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The labial sectional impression technique in the maxillary immediate denture can be done in many different materials with varied results. The use of vinyl polysiloxane putty for this impression technique is demonstrated and shows the superior results both in the ease of use and the detail of the impression surface.
Continued polymerization of impression material stored in a previously used dispensing cartridge of an automixing impression system can lead to untoward results. This article describes a simple technique that will help overcome the problem.
In order to keep the degree of polymerisation of moulding materials as low as possible until they are applied, a lower working temperature for the first and second material is necessary. In addition, the preliminary impression is cooled in ice water so that the flow capacity of the correcting compound in the capillary cleft is improved and unreliable model reduction can thus be avoided.
A technique for making selective tissue placement final impressions for complete dentures using vinyl polysiloxane and custom trays with peripheral relief is presented. This technique is an alternative to the conventional method of border molding using modeling plastic impression compound.
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.
Transfer of the precise position of implants to a master cast is a prerequisite for accurate and passive fit of the superstructure. Implants lack the mobility of natural teeth and, therefore, inaccurate frameworks result in stress within the mechanical parts and the implant-bone interface. Various impression methods have been described to achieve accurate reproduction of the intra-oral relation of the implants. The aim of this experimental study was to compare three different impression materials (polyether, polyvinyl siloxane, hydrocolloid) with the Frialit(R)-2 system and with the indirect technique. In addition, the use of transfer caps (TCs) to improve transfer precision was tested with all three materials. All measurements were performed using a three-dimensional (3D) co-ordinate measuring machine that is capable of locating points in space and calculating the relative distortions as angles of tilt (rot-XY, rot-XZ, rot-YZ) and 3D displacement. The results suggest that addition-silicone (a-silicone) and polyether are the materials of choice for implant transfer procedures. The use of TCs resulted in a significantly reduced rotation in the XY-plane but did not improve the absolute 3D displacement. A-silicone with the use of TCs proved to be most precise. Comparison between polyether and polyvinyl siloxane showed significant differences in the XY-rotation and the 3D displacement in favour of the silicone. Because the mean distortions between the original model and the master casts were about 100 microm, absolutely precise fit may be unattainable owing to the physical properties of the materials. Further studies will have to evaluate the amount of tolerable stress at the implant-bone interface.
OBJECTIVE: The objective of this investigation was to measure and compare the dimensions of casts made using four types of impression trays and two impression materials to the dimensions of the original master model. This study differed from previous studies by using three-dimensional measurement. METHOD AND MATERIALS: Vinyl polysiloxane and polyether impressions were made of two crown preparations of ivorine teeth cemented into an acrylic master model. Two grooves were placed into each of the preparations. In addition, six points were placed on each occlusal surface and six were placed on each finish line. Impressions were poured with a Type IV dental stone at 48 hours. A three-dimensional measuring system was used to determine coordinates of 32 points on the master model and resulting casts. Inter- and intratooth dimensions were calculated from the measured coordinates. RESULTS: The accuracy and precision of the impression techniques were assessed using analysis of variance (ANOVA) and Dunnett's t test. The ANOVA and Dunnett's t test indicated that only the custom tray did not detect any inaccuracies and was as reproducible as the master model. CONCLUSION: This study suggests that the custom tray technique is most accurate, even though all other techniques evaluated apparently produce clinically acceptable results.
OBJECTIVES: To compare the quality of conventional complete dentures fabricated with two different techniques. A randomized controlled clinical trial was conducted to compare traditional (T) and simplified (S) methods of making complete conventional dentures on patients' ratings of satisfaction, comfort and function at 3 and 6 months following delivery. The quality of the prostheses was rated by prosthodontists at 6 months. MATERIALS AND METHODS: One hundred twenty-two male and female edentulous individuals, aged 45-75 years, were randomly allocated into groups that received dentures made with either T or S methods. Following delivery, patients' ratings of several denture-related factors were measured using 100mm visual analogue scales, and denture quality was assessed by blinded prosthodontists using ratings on a validated quantitative scale. RESULTS: There were no significant differences between the two groups in patient ratings for overall satisfaction (3 months: mean T = 83 mm, mean S = 83 mm, P = 0.97; 6 months: mean T = 79 mm, mean S = 79 mm, P = 0.96) or in prosthodontists' ratings of denture quality (T = 66, S = 63; P = 0.38). CONCLUSION: These results show that the quality of complete dentures does not suffer when manufacturing techniques are simplified to save time and materials. Dental educators should consider these findings when re-designing prosthodontic training programs.
Conventionally, custom trays have been made in the laboratory on casts constructed from preliminary impressions. A spaced tray made in this way allows a uniform thickness of impression material of approximately 2 mm which is said to enhance the accuracy of the impression-taking procedure. A technique is described to fulfill this criterion without the need for a primary impression, by constructing a spaced putty custom tray inside the mouth.
Variations in the bulk of wash in a putty-wash impression technique can result in dimensional changes proportional to the thickness of the wash material during setting. The purpose of the study was to determine the amount of wash necessary to achieve accurate stone models while using a two-step putty-wash impression technique with polyvinyl siloxane (PVS) impression material. A total of 45 impressions were made of a stainless steel master model, 15 impressions for each wash thickness (1, 2 and 3 mm). The model contained three full-crown abutment preparations, which were used as the positive control. Accuracy was assessed by measuring six dimensions (occlusogingival and interabutments) on stone dies poured from impressions of the master model. One-way analysis of variance (ANOVA) showed statistically significant differences amongst the three wash bulk groups, for all occlusogingival and interabutment measurements (P < 0.001). The overall discrepancies of the groups using wash thickness of 1 and 2 mm were smaller than the group with 3 mm wash thickness. Therefore, wash bulks of 1 and 2 mm were most accurate for fabricating stone dies, using PVS impression materials. This can be achieved by using the temporary crown to create the desired wash space in the preliminary putty impression. Wash thickness > 2 mm was inadequate to obtain accurate stone dies.
For anyone desiring to cast anatomical models, a simplified technique for external casting has been developed using dental impression materials readily available in dental supply houses. These impressions yield life-like permanent models retaining topographical features of normal as well as pathological skin and nails.
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This article describes the instrumentation, materials, and clinical procedures for the matrix impression system. The matrix impression system uses a custom matrix to control the sulcular environment and to deliver impression material to the subgingival parts to be impressed. It describes the four types of forces involved in gingival displacement during impressions, effective delivery of impression material with simultaneous sulcular cleansing, and simplification of complex impressions with or without segmentation. The application of the matrix impression system is described for making routine impressions and for some atypical problems. The article also provides a detailed description of the formation and design of the matrix.
Well-fitting indirect restorations can only be made if there are accurate models of the oral tissues available, made from high quality impressions. Waiting for an impression to set may be more stressful for the dentist than the patient. Should the impression need to be repeated there is the embarrassment of having to explain this to the patient, the cost implications of material and time wasted and the aggravation of running late for the next appointment. Yet, if a 'Nelsonian' eye is turned to a defective impression we can only expect a substandard restoration in return.
STATEMENT OF PROBLEM: Anecdotal reports of use of double-arch impressions for indirect restorations suggest time and materials savings, but there is little clinical evidence to support their use. PURPOSE: To establish whether a double-arch impression technique could produce restorations comparable with those produced by use of the complete-arch technique and to investigate reported time and material savings. MATERIAL AND METHODS: Five practitioners each recruited 10 adult patients requiring a single complete veneer crown into the study. Two sets of impressions, 1 complete-arch in a stock metal tray, and 1 double-arch in a plastic double-arch tray were made for each patient in addition-polymerized silicones in a random order. The time taken for each impression was recorded along with patient's assessment of comfort, taste, and overall acceptability. One technician, who selected the impressions for the fabrication of each crown according to a predetermined scheme of randomization, fabricated all crowns. Equal numbers of crowns were made from the complete and double-arch impressions. At the time of crown placement, the accuracy of fit, occlusal harmony, and the time taken for try-in were also recorded. The weight of impression material used was measured for each impression. Data were analyzed by use of computerized statistical software (t test for equality of means) at a significance level of 95%. RESULTS: The double-arch technique was faster (222 seconds [SD, 57 seconds] vs 445 seconds [SD, 87 seconds], P=.000), more comfortable (P=.025), better tasting (P=.001), and preferred by 80% of the patients (P=.000). No significant differences were found between the 2 groups for accuracy of fit, occlusion, or time taken for try-in of the restorations. The mean weight of impression material used was 39 g (SD, 10 g) for complete-arch and 20 g (SD, 7 g) for double-arch impressions, a mean difference of 19 g (P=.000). CONCLUSION: Within the limitations of this study, double-arch impressions were found to take less time, to use less material, and to be preferred by patients. Under the conditions of this study, the resulting restorations were no less accurate than those made from complete-arch impressions.
A method is proposed of making amalgam build-ups for coronally debilitated teeth through the use of a stable matrix consisting of a disposable tray and polyvinylsiloxane occlusal registration material. For teeth with minimal remaining coronal tooth structure and/or the absence of adjacent teeth, this technique provides proper stabilization of the matrix band to permit adequate condensation of amalgam.
This article describes dual-arch impression technique (DAIT) used with alginate impression material, to obtain diagnostic models of the prepared and opposing teeth. Using this quick and simple procedure, tooth preparation, abutment parallelism, and occlusal clearance can all be critically assessed outside the mouth. Any problem areas can be corrected at a subsequent appointment, prior to taking the final impression.
The automatic mixing system of an addition silicone impression material yields mixes and set material that comply with ADA specification no. 19 when testing is started at 0.5 minute rather than the specified 1.5 minutes. This change is reasonable because there is zero mixing time rather than the usual 45-60 second needed for standard two-paste rubber impression materials. Uniform mixing of base and catalyst occurs with the automatic system, with a fourth to a fifth as many bubbles in the mix as for comparable mixes obtained by hand spatulation. The automatic feature of the system simplifies mixing and nearly eliminates the training of assistants in the mixing of rubber impression material. The automatic mixing system is economical as it wastes only a third as much material as a typical hand-dispensing and mixing system. The properties and accuracy of the system are excellent and typical of addition silicones, including excellent recovery from deformation, low dimensional change on setting, and low flow. A wash or two-phase impression technique may be used with equal clinical accuracy.