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Condensation of Porcelain for Jacket Crowns*
Co n d e n s a t i o n o f p o r c e l a i n f o r j a c k e t CROWNS* By ALVER SELBERG, D.D.S., M inneapolis, M inn. H E w orld is indebted to F auch ard , G uillim eau and o th e r contem porary dentists of th e eighteenth century fo r the invention and introduction of artificial teeth m ade from m ineral paste or porcelain. T h e contribution of these men has had a far-reaching effect on den tistry, and in the profession, th e ir names may fitly hold a place of honored rem em brance. P revious to the eighteenth century, ivory and various anim al substances w ere used fo r this purpose, b u t all of these w ere rapidly discarded fo r th e m ore n a tu ra l and superior porcelain tooth. F rom the eighteenth century on, this phase of dentistry has seen m any changes, relative to shading, tooth form and stru c tu re in general, and, as a substitute for lost or broken dow n teeth (w herever in dicated ), nothing to d ate has taken its place. A ccordingly, much is in store for those w ho seek the highest a r t in dentis try, a field th a t is only in its infancy, w ith unlim ited possibilities w hen w e realize how m uch can be accomplished in b rin g ing about perfection w ith sim plicity.
T
T h e prim ary purpose of any porcelain tooth in the m outh is substitution w ith o u t detection. A s there are no pits and air pockets in the body of or on the surface of the n a tu ra l tooth, it is reasonable to
*Read before the Section on Partial Den ture Prosthesis at the Seventy-Second Annual Session of the American Dental Association, Denver, Colo., July 24, 1930. Jour. A . D . A . , July, 1931
assume th a t the closer to com plete conden sation w e arriv e in porcelain w ork, the m ore n a tu ra l in appearance w ill the fin ished product be. M agnified, th e perfect piece of porcelain should present a felted mass of m inute crystalline rods imbedded in a m ore glassy substance. O n ly by form ing some such m ental picture, w hich is in harm ony w ith the know ledge ob tained by a microscopic exam ination of th e m aterial, can w e un d erstan d w herein th e real beauty of porcelain resides. T h e question of the glaze, or surface finish, holds an extrem ely im portant place, fo r this is the distinctive m ark of the finest porcelain an d the source of its subtle beauty. In tru e porcelain, th e glaze is composed of m aterials analogous to those used as the fusible ingredients of the paste and as such m aterials a re refractory, they need to be fired a t the same high tem peratu re required to porcelainize the body. U n d e r such circum stances, w e can readily un d erstan d the place condensation of the body of porcelain plays in produc ing th e velvety tone and deep richness found in the p erfect piece. W h e n lig h t falls on a piece of tru e porcelain, it penetrates the layers w hich, so to speak, filter, soften an d subdue it, so th a t th e low est depths shim m er and glisten w ith the lig h t reflected to the observer’s eye th ro u g h successive en velops of m ore tran slu cen t substance. W e can then u n d erstan d th a t a porous body of porcelain w ill, in like m anner, reflect
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T h e Journal of the A m erican D en ta l Association
the air pockets, pits and voids through the glaze to produce a glassy, frosted ap pearance instead of the smooth, solid finish found in the n atu ra l teeth. T h e voids and flaws in the body of the porce lain w hen glazed w ill only be accentu ated, and the m inute bridges of the glaze over the air pockets fractu re to form crypts, w hich collect residue and appear as black specks in the surface. T h erefo re, to arrive at the finest in porcelain, the
much for th e uncondensed body. U n doubtedly, then, condensing of the m in eral body plays an im p o rta n t role, as it aids m aterially in controlling the sh rin k age caused by the fusing. T h is is a great aid in establishing m arg in al fits, fo r both crow ns and inlays. T e sts m ade on baked cubes or porce lain 9 mm. square showed a crushing strength of 65,200 pounds per u n it (square inch) for th e condensed porce-
Fig. 1.—Amalgam die for jacket crown.
Fig. 2.—Part of porcelain placed on die.
body m ust be a dense homogenous mass, because, in reality, it enters into' and be comes p a rt of the glaze. C ylinders of equal size, m ade of high fusing m ineral paste, showed a shrinkage of from 13 mm. to 12 mm. in diam eter for the condensed porcelain ; w hereas, the cylinder built up by the ordinary m ethods shrank to 11 mm. in diam eter. T h e re is a shrinkage of approxim ately tw ice as
lain, and 55,910 pounds for porcelain m ade in the o rd in ary w ay. T h is is an in crease in stren g th of nearly 10,000 pounds per u n it (sq u are in c h ). S tren g th in ceramics is obviously of g reat value. T h e object of this paper is to call the attention of the profession to an existing condition of im perfection in dental ceramics w hich is obvious to m ost of us, nam ely, pits, voids and air pockets found
1317
Selberg— Condensation of Porcelain in the body and surfaces of the jacket crowns, as w ell as in m ost other porcelain restorations now used in dentistry. I t w ill undoubtedly be conceded th a t the foundation of the finest porcelain has basic quality in condensation. I t is w ith this th o u g h t in m ind th a t this paper is pre sented, and, for th a t reason, m inor points
pared for the reception of the crow n. A m odeling com pound impression of the prepared tooth is taken in a copper band. T w o plaster impressions of the p rep ara tion should include several adjacent teeth. T h e reason for the second impression w ill be brou g h t o u t later. A m odeling com pound impression of opposing teeth is then taken. T h e copper band impression of the pre pared tooth is packed w ith am algam , and a brad driven into it w hile still soft. W h e n the am algam is set, the die is trim m ed dow n, as is generally done, and the head of the brad cu t off approxim ately
Fig. 4.—Celluloid tooth form on model. 'C'
Fig. 3.—Celluloid tooth form placed on die. in the construction of porcelain jacket crow ns w ill not be discussed in detail. Before sta rtin g w ork, a m odeling com pound impression should be taken. W h en flowed up w ith plaster, this w ill serve as a study model as w ell as show ing results before and afte r. T h e tooth is then pre
one-fourth inch below the am algam . (F ig . 1.) T h e die is seated in one of the plaster impressions of the case, and flowed up w ith plaster for the cast. W h en set, it is separated, trim m ed and m ounted w ith the bite for articu latio n . A platinum m atrix is burnished and trim m ed so as to have an apron of about 2 mm. Porcelain selected for the gingival shade is padded on a t a 45 degree angle from the gingival m argin up to the w all of the preparation. T h e rem ainder of the preparation is covered w ith a thin layer of porcelain applied w ith a small brush.
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F ig. 5.— C on d en sin g m achine.
Selbe’-g— Condensation of Porcelain (F ig . 2 .) I t is then fired to a high biscuit bake. T h is then serves to make an air-tight m atrix, w hich is im perative in this method of building a crow n, for if there is an escape of air thro u g h the m atrix, it w ill tend to form air pockets in the body of the crow n. I t also keeps the porcelain from flowing between the die and the m atrix d u rin g its condensation. T h e col la r of the porcelain a t the gingival aspect
1319
or occlusal aspect of the crow n. T h is p ro vides a reservoir for excess w ater and for the settlin g of the porcelain d u rin g its condensation. (F ig . 3.) T h e die is now used in the second im pression of the case, and the plaster cast is m ade. W h e n this is separated, the con tact surfaces of the adjacent teeth are removed approxim ately 1.5 m m . T h is second m odel serves tw o purposes: first,
Fig. 6.—Completed crown. controls the shrinkage and prevents dis to rtion of th e m atrix. T h e m atrix, w ith the biscuit bake, is placed on the die and a collar of sticky w ax is run over the apron of the m atrix 0.5 mm. from the shoulder. T h e celluloid tooth form , or tube, is now contoured at the gingival and attached to the sticky w ax. T h is m a trix should extend about one-fourth inch over the finished incisal
providing a guide for establishing alinem ent w hen the celluloid tooth form is attached on the d ie ; and, secondly, allow ing the overbuilding of contact surfaces to com pensate for th e shrinkage of the porcelain w hich takes place during the firing. (F ig . 4 .) T h e die w ith the celluloid m a trix is now placed in the condensing machine, w here it is held by the brad w hich fits
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into the pin vise of the condenser. T h e m achine show n in F ig u re 5 is ru n by a m otor or lathe, so constructed as to cause a sudden ja r w hen the plunger w hich holds the die is forced onto a cam having tw o drop-off steps. T h e porcelain is m ixed thoroughly on a slab as is usually done. T h e shades of porcelain corresponding to the teeth to be m atched are then placed in the cellu loid m a trix and blended w ith a sm all b u t long bristle brush. W h e n th e m a trix is filled, the condensing m achine is then sta rted and ru n a t a speed w hich w ould cause 200 or 300 drops to appear per m in ute. T h e ja rrin g caused by this packer brings the m oisture, bubbles and m any im purities to the surface, w here they are removed by blottin g at intervals w ith a dry tow el. T h e technic of b u ild ing a crow n m ay be different from th a t described abo\e, this depending on the shading and blending desired. W h e n m oisture stops rising to the su r face, the die is removed from th e m a chine. T h e celluloid m a trix is then slit w ith a sm all sharp lance, a fte r w hich it is removed. T h e sticky w ax on the apron of th e m a trix is then cu t or chipped off, and the die placed back in the cast, w hich has had the contact surfaces removed. I t is th en carved to approxim ate form and is rem oved from the die and fired to a high biscuit bake, afte r w hich it is ground to contact and occlusion in the accurately m ounted casts. W h e n the baking is com pleted, the p latinum apron is trim m ed off at the gingival aspect and the crow n placed in the m outh, w here th e finer m arkings, contact points, etc., are verified. T h is procedure being com pleted, the crow n is ready for glazing, a fte r w hich the m atrix is rem oved and the inner surface etched w ith hydrofluoric acid. F ig u re 6 shows the com pleted crow n.
T h e shade of cem ent used in setting a crow n is of extrem e im portance, for, by using the w ro n g cem ent, an otherw ise perfect shade of the crow n m ay be a l tered. F o r this reason, it is advisable to test the shades by m ixing the pow der w ith w a te r and try in g th e crow n in the m outh before the final setting. C O N C L U S IO N
R ealizin g an existing condition of im perfection in th e tex tu re of porcelain and know ing th e im portance of tex tu re as a factor in esthetics, stren g th , and com patibility of the tissues involved, I am subm itting this m ethod of obtaining con densation in porcelain jack et crowns. T h e g reatest crushing stren g th of porcelain is attain ed w hen it has been fired 200 degrees below its fusing point. I t has been found th a t a n a tu ra l surface finish of a condensed crow n can be a r rived at a t from 20 to 40 degrees less th an in the crow n m ade in the o rdinary m anner. T h is is then a factor in gaining g rea ter stren g th in the cro w n and largely elim inating th e possibility of b u rn in g out the coloring ingredients and overglazing the porcelain a t th e tim e th a t it is fused. A fte r g lazing is com pleted, often cor rections, such as the g rin d in g of contact points and m odification of th e length, are necessary. T h is m ay be done w ith o u t re glazing the crow n, for a high finish can be obtained by polishing w ith disks or pumice. T h is gives a surface as beauti fu l as th e original glaze. T ests m ade show a shrinkage approxi m ately tw ice as g reat fo r the uncon densed as fo r the condensed body of porcelain. I t is, therefore, desirable to get condensation, as it aids in securing m arginal fittings. In a n a tu ra l tooth, th ere are no pits or airpockets. F o r this reason, it is obvi ous th a t the denser the porcelain, the
Selberg— Condensation of Porcelain b etter the chance for harm ony and blend ing w ith adjacent teeth. F ro m tests m ade on baked cubes of porcelain 9 m m . square, it w as found th a t condensed porcelain showed a crush ing stren g th of 65,200 pounds per u n it (square inch) and 55,910 pounds for porcelain m ade in the ord in ary w ay, an increase in strength of approxim ately 10,000 pounds per u n it (square in c h ). S tren g th is obviously of g reat im portance in ceramics. I t is through this branch of dentistry, w hich represents the highest a rt in the profession, th a t extrem e satisfaction can be obtained both by th e dentist and those seeking this type of service. I t is my hope th a t this simplified m ethod of condensa tion w ill stim ulate interest and result in a g rea ter endeavor to a ttain perfection. D I S C U S S IO N
This method is very similar to the one described by Dr. LeGro, except that he uses a paper instead of a celluloid matrix. The trouble with that method has been in the shaving and blending, especially in the anterior teeth. It is very satisfactory for posterior teeth. There is no question that one can get a very thor ough condensation of porcelain. I would like to have Dr. Selberg tell us how he would handle the anterior crown, in order to blend the shades properly. L. E. M y ers, O m aha, N ebr.: Dr. Selberg offers something new, and very different from any other method that we have had in con densation of porcelain. Dr. Selberg arrived at each point definitely and concisely. I ques tion whether it is necessary to go to all of this trouble to get condensation of porcelain. It is true that generally the condensation of porcelain is very poor, leaving it very porous. It seems to me that in our recent practice with ceramics, we are getting much better con densation by sucking out the moisture in the porcelain, than we used to. I believe that the old technic in the condensation of porcelain was to burnish with a spatula. Next came the whipping with a sable hair brush. In our present method of condensation, we use A . O. K la ffen b a ck, Io w a C ity, Io w a :
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porcelain very moist, almost in a running stage. We apply it to the matrix, and dip it into some dry porcelain powder. This acts the same as the condensation of the sand on Daytona Beach, the race track for auto mobiles. That is, the suction of the water out of the sand condenses it until we have a per fect race track. The same is true with porce lain. In our office, we use this method, also the sable hair brush. By sucking the moisture out, and then condensing by whipping with the brush and repeating the suction of the moisture, we find that we can get a condensa tion of the porcelain that makes it very easily handled. In fact, we can drop it on the floor, and practically no porcelain comes off. I may be wrong, in regard to Dr. Selberg’s first step of covering the matrix with porcelain. It seems to me that, in order to stop the draw ing of that porcelain, one would get a slight drawing of the matrix. I have not tried that. The three-cornered apron, built up to the side of the matrix is unquestionably a good idea. I also agree to bringing the first bake to a high biscuit, which not only shuts out the air pockets, but also minimizes the shrink age of the porcelain. I gather that Dr. Sel berg bakes this in two operations. It seems to me that is a little too quickly. We use three bakes at least in our office. Dr. Selberg (closing): I usually place shellac on the first baking of porcelain. That allows the shrinkage to take place upward, and I take that into consideration. Regarding the shading for anterior teeth, that can be done by successive bakings, by glazing, with a celluloid matrix, and placing the gingival glaze on and baking it and removing it. Then the incisal color can be placed, and the model made in the same way by placing the sticky wax on the gingival portion and build ing the celluloid matrix and baking that. For the incisal shades, I cut away to the con vexity, and usually the shade runs up to the mesial and distal aspects of the teeth. I then take a wafer of wax, press it against the lingual aspect of the crown and bring it up around the crown on the incisal aspect, and that leaves two folds on the mesial and distal corners. I pinch the wax and foil together and trim it so it is 2 mm. high. Thus a pan is formed which has the wax on the side and the labial surface as a base. I can place the incisal color, hold it in the machine, peel off the wax and bake it.
T
T h e prim ary purpose of any porcelain tooth in the m outh is substitution w ith o u t detection. A s there are no pits and air pockets in the body of or on the surface of the n a tu ra l tooth, it is reasonable to
*Read before the Section on Partial Den ture Prosthesis at the Seventy-Second Annual Session of the American Dental Association, Denver, Colo., July 24, 1930. Jour. A . D . A . , July, 1931
assume th a t the closer to com plete conden sation w e arriv e in porcelain w ork, the m ore n a tu ra l in appearance w ill the fin ished product be. M agnified, th e perfect piece of porcelain should present a felted mass of m inute crystalline rods imbedded in a m ore glassy substance. O n ly by form ing some such m ental picture, w hich is in harm ony w ith the know ledge ob tained by a microscopic exam ination of th e m aterial, can w e un d erstan d w herein th e real beauty of porcelain resides. T h e question of the glaze, or surface finish, holds an extrem ely im portant place, fo r this is the distinctive m ark of the finest porcelain an d the source of its subtle beauty. In tru e porcelain, th e glaze is composed of m aterials analogous to those used as the fusible ingredients of the paste and as such m aterials a re refractory, they need to be fired a t the same high tem peratu re required to porcelainize the body. U n d e r such circum stances, w e can readily un d erstan d the place condensation of the body of porcelain plays in produc ing th e velvety tone and deep richness found in the p erfect piece. W h e n lig h t falls on a piece of tru e porcelain, it penetrates the layers w hich, so to speak, filter, soften an d subdue it, so th a t th e low est depths shim m er and glisten w ith the lig h t reflected to the observer’s eye th ro u g h successive en velops of m ore tran slu cen t substance. W e can then u n d erstan d th a t a porous body of porcelain w ill, in like m anner, reflect
1315
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T h e Journal of the A m erican D en ta l Association
the air pockets, pits and voids through the glaze to produce a glassy, frosted ap pearance instead of the smooth, solid finish found in the n atu ra l teeth. T h e voids and flaws in the body of the porce lain w hen glazed w ill only be accentu ated, and the m inute bridges of the glaze over the air pockets fractu re to form crypts, w hich collect residue and appear as black specks in the surface. T h erefo re, to arrive at the finest in porcelain, the
much for th e uncondensed body. U n doubtedly, then, condensing of the m in eral body plays an im p o rta n t role, as it aids m aterially in controlling the sh rin k age caused by the fusing. T h is is a great aid in establishing m arg in al fits, fo r both crow ns and inlays. T e sts m ade on baked cubes or porce lain 9 mm. square showed a crushing strength of 65,200 pounds per u n it (square inch) for th e condensed porce-
Fig. 1.—Amalgam die for jacket crown.
Fig. 2.—Part of porcelain placed on die.
body m ust be a dense homogenous mass, because, in reality, it enters into' and be comes p a rt of the glaze. C ylinders of equal size, m ade of high fusing m ineral paste, showed a shrinkage of from 13 mm. to 12 mm. in diam eter for the condensed porcelain ; w hereas, the cylinder built up by the ordinary m ethods shrank to 11 mm. in diam eter. T h e re is a shrinkage of approxim ately tw ice as
lain, and 55,910 pounds for porcelain m ade in the o rd in ary w ay. T h is is an in crease in stren g th of nearly 10,000 pounds per u n it (sq u are in c h ). S tren g th in ceramics is obviously of g reat value. T h e object of this paper is to call the attention of the profession to an existing condition of im perfection in dental ceramics w hich is obvious to m ost of us, nam ely, pits, voids and air pockets found
1317
Selberg— Condensation of Porcelain in the body and surfaces of the jacket crowns, as w ell as in m ost other porcelain restorations now used in dentistry. I t w ill undoubtedly be conceded th a t the foundation of the finest porcelain has basic quality in condensation. I t is w ith this th o u g h t in m ind th a t this paper is pre sented, and, for th a t reason, m inor points
pared for the reception of the crow n. A m odeling com pound impression of the prepared tooth is taken in a copper band. T w o plaster impressions of the p rep ara tion should include several adjacent teeth. T h e reason for the second impression w ill be brou g h t o u t later. A m odeling com pound impression of opposing teeth is then taken. T h e copper band impression of the pre pared tooth is packed w ith am algam , and a brad driven into it w hile still soft. W h e n the am algam is set, the die is trim m ed dow n, as is generally done, and the head of the brad cu t off approxim ately
Fig. 4.—Celluloid tooth form on model. 'C'
Fig. 3.—Celluloid tooth form placed on die. in the construction of porcelain jacket crow ns w ill not be discussed in detail. Before sta rtin g w ork, a m odeling com pound impression should be taken. W h en flowed up w ith plaster, this w ill serve as a study model as w ell as show ing results before and afte r. T h e tooth is then pre
one-fourth inch below the am algam . (F ig . 1.) T h e die is seated in one of the plaster impressions of the case, and flowed up w ith plaster for the cast. W h en set, it is separated, trim m ed and m ounted w ith the bite for articu latio n . A platinum m atrix is burnished and trim m ed so as to have an apron of about 2 mm. Porcelain selected for the gingival shade is padded on a t a 45 degree angle from the gingival m argin up to the w all of the preparation. T h e rem ainder of the preparation is covered w ith a thin layer of porcelain applied w ith a small brush.
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F ig. 5.— C on d en sin g m achine.
Selbe’-g— Condensation of Porcelain (F ig . 2 .) I t is then fired to a high biscuit bake. T h is then serves to make an air-tight m atrix, w hich is im perative in this method of building a crow n, for if there is an escape of air thro u g h the m atrix, it w ill tend to form air pockets in the body of the crow n. I t also keeps the porcelain from flowing between the die and the m atrix d u rin g its condensation. T h e col la r of the porcelain a t the gingival aspect
1319
or occlusal aspect of the crow n. T h is p ro vides a reservoir for excess w ater and for the settlin g of the porcelain d u rin g its condensation. (F ig . 3.) T h e die is now used in the second im pression of the case, and the plaster cast is m ade. W h e n this is separated, the con tact surfaces of the adjacent teeth are removed approxim ately 1.5 m m . T h is second m odel serves tw o purposes: first,
Fig. 6.—Completed crown. controls the shrinkage and prevents dis to rtion of th e m atrix. T h e m atrix, w ith the biscuit bake, is placed on the die and a collar of sticky w ax is run over the apron of the m atrix 0.5 mm. from the shoulder. T h e celluloid tooth form , or tube, is now contoured at the gingival and attached to the sticky w ax. T h is m a trix should extend about one-fourth inch over the finished incisal
providing a guide for establishing alinem ent w hen the celluloid tooth form is attached on the d ie ; and, secondly, allow ing the overbuilding of contact surfaces to com pensate for th e shrinkage of the porcelain w hich takes place during the firing. (F ig . 4 .) T h e die w ith the celluloid m a trix is now placed in the condensing machine, w here it is held by the brad w hich fits
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T he Journal of the American D ental Association
into the pin vise of the condenser. T h e m achine show n in F ig u re 5 is ru n by a m otor or lathe, so constructed as to cause a sudden ja r w hen the plunger w hich holds the die is forced onto a cam having tw o drop-off steps. T h e porcelain is m ixed thoroughly on a slab as is usually done. T h e shades of porcelain corresponding to the teeth to be m atched are then placed in the cellu loid m a trix and blended w ith a sm all b u t long bristle brush. W h e n th e m a trix is filled, the condensing m achine is then sta rted and ru n a t a speed w hich w ould cause 200 or 300 drops to appear per m in ute. T h e ja rrin g caused by this packer brings the m oisture, bubbles and m any im purities to the surface, w here they are removed by blottin g at intervals w ith a dry tow el. T h e technic of b u ild ing a crow n m ay be different from th a t described abo\e, this depending on the shading and blending desired. W h e n m oisture stops rising to the su r face, the die is removed from th e m a chine. T h e celluloid m a trix is then slit w ith a sm all sharp lance, a fte r w hich it is removed. T h e sticky w ax on the apron of th e m a trix is then cu t or chipped off, and the die placed back in the cast, w hich has had the contact surfaces removed. I t is th en carved to approxim ate form and is rem oved from the die and fired to a high biscuit bake, afte r w hich it is ground to contact and occlusion in the accurately m ounted casts. W h e n the baking is com pleted, the p latinum apron is trim m ed off at the gingival aspect and the crow n placed in the m outh, w here th e finer m arkings, contact points, etc., are verified. T h is procedure being com pleted, the crow n is ready for glazing, a fte r w hich the m atrix is rem oved and the inner surface etched w ith hydrofluoric acid. F ig u re 6 shows the com pleted crow n.
T h e shade of cem ent used in setting a crow n is of extrem e im portance, for, by using the w ro n g cem ent, an otherw ise perfect shade of the crow n m ay be a l tered. F o r this reason, it is advisable to test the shades by m ixing the pow der w ith w a te r and try in g th e crow n in the m outh before the final setting. C O N C L U S IO N
R ealizin g an existing condition of im perfection in th e tex tu re of porcelain and know ing th e im portance of tex tu re as a factor in esthetics, stren g th , and com patibility of the tissues involved, I am subm itting this m ethod of obtaining con densation in porcelain jack et crowns. T h e g reatest crushing stren g th of porcelain is attain ed w hen it has been fired 200 degrees below its fusing point. I t has been found th a t a n a tu ra l surface finish of a condensed crow n can be a r rived at a t from 20 to 40 degrees less th an in the crow n m ade in the o rdinary m anner. T h is is then a factor in gaining g rea ter stren g th in the cro w n and largely elim inating th e possibility of b u rn in g out the coloring ingredients and overglazing the porcelain a t th e tim e th a t it is fused. A fte r g lazing is com pleted, often cor rections, such as the g rin d in g of contact points and m odification of th e length, are necessary. T h is m ay be done w ith o u t re glazing the crow n, for a high finish can be obtained by polishing w ith disks or pumice. T h is gives a surface as beauti fu l as th e original glaze. T ests m ade show a shrinkage approxi m ately tw ice as g reat fo r the uncon densed as fo r the condensed body of porcelain. I t is, therefore, desirable to get condensation, as it aids in securing m arginal fittings. In a n a tu ra l tooth, th ere are no pits or airpockets. F o r this reason, it is obvi ous th a t the denser the porcelain, the
Selberg— Condensation of Porcelain b etter the chance for harm ony and blend ing w ith adjacent teeth. F ro m tests m ade on baked cubes of porcelain 9 m m . square, it w as found th a t condensed porcelain showed a crush ing stren g th of 65,200 pounds per u n it (square inch) and 55,910 pounds for porcelain m ade in the ord in ary w ay, an increase in strength of approxim ately 10,000 pounds per u n it (square in c h ). S tren g th is obviously of g reat im portance in ceramics. I t is through this branch of dentistry, w hich represents the highest a rt in the profession, th a t extrem e satisfaction can be obtained both by th e dentist and those seeking this type of service. I t is my hope th a t this simplified m ethod of condensa tion w ill stim ulate interest and result in a g rea ter endeavor to a ttain perfection. D I S C U S S IO N
This method is very similar to the one described by Dr. LeGro, except that he uses a paper instead of a celluloid matrix. The trouble with that method has been in the shaving and blending, especially in the anterior teeth. It is very satisfactory for posterior teeth. There is no question that one can get a very thor ough condensation of porcelain. I would like to have Dr. Selberg tell us how he would handle the anterior crown, in order to blend the shades properly. L. E. M y ers, O m aha, N ebr.: Dr. Selberg offers something new, and very different from any other method that we have had in con densation of porcelain. Dr. Selberg arrived at each point definitely and concisely. I ques tion whether it is necessary to go to all of this trouble to get condensation of porcelain. It is true that generally the condensation of porcelain is very poor, leaving it very porous. It seems to me that in our recent practice with ceramics, we are getting much better con densation by sucking out the moisture in the porcelain, than we used to. I believe that the old technic in the condensation of porcelain was to burnish with a spatula. Next came the whipping with a sable hair brush. In our present method of condensation, we use A . O. K la ffen b a ck, Io w a C ity, Io w a :
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porcelain very moist, almost in a running stage. We apply it to the matrix, and dip it into some dry porcelain powder. This acts the same as the condensation of the sand on Daytona Beach, the race track for auto mobiles. That is, the suction of the water out of the sand condenses it until we have a per fect race track. The same is true with porce lain. In our office, we use this method, also the sable hair brush. By sucking the moisture out, and then condensing by whipping with the brush and repeating the suction of the moisture, we find that we can get a condensa tion of the porcelain that makes it very easily handled. In fact, we can drop it on the floor, and practically no porcelain comes off. I may be wrong, in regard to Dr. Selberg’s first step of covering the matrix with porcelain. It seems to me that, in order to stop the draw ing of that porcelain, one would get a slight drawing of the matrix. I have not tried that. The three-cornered apron, built up to the side of the matrix is unquestionably a good idea. I also agree to bringing the first bake to a high biscuit, which not only shuts out the air pockets, but also minimizes the shrink age of the porcelain. I gather that Dr. Sel berg bakes this in two operations. It seems to me that is a little too quickly. We use three bakes at least in our office. Dr. Selberg (closing): I usually place shellac on the first baking of porcelain. That allows the shrinkage to take place upward, and I take that into consideration. Regarding the shading for anterior teeth, that can be done by successive bakings, by glazing, with a celluloid matrix, and placing the gingival glaze on and baking it and removing it. Then the incisal color can be placed, and the model made in the same way by placing the sticky wax on the gingival portion and build ing the celluloid matrix and baking that. For the incisal shades, I cut away to the con vexity, and usually the shade runs up to the mesial and distal aspects of the teeth. I then take a wafer of wax, press it against the lingual aspect of the crown and bring it up around the crown on the incisal aspect, and that leaves two folds on the mesial and distal corners. I pinch the wax and foil together and trim it so it is 2 mm. high. Thus a pan is formed which has the wax on the side and the labial surface as a base. I can place the incisal color, hold it in the machine, peel off the wax and bake it.