delity A. rt University

Sorensen, R.

Seghi,

of California,

of four methods

DMD,a DDS, School

Steve MSC of

and

K. Uri

Okamoto,

of swa

DDS,b

Yaroveskyd

Dentistry, Los Angeles, Calif.

The swaged metal matrix provides a method for rapidly making a metal substructure for ceramic crowns. This study determined the vertical and horizontal marginal fidelity of swaged metal substrate crowns made with four methods. No significant difference in vertical or horizontal marginal fidelity was found for metal margin crowns formed with either a plastic spacer or a paint-on die spacer. The vertical marginal fidelity was significantly better in crowns made with a metal margin (37 pm) than in crowns made with a porcelain facial margin (62 pm), and the latter were significantly better than crowns made with a 360-degree porcelain margin (86 am). Crowns made with all four methods were over-contoured by 46 to 82 pm. The 366degree porcelain margin was technically more difficult and timeconsuming to make. (J PROSTHET DENT 1992;67:162-73.)

number of alternative crown systemshave been developedin an attempt to improve on the traditional cast metal-ceramic restoration. Somesystemshave eliminated the metal substructure, thus exchanging improved esthetics for poorer strength. Others have retained the strengthconferring metal substructure but have modified the method of achieving a metal substrate. In 1978Shoher and Whitemanl introduced a non-cast metal coping technique whereby pleated patterns of high-content precious alloy are adapted to a stone die (Fig. 1). The metal substructure is composedof four layers of high-content preciousmetals that are pressedtogether under high pressureby the manufacturer. The RenaissanceCrown system (Williams Gold Co., Buffalo, N.Y.) forms a metal substructure from prefabricated umbrella-shapedpatterns that are cut, adapted, burnished, and swaged onto a master stone die. The preciousmetal coping is only 0.1 to 0.2 mm thick. According to the manufacturer a 15pm plastic sheetisplaced over the master die to provide a relief spacefor cement. Once formed, the metal substructure is heated in a flame, causing the solder to flow into the pleats and harden the substructure. Becausethe outer layer of the crown form is pure gold and hence no oxide layer will form, an interfacial alSupported Biomedical Research Md. Presented meeting, meeting, dontists emy of Ill. aAssistant bLecturer, CAssistant dCertified

in

part by BRSG SO7 RR05304 awarded by the Research Support Grant Program, Division of Resources, National Institutes of Health, Bethesda,

in part at the Pacific Coast Society of Prosthodontists Berkeley, Calif.; the Academy of Denture Prosthetics Monterey, Calif.; the American College of Prosthomeeting, Williamsburg, Va.; and the American AcadCrown and Bridge Prosthodontics meeting, Chicago, Professor and Director, Graduate Prosthodontics. Removable Prosthodontics. Professor, Operative Dentistry. Dental Technician, Da Vinci Dental Lab.

1011127302 162

Fig.

1.

RenaissanceCrown system pleated patterns.

loy isapplied and fired to provide for bonding of the opaque porcelain. Application of porcelain is then accomphshedin the usual fashion. When the user is properly trained and familiarized,

this

approach

to forming

a metal

substructure

requires considerably lesstime and equipment than the conventional lost-wax casting method. Several studies have demonstrated that the strength of a RenaissanceCrown is comparableto or better than that of all-ceramic crown systems.2,3Advantages with porcelain margins, such as superior esthetics and tissue response, have been discussedin the literature.*, 5 It wouid be advantageousif the benefits of the rapidly formed RenaissanceCrown metal substructure could be combined with the benefits of a facial or 360-degreeporcelain margin. Many approachesto the formation of a porcelain margin have been discussed. These include use of platinum foil,4, 6,7 refractory die,8-11and direct lift.12-15The directlift

technique

is probably

the

simplest

and

easiest

method

for forming an all-porcelain margin FEBRUARY

1992

VOLUME

67

NUMBER

2

SWAGED

METAL

CROWN

MARGINAL

FIDELITY

Fig. 2. Facial veiw of tooth preparation.

This study determined the marginal fidelity produced by four methods of making swaged metal matrix crowns: (1) metal margins formed with a plastic spacer, (2) metal margins formed with a paint-on die spacer, (3) a porcelain labial margin, and (4) a 360-degree porcelain margin. The study by JorgensenI in 1960, in which precementation and postcementation margin adaptation values were compared, suggested that hydraulic pressure developed at the occlusal surface may prevent complete seating of the casting, thereby increasing the marginal discrepancy. Further work by Jorgenseni described the process of filtration wherein pressure applied during cementation of a casting causes the particles of cement to separate from the liquid, with their accumulation increasing overall cement film thickness. Research demonstrated that the closer the adaptation of the casting to the tooth, the more difficult it is for excess cement to escape Is; this would cause hydraulic pressure, which would prevent complete seating of the crown. lg Various methods of overcoming this cementation problem have been suggested, including external venting,i8, 20,21electrolytic etching of the internal surface of the casting,22*24 internal venting,24-28 and application of painton die spacer.20, 28-31 Application of a paint-on die spacer has been the most commonly used technique because of its simplicity and ease of application. Little research is available to determine the ideal thickness of a die spacer necessary to achieve maximum seating of a casting. Empiric guidelines have recommended 25 ym,20, 32whereas others have suggested 40 a. 2g Fusayama and Iwamoto33 established that the optimum shear strength of zinc phosphate cement occurred with a thickness of 31 to 38 pm. Investigations measuring the effect of die spacer on casting retention have been equivocal. Studies have shown no differences in retentive values,34 increased retention20 and decreased retention.35 Jorgensen and Ebensen36 showed that increasing the thickness of cement film from 20 to 140 pm decreased retention by approximately 33 7%.Dimashkieh et al.lg discovered that THE

JOURNAL

OF

PROSTHETIC

DENTISTRY

Fig. 3. Proximal view of tooth preparation.

increasing axial wall taper was a more important factor than venting of the castings in terms of cement film thickness. Studies have demonstrated a statistically significant improvement in the seating of castings with the use of paint-on die spacer. 20,30,37Campagni et a1.38compared the thickness of three types of paint-on spacer. Large variations in thickness were observed, but for all materials, seating but had a consistent arithmetic progression when multiple coats were applied. 38 Belle de St. Claire cement spacer (Chatsworth, Calif.), used in the present study, had a mean thickness of 11 t 4.4 pm per coat.3s In conclusion, the bulk of research would suggest that die relief of approximately 25 to 40 pm improves casting seating and has minimal effect on retention. MATERIAL

AND

METHO

An ivorine maxillary central incisor (Columbia Dentoform Corp., New York, N.Y.) was prepared with a circumferential shoulder margin, °ree axial wall taper, 1.5 mm of axial reduction, and 2 mm of incisal reduction (Figs. 2 and 3). Forty polysulfide (Kerr, Romulus, Mich.) impressions of the master prepared tooth were made and silverplated. The silver-plated dies were divided into four groups of 10 and specifically numbered. Vinyl polysiloxane (Reprosil, L.D. Caulk Co., Milford, Del.) impressions were made from the silver-plated dies and poured in improved die stone (Die Keen, Modern Materials Inc., St. Louis, MO.). The specifically numbered stone dies were then used for indirect fabrication of the Renaissance Crowns. For group 1, no paint-on die spacer was applied. For groups 2 through 4, three layers of paint-on die spacer (Belle de St. Claire) were applied to the axial-gingival line angle, producing a layer approximately 33 pm thick.38 On the facial margin and a portion of the proximal margins of group 3 and the entire margin of group 4, a stone die sealer (Hartebad Sealer, Renfert, Singen, Germany) was applied for fabrication of the porcelain margins” The 15 pm thick sheet of plastic was placed over the die 163

SORENSEMETAL.

Fig. 4. Porcelain facial margin after two bakes.

Pig. 5. Three hundred sixty-degree ter two bakes.

porcelain margin af-

for group I, whereas the paint-on die spacer was used for group 2. The copings were made according to manufacturer instructions. The umbrella-shaped patterns were placed on the working dies, the pleats were gathered and folded, the pattern was burnished, and the excess material was cut away, leaving 0.5 to 1 mm of material beyond the margin. The foil pattern was swaged onto the die with several strokes of the hammer onto a metal housing containing clay. The foil pattern was then passed through the flame of a burner, causing solder to flow into the pleats. An interfacial alloy was applied to the coping and then fired in the porcelain oven to provide an oxide layer for bonding of porcelain. 4 metal collar approximately 0.5 mm wide was made for groups I and 2. For group 3 (porcelain facial margin), the metal substructure fabricated was similar to those for groups 1 and

164

2 except the facial margin was cut back in proximity to the axial-gingival line angle. The entire margin was circumferentially cut back to the axial-gingival line angle of group 4. A standardized regimen of porcelain application and firing cycles was followed according to manufacturer directions (Table I). These included two opaque porcelain bakes, two body porcelain bakes, and one glazing cycle. Before porcelain was applied, a porcelain release agent (Isostick, Renfert) was applied to the stone die. A directlift technique was used to make the porcelain margins. Group 3 (porcelain facial margin) usually required two shoulder porcelain bakes fired independently a.fter opaque porcelain firings (Fig. 4). Group 4 (360-degree porcelain margin) usually required four shoulder porcelain firings (Fig. 5). The porcelain margins were completed before application of veneer porcelain. A porcelain application jig was used to standardize contour and bulk of porcelain between samples (Figs. 6 and 7). Will-Ceram porcelains (Williams Gold Co.) were used, including opaque and body (shade BC), shoulder porcelain V-Series (shade ZC), and incisal (shade S2). Before the glazing bake, the margins were carefully finished to the proper contours with a rubber wheel (White Silicone, Brasseler USA, Savannah, Ga.) (Fig. 8). The 10 crowns in each group were then cemented onto their respective silver-plated master dies with zinc phosphate cement (Flecks, Mizzy, Inc., Clifton Forge, Va.). The crowns were cemented in a standardized manner by applying cement to the crown and rocking it into position. A static loading jig then applied 6 pounds of seating pressure for 10 minutes. The excess cement was removed with an explorer, in a manner similar to the clinical situation. The crown/die complexes were embedded in clear epoxy resin (Hastings Plastics Co., Santa Monica, Calif.) and allowed to cure for 24 hours. Guide marks on the silver-plated dies allowed the samples to be sectioned faciolingually and mesiodistally with a diamond sectioning saw (Isomet, Buehler Ltd., Evanston, Ill.) (Fig. 9). A cross-sectional measuring technique, as outlined previously,3g allows determination of vertical and horizontal marginal discrepancies (Figs. 10 through 12). Three observers measured eight points around each crown, providing 80 measurements for each crown margin group. Mean vertical and horizontal marginal discrepancies and descriptive statistics were calculated. An analysis of variance (ANOVA) was performed to determine whether significant differences existed at the four positions on the crowns and between the four fabrication techniques. ESULTS Table II shows the mean vertical marginal discrepancies for each of the four fabrication techniques at the four positions around the crown, as well as the combined overall marginal discrepancy. Figs. 13 and 14 graphically represent the vertical discrepancy data. A multivariate repeatedmeasures ANOVA demonstrated significant differences

FEBRUARY1992

VOLUME67

NUMBER2

SWAGED

METAL

CROWN

Fig. 6. Porcelain in place.

MARGINAL

application

FjDELITY

jig base with die and crown Fig. 8. Metal margin after removal of excess material finishing with a rubber wheel.

and

Lingual

G H

Facial

Fig. 7. Porcelain application celain crown contours.

jig used to standardize

por-

between the combined vertical overall marginal discrepancies of the four groups (F = 38.022, p < 0.001; Table III). Tukey’s multiple comparison test revealed that for overall vertical marginal discrepancies, there was no significant difference between the use of the plastic spacer (41 pm) and paint-on die spacer (37 pm) (Table IV). However, values for the overall vertical discrepancy of the porcelain facial margin technique (6‘2 pm) and the 360.degree porcelain margin (86 Km) were statistically different at the 95 s;;Cconfidence level. In a comparison of vertical marginal discrepancy for the four methods by surface, ANOVA showed significant differences by surface (F = 4.667, p < 0.003) and an interaction between the two variables (F = 2.823, p < 0.001; Table III). Tukey’s multiple comparison test showed that for both metal margin groups, the facial vertical discrepancy was significantly smaller than the discrepancy for the other aspects of the crown (Table V). For the porcelain facial margin crowns, the discrepancy for the

THE

JOURNAL

OF PROSTHETIC

DENTISTRY

Fig. 9. Diagram illustrates points from incisal view.

sectioning

and

measuring

lingual metal margin was significantly smaller than that for the facial porcelain margin (Table V). The proximal porcelain margins were also significantly better contoured than the facial margin. For the 360.degree porcelain margin, the lingual margin was significantly poorer than the other three margins on the crown (Table V). Table VI shows the mean horizontal marginal discrepancy for each of the four fabrication techniques at the four positions around the crown, as well as the combined overall marginal discrepancy. Positive signs indicate overcontouring, whereas negative signs indicate undercontouring. Figs. 15 and 16 graphically show the horizontal marginal discrepancy data. ANOVA showed significant differences between the combined horizontal marginal discrepancies of the four groups (F = 41.488, p < 0.001; Table VII). Simiiar to the vertical discrepancies, Tukey’s multiple comparison test showed that for overall horizontal marginal discrepancies, there was no significant difference between

165

SORENSEN

Fig.

10. Cross-sectional

view of overcontoured

ig. 11. Cross-sectional view of overcontoured metal margin onto metal collar. (Original magnification X120.)

the use of the plastic spacer (+48 pm) and paint-on die spacer (+46 pm) (Table VIII). However, the overall horizontal discrepancies of the porcelain facial margin (+82 pm) and the 360-degree porcelain margin (+77 pm) were different from those for the metal margin groups (Table VIII). ANOVA showed significant differences among the four surfaces for the four margin design groups (F = 11.378, p < 0.001) and an interaction between the two variables (F = 6.495, p < 0.001; Table VII). The Tukey multiple comparison test demonstrated that the horizontal discrep-

166

ET AL.

metal margin.

with

porcelain

extended

ancy for the plastic spacer metal margin was significantly less overcontoured at the lingual aspect compared to the other three locations (Table IX). For the paint-on spacer metal margin, the facial aspect was slightly undercontoured, whereas the facial and proximal margins were significantly overcontoured. The facial aspect of the porcelain facial margin was significantly undercontoured compared to the highly overcontoured lingual and proximal aspects. For the 360-degree porcelain margin, the mesial position was significantly less overcontoured than the other three positions on the crown.

FEBRUARY

1942

VOLUME

67

NUMBER

2

SWAGED

METAL

CROWN MARGINAL

Fig.

12. Cross-sectional

Fig.

Table

I. Firing

schedule

alloy

Opaque 1 Opaque 2 Shoulder

l-5

Body 1,2 Autoglaze

THE JOURNAL

13. Graph

OF PROSTHETIC

veiw of porcelain

of overall vertical

for swaged metal matrix Drying time (min)

Porcelain Interfacial

FIDELITY

crowns

Heating time (min)

2 6 6

3

6 6 3

DENTISTRY

facial margin.

marginal

(50” C/min

(Original

fidelity

by fabrication

heating

Temperature 1000

magnification

~120.)

method.

rate) “C

Holding time (min)

Vacuum time (min)

2

3

980

1

3

3

970

1

3

3 3 3

960 950 950

1 1

3 3 -

0.7

167

SORENSEN

ET AL.

Fig. 14. Graph of vertical marginal fidelity by position on crown.

Table

II. Mean vertical marginal discrepancy of crowns [in microns (SD)] Crown

margin

Metal margin plastic spacer Metal margin paint-on spacer Porcelain facial 360-Degree porcelain

Table

III.

Facial

Lingual

Mesial

Distal

20 16 92 72

47 42 34 133

43 40 47 78

54 50 74 61

(21) (18) (41) (53)

Margin material Surface Interaction Error

Sum of squares

Degrees freedom

1997072.233 105060.651 444866.392 4554541.450

7 3 21 607

(49) (42) (38) (52)

41 37 62 86

(45) (40) (41) (63)

of Mean

square

F ratio

285296.033 35020.217 21184.114 7503.363

P>F

38.022 4.667 2.823

0.001 0.003 0.001

Standard deviations for all measurementsof vertical and horizontal marginal discrepancy appearedto be large. Our previous measurementtechnique wasshownto have an interobserver error of 9 to 10 pm.39

Table iv. Overall vertical marginal discrepancy [in microns (SD)] by margin designwith Tukey multiple comparisontest for homogeneity margin

Metal margin plastic spacer Metal margin paint-on spacer Porcelain facial 360-Degree porcelain *95% Confidence intervaI; groups are not statistically

168

(52) (47) (32) (60)

Analysis of variance for vertical marginal discrepancy Source

Crown

(45) (38) (24) (64)

Combi

41 (45)

*

37 (40)

*

62 (41) 86 (63) asterisk different.

in same vertical

DISCUSSION Contrary to studiesshowingimproved seatingof castings the useof paint-on die spacer,20, 30, 37 the present study found no difference in vertical marginal fidelity between the 15 pm plastic spaceror the 33 pm paint-on spacer.At best, the plastic spacerprovides 15 pm relief space.If the plastic spacerbecomesstretched and thinned over the incisal edge of the die, then this relief is considerably less with * * line indicates

that

FEBRUARY

1992

VOLUME

67

NUMBER

2

SWAGED

METAL

CROWN

MARGINAL

Fig.

FIDELITY

15. Graph

Table V. Vertical marginal homogeneity within margin

Plastic spacer

Facial Lingual Mesial Distal

Table

VI.

horizontal

discrepancy (in microns) material group

Location

*95% Confidence

of overall

interval;

horizontal

Crown

margin

marginal

location

by fabrication

with Tukey

discrepancy

* * *

34 47 64

that groups are not statistically

of crowns

Facial

multiple

comparison

[in microns

Lingual

* *

test for

360-Degree porcelain margin

92*

42 40 50 line indicates

method.

Porcelain facial margin

16* * * *

asterisk in same vertical

Mean

by margin

fidelity

Paint-on spacer

20* 47 43 54

marginal

72 133 78 61

* *

* * * *

different.

(SD)] Me&al

Distal

Combined

.

Metal margin plastic spacer Metal margin paint-on spacer Porcelain facial 360-Degree porcelain

+63 +65 -19 +98

(41) (37) (102) (83)

than recommended.20s 2g,32 This leads us to question the true effectiveness of die spacer application for the crown system tested under the conditions of this study. Recent work by Gegauff and Rosenstie140 found that paint-on die relief did not significantly improve the seating of castings and that a dynamic seating force was a more important variable for improved seating. They also reported that previous in vitro die-spacer studies used static loading devices that gave unrealistic values for seating discrepancies compared to dynamic seating forces.41 Another possible reason why die spacer did not signifi-

THE

JOURNAL

OF PROSTHETIC

DENTISTRY

+13 (68) -1 (82) f136 (54) +77 (84)

+47 (72) i-36 (69) +120 (87) +34 (59)

+69 (72) +82 (62) +91 (79) +100 (91)

i-48 +46 i-82 t77

(67) (71) (101) (83)

cantly improve the seating of crowns may have been that the master tooth preparation was made at an axial convergence angle of only 8 degrees. The research by Dimashkieh et al.lg showed that axial wall taper was a more important factor in cement film thickness than venting of castings. Gegauff and Rosenstiel’s preparations were also made with an g-degree taper. Gavelis et a1.42 demonstrated the importance of the marginal gap and amount of hyperocclusion from cementation of castings, as a function of margin design. Castings with various margin designs were made, dies were produced

169

SORENSEN

Fig.

Table

VII.

ANOVA

16. Graph

for horizontal

marginal

of horizontal

marginal

Sum of squares

Margin material Surface Interaction Error

3011135.451 365112.764 1414197.041 6293518.311

Crown margin +48 (67)

*

+46 (71)

*

+82 (101) -?-I7 (83)

*95% Confidence interval; asterisk &roups are not statistically different.

* *

in same vertical

line indicates

that

by pouring resin into the castings, and castings were cemented onto the resin dies. The shoulder-bevel margin had a marginal gap of 105 pm and hyperocclusion of 153 pm, whereas the go-degree shoulder margin had a marginal gap of 67 pm and hyperocclusion of 85 pm.42 The present study used a circumferential shoulder margin design to facilitate ali porcelain margins and compare them with metal margins. Gaveiis et al.42 suggested that the shoulder design allows cement to escape more readily without filtration.

170

on crown.

Mean square

7

430162.207 121704.255

21

[in

of

3 607

Table VIII. Overall horizontal marginal discrepancy microns (SlI)j by margin design with Tukey multiple comparison test for homogeneity

Metal margin plastic spacer Metal margin paint-on spacer Porceiain facial 360-Degree porcelain

by position

discrepancy Degrees freedom

Source

fidelity

ET AL.

67342.114

F ratio

P>F

41.488 11.738

0.001 0.001

6.495

0.001

10368.234

Perhaps die spacer is needed only for more complicated margin designs or with certain amounts of axial wall taper. Further research is needed to delineate the effects of these variables. As the metal substrate is formed directly on the master stone die, it would be expected to have excellent vertieal marginal fidelity. A vertical discrepancy of 37 to 41 ym for a metal margin is considered to be an excellent fit. However, there is potential for damage to the stone die margin as a result of burnishing, swaging, and finishing procedures. Tf the metal margin is extended over these stone surfaces of that have been chipped from burnishing or swaging procedures, then these surfaces of overextension could prevent complete seating of the crown on cementation. Another possible problem arising during the cementation of the overextended margin is that the metal margin may distort as a result of the seating pressure, placing the porcelain near the margin in tension and causing porcelain fracture. The overall vertical marginal discrepancy of the porcelain facial margin method was significantly greater than that for crowns with metal margins. A mean vertical gap of 92 pm for the facial margin was significantly larger than that for the proximal porcelain margins. This difference may be due to greater bulk of porcelain at the facial aspect

FEBRUARY

1992

VOLUME

67

NUMBER

2

SWAGED

Fig.

Table

METAL

CROWN

17. Proximal

IX.

homogeneity

MARGINAL

FIDELITY

view of porcelain

facial margin

Fig. 18. Proximal

crown.

Worizontal marginal discrepancy (in microns) within margin fabrication method group

by margin

location

view of 360-degree

with Tukey

multiple

porcelain

comparison

margin.

test for

SO-Degree Plastic spacer

Location

Facial Lingual Mesial Distal *95’S

Confidence

+63* +13 +47*

+65 *

asterisk

in same vertical

*

-1* +36 +82

+69* interval;

line

indicates

that

JOURNAL

OF PROSTHETIC

DENTISTRY

*

-19

* * groups

of the margin and at the proximal surfaces near the lingual metal collar; this bulk provides greater stability during firing. In the fabrication of the direct-lift porcelain margin, several researchers reported the potential for flow of porcelain under the metal coping, preventing complete seating.43s 44 The metal copings were completely seated during shoulder porcelain application, since the lingual metal margin was similar in fidelity to the full metal margin crowns (Fig. 17). As in other studies,45 little pyroplastic slump of the porcelain facial margin was observed when the specially formulated shoulder porcelains were used. The microscopic appearance of these margins will be presented in a later comparative scanning electron microscope study. The 86 pm overall vertical discrepancy of the 360-degree porcelain margin crown was significantly greater than that of the porcelain facial margin. In comparing the various points around the crown, the lingual porcelain marginal gap was nearly double that of the proximal and facial aspects. This probably occurred as a result of the great curvature of the cingulum as it flows into the marginal surface. Extensive shrinkage was observed at the lingual aspect during the firing of the shoulder porcelain (Fig. 18). The ceramist reported much greater difficulty in perfecting the circumferential porcelain margin compared to the porcelain facial margin. Two applications and firings were typically required for the porcelain facial margin, whereas

THE

Porcelain facial margin

Paint-on spacer

are not statistically

porcelain margin

*

+136 +120

*

+91

*

* *

-+98

*

4-77

*

t34 +100

* *

different.

the 360-degree porcelain margin required four to five bakes. Because this study cemented and sectioned crowns, whereas other studies only seated castings on a master die or only embedded crowns, direct comparison of the results may not be possible. However, general correlations can be made for their similarities. Belser et a1.46 found that after cementation, the 46 ym mean vertical opening of the porcelain margin was not significantly different from that of the metal butt margin of cermometal crowns. In uncemented crowns Cooney et a1.47 discovered that vertical marginal openings of porcelain margins formed with platinum foil on stone dies (32 pm) and on silver-plated dies (38 pm) were significantly better than those formed by directlift shoulder porcelain (72 pm) or wax binder (81 pm) techniques. Wanserkski et a1.45 compared the stepwise vertical marginal opening of porcelain margins and found that the direct-lift technique produced porcelain margins with marginal openings (15 qrn) that were as good as those of cast metal margins (20 pm). In fact, they observed that the metal margin adaptation changed more during the stages of fabrication than did the porcelain margin adaptation. In a study by West et a1.,48 uncemented crowns seated on stone dies that were embedded and sectioned showed no significant difference in vertical opening between porcelain margins made with platinum foil and those made with two

171

SORENSEN

19. Metal margin crown cemented onto tive silver-plated die. Fig.

its respec-

different direct-lift techniques. The marginal openings rangedfrom a meanof 14 to 33 pm. It must be emphasized that the researchersmeasuredthe marginal opening not at the margin in line with the emergenceprofile but somewhat axially where “the first effects of marginal rounding could be detected.” If the marginal opening had been measured exactly at the preparation finish line, a marginal opening many times greater would have beenreported. None of the studies was able to quantify the horizontal marginal discrepancy. The overall vertical marginal discrepancy of direct-lift porcelain facial margin crowns (62pm) in the presentstudy would appearto fall within the range of theseother studies. However, the porcelain facial margin was92 pm at the facial point and 47 and 74 pm at the proximal areas. The overall vertical discrepancy of the 360-degreeporcelain margin (86 pm) is excessiveand would be consideredclinically unacceptable. The mean vertical marginal discrepancy of the swagedmetal margins(41 pm) comparesfavorably with that of cast metal margins in other studies.45-48 This crown system has a propensity for overcontouring becausethe manufacturer advocatesa technique where the metal substrate is overextended, then ground and finished back after porcelain application. This approach creates great technique sensitivity, which is highly dependent on the skill of the technician. The ceramistswho made these crowns were experts in this methodology. It would therefore be expected that lessexperienced technicians would produce poorer results for the final vertical and horizontal marginal discrepancies.An additional problem with finishing the overextended metal after porcelain application is completed is that the predictability and degree of control of the opaque porcelain are much poorer. There is a tendency to have excessrough unglazeableopaqueexposed at the porcelain-metal junction (Fig. 19). This excesscreatespoor esthetics aswell asa niche for plaque accumulation.4g Although the vertical discrepancy of the porcelain facial 172

ET AL.

margin (62 pm) was statistically greater than that of the metal margin (41 pm), an additional consideration of the gingival impact of the crown margin is the amount of rough plaque retentive opaque that is exposed, especially when placed subgingivally.4gBecauseof the finishing technique recommended by the manufacturer, larger than normal surfacesof opaque were exposed at the porcelain-metal junction (Fig. 19). The porcelain facial margin eliminates the problem of exposedopaqueby placing glazed and polished body porcelain at the margin. Thus it would be expected that the long-term gingival health would be better with the porcelain facial margin.5,4gHowever, the large 92 pm facial vertical marginal opening is certainly more important to long-term gingival health than the rough exposedopaque. The metal marginswere consistently overcontoured by a mean of 47 pm. The overcontouring is due to the technique sensitivity of finishing the overextended margins downward after porcelain application. The horizontal marginal discrepancy for the porcelain facial margin and 360-degreeporcelain margin crowns was significantly greater than that of the metal margins.The facial aspectof the porcelain facial margin wasactually undercontoured by -19 pm. Apparently it wasmore difficult to judge the correct contours for finishing near the proximal transition from porcelain to metal margin. The circumferential porcelain margin crowns were generally similarly overcontoured at all positions. As demonstratedin the cross-sectionalview of the metal margins (Figs. 10 and ll), the metal substructure is overcontoured as well as overextended apically beyond the margin. It is virtually impossibleto measurethe marginal opening with any degreeof accuracy with the direct-view technique.3gUsing a cross-sectionalview method allows accurate determination of the marginal fidelity by defining the marginal discrepancy into vertical and horizontal components.3g The potential larger surface of exposedopaqueand the prevalence of overcontouring with this crown system create the potential for a negative periodontal impact, especially when the margins are placed subgingivally.“g These problems of overcontouring and exposedopaque may potentially outweigh the relatively goodvertical marginal fidelity values of the metal margins. The maximal acceptable vertical margin opening and degree of overcontouring are presently unknown. Longterm clinical studies correlating vertical and horizontal marginal discrepancieswith the occurrence of secondary caries and gingival inflammation are greatly needed for clinical decisionmaking in dentistry. CONCLUSIONS From this vitro study on crowns made with the swaged metal coping, we made the following conclusions:(1) No significant difference in vertical or horizontal marginal fidelity was found for metal margins made with either a plastic spacer or paint-on die spacer. (2) The overall vertical marginal discrepancieswere 41 pm for metal margin FEBRUARY

1992

VOLUME

67

NUMBER

2

SWAGED

METAL

CROWN

MARGINAL

FIDELITY

plastic spacer, 37 pm for metal margin paint-on die spacer, 62 pm for porcelain facial margin, and 86 pm for 360-degree porcelain margin. (3) The overall horizontal marginal discrepancies for all four methods were overcontoured by 46 to 82 pm. (4) The technique advocated by the manufacturer makes this technique sensitive, with consistent overcontouring. We thank Williams Gold Co. for supplying the Renaissance Crown system, Ms. Irene Petrevicius for her artwork in making the diagrams, and Mr. Dick Friske for his photographic assistance.

25. Tjan AHL, Sarkissian R, Miller GD. Effect of multiple axial grooves on the marginal adaptation of full cast-gold crowns. J PROSTHET DENT 1981;46:399-403. 26. Tjan AHL, Sarkissian R. An internal escape channel: a practical alternative to occlusal venting in full cast crowns, J PROST~ET DENT 1984;52:50-6.

Brose MO, Woelfel JB, Rieger MR, Tanquist DA. Internal channel vents for posterior complete crowns. J PROSTHET DENT 1984;51:755-60. KJ, Bruggers H. Internal venting of castings to improve mar28. Bruggers ginal seal and retention of castings. J PROSTHET DENT 1987;58:270-3. 29. Fusayama T, Ide K, Hosada H. Relief of resistance of cement of full cast crowns. J PROSTHET DENT 1964;14:95-106. WG, Gettleman L. Effect of internal relief, vibration, and 30. Van Nortwick venting on the vertical seating of cemented crowns. J PROSTHET DENT

27.

1981;45:395-9.

REFERENCES 1. Shoher

2. 3. 4. 5. 6. I.

8.

9 10. 11. 12. 13. 14.

15.

16. 17. 18.

19.

20.

21. 22. 23. 24.

THE

I, Whiteman AE. Reinforced porcelain system: a new concept in ceramometal restorations. J PROSTHET DENT 1983;50:489-96. Brukl CE, Ocampo RR. Compressive strengths of a new foil and porcelain-fused-to-metal crowns. J PROSTHET DENT 1987;57:404-10. Jarvis RH, Tallents RH. Comparative impact strengths of existing ceramic systems. (Submitted for publication.) Goodaere CJ, Van Roekel NB, Dykema RW, Ullman RB. The collarless metal-ceramic crown. J PROSTHET DENT 1977;38:615-22. Donovan T, Prince J. An analysis of margin configuration for metal-ceramic crowns. J PROSTHET DENT 1985;53:153-7. Johnston JF, Mumford G, Dykema RW. Modern practice in dental ceramics. Philadelphia: WB Saunders Co, 1967:235. Choung CK, Garlapo DA, Brown MH, Sorensen SE. Procedure for a simplified collarless metal-ceramic restoration using gold powder. J PROSTHET DENT 1982;47:449-53. Vickery RC, Badenelli CA, Walker RW. The direct fabrication of restorations without foil in a refractory die. J PROSTHET DENT 1969;21:227-34. Schneider DM, Levi MS, Mori DF. Porcelain shoulder adaptation using direct refractory dies. J PROSTHET DENT 1976;36:583-7. Sozio RB, Riley EJ. A precision ceramic-metal restoration with a facial burred margin. J PROSTHET DENT 1977;37:517-21. Sozio RB. The marginal aspect of the ceramometal restoration: the collarless ceramometal restoration. Dent Clin North Am 1977;21:787-801. Toogood CD, Archibald JF. Technique for establishing porcelain margins. J PROSTMET DENT 1978;40:464-6. Vryonis P. A simplified approach to the complete porcelain margin. J PROSTHET DENT 1979;42:592-3. Hunt JL, Cruichshanks-Boyd DW. A technique for the production of collarless porcelain crowns using liquid separating media. Dent Update 1980;7:483-7. Prince J, Donovan TE, Presswood RG. The all-porcelain labial margin for ceramometal restorations: a new concept. J PROSTHET DENT 1983;50:793-6. Jorgensen KD. Factors affecting the film thickness of zinc phosphate cements. Acta Odontol Stand 1960;18:479-90. Jorgensen KD. Structure of the film of zinc phosphate cements. Acta Odontol Stand 1960;18:491-501. Jones MD, Dykema RW, Klein AI. Television micromeasurement of vented and nonvented cast cast crown marginal adaptation. Dent Clin North Am 1971;15:663-78. Dimashkieh MR, Davies EH, van Fraunhofer JA. Measurement of the cement film thickness beneath full crown restorations. Br Dent J 1974;137:281-4. Eames WB, O’Neal SJ, Montiero J, Miller C, Roan JD, Cohen KS. Techniques to improve the seating of castings. J Am Dent Assoc 1978;96:432-7. Cooper TM, Christensen GJ, Laswell HR, Baxter R. Effect of venting on cast gold full crowns. J PROSTHET DENT 1971;26:621-6. Lorencki SF. A rationale for electro-deplating a cast restoration. Dent Digest 1968;74:249-51. Pate1 MG. The effect of electrochemical milling on margins of MOD inlays. J PROSTHET DENT 1973;30:66-73. Bassett RW, Stauts BM. Evaluation of electro-chemical milling (stripping) versus etching with Aqua-regia. J South Calif Dent Assoc 1966;34:478-85.

JOURNAL

OF

PROSTHETIC

DENTISTRY

31. Marker VA, Miller AW, Miller BH, Swepston JH. Factors affecting the retention and fit of gold castings. J PROSTHET DENT 1987;57:425-30. ST, Lund MR. Improving marginal fit through finishing pro32. Eliasson cedures. J Ind State Dent Assoc 1974;53:13-7. 33. Fusayama T, Iwamoto T. Relationship between retaining force of inlays and film thickness of zinc oxyphosphate cement [Abstract]. J Dent Res 1960;39:756. JH, Cooper EW. Effect of die relief on retention of cast crowns 34. Hembree and inlays. Operative Dent 1979;4:104-7. 35. Vermilyea SG, Kuffler MJ, Huget EF. The effect of die relief agent on the retention of full coverage castings. J PROSTHET DENT 1983;50:20710. 36. Jorgensen KD, Ebensen AL. The relationship between the film thickness of zinc phosphate cement and the retention of veneer crowns. Acta Odontol Stand 1968;26:169-75. to improve the seating of castings. Quintes37 Eames WB. Techniques sence Dent Technol 1981;5:437-41. 38 Campagni WV, Preston JD, Reisbick MH. Measurement of paint-on die spacers used for casting relief. J PROSTHET DENT 1982;47:606-11. 39. Sorensen JA. A standardized method for determination of crown margin fidelity. J PROSTHET DENT 1990;64:18-24. 40. Gegauff AG, Rosenstiel SF. Reassessment of die-spacer with dynamic loading during cementation. J PROSTHET DENT 1989;61:655-8. 41. Rosenstiel SF, Gegauff AG. Improving the cementation of complete cast crowns: a comparison of static and dynamic seating methods. J Am Dent Assoc 1988;117:845-8. 42. Gavelis JR, Morency JD, Riley ED, Sozio RB. The effect of various finish line preparations on the marginal seal and occlusal seat of full crown preparations. J PROSTHET DENT 1981;45:138-45. 43. Hunt JL, Cruichshanks-Boyd DW, Davies EH. The marginal characteristics of collarless bonded porcelain crowns produced using a separating medium technique. Quintessence Dent Technol 197&9:21. 44. Prince J, Donovan TE. The esthetic metal-ceramic margin: a comparison of techniques. J PROSTHET DENT 1983;50:185-92. 45. Wanserkski DJ, Sobczak KP, Monaco JG, MC Givney GP. An analysis of margin adaptation of all-porcelain facial margin ceramometal crowns. J PROSTHET DENT 1986;56:289-92. 46. Belser UC, MacEntee MI, Richter WA. Fit of three porcelain-fused-tometal marginal designs in viva: a scanning electron microscope study. J PROSTHET DENT 1985:53:24-g. 47. Cooney JP, Richter WA, MacEntee MI. Evaluation of ceramic margins for metal-ceramic restorations. J PROSTHET DENT 1985;54:1-5. 48. West AJ, Goodacre CJ, Moore BK, Dykema RW. A comparison of four techniques for fabricating collarless metal-ceramic crowns. J PR~STHET DENT 1985;55:636-42. 49. Sorensen JA. A rationale for comparison of plaque retaining properties of crown systems. J PROSTHET DENT 1989;62:264-9. Reprint

requests

to:

DR. JOHN A. SORENSEN CHS 33-041 SCHOOL OF DENTISTRY UNIVERSITY OF CALIFORNIA

Los

ANGELES,

CA 90024

Contributing

author:

Robert

C.D.T.,

Miller,

Williams

Gold Co., Buffalo,

N.Y.

173