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Retentive properties of dental cements
RETENTIVE
PROPERTIES
OF DENTAL
CEMENTS
F. OLDHAM, D.D.S.," MARJORIE L. SWARTZ, MS."" RALPH W. PHILLIPS, D.Sc.*** DREW
Indiana
University,
School
of Dentistry,
Indianapolis,
AND
Ind.
METHODS have been employed for investigating the retentive properties of dental cements. Generally, the techniques have involved cementing components such as metal, glass, and tooth structure and then determining the forces required for separation.l-I1 Jensen,12in a study concerned with the influence of variation in the flare of the axial walls on the retention of cemented restorations, presented a method which seemedto offer a practical ineans for evaluating the retentive characteristics of various luting agents. The experiment consisted of cementing plug type inlays into the dentin of extracted teeth and then measuring the tensile stress required to remove the cemented restoration. However, the research of Jensen measured the retentive qualities of only one type of dental cement, that is, zinc phosphate. The purpose of this investigation was to compare the retentive properties of a variety of common cementing materials with those of zinc phosphate cement. In addition, the effect of cavity liners and bases upon the retention afforded by zinc phosphate cement was studied.
V
ARIOUS
METHOD
AND
MATERIALS
Extracted, sound maxillary molar teeth were selected for use in this study. The teeth were stored in tap water immediately following extraction and throughout the course of the experiment. They were embedded in a block of self-curing resin and the occlusal surfaces ground flat, by means of a wet stone, in order that a flat cavosurface angle could be formed at the periphery of the cavity preparation. Cavity preparations were made in the teeth by means of a small, high-speed drill press utilizing dental rotary instruments. The drill press was set to cut to a depth of 2.5 mm. Water was used as a coolant during the cutting procedures. Steel This research supported, in part, by a research grant, D-433, from the National Dental Research, National Institutes of Health, Bethesda, Md. *Instructor, Crown and Bridge Department. **Assistant Professor of Dental Materials. ***Research Professor and Chairman, Department of Dental Materials. 760
Institute
of
gLILle;
144
RETENTIVE
PROPERTIES
OF DENTAL
CEMENTS
761
burs were employed to block out the preparation and a Densco 7-D taper diamond instrument was used to finish the cavity. The finished cavity preparation had a floor diameter of 4.5 mm. and an occlusal opening 5.0 mm. in diameter. The resulting wall flare was 7 degrees. The surface area of the preparation was 0.077 square inches. Cavosurface bevel was omitted in order to control better the length of the axial walls. In this manner standardized cavity preparations, uniform in size, shape, and texture were produced. Direct wax patterns were fabricated from Kerr’s regular blue inlay wax, utilizing a pour-pressure technique. A 10 gauge wax rod was attached at the center of the pattern. This rod was formed into a hook in such a manner that the maximum curvature was directly over the center of the pattern. The hook thus served as a sprue for the inlay. The pattern and the tooth were marked in order that the gold casting could be repeatedly removed and re-inserted into the same position in the cavity preparation. The patterns were invested and reproduced in a Type III dental gold alloy. The retentive ability of six commercial dental cements, representing several different types of cements, was tested. The cavity liners and base materials selected for use in this study were considered to be representative of the proprietary products which are supplied for these purposes. The materials are listed in Table I. The standard consistencies of the cements which are employed in a powder and liquid form were determined by the methods described in American Dental Association Specifications Numbers 8 and 9 for zinc phosphate cement and for silicate cement, respectively. l3 However, these mixes were found to be too thick for the cementation of the cast gold restoration. Upon experimentation it was found that
TABLE
I.
MATERIALSUSEDINTHETESTS
BRANDNAME
MATERIAL
MANUFACTURER
I
Zinc
phosphate
Tenacin
Silica-phosphate
Kryptex
Silicate
New
Filling
Zinc
oxide-eugenol
Temrex
Zinc
oxide-eugenol
Temporary
Zinc
oxide-eugenol
Temp-Bond
Varnish
Copalite
Varnish
Repelac
Calcium hydroxide suspension, polystyrene Zinc oxide-eugenol (base) Ca[taci; hydroxide
Pulpdent Cavitec Dycal
Porcelain
Cement
L. D. Caulk Co. Milford, Del. S. S. White Co. Philadelphia, Pa. S. S. White Co. Philadelphia, Pa. Interstate Dental Co. New York, N. Y. L. D. Caulk Co. Milford, Del. Kerr Co. Detroit, Mich. Harry J. Bosworth Chicago, Ill. L. D. Caulk Co. Milford. Del. Rower Dental Mfg. Corp. Boston, Mass. Kerr Co. Detroit, Mich. L. D. Caulk Co. Milford, Del.
762
OLDHAM,
SWARTZ,
PHILLIPS
Fig. 1.-T ‘he apparatus used to measure the retention of a restoration. to r amove the inlay cemented into standardized cavity preparations with
J. Pros. July-Aug.,
Den. 1961
A tensi ile load is used various lutjng al rents.
Volume Number
14 4
RETENTIVE
PROPERTIES
OF
DENTAL
CEMENTS
763
mixes suitable for cementation could be made with each material by using 75 per cent of the powder required to provide a mix of standard consistency. The powderliquid ratios established in this manner were used throughout the study. Three of the materials (Dycal, Cavitec, and Temp-Bond) are furnished in paste form and these products were proportioned by extruding equal lengths of pastes from the tubes, as directed by the respective manufacturers. Prior to cementation of the inlays, the cavity preparations were carefully cleaned with a pledget of cotton moistened with chloroform and air-dried. The cements were mixed on a cool, dry slab. The entire operation of mixing the cement, seating the restoration, and removing the excess cement was completed within 3 minutes. The cemented specimens were then placed in 100 per cent humidity for 30 minutes, after which they were stored in water for 24 hours, when the retention was measured. In order to measure the effects of cavity varnishes on retentive properties, the varnishes were utilized in conjunction with the zinc phosphate cement, Tenacin. A thin, continuous coat of the varnish was applied to the floor and walls of the cavity preparation by means of a small brush and the varnish was air-dried. No attempt was made to remove the varnish from the margins of the cavity preparations prior to cementation. Pulpdent, the calcium hydroxide liner, was applied to the cavity floor and walls by means of a brush. Great care was taken in application in order to keep the margins free of the liner material. In order to measure the effects of the base materials, Dycal and Cavitec, a “well” or depression was placed in the floor of the cavity preparations by means of a round bur. A narrow ledge of the cavosurface floor was allowed to remain around the periphery of the preparation in order to act as stop for the inlay. The base materials were placed into this depression. After the bases had hardened, the inlays were seated with zinc phosphate cement. In order to measure the amount of tensile force necessary to remove the cemented inlays from the cavity preparations, an apparatus was fabricated for holding the specimens in the testing machine. A diagram of this apparatus is shown in Fig. 1. A wire with a soldered loop on the end was placed in the upper jaws of the testing machine. The tooth with the inlay cemented in place was suspended in this loop by means of the hook on the casting. A wire yoke which fitted over the acrylic resin block holding the tooth was clamped in the lower jaws of the machine. The specimens were loaded at a cross-head rate of 0.020 inch per minute. The amount of stress required to remove the inlays when seated with zinc phosphate cement served as the standard on control. For this reason, each group of inlays was first cemented in the respective cavity preparations with zinc phosphate cement and the retention was tested. Preliminary tests showed some variation in results upon consecutive cementation of an individual inlay, even with the same cementing material. Therefore, every inlay was cemented four consecutive times with each material. A minimum of five inlays was used with each of the materials; hence, each of the values presented is the mean of 20 tests. No more than three products were tested with any given tooth. After each test, the cement was carefully removed from the cavity preparation, and the tooth
764
OLDHAM,
SWARTZ,
RETENTIVE DENTAL TO
PROPERTIES CEMENTS
ZINC
J. Pros. Den. July-Aug., 1964
PHILLIPS
PHOSPHATE
AS
OF COMPARED CEMENT
fzl Zinc 90
Other
Phosphate Control Cementing
Cement Agents
70 !z E!
60
e: 2
50 40
Fig. 2.-The tensile forces required to remove are compared on a percentage basis. Zinc phosphate all other materials are related to this value.
inlays cemented with cement is represented
various luting agents as 100 per cent and
structure was washed with tap water. When cements containing phosphoric acid were employed, the castings were cleaned in 50 per cent hydrochloric acid. When zinc oxide and eugenol cements were employed, chloroform was used to clean the restoration. When either a varnish or zinc oxide cement was used, the cavity preparations were flushed with chloroform. However, the teeth and inlays employed with the zinc oxide-eugenol cements were never re-cemented with any of the materials which contained phosphoric acid as it was feared that these cements might be contaminated by the eugenol. RESULTS
The results of tests conducted to determine the relative retentive properties of the various Wing agents appear in Table II. The average tensile stress required to
Volume 14 Number 4
RETENTIVE
PROPERTIES
OF DENTAL
76.5
CEMENTS
remove inlays seated with each of the cements is compared on a percentage basis to the average tensile stress necessary to remove the restorations when cemented with zinc phosphate cement. In the summary of the data presented in Fig. 2, the experimental materials are compared directly to the amount of tensile stress required to remove each specific group of inlays when seated with zinc phosphate cement. These data differ somewhat in magnitude from those presented in Table II where calculations were based upon the average results obtained with zinc phosphate cement. These data indicate that none of the cements possess retentive properties superior to zinc phosphate cement. Although the average tensile force required to remove inlays cemented with the silica-phosphate cement (Kryptex) was 20 per cent less than when the same castings were cemented with zinc phosphate cement, this difference is approximatelv the same as the coefficient of variation. However, the loss in retention with all of the other cements is greater than the coefficient of variation and is thus considered significant. Restorations cemented with the zinc oxide-eugenol cements exhibited varying degrees of resistance to the tensile load, depending on the composition of the cement. However, in every instance less force was required to remove the restorations
TABLE
II.
TENSILESTRESSREQUIREDTO COMPAREDTOTHOSE
REMOVE INLAYSCEMENTEDWITHVARIOUSAGENTSAS CEMENTEDWITH~INC PHOSPHATE CEMENT
EXPERIMENTALCEMENTING AGENT
P.&I.
PERCENT OF Zll PHoSPHATEj
c.v.*
Kryptex
330
Temrex New Filling Porcelain
210 285
;:12
8:
Cavitec Temporary Cement Temp-Bond
105 180 1.5
11 27
Gi 3
*Per cent C.V. tAverage
TABLE
III.
is Coefacient
stress required
of
Variation =
to remove
the inlays
72
Std. Dev.
x 100
wh%e,%kd
with
zinc phosphate
TENSILE STRESS REQUIRED TO REMOVE INLAYS CEMENTED CEMENT,WITHANDWITHOUTCERTAINVARNISHESANDBASES
cement,
WITH
456 p. s. i.
ZINCPHOSPHATE
P.S.I.
c.v.*
PERCENT OF ZIl PHOSPHATEt
Copalite Repelac
449 495
19 2;
91 100
Pulpdent Dycal
340 540 435
13 11
1:;
LINER
OR BASE
Cavitec
*Per cent C.V. iAverage
is Coefncient
stress required
of Variation
to remove
=
the inlays
Std. Dev. w&E%ed
8.5
x 100 with
zinc phosphate
cement.
496 p, s. i.
766
OLDHAM,
SWARTZ,
J. Pros. July-Aug.,
PHILLIPS
Den. 1964
than with any of the three phosphoric acid materials. Inlays cemented with Cavitec could be displaced with approximately 20 per cent of the amount of force required with zinc phosphate cement while only 3 per cent of the tensile force was required with Temp-Bond. It should be pointed out, however, that Cavitec is not designed for cementation but is recommended as a base or lining agent under other restoratives, and Temp-Bond, as the name implies, is designed only for temporary cementa-
EFFECT ON
THE
OF
CAVITY
RETENTIVE PHOSPHATE
LINERS
AND
PROPERTIES
BASES OF
ZINC
CEMENT
Zinc
Phosphate Control
Zinc
Phosphate
El
Liner
zr
Base
70 !s 5
60
2 &
50 40
30
20
10
Fig. 3.-The amount of tensile force required to remove inlays cemented with zinc phosphate cement is compared to the amount of force required to remove those same inlays when bases and cavity liners were utilized in conjunction with the luting agent. The zinc phosphate cement, when used alone, served as the standard and is represented by 100 per cent. The other experimental groups are plotted accordingly.
\‘olume Sumher
14 4
RETEXTlVE
PROPERTIES
OF DENTAL
CEMEKTS
767
tion. The manufacturer states that the material has a very low strength in order to facilitate removal of cast appliances before permanent cementation. The effects of cavity varnishes, calcium hydroxide and zinc oxide-eugenol bases on the retentive properties of zinc phosphate cement appear in Table III. Again the data presented in the summary (Fig. 3) were computed on the basis of the results obtained with each specific group of inlays when cemented with zinc phosphate cement and hence differ in magnitude from those shown in Table III.The use of the cavity varnishes before cementation did not alter the retentive properties of the cement. The differences are not greater than the coefficient of variation. Likewise, neither the calcium hydroxide base, Dycal, nor the zinc oxideeugenol base, Cavitec, influenced the retention of the inlays. The only reduction in retention which appeared to be significant was induced by the calcium hydroxide liner, Pulpdent. DISCUSSION
The results obtained in this study are in close agreement with those obtained in a similar investigation which was conducted to assess the abilities of cements to retain orthodontic bands.l” In both of these studies, it was found that appreciably higher tensile loads were required to unseat appliances cemented with zinc phosphate and silica-phosphate cement than with zinc oxide-eugenol cement. Although it is true that the phosphoric acid cements are considerably stronger than zinc oxide-eugenol cements and the inlays cemented with the former did exhibit the greater resistance to removal, an unequivocal relationship between compressive strength and retentive properties was not demonstrated in this study. For example, the compressive strength of both silicate and silica-phosphate cement is higher than that of zinc phosphate cement; however, inlays seated with zinc phosphate invariably required higher tensile loads to remove the cemented inlay. These results would suggest that other factors may be involved. For example, silicate and silica-phosphate cement have greater film thicknesses than zinc phosphate cements. 4n investigation of the effect of film thickness on retentive properties might prove interesting. The complexity of the stress patterns present in the oral cavity is appreciated and the difficulty of clinical interpretation of these data recognized. It is felt, however, that certain conjectures can be made on the basis of information obtained in this study. For example, it would not seem wise to utilize a zinc oxide-eugenol material for cementation in areas of high stress or where retention is greatly dependent on the cementing medium. The results also indicate that the precautionary measure of using a cavity varnish prior to cementation, in order to protect the tooth from the phosphoric acid present in certain types of cements, can be recommended without fear of a deleterious effect upon retention. By the same token neither the zinc oxide base nor calcium hydroxide base had a significant effect on retention. Only the calcium hydroxide cavity liner, Pulpdent, when painted on the surfaces of the cavity preparation reduced the retention of the cement. However, if this material had been confined entirely to the floor of the preparation or placed in a depression, as were the base materials, it also might have had uo influence on retention.
768
OLDHAM,
SWARTZ,
PHILLIPS
J. Pros. July-Aug.,
Den. 1964
SUMMARY
The relative retentive properties of various luting agents were investigated by measurement of the tensile force necessary to remove cast gold, occlusal inlays seated with the different cements. The influence of the cement base and cavity liners on retention was also studied. 1. Inlays cemented with the zinc phosphate cement (Tenacin) offered the greatest resistance to removal. The results obtained with Kryptex, the silico-phosphate cement, were essentially the same but the retention decreased when the silicate cement, New Filling Porcelain, was used. 2. Inlays cemented with the zinc oxide-eugenol cements, Temrex, and Temporary Cement, required less force to remove than when the same restorations were seated with the phosphoric acid cements. There were some differences between individual products. One material, Temp-Bond, designed for temporary cementation, exhibited considerably less retention than the others. 3. Varnish-type cavity liners, Copalite and Repelac, did not appreciably alter the retentive properties of zinc phosphate cement, although use of Pulpdent, a liner consisting of a suspension of calcium hydroxide, did impair the retention somewhat. 4. The retention of inlays cemented with zinc phosphate cement was not affected by placing either a zinc oxide-eugenol (Cavitec) base or calcium hydroxide (Dycal) base in a depression in the floor of the cavity. REFERENCES
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. :2:
Berkson, R. : Dental Cement : A Study of Its Property of Adhesion, Am. J. Orthodont. 36:701-710, 1950. Swartz, M. L., and Phillips, R. W.: A Method of Measuring the Adhesive Characteristics of Dental Cement. T.A.D.A. 50:172-177. 1955. Kaufman, E. G., Colin, g, and Coelho, D. H.: Comparison Studies of the Retentive Ability of Temporary Cements, J. D. Res. 39:759, 1960 (Abst.). Swartz, M. L., Phillips, R. W., Day, R., and Johnston, J. F.: A Laboratory and Clinical Investigation of Certain Resin Restorative and Cementing Materials. Part I. In Vitro Tests on Adhesive Characteristics, J. PROS. DEN. 5:698-704, 1955. Rose, E. E., Lal, J., Williams, N. B., and Falcetti, J. P.: Screemng of Materials for Adhesion to Human Tooth Structure, J. D. Res. 34:577-588, 195.5. Buonocore, M. G., Wileman, W. R., and Brudevold, F.: Report on a Resin Composition Capable of Bonding to Human Dentin Surfaces, J. D. Res. 35:846-851, 1956. Fusayama, T., and Iwamoto, T.: Relationship Between Retaining Force of Inlays and Film Thickness of Zinc Oxyphosphate Cement, J. D. Res. 39:756, 1960 (Abst.) . Myers, C. L., Ryge, G., and Glenn J.: In Vivo Test for Bonding to Dentin, I.A.D.R. 40:97, 1962 (Abst.). Christie, D. R.: Acrylic Fillings-General Comments and Some Experimental Data, J. Canad. D. A. 17:427-435, 1951. Swanson, L. T., and Beck, J. F.: Factors Affecting Bonding to Human Enamel, With Special Reference to a Plastic Adhesive, J.A.D.A. 61:581-586, 1960. Mahler, D. B., and Armen, G. K., Jr.: Addition of Amalgam Alloy to Zinc Phosphate Cement, J. PROS. DEN. 12:157-164, 1962. Jensen, J. R., and Hagen, P.: Comparative Retention of Plug Castings, I.A.D.R. 40:93, 1962 (Abst.). American Dental Association : American Dental Association Guide to Dental Materials, 19621963, ed. 5, 1962, Chicago, Ill., American Dental Association. Swartz,. M. L., Phillips, R. W., and Norman, R. D.: The Strength, Hardness and Abrasron Characteristics of Dental Cements, J.A.D.A. 67:367-374, 1963. Phillips, R. W., and Swartz, M. L. : Unpublished data. Williams, J. D.: Adhesive Characteristics of Dental Cements With Some Observations on Etching, Thesis, Indiana University School of Dentistry, 1963. 1121 WEST MICHIGAN STREET INDIANAPOLIS, IND. 46202
PROPERTIES
OF DENTAL
CEMENTS
F. OLDHAM, D.D.S.," MARJORIE L. SWARTZ, MS."" RALPH W. PHILLIPS, D.Sc.*** DREW
Indiana
University,
School
of Dentistry,
Indianapolis,
AND
Ind.
METHODS have been employed for investigating the retentive properties of dental cements. Generally, the techniques have involved cementing components such as metal, glass, and tooth structure and then determining the forces required for separation.l-I1 Jensen,12in a study concerned with the influence of variation in the flare of the axial walls on the retention of cemented restorations, presented a method which seemedto offer a practical ineans for evaluating the retentive characteristics of various luting agents. The experiment consisted of cementing plug type inlays into the dentin of extracted teeth and then measuring the tensile stress required to remove the cemented restoration. However, the research of Jensen measured the retentive qualities of only one type of dental cement, that is, zinc phosphate. The purpose of this investigation was to compare the retentive properties of a variety of common cementing materials with those of zinc phosphate cement. In addition, the effect of cavity liners and bases upon the retention afforded by zinc phosphate cement was studied.
V
ARIOUS
METHOD
AND
MATERIALS
Extracted, sound maxillary molar teeth were selected for use in this study. The teeth were stored in tap water immediately following extraction and throughout the course of the experiment. They were embedded in a block of self-curing resin and the occlusal surfaces ground flat, by means of a wet stone, in order that a flat cavosurface angle could be formed at the periphery of the cavity preparation. Cavity preparations were made in the teeth by means of a small, high-speed drill press utilizing dental rotary instruments. The drill press was set to cut to a depth of 2.5 mm. Water was used as a coolant during the cutting procedures. Steel This research supported, in part, by a research grant, D-433, from the National Dental Research, National Institutes of Health, Bethesda, Md. *Instructor, Crown and Bridge Department. **Assistant Professor of Dental Materials. ***Research Professor and Chairman, Department of Dental Materials. 760
Institute
of
gLILle;
144
RETENTIVE
PROPERTIES
OF DENTAL
CEMENTS
761
burs were employed to block out the preparation and a Densco 7-D taper diamond instrument was used to finish the cavity. The finished cavity preparation had a floor diameter of 4.5 mm. and an occlusal opening 5.0 mm. in diameter. The resulting wall flare was 7 degrees. The surface area of the preparation was 0.077 square inches. Cavosurface bevel was omitted in order to control better the length of the axial walls. In this manner standardized cavity preparations, uniform in size, shape, and texture were produced. Direct wax patterns were fabricated from Kerr’s regular blue inlay wax, utilizing a pour-pressure technique. A 10 gauge wax rod was attached at the center of the pattern. This rod was formed into a hook in such a manner that the maximum curvature was directly over the center of the pattern. The hook thus served as a sprue for the inlay. The pattern and the tooth were marked in order that the gold casting could be repeatedly removed and re-inserted into the same position in the cavity preparation. The patterns were invested and reproduced in a Type III dental gold alloy. The retentive ability of six commercial dental cements, representing several different types of cements, was tested. The cavity liners and base materials selected for use in this study were considered to be representative of the proprietary products which are supplied for these purposes. The materials are listed in Table I. The standard consistencies of the cements which are employed in a powder and liquid form were determined by the methods described in American Dental Association Specifications Numbers 8 and 9 for zinc phosphate cement and for silicate cement, respectively. l3 However, these mixes were found to be too thick for the cementation of the cast gold restoration. Upon experimentation it was found that
TABLE
I.
MATERIALSUSEDINTHETESTS
BRANDNAME
MATERIAL
MANUFACTURER
I
Zinc
phosphate
Tenacin
Silica-phosphate
Kryptex
Silicate
New
Filling
Zinc
oxide-eugenol
Temrex
Zinc
oxide-eugenol
Temporary
Zinc
oxide-eugenol
Temp-Bond
Varnish
Copalite
Varnish
Repelac
Calcium hydroxide suspension, polystyrene Zinc oxide-eugenol (base) Ca[taci; hydroxide
Pulpdent Cavitec Dycal
Porcelain
Cement
L. D. Caulk Co. Milford, Del. S. S. White Co. Philadelphia, Pa. S. S. White Co. Philadelphia, Pa. Interstate Dental Co. New York, N. Y. L. D. Caulk Co. Milford, Del. Kerr Co. Detroit, Mich. Harry J. Bosworth Chicago, Ill. L. D. Caulk Co. Milford. Del. Rower Dental Mfg. Corp. Boston, Mass. Kerr Co. Detroit, Mich. L. D. Caulk Co. Milford, Del.
762
OLDHAM,
SWARTZ,
PHILLIPS
Fig. 1.-T ‘he apparatus used to measure the retention of a restoration. to r amove the inlay cemented into standardized cavity preparations with
J. Pros. July-Aug.,
Den. 1961
A tensi ile load is used various lutjng al rents.
Volume Number
14 4
RETENTIVE
PROPERTIES
OF
DENTAL
CEMENTS
763
mixes suitable for cementation could be made with each material by using 75 per cent of the powder required to provide a mix of standard consistency. The powderliquid ratios established in this manner were used throughout the study. Three of the materials (Dycal, Cavitec, and Temp-Bond) are furnished in paste form and these products were proportioned by extruding equal lengths of pastes from the tubes, as directed by the respective manufacturers. Prior to cementation of the inlays, the cavity preparations were carefully cleaned with a pledget of cotton moistened with chloroform and air-dried. The cements were mixed on a cool, dry slab. The entire operation of mixing the cement, seating the restoration, and removing the excess cement was completed within 3 minutes. The cemented specimens were then placed in 100 per cent humidity for 30 minutes, after which they were stored in water for 24 hours, when the retention was measured. In order to measure the effects of cavity varnishes on retentive properties, the varnishes were utilized in conjunction with the zinc phosphate cement, Tenacin. A thin, continuous coat of the varnish was applied to the floor and walls of the cavity preparation by means of a small brush and the varnish was air-dried. No attempt was made to remove the varnish from the margins of the cavity preparations prior to cementation. Pulpdent, the calcium hydroxide liner, was applied to the cavity floor and walls by means of a brush. Great care was taken in application in order to keep the margins free of the liner material. In order to measure the effects of the base materials, Dycal and Cavitec, a “well” or depression was placed in the floor of the cavity preparations by means of a round bur. A narrow ledge of the cavosurface floor was allowed to remain around the periphery of the preparation in order to act as stop for the inlay. The base materials were placed into this depression. After the bases had hardened, the inlays were seated with zinc phosphate cement. In order to measure the amount of tensile force necessary to remove the cemented inlays from the cavity preparations, an apparatus was fabricated for holding the specimens in the testing machine. A diagram of this apparatus is shown in Fig. 1. A wire with a soldered loop on the end was placed in the upper jaws of the testing machine. The tooth with the inlay cemented in place was suspended in this loop by means of the hook on the casting. A wire yoke which fitted over the acrylic resin block holding the tooth was clamped in the lower jaws of the machine. The specimens were loaded at a cross-head rate of 0.020 inch per minute. The amount of stress required to remove the inlays when seated with zinc phosphate cement served as the standard on control. For this reason, each group of inlays was first cemented in the respective cavity preparations with zinc phosphate cement and the retention was tested. Preliminary tests showed some variation in results upon consecutive cementation of an individual inlay, even with the same cementing material. Therefore, every inlay was cemented four consecutive times with each material. A minimum of five inlays was used with each of the materials; hence, each of the values presented is the mean of 20 tests. No more than three products were tested with any given tooth. After each test, the cement was carefully removed from the cavity preparation, and the tooth
764
OLDHAM,
SWARTZ,
RETENTIVE DENTAL TO
PROPERTIES CEMENTS
ZINC
J. Pros. Den. July-Aug., 1964
PHILLIPS
PHOSPHATE
AS
OF COMPARED CEMENT
fzl Zinc 90
Other
Phosphate Control Cementing
Cement Agents
70 !z E!
60
e: 2
50 40
Fig. 2.-The tensile forces required to remove are compared on a percentage basis. Zinc phosphate all other materials are related to this value.
inlays cemented with cement is represented
various luting agents as 100 per cent and
structure was washed with tap water. When cements containing phosphoric acid were employed, the castings were cleaned in 50 per cent hydrochloric acid. When zinc oxide and eugenol cements were employed, chloroform was used to clean the restoration. When either a varnish or zinc oxide cement was used, the cavity preparations were flushed with chloroform. However, the teeth and inlays employed with the zinc oxide-eugenol cements were never re-cemented with any of the materials which contained phosphoric acid as it was feared that these cements might be contaminated by the eugenol. RESULTS
The results of tests conducted to determine the relative retentive properties of the various Wing agents appear in Table II. The average tensile stress required to
Volume 14 Number 4
RETENTIVE
PROPERTIES
OF DENTAL
76.5
CEMENTS
remove inlays seated with each of the cements is compared on a percentage basis to the average tensile stress necessary to remove the restorations when cemented with zinc phosphate cement. In the summary of the data presented in Fig. 2, the experimental materials are compared directly to the amount of tensile stress required to remove each specific group of inlays when seated with zinc phosphate cement. These data differ somewhat in magnitude from those presented in Table II where calculations were based upon the average results obtained with zinc phosphate cement. These data indicate that none of the cements possess retentive properties superior to zinc phosphate cement. Although the average tensile force required to remove inlays cemented with the silica-phosphate cement (Kryptex) was 20 per cent less than when the same castings were cemented with zinc phosphate cement, this difference is approximatelv the same as the coefficient of variation. However, the loss in retention with all of the other cements is greater than the coefficient of variation and is thus considered significant. Restorations cemented with the zinc oxide-eugenol cements exhibited varying degrees of resistance to the tensile load, depending on the composition of the cement. However, in every instance less force was required to remove the restorations
TABLE
II.
TENSILESTRESSREQUIREDTO COMPAREDTOTHOSE
REMOVE INLAYSCEMENTEDWITHVARIOUSAGENTSAS CEMENTEDWITH~INC PHOSPHATE CEMENT
EXPERIMENTALCEMENTING AGENT
P.&I.
PERCENT OF Zll PHoSPHATEj
c.v.*
Kryptex
330
Temrex New Filling Porcelain
210 285
;:12
8:
Cavitec Temporary Cement Temp-Bond
105 180 1.5
11 27
Gi 3
*Per cent C.V. tAverage
TABLE
III.
is Coefacient
stress required
of
Variation =
to remove
the inlays
72
Std. Dev.
x 100
wh%e,%kd
with
zinc phosphate
TENSILE STRESS REQUIRED TO REMOVE INLAYS CEMENTED CEMENT,WITHANDWITHOUTCERTAINVARNISHESANDBASES
cement,
WITH
456 p. s. i.
ZINCPHOSPHATE
P.S.I.
c.v.*
PERCENT OF ZIl PHOSPHATEt
Copalite Repelac
449 495
19 2;
91 100
Pulpdent Dycal
340 540 435
13 11
1:;
LINER
OR BASE
Cavitec
*Per cent C.V. iAverage
is Coefncient
stress required
of Variation
to remove
=
the inlays
Std. Dev. w&E%ed
8.5
x 100 with
zinc phosphate
cement.
496 p, s. i.
766
OLDHAM,
SWARTZ,
J. Pros. July-Aug.,
PHILLIPS
Den. 1964
than with any of the three phosphoric acid materials. Inlays cemented with Cavitec could be displaced with approximately 20 per cent of the amount of force required with zinc phosphate cement while only 3 per cent of the tensile force was required with Temp-Bond. It should be pointed out, however, that Cavitec is not designed for cementation but is recommended as a base or lining agent under other restoratives, and Temp-Bond, as the name implies, is designed only for temporary cementa-
EFFECT ON
THE
OF
CAVITY
RETENTIVE PHOSPHATE
LINERS
AND
PROPERTIES
BASES OF
ZINC
CEMENT
Zinc
Phosphate Control
Zinc
Phosphate
El
Liner
zr
Base
70 !s 5
60
2 &
50 40
30
20
10
Fig. 3.-The amount of tensile force required to remove inlays cemented with zinc phosphate cement is compared to the amount of force required to remove those same inlays when bases and cavity liners were utilized in conjunction with the luting agent. The zinc phosphate cement, when used alone, served as the standard and is represented by 100 per cent. The other experimental groups are plotted accordingly.
\‘olume Sumher
14 4
RETEXTlVE
PROPERTIES
OF DENTAL
CEMEKTS
767
tion. The manufacturer states that the material has a very low strength in order to facilitate removal of cast appliances before permanent cementation. The effects of cavity varnishes, calcium hydroxide and zinc oxide-eugenol bases on the retentive properties of zinc phosphate cement appear in Table III. Again the data presented in the summary (Fig. 3) were computed on the basis of the results obtained with each specific group of inlays when cemented with zinc phosphate cement and hence differ in magnitude from those shown in Table III.The use of the cavity varnishes before cementation did not alter the retentive properties of the cement. The differences are not greater than the coefficient of variation. Likewise, neither the calcium hydroxide base, Dycal, nor the zinc oxideeugenol base, Cavitec, influenced the retention of the inlays. The only reduction in retention which appeared to be significant was induced by the calcium hydroxide liner, Pulpdent. DISCUSSION
The results obtained in this study are in close agreement with those obtained in a similar investigation which was conducted to assess the abilities of cements to retain orthodontic bands.l” In both of these studies, it was found that appreciably higher tensile loads were required to unseat appliances cemented with zinc phosphate and silica-phosphate cement than with zinc oxide-eugenol cement. Although it is true that the phosphoric acid cements are considerably stronger than zinc oxide-eugenol cements and the inlays cemented with the former did exhibit the greater resistance to removal, an unequivocal relationship between compressive strength and retentive properties was not demonstrated in this study. For example, the compressive strength of both silicate and silica-phosphate cement is higher than that of zinc phosphate cement; however, inlays seated with zinc phosphate invariably required higher tensile loads to remove the cemented inlay. These results would suggest that other factors may be involved. For example, silicate and silica-phosphate cement have greater film thicknesses than zinc phosphate cements. 4n investigation of the effect of film thickness on retentive properties might prove interesting. The complexity of the stress patterns present in the oral cavity is appreciated and the difficulty of clinical interpretation of these data recognized. It is felt, however, that certain conjectures can be made on the basis of information obtained in this study. For example, it would not seem wise to utilize a zinc oxide-eugenol material for cementation in areas of high stress or where retention is greatly dependent on the cementing medium. The results also indicate that the precautionary measure of using a cavity varnish prior to cementation, in order to protect the tooth from the phosphoric acid present in certain types of cements, can be recommended without fear of a deleterious effect upon retention. By the same token neither the zinc oxide base nor calcium hydroxide base had a significant effect on retention. Only the calcium hydroxide cavity liner, Pulpdent, when painted on the surfaces of the cavity preparation reduced the retention of the cement. However, if this material had been confined entirely to the floor of the preparation or placed in a depression, as were the base materials, it also might have had uo influence on retention.
768
OLDHAM,
SWARTZ,
PHILLIPS
J. Pros. July-Aug.,
Den. 1964
SUMMARY
The relative retentive properties of various luting agents were investigated by measurement of the tensile force necessary to remove cast gold, occlusal inlays seated with the different cements. The influence of the cement base and cavity liners on retention was also studied. 1. Inlays cemented with the zinc phosphate cement (Tenacin) offered the greatest resistance to removal. The results obtained with Kryptex, the silico-phosphate cement, were essentially the same but the retention decreased when the silicate cement, New Filling Porcelain, was used. 2. Inlays cemented with the zinc oxide-eugenol cements, Temrex, and Temporary Cement, required less force to remove than when the same restorations were seated with the phosphoric acid cements. There were some differences between individual products. One material, Temp-Bond, designed for temporary cementation, exhibited considerably less retention than the others. 3. Varnish-type cavity liners, Copalite and Repelac, did not appreciably alter the retentive properties of zinc phosphate cement, although use of Pulpdent, a liner consisting of a suspension of calcium hydroxide, did impair the retention somewhat. 4. The retention of inlays cemented with zinc phosphate cement was not affected by placing either a zinc oxide-eugenol (Cavitec) base or calcium hydroxide (Dycal) base in a depression in the floor of the cavity. REFERENCES
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. :2:
Berkson, R. : Dental Cement : A Study of Its Property of Adhesion, Am. J. Orthodont. 36:701-710, 1950. Swartz, M. L., and Phillips, R. W.: A Method of Measuring the Adhesive Characteristics of Dental Cement. T.A.D.A. 50:172-177. 1955. Kaufman, E. G., Colin, g, and Coelho, D. H.: Comparison Studies of the Retentive Ability of Temporary Cements, J. D. Res. 39:759, 1960 (Abst.). Swartz, M. L., Phillips, R. W., Day, R., and Johnston, J. F.: A Laboratory and Clinical Investigation of Certain Resin Restorative and Cementing Materials. Part I. In Vitro Tests on Adhesive Characteristics, J. PROS. DEN. 5:698-704, 1955. Rose, E. E., Lal, J., Williams, N. B., and Falcetti, J. P.: Screemng of Materials for Adhesion to Human Tooth Structure, J. D. Res. 34:577-588, 195.5. Buonocore, M. G., Wileman, W. R., and Brudevold, F.: Report on a Resin Composition Capable of Bonding to Human Dentin Surfaces, J. D. Res. 35:846-851, 1956. Fusayama, T., and Iwamoto, T.: Relationship Between Retaining Force of Inlays and Film Thickness of Zinc Oxyphosphate Cement, J. D. Res. 39:756, 1960 (Abst.) . Myers, C. L., Ryge, G., and Glenn J.: In Vivo Test for Bonding to Dentin, I.A.D.R. 40:97, 1962 (Abst.). Christie, D. R.: Acrylic Fillings-General Comments and Some Experimental Data, J. Canad. D. A. 17:427-435, 1951. Swanson, L. T., and Beck, J. F.: Factors Affecting Bonding to Human Enamel, With Special Reference to a Plastic Adhesive, J.A.D.A. 61:581-586, 1960. Mahler, D. B., and Armen, G. K., Jr.: Addition of Amalgam Alloy to Zinc Phosphate Cement, J. PROS. DEN. 12:157-164, 1962. Jensen, J. R., and Hagen, P.: Comparative Retention of Plug Castings, I.A.D.R. 40:93, 1962 (Abst.). American Dental Association : American Dental Association Guide to Dental Materials, 19621963, ed. 5, 1962, Chicago, Ill., American Dental Association. Swartz,. M. L., Phillips, R. W., and Norman, R. D.: The Strength, Hardness and Abrasron Characteristics of Dental Cements, J.A.D.A. 67:367-374, 1963. Phillips, R. W., and Swartz, M. L. : Unpublished data. Williams, J. D.: Adhesive Characteristics of Dental Cements With Some Observations on Etching, Thesis, Indiana University School of Dentistry, 1963. 1121 WEST MICHIGAN STREET INDIANAPOLIS, IND. 46202