Dimensional change of impressions on sterilization

The volume of impressions, before and after disinfection in a gluteraldehyde solution for longer than ten hours (that is, sterilization), was measured indirectly from dies produced from the impressions. Three elastomeric impression materials were used in both acrylic resin and poly-vinyl-chloride 'trays' to form the impressions. One impression material appeared to be practically superior to the others with respect to variability of volume. The effect of tray material on change in volume (calculated as after disinfection minus before disinfection) was significant for one impression material; acrylic trays produced the greatest effect. The change in volume was significant for two impression materials; acrylic trays were associated with greater increase in volume. It was concluded that if impressions are to be sterilized, a tray material having minimal potential to absorb disinfectant should be used.     

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 polycaprolaitone 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.     

The effect of custom tray material type and fabrication technique on tensile bond strength of impression material adhesive systems

The purpose of this investigation was to evaluate the tensile bond strengths of two impression material systems (polysulphide and polyvinyl siloxane) to two custom tray materials [autopolymerizing and visible light-cured (VLC) acrylic resin]. The effect of polymerizing the tray materials directly against wax spacer and tin foil was evaluated for each material. Polymerizing tray materials against tin foil significantly increased the bond strengths of polysulphide and polyvinyl siloxane impression materials to VLC and autopolymerizing acrylic resin tray materials. Polyvinyl siloxane VLC cured against tin foil combination produced the strongest bond. The VLC resin tray material generated greater bond strength than autopolymerizing acrylic resin when polymerized against tin foil.     

An implant-retained auricular impression technique to minimize soft tissue distortion

Achieving adaptation of an auricular prosthesis begins with an accurate impression. It is important to consider how the selection of the impression materials will affect the final outcome of the prosthesis. A procedure is presented to minimize the distortion of the soft tissues caused by the impression materials and procedure. The procedure consists of splinting the implant impression copings, then recording the soft tissue in silicone impression material, followed by the application of acrylic tray resin to provide rigidity.     

Preliminary Impressions in Microstomia Patients: An Innovative Technique

Microstomia has been defined as an abnormally small oral orifice associated with various etiopathologic factors. Management of these patients poses extreme difficulties in every procedure during prosthesis fabrication. Restricted mouth opening of the patient makes the insertion and the removal of the tray extremely difficult. So sectioning of the existing stock tray is necessary, so that the trays can be inserted and removed in sections. The main problem encountered during this procedure is the reorientation of the tray back in position. This article presents an innovative technique for the easy handling of the sectioned stock impression trays.     

Dimensional accuracy of dental casts: Influence of tray material, impression material, and time

PURPOSE: This study evaluated the influence on dimensional accuracy of dental casts made with different types of trays and impression materials and poured at different and multiple times. MATERIALS AND METHODS: Two types of stock trays (plastic stock tray, perforated metal stock tray) and 4 types of custom tray materials (autopolymerizing acrylic resin, thermoplastic resin, and 2 types of light-polymerized acrylic resins) were used with 2 types of impression materials (addition polymerizing silicone and polyether), to make impressions of a metal master model. Each tray and impression material was used to make 5 impressions. Casts were made by multiple pourings at 30 minutes, 6 hours, 24 hours, and 30 days after impression making. Using a measuring microscope, 12 distances were calculated based on measurements of 8 reference points. The absolute value of the difference of each measurement was calculated, as was the corresponding measurement on the master model. A Bayesian model using a simple noninformative prior was used to analyze these data. RESULTS: Statistical differences within 6 microm were found only with thermoplastic resin tray material for addition silicone, and for thermoplastic resin tray material and 1 type of light-polymerized acrylic resin for polyether. Neither stock trays nor custom trays contributed to the differences in accuracy of the casts. All deviations in casts made with silicone impression material were within a clinically acceptable range. For the polyether, distortions occurred that were clinically unacceptable. Impressions made from polyether distorted over time. Silicone impression material has dimensional stability up to 30 days. CONCLUSION: Accurate casts can be made with either stock trays or custom trays. An impression made from polyether should be poured only once and within 24 hours after impression making, because of the distortion of the material over time. Silicone impression material has better dimensional stability than polyether. .     

Dimensional stability of autopolymerizing acrylic resin impression trays

A study was undertaken to determine the optimal interval between fabrication of an autopolymerizing acrylic resin custom impression tray and making a final impression. Twenty mandibular arch-shaped trays, 10 each of Fastray and Formatray resin, were evaluated for dimensional change. Both materials behaved similarly. Cross-arch contraction of the borders of buccal flanges and unilateral expansion of the borders of buccal-to-lingual flanges were observed. These changes indicate distortion. Linear dimensional changes occurred throughout 6 hours, which suggests that any impression made in a methyl methacrylate acrylic resin custom impression tray should be poured as soon as is conveniently possible. Significant linear dimensional changes were observed for only 40 minutes from the initiation of tray fabrication. This study concludes that while an aged tray is preferred, it is acceptable to make an impression in an autopolymerizing resin custom impression tray after 40 minutes.     

Duplication of interim speech aid for definitive impression tray fabrication.

A wax tray is stable and easily relieved if overextended. Unusual tray undercuts or angles needed for the partial resection patient need not be eliminated before the impression procedure. Relief of these undercuts is necessary with acrylic resin trays to ensure separation from the final stone cast. Because the wax tray is separated easily from the prosthesis during the boil-out, it is not necessary to "burn" or grind acrylic resin from the framework. The tray shape is duplicated from the existing interim prosthesis on the nasopharyngeal and oropharyngeal side. An arbitrarily shaped acrylic resin tray may be grossly overextended and require time-consuming clinical adjustments. An underextended tray on the nasopharyngeal side will not carry or support the impression material around or through the residual soft palate remnant. A tray that closely approximates the final prosthesis will allow use of a tissue conditioner final impression without need for border molding (Fig. 2). Duplicating the oropharyngeal side of the interim speech aid duplicates the previously established plane that is compatible with the tongue. The author has used this technique successfully for eight total and five partial soft palate resections. A cleft palate speech aid prosthesis has also been made with this technique.     

Impression technique for a complete-arch prosthesis with multiple implants using additive manufacturing technologies

This article describes an impression technique for a complete-arch prosthesis supported by multiple implants where additive manufacturing technologies were used to fabricate a splinting framework and a custom tray. The technique presented uses a shim method to control the homogenous splinting acrylic resin and impression material during the procedure, thereby reducing laboratory and chairside time and the number of impression copings and laboratory analogs needed.     

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.     

The effect of tray selection on the accuracy of elastomeric impression materials

This study evaluated the accuracy of reproduction of stone casts made from impressions using different tray and impression materials. The tray materials used were an acrylic resin, a thermoplastic, and a plastic. The impression materials used were an additional silicone, a polyether, and a polysulfide. Impressions were made of a stainless steel master die that simulated crown preparations for a fixed partial denture and an acrylic resin model with cross-arch and anteroposterior landmarks in stainless steel that typify clinical intra-arch distances. Impressions of the fixed partial denture simulation were made with all three impression materials and all three tray types. Impressions of the cross-arch and anteroposterior landmarks were made by using all three tray types with only the addition reaction silicone impression material. Impressions were poured at 1 hour with a type IV dental stone. Data were analyzed by using ANOVA with a sample size of five. Results indicated that custom-made trays of acrylic resin and the thermoplastic material performed similarly regarding die accuracy and produced clinically acceptable casts. The stock plastic tray consistently produced casts with greater dimensional change than the two custom trays.     

Dual-arch impressions

All dual-arch impression techniques utilize special stock impression trays of various designs. These trays are made of flexible plastic with fabric or mesh material placed across the occlusal surfaces of the teeth connecting their buccal and lingual flanges. The presence of this material will result in errors by (1) not allowing complete intercuspation during impression-taking; (2) producing incorrect recording of centric occlusion; and (3) because of the elastic memory of the tray/fabric, creating distortion of the elastic impression material. An impression technique is presented which provides a simple and effective method of obtaining dual-arch impressions for single restorations, post and cores, and small bridges. This technique obivates the need for impression trays thus eliminating the errors outlined.     

Modified custom tray

The use of a custom tray is highly desirable for accurate impression making in situations with multiple abutments. This article describes a modified custom tray fabrication method using autopolymerizing acrylic resin. The custom tray is fabricated by intraoral relining with autopolymerizing resin that is polymerized extraorally. The final impression is obtained during the same session after tray polymerization at 100 degrees C for 5 minutes. Relined areas are refined by trimming excess resin with burs of a known diameter to create a 2-mm clearance for the elastomer. For areas with subgingival finish lines, only 0.5 mm of resin is removed to direct the elastomer into the gingival sulcus. The procedure is time-saving because it reduces the need for a retraction cord and minimizes inaccuracies that would necessitate another impression.     

Simplified Technique for Orbital Prosthesis Fabrication: A Clinical Report

Loss of orbital content can cause functional impairment, disfigurement of the face, and psychological distress. Rehabilitation of an orbital defect is a complex task, and if reconstruction by plastic surgery is not possible or not desired by the patient, the defect can be rehabilitated by an orbital prosthesis. The prosthetic rehabilitation in such cases depends on the precisely retained, user‐friendly removable maxillofacial prosthesis. Many times, making an impression of the orbital area with an accurate record of surface details can be a difficult procedure. The critical areas are making a facial moulage, mold preparation, and attaching the retention device, particularly when eyeglass frames are used. This case focuses on these hindrance factors. A simple basket was used for the impression tray to obtain the facial moulage. A putty mold was used, and attachment of the prosthesis to a retention device was accomplished with positional distance. This method proves to be an economical and simple way of making an orbital prosthesis.     

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.     

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.     

A modified edentulous maxillary custom tray to help prevent gagging

The gag reflex can be a normal, healthy defense mechanism to prevent foreign objects from entering the trachea. During certain dental procedures, however, gagging can greatly complicate the final result, especially during the maxillary complete denture final impression. A modification can be made to the maxillary custom acrylic resin tray to aid in securing a clinically acceptable elastomeric final impression. This modification involves forming a vacuum chamber at the posterior extent of the custom tray to which a saliva ejector tip is embedded. When the saliva ejector is connected to the low-volume evacuation hose, the chamber will trap any excess impression material that might extrude from the posterior border of the loaded tray. This results in a reduced chance of eliciting the patient's gag reflex.     

The Accuracy of Six Impression Techniques for Osseointegrated Implants

Purpose Six impression techniques were evaluated using tapered and square impression copings. Materials and Methods The absolute distortion was measured using a cast metal impression tray with fiduciary reference points external to the impression material. Measurements of the x, y, z coordinates on the master cast and the impressions were directly made with a travelling digitizing microscope. The difference between the coordinates of each of six sites in the impression and the corresponding reference site were compared. Results There was no significant difference between the techniques for the square copings but that there was a significant loss of accuracy in the z-axis with the tapered copings. Conclusions No significant differences were noted.     

Impression material thickness in stock and custom trays

This study did not examine the accuracy of the resultant impressions. Rather, the impression material thickness in impressions made using both the highly advocated custom acrylic resin tray and in the highly used manufactured stock tray was examined. Comparison between the material thickness at the prepared tooth area revealed a mean difference in material thickness of less than 1 mm. The question of the significance of this difference remains to be answered. If the difference is not significant in the success of the impression and the resultant casting, then there are several advantages in using the manufactured stock tray; the first is economy. The average cost of a custom acrylic full arch impression tray is $3.65, compared with an average cost of slightly over $0.30 for the stock tray. The second advantage is the convenience factor. Making a custom tray requires planning, study models, laboratory time, curing interval, and finishing time. In contrast, the stock tray can be selected, adapted, and used in a single visit for both anticipated and unanticipated situations. If the difference in material thickness is significant, the custom tray is indicated. However, attention to detail in making and inserting the tray in the mouth must be observed to maximize the benefits of the custom tray.     

托盘粘接剂对藻酸盐印模材料与三种不同材料托盘间粘接强度的影响

目的研究托盘粘接剂对藻酸盐印模材料与不同材料托盘间粘接强度的影响。方法选择自凝树脂、光固化树脂和不锈钢3种托盘材料,每种材料分2组,一组涂布粘接剂,另一组不涂布粘接剂作为对照,总计6组,每组8个试件。采用藻酸盐通用型粘接剂以及临床常用的藻酸盐印模材料,装置在万能测力仪上进行拉力测试,所得数据用SAS软件进行统计分析。结果研究结果显示所有托盘材料中,应用托盘粘接剂组具有更高的粘接强度（P〈0．01）。不同托盘材料对粘接强度的影响具有统计学意义（P〈0．01）。结论在托盘表面应用粘接剂能改善印模材料和托盘的粘接强度,涂布粘接剂前后不锈钢材料托盘的粘接强度均大于树脂。