Internal escape channel to improve the seating of full crowns with various marginal configurations: A follow-up study

THE JOURNAL

OF

PROSTHETIC DENTISTRY JUNE

. OPERATIVE

FIXED PROSTHODONTICS SI.CTION

VOLUME

53

NUMBER

6

DENTISTRY

EDITORS

SAMUEI. WILLIAM

E. GUYER WILLIAM LEFKOWITZ F. P. MALONE JOHN E. RHOADS

ROBERT C. SPROULL

Internal escape channel to improve full crowns with various marginal A follow-up study Anthony H. L. Tjan, Dr. Dent., D.D.S.,* Ruben Sarkissian, B.D.S., D.D.S.““*

Gary D. Miller,

Loma Linda University, School of Dentistry, Loma Linda, Calif Dentistry, Los Angeles, Calif.

I

ncomplete seating of full cast crowns during cementation is commonly observed by most dentists. Various techniques have been offered to solve the problem.‘-” Factors that affect the film thickness of cement under castings include cementing force, duration of force, type of cement, viscosity of the cement mix, convergence angle, preparation dimension, and finish line of the preparati0n.l~‘~‘~ ” Venting has been reported to improve the seating of crowns during cementation.‘, 3,’ Vibratory pressure used during cementation was found to produce a better marginal adaptation than static pressure alone.‘,” Die seating of also improves the complete spacing crowns.‘, ’ The placement of an internal escape channel (a modified axial groove placed on the preparation, which is not reproduced in the casting) has been found to enhance the marginal adaptation of castings.“.‘” The internal escape channel allows cement to escape marginally more readily, reduces the occlusal cement thickness, and thereby ensures an improved marginal adaptation of full cast crowns. Furthermore, Tjan and Sarkissian” reported that the incorporation of an escape channel did not affect the retentive properties of the restoration. Van Nortwick and Gettleman” reported that venting or internal relief alone effectively improved the seating of cast crowns. However a combination of the two was

*Professor and Director, Biomaterials Research, Department of RCA storative Dentistry, Loma Linda University, School of Dentistry. ** lcsistant . Profccwr and Co-Chairman of the International Studrnt Program. ***(:linic:d Assistant Professor. Restorative Section.

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the seating of configurations:

D.D.S.,**

and University

and of Southern

California,

School of

found to be the most effective. Unfortunately, dentists seem reluctant to place a vent hole in finished full cast crowns because of the additional time required to close the hole and the extra laboratory expense. In addition, the technique is not always practical for ceramometal restorations. The purpose of this study was to investigate the effectiveness of an internal escape channel on the seating of complete cast gold crowns with an accentuated finish line, a 90-degree shoulder, and a 90-degree shoulder with 45-degree bevel.

MATERIAL

AND

METHODS

Thirty extracted human maxillary molars of comparable crown length and size were selected and prepared to receive complete cast gold crowns. The length of the preparations was approximately 6 mm with a buccolingual convergence angle of about 10 degrees and mesiodistal convergence angle of about 6 degrees. The sample was divided into the following three groups (Fig. 1): group No. 1, full crown preparation with accentuated finish lines; group No. 2, 10 full crown preparations with 1.4 mm OO-degree shoulders (Fig. 2); and group No. 3, 10 full crown preparations with 1.4 mm 90-degree shoulders and Its-degree bevels. The roots of the prepared teeth were embedded in phenolic ring forms with epoxy resin (Buehler Ltd., Evanston, Ill.). The long axes were aligned parallel to the wall of the rings. All specimens were kept in a humidor except during cementation and measurement. Castings were fabricated with a standardized method. Patterns were made directly on the prepared teeth with type II blue inlay wax (Kerr Mfg. Co., Romulus, 759

TIAN,

ACCENTUAlED

MILLEK,

4ND

SARKISSlAN

Sl-lOULDER

sktOUJXR-8EVEL Fig. 1. Three marginal finish-line designs. Fig. 3. Indentation milled in center oi casting’s occiu. sal surface is used as reference point to measure vertical discrepancy.

Fig. 4. Device used to measure vertical discrepancy. Fig. 2. Shoulder and shoulder-bevel designs. Mich.). They were then invested in Luster-cast (Kerr Mfg. Co.), a gypsum-bonded investment, with a powder/liquid ratio of 50 gm powder to 14.5 ml distilled water. The investment was vacuum mixed and poured into a casting ring lined with wet asbestos. The casting rings were stored in a humidor for a minimum of 1 hour. The rings were removed, placed in an oven for 30 minutes at 600” I?, and held at 900” F for an additional hour. Castings were made with type III gold (Ney B-2, Bloomfield, Conn.). The resulting crowns were cleaned by pickling in Jel Pat (J.F. Jelenko Co., New Rochelle, N.Y.). Internal relief was not provided except for the removal of nodules that prevented complete seating. Attempts were not made to polish the finished crowns. The base of the ring form in which the specimen was embedded was wet-polished on the Handimet grinder 760

(Buehler Ltd.) with a progressively hner sandpaper from 280 to 600 grit. The occlusal surface of the casting was also made flat and parallel with the base of the ring with a disklike stone .nounted on a porcelain facing drill (Model M-l 1, Mardclle Industrial Products, Monrovia. Calif.). An indentation (dinple) was placed in the center ot the occlusal surface with a No. 6 round bur (Fig. 3). The dimple provided a reference point to ensure an accurate and repeatable measurement of the vertical (gingival) discrepancy with an electronic measuring device (Minicorn micrometer, Tokyo Seimitzu, Tokyo, Japan) (Fig. 4). Placement

of the escape channel

.4 medium diamond bur with a rounded end (Kimberley No. 700, F.G. Atwood, Inc., Tarzana, Calif.) was used to place the escape channel. The depth of the channel was almost equal to the full diameter of the diamond bur. On the accentuated finish line. the channel JUNE 1985

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ESCAPE CHANNEL

Table I. Vertical discrepancy mean (in microns; 10e3 mm)

Totals Mean SD

and mathematic

Group No. 1

Group No. 2

Group No. 3

All groups

20 50 s 35 5 12 28 10 10 8 183 18.30 14.97

28 26 18 16 33 23 18 18 21 20 221 22.10 5.40

56 48 40 26 16 49 19 21 54 40 369 36.90 15.18

773 25.77 14.72

Group No. 1 = Acwntuated finish line; group No. 2 = OO-degree shouldw and qrouv No. 3 = 90.degree shoulder with 45-degree brvel.

terminated about 0.5 mm short of the gingival finish margin. On the shoulder and shoulder with bevel margins, the channels terminated exactly at the junction between the axial wall and the shoulders. Cementation

of the casting

Type I zinc phosphate cement (Fleck’s powder batch No. DOl-042481, liquid batch No. H33-060882; Mizzy, Inc., Clifton Forge, Va.) was mixed and used according to the manufacturer’s recommendation. The ratio of 1.3 gm powder to 0.5 ml liquid was used. Standardization of successive mixes was accomplished by proportioning the cement powder on a precision scale and dispensing the liquid with a 1 cc insulin syringe. The powder was added to the liquid in small increments, and the mixture was spatulated for 90 seconds. Two layers of Copalite (Cooley and Cooley, Ltd., Houston, Tex.) were applied on the preparations. The casting was then filled with the cement to cover the inner surface evenly, seated with finger pressure, and a static load of 12 pounds was applied for 10 minutes with a cementing device (Fig. 5). The room temperature during cementation was 24” C. Assessment

of vertical

discrepancy

A completely seated uncemented casting on its respective tooth preparation was pretreated with a static load of 12 pounds for 5 minutes, and its measurement was used to determine the baseline (zero point) on the micrometer scale. The dimple on the occlusal surface served as the reference point. The value obtained after cementation indicated the vertical discrepancy score of the specimen. A one-way analysis of variance and Duncan’s new multiple-range test were used to establish THE IOURNAL

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DENTISTRY

Fig.

5.

Device used to apply 12-pound static load dur-

ing cementation.

the statistical significance among the means of the groups. RESULTS Table I presents the vertical discrepancy values (gingival discrepancy) of all test specimens, as well as the means and standard deviations. The difference between the means of the accentuated finish line and 90-degree shoulder groups was not significant statistically. However, the difference between the 90-degree shoulder with 45-degree bevel group and the accentuated finish line group was significant statistically at p < .Ol. The difference between the 90-degree shoulder with 45-degree bevel group and the 90-degree shoulder alone was also significant at fi < .05 (Tables II and III). DISCUSSION Marginal configuration of a full crown preparation has been shown to affect the marginal adaptation of full cast crowns.” It was also reported that a feather-edge margin provided a better seal than a 90-degree shoulder.” On the other hand, it has been shown that 761

TJAN,

Table II. Analysis Source

of

variation Between

groups

Within group Total *Crrricnl region i?

MILLER,

AND

SARKlSSJAb

of variance+ Sum

of

squares

df

1930.87 4356.50 6287.37

2 2: 29

Mean square

Computeti f

OhT;42 : ft i ‘I,T

5 OQ

5.39; /, I; (!!

Table III. Duncan’s multiple

range test -~--~-~~.-. ~. -. 2

P

2.888 11.581 _-----.-.

=P %

..~ 3

.-.

3.025 12.170 ._-.- ._~ ,.

terminates 2 mm short of the finish margin was less efFective.‘OWhen the shoulder and bevel design is used, the extension of the escape channel about midway into the shoulder will shorten the distance to the preparation’s margin considerably (Fig. 6), and it is reasonable to assume that this will produce a better marginal fit.

SUMMARY

Fig. 6. Modification of escape channel suggested to attain better results on full crown with shoulder and bevel-margin design.

preparations with a 90-degree shoulder afforded a better seat than either a design with a feather-edge finish line or a 90-degree shoulder with a bevel.‘* An internal escape channel was shown to improve the complete seating of full cast-gold crowns with accentuated finish lines (light chamfer).“, ‘” A vertical discrepancy value of about 115 pm was reported when an escape channel was not provided.” In addition, the internal escape channel’s application on the preparation did not affect the retentive properties of the restoration. This study revealed that an internal escape channel provided a significant improvement on the seating of castings with a 90-degree shoulder or 90-degree shoulder with a 45-degree bevel. A casting with a 90-degree shoulder seemed to have a vertical discrepancy comparable to that of an accentuated finish line. Obviously, the data obtained from this study supports the findings of Gavelis et al.‘* that a 90-degree shoulder seated better than a shoulder with a bevel added. They postulated that the poor seal of a 90-degree shoulder prior to complete cementation contributed to a better seating by allowing the cement to escape marginally more readily without filtration. It has been reported that an escape channel that 762

The effectiveness of an internal escape channel in improving the marginal adaptation of full crowns with various marginal configuration was investigated. Full crowns with 90-degree shoulders had a vertical discrepancy comparable to those of crowns with accentuated finish lines. Although an internal escape channel significantly improved the seating of a full crown with a 90-degree shoulder and 45-degree bevel, its vertical discrepancy was much higher than those of crowns with an accentuated finish line or a 90-degree shoulder. REFERENCES 1

Jbrgenson, K. D.: Factors affecting the ~dm thickness l)t zim phosphate cements. Acta Odontol Sand l&479, 1960. 2. Jorgenson, K. D.: Structure of the film thickness ot /in< phosphate cements. Acta Odontol Stand 18:491. 1960 3 Bassett, R. W.: Solving the problems of cementinS the full vc~~w~ cast gold crown. J PROSWET DENT l&740. 1966. 4. Cooper T. M., Christensen, CG.J., Laweli, II. R.. and Baxtw. R.: Effect of venting on cast gold full crowns. .J PKOS.I.III:~ID:-xY 26:621, 1971 5. Koyano, E., Iwaku, M, and Fusayam;l, ‘I’ : I’ressu~-ing !rI ;Iniques and cement thicknesr for cdst restor;Ilion\. ,J PKOI i!l.l DENT 40:544,

6.

1978.

Oliveira, J. F., Ishikiriama, ,2., Viewa, I> P.. .tnd IZIor~dril~, J Influence of pressure and vibration durmq ccmenration ,I PROSTHET DENT 41:173,

1979

7.

Fusayama, T., Ide, K., and Hosada, H.: Keilel of rcsisitanrr r)t cement of full cast crowns. J PROSTHET DENT 14~94, 1964 8. Eames, S. B., O’Neai, S. J., Monteiro, .J.. \iiller, C., Roan, Jr., .J. D., and Cohen, K. S.: Techniques to improve ihe seatin< ol castings. J Am Dent Assoc 96:432, 1979. 9. Miller, G. D., and Tjan, A. H. L.: The internal escape channel. A solution to incomplete seating of full cas( crowns. .J Am Dent Assoc 104~322, 1982.

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and occlusal seat of full crown preparations. J 45:138, 1981.

10. Tjan. A. H. L., and Sarkissian, R.: Internal escape channel: An alternative to venting complere caSl crowns. J PKOS’I‘HFXDENT 52:50, 1984. Il. Van Nortwick, W. T., and Gettleman, L.: Effect of internal relief, vibration, and venting on the vertical seating of cemented crowns.

12.

.) PROSTHET

DENT

45:395,

PROSTI~ET

DWI

1981.

Gavelis. ~J.R., Morency. J. D., Riley, E. D., and Sozio, R. B.: The elfect of various linish line preparations on the marginal seal

Successful integration prosthodontics Richard

R. Seals, Jr., D.D.S., M.Ed.,*

of fixed and removable and Ivy S. Schwartz,

D.D.S., M.Ed.**

University of Oklahoma, College of Dentistry, Oklahoma City, Okla., and University of Texas, Dental School, San Antonio, Tex.

D

entistry has become sufficiently complex to warrant division into various specialities. Endodontic, orthodontic, periodontic, and surgical procedures have been effectively combined to retain teeth that formerly would have been extracted. The tendency to save teeth has notably improved prosthodontic services. According to the American Dental Association, this trend will continue in private practice and increase the emphasis on fixed and removable prosthodontics.’ The integration of fixed and removable prosthodontics to restore the dentition of a partially edentulous patient poses a challenge and an opportunity. Success requires diagnostic skill, perceptive treatment planning, and diligent execution.*

DIAGNOSIS

AND TREATMENT

PLANNING

Diagnosis of the partially edentulous mouth is accomplished by a thorough review and correlation of diagnostic data from the patient history, health questionnaire, personal interview, head and neck examination, oral examination, radiographic survey, and diagnostic casts mounted on a suitable articulator.3 The diagnostic casts reveal the surfaces for guide planes, retention, and the path of insertion for a removable partial denture. The desired abutment contours may be made on existing teeth, and prepared in sound

Presented at the American Academy of Crown and Bridge Prosthodontics, Chicago, III. *Assistant Professor, Department of Removable Prosthodontics, University of Oklahoma, College of Dentistry. **Assistant Professor, Department of General Practice, University of Texas, Drntal School.

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tooth enamel or in planned restorations. Objectives and mouth preparations are noted and recorded as part of a total treatment plan in advance of definitive therapy. The importance of a comprehensive diagnosis and treatment plan for the patient who receives a combined fixed and removable prosthesis cannot be overemphasized.4 The first requirement in a logical treatment sequence for the partially edentulous mouth is that the dentist must be cognizant of the relative merits of fixed and removable prosthodontics.3 There are indications for each type of prosthesis, and the dentist must evaluate and justify the implementation. A fixed prosthesis is the ideal replacement for missing teeth if the abutment teeth are healthy.3-8 In general, removable prostheses are used when there are insufficient teeth to accommodate a fixed prosthesis or when the removable prosthesis is considered advantageous.5 The following factors are contraindications for fixed partial dentures.‘. lo 1. Excessive edentulous span. Removable dentures receive additional support and stabilization from teeth on the opposite side of the arch and from the residual ridge. 2. Periodontal support of remaining teeth. The total support required of the teeth will be diminished by fitting the denture base to the edentulous ridge, 3. Cross-arch stabilization. The leverage and torque on the abutment teeth can be more evenly distributed by stabilizing the remaining teeth against lateral and anteroposterior forces. 4. Absence of an abutment tooth posterior to the edentulous space. If there is no abutment tooth posterior to the edentulous space, suitable replacements are limited. The customary replacement is a removable partial 763