Search

Background: The dimensional accuracy of impression materials has been evaluated for a long time, but thus far, digital radiography has not been used for this purpose. The dimensional accuracy of impression materials is very important for the final adaptation of dental prostheses., Objectives: The objective of this study was to evaluate the effects of different disinfectant solutions and storage times on the dimensional stability of different impression materials by means of digital radiography., Material and Methods: Polyether (PE), hydrocolloid (IH), condensation silicone (CS), and addition silicone (AS) materials were used for preparing impressions, taken from an acrylic master model with 2 vertical and 2 horizontal reference points. Water (W), sodium hypochlorite (SH) and a disinfectant solution without aldehyde (Z) were applied on the impressions. Half of the impressions were poured over immediately and half of them - 1 day after. Digital radiography was used to determine the dimensional accuracy of the impression materials. The data was analyzed with a variance analysis and Tukey's multiple comparison test., Results: While PE showed the smallest dimensional changes, IH showed the greatest in all lines. Applying SH and pouring 1 day after caused the greatest dimensional changes in all impression materials., Conclusions: Different disinfectant solutions and storage times had a different effect on the impressions, but the dimensional changes were clinically acceptable.

Aims: The aim of this study was to compare the dimensional accuracy of four different implant impression techniques of a mandibular edentulous model with five parallel implants., Materials and Methods: Five dental implants were placed in an edentulous mandibular model in parallel. A total of forty impressions were obtained using four different impression techniques. In Group 1 (G1) and Group 2 (G2), closed tray impressions with and without plastic caps, respectively, were used. In Group 3 (G3) and Group 4 (G4), open tray impressions with a direct splinted technique and an improved direct splinted technique, respectively, were used. All the impressions were poured with Type IV dental stone. Master model and study casts were scanned with a laser optical scanner and aligned by observing the superpositions of the anatomical landmarks using a software program., Statistical Analysis Used: Fifty measurements of the apical, coronal, and angular discrepancies of the master and study casts were obtained (n = 50) and statistically analyzed using a one-way analysis of variance and post hoc (least significant difference ) and Friedman's tests., Results: The lowest accuracy was obtained from G2 when the angular (1.48°), coronal (0.32 μm), and apical (0.14 μm) deviations were tested (P < 0.05), whereas no statistically significant differences were found among the other groups (P < 0.05)., Conclusions: In cases with five parallel mandibular implants, improved accuracy was achieved using the direct splinted technique, the improved direct splinted technique, or the closed tray impression technique with snap on plastic caps., Competing Interests: There are no conflicts of interest

Alginate impression (irreversible hydrocolloid) material is commonly used in dental practice because it is easy to mix, low in cost, and well tolerated by patients. The material is not dimensionally stable, however; thus, it is necessary to pour the impression immediately after the molding is accomplished, or within 60 minutes if the impression is kept in 100% humidity. Excessive contact of the alginate impression with the cast model over time may affect the model's properties. In this study, the authors tested the effect of contact time between an alginate impression and type III dental stone on cast model properties. Sixty-seven cast models were obtained from a stainless steel cylinder by using irreversible hydrocolloid impression material and type III dental stone. Thirty-seven cast models were separated from the impression after 1 hour (control group) and 30 cast models were separated after 6 hours (study group). The samples were evaluated under light microscope for surface details and measured by digital caliper for dimensional stability. An indentation on the cast was made and the depth of the indentation was then measured with a digital caliper to measure hardness. The dimensional stability of the cast models was not affected when contact time was increased from 1 hour to 6 hours (P = .507). Surface details did not deteriorate when contact time was increased, as all of the samples could reproduce all details after the 1-hour and 6-hour interval periods. However, hardness was greater after 1 hour of contact time (P = .001) than after 6 hours of contact time. In conclusion, contact between alginate impression material and type III dental stone up to 6 hours did not affect the dimensional stability and richness of the surface; hardness, though, was significantly affected.

Background/aim: Dental impressions present a negative imprint of intraoral tissues of a patient which is, by pouring in gypsum, transferred extraorally on the working cast. Casting an accurate and precise working cast presents the first and very important step, since each of the following stages contributes to the overall error of the production process, which can lead to inadequately fitting dental restorations. The aim of this study was to promote and test a new model and technique for in vitro evaluation of the dental impression accuracy, as well as to asses the dimensional stability of impression material depending on the material bulk, and its effect on the accuracy of working casts., Methods: Impressions were made by the monophasic technique using the experimental master model. Custom trays with spacing of 1, 2 and 3 mm were constructed by rapid prototyping. The overall of 10 impressions were made with each custom tray. Working casts were made with gypsum type IV. Measurement of working casts was done 24 h later using a co-ordinate measuring machine., Results: The obtained results show that the working casts of all the three custom trays were in most cases significantly different in the transversal and sagittal planes in relation to the master model. The height of abutments was mainly unaffected. The degree of convergence showed certain significance in all the three custom trays, most pronounced in the tray with 3 mm spacing., Conclusion: The impression material bulk of 1–3 mm could provide accurate working casts when using the monophasic impression technique. The increase of the distance between abutment teeth influences the accuracy of working casts depending on the material bulk. [Projekat Ministarstva nauke Republike Srbije, br. TR 35020: Research and development of modelling methods and approaches in manufacturing of dental recoveries with the application of modern technologies and computer aided systems]

Purpose: The aim of this study was to detail and assess the capability of a novel methodology to 3D-quantify tooth wear progression in a patient over a period of 12 months., Materials and Methods: A calibrated stainless steel model was used to identify the accuracy of the scanning system by assessing the accuracy and precision of the contact scanner and the dimensional accuracy and stability of casts fabricated from three different types of impression materials. Thereafter, the overall accuracy of the 3D scanning system (scanner and casts) was ascertained. Clinically, polyether impressions were made of the patient's dentition at the initial examination and at the 12-month review, then poured in type IV dental stone to assess the tooth wear. The anterior teeth on the resultant casts were scanned, and images were analyzed using 3D matching software to detect dimensional variations between the patient's impressions., Results: The accuracy of the 3D scanning system was established to be 33 μm. 3D clinical analysis demonstrated localized wear on the incisal and palatal surfaces of the patient's maxillary central incisors. The identified wear extended to a depth of 500 μm with a distribution of 4% to 7% of affected tooth surfaces., Conclusion: The newly developed 3D scanning methodology was found to be capable of assessing and accounting for the various factors affecting tooth wear scanning. Initial clinical evaluation of the methodology demonstrates successful monitoring of tooth wear progression. However, further clinical assessment is needed.

Purpose: The purpose of this study was to compare the capacity of different impression materials to accurately reproduce the positions of five implant analogs on a master model by comparing the resulting cast with the stainless steel master model. The study was motivated by the knowledge that distortions can occur during impression making and the pouring of casts and that this distortion may produce inaccuracies of subsequent restorations, especially long-span castings for implant superstructures., Materials and Methods: The master model was a stainless steel model with five implant analogs. The impression materials used were impression plaster (Plastogum, Harry J Bosworth), a polyether (Impregum Penta, 3M ESPE), and two polyvinyl siloxane (PVS) materials (Aquasil Monophase and Aquasil putty with light-body wash, Dentsply). Five impressions were made with each impression material and cast in die stone under strictly controlled laboratory conditions. The positions of the implants on the master model, the impression copings, and the implant analogs in the subsequent casts were measured using a coordinate measuring machine that measures within 4 μm of accuracy., Results: Statistical analyses indicated that distortion occurred in all of the impression materials, but inconsistently. The PVS monophase material reproduced the master model most accurately. Although there was no significant distortion between the impressions and the master model or between the impressions and their casts, there were distortions between the master model and the master casts, which highlighted the cumulative effects of the distortions. The polyether material proved to be the most reliable in terms of predictability. The impression plaster displayed cumulative distortion, and the PVS putty with light body showed the least reliability., Conclusions: Some of the distortions observed are of clinical significance and likely to contribute to a lack of passive fit of any superstructure. The inaccuracy of these analog materials and procedures suggested that greater predictability may lie in digital technology.

Purpose: Because there is a paucity of clear-cut evidence regarding which materials and techniques are most accurate for complete-arch, multiple-implant impressions, the current study sought to analyze the data and draw useful conclusions based on the evidence for application in clinical practice., Materials and Methods: Relevant studies published between 1990 and December 2012 were included in the review. The articles were located through PubMed and manually through reviewing references in the literature. Papers examining implant impression accuracy in completely edentulous arches (three or more implants) were included. Clinical case reports, technique articles, abstracts, and review papers were excluded., Results: One of the 34 studies selected for evaluation was clinical; the remaining 33 were in vitro investigations. Ten studies compared polyvinyl siloxane (PVS) and polyether (PE); eight found that these were statistically equal in terms of impression accuracy. The splint effect was examined by 24 studies; 10 failed to observe any differences between splinted and nonsplinted impressions, whereas 7 (> 25%) showed that the splinted technique was better than the nonsplinted technique. Thirteen studies investigated the differences between pickup and transfer impression techniques; six favored pickup over transfer, and five found insignificant differences between the techniques. The effect of nonparallel implants on edentulous multiple-implant impression accuracy was examined by only two studies. Significant differences in accuracy were observed for 15 degrees of angulation., Conclusion: Most of the evidence supports PVS and PE as the most accurate impression materials for edentulous multiple-implant situations, with no clear advantage of either. Conflicting evidence exists regarding the most accurate impression technique (splinted/nonsplinted, pickup/transfer), and no clear recommendation can be made. Inadequate research exists regarding several other factors that might affect edentulous implant impression accuracy. There is a lack of clinical research to support in vitro findings.

Unlabelled: Impressions are taken regularly in practice giving vital information to the dental laboratory, but are there quality assurance systems in place to make sure that they are up to a sufficient standard? As dental professionals we have to appreciate that dental technicians can only work with the information given to them. This makes the skill of taking a good impression vital in order for us as clinicians to provide prostheses of good quality. This paper outlines an audit of alginate impressions and their quality in the making of removable prostheses., Clinical Relevance: To record the quality of impression taking, and how one's own ability to critique an impression may differ from that of our colleagues.

Movement of impression copings inside the impression material using a direct (open tray) impression technique during clinical and laboratory phases may cause inaccuracy in transferring the 3-dimensional spatial orientation of implants intraorally to the cast. Consequently, the prosthesis may require corrective procedures. This in vitro study evaluated the accuracy of 3 different impression techniques using polyether and vinyl polysiloxane (VPS) impression material to obtain a precise cast for multiple internal connection implants. A reference acrylic resin model with 4 internal connection implants was fabricated. Impressions of the reference model were made using 3 different techniques and 2 different impression materials. The study consisted of 24 specimens divided into 6 groups of 4 each. Impressions were poured with ADA type IV stone (Kalrock, Kalabhai Karson Pvt Ltd, Mumbai, India). All casts were evaluated for the positional accuracy (mm) of the implant replica heads using a profile projector. These measurements were compared to the measurements calculated on the reference resin model, which served as a control. Data were analyzed with 2-way analysis of variance (ANOVA) followed by Bonferroni multiple comparison procedures to evaluate group means. The results revealed significant difference for anterior implant distance between the 2 impression materials (P < .01) and also among the 3 different techniques (P < .05). The lowest mean variation was found with the polyether impression material and the splinted technique. For posterior implants, the results suggested no significant difference between the 2 impression materials (P ≥ .05). Although results were not statistically significant, the polyether impression material showed the lowest mean variation as compared to the VPS impression material. However, there was a significant difference among the 3 different techniques (P < .05). Among the 3 different techniques, the lowest mean variation between 2 posterior implants was found in the splinted technique. Casts obtained from impression techniques using square impression copings splinted together with autopolymerizing acrylic resin prior to the impression procedure were more accurate than casts obtained from impressions with nonmodified implant impression copings and with airborne particle-abraded, adhesive-coated copings. Casts obtained from polyether impression material were more accurate than casts obtained from vinyl polysiloxane impression material.

There are few published studies that directly assess the quality of impressions for crowns and bridges in the UK. This paper considers aspects of impression quality with particular attention to factors causing potential occlusal discrepancies in the final restoration. To this end three dental laboratories were visited over a 3-month period. All impressions for conventional crown and bridgework that arrived on the days of the visits were examined and assessed against criteria defined on a custom-designed assessment form. A total of 206 impression cases were considered in this study. Flexible impression trays were used for 65% of working impressions. Their use was more common for NHS work than for private work. 31.9% of all alginate impressions examined were not adequately fixed to the tray. Visible contamination of impressions was not uncommon.

Purpose: To evaluate the effect of two putty-wash impression techniques on the long-term accuracy and dimensional stability of poly(vinyl siloxane) (PVS) in the gingival sulcus area., Materials and Methods: Impressions were taken from a master cast to simulate molar crown preparation. A space around the abutment served as the gingival sulcus. Fifteen impressions using the one- and two-step impression techniques were taken using Express Regular, Express Fast, and President impression materials with custom trays. Using a Toolmaker's microscope, the long (LD) and short distances (SD) of the abutment and the planar distance between two parallel lines (PL) at the circumference of the cast were taken at 0.5, 2, 24, 48, 72, 96, 120, and 144 hours after mixing. ANOVA was performed, with the discrepancy between the distances of the impressions and the master cast as the dependent variable., Results: The differences when different materials and impression techniques were used were significant (p < 0.001) for LD, SD, and PL, as was the interaction between the material, time, and technique (p < 0.001). SD discrepancies were higher than those of LD for all materials and times. The two-step impression technique was more accurate, with smaller discrepancies than the one-step impression technique. For all materials, the PL discrepancy was deemed acceptable (less than 0.5%) for all tested times. President had higher discrepancies than the other materials., Conclusions: When using the two-step putty-wash impression technique, pouring of the impressions may be postponed up to 30 hours; however, when using the one-step impression technique, pouring should be performed within 2 hours., (© 2013 by the American College of Prosthodontists.)

Alginate as a substitute for root-surrounding tissue was investigated. The electronic working lengths of root canals under clinical conditions were compared with an in vitro simulation of the same teeth extracted and embedded in alginate. The working lengths in 26 teeth were determined on two occasions using an electronic apex locator, before extraction and after extraction with the same teeth embedded in an alginate mass. The apical 4 mm of the root canals were exposed following the measurements, and the distances between the apical constrictions and the tips of files repositioned in the canals were measured and recorded. The mean distance between the file tip and the constriction was +0.33 mm (±0.38) in vivo and +0.32 mm (±0.30) in vitro. The Wilcoxon signed-rank test indicated that these means were not significantly different. The apical constriction was assessed to be within the limits of 0.5 mm in 80.7% of in vivo cases and in 76.9% of extracted teeth. Statistical analysis demonstrated that there was no significant difference between the results recorded in vivo and in vitro regarding apical constriction localisation. Based on the results of this study, the alginate mass is a useful tool in evaluating the performance of electronic apex locators., (© 2012 The Authors. Australian Endodontic Journal © 2012 Australian Society of Endodontology.)

Previous studies have found that variations in mixing technique can influence the porosity content of alginate impression material. The aim of this study was twofold: determine whether bubble formation in alginate is influenced by the sequence of water/powder addition prior to mixing, and to compare 4 different mixing techniques. Manual spatulation, an automated spinning bowl, a centrifugal mixer and a vacuum mixer were evaluated for the resulting porosity in the set alginate. It was found that adding powder first, versus water first, made no difference in the bubble content using the 3 automated mixing techniques (P = 0.714). However, porosity was significantly less for powder-first trials using manual spatulation (P < 0.05). It was also found that surface porosity in the resulting impressions was significantly less for centrifugal and vacuum mixing when compared to manual spatulation, while internal porosity was significantly less for centrifugal mixing compared to all other mixing techniques (P < 0.05). The centrifugal mixing and vacuum mixing techniques required the least amount of mixing time.

Purpose: Reuse of metal impression copings may be desirable for both economic and environmental reasons. When impression copings are reused, it is important to be assured that they are as accurate as new ones. The purpose of the present in vitro study was to assess the effect of multiple use of impression copings on the accuracy of direct and indirect implant transfer techniques., Materials and Methods: An acrylic resin cast with five internal connection implants was fabricated. Forty medium-consistency polyether impressions of the cast with direct and indirect techniques were made using four sets (five each) of impression copings (square or conical). Impressions were poured with type IV dental stone. Then, the copings were subjected to a cleaning and sterilization process. The process was repeated 10 times with the same copings. Positional accuracy of the implant replica heads in x-, y-, and z-axes and also angular displacement (Δθ) were assessed using a coordinate measuring machine. These measurements were compared with the measurements made on the resin cast (control). Analysis of covariance for repeated measurements was used for the statistical analysis (α =.05)., Results: There were no significant differences among the following measurements: θx, θz, ;Δθ, and θr (P > .05) in both techniques. Only θy for the open tray impression technique was influenced during repeated use of impression copings (P = .02)., Conclusions: Within the limitations of this study, it could be concluded that impression copings can be successfully used, cleaned and sterilized up to 10 times without compromising the impression accuracy.

In spite of the constant improvement of impression materials impression taking is still rather challenging procedure. Impression quality considerably defines the effectiveness of prosthodontics oral rehabilitation. The method for impression quality assessment was elaborated in the study and used to estimate the quality of impressions taken for fixed prosthesis (teeth preparation quality was not assessed). More than 50% of impressions had improper quality.

Statement of Problem: The accuracy of impressions has been described in 1 or 2 dimensions, whereas it is most desirable to evaluate the accuracy of impressions spatially, in 3 dimensions., Purpose: The purpose of this study was to demonstrate the accuracy and reproducibility of a 3-dimensional (3-D) approach to assessing impression preciseness and to quantitatively comparing the occlusal correctness of gypsum dies made with different impression materials., Material and Methods: By using an aluminum replica of a maxillary molar, single-step dual viscosity impressions were made with 1 polyether/vinyl polysiloxane hybrid material (Identium), 1 vinyl polysiloxane (Panasil), and 1 polyether (Impregum) (n=5). Corresponding dies were made of Type IV gypsum and were optically digitized and aligned to the virtual reference of the aluminum tooth. Accuracy was analyzed by computing mean quadratic deviations between the virtual reference and the gypsum dies, while deviations of the dies among one another determined the reproducibility of the method. The virtual reference was adapted to create 15 occlusal contact points. The percentage of contact points deviating within a ±10 µm tolerance limit (PDP(10) = Percentage of Deviating Points within ±10 µm Tolerance) was set as the index for assessing occlusal accuracy. Visual results for the difference from the reference tooth were displayed with colors, whereas mean deviation values as well as mean PDP(10) differences were analyzed with a 1-way ANOVA and Scheffé post hoc comparisons (α=.05)., Results: Objective characterization of accuracy showed smooth axial surfaces to be undersized, whereas occlusal surfaces were accurate or enlarged when compared to the original tooth. The accuracy of the gypsum replicas ranged between 3 and 6 µm, while reproducibility results varied from 2 to 4 µm. Mean (SD) PDP(10)-values were: Panasil 91% (±11), Identium 77% (±4) and Impregum 29% (±3). One-way ANOVA detected significant differences among the subjected impression materials (P<.001)., Conclusions: The accuracy and reproducibility of impressions were determined by 3-D analysis. Results were presented as color images and the newly developed PDP(10)-index was successfully used to quantify spatial dimensions for complex occlusal anatomy. Impression materials with high PDP(10)-values were shown to reproduce occlusal dimensions the most accurately., (Copyright © 2012 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.)

The purpose of this study was to compare the accuracy of casts made using three different impression techniques to obtain an accurate definitive cast for fabrication of multiple-implant prostheses. Twelve experimental groups were formed combining the following conditions: three impression techniques, two impression materials, and two cast materials. The main effects of the three factors were analyzed by three-way analysis of variance using the full factorial general linear model between factors. The results showed that there were no significant differences in mean values for the transferred dimensions between the control and experimental groups. None of the measurements in the horizontal plane of the definitive casts demonstrated significant differences among the impression techniques with different impression and cast materials (P > .01).

Aims: To evaluate the handling of a new impression mixing device and the associated impression material by general dental practitioner members of the PREP Panel., Design: By means of a questionnaire, the participating practitioners recorded their views on the mixing machine and impression materials, having used these for ten weeks., Setting: UK general dental practices., Participants: General dental practitioner members of a UK practice-based research group., Methods: A questionnaire was designed to elicit views on the performance of the mixing device and impression material under test. This was distributed to the practitioners who had used the test materials for 10 weeks and the data thereby obtained collated and presented, principally in the form of VAS scales., Outcome Measures: Rating of various parameters of the mixing device and impression materials on VAS scales., Results: The Pentamix 3 machine scored well for ease of initial use [4.8 on a visual analogue scale (VAS) where 1 = very difficult to use and 5 = very easy to use]. In a range of criteria (including cleanliness, easy handling, time to fill the tray and overall convenience) the Pentamix scored highly on VAS scales. A maximum score of 5 (on a VAS where 1 = very dissatisfied and 5 = very satisfied) was achieved for reproducible mixing quality. The appreciation of the Pentamix 3 mixing machine was demonstrated by the fact that 85% (n = 11) of evaluators stated that they would recommend it to colleagues. Regarding the impression material under evaluation, 85% (n = 11) of the evaluators stated that they would recommend Impregum Quick impression materials to their colleagues., Conclusions: Within the limitations of this study, the Pentamix 3 automatic impression mixing device scored highly in this assessment, together with the impression materials assessed., (© 2011 FDI World Dental Federation.)

The purpose of this article is to review impression materials used for fabricating fixed restorations in dentistry. Their compositions, properties, advantages, and disadvantages are presented and compared. How these properties influence clinical decisions is also described. This review helps the clinician choose which material is more suitable for a specific case. A broad search of the published literature was performed using Medline to identify pertinent current articles. Textbooks, the Internet, and manufacturers' literature were also used to supplement this information. It is limited to impression materials used in fixed prosthodontics. The review gives basic knowledge of ideal impression material properties and discusses traditional and, primarily, more recently developed products, such as polyethers, poly(vinyl siloxane), polysulfides, and condensation silicone materials. Clear advantages and disadvantages for these impression materials are provided along with the role that compositional variations have on the outcome of the impression. This should enable clinicians and technicians to easily identify the important physical properties of each type of impression material and their primary clinical indications., (© 2011 by The American College of Prosthodontists.)

Purpose: The accuracy of dental impression taking is one major factor influencing the fit of crowns and fixed partial dentures. The aim of this study was to determine the accuracy of three-dimensional (3-D) tooth surface and subgingival tooth surface reproduction using three different silicone materials and the two-stage putty-and-wash technique., Materials and Methods: From 24 probands, three impressions each were taken with Express STD Putty/Wash (3M ESPE), Optosil/Xantopren L (Heraeus Kulzer), and an experimental ultralight body/putty material (3M ESPE) in a randomized order. The preliminary impression was cut according to established procedures for the two-stage putty-and-wash technique. Master casts were manufactured with a standardized procedure and optically digitized. The 3-D accuracy was analyzed with a computer-aided procedure. The Express STD putty-and-wash impressions were used as a reference. Linear models were used for the statistical analysis., Results: Mean deviations of 27.0 microm and -23.6 microm were found for Optosil/Xantopren L and 26.5 microm and -22.6 microm for the experimental material when analyzing 3-D surface reproduction. The tooth surface (buccal/oral) significantly influenced the accuracy of the surface reproduction. Optosil/Xantopren L showed a more complete reproduction of the subgingival tooth surface than either the experimental or reference materials., Conclusion: The accuracy of the 3-D tooth surface reproduction as well as the reproduction of the subgingival tooth surface was not favorably influenced when the ultralight wash material was used with established cutting procedures for the preliminary impression.

Several impression materials are available in the Brazilian marketplace to be used in oral rehabilitation. The aim of this study was to compare the accuracy of different impression materials used for fixed partial dentures following the manufacturers' instructions. A master model representing a partially edentulous mandibular right hemi-arch segment whose teeth were prepared to receive full crowns was used. Custom trays were prepared with auto-polymerizing acrylic resin and impressions were performed with a dental surveyor, standardizing the path of insertion and removal of the tray. Alginate and elastomeric materials were used and stone casts were obtained after the impressions. For the silicones, impression techniques were also compared. To determine the impression materials' accuracy, digital photographs of the master model and of the stone casts were taken and the discrepancies between them were measured. The data were subjected to analysis of variance and Duncan's complementary test. Polyether and addition silicone following the single-phase technique were statistically different from alginate, condensation silicone and addition silicone following the double-mix technique (p < or = .05), presenting smaller discrepancies. However, condensation silicone was similar (p > or = .05) to alginate and addition silicone following the double-mix technique, but different from polysulfide. The results led to the conclusion that different impression materials and techniques influenced the stone casts' accuracy in a way that polyether, polysulfide and addition silicone following the single-phase technique were more accurate than the other materials.

Disinfection of impressions by immersion or spraying with disinfecting solutions is considered nowadays mandatory for effective infection control. The purpose of this review was to examine existing evidence on the effects that chemical disinfection may have on critical qualities of impressions, namely dimensional accuracy and stability over time. A PubMed search was conducted to include original laboratory research articles written in English, published between 1980 and 2005 in peer-reviewed journals and investigating the effect of chemical disinfection, by immersion or spraying, on the dimensional changes that the impression materials experience after setting. Studies were also sought manually, by tracing the references cited in the retrieved articles. The reports on dimensional changes of disinfected impression materials, although rather numerous, are difficult to compare and analyze because of variations of the experimental design. The investigations broadly agree that the disinfection process does not generally affect the dimensional integrity of the impressions, in spite of the statistically significant differences occasionally found. However, the immersion in the disinfecting solution encourages water absorption phenomena in the case of the so-called hydrophilic impression materials, especially after the long-term immersion. Chemical interactions between impressions and disinfectants may occur, but they do not appear to influence the dimensional behaviour of the former. The overall effect of the disinfection is influenced not only by the changes experienced by the impression per se, but also by the alterations of the acrylic tray containing the impression and of the gypsum product poured in it.

Objective: To determine the dimensional stability of alginate impressions poured at varying time intervals in a tropical environment., Materials and Methods: Alginate impressions of a master model of truncated metal cones were made and poured at varying time intervals of 5 minutes, 30 minutes, 1 hour, 2 hours and 4hours. The liner dimensional differences between the master cast and stone casts of alginate impressions poured at varying time intervals was determined., Results: Although, there was observed increasing percentage differences with increasing length of time before pouring of the cast for all the inter-abutment distances measured, there was no statistical significant difference in dimension of the cast at ten minutes for all the distances measured except distance D with mean 50.23 and p value 0.010 while there were statistical significant changes observed at all the other time groups and distances., Conclusion: Alginate impressions should be cast within 10 minutes although, casts obtained from impressions stored by covering with wet gauze as is commonly done, for not more than 30 minutes will be clinically usable.

This study was carried out to measure the dimensional changes in silicone impression material, which can affect the fitness of the prosthesis. Using both single and double mix techniques, 20 impression samples for each of 3 different proprietary silicones, Xantopren-H, President and Fulldent, were made. Selected measurements were made on the stone casts made from each impression. In all 3 cases, the single mix gave more accurate casts than the double mix technique. The Xantopren-H impressions had the most accurate dimensions.

The adequacy of prescription for fabrication of cobalt chromium removable partial dentures is often regarded as being less than ideal. This study examines the nature and quality of written instructions and master impression sent to dental laboratories in Ireland for fabrication of cobalt chromium removable partial denture frameworks. Questionnaires were issued to dental laboratories seeking specific information relating to the materials (impression materials and trays) and written instructions supplied, as well as the technicians' opinion regarding the suitability of these materials. One hundred completed questionnaires were returned. One-third of master impressions were made using a plastic stock tray and alginate; technicians felt that one-fifth of master impressions were unsuitable; almost three-fifths of written instructions were inadequate. The quality of clinical information examined was found to be less than adequate.

One of the most critical problems related to hand mixing of an elastomeric impression material is air entrapment during spatulation. This leads the formation of both surface and subsurface bubbles which in turn may result in inaccurate dental impressions and/or jeopardize their physical properties. In the present study the influence of the mixing technique has been determined by evaluating the surface area and the number of voids in two polyether materials (Permadyne and Impregum, Espe, Seefeld, Germany). The techniques tested were the stropping technique as hand-mixing and the Pentamix device (Espe) as mechanical mixing. Eighty special trays (10 mm x20 mm x43mm) featuring 10 transverse slots were fabricated and divided into four groups of twenty units. Groups 1 and 2 received the hand-mixed materials Permadyne high viscosity and Impregum F, respectively. Groups 3 and 4 (Pentamix group) received the mechanically mixed materials Permadyne Penta H and Impregum Penta, respectively. After polymerization, 10 slices of material were obtained for each tray by sectioning through the tray slots with a surgical blade. The slices were glued on a card and black and white photographs were taken. Subsequently, the negative films were placed on a viewing box and digitized with a video camera. A special software program allowed to identify and calculate the total surface area and the number of voids. Significant differences between the "stropping" groups (groups 1 and 2) and "Pentamix" groups (groups 3 and 4) were found. The mechanical mixing (Pentamix) generated the smallest number and total surface area of voids, while no significant differences were detected between Permadyne Penta H and Impregum Penta. Clearly, mechanical mixing represents a marked improvement over the traditional hand-mixing methods.

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.

Statement of Problem: Monophase addition-cured silicone impression materials in stock trays are considered to be alternatives to two-phase systems used with custom trays., Purpose: This study compared the number of surface defects in addition-cured silicone impressions recorded with monophase materials in stock trays and two-phase impressions in custom trays., Methods: The number of voids visible on the surface of impressions recorded in vitro were counted. Two monophase impression materials. (President Monobody system 75, Bayer Cutter) in stock trays were compared with impressions recorded with two-phase addition silicone materials (President Plus light-body/regular-body and Zhermack Elite light-body/medium-body) in custom trays. A total of 200 automixed impressions, 50 with each material, were recorded of 50 dentoform molar teeth prepared for full veneer crowns. Impressions were examined for surface voids anywhere on the prepared part of the tooth by a trained examiner., Results: Mean number of voids observed for the monophase impressions were 3.0 +/- 2.2 for President Monobody system and 3.4 +/- 2.0 for Bayer Cutter system. Mean number of voids for the two-phase materials were 0.8 +/- 1.0 for President Plus, and 1.0 +/- 1.1 for Zhermack Elite. No significant differences were observed for number of voids between the monophase materials or between the two-phase systems (ANOVA and Neuman-Keuls p > 0.05). However, both two-phase materials in custom trays had significantly fewer surface voids than the two-monophase materials (ANOVA and Neuman-Keuls, p < 0.001) used in stock trays., Conclusion: Monophase addition-cured impression materials in stock trays carries an increased risk of void formation on the surface of the impression when compared with two-phase addition silicone materials in custom trays.

Effect of sodium hypochlorite disinfection of impressions on the size and quality of plaster models is studied. Twenty-minute submerging of silicone impressions in 0.5% sodium hypochlorite solution did not change their size and did not deteriorate the quality of surface and hardness of plaster models. Stomalgin impressions cannot be disinfected by sodium hypochlorite solution because of expressed destructive effect of this disinfectant on the impressions.

Statement of Problem: Storage stability is a critical characteristic for perishable dental materials., Purpose: The purpose of this shelf-life study was to document changes in the properties of an alginate impression material on exposure to various environmental conditions for more than 78 months., Material and Methods: Properties measured included recovery from deformation, strain in compression, compressive strength, tear strength, working time, and creep compliance., Results: Results revealed increases in strength and working time and a decrease in recovery from deformation at 30 to 50 months: strength and recovery then remained constant past 6 years, whereas working time and creep compliance decreased. Only the most stressful environmental conditions (heat and humidity) caused spontaneous failure of the material to set., Conclusions: We concluded that, under most storage conditions, properties of the alginate material tested remain within ADA specification limits well past manufacturer's designated shelf life. ADA specifications should require manufacturers to verify that the shelf life of each perishable material is based on valid data. An accelerated aging test was developed to simulate real time property changes and to assist in evaluating similar materials.

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.

The effect of the technique used for impression making on the accuracy of three types impression materials, (vinyl silicons, condensation silicons and polyether elastomers) was evaluated. Three main impression making techniques were used. Impressions were made for stainless steel master model. The impressions were poured after thirty minutes with improved stone into stone casts. Accuracy was assessed by comparing seven measurements of the master model to their corresponding on the stone case produced. A travelling microscope of 0.001 mm accuracy was used for measurements. The results of the study have shown that all elastomeric impression materials produced accurate impression but with significant difference among them. The polyether was more accurate than silicon impressions. The technique used for making the impression had more effect on the relative accuracy than the type of the material. Reference for the best technique for each type was concluded.

The accuracy of rubber impression materials was evaluated by taking impressions of a steel model, pouring it with stone and comparing certain measurements between steel and stone models. It is assumed that acceptance is achieved when the difference in measurements is within permissible limits, defined by clinical criteria. A mathematical formulation of these criteria will lead to the concept of probability of acceptance. The probability is affected when the limits are changed. The particular case of satisfying two acceptance criteria that contain variables which are not statistically independent is considered, leading to the application of the bivariate normal distribution in the evaluation of acceptance probability.

Four commercial tissue conditioners have been assessed in terms of their dimensional stability and ability to reproduce surface detail according to ADA specification #19 for impression materials. Results have been compared with those of a number of elastomeric impression materials. The tissue conditioners performed adequately and as such could be used as impression materials within 24 hours of their application. While they did not compare well with the elastomeric impression materials they comply with the limitations of the ADA specifications. It is suggested that standards specific to these materials should be developed.

This study investigated the effect of variation in proportioning polysulfide base and catalyst. Light, regular, and heavy-bodied pastes were mixed in linear equivalents of base-to-catalyst proportions of 30/70, 40/60, 50/50, 60/40, and 70/30. Compression set, strain in compression, and consistency tests conformed to the American Dental Association (ADA) Specification 19 guidelines. The amount of solventleachable components and differences in the cross-linked nature of the cured products were studies. Compression set and strain in compression tests met the ADA specification guidelines. Some consistency values fell outside of the ADA specification limits. The leachable content increased with increasing proportions of catalyst, but polymer cross-linking was remarkably similar for all bodied materials tested. Clinicians need not fear a significant property alteration in polysulfide impression material by the differences (within +/- 20% of the manufacturer's suggested lengths) in proportioning the component pastes with "eyeball" estimation as directed in the instructions.

Six interocclusal recording materials: COE Bite Creme, Blu-Mousse, Correct Bite, Blue Velvet, Memosil C.D. and Ramitec brands, were studied for evaluation of their dimensional stability and associated weight change. The materials were divided into six groups of 10 samples and tested between metal dental casts on the hydroptic test and measurement system. Dimensional changes among the materials were not significantly different. Weight changes among materials were significantly different but did not exceed 0.1%. All 6 brands were highly accurate and dimensionally stable.

A new method of measuring both working time and setting time of elastomeric impression materials has been developed. A Displacement Rheometer was used to monitor the development of elasticity in setting elastomers. The results obtained with the Displacement Rheometer were compared to the results of the ISO test as well as those of the Controlled Stress Rheometer. Working time using the ISO method was calculated according to the standard method described in the specification, while for both the Controlled Stress Rheometer and the Displacement Rheometer working times were the times when initial elastic recovery was observed at 23 degrees C. With the Displacement Rheometer the setting time is the time when the mixed material reaches optimal elastic recovery at 37 degrees C. Statistical analysis with ANOVA showed that for five of the test materials there were no differences between the three methods. For three of the materials the working time determined by the ISO method was significantly longer than that determined by the other two methods. The advantages and disadvantages of each method are discussed and the Displacement Rheometer is recommended as a supplement to the standard specification method.

The effect of loading and syringing on void formation in five automixed addition silicones was evaluated by determining the voids created in the first and second halves of material loaded and dispensed from a metal syringe. Impressions were made of a model with six stainless-steel cylinders. The voids were counted at a predetermined site on 3 separate days using a binocular microscope at x 7 magnification. Automixed addition silicones did not confirm the 'last out-fewer bubbles' phenomenon and specific loading and syringing technique did not appear to have a consistent effect on void formation in automixed elastomers.

Infection control in dentistry focuses on the prevention of cross-contamination among patients, dentists and dental personnel. Difficulties in sterilizing impression materials have led to chemical disinfection as an alternative. This study evaluated the efficacy of disinfectants on the surfaces of silicon and irreversible hydrocolloid materials involved microorganisms. All disinfectants used in this study was effective on Pseudomonas aeruginosa and Candida albicans for silicon impression material and Candida albicans for irreversible hydrocolloid.

The purpose of the present investigation was a comparison of three special articulation plasters and three impression plasters. As DIN 13911 does not refer to articulation plasters, the inspection as well as the testing of pouring time, setting time, setting expansion and compressive strength using standard and manufacturer's consistence as carried out conforming to the guidelines for impression plasters. None of the tested plasters could meet the requirements of inspection in all points. Considering the physical parameters all plasters are up to standard, while Alpa quickstone and Arti-Plaster exhibited very low expansion and high compressive strength values. Although the compressive strength standard needs redefining, the value of a standardized testing technique for dental plasters is evident.

The compatibility of four impression materials with 11 different die stones was tested. All the combinations tested performed within the 20 microns ADA standard.

Results of investigations of vinyl polysiloxanes indicate that they produce highly accurate impressions, have excellent elastic recovery, minimal permanent deformation, and adequate tear strength. A number of vinyl polysiloxanes are certified by the American Dental Association. All of these materials provide clinically acceptable results. Advantages of using the vinyl polysiloxanes include the ability of the impression to be poured up after 1 hour or 1 day, or for some products, after 1 week without significant loss of accuracy; the possibility of repouring the impression a second time and producing an accurate cast; the impression materials are available in several viscosities allowing flexibility in choosing an impression technique; and they can be immersed in recommended disinfectants without affecting the accuracy of the impression. The disadvantages of using the vinyl polysiloxanes include a difficulty in lengthening the working time of products without retarders and a high surface tension making it difficult to wet the impression when pouring up a stone cast. Hydrophilic materials appear to facilitate the casting of the impressions with stone. The automixing devices seem to provide convenience without sacrificing the quality of the impression and are currently available for several products. As with all elastomeric impression materials, proper handling is necessary to ensure the best results. The vinyl polysiloxanes seem to be an excellent choice of impression materials for many clinical situations.

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.