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FLOW AND RECOVERY OF DENTURE PLASTICS

S@RENE. SORENSEN,D.D.S., M.S., AND GUNNAR RYGE,D.D.S., M.S.Marquette University, School of Dentistry, Milwaukee, Wis.

D URING THE YEARS, the dental profession has been confronted with the problemof warpage and systematic dimensional changes of dentures. Reports in theliterature have been based upon linear measurements made across the posterior ofa denture1T3 or by the use of various mechanical devices4-6 in order to determine

the adaptation by comparison of dentures and models or impressions and models.Changes up to 0.5 mm. in various parts of a denture have been reported.

Woelfel, Paffenbarger, and Sweeney 7 found that the warpage index wasgreatest for the epoxy resin (0.3 per cent) and lowest for the polystyrene (0.02per cent). The warpage could not be detected clinically.

The fact that some author9 express concern about the effects of flow of den-ture bases and plastic teeth after long-term stress application indicates the needfor more data in this area.

Tylmans has indicated that flow in acrylic resin crowns may be sufficientto break the cement union at the gingival margin.

The purpose of this investigation was to study deformation and delayedelastic recovery of various types of denture-base resins. Permanent deformationrefers in this article to a permanent change in shape of the specimen after ;/shour or after 24 hours of recovery from various loads at certain test temperatures.

METHODS AND MATERIALS

The materials selected for the study are listed in Table I.Experimental Procedures.-The transverse deflection test in A.D.A. specifica-

tion No. 12 for denture-base resin was used to determine whether a permanentchange remained in a specimen of a given material after loading. The test describedin A.D.A. specification No. 15lr for acrylic resin teeth (section 4.3.6) was usedto determine indentation resistance and recovery. A specimen size of 1 sq. inch,with a thickness of g inch, was chosen in accordance with the American Societyfor Testing Materials (D 785-51) test for Rockwell hardness of plastic.*2

Oversized steel specimens were used for the fabrication of the molds forthe heat-curing and self-curing polymethyl methacrylate specimens. The dimensions

This study was supported in part by research grant D-1057 and training grant DT.22from the National Institute of Dental Research, U. S. Public Health Service.

Portions of this paper were taken from a thesis by Dr. Serensep submitted to the facultyof the Graduate School, Marquette University, in partial fulfillment of the requirements forthe degree of Master of Science.

*Assistant Professor; present address: University of Buffalo Dental Srhool, Buffalo. N. Y.**Professor and Chairman, Department of Dental Materials.


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1080 S@RENSEN AND RYGE

TABLE I. LIST OR MATERIALS

MATERIAL

Experimentalheat-curingresin*

Experimentalself-curingresin*

Jectron

Luxene

Epoxolon

TYPE

Clear olymerStrarg t monomerCrosslinked monomert

Pink polymerStraight monomerCrosslinked monomert

Polystyrene

Vinyl-acrylic resin

Epoxy resin

=I

--

-

BATCH

64-221-H, SR 100SR-255SR-253, 64-140-7

12318SR 252, 98-48-3SR 254, 98-48-4

52

Gel batch

DATE

March, 1961

March, 1961

March, 1961March, 1961March, 1961

October, 1960

March, 1961

April, 1961April, 1961

*Material furnished by Sartomer Resins, Inc.. Philadelphia, Pa.tThe crosslinking agent employed was 5 per cent ethylene dimethacrylate.

of the steel specimens were 70 by 10.67 by 3.67 mm. for the transverse deflectiontest specimens and 25.6 by 25.6 by 7 mm. for the Rockwell indentation test. Threedeflection specimens and one indentation specimen were lubricated with a thincoat of petroleum jelly and invested in a denture flask using dental stone as a

mold material . After setting of the stone, the steel specimens were removed, andthe molds were flushed with three applications of hot detergent solution andrinsed with clean boiling water. The resin was packed in a mold lined withtinfoil at a temperature of 23 -L 2 C. A polymer :monomer ratio of 3 :l wasused.

A constant time schedule for mixing, gel formation, and packing of themolds was maintained for all specimens in which the same monomer type wasused. Heat-curing specimens were trial packed twice, self-curing specimens once.The flask with the heat-curing material was held in a spring clamp and polymerizedin a Hanau processing unit. The curing was carried out according to the followingschedule : 73 * 1 C. for 11/z hours and then boiling for @ hour, after whichthe flask in the clamp was cooled in air at 23 r+ 2 C. for 30 minutes and thenimmersed in water at 23 + 1 C. for 15 minutes.

The self-curing specimens were allowed to polymerize for 45 minutes inpress and 45 minutes out of press before the flask was separated.

Oversized wax specimens were used for the preparation of molds for theJectron, Luxene, and Epoxolon test specimens. Manufacturers directions werefollowed in the investing procedures for these specimens.

Five to six wax specimens equally spaced and one wax specimen for theRockwell indentation test were invested in each flask. Except for the Luxeneresin,* all specimens were processed by the investigator; the manufacturersdirections were followed for each material.

*Processed by the cour tesy of the Massey-Otto DentalSupply Company, Milwaukee, Wis.


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Volume 12Number 6 FLOW AND RECOVERY OF DENTURE PLASTICS 10x1.

The Epoxolon specimens were all cured overnight at a temperature of 110F. All specimens were marked after processing with an index number and storedin distilled water at room temperature in labeled bottles. Approximately 14 daysto 3 weeks later, the transverse test specimens were machined to the followingdimension: thickness 2.5 4 0.03 mm., width 10 + 0.03 mm. The cutting wasperformed according to A.D.A. specification No. W (section 4.3.5).

The mean thickness of the specimens was determined to be 2.48 mm., witha standard deviation of 0.02 mm. ; the mean width of the specimens was 9.98 mm.,with a standard deviation of 0.01 mm. The total number of specimens was 174,distributed fairly even between the seven materials.

The specimens for the Rockwell indentations were sanded on all surfacesusing wet 400 A aloxite waterproof Carborundum paper, with the top and bottomsurfaces flat and parallel. Final thickness of these specimens was 6.28 + 0.2 mm

A Hanau curing unit was used as a temperature-controlled water bath inwhich the transverse testing machine was placed. The transverse testing machinewas provided with three stops. Two lateral aluminum stops secured the specimenin position under the metal rod through which the load was applied. The thirdstop provided the end stop for the specimen. In this way, it was possible toreproduce the position of a specimen. During the testing procedures, the transversetesting machine was placed against the back of the Hanau unit 20 cm. from theheating element, and the water level was kept a t least 2 cm. above the specimen.Temperature readings were obtained at a distance of 2.5 cm. from the specimen.

For this investigation, it was decided to study the deflection at four differ-ent loads (600 Gm., 1,500 Gm., 2,500 G m., and 4,000 Gm.) and at three tempera-ture levels (21 C., 34 C., and 58 C.) * using the schedule of loading and readingin A.D.A. specification No. 12i (section 4.3.5).

The delayed elastic recovery was recorded 30 minutes and 24 hours afterremoval of the indicated test load. Randomization of the order of material, speci-men number, and load to be applied was carried out for each of the three tempera-ture levels. All experiments were carried out in duplicate.

Zero readings were performed for all specimens before any test was carried

out. Each specimen was kept in the water bath for 30 to 60 minutes at thetemperature for the performed test.After each deflection test, the specimen was removed from the transverse

testing machine. The specimen was left for recovery in a vertical position in asmall beaker which was placed next to the testing machine in the water bath.After the 30 minute or 24 hour storage period, the specimen was repositionedand the recovery was recorded as the deflection value under the 600 Gm. load.

Indentation resistance was determined according to section 4.3.5 of A.D.A.specification No. 1511on randomized specimens. The tests were performed at roomtemperature (23 3- lC.).

*The temperatures chosen were originally 21 C., 37 C., and 60 C. However, a systematicerror in the temperature recording was noted, and it was found that the actual temperattlreswere 21 C., 34O C. and 58O C. The actual temperatures of the experiments are, therefore, list,edthroughout this report.


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1082 SZRENSEN AND RYGE

EPOXOLONLUXENEJECTRON

I 2 3 4

LOAD IN GRAMS x IO3

Fig. I.-Deflection as a function of load for various denture materials at 21 C.

RESULTS

Mean deflection and recovery values are listed in Table II. Recovery wascalculated in percentage for each specimen, and the means are reported to thenearest 1 per cent. Reading error on deflection values was determined as the

SELF - CURING

34C

I 2 3 4

LOAD IN GRAMS x IO

Fig. 2.-Deflection as a function of load for various denture materials at 34 C.


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Volume 12Number 6 FLOW AND RECOVERY OF DENTURE PLASTICS lOii3

Fig. 3.-Deflection as a function of load for various denture materials at 58O C.

I 2 3 4

LOAD IN GRAMS x IO3

standard deviation on five consecutive readings on the same specimen. The calcu-lated standard deviation was 0.24 mm. Variation in the water bath temperature wascontrolled to + 1 C. of the specified test temperature. Deflection versus loadcurves for the seven materials at the temperatures of 21 C., 34 C., and 58 C.are shown in Figs. 1 to 3.

Table III gives the data for indentation resistance and recovery after flow.The ratio of load to projected area of indentation was calculated according ioequations used by Sweeney, Sheehan, and Yost.i3

The standard deviation was calculated on mean recovery values obtainedwhen testing four specimens of the same type of resin. The standard deviation

was 0.87 per cent.It was originally planned to carry out the study using a factorial designscheme. Since some of the materials did not withstand the loads of 3,500 Gm.and 4,000 Gm. at 58 C., the resulting data did not lend themselves to a com-plete analysis of variance following the factorial design. Sufficient data were ob-tained, however, for deflections at 34 C. and 58 C. for loads of 600 Gm.,1,500 Gm., and 2,500 Gm. and for l/z hour recovery at 34 C. and 58 C. afterloads of 1,500 Gm. and 2,500 Gm., and these data were, therefore, used for theanalysis of variance.

Table IV gives the analysis of variance computed on these deflection values,and Table V gives the analysis of variance with respect to s hour recovery. Thecomputed figures are based on the difference measured in millimeters between theinitial (600 Gm.) deflection value and the lb hour recovery value under GO0 Gm.load.


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1084 S@RENSEN AND RYGE Nol.*k? ?;t%I

DISCUSSION

Deflection and Recovery Values at 21 C. and 34 C.-On the basis of thedeflection values listed in Table II, the materials tested can be rated according

to stiffness. At 21 C. and 34 C., Jectron gives the least deflection for any givenload, followed by Luxene, Epoxolon, heat-curing resins, and self-curing resins, inthat order. No significant differences were observed between deflection values forcrosslinked and noncrosslinked resins. The two heat-curing polymethyl metha-crylate resins and Jectron, Luxene, and Epoxolon recover completely (98 to 100per cent) during the 1h hour storage period after all load applications at both21 C. and 34 C.

At 21 C., the self-curing resins recover completely (99 to 100 per cent)after a load of 3,500 Gm. At 34 C., these resins recover completely (98 to 100per cent) within l/2 hour after 2,500 Gml load application. When a 4,000 Gm.

TABLE II. DEFLECTIONAND RECOVERYVALURSFORSEVRN DENTUREMATERIALS

MATERIAL

Heat-curingstraightmonomer

Heat-curingcrosslinkedmonomer

Self-curing

straightmonomer

Self-curingcrosslinkedmonomer

Jectron

Luxene

Epoxolon

=

-_

-

VALUE

Mean deflectionRecovery W hr.Recovery 24 hr.



Mean deflectionRecovery x hr.Recovery 24 hr.

Mean deflectionRecovery x hr.Recovery 24 hr.

Mean deflectionRecovery g hr.Recovery 24 hr.


=

-

.-

-

TEMPERATURE-

21 c. 34O c.I

58 c.-

LOAD RANGE_-

600-3,500

2.3399%

2.43100%

2.94

99%

2.8199%

1.75101%

2.1199%

2.2899%

-

--

-

T-

600- 600-1,500 2,500_- .-0.78 1.73

100% 98%101% 100%

0.76 1.7099% 100%

100% 100%

1.05 2.35

99% 100%101% 99%

1.00

;:q 0

0.58104%104%

2.3099%99%

1.29100%

99%

1.60100%100%

1.56

-

_-

-

600-%,000

-

--

600-1,500

--

3.1799%

100%

1.2597%

101%

3.38 1.2499% 98%

100% lO2Yo

6.29

93%95%

4.77

88%97%

5.4796%97%

4.3785%96%

2.38

;;q 0

3.10100%100%

0.6695%99%

/

,

I,,

-

1.01103%105%

12.0188%93%

-

--

-

-1

600-2,500

2.9598%

103%

2.8596%

100%

12.31

76%83%

12.3490%92%

1.5299%

103%

2.3697%

1ow?o

12.6082%88%

-

_-

-

600-4,000--

8.19

;g 0

7.8394%98%

2.6996%99%

5.16

Reading emc~ron deflection villues: S.D. 0.024 mm., water bath temperatures f 1W.


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Volume 12Number 6 FLOW AND RECOVERY OF DENTURE PLASTICS

TABLE III. INDENTATION RESISTANCE AND RECOVERY

MATERIAL

Experimental heat-curing resin,straight monomer

Experimental heat-curing resin,crosslinkedmonomer

Experimental self-curing resin,straight monomer

Experimental self-curing resin,crosslinkedmonomer

Jectron

Luxene

Epoxolon

NO. OFOBSER-VATIONS

--

9

9

9

7

6

10

8

-

NO. OFSPECI-

FICATIONS

P

_-

DEPTH DEPTH

iFTER 30 KG. 4FTER 3 KG.LOAD FOR LOAD FOR10 MIN. 10 MIS.

RI?-ZOVERY

(%I

RATIO IXLOAD TO

PROJECTEDAREA OF

INDENTATION(P.S.1.)

0.088

__-__-

0.010 11,000

0.087 0.009 89.6 11,200

,

0.100 0.017 83.0 9,700

0.099 0.018 81.8 9,800

0.076 0.008 89.5 1 12,800

0.090 . 0.015 83.3 / 10,800

0.077 0.007 90.9 1 12,600

-

108.5

Standard deviation on recovery values: 0.87 per cent.

load is applied at 34 C., the noncrosslinked self-curing resins recover 93 percent, whereas the crosslinked self-curing resins give a recovery value of 96 per centafter yi hour. The corresponding values for 24 hour recovery after 4,000 Gm.load application at 34 C. are 95 and 97 per cent. When the total deflectionvalues are below 3 mm., complete recovery r&ults for all materials.

Deflection and Recovery Values at 58 C.-At 58 C., the order of stiffnessof the resins noted above is changed by the fact that Epoxolon exhibits deflectionvalues which are similar to or greater than the deflection values for the self-curing resins.

At this temperature, the deflection values for crosslinked heat-curing resinsare slightly lower than those for the noncrosslinked resins, particularly with thehigher loads.

No significant difference in deflection is noted between crosslinked and non-crosslinked self-curing resins at 58 C. All self-curing resin and Epoxolonspecimens except one collapsed under a total load of 2,300 to 2,500 Gm. oreven under a load of 1,500 Gm. at 58 C. Some recovery values are above 100per cent. The recorded deflection values for recovery are in these instances smallerthan the initial deflection values. These data are explained as a result of con-tinued polymerization of the resin.


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1086 .S@RENSEN AND RYGE N J;pD',o,s.;:";. .

TABLE IV. ANALYSIS OF VARIANCE: DEFLECTIONVALUES

DEGREESOF SUM OF MEANSOURCEOF VARIATION FREEDOM SQUARES SQUARE

----- I -

Material 16ZETdperature

Material and loadMaterial and temDerature

::12

6Temperature andioadMaterial X load X temperatureResidualTotal

128.0222 21.3370109.8286 109.8286175.1232 87.5616

80.0608 6.671797.9795 16.329969.681369.268410.7955

740.7595

F 0.001 (1.40) = 12.61.F 0.001 (12.40) = 3.64.

TABLE V. ANALYSIS OF VARIANCE: RECOVERYVAL.UES(?-$ HR.)

DEGREESOFSOURCEOFVARIATION FREEDOM

----- -

Material 6TemperatureLoad :Material and loadMaterial and temperature 2Temperature and loadMaterial X load X temperature iiResidualTotal

F 0.001 (1.28) = 13.50.F 0.001 (6.28) = 5.24.

SUM OF MEANSQUARES SQUARE

F

-

4;;341

26

1:22

8.12865.88251.00712.11772.74890.99657.40941.6881

29.9788

1.3548

EE0.35290.45810.99651.23490.0603

F

22.4797.5516.705.857.60

16.5220.48

Jectron recovers completely (99 to 100 per cent) after 2,500 Gm. load ap-

plication during a l/2 hour storage period ; 4,000 Gm. total load application re-sults in 96 per cent recovery. After the 24 hour storage period, the recovery is 99per cent.

The heat-curing polymethyl methacrylate resins do not recover 100 per centfrom any of the test loads during the l/i hour storage period. When loadsof 1,500 and 2,500 Gm. are applied, the recovery value is 96 fo 98 per centafter the l/z hour period. The vz hour recovery after 4,000 Gm. load applicationis 92 to 94 per cent. A 24 hour storage period results in values of 100 per centfor loads of 1,500 and 2,500 Gm. and 96 to 98 per cent for the 4,000 Gm. loads.

Epoxolon and self-curing resins show recovery values from 76 to 90 per

cent for loads of 1,500 and 2,500 Gm. Complete recovery results, in all instances,when the total deflection values are below 3 mm.

Analysis of Va&znce.-The analysis of variance given in Tables IV and Vshows that all calculated F ratios are highly significant (p


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Volume 12Number 6 FLOW AND RECOVERY OF DENTURE PLASTICS lOXi

ences in deflection and recovery for materials, temperatures, and loads includedin the analysis are, therefore, considered significant; also, the double interactionsbetween material and load, material and temperature, temperature and load, andthe triple interaction (material, load, and temperaturej are all of statistical signifi-.cance. This analysis, therefore, strongly rejects the null hypothesis that the speci-mens all belong to the same sample population.

Indentation Resistance Values.---Small differences exist between some typesaccording to the data. The t test was performed on the mean recovery values forthe indentation specimens. The values for the two heat-curing resins and Jcc-tron and Epoxolon are found to belong to the same population (differences notstatistically significant). Similarly, the two self-curing resins and Luxene do Ilotexhibit statistically significant differences among each other in indentation re-sistance and recovery values.

Statistically significant differences, however, are found between the twogroups of materials outlined above. The t values obtained from any combinationof materials between the two groups in all instances fall beyond the 99.5 confi-dence level (p


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1088 S#RENSEN AND RYGE J. Pros. Den.Nov..Dec., 1962

9. Additional work is indicated tq establish the exact relationship between tem-peratures and load in their roles as determining factors in permanent deforma-tion of denture resins.

REFERENCES

9.

10.

II.

12.

13.

Skinner, E. W., and Cooper, E. N. : Physical Properti es of Denture Resins. I. CuringShrinkage and Water Sorption, J.A.D.A. 30:1845-1852, 1943.

Methods of Measuring Molding and Post-molding Changes in Acrylic Denture Materials,Vernonite Work Bench 2 :2, 1943.

Woelfel, J. B., and Paffenbarger, G. C. : Dimensional Changes Occurring in ArtificialDentures, Internat. D. J. 9:451-460, 1959.

Rupp, N. W., Dickson, G., Lawson, M. E., Jr., and Sweeney, W. T.: A Method forMeasuring the Mucosal Surface Contours of Impressions, Casts and Dentures,J.A.D.A. 54:24-32, 1957.

Ryge, G., and Fairhurst, C. W.: An Evaluation of Denture Adaptation on the Basisof Contour Meter Recordings, J.PROS. DEN. 9:755-760, 1959.

Anthony, D. H., and Peyton, F. A. : Evaluating Dimensional Accuracy of DentureBases With a Modified Comparator , J.PROS. DEN. g&3-692, 1959.Woelfel, J. B., Paffenbarger! G. C., and Sweeney, W. T.: Change s in Dentur es During

Storage in Water and m Service, J.A.D.A. 62:643-657, 1961.Peyton, F. A., Anthony, D. H., Asgar, K., Charbeneau, G. T., Craig, R. G., and

Meyers, G. E.: Restorative Dental Materials, ed. 1, St. Louis, 1960, The C. V.Mosby Company, p. 399.

Tylman, S. D., and Tylman, S. G.: Theory and Practice of Crown and BridgeProsthodontics, ed. 1, St. Louis, 1960, The C. V. Mosby Company, p. 1032.

Paffenbarger, G. C., Stanford, J. W., and Sweeney, W. T.: American Dental AssociationSpecifications for Dental Materials 1960-1961, ed. 4, Chicago, 1960 , AmericanDental Association. D. 553.

Paffenbarger, G. C., Stanford, J. W., and Sweeney, W. T.: American Dental AssociationSpecifications for Dental Materials 1960-1961, ed. 4, Chicago, 1960, AmericanDental Association. D. 62.

A S T M Standards 1958. Part 9, Philadelphia, 1958, American Society for TestingMaterials, p. 273.

Sweeney, W. T., Sheehan, W. D., and Yost, E. L.:Filling Resins, J.A.D.A. 49:513- 521, 1954.

Mechanical Properties of Direct

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