Computational protocol: Accuracy of Gypsum Casts after Different Impression Techniques and Double Pouring

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Protocol publication

[…] Three photographs (RAW extension; 300 dpi) of the interested region (teeth #13–16) of each patient were obtained in right lateral view using a digital camera (Nikon D7000 DLS-R; Nikon Corporation, Tokyo, Japan) with macro lens (AF-S VR Micro-Nikkor 105 mm f/2.8G IF-ED; Nikon Corporation, Tokyo, Japan) coupled to a circular flash (Sigma EM-140 DG; Sigma Corporation, New York, USA). To standardize the framing and focal length, a camera tripod was used and an occlusal bite registration in acrylic resin (Pattern Resin LS; GC America, Inc., Alsip, IL, USA) was made for each patient over a radiographic positioner, which was coupled to the camera lens (Figs and ).Each photograph was taken in the presence of a caliper (± 0.02 mm; Mitutoyo Sul Americana Ltda., Suzano, SP, Brazil), whose ends were fixed with opening of 1.0 mm (). This step was used for the set scale adjustment of the ImageJ software (version 1.47a; NIH, Bethesda, MD, USA) by which the surface area measurements were performed. The images were imported into the ImageJ and a calibration was made with set scale tool. This software tool allows determining how much an object of known size has in pixels in the digital photos []. Thus, informing how 1.0 mm corresponds to pixels in each image, it was possible to calculate the total buccal surface area (mm2) of the teeth through its perimeter contouring (). To certify the reliability of the readings, clinical photographs were taken in triplicate for each patient, and the total interested area of each image was also measured in triplicate to obtain the means and standard deviations of each experimental group. A maximum 4.0% variance was established for the acceptance and reliability of the clinical images measurements, named as Baseline values. Additional clinical photographs of each patient were taken after all impressions and casts were obtained. The aim of this step was to verify the absence of changes in the gingival margins in relation to their initial condition, which would influence the results, by comparing the present area values to the Baseline.For digitization process of the gypsum casts, the same approach used for the clinical photos acquirement was used. Thus, the respective customized radiographic positioner of each patient, in the presence of the caliper with 1.0 mm opening, was again used to standardize the framing and focal length of the images taken of the gypsum casts (). Digital images were imported into the ImageJ and the total interested area of buccal surface was measured. A single blinded calibrated examiner performed all measurements. The average area of each gypsum cast was compared with the Baseline value of its respective []. The differences between the Baseline values (clinical photographs) and those obtained from their respective casts were expressed in square millimeters. [...] The data assumed normality (Shapiro-Wilk; P≥0.05) and homogeneity of variance (Levene; P≥0.05) for the sake of analysis. Statistical analyzes were applied to evaluate the influence of impression technique and double pouring on the dimensional accuracy of gypsum casts. All analyzes were performed using the IBM SPSS Statistics version 20.0 (IBM Corporation, Armonk, NY, USA).The surface area (mm2) measured in each gypsum cast was subtracted from the respective area measured in intraoral images (Baseline) for each patient. Thus, the ultimate dimensional accuracy resulted from the difference between the dimensions calculated in the casts’ images and the dimensions calculated in the clinical images of each patient. Negative values represented higher average area of the gypsum casts in relation to the Baseline. Data were analyzed by repeated-measures two way-ANOVA, with impression technique as between-subject factor and double pouring as within-subject factor, and by Mauchly’s Sphericity test (α = 0.05). […]

Pipeline specifications

Software tools ImageJ, SPSS
Applications Miscellaneous, Microscopic phenotype analysis
Organisms Homo sapiens
Chemicals Sodium Hypochlorite