Avaliação do escoamento de materiais de moldagem elastoméricos através do teste 'Shark-Fin' modificado / Analysis of flow profile of elastomeric impression materials using a modified 'Shark-Fin' Test

Materiais de impressão com boa fluidez são essenciais para a captura das margens dos preparos dentais. O objetivo deste estudo, para tanto, foi avaliar, por meio do dispositivo de teste 'shark-fin' (3M ESPE), o escoamento de dois materiais de moldagem elastoméricos, um poliéter (PE) e um polivinilsiloxano (PVS). Foi realizada uma modificação no teste 'shark-fin' de modo a permitir a aproximação do estudo in vitro à realidade clínica, avaliando o comportamento de duas viscosidades de cada material aplicadas em um tempo único. Um poliéter (PE) de alta (Impregum Penta Soft / 3M ESPE) e de baixa viscosidade (Impregum Garant L Duosoft / 3M ESPE), um polivinilsiloxano (PVS) de alta (Express XT Penta H / 3M ESPE), de média (Express XT Pasta Fluida de Média viscosidade / 3M ESPE) e de baixa viscosidade (Express XT Pasta Fluida de Baixa viscosidade / 3M ESPE) foram divididos em 21 grupos (n=5) e testados isoladamente e combinados em proporções de 1 : 1, nos tempos de trabalho de 50, 80 e 120 s. Após, as alturas das barbatanas formadas foram medidas com o auxílio de um paquímetro digital. A análise estatística dos resultados foi realizada por análise de variância (ANOVA) one-way seguida pelo teste LSD post hoc (p=0,05). Verificou-se que os valores das alturas das barbatanas diferiram significativamente entre os materiais e a cada intervalo de tempo (p<0,05). As barbatanas diminuíram para todos os grupos com o aumento do tempo de trabalho, exceto para o grupo PE de baixa viscosidade e PVS em múltiplas misturas (alta associada à baixa viscosidade e alta associada à média viscosidade). Todos os grupos de PE apresentaram valores mais altos para as barbatanas formadas em comparação aos grupos de PVS, tanto em uma viscosidade quanto em duas viscosidades associadas, durante todo o tempo de trabalho. O poliéter mostrou um melhor comportamento no que diz respeito ao escoamento quando comparado ao polivinilsiloxano. (AU)

Good flowable impression materials are needed to capture preparation margins. The aim of this study was to evaluate, through the 'shark-fin' test device (3M ESPE), the flow of two elastomeric impression materials, a polyether (PE) and a polyvinylsiloxane (PVS). The 'shark-fin' test was modified to convey the approximation of the in vitro study to the clinical application, assessing the behavior of two viscosities of each material applied at one point in time. A high viscosity polyether (PE) (Impregum Penta Soft / 3M ESPE) and a low viscosity (Impregum Garant L Duosoft / 3M ESPE), a high viscosity polyvinylsiloxane (PVS) (Express XT Penta H / 3M ESPE), a medium viscosity (Express XT Regular Body / 3M ESPE) and a low viscosity (Express XT Light Body / 3M ESPE) were divided into 21 groups (n=5) and tested solely, and in a layered mixture of 1 : 1 at working times of 50, 80 and 120 s. Afterwards, the fin heights were measured with a digital caliper. The statistical analysis was performed by one-way analysis of variance (ANOVA) and LSD post hoc test (p=0,05). It was found that the 'shark-fin' values differed significantly among materials and at each time interval (p<0,05). The fin heights decreased for all groups with increasing of working time, except for the low viscosity PE and PVS in multiple mixtures (high with low viscosity and high with medium viscosity). The PE groups showed the highest 'shark-fins' compared to PVS, both in single and multiple mixtures, during the entire working time. The polyether impression materials had a better flow profile compared to polyvinylsiloxane groups. (AU)

Evaluation of the effect of storage time and disinfectant solutions on the dimensional accuracy of impression materials with digital radiography.

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.

Estabilidade dimensional de moldes obtidos com alginato de armazenamento tardio / Dimensional stability of molds obtained with late storage alginate

Resumo Introdução Recentemente, vêm surgindo no mercado alguns alginatos de armazenamento prolongado. Não há, no entanto, um consenso na literatura a respeito da estabilidade dimensional destes materiais durante este armazenamento Objetivo Avaliar, por meio de método prático experimental, a estabilidade dimensional de um alginato de armazenamento tardio. Material e método O material de moldagem utilizado foi o alginato Hydrogum 5 (Zhermack). Uma matriz metálica cilíndrica foi utilizada para a realização das moldagens, com 38 mm de diâmetro externo, 30 mm de diâmetro interno e cuja superfície superior apresenta três linhas paralelas entre si com 25 mm de comprimento e 20, 50 e 75 µm de largura. Após o tempo de geleificação do material de moldagem, 16 moldes foram colocados em um umidificador e essas amostras foram fotografadas utilizando-se uma câmera digital (Canon EOS Rebel 3Ti, Canon) associada a um software para análise das imagens obtidas (ImageJ 1.52a, U.S. National Institutes of Health; DI). A calibragem da régua foi 10 cm e, posteriormente, três linhas foram medidas três vezes, para se obter uma média dos comprimentos das linhas. As amostras foram fotografadas nos seguintes intervalos: imediatamente, 24, 48, 72, 96 e 120 horas. Resultado Os dados mostraram diferenças estatisticamente significantes para o fator tempo quando comparada a leitura imediata com os demais períodos de tempo de leitura (p<0,001) e quando comparada a leitura após 24 h de armazenagem com os demais períodos de tempo (p<0,001). Não houve diferença estatística (p>0,05) quando os tempos de armazenamento de 48 h, 72 h, 96 h e 120 h foram comparados entre si. Todos os valores encontravam-se dentro dos valores preconizados pela ISO 21563:2013. Conclusão Os moldes dos alginatos testados podem ser armazenados por até cinco dias em 100% de umidade relativa.

Abstract Introduction Recently, some extended-pour alginate impression materials have been placed in the market. However, there is no consensus in the literature regarding the dimensional stability of these materials during these storage. Objective To evaluate, through the experimental model, the durability and velocity with respect to dimensional alteration, analyzing the material and detecting distortions. Material and method The material for molding in this test was alginate (Hydrogum 5, Zhermack). A cylindrical metallic matrix was used to make the moldings with: 38 mm of external diameter, 30 mm of internal diameter and superior of the upper series of the card 3d transport lines with each 25 mm in length and 20, 50 and 75μm in width. After the time of jellification / polymerization of the molding material, 16 molds were inserted in a doser and were photographed with a digital camera (Canon EOS Rebel 3Ti, Canon) associated with a software for analysis of sacred images (ImageJ 1.52a, US National Institutes of Health, DI). The calibration of the ruler was performed in 10 cm and then in 3 lines were means 3 (three) times to obtain a mean of the lengths of the lines. The photographs were taken at the following intervals: immediately, 24, 48, 72, 96 and 120 hours after being cast. Result The data were found when compared with the other parts of the reading time (p <0.001) and when compared to the execution after 24 hours of locomotion with the other parts of the time (p <0.001). The rest time of 48 hours, 72 hours, 96 hours and 120 hours were compared to each other. Conclusion The molds of the tested alginates can be stored for 5 days in 100% relative sauce.

Digital evaluation of the dimensional accuracy of four different implant impression techniques.

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.

Does 6 Hours of Contact With Alginate Impression Material Affect Dental Cast Properties?

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.

A Proposed Methodology to Assess the Accuracy of 3D Scanners and Casts and Monitor Tooth Wear Progression in Patients.

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.

Estudio de dos técnicas de desinfección en un material de impresión / Study of the effect of two disinfection techniques on an impression material

El controlar la infección es una obligación profesional de fundamental importancia así como la reducción del riesgo de contaminacióncruzada durante los procedimientos clínicos para la calidad y la seguridad en la práctica dental. Material y métodos: Un total de 27 impresiones individuales fueron obtenidas de pacientes, las cuales se dividieron en tres grupos para su tratamiento. Grupo control: nueve impresiones individuales usando una silicona por adición, sin desinfectar,fueron sumergidas en agua bidestilada durante 10 minutos. Grupo A: nueve impresiones individuales fueron sumergidas en glutaraldehído al 2 por ciento durante 10 minutos. Grupo B: nueve impresiones individuales fueron esterilizadas mediante autoclave a 134 oC por 15 minutos a 15 psi. Resultados: Después de realizar el conteo bacteriano respectivo de cada grupo de estudio, se observó el crecimiento bacteriano en dosgrupos, siendo notoria la falta de crecimiento en las muestras del grupoB, mientras que en el grupo control la cuenta fue mayor que en el grupo A. Conclusiones: El lavado de la impresión reduce la cantidad de microorganismos presentes mas no la desinfecta. El glutaraldehído al 2 por ciento fue eficaz en la eliminación de microorganismos no esporulados provenientes de la cavidad oral presentes en las impresiones conmaterial elastomérico. La eliminación completa de microorganismos puede ser lograda mediante la esterilización de las impresiones con material elastomérico...

Measurement of the accuracy of dental working casts using a coordinate measuring machine.

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 1­3 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]

A comparison of the accuracy of polyether, polyvinyl siloxane, and plaster impressions for long-span implant-supported prostheses.

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.

Accuracy of impressions of multiple implants in the edentulous arch: a systematic review.

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.

How good are our impressions? An audit of alginate impression quality in the production of removable prostheses.

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.

The quality of impressions for crowns and bridges: an assessment of the work received at three commercial dental laboratories. assessing qualities of impressions that may lead to occlusal discrepancies with indirect restorations.

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.

Evaluation of accuracy of casts of multiple internal connection implant prosthesis obtained from different impression materials and techniques: an in vitro study.

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.

The effect of one-step vs. two-step impression techniques on long-term accuracy and dimensional stability when the finish line is within the gingival sulcular area.

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.

Evaluation of alginate as a substitute for root-surrounding tissues in electronic root canal measurements.

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.

Effects of mixing technique on bubble formation in alginate impression material.

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.

[Estimation of impression quality in fixed prosthesis oral rehabilitation].

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.

Effect of multiple use of impression copings on the accuracy of implant transfer.

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.