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I have attempted to provide information that will help to prevent failures that occur during partial denture construction as a result of unsatisfactory fabrication of crowns. Methods of exposure of the preparation margins, provision of adequate bulk of the elastic impression material, proper selection of die construction, and the removable die technique were discussed.
According to the so-called double-mix technique for impression taking, a material of high and one of low viscosity set against each other. We found that a distortion of the joined materials occurred which may compromise the precision of the impression. The distortion of such combinations of materials of high and low viscosity was measured on beam-like specimens. Significant differences between materials were observed. The phenomenon may be explained by a swelling of the material of low viscosity. The swelling may be associated with a diffusion of unreacted compounds from the material of high viscosity into the material of low viscosity. Measurements of the swelling of specimens immersed in the catalyst component of unset material showed an increase in length of 2-5%.
Many techniques and materials for impressions for removable partial and complete dentures are available. Current materials are extremely accurate, and addition reaction silicones and polyethers provide continuing accuracy for days after the impressions are made. Acceptable techniques are possible for any of the materials, and the selection of one material over another for routine use depends on personal preference and clinical needs.
In the described technique, a vinyl polysiloxane material is used as a matrix for the indirect fabrication of multiple custom-cast posts and cores. The matrix technique enables the clinician to fabricate multiple posts and cores in a short period of time. The form, harmony, and common axis of preparation for all cores are well controlled before the definitive crown/fixed partial denture restorations are fabricated. Oral tissues are not exposed to the heat of polymerization or the excess monomer of the resin material when this technique is used.
The effect of two impression materials used in three different techniques was tested for the accuracy of the marginal fit of metal castings. Sixty identically prepared Ivorine teeth were divided into groups of 20. The following methods were selected to make impressions: (1) putty in a metal stock tray with simultaneous elastomeric impression wash, (2) copper band relined with autopolymerizing acrylic resin and subsequent light-body elastomeric impression material, and (3) copper bands with modeling compound. Faciolingual sections of the Ivorine teeth with cemented metal castings were examined by scanning electron microscopy (SEM) at x 100 magnification. Measurements of the thickness of cement layers were calculated both manually and by use of a recently developed computerized method. The differences in the gingival marginal gaps between various impression materials and techniques at both the facial and lingual surfaces were not statistically significant.
The purpose of this study were to determine the acceptability of silver-plated dies made from representative brands of impression material from each of the four groups of elastomers and to determine the time required for initial plating of dies. Permlastic and Impregum , each previously shown to produce consistent silver-plated dies, were used for comparison. Representatives from the condensation-reaction and addition-reaction ( polyvinylsiloxanes ) silicones groups were tested until satisfactory materials were selected. Citricon and Xantopren - Optosil were tested in the former group and President and Reprosil in the latter. Conclusions include the following: All materials were flash-plated in 10 minutes or less. Acceptable silver-plated dies were obtained from Permlastic and Impregum . Acceptable silver-plated dies were obtained from condensation-reaction silicones with Xantopren - Optosil . From the polyvinylsiloxane group, Reprosil plated more consistently than President. Both produce acceptable dies. The technique modification studied was not effective for Citricon and President. The surface quality of silver-plated dies and the consistency of plating varies with materials. Individual impression materials should be tested prior to their routine clinical use with silver-plating procedures.
The baseplate material that best reproduced the most grooves in a gypsum cast was filled cold cure acrylic resin, followed in turn by modelling wax, grey shellac and finally the pink shellac material. These latter three thermoplastic materials performed best when softened in a water bath and subsequently adapted to a prewarmed cast.
This study was conducted to evaluate the working times of seven elastomeric impression materials according to their detail reproduction and dimensional accuracy. Impressions were made of a standard ADA Specification No. 19 die at 30-second intervals until they were no longer workable. The detail reproduction and dimensional stability of these impressions were evaluated according to the ADA Specification No. 19 criteria and the dimensional stability was analyzed. It was found that the working times of the impression materials according to detail reproduction generally agreed with those estimated according to dimensional stability but not with the manufacturers' suggested working times.
Voids in impressions made by five automixed addition silicone elastomers with and without intraoral delivery tips were investigated. The number of voids were counted at a predetermined site on 3 days. Hand-mixed impressions of the automixed materials were made for comparison. There was no statistically significant difference in the mean number of voids produced in each automixed silicone dispensed with the use of intraoral delivery tips and the number of voids produced without the use of the tips. However, there were significant differences in the number of voids among different materials. The rank order of the automixed silicone elastomers was fairly consistent, with Express producing the highest and Reprosil the lowest number of voids. Automixed silicone materials should only be prepared by automixing for optimal results.
OBJECTIVE: The reproducibility of clinical records of the occlusion was assessed in three dimensions using mounted casts. Three distinct areas were examined: 1) mandibular positions (intercuspal position (IP) or retruded contact position (RCP)), 2) materials used in recording the occlusion, 3) clinical variation. DESIGN: Interocclusal records were made in a random order of three patients: one fixed prosthodontics case, one removable partial denture case and one complete denture case, with two different types of waxes, record rims, two different brands of vinyl polysiloxanes and one irreversible hydrocolloid. SETTING: Private practice and Karolinska Institute, Huddinge, Sweden. SUBJECTS: One general dental practitioner and three voluntary patients. RESULTS: Point estimation of variance components indicate that 70-93% of the variation of the positions of the mounted casts are caused by: 1) clinical variation for all three cases and in three directions, 2) the influence of recording materials 0-29%, and 3) mandibular positions (IP/RCP) 0-11%. The ranges of the positions of the mounted casts were lower for the dentate case (0.04-1.39 mm) than for the partially dentate case (0.17-2.65 mm), which in turn was lower than those for the edentulous case (1.42-5.59 mm). CONCLUSION: Clinical variation seems to dominate the variation in positions of mounting casts when making interocclusal records, rather than mandibular position or the recording materials used. Therefore a dentist who makes one single interocclusal record cannot presume that it will reproduce the interocclusal relationship intended, which in the present study was most obvious for the edentulous case. The results showed that impression materials stabilised by a tray did not differ significantly from waxes and record rims concerning the reproducibility. Therefore the stabilised impression materials are an alternative, which also give additional advantages like reduction of appointments as well as superior accuracy.
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This article describes a convenient technique for making impressions of complete dentures using two newly developed silicone materials. One of these materials, a heavy-bodied silicone material, is used for simultaneous molding of all borders. The material is available in automatic mixing systems, so it can be easily and evenly applied on the tray borders. The material is designed to have a low elasticity after setting so that excess material can be carved or deficient sites corrected with a small mix. The other newly developed material, a light-bodied silicone material, possesses better flow than the usual light-bodied silicones. In addition, since viscosity is controlled and adequate flow is maintained during seating in the mouth, mucosal detail is superior.
STATEMENT OF PROBLEM: It has been stated that reversible hydrocolloid impression material must be poured immediately to remain accurate. This may not be true with modern formulations of reversible hydrocolloid. The accuracy of the impression, if kept at 100% humidity for varying periods, may not be affected as critically as has been suspected. PURPOSE: The purpose of this study was to evaluate the effect of storage time in a 100% humidity environment on the accuracy of gypsum casts poured from a newer formulation of reversible hydrocolloid impressions. MATERIAL AND METHODS: With the use of a stainless steel master model, 5 standardized reversible hydrocolloid impressions were made for each time interval tested (n = 5). Impressions were made with the use of both Cartiloid blue syringe and Slate tray reversible hydrocolloid material (both manufactured by Van R) to simulate a common clinical protocol. Six groups, representing times at 0, 30, 60, 120, 180, and 210 minutes, were evaluated for a total of 30 specimens. Gypsum casts were measured with a traveling microscope, and dimensional changes were compared between groups with ANOVA and Tukey intervals (alpha=.05). RESULTS: Measurements made up to and including the 60-minute storage time showed clinically acceptable distortion levels. These measurements were similar to the metal model and the gypsum casts poured at time 0 minutes. The only statistically significant difference between the gypsum cast and the metal master model was the distance between abutments at storage time 180 minutes (master model = 30.04 mm [SD 0.001]; gypsum casts = 29.944 mm [SD 0.076]). This difference was -91 microm (P=.002). In general, the gypsum abutments became wider and shorter with time. There was no significant difference between any gypsum abutment in regard to width or height when compared with the metal master model for all the storage times tested. However, as time increased, measurement became harder to accomplish, leading to a larger standard deviation and less reliable results. The distance between abutments remained relatively constant for storage times up to and including 60 minutes. For times longer than 60 minutes, the distance between abutments was reduced and more difficult to read. The distance between abutments at the 3-hour storage time was significantly different than the metal standard and time 0 gypsum casts. CONCLUSION: If a discrepancy of 78 microm (twice the 39 microm single margin opening) is clinically acceptable, then the results of this study show that this type of reversible hydrocolloid can be stored in 100% humidity for at least 60 minutes.
Most of the information available to guide the clinician in making occlusal records focuses on the clinical techniques and methods involved. There is little objective information regarding the use of the more recently introduced elastomeric materials which are growing in popularity in the clinic. Much of the published work relies on the clinical experience of the authors rather than the properties of the material to be used to make the occlusal records. This paper aims to review the materials currently available to clinicians for use in occlusal registrations. The materials are discussed with regard to their suitability for the task and suggestions given regarding their use. Setting aside considerations of technique, it is suggested that there would be value in basing the selection of materials for occlusal registration on objective research. However, it may well be that the technique, as with many other things in dentistry, is as important as the specific properties of the materials used.
A method designed to measure the volume of cutaneous ulcers is described that utilizes a silicon rubber dental impression material. This technique is compared to the more popularly used computerized image analysis method in the determination of the size of cutaneous ulcers.
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In the technique described, the search for the peripheral joint and the final impressions are really functional and rely on adapted silicone impression materials. The vertical dimension is investigated physiologically (speech/swallowing). The recording of the centric relation is confirmed graphically with a centric pin. Thus, the patient transcribes his "occlusal signature" and provides both the practitioner and the dental technician with precise data for the mounting of denture teeth.