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.

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.

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.

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.

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.

Qualitative and quantitative three-dimensional accuracy of a single tooth captured by elastomeric impression materials: an in vitro study.

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

Practice-based PREP Panel handling evaluation of a new impression mixing device and the associated material.

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

Impression materials in fixed prosthodontics: influence of choice on clinical procedure.

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

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.

Accuracy and stability of impression materials subjected to chemical disinfection - a literature review.

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

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.

Dimensional accuracy of 3 silicone dental impression materials.

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

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 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.

Influence of dimensional stability of impression materials on the probability of acceptance of a prosthetic restoration.

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

Elasticity of impression materials: IV. Permanent deformation as a function of time.

The permanent deformation-time relationship under constant load, of 15 elastomer impression materials were studied. All materials showed a greater permanent deformation under constant load than with tensile load, except the polyether material. Silicone and polyether materials exhibited perceptibly less permanent deformation than mercaptan materials ten minutes after mixing.

Displacement Rheometer: a method of measuring working time and setting time of elastic impression materials.

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

Accuracy of casts produced from alginate and hydrocolloid impression materials.

It is recognized that alginate impression materials have been used to obtain casts from which castings have been fabricated for a number of years. This study indicates that more dimensionally accurate casts are produced from hydrocolloid compared with casts produced from alginate. The most accurate casts were produced from the polyether impression material.