Gypsum Cast Research Articles

Investigation of Composition and Technological Parameters of Highly Porous Gypsum Products Obtaining

A highly porous structure of a gypsum product creation is possible due to the porisation of gypsum mass, using new types of complex gas-forming components. At the same time, it is necessary to determine the technological conditions for the optimal formation of porous gypsum products structure and methods for increasing their strength. The article proposed to use dispersed calcium carbonate and aluminum sulphate, which interaction is the reaction with the release of СО2 for the porisation of the gypsum cast mixture. Micro-reinforcing additives, such as polymeric, basalt and glass fibers were introduced into gypsum composition together with building gypsum and finely ground calcium carbonate to improve the physico-mechanical properties of gas-gypsum. The best results were shown by the gas-gypsum, which included fiberglass. Glass fiber was pre-ground to a specific surface of 190-240 m2 / kg, in order to improve further the physico-mechanical properties of gas-gypsum.

Digital impressions in dentistry-accuracy of impression digitalisation by desktop scanners.

To test if the partially digital workflow by digitalisation of the impression reveals a comparable accuracy as the indirect digitalisation of the gypsum cast for 4-unit fixed dental prostheses (FDPs). A titanium model with a tapered full veneer preparation of a molar and premolar was used as analysis model. To receive a virtual three-dimensional reference dataset (REF), it was digitised by industrial computed tomography. Three impression materials were used with individual impression trays (N = 36, n/material = 12): (1) PE (Impregum Penta), (2) PVS-I (Imprint 4 Penta: Super Quick Heavy plus Super Quick Light), and (3) PVS-D (Dimension Penta: H Quick plus L). For partially digital workflow (group IMP), two desktop scanners were used: (1) D810 (3Shape D810) and (2) ZZ (Zirkonzahn S600ARTI). For indirect digitalisation (group CAST), gypsum master casts were manufactured and digitalised using the same desktop scanners. Virtual datasets were superimposed by best fit algorithm, and accuracy was analysed by calculating the Euclidean distances (ED) to the REF (Geomagic Qualify). Statistic was determined (Kruskal-Wallis H test, Mann-Whitney U post hoc analysis, two-sample Kolmogorov-Smirnov test, p < 0.05). ZZ showed for positive deviations superior accuracy for IMP than for CAST. PE and PVS-I showed superior accuracy than PVS-D. D810 showed partially significant better performance with PVS-I and PVS-D than ZZ. The partially digital workflow by digitalisation of the impression can be used for clinical indications of small-span fixed dental prostheses. However, for this indication, the impression material and the desktop scanner are more decisive for the accuracy of virtual model datasets. Despite the rapid advancement of the computer-aided technology for dental therapy purposes, the implementation of this technique is not as fast as the technical development. In order to combine the well-established procedure to use elastomeric materials for a conventional impression and to avoid the drawbacks of casting it by gypsum, the digitalisation of the impression itself by a desktop scanner may be a logical procedure as an access point to the digital workflow. However, there is only limited information about the accuracy of this partially digital workflow by the digitalisation of modern impression materials in comparison to the well-known process of indirect digitalisation of gypsum casts.

Accuracy of full-arch digital impressions: an in vitro and in vivo comparison.

Comparison of full-arch digital impressions to conventional impressions in vitro and in vivo. A straight metal bar was fixed between the second upper molars as a reference structure in the mouth of a voluntary patient and a corresponding polymer model. The following digitalization methods were applied: (1) the maxilla was digitized in vivo 12 times with the iTero Element (P-SCAN); (2) the maxilla was captured in vivo 12 times by conventional impression and the impression was digitized by a desktop scanner (P-IMP); (3) the impressions were poured and the 12 referring gypsum master-casts were scanned with the same desktop scanner (P-CAST); (4) the polymer model was digitized in vitro 12 times with the iTero Element (M-SCAN); (5) the polymer model was captured in vitro 12 times by conventional impression and the impression was digitized by a desktop scanner (M-IMP); (6) the impressions were poured and the 12 referring gypsum master-casts were scanned with the same desktop scanner (M-CAST). Datasets were exported and metrically analyzed (Geomagic ControlX) to determine three-dimensional length aberration and angular distortion versus the reference structure. Mann-Whitney U test was implemented to detect differences (p < 0.05). For multiple accuracy parameters, P-SCAN and M-SCAN showed similar or superior results compared to the other digitalization methods. The following length deviations were found: M-SCAN (- 55 to 80μm), M-IMP (110 to 329μm), M-CAST (88 to 178μm), P-SCAN (- 67 to 76μm), P-IMP (125-320μm), and P-CAST (92-285μm). Within the limitations of this study, the iTero-scan seems to be a valid alternative to conventional impressions for full arches. Intraoral scanners are more and more used in daily routine; however, little is known about their accuracy when it comes to full-arch scans. Under optimum conditions, the direct digitalization using the iTero Element intraoral scanning device results in the same and for single parameters (arch width and arch distortion) even in higher accuracy than the indirect digitalization of the impression or the gypsum cast using a desktop scanner.

A comparative evaluation of two contemporary cordless methods of gingival retraction – An In vivo study

Aim: The aim of this study was to compare and evaluate two different cordless methods of gingival retraction. Materials and Methods: For this study, a total of 30 participants aged above 18 years were selected. Out of 30 patients, 15 patients required fixed prosthesis in the anterior arch and 15 patients required fixed prosthesis in the posterior arch with minimum of two abutments surrounded by healthy periodontium, respectively. Same abutments were used for both retraction systems. After tooth preparation, three impressions for each patient were made, one without retraction, second after application of less viscous syringeable retraction paste, and third after 7 days after application of more viscous retraction paste with applicator gun. This was followed by fabrication of definitive Type IV gypsum cast. Undamaged retrieved casts were sawed out, buccolingually with the help of die cutting saw followed by measurement of the width of the retracted gingival sulcus under a stereomicroscope. The width was measured as the distance from the abutment tooth to the crest of the free gingiva. Results: The mean horizontal retraction attained from the control and two gingival retraction systems was compared using one-way ANOVA with the level of significance (P) set at 0.05. Amount of mean horizontal gingival retraction attained by syringeable retraction system was higher than control but statistically not significant in the anterior segment, whereas in the posterior segment, it was statistically significant.

Evaluation of efficacy of Aloe Vera as a Disinfectant by Immersion and Spray methods on Irreversible Hydrocolloid Impression Material and its Effect on the Dimensional Stability of Resultant Gypsum Cast - An in Vitro Study.

The need to use a natural alternative for disinfecting dental impression materials, which should be biocompatible and effective, led us to evaluate the efficacy of Aloe vera as a disinfectant by immersion and spray method on alginate impression material and its effect on the dimensional stability of the resultant gypsum cast.The efficacy of the disinfection procedures against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans was evaluated by determining the number of colony-forming units (CFU) recovered after disinfection of alginate discs inoculated with 1x106 CFU for defined intervals with aloe vera solution (99.96%). Dimensional stability was determined from the mean percentage deviation of three measurements that were taken between the fixed points on the casts using a traveling microscope and compared with corresponding measurements from the master model and controls. Statistical analysis of data was determined by analysis of variance.We found out that there is a mean percentage reduction in colony count of S. aureus, P. aeruginosa, and C. albicans after 3 minutes of immersion in aloe vera and after 3 minutes spray disinfection. Complete elimination of all the microorganism cells after 7 min immersion and spray disinfection. There was a statistically significant difference in the increase of the mean anteroposterior (AP) and cross arch (CA) dimension after 3 and 7 minutes immersion in aloe vera. Spraying with aloe vera for 7 minutes was proved to be the most effective disinfection procedure without altering dimensional stability.

Accuracy of 3-dimensional computer-aided manufactured single-tooth implant definitive casts

Statement of problemThe integration of the digital workflow into routine prosthodontic practice for single-tooth implant surgery and fixed prosthesis fabrication has occurred at a remarkable pace in the last 5 years. With the greater demands of esthetics and precision, the definitive implant analog cast must ensure accurate implant positioning as well as an accurate relationship to adjacent teeth. PurposeThe purpose of this in vitro study was to evaluate the accuracy of the 3-dimensional (3D) implant position of definitive casts produced by 3D printing and analog technology. Material and methodsA master patient model was created from a dentate typodont. The maxillary left central incisor was removed, and a Straumann RC implant was positioned for a screw-retained prosthesis. A laboratory scanner with an accuracy of 5 μm was used for all scanning. A scanbody was connected to the master model implant and scanned to create a master patient file, which served as the control master patient for all comparisons. The two 3D printing systems used for this study were the Statasys Objet500 (group OBJ), an industrial Polyjet production system, and the Formlabs Formlab 2 (group FORM), a budget SLA Vat system. In addition, a conventional gypsum cast (group GYP) with an implant analog was made with elastomeric impression material. With a sample size of 10 per group, each gypsum cast and 2 printed group casts were scanned with the D2000 laboratory scanner 5 times per cast. Convince software (3Shape) was used for 3D analysis to calculate accuracy. The following variables were measured: implant analog vertical displacement, horizontal displacement of implant platform and apex, degree of tilting in the vertical axis, and rotational position change around the vertical axis. Means and standard deviations were calculated for trueness. One-way ANOVA and the post hoc t test with Bonferroni correction were used to investigate any significant differences among the experimental groups (α=.05). ResultsFor vertical displacement of the implant body, group OBJ had the lowest value of –30 ±24 μm. The values obtained for OBJ and FORM were significantly different from that obtained for GYP (P<.05). For horizontal displacement of the implant shoulder, Group OBJ had the lowest value, 85 ±12 μm, and the difference among these groups was significantly different (P<.05). The value for horizontal displacement of the implant apex was 123 ±25 μm for group OBJ and not significantly different from that obtained for group GYP (136 ±40 μm) but significantly different from that obtained for group FORM (326 ±54 µm). Also, the analysis of implant body tilting in the vertical axis showed significant differences between the values obtained for groups GYP and OBJ and between the values obtained for groups OBJ and FORM. With regard to implant rotational position change around the vertical axis, the values obtained for the gypsum cast and group FORM were not statistically different from those obtained for the master patient control model (P>.05). However, the implant orientation of group OBJ was significantly different from the orientation of groups GYP and FORM (P<.05). The actual clinical relevance of these printing system discrepancies is yet to be determined because the level of clinical acceptable discrepancy in the x, y, and z vectors is still undefined. ConclusionsThis study showed statistically significant differences in accuracy among the implant analog cast fabrication systems; however; the level of clinical acceptable discrepancy is still undefined. Although further research is needed, this study supports the conclusion that the Polyjet industrial printing system was more accurate than the conventional implant analog gypsum cast.

Compared Efficacy of Microwave Irradiation with Chemical Compound in Dental Gypsum Casts

Compared Efficacy of Microwave Irradiation with Chemical Compound in Dental Gypsum Casts

Analysis of Bacterial Colonization due to Salivary Contamination on Gypsum Casts and Effect of Various Means of Disinfection of Dental Casts on Bacterial Colonization: An in vitro Study

Analysis of Bacterial Colonization due to Salivary Contamination on Gypsum Casts and Effect of Various Means of Disinfection of Dental Casts on Bacterial Colonization: An in vitro Study

The effect of seal bag storage on dimensional stability of alginate impression material

Background: The dimensional stability of alginate impression material is very important for obtaining an accurate cast. Seal bag storage is one way to maintain dimensional stability of the impression material. Objectives: This research aims to compare the dimensional stability of alginate impressions between imprESSIX Color Change (Alginate A), Algeniux Normal Set Major (Alginate B), and Aroma Fine Plus Normal Set (Alginate C). The alginate impressions were stored in seal bags for 0 min, 10 min, 3h, 24h, 72h, 120h, and 168h. Method: Sixty-three gypsum cast samples were obtained from a master die using 3 different alginate impression materials. The alginate impressions were stored in separate seal bags for each of the seven different time intervals, then the samples were poured with gypsum type III. The buccal cusp length from right first molar to left first molar was measured for each gypsum cast sample using calipers and compared with the master die. The data were analyzed with two-way ANOVA followed by post hoc LSD test. Results: The distance between the mesial buccal cusps of the right and left first molar was 52.280 mm for the master die. Gypsum cast samples of alginate A and B showed shorter lengths compared to master die, but the difference was not significant ( p >0.05). A significant difference in dimensional stability was observed for alginate C ( p <0.05) after 120h (52.080 mm) and 168h (52.057 mm). Conclusion: Dimensional stability of alginate impression was influenced by alginate composition and seal bag storage time. Seal bag storage could hold the dimensional stability of alginate A and B up to 168h, but for alginate C, the stability only lasted for 72h.

Development of Three-Dimensional Dental Scanning Apparatus Using Structured Illumination.

We demonstrated a three-dimensional (3D) dental scanning apparatus based on structured illumination. A liquid lens was used for tuning focus and a piezomotor stage was used for the shift of structured light. A simple algorithm, which detects intensity modulation, was used to perform optical sectioning with structured illumination. We reconstructed a 3D point cloud, which represents the 3D coordinates of the digitized surface of a dental gypsum cast by piling up sectioned images. We performed 3D registration of an individual 3D point cloud, which includes alignment and merging the 3D point clouds to exhibit a 3D model of the dental cast.

Measuring rill erosion using structure from motion: A plot experiment

In this paper the results of a plot experiment on rill erosion are reported. The rill network, manually incised on the soil and further shaped by a clear inflow discharge, was surveyed using the three-dimensional photo-reconstruction (3D-PR) technique which allows to obtain a digital terrain model (DTM) by a large series of oblique images of the channel from consumer un-calibrated and non-metric cameras. The three-dimensional (3D) DTM and the quasi-tridimensional (2.5D) model were generated by Agisoft Photoscan software. For a single rill channel, the reliability of the 3D image-based ground measurements of morphological and hydraulic variables was positively tested by the corresponding measurements carried out on the rill gypsum cast. Moreover, the morphological and hydraulic variables were measured at 11 transects of the plot by a profilometer P, the 2.5D and 3D models. Using the 3D model as reference, the analysis showed that the reliability of the measurements by P and 2.5D methods was comparable and the error was generally lower than 15%. The rill measurements carried out by the three methods agreed with the available literature measurements and supported the applicability of both the empirical relationship between rill length and its eroded volume and the theoretical dimensionless relationship among the morphological variables describing the channelized erosion process. The analysis also showed that the effect of the distance between two consecutive cross sections on the rill volume measurement by 3D model is negligible. Finally, the shaping effect of different flow discharges on three straight rills incised into the plot was tested. In particular, three increasing flow discharges (0.15, 0.35 and 0.5ls−1) were used sequentially in two rills while the maximum discharge of the sequence (0.5ls−1) was used into the third rill. Both the grain-size distribution of the eroded sediment and the total amount of soil loss were affected by the discharge sequence.

Individualized 3D scanning and printing for non-melanoma skin cancer brachytherapy: a financial study for its integration into clinical workflow.

PurposeSkin cancer is the most common tumor in the population. There are different therapeutic modalities. Brachytherapy is one of the techniques used, in which it is necessary to build customized moulds for some patients. Currently, these moulds are made by hand using rudimentary techniques. We present a new procedure based on 3D printing and the analysis of the clinical workflow.Material and methodsMoulds can be made either by hand or by automated 3D printing. For making moulds by hand, a patient’s alginate negative is created and, from that, the gypsum cast and customized moulds are made by hand from the patient’s negative template. The new process is based on 3D printing. The first step is to take a 3D scan of the surface of the patient and then, 3D modelling software is used to obtain an accurate anatomical reconstruction of the treatment area. We present the clinical workflow using 3D scanning and printing technology, comparing its costs with the usual custom handmade mould protocol.ResultsThe time spent for the new process is 6.25 hours, in contrast to the time spent for the conventional process, which is 9.5 hours. We found a 34% reduction in time required to create a mould for brachytherapy treatment. The labor cost of the conventional process is 211.5 vs. 152.5 hours, so the reduction is 59 hours. There is also a 49.5% reduction in the financial costs, mostly due to lack of need of a computed tomography (CT) scan of the gypsum and the mould. 3D scanning and printing offers financial benefits and reduces the clinical workload.ConclusionsAs the present project demonstrates, through the application of 3D printing technologies, the costs and time spent during the process in the clinical workload in brachytherapy treatment are reduced. Overall, 3D printing is a promising technique for brachytherapy that might be well received in the community.

Accuracy of Gypsum Casts after Different Impression Techniques and Double Pouring.

This study evaluated the accuracy of gypsum casts after different impression techniques and double pouring. Ten patients were selected and for each one it was obtained 5 partial putty/wash impressions with vinyl polysiloxane (VPS) material from teeth #13 to #16 with partial metal stock trays. The following techniques were performed: (1) one-step; two-step relief with: (2) PVC film; (3) slow-speed tungsten carbide bur and scalpel blade, (4) small movements of the tray and (5) without relief—negative control. The impressions were disinfected with 0.5% sodium hypochlorite for 10 minutes and stored during 110 and 230 minutes for the first and second pouring, respectively, with type IV gypsum. Three intra-oral lateral photographs of each patient were taken using a tripod and a customized radiographic positioner. The images were imported into ImageJ software and the total area of the buccal surface from teeth #13 to #16 was measured. A 4.0% coefficient of variance was criterion for using these measurements as Baseline values. The casts were photographed and analyzed using the same standardization for the clinical images. The area (mm2) obtained from the difference between the measurements of each gypsum cast and the Baseline value of the respective patient were calculated and analyzed by repeated-measures two way-ANOVA and Mauchly’s Sphericity test (α = 0.05). No significant effect was observed for Impression technique (P = 0.23), Second pouring (P = 0.99) and their interaction (P = 0.25). The impression techniques and double pouring did not influence the accuracy of the gypsum casts.

Cast erosion from the cleaning of debris after the use of a cast trimmer

Statement of problemWhether using tap water to rinse off debris will make a clinical difference to the surface detail of a gypsum cast is unknown. In addition, how best to remove debris from the cast is unknown. PurposeThe purpose of this in vitro study was to evaluate the efficiency of different methods of cleaning a gypsum cast after trimming and the effect of short-term exposure to tap water on the surface quality of the cast. Material and methodsA die fitting American National Standards Institute/American Dental Association specification 25 (International Standards Organization specification 6873) for dental gypsum products was embedded in a Dentoform with the machined lines positioned at the same level as the occlusal surface of the posterior teeth. A flat plate was used to ensure that the plane of occlusion for the die was at the same position as the posterior teeth. Forty polyvinyl siloxane impressions of the Dentoform were made and poured with vacuum-mixed improved Type IV dental stone. Each cast was inspected for the accurate reproduction of the lines. The base of the 2-stage pour was trimmed with a cast trimmer with water, and surface debris was removed by rinsing by hand under tap water for 10 seconds, by brushing the cast with a soft toothbrush for 10 seconds, or by resoaking the cast and using a soft camel hair brush in slurry water for 10 seconds. The amount of debris was evaluated on a scale of 1 to 4, and the quality of the 20-μm line was evaluated on a scale of 1 to 4 under ×15 magnification. The nonparametric Kruskal-Wallis ranks test was used to identify significant differences among the different cleaning methods (α=.05). ResultsResults of the Kruskal-Wallis and Kruskal-Wallis Z-value tests demonstrated that all cleaning methods produced cleaner casts than were observed for uncleansed controls (P<.001), but no differences in debris removal were found among the different cleaning methods (.065≤P≤.901). The ability to see the quality of a 20-μm line (P=.974) was not statistically different among the groups. ConclusionsRinsing the cast under flowing tap water and brushing, or hand washing under flowing tap water, or using a soft camel hair brush in slurry water for 10 seconds had no noticeable effects on the quality of a 20-μm line, and all 3 methods resulted in a clean cast.

Evaluation of Contamination Reduction on Gypsum Casts from Alginate Impressions Disinfected with Four Different Materials

&lt;p&gt;&lt;strong&gt;INTRODUCTION:&lt;/strong&gt; Infection control is one of the most important aspects in dentistry. According to the special features of dentistry, this profession can have a very important role in transmission of infection. This study was conducted by comparing the effects of four common disinfectants on the microbial contamination of alginate impressions and corresponding gypsum casts.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;METHODS &amp;amp; MATERIAL:&lt;/strong&gt; In this experimental study, eleven patients aged 20-30 years old were selected by convenience sampling method. Six alginate impressions for each patient were formed by 24-hour intervals. These sixty six alginate impressions were divided in six groups (control-no wash, wash with water, Micro10, 2% Glutaraldehyde, 5.25% Sodium hypochlorite and Deconex). Disinfection methods were done by spraying (except for glutaraldehyde group that was done by immersing method) and then the alginate impressions were placed in plastic bags for 10 minutes to prevent the evaporation of disinfectants. Sixty six gypsum casts were made from alginate impressions. Microbial swabs were collected from mid palatal region of alginate impressions and gypsum casts for all groups by dried sterile cotton. The swabs were cultured for bacteria by inoculation on Blood Agar at 37°C for 3 days. The positive cultures were counted and the data was analyzed by software SPSS21.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;RESULTS:&lt;/strong&gt; The counting colonies of gypsum casts and alginate impressions which were disinfected by Micro10, 2% Glutaraldehyde, 5.25% Sodium hypochlorite and Deconex were not statistically significant and meaningful.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;CONCLUSION:&lt;/strong&gt; All disinfectants used in this study, had the same and acceptable effect.&lt;/p&gt;

Wax Lining in an Impression Tray and Accuracy in Gypsum Cast Fabrication.

Controversy exists as to whether lining a metal-perforated impression tray with wax will yield a distorted irreversible hydrocolloid impression. Two current textbooks have completely different recommendations, but there is no evidence to support either theory. This project evaluates distortion in gypsum casts that have been prepared from wax-lined and unlined metal impression trays.The purpose of this study was to assess the influence of wax on the border and in the palate of metal-perforated impression trays on the dimensional stability of the resulting irreversible hydrocolloid impression. A dentaform was prepared with marks on the cusp tips of teeth 6 and 11 and distobuccal cusps of teeth 2 and 15. Using a standard maxillary rim lock impression tray, alginate impressions were made using a dentaform with no wax lining, wax lining the border of the tray, and wax lining the border and the palate (n = 10). Casts were randomized. Six measurements were taken using a stereographic measuring microscope, from tooth #6 to #11, #11 to #15, #15 to #2, #2 to #6, #6 to #15, and #2 to #11. An acrylic template was used to position the cast in a reproducible position on the microscope. Trays lined with wax on the border and the palate yielded casts with significantly different dimensions when compared to those poured from unlined or border-lined trays (p < 0.05). Casts produced from unlined and border-lined trays were not significantly different in dimension from the dentaform (p > 0.05). There is no difference between the metal tray with no wax, the metal tray with a wax around the border, and the dentaform. The clinician can make irreversible hydrocolloid impressions using wax on the periphery or without wax on the periphery and feel confident that the impression has not been compromised in its ability to accurately reproduce the maxillary arch when used. Caution should be exercised when adding wax to the palate of the impression tray.

Evaluation of biogeneric design techniques with CEREC CAD/CAM system.

PURPOSEThe aim of this study was to evaluate occlusal contacts generated by 3 different biogeneric design modes (individual (BI), copy (BC), reference (BR)) of CEREC software and to assess the designs subjectively.MATERIALS AND METHODSTen pairs of maxillary and mandibular casts were obtained from full dentate individuals. Gypsum cast contacts were quantified with articulating paper and digital impressions were taken. Then, all ceramic crown preparation was performed on the left first molar teeth and digital impressions of prepared teeth were made. BI, BC, and BR crowns were designed. Occlusal images of designs including occlusal contacts were superimposed on the gypsum cast images and corresponding contacts were determined. Three designs were evaluated by the students.RESULTSThe results of the study revealed that there was significant difference among the number of contacts of gypsum cast and digital models (P<.05). The comparison of the percentage of virtual contacts of three crown designs which were identical to the contacts of original gypsum cast revealed that BI and BR designs showed significantly higher percentages of identical contacts compared with BC design (P<.05). Subjective assessment revealed that students generally found BI designs and BR designs natural regarding naturalness of fissure morphology and cusp shape and cusp tip position. For general occlusal morphology, student groups generally found BI design "too strong" or "perfect", BC design "too weak", and BR design "perfect".CONCLUSIONOn a prepared tooth, three different biogeneric design modes of a CAD/CAM software reveals different crown designs regarding occlusal contacts and morphology.

Scanning accuracy and precision in 4 intraoral scanners: An in vitro comparison based on 3-dimensional analysis

Intraoral scanners may use proprietary acquisition and manufacturing processes. However, limited information is available regarding their accuracy, their precision, and the influence that refraction or coating may have on their output. The purpose of the study was to evaluate the scanning accuracy and precision of 4 intraoral scanners and to assess the influence of different test materials and coating thicknesses. Models were fabricated in 3 materials (polymethyl methacrylate [Telio CAD], titanium, and zirconia) and reference scanned with an industrial optical scanner. The models were scanned with intraoral scanners (3M Lava COS, Cerec AC/Bluecam, E4D, and iTero). A thick layer of coating was applied and scanned (3M Lava COS). Further evaluation on a gypsum cast was undertaken for the E4D system. Data were evaluated by using 3-dimensional analysis with "3D compare" software commands (3D compare analysis) regarding standard, mean, and maximum deviations, with subsequent statistical analysis. The 3M Lava COS, Cerec AC/Bluecam, and iTero generally displayed similar results regarding deviations. Maximum deviations, however, increased by several factors for the noncoating scanners (iTero and E4D). Statistical significance was found regarding material properties for noncoating scanners (P<.05). iTero displayed consistent material-specific, localized errors on the translucent material (Telio CAD). E4D showed the largest deviations. Scans of the gypsum cast displayed specific localized areas with greater deviations. Excessive coating was nonsignificant. Significant differences were found between the coating and noncoating scanners, and specific scanning errors for the system with parallel confocal microscopy were found for certain model materials. Specific areas of sizable deviations for the system with laser triangulation technology can be explained by the scanner design and noncoating technology. Excessive coating had no negative effect.

Analysis of the linear dimensions of the high stability alginate cast models with casting delays

Introduction: Dimensional stability of alginate impression is important to obtain an accurate cast. This study was to find the linear dimensional changes of the cast made from delayed pour high stability alginate impression after 5 days. Methods: This experimental laboratory study used 20 samples, divided into 4 groups. First and third group were the generated cast produced by immediately pour into high stability and conventional alginate impressions. Second and fourth group were the generated cast produced by delayed pour into high stability and conventional alginate impression for 5 days in storage with 100% humidity. Dimensional changes were measured on the upper part of the cast from buccal-lingual and mesial-distal direction beside measuring on the outer distance between the upper cast used Mitutoyo digital caliper scaled 0.01 mm. The data were analyzed using ANOVA (α = 0.05).Results: Mesial-distal (a) diameter average of group I, II, IV were respectively 8.410 mm, 8.520 mm, and 8.620 mm, compared with III as control was 8.420 mm. Meanwhile, diameter averages of mesial-distal (b) were 8.314 mm, 8.416 mm, 8.513 mm, and 8.315 mm. The averages of distance between each teeth (c) were 13.312 mm, 13.240 mm 13.191 mm, and 13.316 mm. The diameter averages of buccal-lingual (d) were 8.411 mm, 8.530 mm, 8.608 mm and 8.410 mm. The diameter averages of buccal-lingual (e) were 8.350 mm, 8.441 mm, 8.524 mm, and 8.340 mm. ANOVA test of the results of distance measurements between teeth (c) produces a calculated F value of 147.850, higher than the F table value (3.239). There were significant diferencess dimensional changes on gypsum cast made from high stability alginate impression and then poured after 5 days. Conclusion: There were diferencess linier dimensional changes on gypsum cast made from high stability alginate impression and then poured after 5 days.

Evaluation of efficacy of microwave irradiation in disinfecting dental gypsum casts: an ex vivo study.

The aim of this study is to assess the efficacy of microwave irradiation in disinfecting gypsum casts and also to compare its efficacy with validated method of chemical disinfection. The present study is an ex vivo study conducted on a sample of five irreversible hydrocolloid impressions in vitro and on ten patients gypsum casts in vivo following standard impression techniques to check the efficacy of microwave oven irradiation and compare its efficacy with standard chemical method of disinfection. Results were analysed using Mann-Whitney test and Wilcoxon signed rank test. 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 5. Microwave irradiation was found to be effective in disinfecting gypsum casts when compared to chemical disinfectant in disinfecting dental impressions.