have served for years, the tooth and surrounding tissue in a state of health. To many, the full crown is a “means of last resort” rather than an “instrument of choice.” What is the place of the full crown? Is it a restoration A disto be avoided if possible or is it the’ answer to many of our problems? cussion of it.s advantages, disadvantages, and use should help to answer these questions. The full veneer crown has a number of advantages over any other individual tooth restoration. One advantage is that no other restoration is as complete a protection to t,he tooth from the inroads of caries as is the full crown. By virtue of its complete coverage and a tight peripheral fit beneath the free gum margin, it seals off the tooth as effectively as is possible and prevents caries from recurring at any point but below the gingival margin, an area rarely susceptible. The cavosurface margin has been reduced to the shortest possible length in proportion to the surface covered. In the case of multiple Presented
lumbia The
*l?mfeSSor
before of
University. ?Tylman, S. D.: C. V. Mosby Co.,
the Bronx-Northern Dentistry, School Theory pp. 1-14.
and
of
Practice
Dental Society, Dental and Oral of 471
Crown
and
March Surgery,
20, 1947. Faculty
Bridge
Prosthesis,
of St.
Medicine,
Co-
Louis,
1940,
472
Gilbert
P. Smith
cavities in an ipdividual tooth, many operators go to great lengths to place separate fillings whose total eavosurface margins are several times greater in length and are in more susceptible areas than that of the full crown. How much more simple it would be to fit a full crown and how much more permanent a restoration it would be ! Another marked advantage of the full crown is its retentive properties. Its complete coverage of the tooth in conjunction with close adaptation to closely paralleled walls of the preparation gives it a degree of retention unequaled by any other restoration. By completely enveloping the tooth, the crown holds together the portions weakened by the inroads of caries to form the strongest possible abutment for a bridge. The inlay, on the other hand, depends upon the strength of remaining portions of the tooth to resist fracture for its retention. The three-quarter crown derives it,s retention from a partial envelopment of the tooth. The margins of inlays, particularly the indirect slice type, and of three-quarter crowns are susceptible to spreading upon application of excessive stresses. The breaking down of cement that accompanies the opening of these margins leads to development of caries, loosening and failure of the bridge. The full crown is immune from this type of distortion and cement beneath it is free from fracture. A third advantage is that no other type of tooth restoration affords the opportunity to improve existing undesirable contours and ocelusal relations as does the full crown. The importance of these factors is well recognized in modern restorative dentistry. The individual tooth is no longer an entity in itself but must be considered in the light of its relation to the mouth as a whole. By virtue of its envelopment, the full crown provides a new contour for the tooth-a form completely subject to the manipulation of the operator. Tipped, tilted, or rotated teeth can rarely be brought into harmonious relation with their neighbors by means of partial restorations. A fourth advantage of the full crown is that its preparation, fabrication, and placement are relatively simple routine procedures. Tooth preparation has been reduced to a definite technique. Accurate impressioning results in a completely indirect method for construction and inaccuracies in the process of fitting and setting are reduced to the minimum. A fifth advantage is pulp protection and preservation of tooth structure, important attributes of the full crown. Adequate cement lining within a full crown provides excellent thermal insulation to the pulp. Tooth crowns weakened structurally by caries to the extent that fillings could no longer be retained can often be crowned and preserved as healthy units. In discussing the disadvantages of the full gold veneer, the first is the excessive display of metal. This is a problem on all anterior teeth and the upper bicuspids and first molars. On the average lower posteriors, the occlusal is the only portion visible in the normal range of lip movements-an area where the metallic display of the full crown varies little from that of the large inlay or three-quarter crown. In teeth where appearance is a factor, the recent innovation of the acrylic veneer facing incorporated in the metal makes an aesthetic restoration comparable with the three-quarter crown.
Full
Crown in Itestorative
Dentistry
The second disadvantage is the excessive reduction of sound tooth structure necessary to permit extension of the margin into the gingival crevice and accurate gingival fit. In this case, the full crown should be used only where other type restorations fail to meet the requirements and the full crown is the only one that is adequate. The third disadvantage of the full crown is that it prevents the use of the electric pulp tester. Since other restorations leave a portion of the tooth surface exposed, it is usually possible to apply the electrode to them in a manner suitable for testing. The full crown must be removed to make such a test. The fourth disadvantage of the full crown often cited is gingival irritation. This is not a just criticism. The carefully fitted crown is no more irritating to the gingival tissues than is the carefully fitted inlay. To further consider the place of the full crown in restorative dentistry it would be, well to consider its many uses. The first and most universal is as a simple restoration for missing tooth structure. The second common use of the full gold crown is as a bridge abutment. It provides the strongest retention of any type of abutment available and in many respects is the most satisfactory. Dr. E. T. Tinker,* though the leading exponent and father of the modern three-quarter crown, stated that the full crown was the ideal fixed bridge abutment and that the more he saw of bridgework the more he used it. This has been echoed by a number’of competent prosthodontists, A third use for the full crown is in conjunction with removable partial dentures. The abutment teeth for a partial denture should be prepared for the reception of stabilizers and retainers. Occlusal rests are more efficient and distribute stresses more advantageously when they are recessed within the contours of the tooth to which they are applied. The normal axial contours of abutment t,eeth often present surfaces unfavorable for retention by clasp arms and for stabilizing contacts. Full crowns present an ideal medium for providing for the recessed rests, for recontouring axial surfaces, and for providing surfaces for denture contact not subject to dental caries. A fourth use of the full crown is in large occlusal reconstruction and mouth rehabilitation cases. The full crown is the best individual tooth restoration for meeting the demands of occlusion, caries prevention, and tooth support. A fifth use of the full crown is as a splinting medium. Very often the demands of occlusion combined with weakened alveolar support require that teeth be tied together for mutual st,rength. The difficulties of fitting, finishing, and cementing multiple inlays are more hazardous than those of multiple crowns. Two or more full crowns soldered together are an efficient and practical means of splinting teeth where required. To further evaluate the full crown, it is well to consider its requisites. What should an acceptable full crown do 8 First, it. should restore missing tooth structure. Caries and all questionable fillings should be completely removed and replaced with suitable base *Personal
communication.
474
Gilbert
P. Smith
material. The crown should cover and extend gingivally beyond all cavity margins into contact with sound tooth structure. Second, a good full crown should restore the tooth to proper occlusion. By reshaping teeth with crowns in indicated cases, faulty occlusal relations can be brought into harmony with the general occlusal pattern of the mouth. Where the occlusion is heavy and the imbedded-root-to-exposed-tooth ratio is disproportionate, the occlusal surface may be reduced in buccolingual width, thus preventing the overloading of the periodontal tissues. Marginal ridges should be re-established in conformity with those of the neighboring teeth. Third, the crown should provide harmonious axial contours. Proximal surfaces should be so shaped as to form interproximal embrasures large enough so that impingement on the interseptal tissues is eliminated. The occlusal sluiceways should blend into the proximolingual and buccal surfaces to provide pathways for the escape of food particles during chewing, reduce occlusal stresses, and thus maintain the health of the septal tissues. Buccal and lingual surfaces should blend into the occlusal contours to produce normal tooth form as closely as possible. Crowns are often placed on teeth when pronounced recession has taken place and they must be extended below the existing free gum margin. This results in a crown longer than the original anatomical crown. The contour of the crown near the gingival tissue is important. Normally, the form of the tooth serves as a protection to the free gingivae. The curvature is greatest on the buccal of lower posteriors but is characteristic of most axial surfaces. On the buccal of lower mola.rs the height, of contour is relatively low and the convergence below this region is fairly marked. This results in a form that is protective to the gingival cuff in that it causes food passing by this point to be diverted off on the buccal side. If this contour is excessive, the gum tissue is not benefited by the detergent action of food and results in an inflammation. If there is insufficient contour, the gum cuff is poorly protected and food particles produce irritation and possible stripping of the gingival tissue resulting in gingival recession. It is important that optimum contour of the crown be established in proper relation to the existing gingival margin. The remainder of the axial surface should blend from this region to the occlusa1 surface. Fourth, properly placed contact, which is positive, should be established with adjoining teeth. We are all familiar with the conditions resultant from inccrrectly placed light contacts. Food impaction, periodontal pockets, mobile teeth and cavities are all too common sequelae. Fifth, accurate marginal gingival fit is essential for all full crowns. It is as important for the margin of a crown to fit properly as it is for any other tooth restoration. Margins placed under the gingivae should be explored for accuracy as carefulIy as those placed above the gingivae, regardless of the type of restoration. What is a proper and accurate margina. fit for a full crown? It should extend into the gingival crevice-experience has taught us that this is an area relatively free from caries and that the gum cuff renders a certain amount of protection. A crown should cover a11 cut tooth surface and should not be
Pull
Crown in Restoratilqe Dentistry
short of the preparation. Ground tooth surfaces present irregularities that invite t)he occurrence of caries and are irritating to gingival tissue. The margin of the crown should be in close contact with the gingival surface of the tooth and no overhang should exist. This does not mean that the margin is undetectable to the explorer; if the previously ment,ioned concept of contour is accepted, a change in contour at the junction of the crown and tooth is inevitable in many instances, It does mean that the explorer point should not be able to go under the crown. The margin of the crown should be even, finished to a knife edge, polished and protected by the gingivae. Sixth, a full crown should provide adequate pulp protection. Overheating of the tooth during grinding must be zealously avoided. Constant application of a stream of tepid water should be routine. Between appointments prepared teeth should be given the protection of temporary caps filled wit,h a sedative paste and the final cementation should be made with a nonirritating mixture of cement preceded by a careful toilet of the prepared stump. When the prepared surface is sensitive to heat and cold, the interior of the crown above the gingival margin may be relieved to provide room for an insulating layer of cement. Seventh, a full crown should provide adequat,e retention. Approximate parallelism of the surfaces of the preparation provides a.mple retention in most cases. Occasionally extremely short or conical teeth present problems in retention but these may be met by preparing parallel axial grooves in the preparation or by the use of ocelusal boxes or pins. In general, the full crown’s retentive powers are ample to meet any demands placed upon it. In discussing the full crown, some reference should probably be made to operative procedures. The first step, the preparation of the tooth for the reception of the crown, can be reduced to a simple routine-mesial and distal slices, buccal and lingual surface reduction, rounding of the line angles, and occlusal clearance. Each step, if executed precisely and completely, results in a preparation being made quickly without waste motion. The surfaces should be smooth, the gingival margin regular and even, and no undercuts should be allowed to remain on the a,xial contours. A carefully finished preparation is the first step in developing a successful crown. The full cast crown is superior to other types which depend upon the adaptation of wrought metal for gingival fit ; namely, the banded cast contour or the swaged crown. This use of wrought metal is usually a direct procedure and permits only limited adaptation. If done indirectly, where swaging is possible, it presents no advantages over the casting process. The full cast crown has been developed to the point where it now is used almost universally when a full gold crown is indicated. The fabrication of a full cast crown is an indirect procedure having the inherent benefits of reducing chair time for the operation and inconvenience for the patient, The fabrication of a direct full crown wax pattern is a difficult procedure fraught with the danger of incorrectable disfortion. Combinations of the direct and indirect procedures introduce unnecessary possibilities for error and negate the advantages of fitting and finishing tipon,:a
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die. A completely indirect procedure permits more accurate control of crown form and fit. The second step in the development of the full crown is the impressioning of the preparation. The accuracy of the fit of the crown depends upon the impression. No other step in construction has more effect on the success of the restoration or is more critical. Perfection in the procedure is mandatory to completion of a satisfactory crown. Probably no step offers more opportunities for advancement than does the taking of an accurate abutment impression. It is a trying procedure and taxes one’s ingenuity. In no other step is misinterpretation so probable. What a boon it would be to have a simple, easy, accurate method for obtaining the impression of a tooth. The impression procedure currently used by the writer uses a low-heat, fine-grained compound confined in a carefully adapted copper band. Meticulous fitting, shaping, and trimming of the band are essential. ’ Step No. 1.-A band is selected that fits fairly snugly on the preparation but does not bind-undersize is preferable to oversize, for the band can be stretched. In trying the band and in taking the impression the band is always inserted and held with its long axis coinciding with that of the preparation. Fitting the band in one inclination and then taking the impression with the band held in another inclination defeats the usefulness of the fitting. Step No. 2.-The band is reshaped from a round cross-sectional form to that of the cross-sectional form of the gingival portion of the preparation. This is most easily done with a fully annealed band. Step No. 3.-The gingival margin of the band is festooned by trimming it until it contacts the gingival tissue in its entire circumference simultaneously when the band is inserted parallel to the axis of the preparation. At this stage the band should slide to place easily on the tooth without binding and with a slight space between it and the gingival periphery of the preparation. It should slip between the free gum margin and the tooth. If it is too snug, it may be stretched; if it stands away at points, these portions may be crimped closer to the tooth. Step No. 4.-A small layer of compound is seared to the inside of the gingival end of the band and seated on the tooth for a trial impression of the gingival margin. It is chilled slightly, removed, and examined. An imprint of the gingival margin should be visible. If it is not and the band was seated properly, it most likely indicates that the festooning of the band is incorrect. To correct the festooning further, the band is reduced at all edges where the impression of the margin of the tooth preparation is visible ; do not trim where the margin cannot be seen. The impressioning and trimming is repeated until the complete tooth margin is visible in the trial impression. Step No. 5.-The band is filled with evenly softened compound and seated on the tooth. This step requires skill that can be developed only by experience. Seating of the band parallel to the axis of the preparation, control of excess compound by forcing it out ahead of the band, relief of pressure and excess material from the occlusal end of the band, avoidance of folds or wrinkles,
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and complete seating of the band are all to be accomplished in one continuous deft movement. Step No. 6.-The impression is cooled in place under pressure and without movement once the insertion stroke is completed. Sufficient time is allowed to ensure dissipation of heat from throughout the body of compound in the impression. Xtep No. 7.-Removal of the impression must be by direct pull in line with the axis of the preparation. Any rocking, twisting, or tilting in withdrawing the impression will result in its distortion and a misfit crown. The impression when completed should be carefully checked for inaccuracies in preparation, such as complete marginal registration, wrinkles, fractures, drawn surfaces, evidence of calculus remaining on the tooth, and gingival tissue trapped within the band. Rarely is it impossible to distinguish the limits of a preparation. Cut or ground surfaces can be discerned from uncut surfaces in an accurate impression even though in the same plane. If the impression is incomplete it should be discarded and another taken without hesitation. Once an accurate impression has been obtained, care must be taken to preserve the accuracy throughout the fabrication of the crown. Careless handling of the die, wax pattern, or casting may invalidate all effort expended in developing the accurate impression. The copper-plat,ed die has proved superior to other types of dies. It requires less time to make than does the amalgam die and is less susceptible to loss of detail during handling. The cutting of a groove on the die 0.5 mm. below the margin of the preparation and 0.5 mm. deep facilitates trimming of the margin in both the wax pattern and the casting. A large inverted cone bur (No. 39 or 40), pointed toward the gingival margin, may be used to cut this groove on the base of the die, The tendency for beginners using this technique is to cut too close to the margin and to try to work too accurately. The groove acts as a guide for the blade in trimming the gingival margin of the wax pattern and greatly simplifies this step. After the casting is seated on the die, the groove is again used to finish the gingival margin. By reversing the direction of approach of the bur, so that it points toward the base of the die, both casting and die are carefully cut back to the exact margin of the preparation. This gives a perfection of fit to the margin limited only by the accuracy of the contributing steps. Disks, rubber wheels, and polishing agents are then used to finish the contour of the crown in harmony with the tenets out,lined earlier in this paper. Full crowns constructed along these lines are tolerated well by mouth tissues and provide t,he safest possible protection for the tooth from dental caries. SUMMARY
What is the place of the full crown in restorative dentistry? It is the foundation of good fixed bridgework. It is a restoration which, when properly used, completely restores a tooth by providing ideal oeclusal, proximal, and
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gingival relations, and the acme of protection to the tooth from caries. It has the greatest margin of tolerance of any restoration-full crowns constructed with the same degree of skill are less susceptible to failure than are threequarter crowns or inlays. It is not the wish of the essayist to convey the opinion that the full crown should supersede all other types of retainers or individual tooth restorations. It is rather to indicate a more intelligent approach to the use of the full crown. A full appreciation of its merits and limitations by dentists and public alike will allay the misapprehensions so commonly encountered. The familiar allusion to infection commonly associated with crowns may be dispelled by adhering to the concept,s of pulpal and gingival health. The complete protection afforded by the full crown is the safest and surest foundation upon which large and involved dental restorations may be built. Neither patient nor dentist should risk extensive replacements on inlays or three-quarter crowns in mouths where the caries frequency is high. The well-executed full crown is a restoration worthy of the confidence of both patient and dentist.