Water temperature and accuracy of alginate impressions

Occlusal records in the production of mounted study casts for tooth wear planning and management

This article forms part of a series looking at management of patients with tooth wear. Articulated study casts can be essential in assisting the clinician to plan and communicate proposed treatment to the dental technician and patient. Their production is often seen as straightforward, but a lack of attention to detail can quickly lead to articulated casts that do not replicate the patient clinical presentation. This in turn will lead to inaccurate planning and potentially a suboptimal treatment outcome. This article discusses a collection of the clinical records needed to produce accurate articulated study casts, which can be utilised for tooth wear planning. It also aims to present the evidence base for the recommendations outlined.

Evaluation of pre-alginate impression preparation methods in the surface accuracy of dental cast

Objective

The aim of this study was to investigate the influence of pre-preparation technique (finger smearing and saliva ejection) of alginate impressions on the quality and accuracy of dental casts.

Materials and methods

Twenty mandibular impressions from 20 patients (10 males, 10 females) with an age range of 20–40 years were recorded using stock trays. A standard impression and pre-preparation technique for alginate were employed. This included removal of saliva with saliva ejector, smearing of alginate on occlusal surfaces of posterior teeth and smoothing of the material in the tray (Group-1: Test) and no drying and smearing or smoothing of the material prior to impression (Group-2: Control). Standardized disinfection, storage, pouring and removal from die stone techniques were used for all samples. Surface defects (nodules/blebs) on the occlusal surface of casts as examined with digital microscope, were classified according to their sizes and surface area into; Type-A (<500); Type-B (>500 <100); Type-C (>1000) in micrometers (μm). Data was tabulated and analyzed by SPSS using Anova and Tukey’s test.

Results

Defects were significantly higher (p < 0.01) in samples in Group-2 (1225.51 ± 823.44 μm) as compared to Group-1 (783.68 ± 501.41 μm). All types of defects (Types A, B and C) were significantly higher in samples from Group-2 as compared to Group-1.

Conclusions

Use of pre-preparation technique of finger smearing and saliva ejector prior to alginate impressions resulted in significant reduction of surface nodules/blebs and enhanced the quality and accuracy of fabricated casts. Therefore, the use of saliva ejector, finger smearing on the occlusal surface of teeth and smoothening of alginate impression, immediately prior to intra-oral placement is clinically recommended.

Assessment of Influence of Contact Time between Alginate and Type III Dental Stone on Properties of Cast Model: An in vitro Study

INTRODUCTION

Alginate is a versatile, irreversible hydrocolloid impression material, which is cost-effective and forms an essential component in dental practice. For elevating the hardness of the cast models, hardeners are combined with stone. Hence, we planned the present study to evaluate the impact of altering the time of contact between alginate and stone after various interim periods.

MATERIALS AND METHODS

The present study included the assessment of impact of time of contact between alginate and stone by the construction of 90 casts using a cylinder model. Two bisecting lines were marked and were named as y and y'. These lines were used for testing the dimensional stability. Using chemically cured acrylic resin, the construction of ten special trays was done. All the impression casts were randomly divided into two study groups, with 45 casts in each group-group I: control group, casts were removed after 60 minutes; group II: study group, casts were removed after 9 hours. A digital caliper was used for measuring the dimensional stability of the cast. All the data were collected and analyzed.

RESULTS

In the specimens of the control group (group I) and the study group (group II), the mean dimensions from y to y' were found to be 17.54 and 17.95 respectively. The mean reading of hardness in the control group and study group was found to be 0.59 and 0.20 respectively. In groups I and II, the number of specimens showing clarity of two lines (X and X") was 0 and 5 respectively.

CONCLUSION

There was no change in the dimensional stability of the dental stone model when the contact time was increased.

CLINICAL SIGNIFICANCE

Within certain limits, the contact time between alginate and stone can be altered without significantly altering the properties of the cast.

The effect of pouring time on the dimensional accuracy of casts made from different irreversible hydrocolloid impression materials

Aims and Objectives:

To determine the time dependent accuracy of casts made from three different irreversible hydrocolloids.

Materials and Methods:

The effect of delayed pouring on the accuracy of three different irreversible hydrocolloid impression materials – Regular set CA 37(Cavex, The Netherlands), regular set chromatic (Jeltrate, Dentsply), and fast set (Hydrogum soft, Zhermack Clinical) was investigated. A brass master die that contained two identical posts simulating two complete crown-tapered abutment preparations with reference grooves served as a standardized master model. A total of 120 impressions were made using specially prepared stock-perforated brass tray with 40 impressions of each material. The impressions were further sub-grouped according to four different storage time intervals: 0 min (immediately), 12 min, 30 min, and 1 h. The impressions were stored at room temperature in a zip-lock plastic bag. Interabutment and intraabutment distances were measured in the recovered stone dies (Type IV, Kalrock) using a profile projector with an accuracy of 0.001 mm. The data so obtained was analyzed statistically.

Results:

Results of this study showed no statistically significant differences in the accuracy of casts obtained at different time intervals.

Conclusion:

Because it is not always possible to pour the impression immediately in routine clinical practice, all irreversible hydrocolloid materials studied could be stored in a zip-lock plastic bag for upto 1 h without any significant distortion.

The influence of tray type and other variables on the palatal depth of casts made from irreversible hydrocolloid impressions

STATEMENT OF PROBLEM

There are conflicting data regarding the effect of various factors on the palatal depth of casts made from irreversible hydrocolloid impressions.

PURPOSE

This study examined the influence of tray type, water temperature, pouring technique, and stone expansion on the palatal depth of casts.

MATERIAL AND METHODS

Irreversible hydrocolloid impressions were made of a model under simulated oral conditions. Palatal depth was measured relative to a reference plane with a microscope. The reference planes were standardized by subjecting the data to three 2-dimensional mathematic rotations. A 2-factor analysis of variance (alpha=.05) was used to determine whether differences existed among tray types and among palatal locations.

RESULTS

The palatal depth of the casts increased approximately 0.06 mm compared with the master model with all but 2 variables. Statistical testing revealed that increased depth was not attributable to water temperature (52 degrees F or 72 degrees F) or tray type (custom resin, perforated metal, metal rimlock, or rimlock with built-up palate). Custom resin tray impressions poured with a lower expansion stone and perforated tray impressions inverted onto a base made from the same mix of stone resulted in casts with palatal depths most similar to that of the master model (P<.001).

CONCLUSIONS

Casts with palatal contours of comparable accuracy were obtained with the use of a stock metal or customized tray and the use of differing water temperatures to mix the impression material.

Dimensional accuracy of three different alginate impression materials

PURPOSE

The purpose of this study was to evaluate the dimensional stability of three different alginate impression materials (Jeltrate [Caulk Dentsply, LD Caulk Division, Dentsply International, Milford, DE], Hydrogum [Zhermack, Padoua, Italy], and a new hydrophilic alginate material [Essential Dental Systems, South Hackensack, NJ] under five different storage conditions.

MATERIALS AND METHODS

The study was divided into four groups with at least eight samples in each group. The five storage conditions were as follows: immediate, 10 minutes with a wet towel, 30 minutes without a wet towel, 1 hour with a wet towel, and 24 hours with a wet towel. A 4 X 5 factorial two-way analysis of variance (P<.05) was used on each dependent variable. Dunnett's test was used to compare each alginate with Jeltrate.

RESULTS

The new hydrophilic alginate (group 4, 2:2) showed smaller measurements in the buccolingual and diagonal dimensions compared with Jeltrate (control).

CONCLUSIONS

The immediate method (measured buccolingually and diagonally) produced more accurate casts for the alginate materials studied. All other materials studied were similar statistically. The new hydrophilic alginate in group 3 resulted in similar dimensional accuracy compared with Jeltrate and Hydrogum and incorporated 25% less water.

Reliability of antagonistic arch impression in dental prostheses: clinical evaluation of different preimpression preparation procedures

This study compared the influence of different methods of preimpression preparation on the quality of occlusal reproduction in irreversible hydrocolloid impressions. A total of 30 impressions of the lower dental arch of a patient were made with five different preimpression preparation procedures. Stone casts were made and analyzed. Critical comparison showed that the preimpression preparation influenced the quality of the occlusal surface of the cast. Fingerpainting the occlusal surface with fluid hydrocolloid before positioning the loaded impression tray, associated with use of a saliva ejector, reduced the incidence of macroscopic defects on the occlusal surface of the impressions.

An investigation into the compatibility of some irreversible hydrocolloid impression materials and dental gypsum products. Part I. Capacity to record grooves on the international standard die

Some alginate impression materials produce rough, chalky, soft surfaces on gypsum casts. This is recognized by various standards, which include tests for an alginate's compatibility with gypsum, and its capacity to record details and impart these to a gypsum cast. These qualities were looked at in this study. The method used closely followed that laid down by International Standard ISO 1563-1978(E) for alginate impression materials. Ten alginates and seven gypsum products were tested. Using the criteria specified by this Standard, it was found that none of the materials tested was able to record the finest (0.020 mm) line on the test block. However, two elastomeric impression materials tested in the same manner also failed to reproduce this line, as did all the gypsum products when tested directly against the block. These findings cast some doubt on the efficacy of utilising such a fine line in the classification of these materials. Only thirty-four of the seventy possible combinations were able to reproduce the 0.050 mm line. Eight combinations reproduced the 0.075 mm line as the finest line, and the remainder (thirty-eight) failed to record any of the lines. Some of the alginate materials were treated with fixing solutions of varying concentrations of potassium sulphate and alum. The results obtained varied, sometimes producing marked improvement, sometimes deterioration in the surface quality of the subsequent gypsum casts, despite the fact that none of the manufacturers of the alginates recommended the use of fixing solutions.

The combined reversible hydrocolloid/irreversible hydrocolloid impression system

1. Dentloid, a reversible hydrocolloid which had been altered to bond to irreversible hydrocolloid, demonstrated a bond with three irreversible hydrocolloids tested in combination with it. 2. Two conventional reversible hydrocolloids exhibited such weak bonding with irreversible hydrocolloid that it was impossible to make impressions with them. 3. The three irreversible hydrocolloids exhibited different bond strengths with Dentloid. 4. The Dentloid/irreversible hydrocolloid combination with the lowest bond strength exhibited the lowest dimensional stability. 5. Combined impressions of Dentloid with two of the three irreversible hydrocolloids exhibited dimensional stability that is a clinically acceptable. 6. Combinations of Dentloid with irreversible hydrocolloids not covered in this report should be verified for acceptable dimensional stability before clinical use. 7. The combination technique, in itself, proved to be easy and practical and overcomes many of the shortcomings inherent to conventional reversible hydrocolloid impression techniques. 8. Strict adherence to laboratory procedures for pouring a cast is as critical as for the conventional technique.

The measurement of distortion: mathematical considerations

The proposed method for accurately determining the coordinates of given points in a three-dimensional space, along with the mathematical rigid body displacements to move these points into some predefined reference position, builds a complete model of the positional relationships of these points. On this basis additional information can easily be extracted, e.g., the distance between any two given points or the angle in degrees between any two given points or the angle in degrees between any three given points. An important advantage of the procedure is that the normally tedious calculations involved with distortions have been computerized, thus eliminating the tedium of repeated calculations. The possibility of calculation error is also reduced. Perhaps the greatest advantage to the investigator arises from the fact that once the procedural routine has been established and the computer programs written, the entire procedure can be done by technical personnel and does not necessarily require a large time committment from the principal researcher. Also, because of the normally small amount of time needed to read the coordinates and compute the inherent distortions, a set of computed distortions which appear unreasonable may be checked by repeating the entire set of coordinate readings and distortion calculations in a relatively short time.

Removal time: a factor in the accuracy of irreversible hydrocolloid impressions

Controversy exists regarding the correct time of removal of an alginate impression from the mouth. To investigate the effect of time of removal on accuracy, a series of alginate impressions were made of the lower left quadrant of a subject having a cast gold crown with four reference marks on tooth no. 19. The impressions were removed from the mouth at 1-5, 2, 3, 4-5 and 7 min after the insertion of the tray. Accuracy of the impressions was assessed by comparing the distances between the reference marks in stone casts with standard measurements taken from the gold crown prior to cementation. Impressions removed at 1-5 and 7 min produced the greatest distortions buccolingually. For the mesio-distal lengths all time intervals produced casts which were larger than the standard. The reasons for these findings are discussed and possible explanations are presented.

The measurement of distortion: theoretical considerations

When very find measurements are recorded for the purpose of establishing distortion values, from the standpoint of accuracy, specific procedures must be developed. In the procedural system defined here, a potential major source of error is indicated and the means of overcoming this error established. From the standpoint of modern electronic technology, the use of an analogue-to-digital interface with a digital computer is considered extremely advantageous and allows the utilization of technical help to carry out the preliminary measurements. Under these circumstances, major error sources, such as reader error and calculation error, are eliminated. Further, multiple readings on each point can be made without significant sacrifice of time. This latter statement can help define the reading accuracy on each point and allows an immediate further set of readings on any point that has a large variation in the initially established set of readings. The applicability of this approach to any system in which an accurate set of readings is required to define distortion or some other parameter is limited only by the imagination of the investigator. Measuring points can be established at any desired location, and the number required is a function of the mathematical analysis being attempted. The use of a digital computer to compute the final values allows an immediate remeasurement of the initial values if necessary, since the computer response time is of the order of seconds for the calculations carried out. This is very important if changes in the experimental setup are likely to occur with time. In general, a computerized scheme such as is proposed here allows the investigator to concentrate on the experiment rather than the calculation of results. Also, the use of technical help to carry out delicate measuring procedures can allow the investigator more time to analyze the final results.

Comparative study of selected alginate materials and devices

Four different brands of alginate impression materials were mixed by hand and ten impressions of each were made of a block for detail reproductions. In addition, two different mechanical devices were used to prepare one of these alginate impression materials. Thus a total of six groups was tested, with ten impressions per group. Stone casts of these 60 impressions were compared by the line study method and the number of surface defects. A statistical analysis was performed on the collected data. The results indicated that the Whip-Mix vacuum mechanical spatulator produced significantly superior results to the Columbus system centrifugal mechanical spatulator, and that among the four alginates hand mixed, the Jeltrate impression material gave better results.

A study of distortion and surface hardness of improved artificial stone casts

1. The single-pour technique is as accurate as the double-pour technique except for point 6 (palatal point). Here the double-pour technique has greater accuracy. Impression material thickness over point 6 was approximately 15 mm. 2. The double-pour technique produced specimens which had superficial hardness values significantly higher than those of casts produced by the single-pour technique. 3. Specimens made with slurry water showed no greater distortion than specimens from other techniques. Surfaces of the specimens made with slurry water were significantly harder than those of specimens made with distilled water. Both types of specimens were made with the single-pour technique. 4. No significant difference in distortion was found in specimens produced with varying thickness of irreversible hydrocolloid impression material over the occlusal pins.