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At least 181 records · Page 10Linked to original sources
PubMed1991

[The bonding properties of various silicone impression materials at standardized surfaces using adhesives].

Light body cured and putty cured silicone impression materials were tested for tensile strength on metallic surfaces. The effect of roughened surface was compared to the effect of tray adhesives. The bonding strength of light body cured materials appeared to be twice as high than that of putty cured materials. Roughening of the surface resulted in an improved adhesion, but the values of tray adhesives were not matched. The highest tensile forces were obtained using those tray adhesives recommended by the manufacturer.

Adhesives↗
PubMed1991

Effect of impression tray design and impression technique upon the accuracy of stone casts produced from a putty-wash polyvinyl siloxane impression material.

This study examined the accuracy of stone casts produced from impressions taken in stock polycarbonate trays, some of which had been strengthened with autopolymerizing polymethyl methacrylate resin. Three techniques were used to make the impression of an acrylic master model of the mandibular arch on which two extracoronal preparations for bridgework and one intracoronal inlay preparation had been carried out. Each preparation had been indented with a reference point for later measurement. The impression material was a putty-wash polyvinyl siloxane material. Five impressions were taken for each type of tray for each impression technique and these were cast in die-stone after 24 h. The distances between the points were measured with a reflex microscope and the means determined for each design of tray. The mean difference between casts produced from the various tray designs and the acrylic master model were determined for each of the distances between the three measuring points for the various impression techniques. Statistical analysis showed that, with the polycarbonate stock trays, there were significant differences between some of the modifications and between them and the acrylic model, for the three distances (P less than 0.05). These differences were limited to one measurement for one design of tray for each of the two-stage impression methods. With the one-stage technique the unreinforced tray and those reinforced with acrylic, over the heels and anteriorly, and the barred design were statistically significantly different from the acrylic model for measurement A-B.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesives↗
PubMed1990

Study of the accuracy of different recording materials.

An experimental study was conducted to determine the three-dimensional errors in mounting casts affected by the interocclusal recording materials. Eight commonly used materials or combinations were tested after various storage periods. The results indicated that all the materials induced asymmetric deviations of the condyles after each storage period. Impression plaster was the most accurate and dimensionally stable material; polyether was the second most accurate material, but it must be used within 6 hours. Correction of the teeth imprints with a low-viscosity material was beneficial only in combination with wax wafers.

Dental Articulators↗
PubMed1992

Accuracy and bond strength of reversible with irreversible hydrocolloid impression systems: a comparative study.

Combinations of three reversible hydrocolloids with five irreversible hydrocolloids were evaluated for dimensional accuracy and bond strength. A stainless steel model representing two teeth prepared for a fixed partial denture was designed for an accuracy study. The recordings were made with a measuring microscope, and the tensile bond strength was determined with an Instron Universal Testing instrument. The accuracy of these materials was clinically acceptable, and the resulting models were suitable. The materials distributed by a common supplier exhibited better tensile strength, although one irreversible hydrocolloid, Jeltrate, performed well in the noncompanion combination groups. This reversible with irreversible hydrocolloid combination impression has an advantage compared with the traditional reversible hydrocolloid impression, because it does not require elaborate, expensive conditioning equipment and water cooled trays.

Agar↗
PubMed2000

Accuracy of three polyvinyl siloxane putty-wash impression techniques.

STATEMENT OF PROBLEM: There is much discussion in the dental literature concerning the effect of the impression technique on the accuracy of cast restorations. PURPOSE: This study assessed the accuracy of 3 putty-wash impression techniques using the same impression material (polyvinyl siloxane) in a laboratory model. MATERIAL AND METHODS: The 3 putty-wash impression techniques used were (1) 1-step (putty and wash impression materials used simultaneously); (2) 2-step with 2-mm relief (putty first as a preliminary impression to create 2-mm wash space with prefabricated copings. In the second step, the wash stage was carried out); and (3) 2-step technique with a polyethylene spacer (plastic spacer used with the putty impression first and then the wash stage). For each technique, 15 impressions were made of a stainless steel master model that contained 3 complete crown abutment preparations, which were used as the positive control. Accuracy was assessed by measuring 6 dimensions (intraabutment and interabutment) on stone dies poured from impressions of the master model. RESULTS: One-way analysis of variance showed statistically significant differences among the 3 putty-wash impression techniques, for all intraabutment and interabutment measurements (P <.001). Overall discrepancies of the 2-step technique with 2-mm relief putty-wash impression technique were significantly smaller than that in the 1-step and polyethylene putty-wash impression techniques. CONCLUSION: The polyvinyl siloxane 2-step, 2-mm, relief putty-wash impression technique was the most accurate for fabricating stone dies.

Analysis of Variance↗
PubMed2000

Dimensional accuracy of an epoxy resin die material using two setting methods.

STATEMENT OF PROBLEM: Resinous die materials have several important advantages including strength, abrasion resistance, and detail reproduction. Despite these advantages, the shrinkage of resinous die materials during polymerization has limited their widespread acceptance. PURPOSE: This study determined whether a retarded setting reaction could improve the accuracy of an epoxy resin die system, and compared the accuracy of this epoxy resin system with gypsum-based die materials. MATERIAL AND METHODS: Four groups were compared: an epoxy resin manipulated according to manufacturer's instructions (Ivoclar, Schaan, Liechtenstein); the same epoxy resin manipulated to undergo a retarded set; a high-strength high-expansion gypsum (Die Keen); and a resin-filled gypsum (Resin Rock). Ten dies were fabricated for each material from a master metal model using conventional prosthodontic laboratory techniques. The mean of 3 independent measurements recorded using a toolmaker's microscope and digital positioners was used to describe each die. RESULTS: One-way ANOVA revealed that significant differences existed among the materials (P <.0001). Tukey's multiple comparisons testing ranked the dies as follows, from largest to smallest: high-strength high-expansion gypsum, resin-filled gypsum, master metal model, retarded epoxy, and manufacturers epoxy (P <.05). CONCLUSION: Retarding the setting reaction of an epoxy resin die material improved its accuracy. Of the materials tested, retarded set epoxy dies had the least mean dimensional change from the metal master. Epoxy resin die materials had a net shrinkage, but the gypsum-based materials had a net expansion. The epoxy resin materials exhibited more variability than the gypsum-based materials.

Analysis of Variance↗
PubMedDate not supplied

Comparative study of dimensional accuracy of different impression techniques using addition silicone impression material.

This study compared dimensional accuracy of the single, double with spacer, double with cut-out and double mix impression technique using addition silicone impression material. A typhodont containing Ivorine teeth model with six (6) full-crown tooth preparations were used as the positive control. Two stone replication models for each impression technique were made as test materials. Accuracy of the techniques were assessed by measuring four dimensions on the stone dies poured from the impression of the Ivorine teeth model. Results indicated that most of the measurements for the height, width and diameter slightly decreased and a few increased compared with the Ivorine teeth model. The double with cut-out and double mix technique presents the least difference from the master model as compared to the two latter impression techniques.

Dental Impression Materials↗
PubMedDate not supplied

Accuracy of implant impression splinted techniques: effect of splinting material.

Three implant impression techniques, using 3 different splinting materials, were assessed for accuracy in a laboratory model that simulated clinical practice. For group A, an autopolymerizing acrylic resin was used to splint transfer copings. In group B, a dual-cure acrylic resin was used, and for group C, plaster, which was also the impression material, was used. A metal implant master cast with an implant master framework was made to accurately fit to the cast. This cast was the standard for all impressions. For each group, 15 impressions were made. Polyether impression material was used for groups A and B. The accuracy of the stone casts with the implant analogues was measured against the master framework, using strain gauges. A multiple analysis of variance with repeated measures was performed to test for significant differences among the 3 groups. Additional analyses of variance were carried out to locate the source of difference. The statistical analyses revealed that a significant difference existed between groups A and B and between groups B and C but not between groups A and C. Impression techniques using autopolymerizing acrylic resin or impression plaster as a splinting material were significantly more accurate than dual-cure acrylic resin. Plaster is the material of choice in completely edentulous patients, since it is much easier to manipulate, less time consuming, and less expensive.

Acrylic Resins↗
PubMed1993

The ratio between vertical and horizontal changes of impressions.

The purpose of this study was to analyze theoretically and experimentally the relations between the horizontal and the vertical changes of impressions taken with a mandibular stock tray. According to the theoretical analysis the ratio between the horizontal (delta X) and the vertical changes (delta Z) can be expressed as: [formula: see text] where mu is the Poisson's ratio and Lx and Lz are the horizontal and vertical dimensions of the die, respectively. With regard to the experimental findings the Poisson's ratio calculated by this expression was mu = 0.44 which fits the range of Poisson's ratio for rubber materials. In addition it was shown that the ratio between the vertical and horizontal strains is constant for a particular impression technique.

Alginates↗
PubMedDate not supplied

Working times of elastomeric impression materials determined by dimensional accuracy.

The working times of five poly(vinyl siloxane) impression materials were estimated by evaluating the dimensional accuracy of stone dies of impressions of a standard model made at successive time intervals. The stainless steel standard model was represented by two abutments having known distances between landmarks in three dimensions. Three dimensions in the x-, y-, and z-axes of the stone dies were measured with a traveling microscope. A time interval was rejected as being within the working time if the percentage change of the resultant dies, in any dimension, was statistically different from those measured from stone dies from previous time intervals. The absolute dimensions of those dies from the rejected time interval also must have exceeded all those from previous time intervals. Results showed that the working times estimated with this method generally were about 30 seconds longer than those recommended by the manufacturers.

Analysis of Variance↗