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Delayed hygroscopic expansion of phosphate-bonded investments
Delayed hygroscopic expansion of phosphate-bonded inw3stments
J. F. Santos, R. Y. Ballester Dental Materials Department, School of Dentistry, University of S~.o Paulo, Brazil
Santos JF, Ballester RY. Delayed hygroscopic expansion of phosphate-bonded investments. Dent Mater 1987: 3: 165-167. Abstract - Delayed hygroscopic expansion is caused by immersion of investments after their nominal final set. Its magnitude was established in a previous paper (1) for gypsum bonded investments. In the present investigation high values of delayed hygroscopic expansion were also found for phosphatebonded investments. In addition, experimental conditions intentionally introduced (liquid concentrations for spatulation and immersion times) caused significant differences upon the measured values of expansion. Such variations if not adequately controlled by the dental laboratory technician can cause severe casting misfits.
The concept of delayed hygroscopic expansion was established in a previous publication (1) and is understood to be caused by later than normal immersion times. For this investigation the specimens were immersed in water 30 rain after spatulation. The hygroscopic expansion of phosphate-bonded investments is used to offset the contraction of high fusing alloys in precision casting techniques (2). However, the expansion mechanism itself and the role that immersion time plays in interfering in the process are not completely understood. The purpose of this research was to verify whether delayed hygroscopic expansion is influenced by different concentrations of the special liquid for spatulation and by varying the immersion times. This investigation is clinically relevant because the dimensional behavior of phosphate-bonded investments can be deeply influenced by changes of environmental humidity and temperature, even after the investment's final set. Therefore, the fit of cast restorations made with high fusing casting alloys can be unpredictably influenced by changes of environmental humidity and temperature after the investment's final set. Methods
Two commonly used phosphatebonded investments were investigated. Their brand names, manufacturers and
Key words: dental casting investment, dental casting technique, hygroscopic expansion. Jose E Santos, Rua Borges Barros, 189-apto 12, 05441-S&o Paulo, SP, Brazil.
ReceivedAugust 4; accepted August 29, 1986.
working conditions are shown in Table 1. Each specimen was prepared with 50 g of powder and its dimensional change from the end of spatulation to
24 h was measured by the device shown in Fig. 1. Delayed expansion data was recorded at the 18 intervals detailed in
A I I
.1
Q
I
G t I
. . . .
i
. . . .
Fig. 1. Measuring device Schematic representation. Frontal view, A; lateral view, B. Modified dial gauge (internal springs removed), 1; Water bath for keeping the temperature uniform, 2; Cover to minimize loss of temperature from the immersion bath, 3; immersion bath recipient, 4; electric resistance, 5; test specimen, 6; terminal wall with a rigid conection with the dial gauge, 7; mobile lateral wall of box mold. Other details as water entrance and exit, thermal insulation, temperature control devices, etc. were omitted from this representation.
166
Santos & Ballester
Table 1. Materials, manufacturer and working conditions investigated. Material
Manufacturer
Spatulation*
Ceramigold
Whip-Mix Co.
Hi-Temp
Whip-Mix Co.
Like recommended by manufacturer Like recommended by manufacturer
temperature of 38~ and a relative humidity of 100%. Thirty minutes after starting to mix the investment, the specimens were immersed in distilled water at 38~ for the following times: zero (control group), 30 s and 4 min. Three repetitions of each experimental condition were made, resulting in 54 independent tests and 973 values of dimensional change (delayed expansion).
* under vacuum. Results
Figs. 2 and 3. During the first 120 min the specimens were kept at a controlled
The linear dimensional change values were transformed into percentage vari-
ations of length. The latter values corresponding to the average of 3 similar experiments were plotted versus the times at which the specimens were measured. Two graphs, each corresponding to a specific material, were constructed. Fig. 2 is the graphic representation of observed expansion of Ceramigold investment and Fig. 3 represents the expansion of Hi-Temp investment. In both cases the axis of ordinates represents the percent dimensional change and the axis of abscissae represents the times on an arbitrary scale ranging from 3-120 min. Resulting from the combinations of 3 concentrations of the special liquid for spatulation and 3 immersion times, 9 curves were drawn for each material.
CERAMIGOLD Discussion
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TIME
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o o.,
1 O0
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0 1 2.
09
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2, 5
75
0
IZ.
5
75
0.5
X
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4 o
9
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i
|
|
0.5
,
0
Z W
|
|
1,5
0
rT W
EL
1
0.5
,,e"?,th' 6
30
'
'
n
60
'
'
I
90
"
",,~1
'
24
"--
I
minut e s . _ _ ~ _ _
hours
TIME Fig. 2. Ceramigold expansion curves from 1 to 9. - Box inside the graph informs experi-
mental conditions: % concentration of special liquid for spatulation; time: 0; 0.5 and 4 rain immersion time.
The two graphs (curves 1, 4, 7, Figs. 2, 3) show that the normal setting expansion of both materials was smaller than expected (3, 4). A possible explanation for such a finding may be that the temperature at which the specimens were kept during the setting reaction period was 38~ However, smaller than expected values of hygroscopic expansion of phosphate-bonded investments have been reported (5). Such a discrepancies seem to be caused by different research methods. Both materials showed hygroscopic expansion of considerable magnitude. This result is intriguing as immersion was at 30 min after start of mix, a time by which final set had probably been reached (5). The expansion of Ceramigold was higher generally than that observed for Hi-Temp. The expansion was also higher for Ceramigold than for Hi-Temp when 100% of the special spatulation liquid was used. With the Ceramigold investment, immersion times of 30 s and 4 min did not significantly influence the delayed higroscopic expansion when the specimens were prepared with 75% and 56.25% concentrations of the special spatulation liquid. The expansion was significantly higher however, when 100% of the special liquid was used, than with the other two concentrations. Different concentrations of the special liquid did not significantly influence the delayed hygroscopic expansion with Hi-Temp. With the exception of Curve 5, Fig. 3 (80% special liquid/ 30 s immersion time in distilled water), the remaining experimental conditions presented similar expansion curves.
Delayed hygroscopic expansion
167
Conclusions
HI - T E M P
Z 9 co
Z
<~ el
|
X LLI
|
| |
Based on the curves representing delayed expansion, the following conclusions can be drawn: (1) normal setting expansion of both investments is not influenced by different concentrations of the special spatulation liquid; (2) in general, Ceramigold demonstrates greater delayed expansion than the HiTemp; (3) special liquid concentration and immersion time do not significantly influence the delayed hygroscopic expansion of Hi-Temp; (4) the results suggest that Hi-Temp was less influenced than the Ceramigold by variations in special liquid concentration and immersion time.
i1
O Z
Acknowledgements" - We wish to thank Dr.
(9
15
iii
f_3 fr Iii fl_
Aldridge Wilder, from the School of Dentistry of the University of North Carolina at Chapel Hill, for his assistance in preparing this article. Research supported by FAPESP (Funda~o de Amparo h Pesquisa do Estado de S~o Paulo), grant n ~ 80/1264.
1
References
05
Q
6
30
60
90
1201
minut e s . _ _ ~ _ _
24
hours
TIME Fig. 3. Hi-Temp expansion curves from i to 9. Box inside the graph indicates experimental
conditions: % concentrations of special liquid for spatulation; time: 0; 0.5 and 4 min of immersion time.
l. Santos JF, Ballester RY. Delayed "hygroscopic" expansion of gypsum products. J Prosthet Dent 1984: 52:366 70. 2. Komoda Y. The effect of restrictive stress on the hygroscopic expansion of phosphate-bonded investment. Shikwa Gaku 1975: 75: 1185-97. 3. Pegoraro LF, Chiodi JN. Hygroscopic and thermal expansion of three phosphate-bonded investments (hygroscopic and thermal setting). Ars Curandi'Odontol 1979: 5: 16-24. 4. Phillips RW. Skinner's science of dental materials. 8th ed. Philadelphia: Saunders 1982: 467. 5. Marsaw FA, Rijk WG, Hesby RA, Hinman RW, Pellev GB. Internal volumetric expansion of casting investments. J Prosthet Dent 1984: 52: 361-66.
J. F. Santos, R. Y. Ballester Dental Materials Department, School of Dentistry, University of S~.o Paulo, Brazil
Santos JF, Ballester RY. Delayed hygroscopic expansion of phosphate-bonded investments. Dent Mater 1987: 3: 165-167. Abstract - Delayed hygroscopic expansion is caused by immersion of investments after their nominal final set. Its magnitude was established in a previous paper (1) for gypsum bonded investments. In the present investigation high values of delayed hygroscopic expansion were also found for phosphatebonded investments. In addition, experimental conditions intentionally introduced (liquid concentrations for spatulation and immersion times) caused significant differences upon the measured values of expansion. Such variations if not adequately controlled by the dental laboratory technician can cause severe casting misfits.
The concept of delayed hygroscopic expansion was established in a previous publication (1) and is understood to be caused by later than normal immersion times. For this investigation the specimens were immersed in water 30 rain after spatulation. The hygroscopic expansion of phosphate-bonded investments is used to offset the contraction of high fusing alloys in precision casting techniques (2). However, the expansion mechanism itself and the role that immersion time plays in interfering in the process are not completely understood. The purpose of this research was to verify whether delayed hygroscopic expansion is influenced by different concentrations of the special liquid for spatulation and by varying the immersion times. This investigation is clinically relevant because the dimensional behavior of phosphate-bonded investments can be deeply influenced by changes of environmental humidity and temperature, even after the investment's final set. Therefore, the fit of cast restorations made with high fusing casting alloys can be unpredictably influenced by changes of environmental humidity and temperature after the investment's final set. Methods
Two commonly used phosphatebonded investments were investigated. Their brand names, manufacturers and
Key words: dental casting investment, dental casting technique, hygroscopic expansion. Jose E Santos, Rua Borges Barros, 189-apto 12, 05441-S&o Paulo, SP, Brazil.
ReceivedAugust 4; accepted August 29, 1986.
working conditions are shown in Table 1. Each specimen was prepared with 50 g of powder and its dimensional change from the end of spatulation to
24 h was measured by the device shown in Fig. 1. Delayed expansion data was recorded at the 18 intervals detailed in
A I I
.1
Q
I
G t I
. . . .
i
. . . .
Fig. 1. Measuring device Schematic representation. Frontal view, A; lateral view, B. Modified dial gauge (internal springs removed), 1; Water bath for keeping the temperature uniform, 2; Cover to minimize loss of temperature from the immersion bath, 3; immersion bath recipient, 4; electric resistance, 5; test specimen, 6; terminal wall with a rigid conection with the dial gauge, 7; mobile lateral wall of box mold. Other details as water entrance and exit, thermal insulation, temperature control devices, etc. were omitted from this representation.
166
Santos & Ballester
Table 1. Materials, manufacturer and working conditions investigated. Material
Manufacturer
Spatulation*
Ceramigold
Whip-Mix Co.
Hi-Temp
Whip-Mix Co.
Like recommended by manufacturer Like recommended by manufacturer
temperature of 38~ and a relative humidity of 100%. Thirty minutes after starting to mix the investment, the specimens were immersed in distilled water at 38~ for the following times: zero (control group), 30 s and 4 min. Three repetitions of each experimental condition were made, resulting in 54 independent tests and 973 values of dimensional change (delayed expansion).
* under vacuum. Results
Figs. 2 and 3. During the first 120 min the specimens were kept at a controlled
The linear dimensional change values were transformed into percentage vari-
ations of length. The latter values corresponding to the average of 3 similar experiments were plotted versus the times at which the specimens were measured. Two graphs, each corresponding to a specific material, were constructed. Fig. 2 is the graphic representation of observed expansion of Ceramigold investment and Fig. 3 represents the expansion of Hi-Temp investment. In both cases the axis of ordinates represents the percent dimensional change and the axis of abscissae represents the times on an arbitrary scale ranging from 3-120 min. Resulting from the combinations of 3 concentrations of the special liquid for spatulation and 3 immersion times, 9 curves were drawn for each material.
CERAMIGOLD Discussion
Z ~o
TIME
,oo , oo
o o.,
1 O0
4
0 1 2.
09
Z <
2, 5
75
0
IZ.
5
75
0.5
X
6 7
,, ,8.,
4 o
9
EE.25]
UJ
Se,25
II
i
|
|
0.5
,
0
Z W
|
|
1,5
0
rT W
EL
1
0.5
,,e"?,th' 6
30
'
'
n
60
'
'
I
90
"
",,~1
'
24
"--
I
minut e s . _ _ ~ _ _
hours
TIME Fig. 2. Ceramigold expansion curves from 1 to 9. - Box inside the graph informs experi-
mental conditions: % concentration of special liquid for spatulation; time: 0; 0.5 and 4 rain immersion time.
The two graphs (curves 1, 4, 7, Figs. 2, 3) show that the normal setting expansion of both materials was smaller than expected (3, 4). A possible explanation for such a finding may be that the temperature at which the specimens were kept during the setting reaction period was 38~ However, smaller than expected values of hygroscopic expansion of phosphate-bonded investments have been reported (5). Such a discrepancies seem to be caused by different research methods. Both materials showed hygroscopic expansion of considerable magnitude. This result is intriguing as immersion was at 30 min after start of mix, a time by which final set had probably been reached (5). The expansion of Ceramigold was higher generally than that observed for Hi-Temp. The expansion was also higher for Ceramigold than for Hi-Temp when 100% of the special spatulation liquid was used. With the Ceramigold investment, immersion times of 30 s and 4 min did not significantly influence the delayed higroscopic expansion when the specimens were prepared with 75% and 56.25% concentrations of the special spatulation liquid. The expansion was significantly higher however, when 100% of the special liquid was used, than with the other two concentrations. Different concentrations of the special liquid did not significantly influence the delayed hygroscopic expansion with Hi-Temp. With the exception of Curve 5, Fig. 3 (80% special liquid/ 30 s immersion time in distilled water), the remaining experimental conditions presented similar expansion curves.
Delayed hygroscopic expansion
167
Conclusions
HI - T E M P
Z 9 co
Z
<~ el
|
X LLI
|
| |
Based on the curves representing delayed expansion, the following conclusions can be drawn: (1) normal setting expansion of both investments is not influenced by different concentrations of the special spatulation liquid; (2) in general, Ceramigold demonstrates greater delayed expansion than the HiTemp; (3) special liquid concentration and immersion time do not significantly influence the delayed hygroscopic expansion of Hi-Temp; (4) the results suggest that Hi-Temp was less influenced than the Ceramigold by variations in special liquid concentration and immersion time.
i1
O Z
Acknowledgements" - We wish to thank Dr.
(9
15
iii
f_3 fr Iii fl_
Aldridge Wilder, from the School of Dentistry of the University of North Carolina at Chapel Hill, for his assistance in preparing this article. Research supported by FAPESP (Funda~o de Amparo h Pesquisa do Estado de S~o Paulo), grant n ~ 80/1264.
1
References
05
Q
6
30
60
90
1201
minut e s . _ _ ~ _ _
24
hours
TIME Fig. 3. Hi-Temp expansion curves from i to 9. Box inside the graph indicates experimental
conditions: % concentrations of special liquid for spatulation; time: 0; 0.5 and 4 min of immersion time.
l. Santos JF, Ballester RY. Delayed "hygroscopic" expansion of gypsum products. J Prosthet Dent 1984: 52:366 70. 2. Komoda Y. The effect of restrictive stress on the hygroscopic expansion of phosphate-bonded investment. Shikwa Gaku 1975: 75: 1185-97. 3. Pegoraro LF, Chiodi JN. Hygroscopic and thermal expansion of three phosphate-bonded investments (hygroscopic and thermal setting). Ars Curandi'Odontol 1979: 5: 16-24. 4. Phillips RW. Skinner's science of dental materials. 8th ed. Philadelphia: Saunders 1982: 467. 5. Marsaw FA, Rijk WG, Hesby RA, Hinman RW, Pellev GB. Internal volumetric expansion of casting investments. J Prosthet Dent 1984: 52: 361-66.