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At least 199 records · Page 11Linked to original sources
PubMed1995

Ability of various impression materials to produce duplicate dies from successive impressions.

This in vitro study evaluated the ability of five different impression techniques to make duplicate dies of two different types of tooth preparation. One mandibular second premolar Ivorine tooth was prepared for a complete crown and one for an onlay. A master impression was made of each tooth preparation with the use of five impression techniques for a total of 10 master impressions, and a master die was made from each of these impressions. Castings were made on these master dies, and the fit of each casting was verified on the respective Ivorine tooth. Marginal openings of the castings on the master dies were recorded under magnification at four predetermined points. Five successive impressions, with the use of each impression material, were then made of each tooth preparation for a total of 50 test impressions, and 50 test dies were made from these impressions. The fit of the respective casting was evaluated under magnification for each test die at the four predetermined points, and marginal openings were recorded. Differences between the marginal discrepancies of the casting on the master die and on the test die were tabulated and the results were statistically analyzed. Results indicated that none of the impression materials was capable of producing exact replicas. Polysulfide rubber performed significantly better than two materials for the production of duplicate dies with the complete crown preparation; and polyvinyl siloxane used with a putty-light body, single-stage technique produced mean marginal discrepancies that were significantly greater than the other four techniques when used for the onlay preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Bicuspid↗
PubMed1990

[Measuring the accuracy of various elastomeric impression materials using a CNC coordinate measuring device (Part 1)].

This study compares the accuracy of 23 impression materials. With each material seven impressions of a stainless steel master die were taken under standardized conditions. Characteristical dimensions of the master die and of the stone dies as well were determined by means of a CNC coordinate measuring device. Differences in prepared tooth heights ranged between -36 and +19 microns. The occlusal distances between prepared teeth were 2 to 54 microns greater on the stone dies than on the master die. Diameters differed by -89 to +52 microns. The two phase impressions tended to result in stone dies of reduced size, whereas single phase and double mix impression techniques produced larger stone dies than the master die.

Dental Impression Materials↗
PubMed1995

Tensile bond strength of polyvinyl siloxane impressions bonded to a custom tray as a function of drying time: Part I.

Time-dependent bond strength studies of two polyvinyl siloxane impression materials to acrylic resin disks with their respective adhesives were studied to determine the optimal time for maximum bond strength. Six groups were tested with varying adhesive dry times of 0, 7, 15, and 60 minutes and 8 and 24 hours before testing. The results indicated that the bond strength of the adhesive increased at least twofold from time zero to 7 minutes adhesive dry time and peaked at 60 minutes for one of the materials and at 8 hours for the other. Bond strengths increased rapidly to the 15-minute test interval and then seemed to plateau. Both materials exhibited decreased adhesive bond strengths at 24 hours.

Acrylic Resins↗
PubMedDate not supplied

Accuracy of 2 impression techniques for ITI implants.

PURPOSE: The aim of this study was to compare the accuracy of casts produced by 2 impression techniques and elastomeric impression materials commonly used for the fabrication of implant-supported fixed prostheses. MATERIALS AND METHODS: A master model with 4 synOcta ITI implants placed unilaterally in place of the mandibular right central incisor, canine, first premolar, and first molar was constructed. Implant-level impressions were made by direct and indirect techniques. In the direct technique, synOcta impression caps with integral guide screws were used to transfer the implants using a custom-made acrylic resin tray and a polyether impression material (the PE direct technique). In the indirect technique, synOcta plastic positioning cylinders with impression caps were used to transfer the implants with either a custom-made acrylic resin tray and polyether impression material (the PE indirect technique) or with a stock tray with a vinylpolysiloxane impression material (the VPS indirect technique). After impression making, all casts (n = 21) were poured in type IV dental stone. Linear changes in -x or -y direction and numeric and descriptive angular changes between the implants were quantified using a coordinate measuring machine. RESULTS: Seven of 12 distance measurements (6 for -x direction, 6 for -y direction) showed differences between groups (P < .05). Of these, 5 were associated with the PE direct versus PE indirect and PE indirect versus VPS indirect, and 3 were associated with PE direct versus VPS indirect. Two implants also showed angular changes but only for the PE indirect technique versus the VPS indirect technique (P < .05). CONCLUSION: The snap-on VPS indirect impression technique using a stock tray, which has the advantages of being clinically convenient and eliminating repositioning after removal of the impression, resulted in dimensional accuracy similar to that achieved with the PE direct technique.

Dental Implants↗
PubMed2000

Dimensional changes and pressure of dental stones set in silicone rubber impressions.

OBJECTIVES: A high expansion stone has been used for improving the adaptation of dentures. Although the method is based on the idea to compensate for the processing shrinkage of the denture base resin with the high expansion stone, there are few studies on the expansion behavior of stones in an impression. The purpose of this study is to clarify the dimensional changes of stones set in silicone rubber impressions using two types of impression tray. METHODS: Impressions of a master model that represents the alveolar ridge were taken using a silicone impression material and the dimensional changes in the stone casts were measured in different directions (x, y and z-axes). Two types of impression tray were used, one with an open surface and the other with a closed surface. In order to evaluate the setting expansion of the stones and the pressure against the impression, stones were poured in other impressions that were taken from a cubic master model. The thickness of the impression was set at 2 mm. RESULTS: A statistical analysis showed that there were significant differences in the dimensional change in the vertical direction (z-axis) and horizontal directions (x- and y-axes) of any stone casts set in the open tray. However, there were no significant differences in the dimensional changes in any direction of each stone cast set in the closed tray. SIGNIFICANCE: The impression tray influences the setting expansion of stones. Stones do not uniformly expand in the open tray and the dimensional changes in the stone casts in the three-dimensions increases, when used with a high expansion stone.

Alveolar Process↗
PubMed2004

Evaluation of transfer impressions for osseointegrated implants at various angulations.

The accuracy of impressions that transfer the relationship of the implant to the metal framework of the prosthesis continues to be a problem. This study was designed to evaluate the accuracy of the transfer process under variable conditions with regard to implant analog angulations, impression materials, and techniques. Replicas (n = 60) of a metal matrix (control) containing four implants at 90 degrees , 80 degrees , 75 degrees , and 65 degrees in relation to the horizontal surface were obtained by using three impression techniques: T1-indirect technique with conical copings in closed trays; T2-direct technique with square copings in open trays; and T3-square copings splinted with autopolymerizing acrylic resin; and four elastomers: "P"-polysulfide; "I"-polyether; "A"-addition silicone; and "Z"-condensation silicone. The values of the implant analog angulations were assessed by a profilometer to the nearest 0.017 degrees , then submitted to analysis of variance for comparisons at significance of 5% (P < .05). For implant analog at 90 degrees , the material "A" associated with T2 and material "Z" with T3 behaved differently (P < .05) from all groups. At 80 degrees , all materials behaved differently (P < .01) with T1. At 75 degrees , when T1 was associated, materials "P" and "A" showed similar behavior, as well as materials "I" and "Z"; however, "P" and "A" were different from "I" and "Z" (P < .01). When T3 was associated, all experimental groups behaved differently among them (P < .01). At 65 degrees , the materials "P" and "Z" behaved differently (P < .01) from the control group with T1, T2, and T3; the materials "I" and "A" behaved differently from the control group (P < .01) when T1 and T2, respectively, were associated. The more perpendicular the implant analog angulation is in relation to the horizontal surface, the more accurate the impression. The best materials were material "I" and "A" and the most satisfactory technique was technique 3.

Dental Casting Technique↗
PubMedDate not supplied

Issues in handling impression materials.

Implant restorations require extreme accuracy since the implants are rigidly fixed. Although impression materials can be highly accurate, small inaccuracies are acceptable because the periodontal ligament allows for tooth movement. This luxury is not available with implants. A problem is the rotation of direct impression copings and distortion of interabutment positions in the master cast. Wee investigated the amount of torque required to displace a coping in eight impression material groups and the positional accuracy of the materials. The initial examination of torque narrowed the acceptable materials to a medium viscosity polyether, a high viscosity addition silicone, and a medium viscosity polysulfide-condensation silicones were eliminated. The results showed that the polyether and addition silicone produced casts with minimal distortion. Finally, it always is prudent to read the manufacturer's recommendations for use of impression materials. Catalyst-to-base ratios vary, as do working and setting times, depending on exact compositions. Impression materials also have various degrees of compatibility with stone, particularly the hydrocolloids, and it is advisable to use the recommended stone. Adhesives should be applied at least 15 minutes prior to loading the impression material. If at all possible, use of a rigid tray is recommended and impressions should be poured in the dental office; this minimizes the error produced at the beginning of the fabrication process. Elimination of errors early in fabrication of a prosthesis help prevent their magnification and result in a better-fitting restoration, requiring minimal adjustment in the end.

Colloids↗
PubMed1999

A predictable and accurate technique with elastomeric impression materials.

A method for obtaining more predictable and accurate final impressions with polyvinylsiloxane impression materials in conjunction with stock trays is proposed and tested. Heavy impression material is used in advance for construction of a modified custom tray, while extra-light material is used for obtaining a more accurate final impression.

Dental Impression Materials↗
PubMed2005

[Influence of the type of impression material, impression tray and making impression technology on the dimensional accuracy and depth of impression material penetration into "gingival sulcus". In vitro study].

Results of the profound study of influence of the type of impression material, impression tray and making impression technology upon main quality characteristics of the precise impression (dimensional accuracy and depth of impression material penetration into gingival sulcus) are reviewed. Original method to investigate depth of impression material penetration into gingival sulcus on experimental model is described. The impression technology exercises more influence on quality characteristics of the precise impression than type of the used material and impression tray. Optimal combination of different viscosity impression materials with technology of making impression has been defined.

Dental Impression Materials↗