Time-dependent accuracy of elastomer impression materials. Part II: Polyether, polysulfides, and polyvinylsiloxane

Evaluation of One- and Two-Step Impression Techniques and Vertical Marginal Misfit in Fixed Prothesis

Methods

12 impressions were made of a resin maxillary model (second premolar and second molar) with two prepared abutment teeth using vinyl polysiloxane (VPS); the margin of the second premolar was 0.5 mm subgingivally; and the margin of the second molar tooth was at the level of the gingiva. Impressions were made using two techniques: one-step and two-step putty/light materials. A three-unit metal framework was fabricated on the master model using the computer-aided design/computer-aided manufacturing (CAD/CAM) technique. The vertical marginal misfit was evaluated in the buccal, lingual, and mesial and distal surfaces of the abutments on the gypsum casts using a light microscope. Data were analyzed using the independent t-test (α < 0.05).

Results

The results showed significantly lower vertical marginal misfit in all six areas evaluated around the two abutments in the two-step impression technique compared with the corresponding values in the one-step technique.

Conclusion

Vertical marginal misfit in the two-step technique with a preliminary putty impression was significantly lower than in the one-step putty/light-body technique.

Clinical evaluation of one-step impression technique and definitive casts

Background/Aim: The purpose of this study was to evaluate the quality of impressions made with vinyl polysiloxane (VPS) material in clinical conditions by using the one-step impression technique, and the quality of casts generated from these impressions. The effect of operator, number and location of abutments, and presence of bleeding were also investigated. Material and Methods: A total of 150 fixed dental prosthesis (FDP) impressions were taken and considered acceptable by 3 experienced prosthodontists in a clinic in an institutional setting. The impressions were evaluated and rated by another experienced prosthodontist and respective casts were evaluated and rated by an experienced dental technician using a digital microscope with ×200 magnification. The defects observed were noted as bubbles, voids, tears, or other defects. A scale was structured for the impressions and casts with ratings of Alpha (excellent; no defects), Bravo (acceptable; small defects), Charlie (inadequate; defects that require remaking of impression), and Delta (unacceptable; substantial defects at preparation finish lines). The data were analyzed with the Chi-square test for inter-operator, number of abutments, and location of prepared tooth variables (a=0.05). Results: The scale ratings were 85 Alpha (57%), 52 Bravo (34%), 6 Charlie (4%), and 7 Delta (5%) for the impressions, and 81 Alpha (54%), 58 Bravo (39%), 4 Charlie (3%), and 7 Delta (5%) for the respective casts. Sixty-nine percent of the impressions and respective casts were rated with the same score. The scale rating results were not influenced by inter-operator variability or number of abutments. Location of the prepared tooth was significant for anterior/posterior (p=0.04), but was not significant for maxilla/ mandible (p>0.05). Bleeding at the preparation site had a significant effect on the acceptability of the impression (p=0.003). Conclusions: The acceptability of VPS impressions using onestep technique was independent of the operator, number of abutments, or whether the prepared tooth was in maxilla or mandible. Impressions of teeth in the anterior region were more acceptable than those located in the posterior. Bleeding negatively affected the acceptability of the impressions. Clinicians may use VPS impressions for the fabrication of FDPs using onestep dual-phase technique. However, clinicians should carefully evaluate their impressions when bleeding is present when using this technique.

Evaluation of the Trueness of Digital Implant Impressions According to the Implant Scan Body Orientation and Scanning Method

This study investigated the trueness of a digital implant impression according to the orientation of the implant scan body (ISB) and the scanning method. With the flat surface of the ISB facing either the buccal or proximal direction, the ISB was scanned using one tabletop scanner (T500) and three types of intraoral scanner (TRIOS 3, CS3600, and i500). The effects of differences in the scanning method and ISB orientation were assessed. Postalignment data were subsequently obtained with the abutments generated using a digital library, and superimposed with reference data using a best-fit algorithm, followed by root-mean-square error (RMSE) analysis. The RMSE was lower in the buccal groups (28.15 ± 8.87 μm, mean ± SD) than in the proximal groups (31.94 ± 8.95 μm, p = 0.031), and lower in the full-scan groups (27.92 ± 10.80 μm) than in the partial-scan groups (32.16 ± 6.35 μm, p = 0.016). When using the tabletop scanner, the trueness was higher when the ISB was connected buccally (14.34 ± 0.89 μm) than when it was connected proximally (29.35 ± 1.15 μm, p < 0.001). From the findings of this study it can be concluded that the operator should connect the ISB so that its flat surface faces the buccal direction, and attempt to scan all areas. Additionally, it is advantageous to connect an ISB buccally when using a tabletop scanner.

Comparison and Evaluation of Linear Dimensional Accuracy of Three Elastomeric Impression Materials at Different Time Intervals Using Vision Inspection System: An In Vitro Study

Background:

Making an impression represents a crucial step in fabrication of a prosthesis. Elastomers are the most commonly used materials for precise and accurate recording and reproduction of tooth morphology and surrounding soft tissue.

Aims and Objective:

The aim of this study was to compare and evaluate the linear dimensional accuracy of three elastomeric impression materials: addition silicone, condensation silicone, and polyether at different time intervals up to 15 days using a vision inspection system.

Materials and Methods:

Dimensional accuracy of impression materials was measured at certain designated time periods using stainless steel die. The impressions of die were made using one representative material of each type of elastomeric impression material. The die along with the impression material in the mold was held using a clamp and put in a water bath maintained at mouth temperature. The linear dimensional changes taking place in each material with time were measured using the vision inspection system.

Results:

On comparison with master die impression at 30min, 1h, and 1½ h time interval, a significant decreased mean dimension of condensation silicone was observed, whereas addition silicone and polyether showed statistically nonsignificant difference. At 2, 3, 4, and 12h time span, a significant difference in mean dimension of addition and condensation silicone was noted, whereas polyether showed a nonsignificant difference. At 24h, 1 week, and 15 days duration, on comparison with the master die, a significant reduction in mean dimension of condensation silicone was discovered, whereas addition silicone and polyether showed nonsignificant difference.

Conclusion:

Polyether showed significantly lesser dimensional changes among all three materials, though the differences were small enough to be considered clinically acceptable.

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 multiple pouring on the accuracy of casts made using 3D-printed custom trays with different spacer thicknesses: A research study

Background. This study aimed to evaluate the effect of different pouring times and spacer thicknesses on the three-dimensional accuracy of casts made of 3D-printed custom trays. Methods. A partial edentulous maxillary model was scanned for fabricating custom acrylic trays. Twenty custom trays were created using a CAD/CAM system and divided into two groups in terms of their spacer thicknesses (2 mm and 4 mm). All the trays were designed with 2-mm thickness, multiple retentive holes measuring 2 mm in diameter, and three interior seating stops (two on the edentulous ridge and one on the incisal edge of the central incisors). Impressions were made using monophasic polyvinyl siloxane and poured in two different times (one hour and 24 hours after removal) with type IV dental stone. All the casts were scanned to measure three distances (inter-buccal cusps, inter-palatal cusps, and inter-fossa distances) between the two first premolars. The data were analyzed with two-way ANOVA and Bonferroni test at a significance level of 0.05. Results. There was no significant difference between the 3D accuracy of casts made using two different spacer thicknesses poured at 1-hour and 24-hour intervals. However, there was a difference between casts made after 1 hour and 24 hours when using custom trays with 2 mm of spacer thickness in terms of inter-buccal distance. Conclusion. There was no significant difference between the accuracy of casts made using custom trays with either 2 or 4 mm of spacer thickness, which were poured 1 hour or 24 hours after tray removal.

Comparative evaluation of elastic recovery of three different elastomeric impression materials on chemical disinfection and autoclaving: An in vitro study

Aim:

The aim of the study was to investigate the effect of disinfection and steam autoclaving on the elastic recovery of three different elastomeric impression materials.

Settings and Design:

In vivo - comparative study.

Materials and Methods:

Ninety dumbbell-shaped specimens of commercially available two addition-cured silicones (AFFINIS and AQUASIL) and one condensation-cured silicone (SPEEDEX) impression materials were prepared and treated with chemical disinfectant and steam autoclaving. Specimens were seal packed and sent to laboratory for testing elastic recovery. After the specimen had been pulled to failure, the broken parts were fitted back together, and the distance between the marks was measured using an electronic Vernier caliper.

Statistical Analysis Used:

one-way analysis of variance test and Tukey post hoc test for multiple comparisons.

Results:

The result showed significant difference in elastic recovery of AFFINIS when it was disinfected and steam autoclaved whereas elastic recovery showed no significant difference when SPEEDEX and AQUASIL were disinfected and steam autoclaved. Similarly, results were alike when AFFINIS, SPEEDEX, and AQUASIL were compared on disinfection. However, significant difference was noted on steam autoclaving, highest being the mean value of AFFINIS.

Conclusion:

Within the limitations of this in vitro study, conclusion was made that the elastic recovery of AFFINIS was the least which improved with disinfection and autoclaving. Elastic recovery of SPEEDEX and AQUASIL was similar. However, all the three materials used in the study can be safely sterilized after clinical use and before being sent to the laboratory without significantly affecting their elastic recovery.

Comparative evaluation of three gingival displacement materials for efficacy in tissue management and dimensional accuracy

Aim:

Displacement of gingiva is essential for obtaining accurate impressions for the fabrication of fixed prostheses, particularly when the finish line is at or within the gingival sulcus. Various newer impression materials have been introduced to achieve gingival displacement while recording the impressions. A comparative evaluation of these new gingival displacement materials was deemed necessary for efficacy in tissue management and dimensional accuracy.

Materials and Methods:

Ten individuals were selected according to the inclusion and exclusion criteria for gingival displacement using retraction cord impregnated with aluminum chloride and two polyvinyl siloxane impression materials (Aquasil and NoCord VPS impression system) according to Latin block design. Intraoral scanner and Vernier caliper were used to study and compare the dimensional accuracy of each die obtained following which the dies were sectioned and evaluated under optical microscope with image analyzer to measure the amount of gingival retraction.

Results and Conclusion:

Statistical analysis showed that the amount of gingival retraction obtained by using retraction cord impregnated with aluminum chloride as gingival retraction agent was maximum as compared to NoCord followed by Aquasil. All three gingival displacement techniques could produce gingival displacement >0.2 mm which is the optimum amount of retraction required for impression making. All the three materials are found to be dimensionally accurate.

Influence of chloramine-T disinfection on elastomeric impression stability

Objective:

The aim of this study was to evaluate the stability of elastomer through detail reproduction and its dimensional stability (DS) after disinfection with 0.2% chloramine-T.

Materials and Methods:

The elastomeric impression dental materials used in this study were polydimethylsiloxane (Oranwash L), polyvinyl siloxane (Express), polysulfide (Permlastic), and polyether (Impregum Soft). The entire press procedure was performed on a matrix in accordance with the ISO 4823. Detail reproduction was analyzed using an optical microscope (Stereozoom Microscope) over the 20-μm line with 25 mm of length at a magnification of ×4. DS was measured using an optical microscope (Scanning Tunneling Microscope) by subtracting the distance between the lines X and X' over the 20-μm line on the matrix (DM) from the distance between the lines on the impression material (DI) divided by DM and multiplied by 100 establishing the equation: DS = ([DI – DM]/DM) ×100; then, 100% was added to the results of the equation. The detail reproduction values were subsequently subjected to descriptive analysis by percentage (%), and the DS values (%) were submitted to Kolmogorov–Smirnov test, two-way ANOVA (material × disinfectant), and Tukey's test (α = 0.05).

Results:

All elastomeric impression materials showed 100% of detail reproduction, regardless of the disinfection procedure. Polysulfide (not disinfected) and polysulfide and polydimethylsiloxane (after disinfection with 0.2% chloramine-T) showed the smaller mean values of DS.

Conclusion:

According to the stability properties analyzed, chloramine-T can be used for disinfection of elastomer molds.

The effect of prolonged storage and disinfection on the dimensional stability of 5 vinyl polyether silicone impression materials

PURPOSE

Vinyl polyether silicone (VPES) has a different composition from other elastomeric impression materials as it combines vinyl polysiloxane (VPS) and polyether (PE). Therefore, it is important to study its properties and behavior under different test conditions. This study investigated the dimensional stability of 5 VPES consistencies when stored for up to 2 weeks, with and without using a standard disinfection procedure.

MATERIALS AND METHODS

40 discs of each VPES consistency (total 200) were made using a stainless steel die and ring as described by ANSI /ADA specification No. 19. 20 discs of each material were immersed in a 2.5% buffered glutaraldehyde solution for 30 minutes. Dimensional stability measurements were calculated immediately after fabrication and repeated on the same discs after 7 and 14 days of storage. The data was analyzed using two-way ANOVA with a significance level set at α = 0.05.

RESULTS

The discs mean contraction was below 0.5% at all test times ranging from 0.200 ± 0.014 to 0.325 ± 0.007. Repeated measures ANOVA showed a statistically significant difference after 2-week storage between the disinfected and non-disinfected groups (P < .001). Although there was no statistically significant difference between the materials at the time of fabrication, the contraction of the materials increased with storage for 1 and 2 weeks.

CONCLUSION

The dimensional changes of VPES impression discs after disinfection and prolonged storage complied with ANSI/ADA standard. The tested VPES impression materials were dimensionally stable for clinical use after disinfection for 30 minutes in glutaraldehyde and storage for up to 2 weeks.

Torque resistance of impression copings after direct implant impression: An in vitro evaluation of impression materials with and without adhesive

STATEMENT OF PROBLEM

No data are available on the ability of an impression coping to resist the manual placement of an abutment replica (implant analog) during prosthodontic laboratory procedures after a direct (pick-up) impression.

PURPOSE

The purpose of this in vitro study was to evaluate the torque resistance of impression copings after a direct impression, that is, the amount of rotational torque sufficient to induce irreversible displacement of impression copings in the impression material bulk once the impression has been made.

MATERIAL AND METHODS

A reference model with 5 abutment replicas was constructed. Five impression copings were screwed onto the abutment replicas, and standardized impressions were made. A controlled twisting force was applied to each impression coping. A torque tester recorded the torque variation. Three elastomeric impression materials were tested. ANOVA and the Tukey test (α=.05) were performed using an average of 30 measurements per impression material, with and without adhesive.

RESULTS

ANOVA and the Tukey test results showed that the adhesive, cohesive, and mechanical bonds between the impression coping and the impression material depended greatly on the type of material and that the average rupture threshold of these bonds was statistically significantly different in pairwise comparisons (P<.05). The curve analysis showed that when the impression materials are used with adhesives, the deformation of the interface is irreversible beyond 5 Ncm of torque.

CONCLUSIONS

The polyether impression material is the direct impression material that showed the highest breakdown threshold for adhesive bonding when used without an adhesive. The use of an adhesive on impression copings leads to irreversible deformation of the interface at torque stresses well below the adhesive bond threshold of the same materials used without an adhesive.

The dimensional accuracy of polyvinyl siloxane impression materials using two different impression techniques: An in vitro study

Aim of the Study:

To evaluate and compare the linear dimensional changes of the three representative polyvinyl siloxane (PVS) impression materials and to compare the accuracy of single mix with double mix impression technique.

Methodology:

A study mold was prepared according to revised American Dental Association specification number 19 for nonaqueous elastic dental impression materials. Three PVS impression materials selected were Elite-HD, Imprint^™ II Garant, Aquasil Ultra Heavy. Two impression techniques used were single mix and double mix impression technique. A total of 60 specimens were made and after 24 h the specimens were measured using profile projector.

Statistical Analysis:

The data were analyzed using one-way analyses of variance analysis and significant differences were separated using Student's Newman–Keul's test.

Results:

When all the three study group impression materials were compared for double mix technique, the statistically significant difference was found only between Imprint^™ II Garantand Elite-HD (P < 0.05). Similarly, using single mix technique, statistically significant difference were found between Elite-HD and Imprint^™ II Garant (P < 0.05) and also between Aquasil Ultra Heavy and Elite-HD (P < 0.05). When the linear dimensional accuracy of all three impression material in double mix impression technique and single mix impression technique were compared with the control group, Imprint^™ II Garant showed the values more nearing to the values of master die, followed by Aquasil Ultra Heavy and Elite-HD respectively.

Conclusion:

Among the impression materials Imprint^™ II Garant showed least dimensional change. Among the impression techniques, double mix impression technique showed the better results.

An in vitro study to evaluate the effect on dimensional changes of elastomers during cold sterilization

OBJECTIVES

This study was planned to evaluate the dimensional stability of elastomers during cold sterilization or immersion disinfection and also to evaluate the same, along with acrylic resin trays which are used in clinical practice.

MATERIALS AND METHODS

A study mold according to revised American Dental Association. Specification no. 19 was used. Polyether, polyvinyl siloxane (PVS) (heavy body), PVS (regular body) and Hydrophilic addition reaction silicon (medium body) were selected for study. 2% glutaraldehyde and 0.525% sodium hypochlorite were the disinfectants used. The study was divided into group-I and group-II. In group-I study, 24 specimens of each impression material were prepared. Eight immersed in 2% glutaraldehyde, eight in 0.525% sodium hypochlorite and rest eight allowed to dry bench cure. After 16 h, the specimens measured under Leica WILD stereomicroscope and dimensions compared with master die. In group II study, 24 specimens of the material with the least dimensional changes were prepared and adhered to 24 acrylic resin disks using tray adhesive. Same immersion procedure was followed as in group I. The data were analyzed by one-way ANOVA and Tukey's multiple tests.

RESULTS

Of four impression materials used, PVS (heavy body) was the most dimensionally stable, and Polyether was the least dimensionally stable in both the groups.

INTERPRETATION AND CONCLUSION

Within the limitation of the study, PVS (heavy body) was most stable, and polyether was least stable of all the impression materials.

Dimensional stability of polyvinyl siloxane impression material reproducing the sulcular area

The dimensional stability of a thin intra sulcular impression material reproducing the preparation finish line was evaluated. Impressions were taken of a stainless-steel master model of a simulated abutment with a 'gingival sulcus' using Express regular, Express fast and Aquasil. The putty-wash two-step technique was applied with spacer thicknesses of 0.5, 1 and 1.5 mm. Mid mesiodistal and bucco-lingual measurements were taken directly from the sulcular impression material after 0.5, 2, 24, 48 and 72 h via a Toolmaker's microscope. The discrepancies between the measurements of the impression material and the master model were calculated. The discrepancies changed significantly over time (p<0.001). The use of a 0.5 mm spacer resulted in a negative deviation from the model (2-46 µm), minimally after 2 h. The use of 1 and 1.5 mm spacers showed a positive deviation from the model (21-52 µm) and both are equally recommended. Investment can be postponed until 72 h.

Effect of the impression margin thickness on the linear accuracy of impression and stone dies: an in vitro study

The space available for impression material in gingival sulcus immediately after the removal of retraction cord has been found to be 0.3-0.4 mm. However after 40 s only 0.2 mm of the retracted space is available. This is of concern when impression of multiple abutments is to be made. Hence a study was planned to determine the minimum width of the retracted sulcus necessary to obtain a good impression. Five metal dies were machined to accurately fit a stainless steel block with a square cavity in the center with spaces, 1 mm deep and of varying widths (0.11-0.3 mm) away from the block. Polyvinyl siloxane impressions were made and poured using a high strength stone. Using traveling microscope, length and widths of abutment, impression and die were measured and compared for linear accuracy and completeness of impression. Results showed 1.5-3 times greater mean distortion and larger coefficient of variance in the 0.11 mm group than in the wider sulcular groups. ANOVA test for distortion also showed statistically significant differences (P < 0.05). 75 % of impressions in 0.11 mm group were defective compared to less than 25 % of impressions in other width groups. It is not always possible to predictably obtain accurate impressions in sulcus width of 0.11 mm or lesser. Dimensionally accurate and defect free impressions were obtained in sulcus width of 0.15 mm and wider. Hence clinicians must choose retraction methods to obtain a width greater than 0.35 mm. Further immediate loading of the impression material after cord removal may improve accuracy.

The effect of one-step vs. two-step impression techniques on long-term accuracy and dimensional stability when the finish line is within the gingival sulcular area

PURPOSE

To evaluate the effect of two putty-wash impression techniques on the long-term accuracy and dimensional stability of poly(vinyl siloxane) (PVS) in the gingival sulcus area.

MATERIALS AND METHODS

Impressions were taken from a master cast to simulate molar crown preparation. A space around the abutment served as the gingival sulcus. Fifteen impressions using the one- and two-step impression techniques were taken using Express Regular, Express Fast, and President impression materials with custom trays. Using a Toolmaker's microscope, the long (LD) and short distances (SD) of the abutment and the planar distance between two parallel lines (PL) at the circumference of the cast were taken at 0.5, 2, 24, 48, 72, 96, 120, and 144 hours after mixing. ANOVA was performed, with the discrepancy between the distances of the impressions and the master cast as the dependent variable.

RESULTS

The differences when different materials and impression techniques were used were significant (p < 0.001) for LD, SD, and PL, as was the interaction between the material, time, and technique (p < 0.001). SD discrepancies were higher than those of LD for all materials and times. The two-step impression technique was more accurate, with smaller discrepancies than the one-step impression technique. For all materials, the PL discrepancy was deemed acceptable (less than 0.5%) for all tested times. President had higher discrepancies than the other materials.

CONCLUSIONS

When using the two-step putty-wash impression technique, pouring of the impressions may be postponed up to 30 hours; however, when using the one-step impression technique, pouring should be performed within 2 hours.

Evaluation and comparison of dimensional accuracy of newly introduced elastomeric impression material using 3D laser scanners: an in vitro study

AIM

Aim of the present study was to comparatively evaluate dimensional accuracy of newely introduced elastomeric impression material after repeated pours at different time intervals.

MATERIALS AND METHODS

In the present study a total of 20 (10 + 10) impressions of master model were made from vinyl polyether silicone and vinyl polysiloxane impression material. Each impression was repeatedly poured at 1, 24 hours and 14 days. Therefore, a total of 60 casts were obtained. Casts obtained were scanned with three-dimensional (3D) laser scanner and measurements were done.

RESULTS

Vinyl polyether silicone produced overall undersized dies, with greatest change being 0.14% only after 14 days. Vinyl polysiloxane produced smaller dies after 1 and 24 hours and larger dies after 14 days, differing from master model by only 0.07% for the smallest die and to 0.02% for the largest die.

CONCLUSION

All the deviations measured from the master model with both the impression materials were within a clinically acceptable range.

CLINICAL SIGNIFICANCE

In a typical fixed prosthodontic treatment accuracy of prosthesis is critical as it determines the success, failure and the prognosis of treatment including abutments. This is mainly dependent upon fit of prosthesis which in turn is dependent on dimensional accuracy of dies, poured from elastomeric impressions.

The influence of tray space and repeat pours on the accuracy of monophasic polyvinylsiloxane impression

AIM

While literature demonstrates that the optimum accuracy is obtained with the custom trays, the use of stock trays for elastomeric impressions appears to be popular in general practice. The aim of the study was to evaluate the effect of thickness of impression material on the dimensional accuracy of impressions made from monophasic polyvinylsiloxane impression material. This study also studies the dimensional stability of the impressions poured at different time intervals.

MATERIALS AND METHODS

A metal model simulating two abutment teeth was fabricated along with reference lines inscribed on them. Custom impression trays were fabricated with spacer thickness of 2, 4 and 6 mm. impressions were made using monophasic polyvinyl siloxane impression material. The impressions were poured and stone models were obtained. The dimensional accuracy of the impressions were determined indirectly by measuring the dimensional changes of the recovered stone models. The dimensional stability was also evaluated by pouring the impressions at time intervals of 1 hour, 24 hours and 7 days. The obtained data was statistically analyzed.

RESULTS

The results of the study indicated that the impressions made from 2 and 4 mm tray space produced more accurate stone models when compared to 6 mm tray space. There was no significant deviation in the mesiodistal and buccolingual dimensions when impressions were made using impression trays with 2, 4 and 6 mm tray spacers. There was a significant decrease in interabutment distance (p = 0.001) and height of the abutment (p = 0.024) when impressions were made using impression trays with a tray space of 6 mm. There were no significant differences found among the stone models obtained from 1 hour, 24 hours and 1 week pour times.

CONCLUSION

The mesiodistal and buccolingual dimensions of the abutments were not affected by the variations in thickness of impression material. There was a decrease in the height of the abutment which was clinically not significant. As the thickness of the impression material increased, the interabutment space decreased, which is a factor of concern when impressions are made for fixed partial dentures.

CLINICAL SIGNIFICANCE

When monophasic polyvinylsiloxane is used as the impression material, stock trays can be used for making impressions for individual castings.

Evaluation of effect of tray space on the accuracy of condensation silicone, addition silicone and polyether impression materials: an in vitro study

Optimal thickness of impression materials in the custom tray in order to get the most accurate impression. To investigate the effect of different tray spacer thickness on the accuracy and the dimensional stability of impressions made from monophasic condensation silicone, addition silicone and polyether impression materials. Three different types of elastomeric monophasic impression materials were used for making the impression of a master die with tray having tray spacer thickness of 2, 4 and 6 mm. Each type of impression was poured in die stone after 1 h. Each cast was analyzed by a travelling microscope and compared with the master die. The data was tabulated and subjected to statistical evaluation. The results of the study indicated that the impressions made from 2 to 4 mm spaced trays produced more accurate stone casts when compared to 6 mm spaced tray. No statistical significant differences were observed between the accuracy and dimensional stability of the three materials tested. Minimum changes were observed when the cast was poured after 1 h and the tray space was 2 mm for all the materials tested. It is therefore advisable not to exceed tray space of 2 mm.

Accuracy of different putty-wash impression techniques with various spacer thickness

One of the most important steps is accurate impression making for fabrication of fixed partial denture.

The two different putty-wash techniques that are commonly used are: (1) Putty-wash one-step technique, (2) putty-wash two-step technique.

A uniform wash space is needed for an accurate impression. Nissan et al recommended the use of two-step technique for accurate impression making as there is uniform wash space for the light body material to polymerize.

The aim of the present study was to compare the accuracy of stone casts obtained from different putty-wash impression techniques using various spacer thickness.

The critical factor that influences the accuracy of putty-wash impression techniques is the controlled wash bulk which is absent in one-step putty-wash impression technique and with polyethylene spacer was used.

How to cite this article: Chugh A, Arora A, Singh VP. Accuracy of Different Putty-Wash Impression Techniques with Various Spacer Thickness. Int J Clin Pediatr Dent 2012;5(1):33-38.

Comparative analysis of dimensional precision of different silicone impression materials

OBJECTIVES

To investigate the accuracy of four commercial types of additional silicone impression materials (AFFINIS®, Virtual®, Relay 2002 CD® and Silagum®).

MATERIALS AND METHODS

The accuracy of impression material was measured indirectly by measuring three dimensions on stone cast poured from impressions of a stainless steel master model. The three dimensions on stone cast were measured at 1 hour, 2 days, 1 and 2 weeks after making the impression. Two impression techniques were used in the current study. The two-step impression technique was used for AFFINIS® and Virtual®, while single-step technique was used for Relay 2002 CD® and Silagum® materials. Twenty impressions were made of the master cast at four different periods for each of the tested four materials with a total of 320 impressions. Two vertical dimensions and one horizontal dimension were measured on master cast using optical microscope. Statistical analysis was run to compare the mean measurements for tested casts from each impression and time interval with the master cast.

RESULTS

No statistical significant differences were found (p > 0.05) in the accuracy of tested materials. There was no significant difference of master cast and impression cast means over time. Additionally, impression technique could be correlated with accuracy.

CONCLUSION

The tested additional silicones showed accuracy over time and they could be delayed up to 4 weeks duration without any significant changes in its dimensional stability. Silagum® impression material was the most accurate followed by Relay 2002 CD®, Virtual® and AFFINIS®.

CLINICAL SIGNIFICANCE

Silagum® impression material is most accurate followed by Relay 2002 CD®, Virtual® and AFFINIS®.

Impression materials in fixed prosthodontics: influence of choice on clinical procedure

The purpose of this article is to review impression materials used for fabricating fixed restorations in dentistry. Their compositions, properties, advantages, and disadvantages are presented and compared. How these properties influence clinical decisions is also described. This review helps the clinician choose which material is more suitable for a specific case. A broad search of the published literature was performed using Medline to identify pertinent current articles. Textbooks, the Internet, and manufacturers' literature were also used to supplement this information. It is limited to impression materials used in fixed prosthodontics. The review gives basic knowledge of ideal impression material properties and discusses traditional and, primarily, more recently developed products, such as polyethers, poly(vinyl siloxane), polysulfides, and condensation silicone materials. Clear advantages and disadvantages for these impression materials are provided along with the role that compositional variations have on the outcome of the impression. This should enable clinicians and technicians to easily identify the important physical properties of each type of impression material and their primary clinical indications.

The elastomers for complete denture impression: A review of the literature

This article reviews the current trends in materials used for complete denture impression. Peer-reviewed articles, published in English and in French between 1954 and 2007, were identified through a MEDLINE search (Pubmed and Elsevier) and a hand search of relevant textbooks and annual publications. Emphasis was made on the characteristics of the elastomers, their manipulation, the different techniques used, and the quality of the impression obtained. The combination of excellent physical properties, handling characteristics, and unlimited dimensional stability assures the popularity of these impression materials.

An Experimental Study on Particular Physical Properties of Several Interocclusal Recording Media. Part I: Consistency Prior to Setting

PURPOSE

To evaluate the consistency prior to the setting of 5 elastomeric interocclusal recording materials in comparison with a wax and a zinc oxide-eugenol paste. This property is related to the viscosity as well as to the working and setting times of these materials.

MATERIALS AND METHODS

Testing of consistency was performed following a modification of the method described in ADA Specification No. 19, for elastomeric impression materials. Each one of the tested materials was mixed for 20 seconds and was then loaded into a 0.5 mL syringe. The material was syringed onto a 10 x 10 x 0.5 cm glass plate. A second 575 g glass plate was placed on top of the unset interocclusal registration material. A total of 10 samples were tested for each material. The surface area covered by the materials was measured with the help of a scanner and the use of appropriate computer software.

RESULTS

One-way ANOVA revealed significant differences among the materials (F = 889.493, p < 0.0005). According to Tukey's honest significant difference test, all materials were significantly different (p < 0.05) from one another. All polyvinylsiloxanes occupied a smaller area than that of the polyether and of the zinc oxide-eugenol paste.

CONCLUSIONS

Zinc oxide-eugenol paste was the most fluid of all materials tested. Polyvinylsiloxanes displayed less flow properties than polyether.

Assessment of preference of mixing techniques and duration of mixing and tray loading for two viscosities of vinyl polysiloxane material

STATEMENT OF PROBLEM

Information regarding operators' preferences for different impression mixing techniques and duration of mixing and tray loading is limited.

PURPOSE

The purpose of this study was to assess operators' preferences, and the duration of mixing and tray loading using different mixing techniques.

MATERIAL AND METHODS

Thirty dentists, 30 dental assistants, and 30 inexperienced dental students evaluated mixing heavy-body vinyl polysiloxane material (VPS) using electronic mixing compared to automixing, and extra-heavy-body material using electronic mixing compared to hand mixing. Participants rated their level of preference using a scale from 0 to 10 for ease of mixing, control of loading, quality of mixing, level of cleanliness, and overall rating. The duration of mixing and tray loading was also measured. Mean values were compared within participant groups using the paired t test (alpha=.05) and between groups using 1-way analysis of variance (ANOVA) (alpha=.05). Holm's procedure was used to adjust the level of significance for the multiple comparisons.

RESULTS

The paired t test showed that mean values of level of preference for electronic mixing were significantly higher (P<.001 to .033) than those for automixing or hand mixing. The mean values of duration of mixing and tray loading with electronic mixing were significantly higher (P<.001 to .002) than those with automixing or hand mixing, except for students using heavy-body materials (P=.31). One-way ANOVA showed that there were no significant differences between the 3 participant groups in preference and duration of mixing and tray loading, both of heavy-body and extra-heavy-body VPS impression materials.

CONCLUSIONS

All participant groups preferred electronic mixing to automixing or hand mixing. Electronic mixing was significantly slower for all groups except for students using heavy-body materials. There was no significant difference between the 3 participant groups in the preference or duration of mixing and tray loading for the mixing techniques tested.

Dentist communication with the dental laboratory for prosthodontic treatment using implants

PURPOSE

A questionnaire was sent to U.S. dental laboratories to evaluate the level of communication between dentists and laboratory technicians and to determine trends in procedures and materials used in fixed and removable implant restorations.

METHODS AND MATERIALS

Dental laboratories were randomly chosen from the National Association of Dental Laboratories for each of the 50 states. The questionnaire was mailed to the laboratory directors for 199 dental laboratories. One hundred fourteen dental laboratories returned the survey, yielding a response rate of 57%. Of those laboratories, 37 indicated that they did not participate in the fabrication of fixed implant restorations, yielding a response rate of 39%. Forty-two dental laboratories indicated that they did not participate in the fabrication of implant-retained overdenture prostheses, yielding a response rate of 36%.

RESULTS

Results from this survey show inadequate communication by dentists in completing work authorization forms. Custom trays are used more frequently for implant-retained overdenture impressions and stock trays for impressions of fixed implant prostheses. Poly(vinyl siloxane) is the material most commonly used for both fixed and removable implant-supported prostheses. Two implants with stud attachments are used more widely than those with bar attachments for implant-retained overdentures.

CONCLUSIONS

Most laboratories working on implant prosthodontic cases report inadequate communication between the laboratory and dentists related to materials and techniques used in fabrication of implant restorations.

A review of contemporary impression materials and techniques

The contemporary restorative dentist has a host of impression materials available for making impressions in fixed prosthodontics,implant dentistry, and operative dentistry. With proper material selection and manipulation, accurate impressions can be obtained for fabrication of tooth- and implant-supported restorations. This article outlines the ideal properties of impression materials and explains the importance of critical manipulative variables. Available impression materials are analyzed relative to these variables, and several "specialized" impression techniques are described. Special attention is paid to polyvinyl siloxane impression materials because they have become the most widely used impression material in restorative dentistry.

Evaluation of dental arch reproduction using three-dimensional optical digitization

STATEMENT OF PROBLEM

Numerous investigations have been done to determine the most accurate method to reproduce a dental arch. Investigations have used different definitive cast configurations, materials, and measuring techniques to evaluate dimensional change, leaving clinicians undecided as to the most accurate method to reproduce a dental arch.

PURPOSE OF STUDY

The purpose of this investigation was to evaluate the effect of impression tray selection on accuracy of reproductions of a dental arch using a 3-dimensional optical digitizer.

MATERIALS AND METHODS

Impressions were made of a stone cast of a dental arch using vinyl polysiloxane impression material in custom and stock impression trays (n=12). Custom trays, designed with full palatal coverage, were fabricated on a separate standard stone cast using 2 layers of pink baseplate wax as the spacer and tissue stops on 1 anterior tooth and both first molar teeth. Impressions were poured with type IV gypsum and allowed to set with the tray inverted (n=5) or not inverted (n=5). The standard cast and resulting casts were digitized using an optical digitizer. Custom software was used to align and process the 3-dimensional images created by the digitizer. Each image was superimposed onto the standard cast image, curves were created of the percent of points less than a defined distance between the 2 superimposed images, and the area under the curve was calculated. A weighted average area was calculated for each cast, and these values were analyzed using a 2-way ANOVA (alpha=.05).

RESULTS

The main effect of tray type, laboratory setting technique, and the interaction between these 2 characteristics was analyzed. None of these effects was significant.

CONCLUSION

The differences in accuracy of reproductions of a dental arch, regardless of the impression and laboratory techniques, were not significant when evaluated using a 3-dimensional optical digitizer.

Laser digitization of casts to determine the effect of tray selection and cast formation technique on accuracy

STATEMENT OF PROBLEM; Several studies have attempted to determine the ideal combination of dental materials and laboratory techniques to produce the most accurate dental cast. Most have made use of 2-dimensional manual measuring devices, which neglect to account for the dimensional changes that exist along a 3-dimensional surface.

PURPOSE

The purpose of this study was to determine the effect of impression tray selection and cast formation techniques on the dimensional change of a dental cast with the use of new, 3-dimensional optical digitizing technology.

MATERIAL AND METHODS

Multiple impressions of a machined steel die that resembled a dental arch were made with custom and stock impression trays and vinyl polysiloxane impression material. The impressions were poured in type V artificial dental stone and allowed to set with the tray inverted or noninverted. The steel master die and stone casts were digitized with the Steinbichler Comet 100 Optical Digitizer, which was developed at the Minnesota Dental Research Center for Biomaterials and Biomechanics. Three-dimensional images of the stone casts were aligned to the 3-dimensional image of the master die and analyzed with AnSur-NT software. Multiple measurements of the master die and stone casts were analyzed to determine the accuracy of the 3-dimensional technology and of the impression and cast fabrication techniques. Planar distances between the center of each crown preparation were measured, as were crown heights. Data were analyzed with analysis of variance (P<.05), and root mean square error values were determined.

RESULTS

Casts were compared with a total of 45 significance tests, of which only 4 yielded P<.05. There was no pattern to these results, which suggests that they were false-positive findings.

CONCLUSION

Results obtained with the use of new optical digitizing technology indicated that neither impression tray type nor cast formation technique affected the accuracy of final casts.

Accuracy of three polyvinyl siloxane putty-wash impression techniques

STATEMENT OF PROBLEM

There is much discussion in the dental literature concerning the effect of the impression technique on the accuracy of cast restorations.

PURPOSE

This study assessed the accuracy of 3 putty-wash impression techniques using the same impression material (polyvinyl siloxane) in a laboratory model.

MATERIAL AND METHODS

The 3 putty-wash impression techniques used were (1) 1-step (putty and wash impression materials used simultaneously); (2) 2-step with 2-mm relief (putty first as a preliminary impression to create 2-mm wash space with prefabricated copings. In the second step, the wash stage was carried out); and (3) 2-step technique with a polyethylene spacer (plastic spacer used with the putty impression first and then the wash stage). For each technique, 15 impressions were made of a stainless steel master model that contained 3 complete crown abutment preparations, which were used as the positive control. Accuracy was assessed by measuring 6 dimensions (intraabutment and interabutment) on stone dies poured from impressions of the master model.

RESULTS

One-way analysis of variance showed statistically significant differences among the 3 putty-wash impression techniques, for all intraabutment and interabutment measurements (P <.001). Overall discrepancies of the 2-step technique with 2-mm relief putty-wash impression technique were significantly smaller than that in the 1-step and polyethylene putty-wash impression techniques.

CONCLUSION

The polyvinyl siloxane 2-step, 2-mm, relief putty-wash impression technique was the most accurate for fabricating stone dies.

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.

Comparing the accuracy of reversible hydrocolloid and elastomeric impression materials

This in vitro investigation evaluated the accuracy of reversible hydrocolloid, vinyl polysiloxane and polyether elastic impression materials used in conjunction with two die stones. The authors made impressions in an experimental environment that approximated clinical conditions in regard to temperature and moisture. Analysis of variance and t-tests were used to compare corresponding measurements on experimental casts made from the various impression materials.

Vertical distortion in distal extension ridges and palatal area of casts made by different techniques

A coordinate measurement machine with laser probe was used to measure the vertical distortion of the casts produced by use of three types of impression materials (irreversible hydrocolloid, condensation silicone, and addition silicone) and two types of trays (stock and custom trays). Results indicated that all impression groups showed positive vertical distortion (ranging from 0.00566 to 0.30299 mm) at the edentulous ridges and palatal area. The amount of the vertical distortion was greatest at the palatal area and was followed by the high edentulous ridge and the low edentulous ridge. Addition silicone, with either custom tray or stock tray, was the most accurate impression material. Condensation silicone was more accurate than irreversible hydrocolloid in custom tray impression. However, in stock tray impression the irreversible hydrocolloid was more accurate than the condensation silicone. The results suggest that, with careful manipulation, irreversible hydrocolloid with stock tray impression may provide a satisfactory cast for fabricating the framework of a distal extension removable partial denture.

Bond strength of two nonaqueous elastomeric impression materials bonded to two thermoplastic resin tray materials

Investigations indicate that custom impression trays enhance the accuracy of the fabrication cast. Multiple materials and techniques exist for custom tray fabrication, and variability in the bonding strength of adhesive agents supplied with nonaqueous elastomeric material have been reported. Bonding between two nonaqueous impression materials and two thermoplastic resin tray materials was assessed in this study. Standard tensile specimens were fabricated and the combinations of Hydrotray resin (smooth) with Hydrosil impression material recorded the greatest bonding strength, 797 kPa. Adhesion to resin tray materials was found to vary with material type and surface preparation.

Effect of disinfection of custom tray materials on adhesive properties of several impression material systems

The effects of impression tray disinfection procedures on the bond strength of impression-material adhesives to two types of resin trays were evaluated with a tensile test. Autopolymerizing acrylic resin and a visible light-curing resin were formed into one-half inch cubes. A screw eye was attached to each cube before polymerization. Perforated trays were fabricated with stops to maintain an even one-eighth inch of impression material over the resin block. Hooks on the opposite side permitted attachment of the metal plate to a mechanical testing machine. Before adhesive was applied, one third of the resin specimens were immersed in a 1:213 iodophor solution; one third in a 10% sodium hypochlorite solution, and one third were kept in the "as fabricated" condition. Polysulfide, polyether, and polyvinyl siloxane impression material-adhesive systems were evaluated. The resin-impression material-metal plate couples were attached to a mechanical testing machine and tensile forces were applied at a separation rate of 5 inches per minute. Mean values for adhesive strength ranged from 3.49 kg/cm2 for the autopolymerizing acrylic resin/iodophor/polyether combination to 10.55 kg/cm2 for the autopolymerizing acrylic resin/untreated/polyvinyl siloxane combination. Differences were detected among materials and disinfecting procedure. Clinically, disinfection of resin trays may adversely affect retention of the impression material to the tray.

Polyvinyl siloxane impression materials: a review of properties and techniques

Polyvinyl siloxane impression materials have been shown to have excellent properties as impression materials; however, they are sensitive to manipulative variables. Several methods of using very high viscosity (putty) materials to form "trays" to obtain uniform bulk of the wash impression are described, and the disadvantages of each of these techniques is pointed out. It is recommended that for best results acrylic resin custom trays should be used routinely. The interaction of polyvinyl siloxane materials with latex products is also discussed and problems that this inhibition can cause are stated. Suggestions to avoid this interaction are outlined. One of the disadvantages of the impression materials is that it has a relatively short working time. Refrigerating the material will increase working time without affecting accuracy.

Comparative elasticity tests for elastomeric (non putty) impression materials

This study was conducted to evaluate the methods used for measuring the elastic recovery of various elastomeric impression materials. One brand from each chemical group was selected to allow relative ranking of the results from each deforming test mode. For compression tests, the polysulphide and silicone specimens made in metal moulds gave significantly less set than those made in acrylic moulds; this was not so for the polysiloxane and polyether specimens. For polysulphide and polyether materials, the set in compression was greater using the BSI balanced beam method than for an optical method without inertia or load effects; this was not so for silicone or polysiloxane materials. The elastic recovery of the materials did not alter significantly after ten minutes of strain release, except in tensile tests, where the elastic recovery continued to change for twenty minutes. The rank ordering of the deformation set showed a relative correlation for the compression test, a new tensile test method, and bend and torsion testing methods. Thus only one method is needed to determine set per cent.

Effect of tray space on the accuracy of monophasic polyvinylsiloxane impressions

The effect of tray space on the dimensional accuracy and stability of impressions made from four brands of monophasic polyvinyl siloxane material was assessed on the recovered stone casts by quantitative and qualitative methods. In general, both evaluation methods agreed that tray space and repeat pour did not affect the accuracy of the dies for individual castings. But disagreement was observed in the findings for fixed partial dentures (FPDs). Quantitative measurement of the interpreparation (IP) dimensions did suggest the possibility of a potential problem when a FPD is cast in one piece because of a significantly reduced distance between the two abutments. However, from the findings of this study it can be concluded that a rigid stock tray can be used with a monophasic polyvinyl siloxane impression material.

A vinyl polysiloxane die used to make interim restorations

A die made of vinyl polysiloxane is a great aid for making interim restorations and for establishing correct gingival contours for finer restorations. This article describes the rationale and procedures for such a procedure.

Laboratory assessment of impression accuracy by clinical simulation

Some laboratory tests of impression material accuracy mimic the clinical situation (simulatory) while others attempt to quantify a material's individual properties. This review concentrates on simulatory testing and aims to give a classification of the numerous tests available. Measurements can be made of the impression itself or the resulting cast. Cast measurements are divided into those made of individual dies and those made of interdie relations. Contact measurement techniques have the advantage of simplicity but are potentially inaccurate because of die abrasion. Non-contact techniques can overcome the abrasion problem but the measurements, especially those made in three dimensions, may be difficult to interpret. Nevertheless, providing that care is taken to avoid parallax error non-contact methods are preferable as experimental variables are easier to control. Where measurements are made of individual dies these should include the die width across the finishing line, as occlusal width measurements provide only limited information. A new concept of 'differential die distortion' (dimensional difference from the master model in one plane minus the dimensional difference in the perpendicular plane) provides a clinically relevant method of interpreting dimensional changes. Where measurements are made between dies movement of the individual dies within the master model must be prevented. Many of the test methods can be criticized as providing clinically unrealistic master models/dies or impression trays. Phantom head typodonts form a useful basis for the morphology of master models providing that undercuts are standardized and the master model temperature adequately controlled.

Effect of impression tray design and impression technique upon the accuracy of stone casts produced from a putty-wash polyvinyl siloxane impression material

This study examined the accuracy of stone casts produced from impressions taken in stock polycarbonate trays, some of which had been strengthened with autopolymerizing polymethyl methacrylate resin. Three techniques were used to make the impression of an acrylic master model of the mandibular arch on which two extracoronal preparations for bridgework and one intracoronal inlay preparation had been carried out. Each preparation had been indented with a reference point for later measurement. The impression material was a putty-wash polyvinyl siloxane material. Five impressions were taken for each type of tray for each impression technique and these were cast in die-stone after 24 h. The distances between the points were measured with a reflex microscope and the means determined for each design of tray. The mean difference between casts produced from the various tray designs and the acrylic master model were determined for each of the distances between the three measuring points for the various impression techniques. Statistical analysis showed that, with the polycarbonate stock trays, there were significant differences between some of the modifications and between them and the acrylic model, for the three distances (P less than 0.05). These differences were limited to one measurement for one design of tray for each of the two-stage impression methods. With the one-stage technique the unreinforced tray and those reinforced with acrylic, over the heels and anteriorly, and the barred design were statistically significantly different from the acrylic model for measurement A-B.(ABSTRACT TRUNCATED AT 250 WORDS)