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Internal escape channel: An alternative to venting complete crowns
Internal escape channel: An alternative complete crowns Anthony H. L. Tjan, Dr.Dent., D.D.S.,* and Ruben Sarkissian, \ ‘nivrrsity of Southern California. School of Dentistry, Los Angeles. Calif.
Ah:.( mcomplete seating of a complete cast crown is a multifactorial phenomenon. The interaction of the contributing factors is still not fully understood. Hydrodynamics has been considered the primary conrideration in all cementations.’ Numerous studies have indicated that occlusal ventmg enhanced complete seating of a complete cast crown hv the release of hydrostatic pressure, which accumuialed in the occlusal portion.-‘-, Unfortunately, most denrists are reluctant to vent a complete cast crown because of the additional chairside time and the extra fer required. In addition, the technique of venting is noi always practical for ceramometal restorations. Eames et al.” and Pusayama et al.” advocated internai surface relief or spacing to reduce gingival discrep;mcy (incomplete seating). -Qan et al.” showed that axial grooves complicated tire cementation of a complete cast crown, but they ~heorizrd that the axial groove used as a cement escape channel might enhance the seating of a complete cast mown. A subsequent study on typodont teeth revealed ihat ;+n internal escape channel placed on the buccal surface enhanced the seating of complete cast c-sowns. The purpose of this study was to verify the effectiveness of the internal escape channel on the seating of complete cast-gold crowns on natural teeth and its effect on retentive properties. This study approached clinical conditions more closely than earlier studies. MATERIAL
AND METHODS
.\n escape channel is basically similar in form to the traditional retentive groove, with two modifications. (I) The usual sharp definite seat of the groove at the gingival end is changed to a gradual round terminus. This can be attained easily with a tapered cylindrical
to venting
B.D.S., D.D.S.**
diamond bur with a rounded end (Kimberley No. 700 F. G.. Atwood Industries, Tarzana, Calif.). (2) It is imperative that the channel have a funnel-shaped communication with the occlusal surface (Fig. 1). The depth of the channel is approximately equal to the diameter of the diamond bur, and it terminates in a gently rounded end approximately 0.5 mm short of the gingival finish margin (Fig. 2). The escape channel can be placed easily on the prepared tooth before or after the final impression is made, while the tooth is still anesthetized. If it is placed before the impression is made, it must be blocked out on the die. Thirty extracted human mandibular molars of comparable length and size were selected and prepared to receive complete cast gold crowns. The length of the preparation was approximately 6 mm, with a buccolingual convergence angle of about 10 degrees and a mesiodistal convergence angle of about 6 degrees. A chamfer finish margin was used. The roots of the prepared teeth were embedded in Bakelite rings (Buehler Ltd., Evanston, Ill.) filled with autopolymerizing acrylic resin (Orthocryl, StratfordCookson Co., Newman, Ga.). The long axes were aligned parallel to the tensile force to be applied. All specimens were stored in a humidor except during cementation, measurement, and tensile testing. Five groups of 10 specimens each were made from the sample. Group No. 1 had no escape channel; this group served as the control. Group No. 2 had a buccal escape channel. Group No. 3 had a buccal escape channel, and two layers of cavity varnish (Copalite, Cooley & Cooley Ltd., Houston, Tex.) were applied to the prepared tooth. Group No. 4 had a lingual escape channel, and in group No. 5 an underextended buccal escape channel was prepared 2 mm short of the finish margin. iZfter they were dislodged by the Instron testing instrument (Model 1350, Instron Corp., Canton, Mass.), the castings for group Nos. 1 and 2 were
[LJLY 1984
VOLUME
52
NUMBER
1
INTERNAL
ESCAPE CHANNEL
Fig. 2. Medium diamond bur with rounded end is used to place escape channel. Terminus is about 0.5 mm short of gingival finish margin.
Fig. 1. A, Escape channel placed on buccal surface of complete crown preparation. B, Diagram depicting escape channel with rounded gingival end and funnel-shaped occlusal end.
cleaned in an ultrasonic bath and reused for group Nos. 3 and 4. Gold castings were made by a standardized method. Direct wax patterns were made on the prepared teeth with type II blue inlay wax (Kerr Mfg. Co., Romulus, Mich.). They were invested in Luster-Cast, a gypsumbonded investment (Kerr Mfg. Co.), with powder/ liquid ratio of 50 mg 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 at least 1 hour. The rings were removed, placed in an oven for 30 minutes at 600“ F, and held at 900” F for an additional hour. Casting was done in a vacuum casting machine (Model No. 270B, Torn, Chayes Virginia Inc., Evansville, Ind.) with type III gold (Rx 41, Jeneric Gold Co., Wallingford, Conn.). The cast crowns were cleaned in a pickling solution (Jel Pat, J. F. Jelenko & CO., New Rochelle, N. Y.). No internal relief was made except for the removal of nodules that prevented complete seating. The finished crowns were not polished. The castings were provided with a ringlike attachment with a flat table at the top. The ring was used to
THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 3. Casting with ring attachment and flat table at
top.
provide a grip for the Instron testing instrument, and the table was used to apply the static load during cementation (Fig. 3). The base of the ring in which the specimen was embedded was polished on the Handimet grinder (Buehler Ltd., Evanston, Ill.) with 280 to 600 grit abrasive papers. The base must be exactly flat and parallel to the loading table at the top of the ring attachment. To obtain exact parallelism, the loading
51
TJAN
AND
SARKISSIAN
Fig. 6. Electronic micrometer used to measure vertical discrepancy.
Cementation of the castings Fig. 4. Device used to obtain parallelism of loading table with base of embedding ring.
Type I zinc phosphate cement (Tenacin, powder batch No. 03478, liquid batch No. 081478, L. D. Caulk Co., Milford, Del.) was mixed according to the manufacturer’s specifications. Standardization of all mixes was accomplished by proportioning the cement powder on a precision scale and dispensing the liquid with a calibrated 1 ml insulin syringe. The powder was added to the liquid in small increments, and the mixture was spatulated for 90 seconds. The inner surface of the crowns was coated with an even thickness of cement. The crown was seated with finger pressure, and a load of 12 pounds was applied for 10 minutes with a cementing device (Fig. 7). To reduce one variable, the cementation was performed by one investigator. The room temperature during cementation was 24’ C.
Assessment of vertical discrepancy
Fig. 5. Dimple in center of loading table is used as reference point to ensure accurate measurement of vertical discrepancy. table was finished by use of a disklike stone mounted on a porcelain facing drill (Model M-l 1, Mardelle Industrial Products, Monrovia, Cal.) (Fig. 4). In the center of the table, an indentation (dimple) was made with a No. 6 round bur (Fig. 5). The indentation was used as a reference point to assure accurate measurement of the vertical (gingival) discrepancy with an electronic measuring device (Minicom micrometer, Tokyo Seimitzu, Tokyo, Japan) (Fig. 6).
52
The measurement of a completely seated uncemented casting on its respective tooth preparation under a static load of 12 pounds for 5 minutes was used to determine the baseline (zero point) on the micrometer scale. The indentation on the table served as the reference point. The difference in value obtained after cementation indicated the vertical discrepancy of the specimen.
Assessment of retention Prior to tensile testing, the cemented specimens were stored in distilled water for 1 week in an incubator at 37” C. The tensile force required to dislodge the crowns was determined by an Instron testing instrument with a crosshead speedof 0.05 inch/min (Fig. 8).
JULY 1984
VOLUME
52
NUMBER
1
INTERNAL
ESCAPE CHANNEL
Fig. 7. Cementing device used to apply load of 12 pounds during cementation of crown.
Fig. 8. Self-aligning ing.
Analysis of variance and Duncan’s new multiple range test were used to establish significance among the experimental groups.
deviations for group Nos. 1, 2, and 1% Statistical analysis of the data by means of the analysis of variance (critical region: F > 5.49, (Y = O.Ol), indicated a statistically significant difference among the three groups. Application of Duncan’s new multiple range test revealed a statistically significant difference between group Nos. 1 and 3 and between group Nos. 2 and 3 at p < .05 significant level. The difference of the means between group Nos. 1 and 2 was not significant. Data collected from this study indicated that the application of two layers of Copalite reduced the retentive property of complete cast-gold crowns (Fig. 9). The means of vertical discrepancies between group Nos. 2 and 4 were not statistically significant at p < .05 significant level. This result indicated that it made no difference whether the escape channel was placed on the buccal or lingual surface of the preparation (Table III). The difference of the means of vertical discrepancies between group Nos. 2 and 5 was statistically significant. The use of an underextended buccal escape
RESULTS The vertical discrepancies, means, and standard deviations for group Nos. 1, 2, and 3 are presented in Table I. Statistical analysis of the data by means of the analysis of variance (critical region: F 1 5.49, a = O.Ol), revealed a statistically significant difference among the three groups. Application of Duncan’s new multiple range test revealed a statistically significant difference between group Nos. 1 and 2 and between group Nos. 1 and 3 at p < .05 significant level. The difference of the means between group Nos. 2 and 3 were not significant. Results of this study show an escape channel placed on the buccal surface of full crown preparations enhances the seating of complete cast gold crowns. Table II presents the retention, means, and standard
THE JOURNAL
OF PROSTHETIC
DENTISTRY
assembly used for tensile test-
53
TJAN
---- -.-
160 m
160
9
140
2 a
120
5 z 0 F z ," w CT
.
100
AND
SARKISSIAN
(CONTROL) (ESC.CHANNEL) (ESC. CHANNEL 8 COPALITE)
%
80 4 60
.
40
.
‘\. ‘-e
20 12345678
9
10
Fig. 9. Retentive values of group No. 1 (control), group No. 2 (with buccal escape channel), and group No. 3 (with buccal escape channel and two layers of Copalite).
Table I. Vertical discrepancy mean (in microns; lo-’ mm)
Group No. 1 (control)
and mathematic
Group No. 2 (buccal escape channel)
Group No. 3 fbuccal escape channel and Copalite) 20 50 i 35 r, 12 28 10 10 8 183 18
14.97
channel (2 mm short of the gingival finish margin) was ineffective. Fig. 10 compares the mathematic means and standard deviations of the five groups. DISCUSSION Incomplete seating is a common dilemma in cementation of a complete cast crown. There are many factors that contribute to vertical discrepancy. Some of them are convergence angle of the preparation, type of cement used, thickness of the cement mix, filtration process, and h ydro dynamics. Hydrodynamics has been termed the primary consideration.’ However, Hoard et
Table II. Tensile force required to dislodge complete cast crowns (in pounds)
Group No. 1 (control)
Group No. 2 (buccal escape channel)
Group No. 3 (buccal escape channel and Copalite) 80 70 80
121 115 89 08 135 101 100 107 150
90
60 74 50 88 98 90 7'80 78 14.85
94 Ill0 111 19.41
al.“’ indicated that the direct role of hydrostatic pressure in resistance to crown seating may have been overestimated. It would be desirable if the problem of complete seating could be reduced significantly by a simpler procedure than venting. The procedure should be performed at the chair with a minimum of time and equipment and require no other alteration on the finished casting. The internal escape channel was designed to offer a simplified and practical solution to the problem of incomplete seating of complete cast crowns. A single
1lJL.Y 1984
VOLUME
52
NUMBER
1
INTERNAL
ESCAPE CHANNEL
t
20
f ii
I
GROUP
I
I
II
I - I III
Iv
Comparison of mean and standard deviation of five groups: I (control); II (buccal escape channel); III (buccal escape channel and Copalite); IV (lingual escape channel), and V (underextended buccal escape channel). Fig.
10.
Table HI. Mathematic deviation
of vertical Group
Mean SD
mean and standard discrepancy (in microns)
h’o. 2
30 16.24
Group No. 4
Group No. 5
42 17.85
60 27.93
internal escape channel placed on the buccal surface of a typodont tooth has significantly enhanced the seating of a complete cast-gold crown.’ An escape channel facilitates the drainage of excess cement and consequently reduces the hydrostatic pressure at the occlusal portion. Fig. 11 shows the excess cement in the vicinity of the escape channel’s orifice. The data collected from this study indicated that escape channels placed on extracted human teeth significantly reduced the vertical discrepancy. Although the result was not significant, the application of Copalite produced slightly better seating. Presumably, the cavity varnish reduced the surface roughness and facilitated the cement flow. Placement of the escape channel on the curved buccal surface or the relatively flat lingual surface made no difference in crown seating. Although this conclusion is not a direct finding from the data analysis, the location of the escape channel is not significant. However, for practical reasons the escapechannel must be placed on the buccal or lingual surface for ease of finishing the margin. Despite better adaptation, the escapechannel did not
THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 11. Excess cement in vicinity orifice.
of escape channel’s
alter retention of the crown. However, the data suggest that the distribution of scores is clustered around the mathematic mean as shown by the small standard deviation (111 k 19.41 pounds). The scores of the control group are more widely dispersed around the mean (114 + 32.42 pounds). The application of two layers of Copalite significantly reduced the retentive property of the crown (Fig. 9). This, also, is due to the decreaseof surface roughness of the preparation necessary for the mechanical bond of the cement to the tooth structure, as evidenced by the retentive failure at the tooth-cement interface. When Copalite was not used, the failure was found at the cement-gold interface. No correlation was found between vertical discrepancy values and retentive properties.
55
TlAN AND SARKISSIAN
Further investigations are required to verify whether internal escape channels can be applied to shoulder or shoulder and bevel marginal design or the use of various kinds of cement. CONCLUSIONS An internal escape channel enhances the seating of complete cast-gold crowns. The presence of a channel neither increases nor decreasesthe retentive property of the crown. The location of the channel does not seem to be significant. However, an underextended channel proved to be ineffective.
micromeasurement of wnted and non-vented cast crown mat $nal adaptation. Drm Clin North ,Zm 15:663. 1971, i Coopc~. ‘1‘ M., Christensen, G. J., Laswell, H. R., and Baxter. K. I3-fect of ventinS on caqt gold full c’rowns ,J PKOSTIICI r)F.S’l 26Z62.1 ! 97 1. (1 Eamth. Ct’. B., O’Neal, S. ,J.. hZontriro, J Miller. C., Roan. Jr , J. I)., and (Zohcn. K. S.: ‘l’echniques to tmprovr the scatiy of castings. J Am Den1 Assoc 96:432, 197X. 7 Fusayamn, T. Ide. K., and Hosada. f-1.: Relief of resistance 01 c‘rment of full cast crowns. J PRoswrr DENT. 14:95. 1964. X Tjan, A. II I.., Sarkissian. R., and hliller, G II. ISect 01 multiple axinl qrooves on thr marginal adaptation of full m-gold crowns. ,J PKO~T~IETDEW 46:399, 198 1. 0 hlillw, C;. LX. and ‘I‘jan. I\. 11. I..: An internal escape channel: .I vimplilied solution to the problem of incomplete xating of full ust-gold CI‘OW~S.J Am Dent Assoc 104~322, 1982. 111. lioard, R. J., (:aputo, .I. I\.. Contino, R. hsl., and Koenig, hf. E.: Intratoron;d pressure during crown crmentation. J PRO\rltll DEYI 40:5?0. 1978
IULY 1984
VOLUME 52
NUMBER 1
Ah:.( mcomplete seating of a complete cast crown is a multifactorial phenomenon. The interaction of the contributing factors is still not fully understood. Hydrodynamics has been considered the primary conrideration in all cementations.’ Numerous studies have indicated that occlusal ventmg enhanced complete seating of a complete cast crown hv the release of hydrostatic pressure, which accumuialed in the occlusal portion.-‘-, Unfortunately, most denrists are reluctant to vent a complete cast crown because of the additional chairside time and the extra fer required. In addition, the technique of venting is noi always practical for ceramometal restorations. Eames et al.” and Pusayama et al.” advocated internai surface relief or spacing to reduce gingival discrep;mcy (incomplete seating). -Qan et al.” showed that axial grooves complicated tire cementation of a complete cast crown, but they ~heorizrd that the axial groove used as a cement escape channel might enhance the seating of a complete cast mown. A subsequent study on typodont teeth revealed ihat ;+n internal escape channel placed on the buccal surface enhanced the seating of complete cast c-sowns. The purpose of this study was to verify the effectiveness of the internal escape channel on the seating of complete cast-gold crowns on natural teeth and its effect on retentive properties. This study approached clinical conditions more closely than earlier studies. MATERIAL
AND METHODS
.\n escape channel is basically similar in form to the traditional retentive groove, with two modifications. (I) The usual sharp definite seat of the groove at the gingival end is changed to a gradual round terminus. This can be attained easily with a tapered cylindrical
to venting
B.D.S., D.D.S.**
diamond bur with a rounded end (Kimberley No. 700 F. G.. Atwood Industries, Tarzana, Calif.). (2) It is imperative that the channel have a funnel-shaped communication with the occlusal surface (Fig. 1). The depth of the channel is approximately equal to the diameter of the diamond bur, and it terminates in a gently rounded end approximately 0.5 mm short of the gingival finish margin (Fig. 2). The escape channel can be placed easily on the prepared tooth before or after the final impression is made, while the tooth is still anesthetized. If it is placed before the impression is made, it must be blocked out on the die. Thirty extracted human mandibular molars of comparable length and size were selected and prepared to receive complete cast gold crowns. The length of the preparation was approximately 6 mm, with a buccolingual convergence angle of about 10 degrees and a mesiodistal convergence angle of about 6 degrees. A chamfer finish margin was used. The roots of the prepared teeth were embedded in Bakelite rings (Buehler Ltd., Evanston, Ill.) filled with autopolymerizing acrylic resin (Orthocryl, StratfordCookson Co., Newman, Ga.). The long axes were aligned parallel to the tensile force to be applied. All specimens were stored in a humidor except during cementation, measurement, and tensile testing. Five groups of 10 specimens each were made from the sample. Group No. 1 had no escape channel; this group served as the control. Group No. 2 had a buccal escape channel. Group No. 3 had a buccal escape channel, and two layers of cavity varnish (Copalite, Cooley & Cooley Ltd., Houston, Tex.) were applied to the prepared tooth. Group No. 4 had a lingual escape channel, and in group No. 5 an underextended buccal escape channel was prepared 2 mm short of the finish margin. iZfter they were dislodged by the Instron testing instrument (Model 1350, Instron Corp., Canton, Mass.), the castings for group Nos. 1 and 2 were
[LJLY 1984
VOLUME
52
NUMBER
1
INTERNAL
ESCAPE CHANNEL
Fig. 2. Medium diamond bur with rounded end is used to place escape channel. Terminus is about 0.5 mm short of gingival finish margin.
Fig. 1. A, Escape channel placed on buccal surface of complete crown preparation. B, Diagram depicting escape channel with rounded gingival end and funnel-shaped occlusal end.
cleaned in an ultrasonic bath and reused for group Nos. 3 and 4. Gold castings were made by a standardized method. Direct wax patterns were made on the prepared teeth with type II blue inlay wax (Kerr Mfg. Co., Romulus, Mich.). They were invested in Luster-Cast, a gypsumbonded investment (Kerr Mfg. Co.), with powder/ liquid ratio of 50 mg 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 at least 1 hour. The rings were removed, placed in an oven for 30 minutes at 600“ F, and held at 900” F for an additional hour. Casting was done in a vacuum casting machine (Model No. 270B, Torn, Chayes Virginia Inc., Evansville, Ind.) with type III gold (Rx 41, Jeneric Gold Co., Wallingford, Conn.). The cast crowns were cleaned in a pickling solution (Jel Pat, J. F. Jelenko & CO., New Rochelle, N. Y.). No internal relief was made except for the removal of nodules that prevented complete seating. The finished crowns were not polished. The castings were provided with a ringlike attachment with a flat table at the top. The ring was used to
THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 3. Casting with ring attachment and flat table at
top.
provide a grip for the Instron testing instrument, and the table was used to apply the static load during cementation (Fig. 3). The base of the ring in which the specimen was embedded was polished on the Handimet grinder (Buehler Ltd., Evanston, Ill.) with 280 to 600 grit abrasive papers. The base must be exactly flat and parallel to the loading table at the top of the ring attachment. To obtain exact parallelism, the loading
51
TJAN
AND
SARKISSIAN
Fig. 6. Electronic micrometer used to measure vertical discrepancy.
Cementation of the castings Fig. 4. Device used to obtain parallelism of loading table with base of embedding ring.
Type I zinc phosphate cement (Tenacin, powder batch No. 03478, liquid batch No. 081478, L. D. Caulk Co., Milford, Del.) was mixed according to the manufacturer’s specifications. Standardization of all mixes was accomplished by proportioning the cement powder on a precision scale and dispensing the liquid with a calibrated 1 ml insulin syringe. The powder was added to the liquid in small increments, and the mixture was spatulated for 90 seconds. The inner surface of the crowns was coated with an even thickness of cement. The crown was seated with finger pressure, and a load of 12 pounds was applied for 10 minutes with a cementing device (Fig. 7). To reduce one variable, the cementation was performed by one investigator. The room temperature during cementation was 24’ C.
Assessment of vertical discrepancy
Fig. 5. Dimple in center of loading table is used as reference point to ensure accurate measurement of vertical discrepancy. table was finished by use of a disklike stone mounted on a porcelain facing drill (Model M-l 1, Mardelle Industrial Products, Monrovia, Cal.) (Fig. 4). In the center of the table, an indentation (dimple) was made with a No. 6 round bur (Fig. 5). The indentation was used as a reference point to assure accurate measurement of the vertical (gingival) discrepancy with an electronic measuring device (Minicom micrometer, Tokyo Seimitzu, Tokyo, Japan) (Fig. 6).
52
The measurement of a completely seated uncemented casting on its respective tooth preparation under a static load of 12 pounds for 5 minutes was used to determine the baseline (zero point) on the micrometer scale. The indentation on the table served as the reference point. The difference in value obtained after cementation indicated the vertical discrepancy of the specimen.
Assessment of retention Prior to tensile testing, the cemented specimens were stored in distilled water for 1 week in an incubator at 37” C. The tensile force required to dislodge the crowns was determined by an Instron testing instrument with a crosshead speedof 0.05 inch/min (Fig. 8).
JULY 1984
VOLUME
52
NUMBER
1
INTERNAL
ESCAPE CHANNEL
Fig. 7. Cementing device used to apply load of 12 pounds during cementation of crown.
Fig. 8. Self-aligning ing.
Analysis of variance and Duncan’s new multiple range test were used to establish significance among the experimental groups.
deviations for group Nos. 1, 2, and 1% Statistical analysis of the data by means of the analysis of variance (critical region: F > 5.49, (Y = O.Ol), indicated a statistically significant difference among the three groups. Application of Duncan’s new multiple range test revealed a statistically significant difference between group Nos. 1 and 3 and between group Nos. 2 and 3 at p < .05 significant level. The difference of the means between group Nos. 1 and 2 was not significant. Data collected from this study indicated that the application of two layers of Copalite reduced the retentive property of complete cast-gold crowns (Fig. 9). The means of vertical discrepancies between group Nos. 2 and 4 were not statistically significant at p < .05 significant level. This result indicated that it made no difference whether the escape channel was placed on the buccal or lingual surface of the preparation (Table III). The difference of the means of vertical discrepancies between group Nos. 2 and 5 was statistically significant. The use of an underextended buccal escape
RESULTS The vertical discrepancies, means, and standard deviations for group Nos. 1, 2, and 3 are presented in Table I. Statistical analysis of the data by means of the analysis of variance (critical region: F 1 5.49, a = O.Ol), revealed a statistically significant difference among the three groups. Application of Duncan’s new multiple range test revealed a statistically significant difference between group Nos. 1 and 2 and between group Nos. 1 and 3 at p < .05 significant level. The difference of the means between group Nos. 2 and 3 were not significant. Results of this study show an escape channel placed on the buccal surface of full crown preparations enhances the seating of complete cast gold crowns. Table II presents the retention, means, and standard
THE JOURNAL
OF PROSTHETIC
DENTISTRY
assembly used for tensile test-
53
TJAN
---- -.-
160 m
160
9
140
2 a
120
5 z 0 F z ," w CT
.
100
AND
SARKISSIAN
(CONTROL) (ESC.CHANNEL) (ESC. CHANNEL 8 COPALITE)
%
80 4 60
.
40
.
‘\. ‘-e
20 12345678
9
10
Fig. 9. Retentive values of group No. 1 (control), group No. 2 (with buccal escape channel), and group No. 3 (with buccal escape channel and two layers of Copalite).
Table I. Vertical discrepancy mean (in microns; lo-’ mm)
Group No. 1 (control)
and mathematic
Group No. 2 (buccal escape channel)
Group No. 3 fbuccal escape channel and Copalite) 20 50 i 35 r, 12 28 10 10 8 183 18
14.97
channel (2 mm short of the gingival finish margin) was ineffective. Fig. 10 compares the mathematic means and standard deviations of the five groups. DISCUSSION Incomplete seating is a common dilemma in cementation of a complete cast crown. There are many factors that contribute to vertical discrepancy. Some of them are convergence angle of the preparation, type of cement used, thickness of the cement mix, filtration process, and h ydro dynamics. Hydrodynamics has been termed the primary consideration.’ However, Hoard et
Table II. Tensile force required to dislodge complete cast crowns (in pounds)
Group No. 1 (control)
Group No. 2 (buccal escape channel)
Group No. 3 (buccal escape channel and Copalite) 80 70 80
121 115 89 08 135 101 100 107 150
90
60 74 50 88 98 90 7'80 78 14.85
94 Ill0 111 19.41
al.“’ indicated that the direct role of hydrostatic pressure in resistance to crown seating may have been overestimated. It would be desirable if the problem of complete seating could be reduced significantly by a simpler procedure than venting. The procedure should be performed at the chair with a minimum of time and equipment and require no other alteration on the finished casting. The internal escape channel was designed to offer a simplified and practical solution to the problem of incomplete seating of complete cast crowns. A single
1lJL.Y 1984
VOLUME
52
NUMBER
1
INTERNAL
ESCAPE CHANNEL
t
20
f ii
I
GROUP
I
I
II
I - I III
Iv
Comparison of mean and standard deviation of five groups: I (control); II (buccal escape channel); III (buccal escape channel and Copalite); IV (lingual escape channel), and V (underextended buccal escape channel). Fig.
10.
Table HI. Mathematic deviation
of vertical Group
Mean SD
mean and standard discrepancy (in microns)
h’o. 2
30 16.24
Group No. 4
Group No. 5
42 17.85
60 27.93
internal escape channel placed on the buccal surface of a typodont tooth has significantly enhanced the seating of a complete cast-gold crown.’ An escape channel facilitates the drainage of excess cement and consequently reduces the hydrostatic pressure at the occlusal portion. Fig. 11 shows the excess cement in the vicinity of the escape channel’s orifice. The data collected from this study indicated that escape channels placed on extracted human teeth significantly reduced the vertical discrepancy. Although the result was not significant, the application of Copalite produced slightly better seating. Presumably, the cavity varnish reduced the surface roughness and facilitated the cement flow. Placement of the escape channel on the curved buccal surface or the relatively flat lingual surface made no difference in crown seating. Although this conclusion is not a direct finding from the data analysis, the location of the escape channel is not significant. However, for practical reasons the escapechannel must be placed on the buccal or lingual surface for ease of finishing the margin. Despite better adaptation, the escapechannel did not
THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 11. Excess cement in vicinity orifice.
of escape channel’s
alter retention of the crown. However, the data suggest that the distribution of scores is clustered around the mathematic mean as shown by the small standard deviation (111 k 19.41 pounds). The scores of the control group are more widely dispersed around the mean (114 + 32.42 pounds). The application of two layers of Copalite significantly reduced the retentive property of the crown (Fig. 9). This, also, is due to the decreaseof surface roughness of the preparation necessary for the mechanical bond of the cement to the tooth structure, as evidenced by the retentive failure at the tooth-cement interface. When Copalite was not used, the failure was found at the cement-gold interface. No correlation was found between vertical discrepancy values and retentive properties.
55
TlAN AND SARKISSIAN
Further investigations are required to verify whether internal escape channels can be applied to shoulder or shoulder and bevel marginal design or the use of various kinds of cement. CONCLUSIONS An internal escape channel enhances the seating of complete cast-gold crowns. The presence of a channel neither increases nor decreasesthe retentive property of the crown. The location of the channel does not seem to be significant. However, an underextended channel proved to be ineffective.
micromeasurement of wnted and non-vented cast crown mat $nal adaptation. Drm Clin North ,Zm 15:663. 1971, i Coopc~. ‘1‘ M., Christensen, G. J., Laswell, H. R., and Baxter. K. I3-fect of ventinS on caqt gold full c’rowns ,J PKOSTIICI r)F.S’l 26Z62.1 ! 97 1. (1 Eamth. Ct’. B., O’Neal, S. ,J.. hZontriro, J Miller. C., Roan. Jr , J. I)., and (Zohcn. K. S.: ‘l’echniques to tmprovr the scatiy of castings. J Am Den1 Assoc 96:432, 197X. 7 Fusayamn, T. Ide. K., and Hosada. f-1.: Relief of resistance 01 c‘rment of full cast crowns. J PRoswrr DENT. 14:95. 1964. X Tjan, A. II I.., Sarkissian. R., and hliller, G II. ISect 01 multiple axinl qrooves on thr marginal adaptation of full m-gold crowns. ,J PKO~T~IETDEW 46:399, 198 1. 0 hlillw, C;. LX. and ‘I‘jan. I\. 11. I..: An internal escape channel: .I vimplilied solution to the problem of incomplete xating of full ust-gold CI‘OW~S.J Am Dent Assoc 104~322, 1982. 111. lioard, R. J., (:aputo, .I. I\.. Contino, R. hsl., and Koenig, hf. E.: Intratoron;d pressure during crown crmentation. J PRO\rltll DEYI 40:5?0. 1978
IULY 1984
VOLUME 52
NUMBER 1