|
Accuracy And Reproducibility Of Reversible Hydrocolloids Versus Elastomers Duplicating Materials
Salma Bahannan, BDS, MS*,
Ahmed Abd. El-Hamid, BDS, MS, PhD*,
Mohammad Abd. El-Halim, BDS, MS, PhD**
* Faculty of Dentistry, King Abdulaziz University, P.O. Box 10390, leddah 21433,
Kingdom of Saudi Arabia.
** Lecturer, Prosthetic Department, Faculty of Dentistry, El-Mansoura University, Egypt.
The dimensional accuracy of four duplicating materials, including one
brand of agar reversible hydrocolloid, one brand of polyether rubber,
and two brands of polyvinyl siloxane (addition silicone) rubber was
studied. A standard stainless steel specimen of 76 x 76 x 9.5 mm was
made. Vertical and horizontal grooves were made on the specimen as
reference marks. The horizontal grooves were in different depths and
widths. The duplicating materials were prepared and poured over the
standard die to make a negative likeness. These negatives were poured
with the same investment material. Twelve investment specimens were
measured for accuracy and detail reproduction with a Talysurf finish
analyzer. Results of this study indicated that polyvinyl siloxane and
polyether rubbers are superior in accuracy compared to the agar
reversible hydrocolloid. No significant differences in detail
reproduction were noted in any of the duplicating materials tested.
The ultimate success of any removable metallic prosthesis or implant
prosthesis is attributed to the duplicated casts which should be accurately reproduced
from the master casts.12 The duplicating materials evaluated by the
American Dental Association (ADA) No. 20 were divided into thermally reversible
and irreversible materials.3
An accurate refractory cast may be obtained when an
impression of the original cast is made in an elastic material and poured with
investment. The most common duplicating materials are reversible hydrocolloid
compounds. The composition of these compounds is quite similar to agar
impression material, but the percentage of agar is about 5% while the
impression materials may contain 10-15% agar. In addition, reversible hydrocolloid
duplicating material does not contain waxes, fillers and other modifiers common
to impression materials.4
Agar duplicating materials are reversible and have
adequate strength and elastic properties to make duplication of minor undercuts
possible. These materials may be reused many times which makes them less
expensive to use than other duplicating materials. The disadvantages of this material
are its susceptibility to dimensional changes if stored in air or water. It is
a polysaccharide material and will gradually hydrolyze at storage temperature
with an eventual loss of elasticity and strength.14
Other types of elastomeric materials, such as silicone
rubber and polyether, are used recently as duplicating materials. The
advantages of these elastomeric materials over reversible agar duplicating
materials are that multiple casts can be made from a single mold and it is
possible to wait for an extended period of time before pouring the mold with
the investment materials.56 They are considerably more expensive to
use than the agar material but are preferred by some laboratories for making
multiple casts from the same mold.
This study compared the accuracy and detail reproduction
of four types of duplicating materials.
Four duplicating materials were used: a Castogel* agar
reversible hydrocolloid, Reprogum** polyether, Elite Doublet and Wirosiltt
polyvinyl siloxane (addition silicone) eslatomers.
A stainless steel die was made according to ADA specification No. 20
[Fig. 1] and was 76 x 76 x 9.5 mm. On the highly polished surface of the die, two
vertical lines (F1 and F2) were made with a diamond
indenter. These reference marks were made 19 mm from each edge for the linear dimensional
change test. Another 14 horizontal lines of varying depth and width were made
for testing the reproduction of details. These horizontal lines were parallel
to each other, 2.5 mm apart, at right angles to the lines F1 and F2
[Fig. 11.]
Agar reversible hydrocolloid was prepared according to
the manufacturer's directions. It was poured into a plastic duplicate container
over the metal die at 40° ± 2°C. The thickness of this duplicating material was
6 mm. It was placed in a cooler* for 60 minutes to allow indirect proper cooling.
Polyvinyl siloxane and polyether duplicating materials were mixed at room temperature
(22° ± 2°C) according to the manufacturer's instructions. The base and catalyst
were mixed in the ratio of 1:1 until a homogenous color was obtained. Then it
was poured in a thin stream into a plastic duplicate flask over the metal die.
The thickness of these duplicating materials was 4 mm. [Fig. 2]. Each
duplicating material was separated from the metal die after it has set. All die
molds were poured with the same dental investment material** following the
manufacturer's instructions. The investment mix was mechanically spatulated for
60 seconds in a vacuum mixer.t The investment samples were allowed to set for
one hour before separation from the molds. Three investment specimens were made
for each duplicating material.
The master stainless steel die and the investment
specimens that corresponded to the different types of
duplicating materials were measured with a Talysurf surface analyzer+t [Fig.
3]. For the linear dimensional shrinkage change test, the distance between the reference
points (F1-F2) was measured. Detail reproduction was
determined by measuring the width and depth of the horizontal lines. The
Talysurf surface finish analyzer was connected to a computerized printer
machine. The computer printouts contained all the measurements recorded from
the stylus which contacts the specimens to record all dimensions (depth, width
and length). These computer printouts were assessed to the nearest millimeter. The
results were collected, tabulated and statistically analyzed using
Student-Newmen-Keuls Sequential Range Test (SINK Test) and analysis of variance
(ANOVA).
Tables 1 and 2 and Figures 4 and 5 represent the results of this
investigation. Table 1 and Figure 4 present the arithmetic means and standard deviations of the percentage
of linear dimensional change of the investment specimens obtained from the
molds of the duplicating materials.
The results of this study indicate that only agar reversible
hydrocolloid has a significant change in linear dimensional change compared to
the master specimen in the form of a contraction (P < 0.05). Student-Newman-Keuls
Sequential Range Tests were performed as indicated in Table 1.
Table 2 and Figure 5 present the arithmetic means and
standard deviation of the average width and depth of the lines in millimeter.
The four duplicating materials reproduced all lines of different widths and
depths. The results indicated no significant difference in detail reproduction among
the four duplicating materials (P < 0.05).
The most important characteristics of any dental duplicating
material should include high accuracy, exact reproduction of details,
controllable dimensional changes, good flow ability and easy removal and
handling.
A comparison of the linear dimensional change of the
duplicating materials evaluated in this study illustrates that Castogel (agar
reversible hydrocolloid) has a greater linear dimensional change in the form of
contraction which is statistically significant. This may be attributed to the greater
proportion of water content in agar duplicating material and the presence of
syneresis property of this material.1'47 In addition,
there are other factors that affect the dimensional stability, such as the
number of reboiling cycles, variation of water content and delay in pouring.89
On the other hand, the specimens obtained from Reprogum
(polyether), Elite and Wirosil (addition silicone materials) indicated no
significant difference as compared to the standard specimen. This stability may
be attributed to the absence of volatile reaction products, such as water and alcohol.1011'12
According to the detail reproduction test, the results
indicated that all duplicating materials have fine detail reproduction ability.
Although Elite double (addition Silicone) and Reprogum (polyether) showed
superior means for detail reproduction than Castogel (agar) and Wirosil (addition
silicone), there was no statistically significant difference among the four
duplicating materials.
This study supports the findings of Herring et al13
that no difference existed in the accuracy among
the addition silicone and polyether impression materials. Herfort et
aP4 found that the addition silicones have the smallest change
followed by polyether impression material, however. In other studies1516
polyether impression materials gave some expansion during setting which
resulted in under-sized dies.
The accuracy and detail reproduction of four different
types of duplicating materials were assessed. The authors conclude that further
studies are essential to investigate the difference of the other factors
affecting duplicating materials as performed with impression materials, such as
time of pouring,14 the effect of bulk on accuracy,13 and elastic
recovery.17
The findings of this study indicated that polyvinyl siloxane
and polyether duplicating materials are superior in accuracy than agar
reversible hydrocolloid duplicating materials. However, the four materials
studied provided fine reproduction ability without significant difference among
them.
- Craig RG. Restorative dental materials. 8th ed. St. Louis:CVMosby,
1989:307-08.
-
Williams EO, Hartman GE. Compatibility of reversible hydrocolloid
duplicating materials and dental stones. J Prosthet Dent 1984;52:699-703.
-
Council on Dental Materials and Devices. American Dental
Association Specification No. 20 for dental duplicating materials. J Am Dent
Assoc 1978; 1.
-
Craig RG, Peyton FA. Physical properties of elastic duplicating
materials. J Dent Res 1960; 39:391 -401.
-
Craig RG. Review of rubber impression materials. ) Mich Dent Assoc
1977;58:254-61.
-
Stackhouse JA Jr. The accuracy of stone dies made from rubber
impression materials. J Prosthet Dent 1970;24:377-86.
-
Marget PM, Hansen WC. changes in agar-agar type duplicating
material and agar-agar on heating and storage. J Am Dent Assoc 1957;54:737-43.
-
Klooster J, Logan
Gl, Tjan AH. Effects of strain rate on the behavior of elastomeric impression.
J Prosthet Dent 1991;66:292-98.
-
Duke BR, Ryge G. Properties of laboratory duplicating materials.
D Prog 1961 ;1:88-93.
-
Phillips
RW. Skinner's science of dental materials. 9th ed. Philadelphia:WB Saunders Co, 1991:146-47.
-
Hembree
JH Jr, Nunez Lj. Effect of moisture on polyether impression materials. J Am
Dent Assoc 1974,89:1134-36.
-
Leinfelder KF, Lemons JE. Clinical restorative materials and techniques.
Chicago:Lea
& Febiger, 1988:181-86.
-
Herring HW, Tames MA, Zardiackas LD. Comparison of dimensional accuracy
of a combined reversible/ irreversible hydrocolloid impression system with
other commonly used impression materials. J Prosthet Dent 1984;52:795-99.
-
Herfort TW, Gerberich WW, Macosko CW, Goodkind RJ. Viscosity of
elastomeric impression materials. ) Prosthet Dent 1977;38:396-404.
-
Eames WB, Sieweke JC, Wallace SW, Rogers LB. Elastomeric impression
materials: effect of bulk on accuracy. J Prosthet Dent 1979;41:304-07.
-
Williams PT, Jackson
DG, Bergman W. An evaluation of the time dependent dimensional stability of
eleven elastomeric impression materials. J Prosthet Dent 1984;52:120-25.
- Craig RG, Gehring PE, Payton FA. Aging characteristics of elastic
duplicating compounds. J Dent Res 1962;41:196- 206.
|