A standardized fidelity John A. Sorensen, University
of California,
method
for determination
of crown
margin
D.M.D.* School of Dentistry,
Los Angeles, Calif.
Previous research on crown margin fidelity is reviewed and methods of measurement are compared and scrutinized. A standardized method for the determination of crown margin fidelity is introduced. A biologically oriented rationale is presented for analysis of the measurement parameters. This system places a strong emphasis on measuring factors that impact upon accumulation of plaque and the microbiologic environment around crowns, ultimately affecting gingival health. Crown samples were cemented on master dies and were embedded for sectioning buccolingually and mesiodistally. Photographs of margins with plastic overlays indicating emergence profiles were used to determine vertical and horizontal marginal discrepancies. Three observers measured seven crown systems for the vertical and horizontal marginal discrepancies of each crown system. The interobserver variance was 10 pm for the horizontal and 9 sm for the vertical marginal discrepancy. (J PROSTHET DENT 1990;64:18-24.)
N
o standardized method for measurement of crown margin adaptation exists. There is disagreement regarding the parameters to evaluate and where the marginal opening should be measured. Fidelity refers to faithfulness of reproduction. In dentistry, fidelity means faithfulness of reproduction of the tooth preparation margin with the restoration. Poor marginal fidelity resulting in a large marginal gap, overcontouring, or a rough surface finish increases plaque accumulation, inducing gingival inflammation.’ This article presents a standardized method for measurement of crown margin fidelity using a biologically oriented rationale. Strong emphasis is placed on measuring those factors that affect plaque accumulation and subsequent gingival health.
REVIEW OF METHODS FOR MEASUREMENT OF MARGINAL DISCREPANCY The many methods for measuring marginal fidelity include four basic categories. These are: (1) direct view, (2) cross-sectional, (3) impression technique, and (4) explorer and visual examination. Researchers use techniques for measurement of marginal fidelity tailored for specific factors to be studied. The direct view, by virtue of its nondestructive nature,
Presented in part before the Academy of Denture Prosthetics, Monterey, Calif. This project was supported in part by BRSG No. SO?‘-RR05304 awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health, Bethesda, Md. *Assistant Professor and Director, Graduate Prosthodontics.
10/l/20323 18
is often used to monitor stepwise distortion. To measure distortion of metal ceramic restoration margins during the various steps of the firing cycle requires that the crown be fired and then repositioned on a measuring stage in a repeatable manner. Shillingburg et al2 popularized this method to compare firing distortion of various margin designs. A number of studies have used this system for measuring marginal distortion at each stage of the porcelain firing process,3-6for assessing marginal fidelity of metal ceramic fixed partial dentures,7 for determining marginal fidelity of different types of crown systems,5r8-11for assessing marginal fidelity of different metal ceramic alloys during the porcelain firing process,12’I3 for determining marginal fidelity of provisional composite resin crowns,14 and for comparing the fit of castings made with various investments. l5 Cooney et all6 seated crowns on a master die and then made impressions of the margins. Resin replicas were formed in the impressions for scanning electron microscopy @EM) measurement of marginal gaps. Faucher and Nicholls17 followed marginal distortion during porcelain firing steps by placing the casting in a jig and tracing the margin with a profile projector. The direct view method is convenient, easy, and rapid because the crown is retrievable, unlike the cementation, embedment, and sectioning method, which causesdestruction of the crown (Table I). However, repeated seating of sample crowns on a master die can damage the margin by abrasion. In addition, the inability to measure and replace the crown precisely on the master die will produce increased standard deviation and decreased statistical significance. A disadvantage of this method is that a rounded margin examined microscopically has no repeatable point of reference on the curved surface. It is difficult to determine marginal overcontouring by direct viewing. The cross-sectional method measures marginal fidelity by placement of crowns on dies, which are embedded in JULY
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Table I. Comparison of measuring techniques Disadvantages
Advantages Direct 1.
view
Expedient, rapid, and simplified method for measurement
2. Does not require additional steps
3. Allows measurement at various stages of crown fabrication
Cross-sectional
1. Samples must be sacrificed for sectioning procedure Fig.
of measurement
A scientific method for measurement of crown margin discrepancy should be consistent, reproducible, and have JOURNAL
OF PROSTHETIC
1. Cross-sectional view of tooth-crown margin.
2. Cannot measure marginal fidelity at various stages of crown fabrication 3. Requires additional steps of embedding and sectioning; more time-consuming
resin and sectioned. This technique has been used to measure margin discrepancies for cemented crownsg-il* 18-21 and uncemented crowns, 22to permit comparison of different margin designs of metal ceramic restorations,23 and to evaluate the fit and strength of all-ceramic fixed partial dentures.24 The technique is time-consuming, requires additional steps, and sacrifices the crowns (Table I). This method precludes measurement of marginal distortion at the various stages of porcelain firing on the same samples, but the additional steps and effort provide more information and greater precision of measurement. The cross-sectional evaluation of margins allows greater precision in determination of measuring points and permits determination of the degree of horizontal discrepancy (overcontouring) that is not possible with the direct viewing technique. There is a need for standardization of methodology for measurement of marginal fidelity and delineation of the parameters to be measured.
THE
Tooth
view
1. Greater precision in measurements as measurement points are more accurate and repeatable 2. Allows determination of horizontal marginal fidelity; overcontouring 3. As crown is cemented to die, avoids potential damage from repeated use of master die
Parameters
Cr own
1. With a rounded margin, difficult to determine what point to measure from 2. Less precision due to inaccuracies in repositioning crowns on master die 3. Difficult to assess overcontouring of crown margin 4. With repeated use of master die, potential for wear and damage to master die margin
DENTISTRY
Fig. 2. Cross-sectional high magnification view of crown preparation tooth margin.
standardized points of measurement. Consistent points of measurement are necessary for an impartial comparison of different crown systems. For example, if a crown system has pyroplastic slump or marginal rounding, where should the marginal gap be measured? When a rounded margin is viewed directly from a perpendicular or an impression is made of the margin and is viewed with a SEM, the tendency is to measure at the point of the edge of the cement (Fig. 1, points a and 6), rather than at a point where the gap is created from marginal rounding (Fig. 1, points a to c). For consistency of measurement and a realistic evaluation of the marginal gap, the crown-die complex should be sectioned and viewed in cross-section. This view produces a more reliable assessment of the actual surface of marginal 19
SORENSEN
Lingual
dies, the samples were sectioned faciolingually and mesiodistally with an Isomet low-speed diamond sectioning saw (Buehler Ltd, Lake Bluff, Ill.). This sectioning allowed examination at eight points around the crown, one view on each side of the cut (Fig. 3).
Measurement
Facial
Fig. 3. Incisal view of crown; faciolingual and mesiodistal sectioning measurement points.
opening for plaque habitation (Fig. 1, points a to c). Some methods measure at point d (Fig. 1). However, this point is not an accurate reflection of the dimension of the niche created for microorganisms. Clinically, to get to point d (Fig. l), the cement would have to be chipped away or dissolved in oral fluids from point e to point d (Fig. l), creating a recess of increasing space. During clinical procedures, the margins of a crown preparation appear sharp. However, with microscopic examination, the margin of a crown preparation or a die appears rounded, causing difficulty in selecting a point where the marginal opening is to be measured. Three main points can be used for measurement. Reasonable arguments for the use of points f, g, or h (Fig. 2) for measurement locations can be made. Point f (Fig. 2) most accurately reflects the dimensions of the niche for plaque habitation. Consistency in the point of measurement is more important than the actual point of measurement on the tooth and die.
METHODS A maxillary central incisor ivorine tooth was prepared to a 1.5 mm axial reduction and to 2 mm incisally. A go-degree butt-joint shoulder margin was used according to the manufacturer’s directions. Ten silver-plated master dies were created from the ivorine prepared tooth for each crown system. The 10 silver-plated dies in each group were specifically numbered and impressions were made for indirect fabrication of the crowns. Ten crowns of each brand were made according to manufacturers’ recommendations. The crowns were cemented in a standardized manner with a loading jig that applied 6 pounds of seating pressure for 10 minutes. The crown-die complexes were embedded in epoxy resin and were allowed to cure for 24 hours. Using guide marks on the silver-plated
20
of marginal
fidelity
The objective in using the following method was to gain maximum information regarding the potential biologic response to a margin. The epoxy-embedded, sectioned crowns were photographed at 120 power magnification with an Olympus zoom stereomicroscope, Model SZ-Tr, and PM-6 camera (Olympus Optical Co., Ltd., Tokyo, Japan). A custom-made camera reticle with a scale divided into 5 pm increments provided pictures with the scale superimposed on the prints for standardization and calculations. The 3- X B-inch color prints were then used for measurement of the margin discrepancies. Three independent observers made determinations of the vertical and horizontal marginal fidelity. A plastic overlay was superimposed on the 120 power color photographs of the crown margins with a vertical line corresponding to the root surface and emergence profile (Fig. 4). A second horizontal line coincided with the finish line of the preparation and extended axially along the finish line and away from the tooth (Fig. 4). Because the angulation of tooth structure below the finish line varies with the position on the tooth, three transparent overlays with lines were made. Overlays with grids were made for marginal assessment at the facial (points A and B, Fig. 3), lingual (points E and F, Fig. 3), and proximal (points C, D, E, and F, Fig. 3) surfaces. Measurement of the horizontal and vertical margin discrepancies were then made using glass squares marked with a scale divided into 5 Mm increments. The plastic overlay was correctly aligned with the tooth using the vertical emergence profile line and the preparation finish line for the horizontal line (Fig. 4). The glass square was first moved along the horizontal line until the vertical portion of the glass square intersected the vertical line of the overlay to calculate the amount of vertical margin opening (Fig. 5, A). If the margin was deficient and did not transect the vertical line, the first point on the crown margin that was tangential to the vertical surface of the glass square was selected as the point of measurement. The horizontal margin discrepancy was determined by moving the glass square along the horizontal overlay line until the vertical edge of the glass square intersected the first tangent on the crown margin. Deficient or short margins were calculated by assessing the distance from the tangential intersection to the overlay vertical emergence profile line (Fig. 5, B). The distance was recorded with a negative sign to denote a horizontally deficient margin. The crown margin was judged as overcontoured or excessive when the angle of intersection between crown margin and
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Fig. 4. Measurement technique with plastic overlays and glass square.
the overlay vertical line was greater than 45 degrees (Fig. 5, C). Upon being ruled as overcontoured, the dimension of overcontour was determined by moving the glass square along the horizontal overlay line until the vertical edge of the glass square transected the first tangent on the margin (Fig. 5, D). The distance from the intersection point to the vertical emergence profile line was recorded with a positive sign, denoting a horizontally excessive margin.
RESULTS Seven crown systems with 10 samples in each group were sectioned into quarters, yielding eight measurement points for each crown. The mean vertical and horizontal marginal discrepancies were determined by calculating the mean values, which were determined from the values recorded by the three observers. For each crown system 240 vertical and 240 horizontal marginal discrepancy measurements were made. The interobserver variance or accuracy of measurement was 9 km for the vertical discrepancy and 10 Frn for the horizontal marginal discrepancy (Table II).
DISCUSSION The cementation phenomenon adds another important variable to the vertical marginal discrepancy of a crown system. Jorgensen’sz5 study, which compared pre- and post-cemenation marginal adaptation values, clearly showed that any study aimed at determining the marginal adaptation of a crown system requires cementation of the crowns with procedures that simulate the clinical situation. The hydrodynamic intracoronal pressures that develop
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
during cementation and that prevent complete seating of crowns have been well documented.25-31Studies that seat various crowns on test dies and measure marginal openings without cementation will not correctly reflect the marginal adaptation. Highly porous ceramic cores or substructures may alter cement filtration dynamicss Porous core materials may absorb a portion of the cement luting agent, effectively reducing the cement film thickness and allowing the crown to seat more closely to the prepared tooth. Margin studies that do not cement the crowns are unable to detect these differences. Additionally, ifall-ceramic crowns or porcelain labial margin crowns are not cemented, researchers cannot record the fracturing or chipping of ceramic margins that occur when porcelain margins are overextended and fracture from seating pressure. These chips in the porcelain margin can significantly increase the standard deviation in marginal fidelity measurements.
Biologically
oriented
rationale
The primary role of plaque in the etiology of caries and gingival inflammation has been clearly established.’ Dentists are concerned with the quality of the marginal fit of a restoration because of the biologic ramifications. By minimizing the degree of marginal opening, the surface of exposed cement will be decreased, reducing the rate of dissolution of cement that occurs in oral fluids. When the cement is washed out or is chipped out during the removal of excess cement, a recess is created that harbors microorganisms. When this gap is supragingival, the primary concern is caries. When the marginal gap is subgingival and the
21
SORENSEN
Fig. 5. Cross-sectional view of tooth-crown junction. Measuring methodoiogy for vertical and horizontal marginal discrepancies. A, Measurement of vertical marginal discrepancy. B, Measurement of horizontal marginal discrepancy (undercontoured). C, Application of cibdegree rule for determination of overcontoured margin. D, Measurement of horizontal marginal discrepancy (overcontoured).
gingival tissues are in intimate contact with the margin, both gingival inflammation and caries are a concern.
Subgingival
margin placement
The importance of the contour of the margin was discussed in Part 1.r Marginal contouring affects accessfor plaque control. Overcontouring of subgingival margins make plaque control difficult or impossible for home hygiene (Fig. 6). At cementation, an overcontoured margin prevents the dentist from removing the excess subgingival
22
cement from the underside of the margin with an explorer or scaler (Fig. 6), and the surface of rough plaque-retentive cement is greatly increased. To further compound the problem, the microorganisms that colonize the subgingival cement under an overcontoured margin have a greater pathogenicity than supragingival plaque organisms.32 A crown margin emergence profile that is continuous with.the root surface is most desirab1e.r If the crown margin discrepancy is in the horizontal dimension, an undercontoured margin is more desirable than an overcontoured
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Fig. 6. Cross-sectional view of dentogingival junction of overcontoured crown.
Fig. ‘7. Cross-sectional view of dentogingival junction of undercontoured crown.
margin (Fig. 7). Access for removal of excess cement during cementation and for patient plaque removal is much greater with an undercontoured margin. In measuring the marginal opening and contour, the vertical and horizontal margin discrepancy data yield an approximation of the dimensions of the marginal opening. The total area of marginal discrepancy is critical to the gingival response, since it defines the extent of the niche for bacterial plaque habitati0n.l The tissue interface at the marginal discrepancy will be composed of either rough cement or will appear as a recess bordered by tooth, restoration, and/or cement. The result of either of the tissue-restoration interfaces is a protected niche for bacterial plaque colonization.
Table II.
CLINICAL
IMPLICATIONS
The existence of iatrogenic periodontal disease around esthetic crowns is well d0cumented.l Clinicians placing these restorations need to be aware of the periodontal results of their restorative dentistry. The marginal fidelity of various crown systems is not just an academic pursuit but is of strong clinical concern, affecting the health and esthetics of their patients. SUMMARY A standardized method for the determination of crown margin fidelity is presented. Crown samples were cemented on master dies and embedded for sectioning buccolingually
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Interobserver variance Horizontal 10 pm
Vertical 9
firn
and mesiodistally for determination of vertical and horizontal marginal discrepancies. Three observers measured the vertical and horizontal marginal discrepancies. For the seven crown systems measured, the interobserver variance was 10 pm. This article presents a biologic rationale for a standardized method of measurement of vertical and horizontal marginal discrepancies that will be used to compare various crown systems in future articles. The author thanks Ms. Irene Petrivicius
for her art work.
REFERENCES 1. Sorensen JA. A rationale for comparison of plaque-retaining properties of crown systems. J PROSTHET DENT 198%62:264-g. 2. Shillingburg HT, Hobo S, Fisher DW. Preparation design and margin distortion in porcelain-fused-to-metal restoration. J PROSTHET DENT 1973;29:276-84.
3. Ando N, Hakamura K, Namiki T, Sugata T, Suzuki T, Moriyama K. Deformation of porcelain bonded gold alloys. J Jpn Sot Appar Mater 19’72;13:237-48. 4. Hamagucbi H, Cacciatore A, Tueller VM. Marginal distortion of the porcelain-bonded-to-metal complete crown: sn SEM study. J PROSTHET DENT 1982;47:146-53.
23
5. Wanserski DJ, Sobczak KP, Monaco JG, McGiveny GP. An analysis of margin adaptation of all-porcelain facial margin ceramometal crowns. J PROSTHFXDENT 1986;56:289-92. 6. Anusavice KJ, Carroll JE. Effect of incompatibility stress on the fit of metal-ceramic crowns. J Dent Res 1987;66:1341-4. 7. Van Rensburg F, Strating H. Evaluation of the marginal integrity of ceramometal restorations. Part II. J PROSTHET DENT 1984,52:!210-4. 8. Schneider DM, Levi MS, Mori DF. Porcelain shoulder adaption using direct refractory dies. J PROSTHET DENT 1976;36:583-7. 9. Sato T, Wohlwend A, Scharer P. Marginal fit in a “shrink-free” ceramic crown system. Int J Periodont Rest Dent 1986;3:9-21. 10. Brukl CE, Philp GK. The fit of molded all-ceramic, twin foil, and conventional ceramic crowns. J PROSTHETDENT 1987;58:408-13. 11. Scharer P, Sato T, Wohlwend A. Marginal fit in the cera-platin crown system. Quint Dent Technol 1987;11:11-25. 12. Buchanan WT, Svare CW,Turner KA. The effect of repeated firings and strength on marginal distortion in two ceramometal systems. J PROSTHET DENT 1981;45:502-6.
13. Dederich DN, Svare CW, Peterson LC, Turner KA. The effect of repeated firings on the margins of nonprecious ceramometals. J PROSTHET DENT 1984;51:628-30. 14. Tjan AHL, Tjan AH, Grant BE. Marginal accuracy of temporary composite crowns. J PROSTHETDENT 1987;58:417-21. 15. Cooney JP, Doyle TM, Caputo AA. Surface smoothness and marginal fit with phosphate-bonded investments. J PROSTHETDENT 1979;41: 411-7. 16. Cooney JP, Richter WA, MacEntee MI. Evaluation of ceramic margins for metal-ceramic restorations. J PROSTHETDENT 1985;54:1-5. 17. Faucher RR, Nicholls JI. Distortion related to margin design in porcelain-fused to metal restorations. J PROSTHETDENT 1980;43:149-55. 18. Hunt JL, Cruickshanks-Boyd DW, Davies EH. Marginal characteristics of collarless bonded porcelain crowns produced using a separating medium technique. Quint Dent Technol 1978;9:21-6. 19. Faul TW, Hesby RA, Pelleu GB, Eastwood GW. Marginal opening of single and twin platinum foil-bonded aluminous porcelain crowns. J PROSTHETDENT 1985;53:29-33. 20. Chan C, Haraszthy G, Gerstorfer JG, Weber H. The marginal fit of Cerestore full-ceramic crowns-a preliminary report. Quint Intern 1985:6:399-402.
21. Davis DR. Comparison of fit of two types of all-ceramic crowns. J PROSTHET DENT 1988;59:12-6. 22. Ulman JL. Collarless binded porcelain crowns, a comparison of fahrieating techniques. M.D.S. Thesis, Indiana University, Indianapolis, Ind., 1972. 23. Panno FV, Vahidi F, Gulker I, Ghalili KM. Evaluation of the 45-degree labial bevel with a shoulder preparation. J PROSTHET DENT 1986;56: 655-61. 24. Campbell SD, Sozio RB. Evaluation of the fit and strength of an allceramic fixed partial denture. J PR~WHET DENT 1988;59:301-6. 25. Jorgensen KD. Structure of the film of zinc phosphate cement. Acta Odontol Stand 1960;18:491-501. 26. Fusayama T, Ide K, Kurosu, Hosada H. Cement thickness between cast restorations and preparation walls. J PROSTHETDENT 1963;13:354-64. 27. Basset RW. Solving the problems of cementing the full veneer cast gold crown. J PRCISTHETDENT 1966;16:740-7. 28. Ishikiriama A, Oliveira CD, Viera DF, Mondelh DC. Influence of some factors on the fit of cemented crowns. J PROSTHETDENT 1981;45:400-4. 29. Webb EL, Murray HV, Holland GA, Taylor DF. Effect of preparation relief and flow channels on seating full coverage castings during cementation. J PROSTHETDENT 1983;49:777-80. 30. Eames WB, G’Neal SJ, Monteiro J, Miller C, Roan JD, Cohen KS. Techniques to improve the seating of castings. J Am Dent ASSOC 1978;96:432-7. 31. Gavelis JR, Morency JD, Riley ED, Sozio RB. Effect of various finish line preparations on the marginal seal and occlusal seat of full crown preparations. J PROSTHETDENT 1981;45:138-45. 32, Lang NP, Kiel RA, Anderhalden K. Clinical and microbiological effects of subgingival restorations with overhanging or clinically perfect margins. J Clin Periodont l&563-78. Reprint requests to: DR. JOHN A. SORENSEN CHS 33-041 SCHOOLOF DENTISTRY UNIVEFWTYOF CALIFORNIA Los ANGELES,CA 90024
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1
24
JULY
1990
VOLUME
64
NUMBER
1
of California,
method
for determination
of crown
margin
D.M.D.* School of Dentistry,
Los Angeles, Calif.
Previous research on crown margin fidelity is reviewed and methods of measurement are compared and scrutinized. A standardized method for the determination of crown margin fidelity is introduced. A biologically oriented rationale is presented for analysis of the measurement parameters. This system places a strong emphasis on measuring factors that impact upon accumulation of plaque and the microbiologic environment around crowns, ultimately affecting gingival health. Crown samples were cemented on master dies and were embedded for sectioning buccolingually and mesiodistally. Photographs of margins with plastic overlays indicating emergence profiles were used to determine vertical and horizontal marginal discrepancies. Three observers measured seven crown systems for the vertical and horizontal marginal discrepancies of each crown system. The interobserver variance was 10 pm for the horizontal and 9 sm for the vertical marginal discrepancy. (J PROSTHET DENT 1990;64:18-24.)
N
o standardized method for measurement of crown margin adaptation exists. There is disagreement regarding the parameters to evaluate and where the marginal opening should be measured. Fidelity refers to faithfulness of reproduction. In dentistry, fidelity means faithfulness of reproduction of the tooth preparation margin with the restoration. Poor marginal fidelity resulting in a large marginal gap, overcontouring, or a rough surface finish increases plaque accumulation, inducing gingival inflammation.’ This article presents a standardized method for measurement of crown margin fidelity using a biologically oriented rationale. Strong emphasis is placed on measuring those factors that affect plaque accumulation and subsequent gingival health.
REVIEW OF METHODS FOR MEASUREMENT OF MARGINAL DISCREPANCY The many methods for measuring marginal fidelity include four basic categories. These are: (1) direct view, (2) cross-sectional, (3) impression technique, and (4) explorer and visual examination. Researchers use techniques for measurement of marginal fidelity tailored for specific factors to be studied. The direct view, by virtue of its nondestructive nature,
Presented in part before the Academy of Denture Prosthetics, Monterey, Calif. This project was supported in part by BRSG No. SO?‘-RR05304 awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health, Bethesda, Md. *Assistant Professor and Director, Graduate Prosthodontics.
10/l/20323 18
is often used to monitor stepwise distortion. To measure distortion of metal ceramic restoration margins during the various steps of the firing cycle requires that the crown be fired and then repositioned on a measuring stage in a repeatable manner. Shillingburg et al2 popularized this method to compare firing distortion of various margin designs. A number of studies have used this system for measuring marginal distortion at each stage of the porcelain firing process,3-6for assessing marginal fidelity of metal ceramic fixed partial dentures,7 for determining marginal fidelity of different types of crown systems,5r8-11for assessing marginal fidelity of different metal ceramic alloys during the porcelain firing process,12’I3 for determining marginal fidelity of provisional composite resin crowns,14 and for comparing the fit of castings made with various investments. l5 Cooney et all6 seated crowns on a master die and then made impressions of the margins. Resin replicas were formed in the impressions for scanning electron microscopy @EM) measurement of marginal gaps. Faucher and Nicholls17 followed marginal distortion during porcelain firing steps by placing the casting in a jig and tracing the margin with a profile projector. The direct view method is convenient, easy, and rapid because the crown is retrievable, unlike the cementation, embedment, and sectioning method, which causesdestruction of the crown (Table I). However, repeated seating of sample crowns on a master die can damage the margin by abrasion. In addition, the inability to measure and replace the crown precisely on the master die will produce increased standard deviation and decreased statistical significance. A disadvantage of this method is that a rounded margin examined microscopically has no repeatable point of reference on the curved surface. It is difficult to determine marginal overcontouring by direct viewing. The cross-sectional method measures marginal fidelity by placement of crowns on dies, which are embedded in JULY
1990
VOLUME
64
NUMBER
1
MARGINAL
FIDELITY
Table I. Comparison of measuring techniques Disadvantages
Advantages Direct 1.
view
Expedient, rapid, and simplified method for measurement
2. Does not require additional steps
3. Allows measurement at various stages of crown fabrication
Cross-sectional
1. Samples must be sacrificed for sectioning procedure Fig.
of measurement
A scientific method for measurement of crown margin discrepancy should be consistent, reproducible, and have JOURNAL
OF PROSTHETIC
1. Cross-sectional view of tooth-crown margin.
2. Cannot measure marginal fidelity at various stages of crown fabrication 3. Requires additional steps of embedding and sectioning; more time-consuming
resin and sectioned. This technique has been used to measure margin discrepancies for cemented crownsg-il* 18-21 and uncemented crowns, 22to permit comparison of different margin designs of metal ceramic restorations,23 and to evaluate the fit and strength of all-ceramic fixed partial dentures.24 The technique is time-consuming, requires additional steps, and sacrifices the crowns (Table I). This method precludes measurement of marginal distortion at the various stages of porcelain firing on the same samples, but the additional steps and effort provide more information and greater precision of measurement. The cross-sectional evaluation of margins allows greater precision in determination of measuring points and permits determination of the degree of horizontal discrepancy (overcontouring) that is not possible with the direct viewing technique. There is a need for standardization of methodology for measurement of marginal fidelity and delineation of the parameters to be measured.
THE
Tooth
view
1. Greater precision in measurements as measurement points are more accurate and repeatable 2. Allows determination of horizontal marginal fidelity; overcontouring 3. As crown is cemented to die, avoids potential damage from repeated use of master die
Parameters
Cr own
1. With a rounded margin, difficult to determine what point to measure from 2. Less precision due to inaccuracies in repositioning crowns on master die 3. Difficult to assess overcontouring of crown margin 4. With repeated use of master die, potential for wear and damage to master die margin
DENTISTRY
Fig. 2. Cross-sectional high magnification view of crown preparation tooth margin.
standardized points of measurement. Consistent points of measurement are necessary for an impartial comparison of different crown systems. For example, if a crown system has pyroplastic slump or marginal rounding, where should the marginal gap be measured? When a rounded margin is viewed directly from a perpendicular or an impression is made of the margin and is viewed with a SEM, the tendency is to measure at the point of the edge of the cement (Fig. 1, points a and 6), rather than at a point where the gap is created from marginal rounding (Fig. 1, points a to c). For consistency of measurement and a realistic evaluation of the marginal gap, the crown-die complex should be sectioned and viewed in cross-section. This view produces a more reliable assessment of the actual surface of marginal 19
SORENSEN
Lingual
dies, the samples were sectioned faciolingually and mesiodistally with an Isomet low-speed diamond sectioning saw (Buehler Ltd, Lake Bluff, Ill.). This sectioning allowed examination at eight points around the crown, one view on each side of the cut (Fig. 3).
Measurement
Facial
Fig. 3. Incisal view of crown; faciolingual and mesiodistal sectioning measurement points.
opening for plaque habitation (Fig. 1, points a to c). Some methods measure at point d (Fig. 1). However, this point is not an accurate reflection of the dimension of the niche created for microorganisms. Clinically, to get to point d (Fig. l), the cement would have to be chipped away or dissolved in oral fluids from point e to point d (Fig. l), creating a recess of increasing space. During clinical procedures, the margins of a crown preparation appear sharp. However, with microscopic examination, the margin of a crown preparation or a die appears rounded, causing difficulty in selecting a point where the marginal opening is to be measured. Three main points can be used for measurement. Reasonable arguments for the use of points f, g, or h (Fig. 2) for measurement locations can be made. Point f (Fig. 2) most accurately reflects the dimensions of the niche for plaque habitation. Consistency in the point of measurement is more important than the actual point of measurement on the tooth and die.
METHODS A maxillary central incisor ivorine tooth was prepared to a 1.5 mm axial reduction and to 2 mm incisally. A go-degree butt-joint shoulder margin was used according to the manufacturer’s directions. Ten silver-plated master dies were created from the ivorine prepared tooth for each crown system. The 10 silver-plated dies in each group were specifically numbered and impressions were made for indirect fabrication of the crowns. Ten crowns of each brand were made according to manufacturers’ recommendations. The crowns were cemented in a standardized manner with a loading jig that applied 6 pounds of seating pressure for 10 minutes. The crown-die complexes were embedded in epoxy resin and were allowed to cure for 24 hours. Using guide marks on the silver-plated
20
of marginal
fidelity
The objective in using the following method was to gain maximum information regarding the potential biologic response to a margin. The epoxy-embedded, sectioned crowns were photographed at 120 power magnification with an Olympus zoom stereomicroscope, Model SZ-Tr, and PM-6 camera (Olympus Optical Co., Ltd., Tokyo, Japan). A custom-made camera reticle with a scale divided into 5 pm increments provided pictures with the scale superimposed on the prints for standardization and calculations. The 3- X B-inch color prints were then used for measurement of the margin discrepancies. Three independent observers made determinations of the vertical and horizontal marginal fidelity. A plastic overlay was superimposed on the 120 power color photographs of the crown margins with a vertical line corresponding to the root surface and emergence profile (Fig. 4). A second horizontal line coincided with the finish line of the preparation and extended axially along the finish line and away from the tooth (Fig. 4). Because the angulation of tooth structure below the finish line varies with the position on the tooth, three transparent overlays with lines were made. Overlays with grids were made for marginal assessment at the facial (points A and B, Fig. 3), lingual (points E and F, Fig. 3), and proximal (points C, D, E, and F, Fig. 3) surfaces. Measurement of the horizontal and vertical margin discrepancies were then made using glass squares marked with a scale divided into 5 Mm increments. The plastic overlay was correctly aligned with the tooth using the vertical emergence profile line and the preparation finish line for the horizontal line (Fig. 4). The glass square was first moved along the horizontal line until the vertical portion of the glass square intersected the vertical line of the overlay to calculate the amount of vertical margin opening (Fig. 5, A). If the margin was deficient and did not transect the vertical line, the first point on the crown margin that was tangential to the vertical surface of the glass square was selected as the point of measurement. The horizontal margin discrepancy was determined by moving the glass square along the horizontal overlay line until the vertical edge of the glass square intersected the first tangent on the crown margin. Deficient or short margins were calculated by assessing the distance from the tangential intersection to the overlay vertical emergence profile line (Fig. 5, B). The distance was recorded with a negative sign to denote a horizontally deficient margin. The crown margin was judged as overcontoured or excessive when the angle of intersection between crown margin and
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Fig. 4. Measurement technique with plastic overlays and glass square.
the overlay vertical line was greater than 45 degrees (Fig. 5, C). Upon being ruled as overcontoured, the dimension of overcontour was determined by moving the glass square along the horizontal overlay line until the vertical edge of the glass square transected the first tangent on the margin (Fig. 5, D). The distance from the intersection point to the vertical emergence profile line was recorded with a positive sign, denoting a horizontally excessive margin.
RESULTS Seven crown systems with 10 samples in each group were sectioned into quarters, yielding eight measurement points for each crown. The mean vertical and horizontal marginal discrepancies were determined by calculating the mean values, which were determined from the values recorded by the three observers. For each crown system 240 vertical and 240 horizontal marginal discrepancy measurements were made. The interobserver variance or accuracy of measurement was 9 km for the vertical discrepancy and 10 Frn for the horizontal marginal discrepancy (Table II).
DISCUSSION The cementation phenomenon adds another important variable to the vertical marginal discrepancy of a crown system. Jorgensen’sz5 study, which compared pre- and post-cemenation marginal adaptation values, clearly showed that any study aimed at determining the marginal adaptation of a crown system requires cementation of the crowns with procedures that simulate the clinical situation. The hydrodynamic intracoronal pressures that develop
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during cementation and that prevent complete seating of crowns have been well documented.25-31Studies that seat various crowns on test dies and measure marginal openings without cementation will not correctly reflect the marginal adaptation. Highly porous ceramic cores or substructures may alter cement filtration dynamicss Porous core materials may absorb a portion of the cement luting agent, effectively reducing the cement film thickness and allowing the crown to seat more closely to the prepared tooth. Margin studies that do not cement the crowns are unable to detect these differences. Additionally, ifall-ceramic crowns or porcelain labial margin crowns are not cemented, researchers cannot record the fracturing or chipping of ceramic margins that occur when porcelain margins are overextended and fracture from seating pressure. These chips in the porcelain margin can significantly increase the standard deviation in marginal fidelity measurements.
Biologically
oriented
rationale
The primary role of plaque in the etiology of caries and gingival inflammation has been clearly established.’ Dentists are concerned with the quality of the marginal fit of a restoration because of the biologic ramifications. By minimizing the degree of marginal opening, the surface of exposed cement will be decreased, reducing the rate of dissolution of cement that occurs in oral fluids. When the cement is washed out or is chipped out during the removal of excess cement, a recess is created that harbors microorganisms. When this gap is supragingival, the primary concern is caries. When the marginal gap is subgingival and the
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SORENSEN
Fig. 5. Cross-sectional view of tooth-crown junction. Measuring methodoiogy for vertical and horizontal marginal discrepancies. A, Measurement of vertical marginal discrepancy. B, Measurement of horizontal marginal discrepancy (undercontoured). C, Application of cibdegree rule for determination of overcontoured margin. D, Measurement of horizontal marginal discrepancy (overcontoured).
gingival tissues are in intimate contact with the margin, both gingival inflammation and caries are a concern.
Subgingival
margin placement
The importance of the contour of the margin was discussed in Part 1.r Marginal contouring affects accessfor plaque control. Overcontouring of subgingival margins make plaque control difficult or impossible for home hygiene (Fig. 6). At cementation, an overcontoured margin prevents the dentist from removing the excess subgingival
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cement from the underside of the margin with an explorer or scaler (Fig. 6), and the surface of rough plaque-retentive cement is greatly increased. To further compound the problem, the microorganisms that colonize the subgingival cement under an overcontoured margin have a greater pathogenicity than supragingival plaque organisms.32 A crown margin emergence profile that is continuous with.the root surface is most desirab1e.r If the crown margin discrepancy is in the horizontal dimension, an undercontoured margin is more desirable than an overcontoured
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Fig. 6. Cross-sectional view of dentogingival junction of overcontoured crown.
Fig. ‘7. Cross-sectional view of dentogingival junction of undercontoured crown.
margin (Fig. 7). Access for removal of excess cement during cementation and for patient plaque removal is much greater with an undercontoured margin. In measuring the marginal opening and contour, the vertical and horizontal margin discrepancy data yield an approximation of the dimensions of the marginal opening. The total area of marginal discrepancy is critical to the gingival response, since it defines the extent of the niche for bacterial plaque habitati0n.l The tissue interface at the marginal discrepancy will be composed of either rough cement or will appear as a recess bordered by tooth, restoration, and/or cement. The result of either of the tissue-restoration interfaces is a protected niche for bacterial plaque colonization.
Table II.
CLINICAL
IMPLICATIONS
The existence of iatrogenic periodontal disease around esthetic crowns is well d0cumented.l Clinicians placing these restorations need to be aware of the periodontal results of their restorative dentistry. The marginal fidelity of various crown systems is not just an academic pursuit but is of strong clinical concern, affecting the health and esthetics of their patients. SUMMARY A standardized method for the determination of crown margin fidelity is presented. Crown samples were cemented on master dies and embedded for sectioning buccolingually
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Interobserver variance Horizontal 10 pm
Vertical 9
firn
and mesiodistally for determination of vertical and horizontal marginal discrepancies. Three observers measured the vertical and horizontal marginal discrepancies. For the seven crown systems measured, the interobserver variance was 10 pm. This article presents a biologic rationale for a standardized method of measurement of vertical and horizontal marginal discrepancies that will be used to compare various crown systems in future articles. The author thanks Ms. Irene Petrivicius
for her art work.
REFERENCES 1. Sorensen JA. A rationale for comparison of plaque-retaining properties of crown systems. J PROSTHET DENT 198%62:264-g. 2. Shillingburg HT, Hobo S, Fisher DW. Preparation design and margin distortion in porcelain-fused-to-metal restoration. J PROSTHET DENT 1973;29:276-84.
3. Ando N, Hakamura K, Namiki T, Sugata T, Suzuki T, Moriyama K. Deformation of porcelain bonded gold alloys. J Jpn Sot Appar Mater 19’72;13:237-48. 4. Hamagucbi H, Cacciatore A, Tueller VM. Marginal distortion of the porcelain-bonded-to-metal complete crown: sn SEM study. J PROSTHET DENT 1982;47:146-53.
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5. Wanserski DJ, Sobczak KP, Monaco JG, McGiveny GP. An analysis of margin adaptation of all-porcelain facial margin ceramometal crowns. J PROSTHFXDENT 1986;56:289-92. 6. Anusavice KJ, Carroll JE. Effect of incompatibility stress on the fit of metal-ceramic crowns. J Dent Res 1987;66:1341-4. 7. Van Rensburg F, Strating H. Evaluation of the marginal integrity of ceramometal restorations. Part II. J PROSTHET DENT 1984,52:!210-4. 8. Schneider DM, Levi MS, Mori DF. Porcelain shoulder adaption using direct refractory dies. J PROSTHET DENT 1976;36:583-7. 9. Sato T, Wohlwend A, Scharer P. Marginal fit in a “shrink-free” ceramic crown system. Int J Periodont Rest Dent 1986;3:9-21. 10. Brukl CE, Philp GK. The fit of molded all-ceramic, twin foil, and conventional ceramic crowns. J PROSTHETDENT 1987;58:408-13. 11. Scharer P, Sato T, Wohlwend A. Marginal fit in the cera-platin crown system. Quint Dent Technol 1987;11:11-25. 12. Buchanan WT, Svare CW,Turner KA. The effect of repeated firings and strength on marginal distortion in two ceramometal systems. J PROSTHET DENT 1981;45:502-6.
13. Dederich DN, Svare CW, Peterson LC, Turner KA. The effect of repeated firings on the margins of nonprecious ceramometals. J PROSTHET DENT 1984;51:628-30. 14. Tjan AHL, Tjan AH, Grant BE. Marginal accuracy of temporary composite crowns. J PROSTHETDENT 1987;58:417-21. 15. Cooney JP, Doyle TM, Caputo AA. Surface smoothness and marginal fit with phosphate-bonded investments. J PROSTHETDENT 1979;41: 411-7. 16. Cooney JP, Richter WA, MacEntee MI. Evaluation of ceramic margins for metal-ceramic restorations. J PROSTHETDENT 1985;54:1-5. 17. Faucher RR, Nicholls JI. Distortion related to margin design in porcelain-fused to metal restorations. J PROSTHETDENT 1980;43:149-55. 18. Hunt JL, Cruickshanks-Boyd DW, Davies EH. Marginal characteristics of collarless bonded porcelain crowns produced using a separating medium technique. Quint Dent Technol 1978;9:21-6. 19. Faul TW, Hesby RA, Pelleu GB, Eastwood GW. Marginal opening of single and twin platinum foil-bonded aluminous porcelain crowns. J PROSTHETDENT 1985;53:29-33. 20. Chan C, Haraszthy G, Gerstorfer JG, Weber H. The marginal fit of Cerestore full-ceramic crowns-a preliminary report. Quint Intern 1985:6:399-402.
21. Davis DR. Comparison of fit of two types of all-ceramic crowns. J PROSTHET DENT 1988;59:12-6. 22. Ulman JL. Collarless binded porcelain crowns, a comparison of fahrieating techniques. M.D.S. Thesis, Indiana University, Indianapolis, Ind., 1972. 23. Panno FV, Vahidi F, Gulker I, Ghalili KM. Evaluation of the 45-degree labial bevel with a shoulder preparation. J PROSTHET DENT 1986;56: 655-61. 24. Campbell SD, Sozio RB. Evaluation of the fit and strength of an allceramic fixed partial denture. J PR~WHET DENT 1988;59:301-6. 25. Jorgensen KD. Structure of the film of zinc phosphate cement. Acta Odontol Stand 1960;18:491-501. 26. Fusayama T, Ide K, Kurosu, Hosada H. Cement thickness between cast restorations and preparation walls. J PROSTHETDENT 1963;13:354-64. 27. Basset RW. Solving the problems of cementing the full veneer cast gold crown. J PRCISTHETDENT 1966;16:740-7. 28. Ishikiriama A, Oliveira CD, Viera DF, Mondelh DC. Influence of some factors on the fit of cemented crowns. J PROSTHETDENT 1981;45:400-4. 29. Webb EL, Murray HV, Holland GA, Taylor DF. Effect of preparation relief and flow channels on seating full coverage castings during cementation. J PROSTHETDENT 1983;49:777-80. 30. Eames WB, G’Neal SJ, Monteiro J, Miller C, Roan JD, Cohen KS. Techniques to improve the seating of castings. J Am Dent ASSOC 1978;96:432-7. 31. Gavelis JR, Morency JD, Riley ED, Sozio RB. Effect of various finish line preparations on the marginal seal and occlusal seat of full crown preparations. J PROSTHETDENT 1981;45:138-45. 32, Lang NP, Kiel RA, Anderhalden K. Clinical and microbiological effects of subgingival restorations with overhanging or clinically perfect margins. J Clin Periodont l&563-78. Reprint requests to: DR. JOHN A. SORENSEN CHS 33-041 SCHOOLOF DENTISTRY UNIVEFWTYOF CALIFORNIA Los ANGELES,CA 90024
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