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COMPARISON OF DIMENSIONAL ACCURACY USING TWO ELASTOMERIC IMPRESSION MATERIALS IN FIXED PROSTHODONTICS.

Byline: PARDEEP K BANSAL - Email: drpardeepbansal@yahoo.com

ABSTRACT

This study compared the dimensional accuracy of monophasic and putty-wash polyvinyl siloxanes on the inter preparation distance in fixed prosthodontics. It was carried out at the Department of Prosthodontics and Maxillofacial Prosthetics at Dashmesh Institute, Faridkot, India.

A brass die simulating three unit fixed partial denture was fabricated. Two different commercially available products were used. Impressions for Putty wash (using stock tray) and Monophase (using custom tray) were made and poured with Type IV Die stone. A total of 60 impressions were made. A set of 20 impressions were poured after one hour, another set of 20 impressions were poured after 24 hours and the last set of 20 impressions were poured after 7 days. Inter-preparation distances were measured on the stone dies and compared with the master model.

Results indicated that most of the inter-abutment dimension values deviated from the master model within range of (-0.11% - +0.16%) percentage deviation.

Under the conditions of this study, the Putty-wash and Monophase impression techniques were equally dimensionally accurate and the time of the pour did not affect the accuracy.

Key words: Polyvinyl siloxane elastomer, Monophase, Putty-wash

INTRODUCTION

Impression making represents a crucial step in processing and fitting dental prosthesis. For that rea-son, the quality of the impression is decisive for final fitting accuracy, and consequently for the success of the dental restoration. Accurate replication of tooth preparations and their arch positions require impres-sion materials that exhibit good dimensional stability. 1 The elastomeric impression materials, especially addi-tion polyvinyl siloxanes have been reported to be the most accurate in dimensional stability and surface reproduction.2,3,4,5,6

In addition, clinicians have devel-oped specific impression techniques which skillfully combine the special advantages of given types of im-pression materials and thus make it possible to achieve optimum reproduction of the finest details and the accuracy which is acquired in master cast. Of the several techniques available, Putty-wash is most com-monly used these days.7 Two variations of the putty wash technique exist, namely a one-stage technique that records putty and wash simultaneously and a two-stage technique in which an initial putty impression is subsequently relined with a wash materia1.8,9,10,11 While earlier studies showed no difference in terms of accuracy between the two techniques, more recently the two-stage technique (with 2mm space) has been shown to be more accurate.12,13,14 Monophase technique is also gaining because of the ease of mani-pulation.15,16,17

The contribution of the impression materials to a successful fixed partial denture can be increased by either selecting a material that is dimensionally stable or by pouring the impression immediately. Due to a host of contingencies, it may not be possible to pour the impressions immediately and it may be necessary to pour it at various intervals of time. The introduction of new impression materials makes the research in this area very much necessary.18

The purpose of this study was to quantitatively evaluate the dimensional accuracy of putty-wash and monophase polyvinyl siloxane impression materials by measuring the linear changes in the inter-preparation dimension on recovered stone dies and also to deter-mine the effect of delayed pours at varying periods of time.

METHODOLOGY

A machined standard brass die was made to serve as a model simulating a three-unit fixed partial den-ture. The die preparation was made so as to simulate a three-unit fixed partial denture situation replacing a mandibular first molar (Fig 1). The abutments had a uniform 6 degree angle of draw with the vertical axis and were firmly attached to the platform and thereby immobilized during impression making.

Reference lines in the shape of '+', were inscribed on the occlusal surfaces of the two abutments, which were used for assessing the linear change in the inter-preparation distance.

For putty wash technique, a perforated stainless steel stock tray was fabricated. The tray was fabricated in such a way that the edges of the tray fitted into the 2mm deep orientation grooves placed on the platform. In this way, the tray could be repeatedly and consis-tently seated in a self limiting way each time an impression was made. Standard 2mm thick brass copings were fabricated for each abutment with the purpose of producing uniform space for wash material in the putty impressions.

Acrylic resin custom trays were used for the Monophase technique. Acrylic resin trays with 2mm space between the abutments and inner tray walls were fabricated. To standardize the size and critical spatial dimensions of the trays, each tray was fabri-cated using the same spacer.

After placing the spacer over abutments, an algi-nate impression was made and immediately poured in dental stone. The impressions were separated after 1 hour and used as models for the fabrication of acrylic custom trays using salt and pepper (sprinkle- on) method. To allow for polymerization shrinkage, all the trays were fabricated at least 24 hours prior to use (Fig 2).

For putty wash technique, perforated metal tray was used. The tray adhesive supplied by the manufac-turer was evenly applied over the inner surface of the tray and extended approximately 2mm on the outer surface along the periphery of the tray. The adhesive was allowed to dry before the impressions were made. Putty was mixed in the manufacturer's recommended proportions, loaded in the tray and the tray seated over the master model as guided by the alignment grooves and until firm contact was made, indicating that seat-ing had occurred to the predetermined degree. To allow space for the wash thickness, brass spacer was placed on the abutments before making putty impression. After seating the tray, the impression was held with gentle finger pressure and allowed to polymerize for 10 minutes, which was twice the manufacturer's recom-mended setting time, to compensate for the ambient room environment.

After removal and after allowing for a short period of elastic recovery, light body was introduced into the prespaced putty impression. The impression was held in place for adequate amount of time to ensure that setting reaction was complete before removal. Since the reaction took place at a room temperature, which is lower than the mouth temperature, the tray was held in place for a longer duration than the manufacturer's recommendation to ensure complete polymerization. The impression was checked for any voids and other inaccuracies.

For monophase technique, autopolymering acrylic resin tray was used. A thin coat of tray ad-hesive was applied on the tray and was allowed to dry for at least 15 minute. Impression material was injected around the metal abutments and some material was placed in the tray. The tray was seated with light pressure until it was settled in place. Once in place, the tray was held with minimum finger pressure until it was completely set. The impression were separated from the model by hand with a straight pull directed along the path of withdrawal of the preparations.

Two different brands of impression materials were used (Table 1). For each brand (Kettenbach and Dentsply) 30 impressions were made, 15 for the Monophase technique and 15 for the Putty-wash tech-nique. So a total of 60 impressions were made. Out of these, a set of 20 impressions (Kettenbach Monophase-5 Kettenbach Putty-wash-5,Dentsply Mono-phase-5, Dentsply Putty-wash-5) were poured with high strength stone after one hour. Another set of 20 impressions were poured after 24 hours and the last set of 20 impressions were poured after one week. Thus a total of 60 casts were reproduced which were labeled with a combined alpha numeric and numeric coding (variable coding). For example, the first letter of the brand name coded the brand of the material. Similarly, the technique used for that cast was coded by the first letter of technique.

Numbers coded the pouring time (Fig 3). To standardize the effect of the setting expansion of the improved stone, the powder was accurately weighed (Sartorius Analytic) and water was dispensed using a graduated test tube and a product of similar batch number was used to pour all the impressions.

The casts were allowed to air dry for at least 48 hours before measurements were made. A traveling microscope (Parco) capable of measuring to 0.001 cm was used (Fig 4). Each measurement was repeated 3 times on the stone casts to ensure its reproducibility and the mean was recorded for the inter-preparation distance. The accuracy of casts was expressed as % deviation from the standard model values. To elimi-nate individual variability, all measurements were made by the same individual.

RESULTS

Table 2 shows the mean and standard deviation of the inter-preparation dimension (in mms) between monophase and putty-wash techniques in Kettenbach group, relative to the time of pouring i.e. after one hour, 24 hours and one week respectively. Mann-

Whitney 'U' test between two techniques for one hour and 24 hours revealed no statistically significant differ-ence whereas for one week interval, the difference was significant (p=0.02). Table 3 shows the mean and standard deviation of the inter-preparation distance between monophase and putty wash techniques in Dentsply group relative to the time of pour. Mann-Whitney 'U' test revealed statistically significant difference at one week pour (p=0.28). Table 4 shows the mean and standard deviation of the inter-prepara-tion distance between Monophase techniques of both Kettenbach and Dentsply group relative to the time of pour. Mann-Whitney 'U' test revealed sta-tistically significant difference at one hour pour (p=0.0I6). Table 5 shows the mean and standard devia-tion of the inter-preparation distance between Putty-wash techniques of both Kettenbach and Dentsply group relative to the time of pour. Mann-Whitney 'U' test revealed no statistically significant difference at any time interval.

Table 6 shows the percentage deviation of mean inter-preparation distance (measured on stone dies) between Monophase tech-nique for both groups from the master model relative to the time of pouring. Mann-Whitney 'U' test revealed no statistically significance difference at any time interval. Table 7 shows the percentage deviation of mean inter-preparation distance (measured on stone dies) for Putty wash technique from the master model relative to the time of pouring. Mann-Whitney 'U' test revealed statistically significant difference at one-hour time interval of pouring casts (p=0.046). Table 8 shows the mean and standard deviation of inter-preparation distance for each technique and each group individu-ally between different time intervals i.e. from 1 hour to 24 hours, one hour to 7 days and from 24 hours to 7 days.

Wilcoxon signed rank sum test revealed statisti-cally significant difference in Monophase technique (Kettenbach group) for the time interval one hour to 24 hours (p=0.042) and between 24 hours to one week (p=0.043).

TABLE 1: IMPRESSION MATERIALS

###TABLE 1: IMPRESSION MATERIALS

Panasil putty###B.No.11100###Kettenbach GmbH and Co, Germany

Panasil contact plus###B.No.11889###Kettenbach GmbH and Co, Germany

Monopren transfer###B.No.11852###Kettenbach GmbH and Co, Germany

Aquasil monophase###B.No.678100###Dentsply / Caulk, USA

Aquasil Putty and wash cartridge system###B.No.60578131###Dentsply / Caulk, USA

TABLE 2: MEAN AND STANDARD DEVIATION OF INTERPREPARATION DISTANCE BETWEEN MONOPHASE AND PUTTY-WASH TECHNIQUE (KETTENBACH GROUP)

###Std###

###CLASS###N###Mean###Deviation###Za

TIME###KM###5###1.973###.002###.7450

###KP###5###1.974###.002###p=.456

TIME2###KM###5###1.977###.001###1.7020

###KP###5###1.973###.003###p=.089

TIME###KM###5###1.972###.002###2.3260

###KP###5###1.976###.002###p=.02

a. Z= Mann- Whitney U

TABLE 3: MEAN AND STANDARD DEVIATION OF INTERPREPARATION DISTANCE BETWEEN

MONOPHASE AND PUTTY-WASH TECHNIQUE (DENTSPLY GROUP)

###Std###

###CLASS###N###Mean###Deviation###Z

TIME1###KM###5###1.978###.002###1.57600

###DP###5###1.976###.001###p=.115 ns

TIME24###DM###5###1.978###.002###1.57600

###DP###5###1976###.001###p=.115 ns

TIME7###DM###5###1.973###.002###2.19300

###DP###5###1976###.001###p=.028 sig

TABLE 4: MEAN AND STANDARD DEVIATION OF INTERPREPARATION DISTANCE FOR MONOPHASE TECHNIQUE (KETTENBACH AND DENTSPLY GROUP)

###Std###

###CLASS###N###Mean###Deviation###Z

TIME1###KM###5###1.973###.002###2.41700

###DM###5###1.978###.002###p=.016 sig

TIME24###KM###5###1.977###.001###1.8500

###DM###5###1978###.002###p=.236 ns

TIME7###KM###5###1.972###.002###.52900

###DM###5###1973###.002###p=.597 ns

TABLE 5: MEAN AND STANDARD DEVIATION OF INTERPREPARATION DISTANCE FOR PUTTY-WASH TECHNIQUE (KETTENBACH AND DENTSPLY GROUP)

###Std###

###CLASS###N###Mean###Deviation###Z

TIME1###KP###5###1.974###.002###1.78100

###DP###5###1.976###.001###p=.075 ns

TIME24###KP###5###1.973###.003###1.57600

###DP###5###1.976###.001###p=115 ns

TIME7###KP###5###1.976###.002###.31800

###DP###5###1.976###.001###p=.75 ns

TABLE 6: MEAN PERCENTAGE DEVIATION OF INTERPREPARATION DISTANCE FROM MASTER MODEL FOR MONOPHASE TECHNIQUE (KETTENBACH AND DENTSPLY GROUP)

###Std###

###CLASS###Mean###Deviation###Z

PD1###KM###.1012###.1518###1.5280

###DM###-.118###.0940###p=.127 ns

PD2###KM###-.118###.0774###.2180

###DM###-.118###.0940###p=.827 ns

PD7###KM###.1688###.0293###.6550

###DM###.045###.1820###p=.513 ns

TABLE 7: MEAN PERCENTAGE DEVIATION OF INTERPREPARATION DISTANCE FROM MASTER MODEL FOR PUTTY-WASH TECHNIQUE (KETTENBACH AND DENTSPLY GROUP)

###Std###

###CLASS###Mean###Deviation###Z

PD1###KP###.0675###.0293###1.9930

###DP###-.062###.0682###p=.046 sig

PD2###KP###-.017###.1054###1.1070

###DP###-.062###.0682###p=.268 ns

PD7###KP###-.1013###.0877###.2210

###DP###-.1013###.0676###p=.825 ns

TABLE 8: MEAN AND STANDARD DEVIATION OF INTERPREPARATION DISTANCE BETWEEN VARIOUS TIME INTERVALS FOR MONOPHASE AND PUTTY-WASH TECHNIQUE

###Paired###

###Std.###

###CLASS###Mean###Deviation###Z###p

KM###TIME1 - TIME24###-.004###.003###2.032###0.042 sig

###TIME1 - TIME7###.001###.004###.405###.686 ns

###TIME24 - TIME7###.005###.002###2.023###.043 sig

KP###TIME1 - TIME24###.000###.004###.000###0.90 ns

###TIME1 - TIME7###-.002###.004###1.361###.174 ns

###TIME24 - TIME7###-.002###.003###1.361###.174 ns

DM###TIME1 - TIME7###.005###.004###1.753###.08 ns

###TIME24 - TIME7###.005###.004###1.753###.08 ns

DP###TIME1 - TIME7###.000###.002###.365###0.715 ns

###TIME24 - TIME7###.000###.002###.365###0.715 ns

a. Z=Wilcoxon Signed Rank sum test

DISCUSSION

Findings of this study indicated that the technique used for making the final impression did not influence the dimensional accuracy and stability regarding the inter-preparation distance. Slight deviations in the inter-preparation distance were noted among brands of products compared to the model values, when mea-sured by a quantitative evaluation method. However, all appeared to be comparable with reported values for conventional addition silicones, and were considered to be within clinically acceptable limits of accuracy.2,5,19

Monophase impression material showed slightly decreased inter-abutment distance from one hr to 24 hrs and from 24 hrs to 7 days (Table-8). This reduction in the inter-preparation dimension is similar to that reported by Tjan et al.20 This decrease in dimension could be attributed to polymerization shrinkage and residual polymerization resulting in shrinkage with time. It was suggested that the polymerization shrink-age increases with the number of covalent bonds formed.20 Anusavice and Marker2 explained that a bulk amount of the single viscosity material may have more polymerization shrinkage than a bulk amount of the putty / heavy body material that have higher filler contents.

Most of the inter-abutment dimension values devi-ated from the master model within range of (0.11% - +0.16%) percentage deviation (Fig 5). Several studies reported an increase or decrease in the inter-prepara-tion dimension from -0.16% to 0.23% (Johnson and Craig)21,22; +-0.23% to +-0.38% (Rueda et al)23 and -0.91 to +0.91% (Idris, Houston and Claffey).9

From a clinical perspective, these deviations in the inter-preparation distance from the master model are not of sufficient magnitude to cause difficulty when the inherent elasticity of the relevant intraoral tissues is considered.2 In this study, we have made special tray for monophase technique in such a way that it is well contoured over the abutments and over the ridge whereas in earlier studies (Tjan et al)20, tray design was not contoured and was made flat over the abutments & the ridge at the occlusal level. The reason why Tjan et al got the results showing reduction in the inter-preparation distance in the stone casts can be attrib-uted to the tray design because there is more bulk of impression material between the abutments (there-fore more shrinkage).

Consistent with previous studies on addition sili-cone1,22,24,25,26, the materials used in this study were found to be dimensionally accurate even up to one week. This is advantageous because casts can be poured up to one week without concern for dimensional accuracies as in the case when impression needs to be sent to the laboratory for pouring. The dimensional change of these materials was found to be well within the revised ADA specification No. 19, which recom-mends a maximum change in dimension to be 0.50% after a minimum of 24 hours.19

In this study we have taken two commercially available addition polyvinyl siloxane groups. But we cannot assume that these products to be representa-tive of all the materials available in the market. Distances were measured only at the occlusal level and restricted to the horizontal plane. Measure-ments made at the level of the finish lines for the cast restorations would have been more clinically relevant. However, occlusal level, measurements were used because of the technical difficulties associated with the marking/measurements of the dimensions at the gingival level. Though every effort was made to simulate oral conditions, the experiment could not be performed identically to pouring a cast from an in-traoral impression. Condition not examined included the effect of oral fluids, gravity, rotational path of impression removal, soft tissue and differing arch forms.

CONCLUSION

Under the conditions of this investigation and based on the study results, the following conclusions can be made:

The technique used (Monophase and Putty-wash) for making the final impression did not influence the dimensional accuracy and stability regarding the inter-preparation distance. The difference that was very small (0.02%) may not be sufficient enough to cause clinically important difficulties in the fit of the casting.

The time of pour did not affect the accuracy. This is advantageous because casts can be poured over a longer period without concern for dimensional accuracy.

Contouring the tray over the abutment prepara-tions and ridge in Monophasic impression im-proves the dimensional accuracy.

REFERENCES

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Correspondence: Dr Pardeep K Bansal, Asst Professor, Department of Prosthodontics and Maxillofacial Prosthetics, Dashmesh Institute of Research and Dental Sciences, Faridkot (Punjab), India, Mobile: 09814282284, Fax: 01639251666,
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Author:Bansal, Pardeep K.
Publication:Pakistan Oral and Dental Journal
Article Type:Report
Geographic Code:9PAKI
Date:Dec 31, 2010
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