Impression materials and electrodeposits. Part I: Impression materials

James A. Stackhouse, Jr., D.D.S., M.S.D.* College of Medicine and Dentistry of New Jersey, New Jersey Dental School, Newark, N. J

M odeling compound and mercaptan rubber impressions have long been advocated as suitable substrates for electroformed dies. The use of conven- tional silicone materials in this application is con- troversial, having both supporters’, ‘T and oppo- nents.“.” Polyethers and polyvinyl silicones as sub- strates have received insufficient investigation to allow routine clinical usage, although recent advances have been made by several investiga- tors.“-”

The use of representative impression materials as substrates for electrodeposited metals will be de- scribed in Part II.

OBJECTIVES

The objectives of this study were to (1) determine the dimensions of five substrates prior to the electro- plating process and (2) measure the dimensions of polyether and polyvinyl silicone specimens prepared under three different lo-minute polymerization con- ditions for long-term, dry bench set tests and for immersion tests in electroplating baths.

MATERIALS AND METHODS Preparation of specimens

The five impression materials were modeling com- pound,“f: a mercaptan rubber,# a condensation siii- cone,// a polyether, f and an addition silicone.??

The modeling compound was warmed to 55” C. pressed against the master die within the confining

*Professor, Dental Biomaterials and Fixed Prosthodontics.

tChristensen, G. J.: Personal communication, Feb. 8. 1977

$Type I, Kerr Sybron Corp., Romulus, Mich. SPermlastic, Kerr Sybron Corp., Romulus, Mich. /[Elasticon, Kerr Sybron Corp., Romulus, Mich.

IPolyjel, L. D. Caulk Co., Milford, Del. #President, Coltene, Inc., AltstBlten, Switzerland.

44 JANUARY 1981 VOLUME 45 NUMBER 1

ring described by the American Dental Association’s Specification No. 19,“’ allowed to cool to room temperature, removed from the ring, and measured within 5 to 10 minutes.

The base and catalyst of the elastomers were dispensed according to manufacturers’ recommenda- tions, mixed within 2 minutes, introduced into the master die ring, and pressed against the master die with a glass plate. The assembly was allowed a lo-minute polymerization period under one of the following three environments (Table I): rendition ‘4 --a dry bench cure at 23” C; condition B-immersion in a water bath of 32” C; and condition C- immersion in a water bath of 38” C. Following the polymerization period, the specimens were removed from the ring, measured within 5 to 10 minutes for the first reading. and used for one of the following three purposes:

1. Specimens for electroplating. These were prepared according to condition C and used for electroplating.

2. Specimens of President and Polyjeel for dv bench set.

These were six groups of 10 specimens each, pre- pared under conditions A, B, and C, allowed a bench set, and measured at irregular intervals throughout a 3-week period.

3. Specimens of President and Polyjeelfor immersion tesh. Ten President specimens were prepared according to condition C, measured, then immersed in an acid copper-sulfate electroplating bath at room tempera- ture. The Polyjel specimens were immersed in both copper-sulfate and silver-cyanide baths. They were removed at hourly intervals, measured, and then immediately returned to the bath. The final mea- surement was made after the fifth hour of immer- sion.

Measurements

All the impression materials recorded the lines clearly on the face of the master die, and measure-

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IMPRESSION MATERIALS

Fig. 1. Master die block described by American Dental Association Specification No. 19. The two uerficai lines are the bench marks. Measurements of the impression materials were made along the top line.

Table I. LJses and preparation conditions of impression material specimens

Material Electro-

deposition

Polymer- ization

condition” J-week

dry bench set

Polymer- L&ion

condition Immersion

tests

Poly- meri- zation

condition

Modeling compound Yes Perrnlastic Yes Elasticon Yes Polyjel Yes President Yes

No No No Yes Yes

-

A,B,C A,BS

No No No Yes Yes

- - -

C C

Conditions: A = 23” C, no water bath; B = 32” C, with water bath; C = 38” C, with water bath. *The setting mechanism for modeling compound was by thermoplastic means rather than by polymerization

ments were made along the upper horizontal line between the vertical bench marks (Fig. 1). The measuring instrument was a Nikon toolmakers’ microscope* magnifying 30 diameters and having micrometers divided into 0.0001 inch increments.

Ten measurements of the master die produced a mean of 0.9952 inch with a standard deviation of 0.00025 inch. All impression material data were compared to the master die and converted to per- centage differences.

RESULTS Specimens for electroplating

All substrates showed a decrease of from 0.07% to 0.23% from the master die dimensions (Table II). This decrease was caused by such factors as polymer- ization shrinkage, volatilization of some components, thermal changes, and stress release.

At least 10 replicate specimens were prepared for each test condition. One hundred fifty-six specimens were used in the investigation.

*Nikon, Nippon Kogaku, K. K., Japan

Specimens of President and Polyjel- Dry bench set

President specimens which had polymerized at 23” C (condition A) showed a decrease in length of 0.11% within 1 hour and a decrease of less than 0.20% at the end of 3 weeks (Fig. 2). Polyjel speci- mens polymerizing under similar conditions had

THE JOURNAL OF PROSTHETIC DENTISTRY 45

-5-I A= 23°C NO WATER BATH B= 32°C WATER BATH X---X PRESIDEN r

C=38”C WATER BATH (z>--Cl POLY J E I.

Fig. 2. Dimensional changes of President and Polyjel during dry bench set. The horizontal axis is a logarithmic representation of hours, and the vertical axis is the percentage of change from the master die. The conditions of polymerization in the master die ring assembly are conditions A, B, and C in Table I. Omitted from the figure are the standard deviations of the means of each point, which varied from 0.01% to 0.08%.

X- --x PRESIDENI (.2----.-Q POLY JE L.

Fig. 3. These “base line” curves of President and Polyjel during dry bench set were used for comparisons in immersion tests. Both materials polymerized under condi!ian C.

Table II. Shrinkage of impression materials used as substrates for electrodeposition

Material Mean SD

Modeling compound -0.21 0.13 Permlastic -0.07 0.15 Elasticon -0.21 0.10 Polyjel* -0.22 0.08

Polyjeli -0.16 0.05

President -0.23 0.06

*Polyjel as substrate for silver. iPolyje1 as substrate for nickel.

decreased 0.13% in 1 hour and 0.24% at the end 01’ 3 weeks (Fig. 2).

Both President and Polyjel specimens which had polymerized under conditions R and C,’ shrank consid- erably from the effect of the elevated temperatures by the end of the first hour. Thereafter, they rverr stable during the 3-week period (Fig. 2).

The dimensional change curves of both President and Polyjel prepared under condition C: were used as “base lines” for subsequent comparison of materials utilized in other tests in both Parts I and II (Fig. 3).

46 JANUARY 1981 VOLL’MT ?5 NUMBER I

IMPRESSION MATERIALS

HOURS ‘(4 l/2 I 2 345 IO 24 100 168 336594

I

~. A---.L...--L~- L- --.-, I DAY

$3 I WK 13)‘KS

1 2’fv’Ks

+5 t tt

ki -4

z -.5- a 1-6 v :

- 71 0-a

-8 I b-Q

PRESIDENT

DRY BENCH SET ~Afk~lD ELECTROPLATING

-9

-10 1

Fig. 4. Dimensional change of President specimens immersed in acid electroplating bath (dotted line) superimposed over the unbroken dry bench set base line from Fig. 3. Both groups of specimens polymerized under condition C.

-- ~. Al-.-

POLYJEL B---U DRY BENCH SET

-- 7 b -6 !A$klD ELECTROPLATING

-8 - 9~.

I

o- -a IN ALKALINE ELECTROPLATING BATH

-10-J

Fig. 5. The dimensional changes of Polyjel in acid and alkaline electroplating baths compared to the base line of dry bench set from Fig. 3. All specimens polymerized under condition C.

Specimens of President and Polyjel- Immersion tests

Fig. 4 shows a comparison of the curve of Presi- dent-immersed specimens superimposed over the “base line” of dry bench set President specimens.

There was little difference between the two curves, showing that immersion had little effect on Presi- dent’s dimensional stability.

The Polyjel specimens, however, immediately demonstrated the effect of immersion in both the

THE JOURNAL OF PROSTHETIC DENTISTRY 47

acid and the alkaline electroplating baths by the divergence of their curves from the dry bench set base line (Fig. 5).

DISCUSSION

When this work was started, a water bath of 37 -t lo C (condition C) was recommended for the in

vitro testing of impression elastomers.” This was believed to simulate the intraoral condition of impression materials. However, a 32 f 2” C water bath (condition B), is now thought to more realistical- ly represent the intraoral environment of impression materials.“‘. ”

The slight dimensional changes during the first hour of the elastomers processed under condition A occurred without the influences of temperature change or water bath effect and were probably due to polymerization shrinkage.

The dimensional changes of the immersed Polyjel specimens were not unlike those published in a previous report (Fig. 5).“’

CONCLUSIONS

1. When compared to the master die, all five impression material specimens showed a shrinkage of from 0.07% to 0.23%. When used as substrates for electrodeposition, these dimensions partly predeter- mined the dimensions of the electrodeposits. (This will be discussed in Part II of this study.)

2. When polymerized and maintained at room temperature, both President and Polyjel demon- strated a slight polymerization shrinkage then remained stable during a 3-week bench set.

3. When polymerized at higher temperatures, both President and Polyjel demonstrated consider-

able dimensional changes during the first hour as they cooled to room temperature then remained stable during the 3-week dry bench set.

4. President was little affected by a 5-hour immer- sion in an acid electroplating bath.

5. Polyjel, during 5 hours of immersion, tended to

expand in both acid and alkalinr rlectroplatine baths.

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48 JANUARY 1981 VOLUME 45 NUMBER I