Polyvinyl Siloxane Impression Material Research Articles

An In Vitro Study to Compare the Accuracy of the Master Cast Fabricated by Four Different Transfer Impression Techniques for Single-Tooth Implant Replacement

Single tooth implant retained crowns have become a recognized technique for the replacement of the missing teeth. With the predictable integration of implants, the emphasis is shifted towards precise prosthesis. Minor movement of the impression coping retained inside the impression material can occur during all the procedures, leading to the three-dimensional spatial inaccuracies in the master casts. Therefore, the present study was undertaken with the purpose to evaluate the accuracy of single-tooth implant impression techniques using four different impression copings, so as to obtain a precise definitive cast for a single-unit implant restoration. A maxillary acrylic resin model with a standard single implant in the first molar region was used to simulate a clinical situation. A total of 60 impressions were made with polyvinylsiloxane impression material, which were divided into four groups of 15 impressions each. Group I used non-modified square impression coping, while in group II, III and IV square impression coping were modified differently. Master casts fabricated for all the groups were analyzed to detect rotational position change of the hexagon on the implant replicas in the master casts in reference to the resin model. The master casts obtained with the roughened and adhesive-coated impression copings showed a lower amount of rotational movement than the masters casts achieved with the non-modified impression copings. Hence, the clinician should use sandblasted and adhesive coated impression copings to achieve a more accurate and precise orientation of the implant replicas in the laboratory master casts in single-tooth implant restorations.

Effect of infection control aids on polymerization inhibition of polyvinyl siloxane impression materials – An invitro study

ObjectivesTo evaluate the effect of infection control aids (latex gloves in contact with surfactants) upon polymerization during manipulation of different types of polyvinyl siloxane impression materials. MaterialsThree types of polyvinyl siloxane impression materials, (Examix, Affinis and Aquasil Ultra) were tested under four surface treatment conditions (alcohol, water, soap/water and unexposed glass surface as control) with two types of latex gloves (powdered and powder free). This resulted in a 3 × 4 × 2 experimental design of 24 cells with 20 specimens each. MethodsPVS impression material was expressed onto the glass surface conditioned with surfactant resulting in specimens (n = 20). The specimens were lifted from the testing surface at the applicable time, and the contact areas were examined independently by 2 of the authors to subjectively determine whether polymerization inhibition had occurred. Polymerization inhibition frequency was calculated for each group, and chi-square analysis and fissures exact test were used to determine whether there was a statistically significant relationship between polymerization inhibition in any of the study conditions (P < 0.05). ResultsThe results of this data showed significant increase in the polymerization inhibition of Examix and Affinis along with glove/alcohol combination. Comparison of the powdered/powder free glove groups found that there is no significant difference between these groups. Conclusion/clinical significanceUse of latex gloves along with alcohol should be avoided (simulation can happen during clinical practice) while manipulating polyvinyl impression materials.

An In Vitro Study of the Bond Strength of Five Adhesives Used for Vinyl Polysiloxane Impression Materials and Tray Materials

Although stock trays often provide mechanical retention for elastomeric impression materials, manufacturers typically recommend the use of an adhesive, whether a stock or custom tray is used. The mention of the bond strength on the adhesive packaging is not available, therefore the clinician has no idea whatsoever of the ideal adhesive. The aim of this study was to evaluate the bond strength of three vinyl polysiloxane (VPS) materials, one with a poly(methyl methacrylate) autopolymerizing (PMMA) specimen and another with a light-polymerizing tray material (VLC), using the adhesive recommended by the manufacturer of the impression material, and two universal adhesives. A total of ninety specimens (15×15×20mm) were used, 45 specimens were made in PMMA and rest 45 was made in VLC. Five paint-on adhesives (Coltene, Caulk, 3M, universal Zhermack and universal GC) were applied. Three impression materials, Affinis, Reprosil, and 3M, were mixed and injected into a perforated poly vinyl chloride cylinder. Tray specimens were positioned against the open cylinder end in contact with the VPS material. Tensile strength tests were conducted until adhesive separation failure. Mean values and standard errors of the adhesive strength were recorded in MPa for each material combination. GC paint-on universal adhesive provided significantly higher adhesive strength values.

Evaluation of Accuracy of Complete-Arch Multiple-Unit Abutment-Level Dental Implant Impressions Using Different Impression and Splinting Materials

This in vitro study evaluated the accuracy of multiple-unit dental implant casts obtained from splinted or nonsplinted direct impression techniques using various splinting materials by comparing the casts to the reference models. The effect of two different impression materials on the accuracy of the implant casts was also evaluated for abutment-level impressions. A reference model with six internal-connection implant replicas placed in the completely edentulous mandibular arch and connected to multi-base abutments was fabricated from heat-curing acrylic resin. Forty impressions of the reference model were made, 20 each with polyether (PE) and polyvinylsiloxane (PVS) impression materials using the open tray technique. The PE and PVS groups were further subdivided into four subgroups of five each on the bases of splinting type: no splinting, bite registration PE, bite registration addition silicone, or autopolymerizing acrylic resin. The positional accuracy of the implant replica heads was measured on the poured casts using a coordinate measuring machine to assess linear differences in interimplant distances in all three axes. The collected data (linear and three-dimensional [3D] displacement values) were compared with the measurements calculated on the reference resin model and analyzed with nonparametric tests (Kruskal-Wallis and Mann-Whitney). No significant differences were found between the various splinting groups for both PE and PVS impression materials in terms of linear and 3D distortions. However, small but significant differences were found between the two impression materials (PVS, 91 μm; PE, 103 μm) in terms of 3D discrepancies, irrespective of the splinting technique employed. Casts obtained from both impression materials exhibited differences from the reference model. The impression material influenced impression inaccuracy more than the splinting material for multiple-unit abutment-level impressions.

Comparison of the effect of different medicaments on surface reproduction of two commercially available Polyvinyl Siloxane impression materials - An Invitro Study

Objective:To determine the effect of different retraction cord medicaments on surface detail reproduction of polyvinyl siloxane impression materials and compare this effect on any two brands of commercially available polyvinyl siloxane impression materials. Material and methods: Four stainless steel dies were made according to ADA specification no.19. Three dies were treated with aluminium chloride (5%), ferric sulphate (13.3%) and epinephrine (0.1%) while the fourth one was left untreated to serve as control. Two impression materials (Dentsply and 3M ESPE) were used. Results: All the three medicaments adversely affected the surface detail reproduction of both the brands of the polyvinyl siloxane impression materials. These effects were statistically significant as compared to untreated control. The impressions of 3M ESPE brand have shown better surface detail reproduction as compared to Dentsply impression material. Conclusion: Surface detail reproduction of the polyvinyl siloxane impression materials is adversely affected by the retraction cord medicaments. The presence of moisture or any traces of the medicaments should be removed from the tooth surface to provide a dry field for the correct reproduction of the surface detail of these materials. Key words:Polyvinyl Siloxane, retraction cord medicaments, surface detail reproduction.

Evaluation and Comparison of Dimensional Accuracy of Newly Introduced Elastomeric Impression Material using 3D Laser Scanners: An in vitro Study

Aim of the present study was to comparatively evaluate dimensional accuracy of newely introduced elastomeric impression material after repeated pours at different time intervals. 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. 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. All the deviations measured from the master model with both the impression materials were within a clinically acceptable range. 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.

Surface Roughness of Polyvinyl Siloxane Impression Materials Following Chemical Disinfection, Autoclave and Microwave Sterilization

Autoclave sterilization and microwave sterilization has been suggested as the effective methods for the disinfection of elastomeric impressions, but subjecting elastomeric impressions to extreme temperature may have adverse effects on critical properties of the elastomers. To evaluate the effect of chemical disinfection as well as autoclave and microwave sterilization on the surface roughness of elastomeric impression materials. The surface roughness of five commercially available polyvinyl siloxane impression materials (Coltene President, Affinis Perfect impression, Aquasil, 3M ESPE Express and GC Exafast) were evaluated after subjecting them to chemical disinfection, autoclaving and microwave sterilization using a Talysurf Intra 50 instrument. Twenty specimens from each material were fabricated and divided into four equal groups, three experimental and one control (n=25). The differences in the mean surface roughness between the treatment groups were recorded and statistically analyzed. No statistically significant increase in the surface roughness was observed when the specimens were subjected to chemical disinfection and autoclave sterilization, increase in roughness and discoloration was observed in all the materials when specimens were subjected to microwave sterilization. Chemical disinfection did not have a significant effect but, since it is less effective, autoclave sterilization can be considered effective and autoclaving did not show any specimen discoloration as in microwave sterilization. Microwave sterilization may be considered when impressions are used to make diagnostic casts. A significant increase in surface roughness may produce rougher casts, resulting in rougher tissue surfaces for denture and cast restorations. Autoclave sterilization of vinyl polysiloxane elastomeric impressions for 5 minutes at 134°C at 20 psi may be considered an effective method over chemical disinfection and microwave sterilization, because chemical disinfection does not eliminate all disease-causing microorganisms and microwave sterilization leads to a rougher impression surface.

The effect of surface treatment and salivary contamination on the tensile bond strength between acrylic custom tray and monophase polyvinyl siloxane impression material.

Monophase elastomeric impression materials are commonly used with acrylic custom trays. Every effort is made to maximize bonding between the two. Lot of studies have focused on variables like adhesive drying time, tray material and type of elastomer but very few have solely concentrated on efficacy of surface treatment and effect of salivary contamination of the custom tray. The objective of this study was to find out the most effective surface treatment for the custom tray and also find out the extent to which salivary contamination could affect bond strengths. This invitro study was carried out in two parts using 40 samples. The materials used were Reprosil monophase impression materials and autoploymerizing acrylic blocks. The samples were divided into four groups of five samples each. The first part of the study concentrated on finding out the effect of surface treatment of the tray and the second part focused on the effect of salivary contamination. The specimens were tested in an Instron testing machine and the results of the study were interpreted by statistical analysis to arrive at the conclusions. The results showed statistically significant increase in tensile strengths for surfaces subjected to grit blasting and roughening with bur and decrease for specimens cured against wax. Salivary contamination of the tray prior to adhesive application decreased bond strengths significantly. It was concluded from the study that mechanical treatment of the tray prior to adhesive application maximizes adhesion of the impression material and that salivary contamination of the custom tray prior to adhesive application reduces adhesion between tray and elastomer regardless of the surface treatment carried out

“Grab the flab” window impression technique: A case report

Aims and objective: Making of a definitive, secondary or wash/final impression of displaceable flabby tissues with minimum or no displacement of tissue by using window impression technique. Background: Denture fabrication on flabby ridges is testing situations for a clinician as it adversely affects retention and stability of complete dentures. The difficulties encountered in these patients need to be overcome by modified techniques in denture fabrication that are not time consuming and make use of materials that are easy to use. Materials and Methods: This window impression technique, uses a custom tray with a window over flabby tissues and a mucostatic impression material to minimize distortion of tissues while making a impression. First, an accurate record of the denture supporting and limiting structures is made except for the mobile tissues which are recorded in second step using light body Polyvinyl siloxane impression material in the window area of special tray. Conclusion: The use of window impression technique helps in maintaining the contour and recording the details of the tissues without displacing the flabby tissues. Hence, it improves the prognosis for complete denture without surgical removal of hyperplastic tissues.

The effect of tray selection and viscosity of impression materials on the accuracy of dies produced from dual arch impressions – An in-vitro study

Objectives :The aim of this in-vitro study was to compare the accuracy of dies generated from metal and plastic dual arch trays impressions using two different viscosities of polyvinyl siloxane impression material and comparing the results to that obtained using a conventional full arch custom impression technique. Materials and method: Seven set of impressions were made of an experiment model using different combinations of, dual arch trays and viscosities of impression materials and the dimensions of the dies thus obtained were compared with those obtained from conventional full arch custom arch tray and medium viscosity impression material. Results: The gypsum dies prepared, from the complete arch custom tray technique and the dual arch impression technique using plastic and metal dual arch trays were generally larger in bucco-lingual dimension and shorter in mesio-distal dimension. Conclusions: All the seven types of impression techniques produced clinically successful impressions of standard brass die and dies so developed were within clinical standards to produced clinically successful restorations.

Effect of post-silanization heat treatments of silanized feldspathic ceramic on adhesion to resin cement.

To evaluate the effect of post-silanization heat treatment of a silane agent and rinsing with hot water of silanized CAD/CAM feldspathic ceramic surfaces on the microtensile bond strength between resin cement and the ceramic, before and after mechanical cycling. Blocks measuring 10 x 5.7 x 3.25 mm3 were produced from feldspathic ceramic cubes (VITA Mark II, VITA Zanhfabrik). Each ceramic block was duplicated in composite resin using a template made of polyvinylsiloxane impression material. Afterwards, ceramic and corresponding resin composite blocks were ultrasonically cleaned and randomly divided according to the 5 strategies used for conditioning the ceramic surface (n = 10): GHF: etching with hydrofluoric acid 10% + rinsing with water at room temperature + silanization at 20°C; G20: silanization; G77: silanization + oven drying at 77°C; G20r: silanization + hot water rinsing; G77r: silanization + oven drying at 77°C + hot water rinsing. The resin and ceramic blocks were cemented using a dualcuring resin cement. Every group was divided in two subgroups: aging condition (mechanical cycling, designated as a) or non-aging (designated as n). All the bonded assemblies were sectioned into microsticks for microtensile bond strength (µTBS) testing. The failure mode of the tested specimens was assessed and µTBS data were statistically analyzed in two ways: first 2-way ANOVA (GHF, G20 and G77 in non-aging/aging conditions) and 3-way ANOVA (temperature x rinsing x aging factors, excluding GHF), followed by Tukey's test (p = 0.05). The 2-way ANOVA revealed that the µTBS was significantly affected by the surface treatment (p < 0.001) but not by aging (p = 0.68), and Tukey's test showed that G77-n/G77-a (18.0 MPa) > GHF-n/GHF-a (12.2 MPa) > G20-n/G20-a (9.1 MPa). The 3-way ANOVA revealed that the µTBS was significantly affected by the "heat treatment" and "rinsing" factors (p < 0.001), but not affected by "aging" (p = 0.36). The rinsing procedure decreased, while oven drying increased the bond strengths. Group G77, in both non-aging and aging conditions (18.6-17.4 MPa), had the highest bond values. Failure modes were mainly mixed for all groups. Oven drying at 77°C improved the bond strength between the resin cement and feldspathic ceramic, but hot water rinsing reduced the bond strength and should not be recommended.

The effect of various core build-up materials on the polymerization of elastomeric impression materials

ObjectivesThe purpose of this study was to detect whether core build-up materials could be isolated as an inhibitory factor in the polymerization of commonly used types of elastomeric regular set impression materials, and to evaluate several decontamination methods to eliminate the inhibitory effect of core build-up materials. Materials and MethodsThe polymerization of six brands of elastomeric impression materials (Virtual, Aquasil, Genie, Correct Plus, Express and Impregum) was evaluated in vitro after direct contact with various core build-up materials (composite resin, flowable composites and resin-modified glass ionomers). The setting of impression materials was visually scored as either inhibited or non-inhibited independently by three different general practitioners. Different methods to prevent inhibition were also tested. The materials were dispensed according to the manufacturers’ instructions on exposed dentin of the premolar teeth mounted in dental stone. A Chi-square analysis was used to evaluate the results (p<0.05). ResultsSetting inhibition was found with five brands of Polyvinyl siloxane impression materials when they directly contact four types of core build-up materials. None of the materials used caused inhibition to the polyether impression material. No decontamination method proved adequate in preventing impression material inhibition except grinding 1mm from the multicore restoration surface. Examiners were in complete agreement (kappa +1). ConclusionsBased on the results of our study and for optimal results, when using Multicore composite as a core build-up material, at least 1mm from the restoration surface should be grinded before the PVS final impressions are taken. Flowable composites should not be used as a core build-up material with PVS impression materials, so polyether is the material of choice.

Fabrication of a unilateral oral commissure retractor

The fabrication of a unilateral device to treat microstomia after trauma is presented. Maximum opening was recorded before treatment. A dual arch impression that captured the dentition and commissure on the affected side was made with vinyl polysiloxane (VPS) impression material. A 1 mm vacuum formed template (VFT) was fabricated over the maxillary dentition, and a 2 mm VFT was fabricated around the commissure. A 0.9 mm (0.036") stainless steel wire was attached with acrylic resin to both templates in order to apply a constant force to the commissure. The use of a helix in the wire allowed for flexibility and adjustment of the retractor. The patient was instructed to wear the retractor for 6 hours per day, and, during a 10-week period, the maximum opening increased from 30 mm to 45 mm.

Pressure Produced on the Residual Maxillary Alveolar Ridge by Different Impression Materials and Tray Design: An In Vivo Study

Increased ridge resorption may occur due to inappropriate pressure applied during final impression making phase of complete denture fabrication. This study was done to evaluate the pressure applied on the residual ridge while making impressions with two tray designs (with and without spacer) using, zinc oxide eugenol and light body polyvinyl siloxane impression material. Five edentulous subjects were randomly selected. For each of the five subjects four maxillary final impressions were made and were labelled as, Group A-Impression made with tray without spacer using zinc oxide eugenol impression, Group B-Impression made with tray with spacer using zinc oxide eugenol impression material, Group C-Impression made with tray without spacer using light body polyvinyl siloxane impression material, Group D-Impression made with tray with spacer using light body polyvinyl siloxane impression material. During the impression procedure a closed hydraulic system was used to remotely measure the pressures produced in three areas. The pressure produced were calibrated according to the micro strain record. Statistical comparisons of readings were done using t test and ANOVA. The acquired data revealed that ZOE produced an average pressures value of 26.534 and 72.05 microstrain, while light body PVS produced 11.430 and 37.584 microstrain value with and without spacer respectively. Significantly high values were recorded on the vault of the palate when using trays without spacer. The use of light body polyvinyl siloxane and zinc oxide eugenol impression material showed insignificant difference. Within the limitations of this study, tray design has a significantly effected on the pressures produced, while the impression materials does not have any significant difference.

Differential reflectometry versus tactile sense detection of subgingival calculus in dentistry

Detecting dental calculus is clinically challenging in dentistry. This study used typodonts with extracted premolar and molar teeth and simulated gingival tissue to compare the performance of differential reflectometry and periodontal probing. A total of 30 extracted teeth were set in an anatomical configuration in stone to create three typodonts. Clear polyvinyl siloxane impression material was placed to replicate the periodontal soft tissues. Pocket depths ranged from 10 to 15 mm. The three models were placed in a phantom head, and an experienced dentist assessed the presence of subgingival calculus first using the DetecTar (differential reflectometry) and then a periodontal probe. Scores from these two different methods were compared to the gold standard (direct examination of the root surface using 20× magnification) to determine the accuracy and reproducibility. Differential reflectometry was more accurate than tactile assessment (79% versus 60%), and its reproducibility was also higher (Cohen kappa 0.54 versus 0.39). Both methods performed better on single rooted premolar teeth than on multirooted teeth. These laboratory results indicate that differential reflectometry allows more accurate and reproducible detection of subgingival calculus than conventional probing, and supports its use for supplementing traditional periodontal examination methods in dental practice.

The Bond Strength of Different Tray Adhesives on Vinyl Polysiloxane to Two Tray Materials: An In Vitro Study

There has been no established chemical bonding between custom tray resin and the elastomeric impression materials without the use of manufacturer's recommended specific tray adhesive. The present study was aimed to compare the bond strength of the manufacturer recommended tray adhesives with the universal tray adhesives using the medium body consistency vinyl polysiloxane (VPS) material and custom tray made of autopolymerising resin and visible light cure (VLC) resin. A total 90 cubicle specimens of autopolymerising resin and 90 specimens of VLC resin were tested for its tensile bond strength. Effectiveness of universal tray adhesive was compared with manufactured tray adhesive. Each of these specimens was then subjected to tensile load in hounsefield universal testing machine at a cross head speed of 5mm/min and the results were compared and evaluated using one way analysis of variance and post hoc Tuckey's test. Analysis of bond strength revealed that the universal tray adhesive showed better strength and was statiscally significant when compared to the manufacture supplied tray adhesive. Comparison between both the groups, VLC resin showed better bond strength as compared to autopolymerizing resin. Universal tray adhesive had better tensile bond strength than the manufacturers recommended tray adhesive with the medium body viscosity VPS impression material for both autopolymerising and VLC tray resin.

Clinical efficacy of veneered zirconium dioxide-based posterior partial fixed dental prostheses: five-year results

In recent years, zirconium dioxide-based partial fixed dental prostheses (FDP) have been suggested as an alternative treatment to traditional metal ceramic FDPs. However, clinical studies evaluating their longevity and related complications are limited. The purpose of this cohort clinical study was to assess the efficacy of zirconium dioxide-based posterior 3-unit FDPs. Twenty 3-unit posterior FDPs (Lava) were placed in 16 participants missing a second premolar or a first molar. All participants met specific inclusion and exclusion criteria and provided informed consent. All teeth were prepared in a standardized manner: occlusal reduction of 1.5 to 2 mm; axial reduction of 1 to 1.5 mm; a 1.0 mm 360-degree rounded shoulder placed 0.5 mm subgingivally on the facial aspect and supragingivally on the lingual aspect on sound tooth structure; and rounded internal line angles. Definitive impressions were made with vinyl polysiloxane impression material. Frameworks were fabricated by using computer-aided design and computer-aided manufacturing (CAD/CAM) technology with a uniform retainer thickness of 0.6 mm and a minimal connector surface area of 9 mm(2). Restorations were luted with resin-modified glass ionomer cement (Rely-X Luting). Participants were recalled at 2 weeks, 6 months, and 12 months, and thereafter, annually for up to 60 months. Clinical fracture measurements, marginal discoloration, marginal adaptation, radiographic proximal recurrent caries, and periapical pathoses were assessed over time by using modified Ryge criteria. The probability distributions of these variables were calculated for the baseline data and for the recall data. An analysis of survival was made by using the Kaplan-Meier method. Eighteen FDPs were clinically evaluated at 5 years and 1 at 48 months. Fifteen were rated Alpha for fracture measurements, and 2 were rated Bravo (minor chipping of veneering porcelain and not requiring restoration replacement). Two were rated Charlie (major chipping of veneering porcelain and requiring restoration replacement). Eighteen FDPs were rated Alpha for marginal integrity, and 1 rated Bravo. All restorations were rated Alpha for marginal discoloration. One participant experienced root fracture after 60 months, while another was treated surgically for a periapical pathosis on an endodontically treated abutment. Zirconium dioxide-based posterior 3-unit FDPs performed well after 5 years of service.

The influence of implant placement depth and impression material on the stability of an open tray impression coping

Subgingival positioning of a single dental implant may result in a less stable impression coping in a polymerized impression material. The purpose of this study was to evaluate the influence of a single dental implant placement depth and different impression materials on the stability of an open tray impression coping. Six polyvinyl chloride-based plastic models with single embedded internal hexagon implant analogs were fabricated. The implant analogs were placed equally with their surface 0, 1, 2, 3, 4, or 5 mm below the simulated gingival margin. Open tray impression copings were connected to the embedded implant analogs, and impressions were made with different vinyl polysiloxane (VPS) impression materials, polyethers, and an addition silicone-based occlusal registration material. The laboratory analogs were connected to the impression copings and the plastic trays were placed in a locking device. A measuring device, consisting of a compression force gauge connected to a platform moving at a speed of 3.2 mm/s, was fabricated. The impression trays were fixed so that the pole of the force gauge would touch the surface of the implant analog in the same place and push it 1.0 mm. Measurements of each specimen were made 5 times. Statistical analysis was performed with a 1-way ANOVA, the Tukey test, and the Pearson correlation coefficient (α=.05). There was a significant negative correlation between the dental implant placement depth and the force needed to move the impression coping (P<.05). In all depth groups, the impression coping was significantly more stable when the impressions were made with the occlusal registration material (P<.05). As the dental implant placement depth increased, the force needed to move the impression coping decreased. The coping was significantly more stable when an occlusal registration material was used to make the impression.

Rheological properties of polyvinylsiloxane impression materials before mixing and during setting related to handling characteristics

The purpose of this study is to determine and compare the handling and rheological properties of polyvinylsiloxane impression pastes before mixing and during setting, and to investigate the effect of its constituents on the properties of the materials. Five polyvinylsiloxane impression materials (Examixfine, Extrude, Honigum, Imprint II, and Express) were used. A flow test and a drip test were performed to determine the handling characteristics. The rheological properties of each impression material prior to mixing (shear stress, viscosity) and during setting (storage modulus G ’ , loss modulus G ’’ , loss tangent tanδ) were measured with a stress-controlled rheometer at 25 o C and 32 o C, respectively. Inorganic filler content of each impression material was measured and observed with a SEM. The molecular weight distribution of polymer matrix was determined with a gel permeation chromatography (GPC). Express and Honigum display lower flow compared to the other materials, due to their high yield-stress values. Examixfine exhibits the greatest flow. All materials display pseudoplastic behavior, excluding the Examixfine catalyst. The viscosities at low shear rate are greatest for Express and Honigum; however, under high shear conditions, the viscosities of Extrude and Honigum are the lowest. Following mixing, each material show an increase in G ’ , finally reaching a plateau, and the tanδ rapidly decreases with time. Imprint II shows the highest final G ’ as well as the most rapid decrease in tanδ. Express and Imprint II present the highest filler content and rough filler surface, while Honigum shows the lowest filler content and small filler particles. Most products are composed of polymers over 30 kDa and oligomers less than 1 kDa. Each impression material possesses different rheological properties, which significantly affect the handling characteristics. The yield stress of the impression material minimizes unnecessary flow prior to and after seating. Viscoelastic change during setting of each impression material determines the setting time and the stiffness after setting. These rheological properties of impression materials are affected by the filler content and molecular weight distribution of polymer matrix.

Evaluation of Dimensional Stability and Accuracy of Autoclavable Polyvinyl Siloxane Impression Material

Dimensionally stable autoclavable impressions will be effective in controlling the cross-infection and contamination caused by patient's saliva and other oral secretions. The accuracy of newly introduced autoclavable polyvinyl siloxane impression material was assessed for its dimensional stability and accuracy. A standard metal model (Dentoform, U-501, Columbia) was customised for impression making. The impressions were made using the newly introduced polyvinyl siloxane impression materials (AFFINIS, Coltene/Whaledent AG, 9450 Alstalten, Switzerland). Fifty impressions were made and were divided into two groups A and B of 25 each. Group A was the control sample (non-autoclaved impressions) and group B was the test sample (autoclaved impressions), which was subjected to the steam autoclave procedure at 134°C for 18min, casts were poured in type IV gypsum products. The customised metal model, casts obtained from control and test group were subjected to laboratory evaluation with help of a travelling microscope (×10 magnification), and digital vernier calliper (0.01mm/10μm accuracy). Data analysis was done using one-way ANOVA and One-Sample t test to evaluate the overall accuracy (P<0.005). As a result, there was an average reduction of 0.016μm in overall dimension between the test and the control group when compared with the master model, which is not statistically or clinically significant. The newly introduced polyvinyl siloxane impression material is accurate and dimensional stable for clinical use when steam autoclaved at 134°C for 18min.