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PubMedDate not supplied

Materials for impressions--2003.

Thirty years ago the author set out the logical sequence of dimensional changes that could occur in the impression materials of the 1970s. In the 21st Century, it appears that little has changed and that what the dental practitioner requires today is the same as it always was--a forgiving material that produces perfect impressions with a minimum of trauma to the patient, dentist and technician.

Alginates↗
PubMed1980

Impression materials for recording the denture bearing mucosa.

To accurately record the denture bearing mucosa at rest or with the least possible tissue movement, the following suggestions should be considered: The denture bearing mucosa should be healthy and firm. Impression materials used should be of low viscosity. Materials which rapidly increase in viscosity after mixing should be placed in the mouth as soon as possible without compromising acceptable clinical procedures. The zinc oxide-eugenol materials have an advantage of a much longer working time. Materials with low contact angles with water may have flow characteristics that are more favorable for making impressions of the denture bearing mucosa. The pressure used to seat and hold an impression of the denture bearing mucosa should be kept at the minimum necessary to achieve adequate flow for that impression material. From this discussion, it is evident that no single impression material is ideally suited for making edentulous impressions. Perhaps in the future the dental manufacturers will consider developing and marketing products with the specific performance characteristics that have been outlined. Until that time, clinicians should be aware of the characteristics of the material they are using and modify their techniques accordingly.

Agar↗
PubMed2005

Trends in indirect dentistry: 5. Impression materials and techniques.

UNLABELLED: A fundamental pre-requisite for the construction of satisfactory indirect restorations is the ability to record an accurate and detailed impression of the dental structures. Knowledge of the key properties of the available impression materials and their handling behaviour is necessary if they are to be used effectively. A variety of techniques can be employed in different situations, each of which can be highly successful, but only if attention is paid to the detail of their execution and the clinician is aware of their individual limitations and pitfalls. Where imperfections occur, an appreciation of how they have been caused, and the strategies to take to prevent them will lead to greater success in impression taking. CLINICAL RELEVANCE: Current materials exceed our needs in terms of accuracy and stability, and yet the impressions produced are frequently flawed. By realizing why faults occur, being aware of the range of techniques available and having an understanding of the behaviour of materials, clinicians can achieve the quality in their impressions that is possible and necessary to provide excellence in indirect restorations.

Dental Impression Materials↗
PubMedDate not supplied

A laboratory investigation of the accuracy of two impression techniques for single-tooth implants.

PURPOSE: This laboratory study investigated the accuracy of four implant impression procedures using two impression techniques and two different materials. MATERIALS AND METHODS: A master model was used to produce 40 different stone casts incorporating laboratory implant or abutment analogues from the different combinations of two impression techniques (the repositioning impression coping technique at the implant level and the pickup impression technique at the abutment level) and materials (President polyvinyl siloxane and Impregum F polyether). Variations in the resulting working casts were measured using the Reflex Microscope to derive distances and angles from the three-dimensional coordinates of optical targets that were attached to a test coping placed on the implant analogue and on a reference device positioned on the occlusal surfaces of the casts. RESULTS: The results showed greater variations in analogue position with the repositioning impression technique than with the pickup technique. The rotational errors were large enough to be of clinical concern. No significant differences were found between polyvinyl siloxane and polyether impression materials for the two tested types of impression techniques. CONCLUSION: The repositioning impression technique at the implant level can produce less predictable results than the pickup technique at the abutment level. The choice of impression material made no significant difference.

Analysis of Variance↗
PubMed2006

Impression techniques and misfit-induced strains on implant-supported superstructures: an in vitro study.

The purpose of this study was to compare misfit-induced strains on implant-supported superstructures fabricated by two impression techniques and two different elastomeric impression materials. A master cast hosting four Straumann implants was constructed. On this cast, a total of 21 implant-level impressions were made by the direct technique using a polyether impression material and synOcta screwed aluminum impression caps (PE-D), and by the indirect technique using polyether (PE-IN) or polyvinylsiloxane impression material (VPS-IN) with snap-on impression caps and synOcta plastic positioning cylinders. Two casts were randomly selected from each group of seven, and a total of four screw-retained superstructures, supported by either two or four implants (one of each type on both casts), were cast in a gold alloy for each group. Linear strain gauges were bonded on the superstructures, and misfit-induced strains were recorded during superstructure connection on each of the working casts and on the master cast using a data acquisition system and corresponding software at a sample rate of 10 kHz. Connection on the implants in the master cast increased strains considerably on most of the superstructures, in comparison with strain gradients measured when the superstructures were connected on the casts from which they were fabricated (P <.05). The differences in strain amplitude between connection on the cast from which the superstructure was fabricated and on the master cast were higher for superstructures fabricated by PE-D than for those fabricated by PE-IN and VPS-IN. The snap-on indirect impression technique for Straumann implants leads to acceptable superstructures, regardless of the impression material used.

Aluminum↗
PubMed1992

Compatibility of Type IV dental stone with polysulfide impression materials.

PURPOSE: In the American National Standards Institute/American Dental Association specification no. 19, compatibility of impression materials with dental stones is assessed by the presence of a 20-microns-wide line reproduced on an unmodified calcium sulfate dihydrate cast. In actual dental practice, modified type IV dental stones are used, although little is known of their compatibility with polysulfide impression materials. This study evaluated the compatibility of 6 polysulfide impression materials and 11 modified type IV dental stones. MATERIALS AND METHODS: A line 20 microns wide was etched on four glass dies. Four samples of each combination of impression material and dental stone were prepared according to the manufacturer's directions with an additional 3 minutes for the final setting time. Compatibility was determined by the presence of the reproduced line on the dental stones, as observed under low angle 10 x magnification by four rater groups. RESULTS: The line was reproduced on all of the impression specimens, and the examiners recorded 66 positive identifications of the line on the stone casts out of a possible 1,056 ratings for a total of 6.25% of the specimens. Out of a possible 66 impression-stone combinations, only 18 reproduced the 20-microns line. The combinations reproducing the lines most frequently (75%) were Neoplex with Blue Die Stone (Columbus Dental, St Louis, MO) and Coeflex with Indic Die Stone (Coe Lab Inc, Chicago, IL). CONCLUSIONS: The study showed that many combinations of polysulfide impression materials and modified type IV dental stones did not reproduce the 20-microns line; therefore, not every polysulfide is compatible with every type IV dental stone.

Calcium Sulfate↗
PubMed1990

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.

Acrylic Resins↗
PubMed1997

Trouble-shooting dual arch impressions II.

Dual arch impression procedures can produce accurate impressions and bite registrations for the fabrication of single crowns. To accomplish this, the dentist must select an appropriately sized and shaped tray, appropriate impression material and a dual arch impression procedure suitable for each case. Dual arch impression procedures can save impression material and chair time.

Crowns↗