The effect of tray selection on the accuracy of elastomeric impression materials

This study evaluated the accuracy of reproduction of stone casts made from impressions using different tray and impression materials. The tray materials used were an acrylic resin, a thermoplastic, and a plastic. The impression materials used were an additional silicone, a polyether, and a polysulfide. Impressions were made of a stainless steel master die that simulated crown preparations for a fixed partial denture and an acrylic resin model with cross-arch and anteroposterior landmarks in stainless steel that typify clinical intra-arch distances. Impressions of the fixed partial denture simulation were made with all three impression materials and all three tray types. Impressions of the cross-arch and anteroposterior landmarks were made by using all three tray types with only the addition reaction silicone impression material. Impressions were poured at 1 hour with a type IV dental stone. Data were analyzed by using ANOVA with a sample size of five. Results indicated that custom-made trays of acrylic resin and the thermoplastic material performed similarly regarding die accuracy and produced clinically acceptable casts. The stock plastic tray consistently produced casts with greater dimensional change than the two custom trays.     

Dimensional accuracy of dental casts: Influence of tray material, impression material, and time

PURPOSE: This study evaluated the influence on dimensional accuracy of dental casts made with different types of trays and impression materials and poured at different and multiple times. MATERIALS AND METHODS: Two types of stock trays (plastic stock tray, perforated metal stock tray) and 4 types of custom tray materials (autopolymerizing acrylic resin, thermoplastic resin, and 2 types of light-polymerized acrylic resins) were used with 2 types of impression materials (addition polymerizing silicone and polyether), to make impressions of a metal master model. Each tray and impression material was used to make 5 impressions. Casts were made by multiple pourings at 30 minutes, 6 hours, 24 hours, and 30 days after impression making. Using a measuring microscope, 12 distances were calculated based on measurements of 8 reference points. The absolute value of the difference of each measurement was calculated, as was the corresponding measurement on the master model. A Bayesian model using a simple noninformative prior was used to analyze these data. RESULTS: Statistical differences within 6 microm were found only with thermoplastic resin tray material for addition silicone, and for thermoplastic resin tray material and 1 type of light-polymerized acrylic resin for polyether. Neither stock trays nor custom trays contributed to the differences in accuracy of the casts. All deviations in casts made with silicone impression material were within a clinically acceptable range. For the polyether, distortions occurred that were clinically unacceptable. Impressions made from polyether distorted over time. Silicone impression material has dimensional stability up to 30 days. CONCLUSION: Accurate casts can be made with either stock trays or custom trays. An impression made from polyether should be poured only once and within 24 hours after impression making, because of the distortion of the material over time. Silicone impression material has better dimensional stability than polyether. .     

Dimensional stability of elastomeric impression materials in custom-made and stock trays

Elastomeric impression materials for fixed prosthodontics are considered most stable when they have an even thickness of 2 to 4 mm. To obtain this, a custom-made impression tray is recommended. The purpose of the present study was to compare the stability of impressions made in custom trays and trays made of chromium-plated brass. The impression materials chosen were polyether and silicone.Two master models of the upper jaw were made of metal. The canines and first molars represented abutment teeth with flat occlusal surfaces. An engraved cross on each surface made it possible to measure in a microscope the distances between the abutment teeth on the models and in the impressions. The accuracy of the method was within ±8 μm. Twelve standardized impressions were made with each impression material in the two types of trays. The distances between the abutment teeth were measured immediately on removal of the impression, and after 1 and 24 hours. Although ample amount of impression material (2 to 9 mm) was allowed, the linear dimensional stability of the impressions made in stock trays was not inferior to the stability of impressions made in custom-made trays.     

藻酸盐印模材取模的三维精度变化

通过对石膏模型的定量测量评价六种牌号藻酸盐印模材的取模精度,实验金属模型模仿三单位固定义齿,在显微镜放大25倍下,对金属模型翻制的石膏模型上观测线交叉点的间距进行测量,测距包括:颊舌向(BL)、近远中向(MD)、(牙合)龈向(OG)和基牙间距离(IP).结果表明所有牌号的印模材制取的印模均无统计学上显著的三维尺寸变化,石膏模型精度临床可接受.但只有AP组印模材制取的石膏模型可补偿后续制做中的收缩.     

What is the evidence base for the efficacies of different complete denture impression procedures? A critical review

ObjectivesMany procedures used in prosthodontics, including the materials and methods used for complete denture impressions, lack support of good evidence. The aims were to systematically, and critically, review the literature on complete denture impression materials and methods to identify an impression procedure that can be considered expedient for achieving a satisfactory clinical outcome for complete denture wearers.Data and sourcesMEDLINE/PubMed and the Cochrane Library were searched for studies on impression procedures used in the clinical fabrication of complete dentures. The search focused on best available evidence with respect to clinical outcome.Study selectionPubMed listed 1201 titles for the combination terms of complete denture and impression. Five relevant randomized controlled trials were identified. No review of complete denture impressions was found in the Cochrane Library.ResultsTwo-step procedures for complete denture impressions dominate all textbooks, teaching and specialist practice, despite an absence of convincing evidence of its superiority. No controlled studies supporting the use of border moulding, post-dam, and functional and mucostatic impressions, were identified. Two studies showed that a one-step method using alginate in a stock tray offers a similar clinical result to more complicated, expensive and time-consuming two-step material and technique combinations.ConclusionsThere was no support for the frequent textbook statement that the two-step procedure is necessary and superior to the one-step method. While some special clinical situations may benefit from other combinations of materials and techniques, the results suggest that the simple and inexpensive one-step procedure can serve the needs of the majority of edentulous patients.Clinical significanceIn spite of the fact that two-step procedures for complete denture impressions dominate textbooks, teaching and specialist practice, the results of this review suggest that a simple and inexpensive one-step procedure can serve the needs of the majority of edentulous patients.     

Comparison of impression materials for direct multi-implant impressions

STATEMENT OF PROBLEM: Given that meticulous implant prosthodontic procedures are recommended to obtain the best possible intraoral fit, impression materials that are suitable for use with a direct impression technique warrant further investigation. PURPOSE: This in vitro study compared the amount of torque required to rotate a square impression coping in an impression and evaluated the accuracy of solid implant casts fabricated from different impression materials. MATERIAL AND METHODS: Two direct transfer implant impressions were made using 8 impression materials; the torque required to rotate an impression coping in the impressions was calculated. Ten direct transfer implant impressions were made from the master model and poured in a die stone (Resin Rock) for 3 of the 8 initial impression material groups. Linear distances between steel balls placed on each abutment replica were measured with a traveling microscope to determine distortion in the impression procedure for each group. Data were analyzed (P =.05) with ANOVA and Ryan-Einot-Gabriel-Welsch multiple range test for post hoc. RESULTS: With a 1-way ANOVA, average torque values among the material groups differed significantly (P =.001). Polyether (medium consistency) was found to produce the highest overall torque values, followed by addition silicone (high consistency), and then polysulfide (medium consistency). Statistically significant difference was also found among the 3 material groups' mean absolute cast error using a 1-way ANOVA (P =.0086). Implant casts made from polyether (medium) or addition silicone (high) impressions were significantly more accurate than casts made from polysulfide medium impressions. CONCLUSION: On the basis of the results of this study, the use of either polyether (medium) or addition silicone (high) impression is recommended for direct implant impressions.     

Gingival sulcus simulation model for evaluating the penetration characteristics of elastomeric impression materials

PURPOSE: This study evaluated the ability of five elastomeric impression materials to penetrate the gingival sulcus beyond the preparation margin. MATERIALS AND METHODS: A model of brass and agar gel was made to simulate human sulci and clinical gingival conditions. Two addition-curing silicones, one condensation-curing silicone, one polyether, and one polysulfide were tested. Ninety impressions of the model were made, six impressions with each material with differing sulcular widths. The centers of sulcular extension of these impressions were found with a measuring microscope. RESULTS: Two-way ANOVA showed significant differences among impression materials, sulcular widths, and their interactions. The penetration ability of polyether showed greater extension than the other materials, regardless of sulcular width. Polysulfide penetrated less than the two silicones with 0.2- and 0.1-mm sulcular widths but more with the narrow 0.05-mm sulcular width. CONCLUSION: These results suggest that the viscoelastic behavior of elastomers depends on the width of sulci. Moreover, the sulcus simulation model effectively contributes to the investigation of their characteristics.     

Pressure Produced on the Residual Maxillary Alveolar Ridge by Different Impression Materials and Tray Design: An In Vivo Study

Increased ridge resorption may occur due to inappropriate pressure applied during final impression making phase of complete denture fabrication. This study was done to evaluate the pressure applied on the residual ridge while making impressions with two tray designs (with and without spacer) using, zinc oxide eugenol and light body polyvinyl siloxane impression material. Five edentulous subjects were randomly selected. For each of the five subjects four maxillary final impressions were made and were labelled as, Group A-Impression made with tray without spacer using zinc oxide eugenol impression, Group B-Impression made with tray with spacer using zinc oxide eugenol impression material, Group C-Impression made with tray without spacer using light body polyvinyl siloxane impression material, Group D-Impression made with tray with spacer using light body polyvinyl siloxane impression material. During the impression procedure a closed hydraulic system was used to remotely measure the pressures produced in three areas. The pressure produced were calibrated according to the micro strain record. Statistical comparisons of readings were done using t test and ANOVA. The acquired data revealed that ZOE produced an average pressures value of 26.534 and 72.05 microstrain, while light body PVS produced 11.430 and 37.584 microstrain value with and without spacer respectively. Significantly high values were recorded on the vault of the palate when using trays without spacer. The use of light body polyvinyl siloxane and zinc oxide eugenol impression material showed insignificant difference. Within the limitations of this study, tray design has a significantly effected on the pressures produced, while the impression materials does not have any significant difference.     

Vinyl polysiloxane impression material in removable prosthodontics. Part 2: Immediate denture and reline impressions

Accurate impressions are important elements in both the fabrication and maintenance phases of complete denture therapy. For patients possessing nonrestorable, periodontally hopeless residual dentitions, immediate denture therapy is often the treatment of choice. An impression procedure capable of accurately registering functional vestibular anatomy facilitates successful therapy. For complete dentures currently in function, periodic assessment and correction of fit extends long-term prosthesis performance. To maintain optimal tissue-base relationships, use of specialized impressions, and subsequent laboratory reline procedures is often indicated. For both of these impression procedures (ie, immediate denture impressions and denture reline impressions), vinyl polysiloxane (VPS) impression material offers distinct advantages. Part 2 of this article series reports on the use of VPS for immediate denture and reline impression procedures.     

Influence of impression material and time on the 3-dimensional accuracy of implant impressions.

OBJECTIVE: To investigate, in vitro, the effect of time on the 3-dimensional accuracy of open-tray implant impression copings made of polyvinyl siloxane and polyether impression materials. METHOD AND MATERIALS: Reference models with 4 internal connection implants were fabricated. Four sets of 71 direct impressions were made with square impression copings using an open-tray technique. One set of impressions was made with polyether material (material A) and each of 3 polyvinyl siloxane materials (materials B, C, and D). Three-dimensional changes in spatial orientation of the implant analogs were measured over 48 hours using an optical measurement device. Deviation values were summed over 4 points and averaged per impression. Global differences were tested with a nonparametric Kruskal-Wallis test followed by pairwise comparisons using the Mann-Whitney U test. RESULTS: The mean dimensional accuracy of implant impressions significantly differed over time (P < .001). Materials A and B were found to produce comparable results, For materials C and D there was a significant increase in deviations, with a maximum increase at 2 hours. Deviations for material C were comparable to materials A and B at 48 hours. Baseline values were not maintained by any material. CONCLUSIONS: Within the limits of this in vitro study, it can be concluded that time cannot be neglected as a factor affecting the accuracy of implant master casts.     

Application of a 3-dimensional measurement system to complete denture impressions

STATEMENT OF PROBLEM: Little is known about tissue displacement at the tissue/denture base interface during impression making. PURPOSE: This study used a new 3-dimensional measurement system to analyze and compare 2 complete denture reline impression techniques (1 occluding and 1 digital) to determine which resulted in less displacement of the tissue/denture base interface during impression making. MATERIAL AND METHODS: The experiment included 10 completely edentulous subjects. For each subject, 3 mandibular casts were obtained: (1) a reference cast of the existing denture base, (2) a cast made with an occluding reline impression technique, and (3) a cast made with a digital reline impression technique. With the use of an optical 3-dimensional measurement system, the corresponding casts in a common coordinate system were analyzed geometrically. For each cast, the coordinates of the barycentric point and the high point were determined. For the same subject, the differences between the coordinates of the barycentric points of the 3 casts were calculated 2-by-2. The same calculation was performed for the high points. To determine whether these differences, which represent the displacements of the barycentric points and the high points, were statistically significant, the Wilcoxon signed-rank test for paired group comparisons was applied (P<.05). Cartographic differences among the casts from the same subject also were compared. RESULTS: The uncertainty of measurement for the location of the barycentric and highest point was +/-57 microm. The uncertainty in the differences among the cartographic displays was +/-0.1 mm. Vertically, the mean distance that separated the barycentric points obtained with the 2 impression methods was 0.04 mm. Cartography data showed that the greatest dimensional differences between the 2 impression techniques (minimum 0.25 mm; maximum 1.5 mm) were located near the retromolar pad and along the lingual flange. CONCLUSION: Within the limitations of this 3-dimensional in vivo study, displacement of the tissue/denture base interface was essentially equivalent with the use of an occluding and a digital mandibular impression technique.     

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目的比较硅橡胶闭口式印模法和开口式印模法在无牙颌义齿修复中的临床疗效。方法收集2008年3月至2011年9月福建医科大学附属第一医院口腔科收治的无牙颌修复患者30例,按初诊时间顺序随机分为闭口式印模组和对照组,分别使用闭口式和开口式印模法制作全口义齿,3个月后复查其吸附力和压痛修改情况。结果用闭口式印模法制作的全口义齿,吸附力好于开口式印模法,其压痛修改次数也明显减少。结论对于无牙颌全口义齿的制作,硅橡胶闭口式印模法优于开口式印模法。     

消毒液浸泡消毒对藻酸盐印模尺寸稳定性影响的评价研究

目的评价用三种消毒液浸泡不同时间后,四种藻酸盐印模的尺寸稳定性。方法采用符合YY1027国家行业标准和ISO 1563国际标准的标准试验装置,制取四种藻酸盐印模材料的标准印模,每种材料制取6组,每组5个印模,共120个印模。分别用2%戊二醛和84消毒液浸泡30分钟和40分钟、邻苯二甲醛消毒液(Ortho-phthalaldehyde,OPA)浸泡20分钟和30分钟。使用工具显微镜测量浸泡消毒处理前后各组印模的标志线长度,比较浸泡前后印模线性尺寸变化率,并对所得结果应用SPSS10.0软件进行统计学分析。结果①使用2%戊二醛、84消毒液浸泡处理前后,全部印模均发生显著膨胀形变(P<0.05),且形变随浸泡时间的延长而增大。②使用邻苯二甲醛消毒液浸泡处理前后,全部印模均发生显著收缩形变(P<0.05),且形变随浸泡时间的延长而增大。③不同材料的印模之间尺寸变化率的差异有显著性(P<0.05)。登士柏翡翠Jeltrate的形变率最小。④不同消毒液不同浸泡时间处理对印模尺寸稳定性影响的差异有显著性(P<0.05)。在相同浸泡时间时,使用2%戊二醛浸泡处理的印模形变率比使用84消毒液浸泡处理的印模形变率要小。结论①消毒...     

几种常用印模材制取固定义齿模型伯三维精度比较

目的：评价硅橡胶类、琼脂类、藻酸盐类（水粉剂与糊剂）等4各临床常用印模材料的取模精度。方法：分别用4种模型材料制取10个同一金属实验模具的石膏模型,用测量显微镜测量金属模型和石膏模型上各标志点的距离,精度为0．001mm,所得数据进行统计分析。结果：藻酸盐糊剂印模材料制取的石膏模型在长径方向上与其他组有显著差异,且超出了临床允许的精度范围;硅橡胶印模材料制取的石膏模型线性变化率最小且比金属模型略大;琼脂印模材料与藻酸盐印模材料（水粉剂）制取的印模在三维尺寸变化率方面无显著差异。结论：藻酸盐糊剂印模材料取模精度差;硅橡胶印模材料的取模精度最高,且可以起到补偿义齿后续操作中的收缩及提供冠桥粘结剂间隙的作用;琼脂印模材料具有印模精度高,操作比较简单,且价格易于接受等优点,值得在临床应用中进一步普及和推广。     

Evaluation of accuracy of the wash impression technique to rebase and replace the resilient part of a soft-lined denture

The dimensional inaccuracies that might be introduced during a wash impression technique within a heat-cured acrylic resin tray lined with a silicone resilient denture base material were investigated with the use of an electronic digitizer. Casts were poured from impressions of a machined metal die using a light- and heavy-bodied addition silicone in the soft-lined tray and compared with casts poured from impressions made in a hard-based tray and with the master die itself. The dimensions of the casts poured from the heavy-bodied impression in the soft-lined trays were significantly different from those poured from impressions in the hard-based tray when compared with the metal die. Those produced from the light-bodied material showed no statistically significant dimensional difference.     

Complete denture prosthodontics for a patient with Parkinson's disease using the neutral zone concept: a clinical report

A patient with Parkinson's disease was given new dentures made by utilizing the neutral zone concept. Many modeling oral functions (including swallowing, phonation, sucking, smiling, and grimacing) and two materials were used to shape six neutral zone impressions but only one impression was deemed satisfactory for the patient. The patient's lack of neuromuscular control coupled with xerostomia made it impossible to construct a denture with perfect, absolute equilibrium and no displacement; however, denture stability was improved considerably and the patient wore the dentures for several years. Based on this case, a slow-setting material of low viscosity was preferable for shaping the neutral zone.     

A retrospective comparison of two definitive impression techniques and their associated postinsertion adjustments in complete denture prosthodontics

PURPOSE: To compare the number of postinsertion adjustment visits required by edentulous patients whose dentures were made from border-molded definitive impressions using modeling plastic impression compound (traditional technique) with patients whose dentures were made from border-molded definitive impressions using heavy-body vinyl polysiloxane impression material. MATERIALS AND METHODS: In this retrospective clinical study, 78 patients were treated with the traditional technique (custom impression trays border molded with gray modeling plastic impression compound) and 78 were treated with the modified technique (custom impression trays border molded with heavy-body vinyl polysiloxane impression material). In both techniques, definitive wash impressions were made with light-body vinyl polysiloxane impression material. Postinsertion visits were quantified for 1 year after the dentures were inserted. RESULTS: The average number of adjustment visits for patients treated with the traditional technique was 2.68. The average number of adjustment visits for patients treated with the modified technique was 2.68. The data were compared using Student t tests. There was no significant difference in the number of adjustments required for patients whose dentures were made with either technique (t = 0.000, p = 1.00). There was no significant difference in the number of post-insertion visits required by patients from either population. CONCLUSIONS: Within the limitations of this clinical study, border-molding custom denture impression trays with vinyl polysiloxane impression material provided similar results in terms of postinsertion visits for one year as compared to dentures made from impressions border molded with modeling plastic impression compound.     

Effect of operator variability on void formation in impressions made with an automixed addition silicone

This study examined voids produced in impressions of an automixed addition-reaction silicone. Two operators took the impressions using material dispensed from either intra-oral tips or an impression syringe. The material was also hand-mixed for comparison. There were no differences in the number of voids in the automixed material dispensed using the intra-oral tip or impression syringe. Automixing produced substantially fewer voids than hand-mixing. There was a significant difference in the number of voids in the impressions made by the two operators.     

Effect of impression tray design and impression technique upon the accuracy of stone casts produced from a putty-wash polyvinyl siloxane impression material.

This study examined the accuracy of stone casts produced from impressions taken in stock polycarbonate trays, some of which had been strengthened with autopolymerizing polymethyl methacrylate resin. Three techniques were used to make the impression of an acrylic master model of the mandibular arch on which two extracoronal preparations for bridgework and one intracoronal inlay preparation had been carried out. Each preparation had been indented with a reference point for later measurement. The impression material was a putty-wash polyvinyl siloxane material. Five impressions were taken for each type of tray for each impression technique and these were cast in die-stone after 24 h. The distances between the points were measured with a reflex microscope and the means determined for each design of tray. The mean difference between casts produced from the various tray designs and the acrylic master model were determined for each of the distances between the three measuring points for the various impression techniques. Statistical analysis showed that, with the polycarbonate stock trays, there were significant differences between some of the modifications and between them and the acrylic model, for the three distances (P less than 0.05). These differences were limited to one measurement for one design of tray for each of the two-stage impression methods. With the one-stage technique the unreinforced tray and those reinforced with acrylic, over the heels and anteriorly, and the barred design were statistically significantly different from the acrylic model for measurement A-B.(ABSTRACT TRUNCATED AT 250 WORDS)     

The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions

Five disinfectants applied by spray atomization were examined for possible dimensional distortion of elastomeric impression materials, polyether, polysulfide, and addition silicone, and the associated improved, type IV gypsum casts. The disinfectants did not affect, in a clinically significant manner, the three dimensions measured with an instrument accurate to 1 micron on improved gypsum casts that reproduced a stainless steel standard. The master cast represented two teeth of a fixed partial denture prepared for complete veneer retainers. The use of control casts from elastomeric impressions that were not treated with the disinfectants further supported previous investigations reporting the accuracy of dental casts as the function of the impression material. The use of a spray disinfectant will not appreciably alter the dimensional accuracy of improved stone casts made within elastomeric impressions. The most accurate stone cast system was produced by addition silicone impressions disinfected by a surface spray. It was also shown that four of the disinfectants applied by spray atomization were effective in disinfecting the surface of an elastomeric impression material contaminated with selected test organisms.