water ratio of irreversible hydrocolloid on the bond strength of irreversible hydrocolloid and agar combinations

The effect of powder/water ratio of irreversible on the bond strength of irreversible hydrocolloid combinations

hydrocolloid and agar

Israel Lewinstein, D.M.D., Ph.D.,* and Robert G. Craig, Ph.D.** The University of Michigan, School of Dentistry, Ann Arbor, Mich. This study investigated the effect of powederiwater ratios of irreversible hydrocolloid on the tensile bond strength of several irreversible hydrocolloid and agar combinations. Each irreversible hydrocolloid was prepared in three different powder/water ratios as follows: (1) normal recommended ratio, (2) 10% more water than normally recommended, and (3) 10% less water than normally recommended. The irreversible hydrocolloid and the agar were joined together in a special loading assembly, which was subjected to tensile loading. The results suggest that except for one irreversible hydrocolloid and agar combination the powder/water ratio had no significant effect on the bond strength. In addition, the results indicate that for a successful bond it is important to choose not only a reformulated agar but a compatible irreversible hydrocolloid. (J PROSTHET DENT 1989;62:412-6.)

T

he combination of agar and irreversible hydrocolloid was suggested as an impression material by Schwartz1 in 1951. Skinner and Hoblitz reported adequate dimensional stability with this combination. Appleby et a1.3evaluated the accuracy and bond strength of nine irreversible hydrocolloid and agar combinations and indicated that it was more critical to choose the appropriate reversible hydrocolloid instead of the irreversible hydrocolloid. On the basig of a pilot study, they suggested adding 10% more water to the regular irreversible hydrocolloid powder/water (P/W) ratio. Because this water-enriched ratio decreased the viscosity and increased the working time, some manufacturers advised adding 10% to 15% more water than recommended for the irreversible hydrocolloids. However, the effect of additional water on the tensile bond strength was not determined.

MATERIAL

AND METHODS

The tensile bond strength between irreversible hydrocolloid and agar was determined with an Instron testing machine (In&on Corp., Canton, Mass.) by using a specially designed two-part mold4 (Fig. 1). Each irreversible hydrocolloid was prepared at room temperature (23’ C) in three different P/W ratios as follows: (1) the recommended ratio, (2) 10% more water than recommended, and (3) 10% less water than recommended. The cartridges containing agar were boiled for 10 minutes in a water bath and then allowed to cool to 65” C. The cartridges remained at this temperature for at least 10 minutes prior to use.

*Visiting Lecturer, Department of Biologic and Materials Sciences.

**Professor, Department of Biologic and Materials Sciences. 10/l/12237

412

Fig. 1. Two-part mold for testing bond strength between agar and irreversible hydrocolloid impression materials. The irreversible hydrocolloid was mixed and loaded in one half of the mold within 40 seconds and the warm agar was injected into the other half. The two parts were then joined together without rotation within 1 minute from the start of mixing, and the excess material was wiped from the junctional zone. Two minutes after the start of mixing, the assembly was placed in an oven at 37” C for 3% minutes. The loading assembly was removed and the materials were subjected to tensile loading 1 minute later. The load was recorded at 2000 gm full scale by using a loading rate of 30 cm/min. Two agar and five irreversible hydrocolloid products were tested in different combinations (Table I).

RESULTS The mean bond strengths of agar and irreversible hydrocolloid products for different, P/W ratios are summarized in Table II and graphed in Fig. 2. A cohesive-type failure was observed in more than 80% of the samples with bond strenths greater than 800 gm/cm2. All of the cohesivetype failures occurred in the agar, except for the C-Jp$ combinaiion with 10% more water, which occurred within the irreversible hydrocolloid. Both cohesive and adhesive failure was observed in a few caseswhere the bond strength was between 700 and 900 gm/cm.2 An adhesive failure always resulted in the Ca-W and P-W combinations. OCTOBER

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Table

I. Impression materials tested

Product

name

RATIO

Recommended P/W (g/ml)

Symbol

Type

Supplier

Batch date

Shur gel

s

Irreversible hydrocolloid

07/23/87

7,‘N

JLB

J

Irreversible hydrocolloid

Dec. 86

rC,O:

Coe Alginate

c

Irreversible hydrocolloid

Cadco Alginate

Ca

Irreversible hydrocolloid

Proof

P

Irreversible hydrocolloid

JLB Plus

JP

Agar

JLB Plus§

JP§

Agar

Witness

W

Agar

Columbus Dental St. Louis, MO. Brasseler USA Inc. Savannah, Ga. Coe Laboratories Chicago, Ill. Cadco Products Los Angeles, Calif. Kerr/Sybron Romulus, Mich. Brasseler U.S. Inc. Savannah, Ga. Brasseler U.S. Inc. Savannah, Ga. Columbus Dental St. Louis, MO.

07/01/87

9.5/2-

01/27/87

Y/l6

10/03/86

WI9

02/28/86

.-

O1/31/86

.-

09/29/87

Table II. Mean bond strengths* (gm/cm2), standard deviations (SD), and sample size (n) of seven irreversible hydrocolloidlagar combinations for three powder/water ratios Recommended P/w ratio

10% Less water Powder/water Irreversible hydrocolloid/agar

J-JP§ C-JpfZ$ S-Jp

10% More water

z

SD

11

?I

SD

II

3

SD

n

1186 1243

5 5 4 4 4 4 4

1190 1204 810 925 982 144 120

40 113 99 16 72 23 13

5 8 4 4 4 4 4

1208 909 891 926 986 127 118

72 61 49 31 II 16 21

5 5 4 4 4 4 4

s-w c-w Ca-W

820 972 951 124

35 56 82 67 30 13

P-W

108

7

*Significant figure based on precision of load is 10 gm/cm2.

Table

III.

ANOVA table for two-factor analysis of variance on bond strength df

Source

Irreversible hydrocolloid-agar Conditions-P/W ratio Interaction Error

5 2

10 57

Sum of squares

Mean square

F-test

P value

13454285 3881 22821 129446

2690857 1940 2283

1185.884 ,854 1.005

0.0001 0.4309 0.4504

The results of two-factor ANOVA (1 - cy= 0.95) excluding the C-Jp§ combination are presented in Table III. The results indicated a main effect for the irreversible hydrocolloid-agar combination, whereas interaction between the combinations and conditions was not significant. When CJp$ was included in the ANOVA, a significant interaction between the categories was evident. The Tukey multiple comparison was performed and the different combinations were ranked by tensile bond strength as follows: J-Jp§ > C-JpS > C-W: S-W > S-Jp > Ca-W: P-W THE

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where underscoring indicated means that were not different at LY= 0.05. The mean bond strength of the C-JpJ combination with 10 % more water was significantly smaller (p < 0.001) than the other two means of the same combination under different conditions. The bond strengths of other combiantions were not significantly affected by the P/W ratio of the irreversible hydrocolloid. DISCUSSION Except for the Ca-W and P-W combinations, the bond strengths ranged from 810 to 1243 gm/cm2. Johnson and 413

LEWINSTEIN

q q

J-JP§

C-JP§

S-Jp

Fig. 2. Means of tensile bond strength combinations

of different

CRAIG

10% LESS WATER REC. P/W RATIO 10% MORE WATER

C-W

Ca-W

irreversible

P-W

hydrocolloid

and agar

for three P/W ratios.

Fig. 3. SEM image of agar Jp§ illustrating structures. (Magnification x200.)

Craig 4 recorded bond strengths in the range of 591 to 1080 gm/cm2 with different irreversible hydrocolloid and agar combinations. They observed complete cohesive failure for all samples, in only two different combinations with mean bond strengths of 970 and 1080 gm/cm2 (Coe irreversible hydrocolloid-Dentloid Super Green and Coe irreversible hydrocolloid-Dentloid Brown, respectively). In that study the irreversible hydrocolloid and agar were joined after approximately 1.5 minutes from start of mixing, compared with 1 minute in this study. Despite the different combinations assessed in both investigations, the difference in

414

S-W

AND

nonhomogeneous

surface with “sea plant”-like

timing may be the reason for the more cohesive-type failure and higher bond strengths recorded in this study. In one case (C-Jp§) the addition of 10% more water to the irreversible hydrocolloid resulted in a reduced bond strength (909 gm/cm2) and a cohesive failure within the irreversible hydrocolloid. With the same agar (Jp$), but a different irreversible hydrocolloid (J), the additional water did not afFect the bond strength and a cohesive failure was noted within the agar. When the same agar (Jp) from a different batch date was combined with irreversible hydrocolloid S, the additional water did not decrease the mean bond

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Fig. 4. SEM image of sea plant-like

structure. (Magnification

x500.)

Fig. 5. (A) SEM image of irreversible hydrocolloid/agar (J-Jp) interface. Agar, located in lower half of photograph is locked into irreversible hydrocolloid. (B) Backscatter electron image of same area. (Magnification x300.)

strength, tmd cohesive failure was observed within the agar. Although a Iliminished bond strength was not demonstrated in thl e S-Jp combination, the total average bond strength (,for all three P/w conditions) was significantly smaller (1D< 0.05) than the J-Jp$ combination. These findings ir ldic fated that the tensile strength of the same agar hydrocollc Gd might differ with each batch date. In this study, the! te!nsile strength of the agar Jp§, was relatively

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high, while the additional water deteriorated I the ,t ensile strength of the alginate C, resulting in cohe!eive faiilures within the irreversible hydrocolloid with a mean bond strength of 909 gm/cm2. Figs. 3 and 4 display the s1zface of agar Jp§ in which unprocessed materials E;uch a:s “sea plant”-like structures can be distinguished Th iis nonid may homogeneous character of the agar hydrol co110 explain the different tensile strengths between the 1oatches.

415

LEWINSTEIN

Appleby et al3 stated that it is more important to choose the reversible hydrocolloid with the highest bond strength than to avoid the irreversible hydrocolloid with the lowest mean bond strength. However, the low bond strengths demonstrated in Ca-W and P-W combinations suggested that for a successful impression, it is also crucial to choose a compatible irreversible hydrocolloid for the agar. Skinner and Hoblit2 warned that the bond between agar and irreversible hydrocolloid was solely mechanical and suggested placing a wire between the materials. In a preliminary study, agar Jp and irreversible hydrocolloid J were bound together. The specimen was dried and then polished with Carborundum paper (600-grit) (Fig. 5). There was a “rete-peg” penetration of each material to another (Fig. 5, A), but the backscatter electron imaging (Fig. 5, B) demonstrated minimal penetration. Even though the specimen was dried, a debonding or crack was not evident within the interface of the two materials. This observation and the incompatibility of some irreversible hydrocolloid products with the agar might suggest the presence of chemical bonds (molecular linking) in addition to the mechanical bond. However, more studies are required to explore the nature of the bond between the reversible and irreversible hydrocolloid.

AND CRAIG

loid and agar combinations was investigated. The P/W ratio included: (1) the recommended P/W rato, (2) a 10% decrease in water, and (3) a 10% increase in water. Except for one irreversible hydrocolloid and agar combination, CJp$, the P/W ratio did not have a signficiant effect on the bond strength. Two combinations (Ca-W and P-W) demonstrated a weak bond, indicating that for a successful bond it is important to select not only a reformulated agar, but also, a compatible irreversible hydrocolloid. REFERENCES 1. Schwartz JR. The use of hydrocolloids or alginates as impression ma-

terials for indirect or indirect-direct inlay construction procedure. Dent Items Interest 1951;73:379-89. 2. Skinner EW, Hohlit NE. Study of accuracy of hydrocolloid impressions. J PROSTHET DENT 1956;6:80-6. 3. Appleby DC, Pameijer CH, Boffa J. The combined reversible hydrocollaid/irreversible hydrocolloid impression system. J PROSTHET DENT 1980:44:27-35.

4. Johnson GH, Craig RG. Accuracy and bond strength of combination agar/alginate hydrocolloid impression materials. J PROSTHET DENT 1986;55:1-6.

Reprint requests to; DR. ISRAEL LEH~~NSTEIN HEBREW UNFZERSITY-HADA~SAH SCHOOL OF DENTAL MEDICINE

P.O.B. 12000 JERUSALEM 91120 ISRAEL

SUMMARY The effect of P/W ratio of irreversible hydrocolloid on the tensile bond strengths of various irreversible hydrocol-

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