Improved accuracy by reheating addition-reaction silicone impressions

A Comparative Study to Evaluate the Accuracy of Various Spacer Thickness for Polyvinyl Siloxane Putty-wash Impression Techniques: An In Vitro Study

INTRODUCTION

An accurate impression is one of the prime factors for success of any restoration, more so in field of fixed prosthodontics. The critical aspect is to reproduce fine surface details along with ease of use. Knowledge of impression materials and the techniques to which each is best suited is essential in achieving consistent results.

OBJECTIVE OF THE STUDY

The purpose of this study is to evaluate the accuracy of various putty-wash techniques in a laboratory model that simulated the clinical practice.

MATERIALS AND METHODS

A metal master model, containing three full crowns fixed partial denture (FPD) abutment preparations, was fabricated. A perforated custom tray was fabricated that can be placed in the same position on the master model for each impression. For each technique, 10 impressions of the master model were made and poured using a die stone. The measurements were made of the models using a measuroscope and the accuracy of the impressions was recorded.

RESULTS

The statistical comparison between groups I, II, III, and IV casts measurements by using the Mann-Whitney test showed highly significant statistical difference between the various groups from each other (p < 0.001).

CONCLUSION

The accuracy of the working casts obtained from group III impression (two-step using 1 mm coping) was the best, whereas it was least with group II impression (two-step using polyethylene spacer).

HOW TO CITE THIS ARTICLE

Gautam N, Ahmed R, Sharma S, et al. A Comparative Study to Evaluate the Accuracy of Various Spacer Thickness for Polyvinyl Siloxane Putty-wash Impression Techniques: An In Vitro Study. Int J Clin Pediatr Dent 2020;13(5):536-542.

Effect of different impression techniques on the dimensional accuracy of impressions using various elastomeric impression materials: an in vitro study

Production of exemplary crowns and fixed partial dentures depends upon the usage of impression material and its technique of usage that accurately reproduces prepared teeth and their relationship to the adjacent oral structure.

AIM

To evaluate the linear dimensional accuracy of the elastomeric impressions using various impression techniques using different combinations of viscosities of impression materials.

MATERIALS AND METHODS

Crown preparation was done in a dentulous acrylic resin denture base model with six natural teeth embedded into it was made to represent the dentulous maxillary arch. A total of 55 impressions were obtained and poured in die stone using various impression techniques with different combinations of viscosities of impression materials.

RESULTS

Among the six techniques used, the heavy body light body two-step technique using custom tray showed the least distortion which was closely followed by the putty wash two-step technique with 2 mm spacer using stock tray.

CONCLUSION

The study revealed that the heavy body light body two-step technique with custom tray provided the best results.

CLINICAL SIGNIFICANCE

Dimensional accuracy of impressions is very much required for precisely fitting of prosthesis. This study may be helpful to select the technique and materials as per clinical requirement of accuracy of impressions.

Elastomeric impression materials: a comparison of accuracy of multiple pours

AIM

The aim of the present study is to compare the various elastomeric impression materials in terms of accuracy and dimensional stability, with respect to obtaining multiple casts from a single elastomeric impression at various times of pours.

MATERIALS AND METHODS

Three master dies were prepared for the impression making, two of these were made of brass containing a central hole with undercuts. The third die simulated a conventionally prepared typodont maxillary central incisor. Three elastomeric impression materials were chosen for the study. Each impression was poured at various time periods. Casts thus obtained were evaluated under a traveling microscope to evaluate various dimensional changes.

RESULTS

Addition silicones provided dies which were shorter in height and bigger in diameter. Polyethers provided dies which were shorter in both height and diameter. Condensation silicones showed insignificant changes from the master die at the immediate pour but deteriorated rapidly after that in subsequent pours.

CONCLUSION

None of the impression material showed a consistent behavior up to the fourth pour. They occasionally showed deviation from the pattern, but all these values were statistically insignificant. Polyethers showed lesser ability than both the addition silicones as well as the condensation silicones to recover from induced deformation.

CLINICAL SIGNIFICANCE

Addition silicones as well as the condensation silicones have better ability to recover from induced deformation when compared to polyether.

Effect of conventional and experimental gingival retraction solutions on the tensile strength and inhibition of polymerization of four types of impression materials

In the present study, two types of tests (tensile strength test and polymerization inhibition test) were performed to evaluate the physical and chemical properties of four impression materials [a polysulfide (Permlastic), a polyether (Impregum), a condensation silicone (Xantopren) and a polyvinylsiloxane (Aquasil)] when polymerized in contact with of one conventional (Hemostop) and two experimental (Vislin and Afrin) gingival retraction solutions. For the tensile strength test, the impression materials were mixed and packed into a steel plate with perforations that had residues of the gingival retraction solutions. After polymerization, the specimens were tested in tensile strength in a universal testing machine. For the polymerization inhibition test, specimens were obtained after taking impressions from a matrix with perforations that contained 1 drop of the gingival retraction solutions. Two independent examiners decided on whether or not impression material remnants remained unpolymerized, indicating interference of the chemical solutions. Based on the analysis of the results of both tests, the following conclusions were reached: 1. The tensile strength of the polysulfide decreased after contact with Hemostop and Afrin. 2. None of the chemical solutions inhibited the polymerization of the polysulfide; 3. The polyether presented lower tensile strength after polymerization in contact with the three gingival retraction agents; 4. The polyether had its polymerization inhibited only by Hemostop; 5. None of the chemical solutions affected the tensile strength of the condensation silicone; 6. Only Hemostop inhibited the polymerization of the condensation silicone; 7. The polyvinylsiloxane specimens polymerized in contact with Hemostop had significantly lower tensile strength; 8. Neither of the chemical solutions (Afrin and Vislin) affected the tensile strength of the polyvinylsiloxane and the condensation silicone; 9. Results of the tensile strength and polymerization inhibition tests suggest that Vislin can be used as substance of gingival retraction without affecting the tested properties of four impression materials.

The effect of temperature changes on the dimensional stability of polyvinyl siloxane and polyether impression materials

STATEMENT OF PROBLEM

Dental impressions are commonly mailed to remote dental laboratories and can be subjected to extreme temperature changes; however, the effects of these temperature changes on the accuracy of elastomeric impression materials are unknown.

PURPOSE

This study evaluated the dimensional changes of polyether and polyvinyl siloxane impression materials as a function of storage temperature.

MATERIAL AND METHODS

A total of 144 impressions were made of a stainless steel die similar to ADA Specification No. 19. Half of the impressions were made in perforated custom trays and the other half in solid trays. Measurements of the vertical and horizontal lines on the impressions were made at 10 minutes, 1 hour, 24 hours, and 26 hours, and storage temperatures ranged from 4 degrees C to 40 degrees C.

RESULTS

Changes in storage temperature had a statistically significant effect on the dimensional stability of the horizontal and vertical lines. However, overall dimensional changes were extremely small.

CONCLUSIONS

Storing both impression materials at 4 degrees C for 24 hours and then allowing the impressions to reach room temperature resulted in a slightly expanded impression that partially compensated for the contraction that occurred from polymerization shrinkage. Similar results occurred for polyether material only, when stored at 40 degrees C.

Effects of the setting stage on the accuracy of double-mix impressions made with addition-curing silicone

This study investigated the accuracy of double-mix impressions relative to the time of placing the tray impression material on preparations covered with medium-viscosity silicone. The curing kinetics of the addition-curing silicone impression materials and the accuracy of impressions were investigated. The observed kinetics showed the possibility of the appearance of elastic characteristics of the syringed material before the tray impression was placed. The accuracy of the impressions was not statistically different unless the setting reactions had progressed so that the consistencies of both the syringed and the tray impression were high. These results indicated that the double-mix impression was accurate independent of the curing kinetics of the syringed material alone.

Distortion of impression materials used in the double-mix technique

According to the so-called double-mix technique for impression taking, a material of high and one of low viscosity set against each other. We found that a distortion of the joined materials occurred which may compromise the precision of the impression. The distortion of such combinations of materials of high and low viscosity was measured on beam-like specimens. Significant differences between materials were observed. The phenomenon may be explained by a swelling of the material of low viscosity. The swelling may be associated with a diffusion of unreacted compounds from the material of high viscosity into the material of low viscosity. Measurements of the swelling of specimens immersed in the catalyst component of unset material showed an increase in length of 2-5%.

Effects of reheating on the accuracy of addition silicone putty-wash impressions

The effect of the relatively high thermal contraction of addition silicones (polyvinylsiloxane) on the accuracy of stone casts was evaluated using the putty/wash relining impression technique and acrylic resin trays. Impressions were made at 37 degrees C and were divided into two groups. One group was poured at room temperature (22 degrees +/- 2 degrees C) and another group was reheated to 37 degrees C before pouring. Measurement of the dimensional changes failed to reveal improved accuracy of the stone casts poured at the same temperature as that reached during impression making. On the basis of this limited sample, it can be concluded that reheating the impression using the putty/wash relining technique did not improve the accuracy of the stone cast.

Review of dental impression materials

Major advances in impression materials and their application have occurred during the last decade, with greater emphasis being placed on rubber impression materials than on dental compound, zinc oxide-eugenol, and agar and alginate. Of particular interest has been the effect of disinfection solutions on the qualities of impressions and the biocompatibility of impression materials. The principal advance in hydrocolloids has been the introduction of the agar/alginate impression technique, which has simplified the procedure and improved the quality of gypsum dies compared with those prepared in alginate impressions. The tear strength of some alginates has been improved, and some have been formulated so that the powder is dustless, thus reducing the health hazard as a result of patient inhalation of dust during the dispensing process. Polyether and silicone impression materials have been modified so that the working time, viscosity, and flexibility of the polyethers have been improved and, with the introduction of addition silicones, their accuracy has become exceptional. Although the early addition silicones liberated hydrogen after setting, thus delaying the pouring of models and dies, most addition silicones have been improved so that no hydrogen is released and dies can be poured immediately. The introduction of automatic mixing systems for addition silicones has simplified their manipulation, has reduced the number of voids in impressions, and has reduced the amount of material wasted. The incorporation of surfactants into addition silicones has made them hydrophilic, with wetting properties similar to those of polyethers, and has made pouring bubble-free gypsum dies easier.

This review is confined to published and unpublished information of the past decade. It will also suggest trends that should be anticipated in the near future based on this information. The review will not present information developed before 1975, which is available in several textbooks on dental materials by Craig (1985a), Phillips (1982), and Williams and Cunningham (1979).