The effect of disinfecting alginate and addition cured silicone rubber impression materials on the physical properties of impressions and resultant casts

Four commercially available disinfectants were tested and the dimensional stability and detail reproduction of impressions and their resultant casts were measured according to ANSI/ISO specifications. Results showed that alginate impressions immersed in chlorhexidine exhibited considerable dimensional change if not poured immediately. Moreover, alginate impressions soaked in a paraldehyde agent (Virkon) for more than 2 minutes produced casts of inferior surface quality whilst those sprayed and left in contact with phenol derivatives (C&J Spray) for 30 minutes resulted in casts which demonstrated statistically and clinically significant dimensional changes. Addition cured silicone impressions exhibited minimal dimensional change regardless of the disinfection regime employed and the resultant casts were accurate with acceptable surface quality.     

The effect of a range of disinfectants on the dimensional accuracy of some impression materials

In this study the dimensional accuracy of two model materials; dental stone and plaster of Paris, reproduced from three commonly used impression materials; alginate, polyether and addition-cured silicone, retained by their adhesives in acrylic resin trays and exposed to four disinfectant solutions was evaluated. Ninety casts were used to investigate the effect of the four disinfectants on the dimensional accuracy of alginate, polyether and addition-cured silicone impression material. For each impression material 30 impressions were taken, half were poured in dental stone and half in plaster of Paris. The disinfectants used were Dimenol, Perform-ID, MD-520, and Haz-tabs. Measurements were carried out using a High Precision Reflex Microscope. For the alginate impressions only those disinfected by 5-minute immersion in Haz-tabs solution and in full-strength MD 520 were not adversely affected by the disinfection treatment. All polyether impressions subjected to immersion disinfection exhibited a clinically acceptable expansion. Disinfected addition-cured silicone impressions produced very accurate stone casts. Those disinfected by spraying with fill-strength Dimenol produced casts that were very similar to those left as controls, but those treated by immersion disinfection exhibited negligible and clinically acceptable expansion. The results of the studied demonstrated that the various disinfection treatments had different effects on the impression materials. It is important that an appropriate disinfectant is used for each type of impression material.     

Effects of disinfection of combined agar/alginate impressions on the dimensional accuracy of stone casts

This study investigated the effects of disinfection of combined agar/alginate impressions on the dimensional accuracy of resultant stone casts. Impressions of a master cast designed to simulate an abutment tooth were prepared by combining each of two brands of cartridge-form agar impression materials with an alginate impression material. The impressions were immersed in 1% sodium hypochlorite for 10 minutes or 2% glutaraldehyde for 30 minutes. The remaining impressions were sprayed with these two disinfectants and then stored in sealed bags for 10, 30, 60, and 120 minutes. Stone casts obtained from the non-disinfected impressions were also prepared as control. Changes in diameter of the stone casts were then measured. Results indicated that storage for 10 minutes after spraying with 1% sodium hypochlorite was an appropriate disinfection method for combined agar/alginate impressions, as well as immersion in 1% sodium hypochlorite for 10 minutes.     

Some effects of disinfecting solutions on the properties of alginate impression material and dental stone

The study investigated the effect of two disinfecting solutions on one brand of alginate impression material and dental stone. Control impressions were immersed in water for equivalent periods and the effect of storage of impressions after disinfection or control immersion in water was also investigated. There were no significant dimensional changes in impressions poured after one hour. All impressions stored for 16 hours before pouring showed significant dimensional changes. Mixing dental stone with one disinfectant caused a significant softening of the cast. It is strongly recommended that all impressions are thoroughly rinsed with water after disinfection to prevent incorporation of disinfectant in the cast.     

Effect of disinfectant agents on dimensional stability of elastomeric impression materials

STATEMENT OF PROBLEM: Difficulties in sterilizing impressions by traditional methods have led to chemical disinfection as an alternative, and some studies have shown that disinfectants may adversely affect impressions. PURPOSE: This study investigated the effect of disinfection methods on the dimensional stability of 6 elastomeric materials. MATERIAL AND METHODS: Impression materials were submitted to the following treatments: immersion in 5.25% sodium hypochlorite solution for 10 minutes, immersion in 2% glutaraldehyde solution for 30 minutes, and no immersion (control). After treatments, impressions were poured, and respective stone casts were measured with a Nikon Profile projector and compared with the master model. RESULTS: The elastomeric materials had different reproduction capacities, and the disinfecting treatments did not differ from the control.     

Evaluation of disinfected casts poured in gypsum with gum arabic and calcium hydroxide additives

STATEMENT OF PROBLEM: Disinfection of stone casts is an important measure for the control of cross-contamination. Many approaches have been used to disinfect stone casts, but information regarding the accuracy of the resultant casts is limited. PURPOSE: The purpose of this in vitro study was to evaluate the dimensional accuracy, incidence of abutment fracture, and the abutment reproduction of disinfected stone casts made from elastomeric impressions and to determine the effect of gum arabic and calcium hydroxide additives on these properties. MATERIAL AND METHODS: Two aqueous solutions of chemical disinfectants (0.525% sodium hypochlorite and 0.1% povidone iodine) were used as mixing water substitutes for 3 types of dental stone: Types III (Lab Stone), IV (Mile Stone), and V (Die Keen). These stone powders were subjected to further modification by adding 1% gum arabic and 0.132% calcium hydroxide before mixing at the manufacturer-recommended liquid/powder ratios (0.30 for Type III, 0.21 for Types IV and V, respectively). As these additives increased the fluidity of the mix, reduced liquid/powder ratios (0.26 for Type III, 0.19 for Types IV and V, respectively) were also evaluated. Unmodified stone powder mixed with water served as the control. These modifications resulted in 7 test groups for each type of stone. Mixed stones of these groups were poured into 10 putty/wash vinyl polysiloxane impressions made of a customized definitive cast. The percentage of abutments fractured at the time of releasing the resultant casts, as well as the percentages of incompletely reproduced abutments, abutments with air bubbles, and abutments with defective finish lines were compared statistically among the tested groups using the chi-square test (alpha=.05). The average dimensional deviations of the resultant cast from the definitive cast measured in mm were statistically analyzed using 1-way ANOVA (alpha=.05) followed by the Dunnett test to detect any differences among the tested groups. RESULTS: No significant difference was found in abutment fracture or abutment defects for the different formulations of each type of stone used. The resultant casts showed no significant dimensional changes except for Type III and IV stones modified by gum arabic and calcium hydroxide additives and mixed at the recommended liquid/powder ratios. CONCLUSION: Both 0.525% sodium hypochlorite and 0.1% povidone iodine can be used to disinfect dental gypsum with no significant effect on the dimensional accuracy and reproducibility of the resultant casts. Addition of gum arabic and calcium hydroxide to the hemihydrate powders before mixing does not aid in reducing the incidence of defective abutment reproduction.     

Laser digitization of casts to determine the effect of tray selection and cast formation technique on accuracy

STATEMENT OF PROBLEM; Several studies have attempted to determine the ideal combination of dental materials and laboratory techniques to produce the most accurate dental cast. Most have made use of 2-dimensional manual measuring devices, which neglect to account for the dimensional changes that exist along a 3-dimensional surface. PURPOSE: The purpose of this study was to determine the effect of impression tray selection and cast formation techniques on the dimensional change of a dental cast with the use of new, 3-dimensional optical digitizing technology. MATERIAL AND METHODS: Multiple impressions of a machined steel die that resembled a dental arch were made with custom and stock impression trays and vinyl polysiloxane impression material. The impressions were poured in type V artificial dental stone and allowed to set with the tray inverted or noninverted. The steel master die and stone casts were digitized with the Steinbichler Comet 100 Optical Digitizer, which was developed at the Minnesota Dental Research Center for Biomaterials and Biomechanics. Three-dimensional images of the stone casts were aligned to the 3-dimensional image of the master die and analyzed with AnSur-NT software. Multiple measurements of the master die and stone casts were analyzed to determine the accuracy of the 3-dimensional technology and of the impression and cast fabrication techniques. Planar distances between the center of each crown preparation were measured, as were crown heights. Data were analyzed with analysis of variance (P<.05), and root mean square error values were determined. RESULTS: Casts were compared with a total of 45 significance tests, of which only 4 yielded P<.05. There was no pattern to these results, which suggests that they were false-positive findings. CONCLUSION: Results obtained with the use of new optical digitizing technology indicated that neither impression tray type nor cast formation technique affected the accuracy of final casts.     

Accuracy of complete dental arch impressions and stone casts using a three-dimensional measurement system. Effects on accuracy of rubber impression materials and trays

The purpose of this study was to investigate and compare the accuracy of complete dental arch impressions and stone casts made with two kinds of impression materials (addition-type silicone and polysulfide rubber) and trays (custom tray and modified custom tray). In addition, the effect of the quantity of stone was examined. Impressions were made from a metallic model of a simplified maxillary dentition. Impressions and stone casts were measured respectively with a three-dimensional measuring microscope. The results were as follows: 1. Distortions of impressions were so small that the reproducibilities of impressions were superior three-dimensionally. These kinds of impressions and trays did not influence the accuracy of impressions. 2. The setting expansion of the stone in the impression occurred in the outward direction and was affected by the kinds of impressions and trays. 3. The arch widths and lengths of the stone casts tended to increase in number. 4. Stone casts made with addition-type silicone impression material and a custom tray were the most accurate because the combination of the impression material and tray effectively suppressed the setting expansion of stone. 5. The accuracy of stone casts could be improved by controlling the quantity of stone.     

Bactericidal effect of a disinfectant dental stone on irreversible hydrocolloid impressions and stone casts

Infection control in dentistry focuses on the prevention of cross-contamination among patients, dentists, and dental auxilary personnel. This study evaluated the bactericidal effect of a dental gypsum material containing 0.25% chloramine-T on oral irreversible hydrocolloid impressions and dental casts. Eighty irreversible hydrocolloid impressions from 40 human volunteers were prepared. Forty impressions were poured with the disinfectant dental stone and a similar number were poured with a comparable, nondisinfectant stone. After setting for 60 minutes, the impressions and separated casts were sampled for bacterial contamination. The disinfectant stone inhibited bacterial growth in 39 of 40 impressions and casts, whereas all casts and impressions poured with the nondisinfectant stone were contaminated. The disinfectant dental stone containing chloramine-T was effective in eliminating bacterial contamination of both the irreversible hydrocolloid impression and stone cast.     

Dimensional changes and pressure of dental stones set in silicone rubber impressions.

OBJECTIVES: A high expansion stone has been used for improving the adaptation of dentures. Although the method is based on the idea to compensate for the processing shrinkage of the denture base resin with the high expansion stone, there are few studies on the expansion behavior of stones in an impression. The purpose of this study is to clarify the dimensional changes of stones set in silicone rubber impressions using two types of impression tray. METHODS: Impressions of a master model that represents the alveolar ridge were taken using a silicone impression material and the dimensional changes in the stone casts were measured in different directions (x, y and z-axes). Two types of impression tray were used, one with an open surface and the other with a closed surface. In order to evaluate the setting expansion of the stones and the pressure against the impression, stones were poured in other impressions that were taken from a cubic master model. The thickness of the impression was set at 2 mm. RESULTS: A statistical analysis showed that there were significant differences in the dimensional change in the vertical direction (z-axis) and horizontal directions (x- and y-axes) of any stone casts set in the open tray. However, there were no significant differences in the dimensional changes in any direction of each stone cast set in the closed tray. SIGNIFICANCE: The impression tray influences the setting expansion of stones. Stones do not uniformly expand in the open tray and the dimensional changes in the stone casts in the three-dimensions increases, when used with a high expansion stone.     

两种消毒液调拌藻酸盐印模材对印模尺寸稳定性的影响

目的：评价用两种消毒液直接调拌藻酸盐印模材对印模尺寸稳定性有无影响。方法：分别用蒸馏水、0．2％的次氯酸钠和0．1％的洗必泰调拌藻酸盐印模材,对同一试件制取20组印模,以蒸馏水调拌者为对照组。用超硬石膏灌模,40rain脱模静置24h测量模型三维标志点的长度再进行统计学分析。结果：试验组和对照组模型三维标志点长度无显著性差异。结论：0．2％的次氯酸钠或0．1％的洗必泰直接调拌藻酸盐印模材进行印模消毒不影响印模尺寸稳定性,可用于口腔科印模消毒。     

Dimensional stability of impression materials immersed in an iodophor disinfectant

The potential for disease transmission has increased the importance of infection control in the dental laboratory. Impressions must be disinfected without altering their accuracy. The purpose of this study was to determine the dimensional stability of three impression materials: irreversible hydrocolloid, reversible hydrocolloid, and poly(vinyl siloxane). Thirty-six impressions were made with each material and divided into control, 10-minute, and 30-minute immersion groups using an iodophor as the disinfectant. A microscope was used to measure dimensional changes in the stone casts made from each group of impressions, and the percent change was analyzed using a two-way ANOVA. All dimensional changes after iodophor disinfection were small and within established limits.     

高温高压消毒对超硬石膏模型三维精度的影响

目的：评价高温高压消毒对超硬石膏模型三维精度有无影响。方法：对30例患者制取藻酸盐印模,再用超硬石膏灌模,1h后脱模,静置24h定标志点。石膏模型扫描成数字模型后用测量软件进行标志点三维测量。测量后进行高温高压消毒。消毒后用同种方法测量标志点距离。最后用SPSS软件分析消毒前后数据。结果：高温高压消毒后对超硬石膏模型三维精度无统计学差异。结论：高温高压消毒对超硬石膏模型三维精度无明显影响。     

High-level microwave disinfection of dental gypsum casts

PURPOSE: To test whether microwave oven irradiation can disinfect gypsum casts in compliance with current disinfection requirements, and to determine whether this procedure would be as effective as a validated method of chemical disinfection of impressions. MATERIALS AND METHODS: In 2 in vitro experiments, samples of 5 irreversible hydrocolloid impressions of a disinfected acrylic resin model were contaminated with suspensions of recommended test organisms Staphylococcus aureus and Pseudomonas aeruginosa, respectively. In 1 in vivo experiment, 10 impressions were made of 10 subjects. All impressions were poured and the resulting casts cut in 2 halves. One half of each cast was exposed to 5 minutes of irradiation in a microwave oven at 2,450 MHz and 900 W. The other halves were left untreated as controls. In a second in vivo experiment, 10 impressions were disinfected by immersion in a 0.07% solution of NaOCl at pH of about 10 for 3 minutes, and then poured. All casts were incubated aerobically in Bacto tryptic soy broth at 37 degrees C for 6 hours and assessed for bacterial growth by counting colony-forming units per milliliter (cfu/mL) of the culture. The results were analyzed using the Wilcoxon signed-rank test. RESULTS: Untreated gypsum casts showed cfu/mL counts with a median log value of 6, while microwave-irradiated ones had median cfu/mL counts of 0. Casts poured from chemically disinfected impressions demonstrated cfu/mL counts with a median log value of 4. CONCLUSION: Under the described conditions, microwave-irradiated gypsum casts satisfy current disinfection requirements, but gypsum casts poured from chemically disinfected impressions do not.     

三种模型材料在不同印模材料中尺寸变化的实验研究

目的：本实验旨在观察印模材料对工作模型精度的影响以及模型材料与印模材料间的配伍性。方法将普通石膏、硬石膏、超硬石膏３种模型材料分别灌入金属印模,硅橡胶印模,藻酸盐印模和旨印模中,用激光热膨胀仪（日本产１０００型）测量各组试件的凝固时的尺寸变化,将所得数据换算成尺寸变化率并进行统计分析。结果①普通石 在金属印模中呈现为收缩,而在硅橡胶,藻酸盐及琼脂印模中为高度膨胀,其在各种印模材料中的凝固尺寸变化率有显著性差异。②硬石膏在四种印模材料中的凝固尺寸变化率为均小于０．１５％,尤以在金属及藻酸盐印模中尺寸变化较小,性能较稳定。③超硬膏在金属印模中呈现为膨胀,在硅橡胶及藻酸盐印模中尺寸变化稳定,均不超过０．１０％。而在琼脂中表面为明显的收缩。结论各种模型材料同一种印模中的尺寸变化率不同,同一种模型材料在不同的印模中尺寸变     

Disinfection procedures: their effect on the dimensional accuracy and surface quality of irreversible hydrocolloid impression materials and gypsum casts.

OBJECTIVES: This study primarily investigated the effect of disinfection procedures (Perform and sodium hypochlorite) on the dimensional accuracy and surface quality of four irreversible hydrocolloid impression materials and the resultant gypsum casts. The antibacterial efficacy of the procedures was also studied. METHODS: Dimensional accuracy was determined from the mean percentage deviation of six measurements taken from casts made from disinfected impressions compared with corresponding measurements from the master model and controls. Statistical analysis of data was determined by analysis of variance. Surface quality was determined using a stainless steel test block in accordance with ISO 1563. RESULTS: The dimensional accuracy of the impression materials tested were of a comparable standard following disinfection. The surface quality of casts taken from Blueprint Cremix impressions were unaffected by the disinfection procedures. The remaining impression materials studied showed greater surface deterioration on casts following disinfection with sodium hypochlorite than immersion in Perform. All disinfection procedures selected proved appropriate for antibacterial purposes. SIGNIFICANCE: Individual analysis of impression materials is required to determine their suitability to a given disinfection protocol.     

洗必泰溶液调拌藻酸盐印模的模型精度研究

目的:研究0.2%洗必泰溶液调拌藻酸盐印模材料,观察其对模型精度的影响.方法:以教学用标准树脂模型为母模,采用实验法(0.2%洗必泰作调拌液)和常规法(自来水作调拌液)调拌藻酸盐粉剂,各取下颌印模10个,灌注石膏模型后用螺旋CT扫描,利用软件做三维重建处理,计算机自动测量三维图像中有关线距.用单因素方差分析和单样本t检验进行统计分析.结果:洗必泰溶液调拌组和常规调拌组印模精度无显著性差异.结论:0.2%洗必泰调拌藻酸盐印模材料不影响印模精度.     

Dimensional stability of reversible hydrocolloid impressions immersed in selected disinfectant solutions

Full-arch reversible hydrocolloid impressions of a dentoform arch (Columbia) containing an extracted first premolar prepared for a distal-occlusal inlay were immersed for 30 minutes in selected disinfectant solutions. The impressions were poured with die stone, and three cast inlays were fabricated on each die. The results of this procedure indicate that a 30-minute immersion of reversible hydrocolloid impressions in diluted solutions of iodophor, commercial hypochlorite, or 2% acidic glutaraldehyde does not adversely affect the dimensional stability of these impressions.     

Dimensional accuracy of resultant casts made by a monophase, one-step and two-step, and a novel two-step putty/light-body impression technique: an in vitro study

STATEMENT OF PROBLEM: Dimensional accuracy when making impressions is crucial to the quality of fixed prosthodontic treatment, and the impression technique is a critical factor affecting this accuracy. PURPOSE: The purpose of this in vitro study was to compare the dimensional accuracy of a monophase, 1- and 2-step putty/light-body, and a novel 2-step injection impression technique. MATERIAL AND METHODS: A stainless steel model with 2 abutment preparations was fabricated, and impressions were made 15 times with each technique. All impressions were made with an addition-reaction silicone impression material (Aquasil) and a stock perforated metal tray. The monophase impressions were made with regular body material. The 1-step putty/light-body impressions were made with simultaneous use of putty and light-body materials. The 2-step putty/light-body impressions were made with 2-mm-thick resin-prefabricated copings. The 2-step injection impressions were made with simultaneous use of putty and light-body materials. In this injection technique, after removing the preliminary impression, a hole was made through the polymerized material at each abutment edge, to coincide with holes present in the stock trays. Extra-light-body material was then added to the preliminary impression and further injected through the hole after reinsertion of the preliminary impression on the stainless steel model. The accuracy of the 4 different impression techniques was assessed by measuring 3 dimensions (intra- and interabutment) (5-mum accuracy) on stone casts poured from the impressions of the stainless steel model. The data were analyzed by 1-way ANOVA and Student-Newman-Keuls test (alpha=.05). RESULTS: The stone dies obtained with all the techniques had significantly larger dimensions as compared to those of the stainless steel model (P<.01). The order for highest to lowest deviation from the stainless steel model was: monophase, 1-step putty/light body, 2-step putty/light body, and 2-step injection. Significant differences among all of the groups for both absolute dimensions of the stone dies, and their percent deviations from the stainless steel model (P<.01), were noted. CONCLUSIONS: The 2-step putty/light-body and 2-step injection techniques were the most dimensionally accurate impression methods in terms of resultant casts.     

Dimensional stability of a polyvinylsiloxane impression material following ethylene oxide and steam autoclave sterilization

Polyvinlsiloxane impressions were made from a stainless steel master die machined to stimulate five full veneer crown preparations symmetrically placed in an arch form. Three groups of 10 impressions each were made. Treatment groups were sterilized using an ethylene oxide gas and a conventional steam autoclave. Casts were poured and intrapreparation, height, and diameter measurements were made using a stereomicroscope, a digital electronic caliper, and a 1-inch travel dial indicator. Analysis of dimensional changes for the two groups showed that casts made from impressions sterilized by ethylene oxide are acceptable for use in the construction of fixed or removable prostheses. Casts made from impressions sterilized in a steam autoclave can be used for the fabrication of diagnostic casts and some transitional prostheses, but not for routine construction of crowns or fixed partial dentures.