Polysulfide Impression Material Research Articles

Elastomeric impression materials used in modern orthopedic dentistry

This article presents a review of elastomeric impression materials currently used in orthopedic dentistry. The elastomer group is divided into silicone, polyester, and thiocol (polysulfide) materials. Silicone impression materials are widely used in orthopedic dentistry. Their structural basis is polymethylsiloxane with active terminal hydroxyl groups. Polyester materials consist of the main and catalyst components (pastes). The main component contains a polymer with imine groups, fillers, and plasticizers. Sulfonic acid ester is present in the catalyst paste. When these two components are mixed, ionic (cationic) polymerization occurs. Polysulfide materials are produced as base and catalyst pastes. The structural unit of the main paste is polysulfide or mercaptan rubber, and the catalyst paste acts as an oxidizer. Lead dioxide is often used as an oxidizer. The resulting polymer does not have a stereoregular structure, which causes its stickiness. It is technologically challenging to obtain a polymer with a stereoregular structure.
 When theoretically comparing the listed types of elastomeric impression materials, according to their properties, chemical composition, advantages, and disadvantages, polyester and polysulfide impression materials can be distinguished as more advanced. Silicone materials have disadvantages; however, they are often used for domestic dentistry owing to the presence of domestic manufacturers and relatively low cost.

Three-dimensional differences between intraoral scans and conventional impressions of edentulous jaws: A clinical study

Statement of problemUsing intraoral scans for removable dentures has been questioned because of a suggested lack of accuracy. However, data regarding the accuracy of digital intraoral complete-arch scans are sparse, present some methodological issues, and mostly come from in vitro studies on dentate casts, which are very different from edentulous arches. PurposeThe purpose of this clinical study was to evaluate 3D differences between intraoral scans (IOS) and conventional impressions of edentulous arches by means of digital analysis. Material and methodsTen maxillary and 10 mandibular edentulous arches were investigated. For each of them, IOS was performed, and a custom tray was digitally designed based on these scans. Trays were built by using a 3D printer and used to make a conventional impression with a polysulfide impression material. The conventional impression was scanned immediately by using the same intraoral scanner and by the same dentist. Standard tessellation language (STL) files of IOS and the scans of the corresponding conventional impressions (CIS) were superimposed with a 2-phase best-fit alignment in a reverse engineering software program. The corresponding full-scan, 3D mean distance was measured. This procedure was repeated after trimming the IOS and CIS to eliminate peripheral areas not present in both files, as well as nonmatching areas caused by practical aspects related to obtaining the IOS (mobile tissue stretching) and the conventional impressions (mobile tissue compression and folding at the margin of impression), which could have impaired alignment and, consequently, measurement accuracy. The mean distance between the full and trimmed IOS and CIS was statistically investigated, and subgroup analysis was performed for the maxillary and mandibular arches. The statistical significance of the differences between the 2 impression methods was also investigated. ResultsThe full-scan mean distance between the IOS and CIS (−0.19 ±0.18 mm) was significantly different from that of the trimmed scan mean distance (−0.02 ±0.05 mm), with no significant differences for maxillary and mandibular arches. The differences between the IOS and CIS were statistically significant for full scans; they were not significant for trimmed scans, except for the maxillary subgroup. ConclusionsThe mean distance between the IOS and CIS may be significantly different if they are not properly superimposed. The mean distance (−0.02 ±0.05 mm) between the IOS and CIS falls within the range of mucosa resilience. Thus, 3D differences between the IOS and CIS can be attributed to the different physics behind the 2 impression methods and not to defects in accuracy of one method compared with the other. The size of the measured difference between the 2 impression methods was not statistically significant and was not clinically significant for removable denture fabrication.

A Comparative Study to Determine the Wettability and Castability of Different Elastomeric Impression Materials

The aim of this study was to determine the wettability of different hydrophilic and hydrophobic elastomeric impression materials and the gypsum castability. The wettability was evaluated by determining the contact angles of different elastomeric impression materials. The contact angle was determined by placing a drop of aqueous solution of calcium sulfate dihydrate on the flat surface of impression material and specimens were measured using a profile projector. Gypsum castability was determined by counting the number of voids formed in the die stone cast made from the impressions of a aluminum die. The voids were counted using an diopter magnifying lens. Polyether, different viscosities of polyvinyl siloxane, and condensation silicone impression materials exhibited low contact angle values and least number of voids in the die stone cast when compared with polysulfide impression material. There was significant correlation between the contact angle and voids formed in the die stone casts when fabricating die stone casts from various elastomeric impression material impressions. Accurate reproduction of prepared tooth or edentulous arch is of clinical importance in the fabrication of a fixed or removable prosthesis. Inaccuracies in the replication processes will ultimately have an adverse effect on the fit and adaptation of final restoration. The interaction is determined in part by hydrophilic and hydrophobic nature of the elastomeric impression material. Inadequate wetting of an impression results in voids in the stone casts.

Influence of root embedment material and periodontal ligament simulation on fracture resistance tests

The aim of this study was to evaluate the influence of the embedment material and periodontal ligament simulation on fracture resistance of bovine teeth. Eighty bovine incisor teeth were randomized into 8 groups (n = 10), embedded in acrylic or polystyrene resin using 4 types of periodontal ligament simulation: 1--absence of the ligament; 2--polyether impression material; 3--polysulfide impression material; 4--polyurethane elastomeric material. The specimens were stored at 370C and 100% humidity for 24 hours. Specimens were submitted to tangential load on the palatal surface at 0.5 mm/minute crosshead speed until fracture. The fracture modes were analyzed as follows: 1--coronal fracture; 2--cemento-enamel junction fracture; 3--partial root fracture; 4--total root fracture. Statistical analyses by two-way ANOVA and Tukey's test were applied (p < 0.05). The results showed that root embedment method and periodontal ligament simulation have a significant effect on fracture resistance. Artificial periodontal ligament modified the fracture modes.

Pressure generated on a simulated oral analog by impression materials in custom trays of different designs

To measure the pressure exerted by maxillary edentulous impressions composed of 3 commonly used impression materials using four different impression tray configurations. The study was performed using an oral analog that simulated an edentulous maxillary arch. Three pressure transducers were imbedded in the oral analog, 1 in the mid-palate area and the other 2 in the right and left ridge (maxillary first premolar areas). Custom trays of 4 different configurations were fabricated. The 3 impression materials tested were irreversible hydrocolloid, light-body and medium-body vinyl polysiloxane, and polysulfide. A total of 128 impressions were made. The custom tray and the oral analog were mounted using a reline jig. A Satec universal testing machine was used to apply a constant pressure of 2 kg/cm(2) over a period of 5 minutes on the loaded custom tray. The pressure was recorded every 10 seconds. Factorial analysis of variance and Tukey's multiple comparison test were used to analyze the results. A significant difference in the pressure produced using different impression materials was found (p < or =0.001). Irreversible hydrocolloid and medium-body vinyl polysiloxane produced a significantly higher pressure than light-body vinyl polysiloxane and polysulfide impression materials. The presence of holes and/or relief did not significantly alter the magnitude of pressure. All impression materials produced pressure during maxillary edentulous impression making. Tray modification was not important in changing the amount of pressure produced. The impression materials used had more effect on the pressure produced during impression making on the simulated oral analog.

Sectional impressions for mandibular distal extension removable partial dentures

Statement of problem. Corrected impression procedures provide the best possible support to be gained from an edentulous ridge for a removable partial denture, but they are time-consuming and technique sensitive. Purpose. An experimental mandibular distal extension removable partial denture was used to measure the vertical movement of denture bases during biting. Material and methods. Five patients participated for whom vertical movement of denture bases was measured by comparing the thickness of plaster interocclusal records made with the denture at rest and under biting pressure. Denture bases were processed on master casts formed from final impressions made in full arch custom trays. Secondly, bases were readapted using sectional relining impressions with the same regular body polysulfide impression material. Results. Statistical analysis of the vertical movement of denture bases during biting at 4 points on the right and left denture bases showed a significant decrease in vertical movement with sectional impression. The reduction was less than a 0.1 mm, a result that questions the routine use of sectional impression for every distal-extension mandibular removable partial denture. Conclusion. Supportive form of distal-extension edentulous ridges can be recorded successfully by full arch impressions in custom trays. (J Prosthet Dent 1998;80:216-9.)

The effect of tray material and surface condition on the shear bond strength of impression materials

This study compared the adhesive shear bond strength of three selected impression materials with that of thermoplastic and acrylic resin tray materials as a function of surface preparation. Polyether (Impregum), polyvinylsiloxane (Reprosil), and polysulfide (Permlastic) impression materials were evaluated on smooth, rough, and contaminated tray surfaces. Smooth surface samples were formed against glass and served as the control groups. Experimental groups consisted of samples contaminated with artificial saliva and rough surface samples that were abraded with 110 microns of Al203. A total of 126 samples were subdivided into 18 groups of seven specimens each. Each sample consisted of a 1 inch square, 3 mm thick mass of an impression material sandwiched between the prepared surfaces of a pair of resin plates. Each specimen was tested in a universal testing machine for adhesive shear bond strength. Data were analyzed with three-way analysis of variance and Scheffe's test. The results indicated that the thermoplastic resin material had better adhesive properties than the acrylic resin. For both tray materials mean adhesive shear bond strengths for Impregum and Reprosil were significantly greater than those of Permlastic. Tray surface contaminated with saliva decreased the adhesive shear strength at the tray adhesive impression interface.

Proportioning effect on physical and chemical properties of polysulfide impression material

This study investigated the effect of variation in proportioning polysulfide base and catalyst. Light, regular, and heavy-bodied pastes were mixed in linear equivalents of base-to-catalyst proportions of 30 70 , 40 60 , 50 50 , 60 40 , and 70 30 . Compression set, strain in compression, and consistency tests conformed to the American Dental Association (ADA) Specification 19 guidelines. The amount of solvent-leachable components and differences in the cross-linked nature of the cured products were studied. Compression set and strain in compression tests met the ADA specification guidelines. Some consistency values fell outside of the ADA specification limits. The leachable content increased with increasing proportions of catalyst, but polymer cross-linking was remarkably similar for all bodied materials tested. Clinicians need not fear a significant property alteration in polysulfide impression material by the differences (within ±20% of the manufacturer's suggested lengths) in proportioning the component pastes with “eyeball” estimation as directed in the instructions.

Evaluation of polycaprolaitone custom tray material.

Custom impression trays are necessary for accurate impressions in fixed prosthodontics when using polysulfide impression materials. These custom impression trays are needed to provide for a uniform thickness of impression material to minimize distortion. Custom impression trays have historically been made from acrylic resin. New materials have been developed as alternatives to acrylic resin, and this study evaluates one product currently available that is composed of polycaprolaitone. This study evaluates the modulus of elasticity of polycaprolaitone as compared with acrylic resin, and also evaluates the amount of permanent deformation of the new material when placed under a load. The elastic modulus of polycaprolaitone was tested using three-point bending of specimens placed in a universal mechanical test system. The elastic modulus of the new material was found to be significantly lower than that of acrylic resin. The next test evaluated the amount of permanent deformation of the polycaprolatione material when specimens approximating the shape and size of custom impression trays were placed under a load. These trays were placed in a universal mechanical test system and differing loads were placed on them. Results showed that although the trays deformed at relatively low loads, all deformation was fully recovered within a clinically insignificant period of time (less than 30 seconds). From these experiments it was concluded that although the polycaprolaitone material has a lower modulus of elasticity and will deform under relatively low loads, the material recovers completely, and thus the deformation would not interfere with the clinical performance of polycaprolaitone as a custom tray material.

Preventing distortion of removable partial denture frameworks during deflasking process

The opinions or assertions contained herein are the private views of the author and are not to be construed as of??cial or as reflecting the views of the United States Army, or the Department of Defense. aLieutenant Colonel, U.S. Army, DC. 10/4/38202 Dent-Kote (Dentsply International, York, Pa.) around clasps and minor connections that are subject to distortion when the waxed partial denture is ready to flask. The elastomer should not completely encircle the clasps and minor connectors, because this might complicate removal of the elastomer. Contraindicated materials are: polysulfide impression materials (because of the stain and odor imparted to acrylic resin), polyethers, and monophasic addition silicone impression materials, which have relatively high rigidity.

The bond strength of elastomer tray adhesives to thermoplastic and acrylic resin tray materials

This study evaluated the bond strength of selected impression materials (Permlastic, Express, and Hydrosil) to a thermoplastic custom tray material as a function of drying time of the adhesive after application to a tray material. In addition, bond strengths of a polysulfide impression material to an acrylic resin tray material and to a thermoplastic tray material made directly against wax were evaluated. Bond strengths were obtained directly from values of applied load at failure and important conclusions were drawn.

Adhesive properties of several impression material systems: Part I

The tensile adhesive bond strength of five impression adhesive systems was studied: polysulfide, polyether, polyvinylsiloxane, condensation silicone impression, and polyvinylsiloxane putty adhesive systems. Results showed no significant difference in adhesive bond strength to autopolymerizing acrylic resin between the former four impression materials studied. Polyether and medium-viscosity polyvinylsiloxane demonstrated significantly higher adhesive bond strength to polystyrene than either polysulfide or condensation silicone. The medium-viscosity polyvinylsiloxane impression material showed significantly higher adhesive bond strength to polystyrene than autopolymerizing acrylic resin whereas polysulfide and condensation silicone impression materials adhered significantly better to autopolymerizing acrylic resin than polystyrene. The polyvinylsiloxane putty did not adhere to its impression adhesive. Variation of the speed of tensile testing between 5 to 20 inches per minutes did not affect the adhesive bond strength of a polysulfide impression material.

An effect of tray design and material retention on the linear dimensional changes in polysulfide impressions

One-unit fixed partial dentures, which fit accurately on the laboratory dies made from polysulfide impression materials, often pose a problem in seating completely in the mouth of the patient. Sectioning of the fixed partial denture units allows the individual units to seat accurately in the mouth but requires a soldering procedure. Linear distortion of the mercaptan (polysulfide) rubber base that takes place during setting is a cause of this problem. The distortion is directly related to (1) tray design, (2) area of adhesive placement, and (3) excessive bulk of material on the tray border during impression making. A controlled amount of adhesive and impression material in a new design for a custom tray must be used to minimize this distortion. When these factors are controlled, the resulting impression is unrestricted, and a more accurate working die is obtained. This results in a better fit of one-unit fixed partial dentures in the mouth.

Mold inversion and abrasion resistance of a Type IV stone

The objective of this study was to determine whether placing the impression and diestone so the impression is on the top during setting affects the resulting die's abrasion resistance. Impressions of a brass bar with a milled 90° edge were obtained by use of a polysulfide impression material in a rigid brass tray. A Type IV diestone was vacuum-mixed and vibrated into the impression. Eight procedures were compared: (1) no inversion; (2) inversion at initial set; (3,4) inversion one or two min before initial set; and (5,6,7,8) inversion 1.5, 3, 5, or 12 min after initial set. Each specimen was abraded 24 hours after mixing. Specimens inverted at 1.5 and 3 min after initial set were significantly more abrasion-resistant than were all other treatments.

Comparison of some properties of polyether and polysulfide materials

Based on the present measurements on working time, setting time, and compression set of polyether and polysulfide materials, the following observations were made: 1. The manufacturer recommends a working time for polyether that is approximately 40 seconds more than that indicated by the clinical or ADA test. 2. Clinically, if more working time is desired, polysulfide impression material should be used. 3. Polysulfide material is more sensitive to temperature change than the polyether material. 4. If the material is allowed to set longer, the percentage change in compression set decreases. 5. For polyether, an increase in setting time of 2 minutes will significantly reduce the distortion of the impression upon removal.

Evaluation of a rubber-base impression material

A laboratory experiment has been described that utilized materials found in most dental offices and that was designed to evaluate a distinctly different polysulfide impression material. In this experiment the largest duplicating errors were produced with use of the stock tray and single-mix technique recommended by the manufacturer. This study therefore supports the use of the custom tray and double-mix technique for dental duplication procedures utilizing Neo-Plex impression material. Further investigation is necessary before stock trays and single-mix techniques can be recommended for routine use in fixed prosthodontics.

Dental plaque morphology as revealed by direct observation and by replicating techniques

The ability of four elastomer impression materials to reproduce details of bacterial plaque structures was studied by comparing areas of the replica models with corresponding areas of the replicated plaque. Plaque was grown on hydroxyapatite splint segments for 48 hours and replica models were made from three different resins. One of the resins, a methacrylate material, was not suited for this purpose due to its content of spherical particles. The polysulfide and polyether impression materials reacted with the heat curing epoxy resin, and less satisfactory results were obtained with cold curing epoxy resin. Best results were obtained by a combined use of low viscosity silicone impression materials and cold or heat curing epoxy resins as model materials. However, a considerable loss of detail occurred in the replica models compared with observations of plaque directly on splint surfaces. Outlines of individual bacteria could sometimes be seen in the models, but generally several cells seemed to fuse, and appeared like small globular structures where cells and pellicle were difficult to distinguish. The bacterial colonization started near the gingival border of the surface, initiated by attachment of individual bacteria to the pellicle surface.

The contact angles of die stone on impression materials

0 bservations in the clinic at the Medical College of Georgia, School of Dentistry, indicated that certain impression materials appeared to yield casts that contained more entrapped air bubbles than appeared with other impression materials when the same die stone was used. As a result of these observations, an investigation was performed to determine the advancing contact angle of die stone on silicone, polysulfide, polyether, and colloidal impression materials. The rationale of this approach is that if the die stone forms an advancing contact angle with the impression material approximating or greater than 90 degrees, there is a high probability for entrapment of air bubbles during the pouring of the impression. If the contact angle is relatively low, there is less chance of air entrapment.