Pressure Generated on a Simulated Mandibular Oral Analog by Impression Materials in Custom Trays of Different Design

PURPOSE: The purpose was to measure the pressure exerted under a simulated mandibular edentulous impression at different locations using commonly used impression materials and four impression tray configurations. MATERIALS AND METHODS: This study was performed using an oral analog that simulated an edentulous mandibular arch. Three pressure transducers were embedded in the oral analog-one pressure transducer in the anterior ridge area, and the other two in the right and left buccal shelves. Four configurations of custom trays were fabricated: trays with no relief, with and without holes; and trays with relief, with and without holes. The impression materials tested were light body polysulfide, light body vinyl polysiloxane, medium body vinyl polysiloxane, and irreversible hydrocolloid. The custom tray and the oral analog were mounted using a reline jig, and a Satec universal testing machine was used to apply a constant pressure of 1 kg/cm(2) over a period of 5 minutes on the loaded custom tray. Eighty impressions for the 16 groups (n = 5) were made, and pressures were recorded every 10 seconds. Factorial ANOVA and Tukey Multiple Comparison Test were used to analyze the results (p < 0.05). RESULTS: A significant difference was found in the pressure produced using different impression materials. Irreversible hydrocolloid and medium body vinyl polysiloxane produced significantly higher pressure than light body polysulfide and light body vinyl polysiloxane impression materials. The presence of holes and/or relief significantly altered the magnitude of pressure produced by irreversible hydrocolloid and medium body vinyl polysiloxane but not light body polysulfide and light body vinyl polysiloxane. CONCLUSION: All impression materials produced pressure during simulated mandibular edentulous impression making. For making mandibular edentulous impressions, low-viscosity impression materials-light body polysulfide and light body vinyl polysiloxane-are recommended. Tray modification was not important in changing the amount of pressure produced for the low-viscosity impression materials.     

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

PURPOSE: To measure the pressure exerted by maxillary edentulous impressions composed of 3 commonly used impression materials using four different impression tray configurations. MATERIALS AND METHODS: 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. 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. CONCLUSION: 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.     

Properties of the tray adhesive of an addition polymerizing silicone to impression tray materials

Adhesive bond strength studies for the tray adhesive of an addition vinyl polysiloxane (President) impression material were conducted with an acrylic resin, chromium-plated brass, and plastic trays. Tensile and shear stress studies were performed on the Instron Universal testing machine. Acrylic resin specimens roughened with 80-grit silicon carbide paper exhibited appreciably higher bond strengths compared with different types of tray material and methods of surface preparation.     

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A technique has been described for utilizing polyether interocclusal registration material in place of utility wax to form a border prior to boxing an impression. The material is simple to use, readily adheres to the impression size and shape, and can be used with polyether as well as vinyl polysiloxane impression materials. (The adhesive supplied with the vinyl polysiloxane must be used with that material.)     

Distortion of disposable plastic stock trays when used with putty vinyl polysiloxane impression materials

STATEMENT OF PROBLEM: Impressions are made using high-viscosity putty vinyl polysiloxane impression materials in conjunction with disposable plastic stock trays. The impression materials have been shown to be dimensionally stable. However, it remains unclear if the disposable plastic stock trays are rigid enough to resist deformation thus yielding potentially unreliable results. PURPOSE: This study evaluated the rigidity and ability to resist deformation of 6 commercially available disposable plastic stock trays and 1 metal stock tray when used in conjunction with a high-viscosity vinyl polysiloxane impression material. MATERIAL AND METHODS: Ten impressions were made with 1 putty vinyl polysiloxane material (Reprosil Putty) using each of the 6 tested disposable plastic stock trays, Sani-Trays (perforated), Sani-Trays (nonperforated), COE Disposable Spacer Tray (perforated), COE Disposable Spacer Tray (nonperforated), Bosworth Tray-Aways (perforated), Track-it Trays (perforated), and 1 metal stock tray (nonperforated), Cadco Dental Products, as a control on a mandibular plastic model. The dimensions of the tray in cross section at the mandibular right first molar area were measured before, during, and after the impression procedures with an electronic digital caliper. The cross-arch dimensions of the tray were measured at similar intervals. One examiner made all measurements and each measurement was repeatable within +/-0.01 mm. A split plot repeated measures analysis of variance (ANOVA) was performed and 2-sided P -values were calculated (alpha=.05). RESULTS: The results indicated that the disposable plastic trays tested were not sufficiently rigid to resist deformation when used with very high-viscosity putty material. Metal stock trays showed significantly less change in cross-arch dimension than plastic trays (F(1.68)=11.25, P =.001). Metal stock trays also showed significantly less change in cross-sectional arch dimension than plastic trays (F(1.68)=15.15, P<.001). CONCLUSION: When disposable plastic stock trays were tested in conjunction with very high-viscosity impression materials there was distortion of the tray both across the arch and in cross section.     

Rheological properties of vinyl polysiloxane impression pastes

OBJECTIVES: Some vinyl polysiloxane impression (VPS) materials are claimed to be 'thixotropic' so that they will have 'non-drip' properties and not flow off an impression tray during insertion of the material into the mouth. This work was carried out to investigate rheological properties of VPS materials by determination of their flow properties under different experimental conditions relevant to their dental application. METHODS: The rheological characteristics of each component paste of two low viscosity VPS materials were assessed by a Dynamic Stress Rheometer using cone and plate geometry. RESULTS: Both pastes of one product (Imprint II) showed a yield stress of around 40 Pa in addition to some degree of true thixotropy. In contrast, both Examix pastes had no yield stress value, but the catalyst paste was markedly thixotropic, as shown by a drop in viscosity as a result of application of shear force over time. Both products had thixotropic properties. The Imprint II in addition showed a yield stress that would also contribute to the 'non-drip' properties. SIGNIFICANCE: Combination of yield stress and thixotropy will prevent the undesirable drip of the materials once it has been injected around the tooth preparation until the impression tray is loaded and seated. After seating the tray, a thixotropic material will not flow.     

An evaluation of three implant level impression techniques for single tooth implant

This laboratory study investigated the hypotheses that there is no difference between three implant level impression techniques using vinyl polysiloxane impression material. The tested techniques were 1)- the repositioning technique. 2)-The pickup technique. 3)- The pickup technique with the impression copings splinted to the impression trays with autopolymerising acrylic resin. The Reflex Microscope was used for 3D measurement of distances and angles. Analysis of variance and Tukey's multiple comparisons test were applied to analyse the data. The results showed significant differences in implant analogue position with the repositioning and the pickup (unsplinted) impression techniques from the master model. Alarming rotational errors were recorded with the repositioning and the pickup (unsplinted) techniques. However, connecting the impression coping to the impression tray improves the accuracy of the pickup impression technique.     

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 5 mm/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.     

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 × 20 mm) 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.     

A retrospective comparison of two definitive impression techniques and their associated postinsertion adjustments in complete denture prosthodontics

PURPOSE: To compare the number of postinsertion adjustment visits required by edentulous patients whose dentures were made from border-molded definitive impressions using modeling plastic impression compound (traditional technique) with patients whose dentures were made from border-molded definitive impressions using heavy-body vinyl polysiloxane impression material. MATERIALS AND METHODS: In this retrospective clinical study, 78 patients were treated with the traditional technique (custom impression trays border molded with gray modeling plastic impression compound) and 78 were treated with the modified technique (custom impression trays border molded with heavy-body vinyl polysiloxane impression material). In both techniques, definitive wash impressions were made with light-body vinyl polysiloxane impression material. Postinsertion visits were quantified for 1 year after the dentures were inserted. RESULTS: The average number of adjustment visits for patients treated with the traditional technique was 2.68. The average number of adjustment visits for patients treated with the modified technique was 2.68. The data were compared using Student t tests. There was no significant difference in the number of adjustments required for patients whose dentures were made with either technique (t = 0.000, p = 1.00). There was no significant difference in the number of post-insertion visits required by patients from either population. CONCLUSIONS: Within the limitations of this clinical study, border-molding custom denture impression trays with vinyl polysiloxane impression material provided similar results in terms of postinsertion visits for one year as compared to dentures made from impressions border molded with modeling plastic impression compound.     

Determining the accuracy of stock and custom tray impression/casts

SUMMARY A study was conducted to evaluate the accuracy of casts made from stock tray and custom tray impressions using polysiloxane impression material. The results indicate that all casts distort but that impressions made from custom trays were more accurate and consistent in reproduction than were stock tray impressions.     

Accuracy of casts generated from dual-arch impressions

STATEMENT OF PROBLEM: Dual-arch trays are often used to make simultaneous impressions of a prepared tooth and the opposing teeth. Many dentists are concerned with the accuracy of the casts generated from this type of impression. PURPOSE: The purpose of this investigation was to compare the accuracy of stone casts of a prepared tooth generated using 2 types of dual-arch impression tray/impression material combinations. MATERIAL AND METHODS: The maxillary left first molar on a dentoform mounted on an articulator was prepared for a full-coverage gold crown. Ten impressions were made with either a plastic (P) or metal (M) tray and a polyether (PE) or vinyl polysiloxane (VPS) impression material. Each impression was cast in improved dental stone, and the buccolingual dimension of the die was measured at the midpoint of the buccal and lingual gingival margins. The prepared tooth (T) served as the control. The data were analyzed using a 2-factor analysis of variance (ANOVA) alpha=.05. RESULTS: The P/VPS combination (10.673 mm) produced the largest die, followed by P/PE (10.602), T (10.508), M/PE (10.484), and M/VPS (10.472). The 2-factor ANOVA showed a significant difference between the tray types but not between the impression materials. CONCLUSION: The metal trays produced dies smaller than the tooth, and the plastic trays produced dies that were larger.     

The effect of different adhesives on vinyl polysiloxane bond strength to two tray materials

STATEMENT OF PROBLEM: 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. Universal adhesives for vinyl polysiloxane (VPS) are used in practice, but comparative bond strengths have not been reported. PURPOSE: The aim of this study was to evaluate the bond of 3 VPS materials with a methylmethacrylate autopolymerizing and a light-polymerizing tray material, using the adhesive recommended by the manufacturer of the impression material, and 2 universal adhesives (paint-on and spray-on). MATERIAL AND METHODS: Ten specimens per group, for a total of 180 flat 15 x 15 x 20-mm specimens, were made from the 2 tray materials and finished to 320 grit with silicon carbide paper. Four paint-on adhesives (Coltene, Caulk, Kerr VPS, or universal VPS) and 1 spray-on adhesive (Sili Spray) were applied and dried following manufacturers' instructions or for 10 minutes. Three impression materials, Affinis, Aquasil, and Take I, were automixed and injected into a perforated cylinder positioned in a universal testing machine. Tray specimens were positioned against the open cylinder end in contact with the VPS material. Tensile tests (cross-head speed 5 mm/min) were conducted until adhesive separation failure. Mean values and standard errors of the adhesive strength were recorded in MPa for each material combination. Data were first analyzed with Welch analysis of variance (ANOVA) to determine overall significance, and then with a 3-way ANOVA and the Tukey HSD test to make pairwise comparisons, with alpha=.05 for all testing. RESULTS: For all impression materials tested, the universal spray-on adhesive consistently demonstrated significantly lower bond strengths than all other adhesives (P<.05). Equivalent or significantly (P<.05) higher bond strength values were found for the universal paint-on adhesive for the 3 impression materials tested. CONCLUSION: The use of GC paint-on universal adhesive provided significantly higher adhesive values than those obtained with the adhesives supplied by the manufacturers of the impression materials tested, with the exception of the Kerr impression and adhesive material combination where no significant differences were found.     

Peel bond strength between 3D printing tray materials and elastomeric impression/adhesive systems: A laboratory study

ObjectivesThe present study aimed to evaluate the bonding between three 3D printed custom tray materials and three elastomeric impression/adhesive systems using the peel test.MethodsTest blocks were 3D printed by three different technologies using Dental LT, FREEPRINT tray, and polylactide (PLA) tray materials. The reference test blocks were conventionally fabricated with Zeta Tray LC, a light-curing resin. The surface topographies of the four tray materials were investigated by scanning electron microscopy (SEM) analyses and roughness measurements. The peel bond strength between the four tray materials and three impression/adhesive systems, vinylsiloxanether (VSXE), vinyl polysiloxane (VPS), and polyether (PE), was measured (n = 12 per group). The peeling failure modes and rupture sites were identified microscopically.ResultsThe four tray materials featured different surface topographies. The peel bond strength was not significantly different with VSXE and PE, but PLA and the reference showed higher peel bond strength with VPS than the Dental LT and FREEPRINT tray (p < 0.05). The rupture site of adhesive failure in all groups was partly at the adhesive-impression material interface and partly within the adhesive but never at the adhesive-tray material interface.SignificanceThe 3D printed tray materials can achieve satisfactory chemical compatibility with the adhesives of VSXE, VPS, and PE. Surface topographies generated by the 3D printing technologies may affect bonding. Generally, 3D printed tray materials can provide clinically adequate bond strength with the elastomeric impression/adhesive systems. PLA is recommended for bonding with VPS when severe impression removal resistance is detected.     

Using the neutral zone to obtain maxillomandibular relationship records for complete denture patients

A technique for obtaining maxillomandibular registration for complete denture patients is presented. The maxillary rim is formed with the use of conventional techniques. The mandibular rim is made from modeling plastic impression compound on a record base formed by the patient into the neutral zone. The mandibular rim then is reheated, and the patient determines the occlusal vertical dimension by swallowing. An imprint of the maxillary rim is made on the mandibular rim at the occlusal vertical dimension. The posterior extent of the mandibular rim is relieved 1 mm. Orientation notches are placed in both rims, and centric relation is recorded with a fast-setting vinyl polysiloxane material.     

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.     

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.     

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.     

A functional open-tray impression technique for implant-retained overdenture prostheses

Several implant impression techniques with different materials have been described in the literature. Generally, border molding, functional, and final impressions have been made with 3 different materials, which makes the procedure technique-sensitive and time-consuming. A combination of open-tray and functional impression techniques is described in this technical report. Border molding and functional impression procedures are made at the same time using a vinyl polysiloxane impression material, which makes this technique a simple and time-efficient alternative for clinicians.     

Direct pressure provisionalization technique: a new open-tray technique for complete-arch rehabilitations.

An innovative direct technique that improves the accuracy of provisional acrylic resin restorations is introduced. A custom impression tray is modified to facilitate complete occlusal closure. This open tray is used to make an accurate overimpression prior to beginning tooth preparation procedures. Following tooth preparation, the acrylic resin-filled overimpression is returned to its intraoral position, and the patient occludes into the previously indexed impression material. The pressure overimpression technique is offered as an expedient technique for improving the accuracy of provisional restorations.