Viscoelastic properties of setting elastomeric impression materials

Viscoelastic properties of setting elastomeric impression materials P. A. de Araujo, Ph.D.,* K. D. Jorgensen, Dr.Odont., Mag. Scient.,** and W. Finger, Dr.Med.Dent.*** University Denmark;

of Sao Paulo, Faculty of Dentistry, Bauru, Sao Paulo, Brazil; and University of Achen, Achen, West Germany

T

Material

materials

Manufacturer

Polysulfide

President

Addition

silicone

Permagum

Addition

silicone

Impregum

Polyether

College,

Copenhagen,

MATERIAL

AND METHODS

The materials listed in Table I were mixed in accordance with the manufacturers’ instructions. Correct proportioning of the two pastes was obtained with paired plastic syringes. The total volume of 1 cm3 was mixed 30 -t 5 seconds for each test in the cone and plate rheometer. The materials were mixed at ambient room temperature (21” f 2” -C) and immediately transferred to the rheometer in a controlled temperature room (37” f 0.2” C). Construction and mode of operation of the cone and plate rheometer were previously described.* Thirty minutes before loading the rheometer, the conical and circular brass surfaces of the apparatus were painted with a thin film of adhesive diluted 1: 1 by volume with a rapidly evaporating solvent (Table I). The maximum tensile strain induced with different eccentrics was 16.4%, 24.3%, 37.4%, or 60% established over 3 seconds,

tested

We

Permlastic

Dental

induced and permanent tensile deformation of elastomeric dental impression materials during and after setting. The equipment also permitted the measurement of the elastic relaxation of materials after deformation.’

he viscoelastic properties of elastomeric impression materials are commonly recorded by methods similar to those of the American Dental Association Specification No . 19.‘-4 Inoue and Wilson’ used a modification of the oscillating rheometer designed for composite materials by Bovis et al.” They found that the modified apparatus was also suitable for measuring the rheological properties of elastomeric impression materials during setting. Arikawa et al.’ modified Wilson’s reciprocating rheometer and believed that the customized instrument could monitor the rheological properties of elastic impression materials. Jorgensen* described a rheometer based on the coneplate principle, which enables electronic recording of basic creep during setting of elastic impression materials. The present study recorded the relationship between

Table I. Impression

Royal

Kerr Scafati, Italy Coltene Inc. Altstatten, Switzerland Espe Seefeld/Oberbay, W. Germany Espe Seefeld/Oberbay, W. Germany

Consistency LB R HB LB R HB LB R HB

R

Batch No. 0208821349 0318812056 0610822126 220282-45 150382-65 120282-48 BH26796(CH266) BH01520(CH020) BH30370(CH295) B 0093 (1096) c 0022

Adhesive

Solvent

Permlastic adhesive

Acetone+

GC adhesive*

Benzenet

GC adhesive’

Benyenet

lmpregum adhesive

Chloroform+

*(X adhesive for Exallex, CX Dental Ind. Corp., Tokyo, Jqxm. tS[rucrq Scient. Instr., Copenhagen, Denmark. THE JOURNAL

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DE ARAUJO,

Table II. Constants a and b in equation No. 1 and coefficients Material

ID (o/o)

Permlastic

Permlastic

Permlastic

President

President

President

Permagum

of correlation

LB

R

HB

LB

R

HB

LB

Permagum

R

Permagum

HB

Impregum

16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0

b . IO-”

-0.3 1.3 0.6 1.9 -0.8 -0.2 0.5 1.4 -1.3 -0.9

9.3 2.2 16.4 8.0 11.6 12.1

0.0 0.8 -1.4 -0.8

0.1 1.2 -1.1 -0.6 0.6 1.8 -1.3 -0.6

-0.1 1.1 -3.0 -2.2 -0.8

-0.1 -1.9 -0.3 0.3 1.4 -1.9 -0.8

0.0 1.2

-1.1 0.1 0.6 1.2

11.0 9.0 20.6 20.1 16.9 20.5 3.7 5.3 5.1 4.5 5.1 5.6 4.5 3.4 5.1 5.1 5.2 4.2 9.1

10.0 6.6 6.4 5.4 4.1 3.8 3.3 6.1 5.1 4.4 3.6 2.8 1.3 1.4 1.3

r

FINGER

0.85 0.90 0.90 0.94 0.83 0.97 0.99 0.98 0.97 0.96 0.99 0.98 0.92 0.94 0.95 0.99 0.96 0.99 0.96 0.99 0.98 0.97 0.98 0.99 0.98 0.95 0.95 0.91 0.95 0.98 0.99 0.96 0.99 0.99

0.99 0.99 0.81 0.98 0.95

0.89

Recovery time (min) Material

ID (o/o)

Permlastic

LB

Permlastic

R

Permlastic

HB

President

LB

President

R

President

HB

Permagum

LB

Permagum

R

Permagum

HB

Impregum

ID = Induced deformation.

and at times of 1.5, 2, 3, 4, 5, 7, 10, and 15 minutes initiated on finishing the mix. The test at 15 minutes was omitted for the addition type silicone materials. Three tests were performed for each combination of variables. The creep curves were recorded electronically and the permanent deformation or secondary creep was noted only after the instrument registered complete relaxation. The data were subjected to a regression analysis using the empirical equation Inpa+b.$ with the purpose of obtaining a representative graph of the relationship between the time at which deformation was induced and permanent deformation occurred. 634

AND

Table III. Elastic recovery time dependent on percent induced deformation (n = 3)

(r)

a

JORGENSEN,

16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0 16.4 24.3 37.4 60.0

Mean

Range

2.8 4.4 4.3 5.0 2.9 2.8 5.5 7.0 3.3 3.8 3.9 5.2 3.0 3.8 8.2 8.8 3.2 4.2 4.5 6.2 3.8 4.3 4.7 5.0 2.3 2.8 3.3 4.2 4.7 4.8 5.8 7.0 3.5 3.8 5.3 6.5 5.7 6.1 6.3 6.8

2.7-3.0 4.3-4.5 4.0-4.5 4.8-5.2 2.8-3.0 2.5-3.0 5.0-6.0 6.7-7.3 3.2-3.3 3.7-4.0 3.8-4.0 5.0-5.3 2.9-3.2 3.7-4.0 8.0-8.3 8.5-9.2 3.0-3.3 4.0-4.3 4.3-4.7 6.0-6.3 3.7-4.0 4.2-4.5 4.5-4.8 4.8-5.2 2.2-2.5 2.7-3.0 3.0-3.7 4.0-4.3 4.3-5.0 4.7-5.0 5.5-6.2 6.8-7.2 3.3-3.7 3.7-4.0 5.0-5.7 6.3-6.7 5.0-6.3 6.0-6.2 6.2-6.3 6.5-7.2

11) = Induced deformation.

The recorded permanent deformation is represented by y, and x is the time in seconds after mixture when the deformation was induced. The coefficient of correlation (r) between In y and L was calculated for the recordX3 ings.

RESULTS Fig. 1 illustrates the curves obtained for the four regular-type impression materials from the time of induced deformation to the time of permanent deformation. Table II presents the constants a and b calculated from equation No. 1 for materials listed in Table I. The NOVEMBER

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VISCOELASTICITY

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MATERIALS

Fig. 1. Relation between time of induced deformation (abscissa) and resulting permanent deformation (ordinate) for four elastomeric materials. Curves of four diagrams represent induced deformation of 16.4%, 24.3%, 37.4%, and 60%, respectively. reliability of the equation used for the linear regression analysis of the data was confirmed by the high correlation coefficients obtained and shown in Table II. Fig. 2 depicts one of the calculated curves and the recorded points. Table III shows the mean elastic recovery time for the materials. Elastic recovery was defined as the time from the moment the deformation was induced to the moment the tracing of the recording became parallel.* The elastic recovery time was recorded for set materials after the deformation was induced; that is, 10 minutes after mixing the silicone or 15 minutes after mixing the polyether and the polysulfide materials.

DISCUSSION Fig. 1 demonstrates that the earlier the deformation was induced after mixing the impression material, the greater the permanent deformation. The curves in Fig. 1 also depict the gradual increase in time of the elastic recovery of the materials. When the inclination of the curves is reduced to less than 0.1% permanent deformation per minute, the setting of the materials may be considered clinically sufficient. Setting times thus defined were calculated with equation No. 1 and are shown in Table IV. Setting THE JOURNAL

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Fig. 2. Relation between recorded values of permanent deformation at individual points and curve calculated using equation No. 1. Deformation indu,ced at different times after mix was 37.4%. times recommended by the manufacturers are also presented for comparison. The times for elastic recovery are presented in Table III and suggest that die pouring may be performed 7 to 10 minutes after impressions are obtained. The induced deformation of materials in this study are rational. Jorgensen8 demonstrated that a 60% deforma635

DE ARAUJO,

Permlastic

President

Permagum

Consistency

LB R HB LB R HB LB R HB

Impregum

Se (ID

%)

16.4

24.3

37.4

60

6

6

6 6 4-5 4-5 4-5 3-4 5-6 5-6 4-5

6 6 4 4 4 4 4 4 3

6 6 6 5 5 5 4 5 5 4

8 7 7 5 6 5 5 5 5 4

9 8 9 7 7 6 6 8 6 5

Sm

AND

FINGER

materials during and after setting. The method accurately recorded viscoelastic properties of impression materials.

Table IV. Setting time in minutes as suggested by manufacturers (Sm) and as found experimentally (Se)

Material

JORGENSEN,

ID = Induced deformation.

tion was induced in an elastomeric impression material when removing it from structures with undercuts 1 mm high and deep. The impressions were obtained using a rigid tray with 1 mm distance between the tray and the buccal-lingual surface of the dies.

REFERENCES 1. American Dental Association: Specilication No. 19 for elastomeric impression materials. In: Guide to Dental Materials and Devices, cd 8. Chicago, 1976, American Dewal Association. 2. Wilson HJ: Elastomeric impression materials. Part 2: The set material. Br Dent J 1!21:322, 1966. .3 McPherson GW, Craig RC, Peyton FA: hlerhanical properties of hydrocolloid and rubber impression materials. J Dent Res 46:714, 1967. 4. Goldberg AS: Viscoelastic properties of silicone, polysulfide and polyether impression materials. J Dent Res 53:1033. 1974. 5. Inoue K, Wilson HJ: Viscoelastic properties of elastomeric impression materials. J Oral Rehabil 5%‘). 1978. 6. Bovis SC, Harrington E, Wilson HJ: Setting characteristics of composite filling materials. Br Dent J 131 352, 1971. 7. Arikawa H, Fojii K, Kanie T. Joshin K, Inoue K, Onizuka ?‘, Jimi T: A method for the determination of !.etting characteristics of clasclomeric impression materials. Dent Mater J 1:67, 1982. 8. Jgirgensen KD: A new method of recording the elastic recovery of dental impression materials. Sand J Drnt Res 84:175, 1976.

SUMMARY An instrument was introduced to determine the relationship between induced and permanent tensile deformation of selected elastomeric dental impression

A comparison of four techniques collarless metal-ceramic crowns

for fabricating

A. J. West, B.D.Sc., M.S.D.,* C. J. Goodacre, D.D.S., M.S.D.,** R. W. Dykema, D.D.S., M.S.D.****

B. K. Moore,

Ph.D.,***

and

Indiana University, School of Dentistry, Indianapolis, lnd.

D

uring much of this century, efforts have been made to fabricate strong, esthetic, full-coverage restorations. In 1956, Brecker’ reported on the first metal-ceramic crowns made with newer more compatible materials. He discussed the mechanical advantages of these restorations *Private practice, North Caulfield, Victoria, Australia. **Associate Professor, Department of Fixed and Removable Partial Prosthodontics. ***A\ssoc%w Professor, Department of Dental Materials. ****Professor, Department of Fixed and Removable Partial Prosthodontics.

636

but also suggested that cervical esthetics could be improved by eliminating the facial cervical metal collar and fabricating a collarless metal-ceramic crown. Since that time different techniques have been developed for fabricating these restorations. Initial methods used a metal substructure cast around a platinum foil matrix.‘, 3 Later, refractory die systems were developed to fire porcelain directly against the die without the use of platinum foi1.4-7Other techniques were developed for attaching the platinum foil matrix to the casting after it was prepared for porcelain application.‘*” More recent-

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