الفهرس 
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Abstract
This study was done to assess the dimensional accuracy of the newly
introduced vinyl siloxanether impression material in comparison with the
commonly used polyether and Vinyl polysiloxane impression materials.
The impression materials used in this study were automixed medium
viscosity for monophase one step impression technique (vinyl siloxanether,
polyether and vinyl polysiloxane impression materials).
The master model was made similar to that used in previous
studies.[5,14,15] It contained stainless steel first molars in both sides with
occlusal reference points and central incisors with lingual reference points.
These reference points provided for measuring anteroposterior and cross-arch
dimensions. Additionally, the master model contained a stainless steel crown
preparation in position of the mandibular right first premolar and it was
machined with reference points provided for measuring mesiodistal,
buccolingual and occlusogingival dimensions. A cold-curing orthodontic
acrylic resin was fabricated in the labial surface of the base of the master
model from the right canine to the left canine and in the lingual surface of the
base of the master model from the first molar to the third molar in both sides’
right and left. It was made to standardize the seating of tray during impression
making and to uniform the thickness of impression material.
Custom made chrome cobalt tray was fabricated to improve the
accuracy of working model. To standardize the passive seating and centering
of tray during impression making, a custom device for holding the tray was
made with weight of 1.2 kg to apply the same amount of force during
impression making.[87]
A total of 30 impressions of the master model were made by using
three impression materials, using standardized one step monophase technique
following the manufacturers’ directions. These impressions were divided into
3 groups according to the impression material, 10 impressions in each group.
Each group was subdivided into 2 sub-groups (sub-group A, sub-group B) 5
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impression for each sub-group. The specimens of sub-groups (A) were
disinfected by immersion in 2% glutaraldehyde solution for 10 min and that
of sub-groups (B) were not disinfected.
Impressions within the disinfection group in ambient laboratory
atmospheric for 110 min before pouring while impressions with the nondisinfected
were left in ambient laboratory atmospheric for 120 min. All
impressions were poured with dental stone according to the manufacturer’s
directions
All stone casts were measured 48 hours after retrieval from the
impressions to ensure complete polymerization of the stone material.
Testing the accuracy of the obtained stone casts were carried out
through measuring five dimensions on each cast; the anteroposterior
measurement (from central incisors to the left first molar), the cross arch
measurements (from left first molar to right first molar), mesiodistal,
buccolingual, and occlusogingival dimensions of premolar preparation. These
measurements were done by using universal measuring microscope (Carl
Zeiss, Germany) capable of measuring to 0.001 mm. Measurements of the
stone casts were compared to their corresponding measurements of the
stainless steel master model.
All calculations were performed and values recorded. Statistical
analysis was done to evaluate and identify any significant differences between
dimensions of the master model and those of stone casts from each impression
material and also between dimensions of stone casts that poured from
disinfected and not disinfected impressions of the three impression materials.
All tests showed that there were no significant differences among the three
materials and that disinfection did not affect the dimensional accuracy.