A Comparative Study on Accuracy and Reproducibility of Alginate and Addition Reaction Silicone as an Impression Materials

Assistant Professor & Head, Dept. of Science of Dental Materials, Holy Family Red Crescent Medical College Hospital Assistant Professor & Head of the Unit, Sher-e-Bangla Medical College, Dental Unit, Barisal Oral & Dental Surgeon, Z & Z Orthodontic & Dental Clinic, Uttara, Dhaka Registrar, Dental Unit, Holy Family Red Crescent Medical College Hospital Assistant Professor & Head, Department of Conservative Dentistry and Endodontics, Saphena Women’s Dental College, Dhaka


Introduction:
Impression material is used to record the intraoral structure.Ideally the material should be extremely accurate, and virtually distortion free.The accuracy allows to record minute details without taking additional impression.
The material is very soft elastic, & resistance to tear while removes from the undercut 1 .Clinically, there are many kinds of impression materials available for dental use.Generally, they can be divided into two large groups: (1) Synthetic elastomeric impression materials that include Polysulfide, Condensation Silicone, Addition Silicone and Polyether.Silicone impression materials are the most acceptable in this group.(2) Hydrocolloid impression materials, this group includes Agar Agar and Alginate impression materials, the latter being more popular.Clinicians are not agreed which of these two groups is better but, because Alginate is cheaper than other materials, it is hoped that it may become the material of choice.
Accurate impression of is important for the success of removable metallic fixed and implants prosthesis.The properties of impression materials are responsible for reproducing the surface accurately and dimensionally stable as well.
An accurate refractory cast may be obtained when an impression of the original cast is made in a material with elastic property & poured with investment.
The most important characteristics of impression material include high accuracy, exact reproduction of details, controllable dimensional changes, good flow ability and easy removal and handling.
Several types of impression materials are available in dentistry.Every material has some strength and limitation.Alginate is one of the most frequently used dental impression materials.It is an elastic irreversible hydrocolloid and is used for study casts, master casts and working models for the fabrication of intraoral appliances Preparation of Alginate impression -material specimen: Required amount of Alginate powder and water were taken according to the manufacturer's recommendations at room temperature.The measured powder was shifted into premeasured water that has already been poured into a clean rubber bowl.The plastic spatula which was sufficiently flexible to adapt well to the wall of the mixing bowl was used to mix the powder and water.After maintaining the mixing time, impression material was placed on the ruled surface of the test block after placing the round metal ring .Then the metal tray was placed over it for impression making.The impression was removed after setting and the measurement was taken.
Preparation of Addition Reaction Silicone impression material specimen: Very high viscosity Addition Reaction Silicone duplicating material (putty consistency) was taken.Base and catalyst was taken according the manufactures recommendation and kneaded with clean finger instead of wearing latex gloves to prevent sulfur contamination from these gloves which inhabits the setting of the silicone impression materials and may produce major distortion.After maintaining the mixing time impression material was placed on the ruled surface of the test block after placing the round metal ring .Then the metal tray was placed over it for impression making.The impression was removed after setting and the measurement was taken.
Study procedure: In this study, impression was made from a standard stainless steel die for measuring dimensional accuracy and surface detail reproduction.The impression materials were prepared according to manufacturer's instruction at room temperature.Mixing time was maintained carefully .Then it was placed in the marked surface of round test block after placing the round metal ring .The metal tray was placed over the impression .A gradual, constantly increasing pressure was applied to the tray in order to remove excess material till it seats perfectly on the ring.Then 0.5 kg weight was placed over the tray and the impression were separated from the test block after their setting.Then the impression was checked for inclusion criteria in the study.All the sample of impression was tested for horizontal and vertical distance by travelling microscope and measurement of surface details by using stereomicroscope (10x).
Testing effects on dimensional accuracy Dimensional accuracy was measured by measuring length of the middle horizontal line guarded by the vertical line (20 mm) and the distance between the top and bottom horizontal line (4 mm).Every measurement was taken three times and their average values were placed on the data sheet.Measurements were taken by using a traveling microscope (sensitivity 0.01 mm) was used.
Testing effect on surface detail reproduction The impressions were separated from the test block after setting, and their surfaces was assessed by using a stereomicroscope for reproduction of the lines from the test block surface at a magnification of 10X.Then their photographed was recorded.The samples were graded as follows 9 . Grade.

Results:
All samples were evaluated under two parameters and those evaluations described in tables.In terms of dimensional accuracy, analysis revealed that Addition Reaction Silicone impression material is dimensionally more accurate than Alginate impression material which is statistically significant.Furthermore; according to surface detail reproduction Addition Reaction Silicone produce better surface details than Alginate impression material which is also statistically significant.Group A = 30 impressions of Addition Reaction Silicone Group B = 30 impressions of Alginate ab= Length of the horizontal line in between the vertical line of stainless steel die.Table I shows that length of the horizontal line in between the vertical line (ab=20 mm) of Group A mean±SD is 19.91±0.11mm and Group B mean±SD is 19.72±0.18mm.Analysis revealed that Addition Reaction Silicone impression material (Group A) is dimensionally more accurate than Alginate impression material (Group B) which is statistically significant between two groups (P<0.05).The difference was statistically significant between two groups (P<0.05).

DISCUSSION:
As accuracy and exact reproduction of details is very important for making accurate prosthesis, in this regard choosing a more effective impression material is vital.To select the best impression material several researchers conducted different studies in this area, the present study was also concerned about the same issue.
Current study evaluated the accuracy and reproducibility of impression material to compare the dimensional stability and surface detail change of Alginate and Addition Reaction Silicone impression material.
All impression materials were taken from stainless steel test block for dimensional change and surface detail reproduction.The impression materials, specifically very high viscosity Addition Reaction Silicones (Putty consistency) and Hydrocolloids impression materials, specifically irreversible hydrocolloid (Alginate), were used as impression material in this study.
In terms of dimensional accuracy according to the present study findings addition Reaction Silicone impression material showed better performance than the Alginate.Because the diameter of horizontal length in between vertical line and top and bottom horizontal line of stainless steel die is more accurate in Addition Reaction Silicone than Alginate.Similar study conducted by 10 supported the present study results Where they also considered Addition Reaction Silicone as a better impression material in comparison to Alginate.
Another study 11 found that Addition Reaction Silicone had greatest accuracy as well as good resistant to permanent deformation and considered the most dimensionally stable impression material when compare to Alginate which concur with the result of the present study.Regarding Surface Detail Reproduction Group-A representing 93.33% good surface details and 6.67% poor details where as Group-B representing 66.67% good surface details 33.33% poor details.The study showed that Addition Reaction Silicone can produce better surface details than Alginate.
Similarly, 12 also found in one of his studies, conducted in 2010, where the Addition Reaction Silicone also showed the best performance in terms of overall surface quality and accuracy.

CONCLUSION:
At the end of the study it could be concluded that the Addition Reaction Silicone is a better option for the taking accurate impression, as because it has good surface reproduction capacity and dimensional accuracy.The study has some limitations: (I) Dimensional stability of Alginate changed within 15 minutes.Measuring through travelling microscope takes more time.It is helpful for us to get rapid measuring tools.(II) Larger sample size can be used.(III) Time dependent dimensional stability can be recorded.

RECOMMENDATION:
Although most of the previous studies including the present study evaluated the Addition Reaction Silicone as a best impression material.In many other studies the performance of Alginate impression material also showed very close result to the Addition Reaction Silicone.Therefore further study could be conducted to overcome the existing confusion and also the limitations of the present study to select the best impression material.
This study is aimed to compare the impression materials in terms of accuracy and detail reproduction between Alginate and Addition Reaction Silicone.
8,3.It is also used for creating the opposing model for crown & bridge, It is hygienic, inexpensive, does not lose surface detail in wet mouth ,simple cost effective, form an inseparable part of indirect restorations4. But  many shortcomings as an ideal impression material5.This material does not readily flow into areas in which the tray does not extend.If distortion occurs, it cannot be corrected.Compared the accuracy of Alginate and Elastomeric impression materials8.They found that Alginate impression materials had a degree of accuracy comparable with other elastomeric impression materials.