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| 2010-22 |
| 22-1 |
ISSN (Print) 1013-9052
EISSN 1658-3558
P.O. Box 52500,
Riyadh 11563,
Kingdom of Saudi Arabia
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966-1-467-7328 |
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933-1-467-7308 / 966-1-467-7534 |
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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.
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.
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.
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
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