1http://dx.doi.org/10.20396/bjos.v18i0.8657273 Volume 18 2019 e191692 Original Article 1 Department of Dental Materials and Prosthodontics, Araraquara Dental School, Unesp – Sao Paulo State University, Araraquara, São Paulo, Brazil. 2 Division of Oral Health and Society, Faculty of Dentistry, McGill University, Montreal, Quebec, Canada. Corresponding author: José Maurício dos Santos Nunes Reis Humaitá Street, 1680 - Araraquara /SP- Brazil ZIP Code: 14801-903 Pabx: +55 16 33016300 E-mail: jm.reis@unesp.br Received: June 28, 2019 Accepted: September 11, 2019 Comparison of impression techniques and double pouring by dental cast’s accuracy. Preliminary clinical-lab trial Aion Mangino Messias1,*, Stephania Caroline Rodolfo Silva1, Filipe de Oliveira Abi-Rached1, Raphael de Freitas Souza2, José Maurício dos Santos Nunes Reis1 Aim: This study compared impression techniques and double pouring by means of cast’s accuracy. Methods: For each patient (n=10), impressions from right maxillary canine to first molar were made with acrylic resin trays and vinyl-polysiloxane using one single-step, and four two-steps techniques: relief with poly(vinyl chloride) film; tungsten- carbide bur/scalpel blade; small movements of the tray; non-relief. Total visible buccal surface area of crowns was measured three times using photographs from patients (Baseline) and casts. Mean area values (mm2) between Baseline and casts differences were analyzed by two-way repeated-measures ANOVA (α=.05; 1-β=85%). Results: No significant differences were observed for Impression Techniques (P=.525), Double Pouring (P=.281), and their interaction (P=.809). Conclusion: All impression techniques and double pouring produced casts with similar accuracy. Keywords: Dental impression materials. Dental impression technique. Photography, dental. Dimensional measurement accuracy. 2 Messias et al. Introduction Dimensionally accurate impression is an integral step for fabricating well-fitting resto- rations. Among elastomeric materials, vinyl-polysiloxane (VPS) stands out due to its excellent chemical and physical properties1. Although impressions can be made with custom or stock trays, the optimum accuracy is obtained with the custom ones2. How- ever, regarding the techniques, there is no consensus with respect to the best one. To fabricate fixed prostheses, stone dies must be made for improving marginal fit of crowns. Although current techniques for making removable dies have become more accurate, cutting a stone die out may result in dimensional change between abutments3. Therefore, producing more than one cast from the same impression is an option for preserving marginal fit. This study aimed to compare impression tech- niques and double pouring by means of cast’s accuracy. Materials and Methods For each recruited patient (n=10; Table 1), impressions from right maxillary canine to first molar were made (Chart 1) with partial trays (Figure 1) and VPS material Table 1. Criteria used for patients’ recruitment accepted by the Araraquara Dental School Research and Ethics Committee (#75/11-FOAr/UNESP). Criteria of Inclusion Criteria of Exclusion Age between 18-80 years Pregnancy Absence of caries and/or periodontal disease in the maxillary right quadrant. Allergic reaction known and informed of any material used. Teeth of the right maxillary quadrant healthy or with satisfactory direct restorations. Periodontal disease or impaired by caries / trauma / unsatisfactory restorations of the teeth of interest. Use of orthodontic braces. Concurrent or recent participation in another clinical study. Chart 1. Impression techniques. Impression Techniques Codes Descriptions Single-step SS 1) Putty and light body materials were used simultaneously. Poly(vinyl chloride) (PVC) film PVC 1) A sheet of PVC film covered the putty body material and it was removed after the impression has been taken off from the oral cavity. 2) Putty body material was relined with light body material. Tungsten carbide bur / scalpel blade BUR 1) After impression with putty body material, the axial region of the teeth was worn (5 s) with a slow-speed tungsten carbide bur (maxicut #1520; Edenta AG,). A scalpel blade (15C; Swann Morton Ltd.) was used to cut the inter-proximal embrasures. 2) Putty body material was relined with light body material. Small movements of the tray MOV 1) Putty body material was inserted in the oral cavity and compressed in the interested area. Buccal-lingual small movements of the tray were made (5 s) until material’s polymerization. 2) After impression was removed from the oral cavity, putty body material was relined with the light body material. Non-relief NR 1) Putty body material was compressed in the interested area. 2) The impression was removed from the oral cavity and relined with the light body material. 3 Messias et al. (Express XT, 3M ESPE). A single operator randomly made the impressions following the CONSORT statement. After the waiting time (120 min) recommended by the VPS manufacturer, casts were poured using vacuum mixed (Turbo Mix, EDG Equipment and Controls Ltd) type-IV gypsum (GC Fuji Rock EP, GC Europe), following the rec- ommended water/powder ratio by its manufacturer. After removal of the first cast, the second pouring employed these same parameters, waiting 120 min as an elastic recovery time. Three intra-oral photographs (RAW extension, 300 dpi) of each patient were taken in lat- eral view with digital camera (D7000, Nikon Corporation) coupled to a ring flash (Sigma EM-140DG, Sigma Corporation) (Figure 2). The images (Figure 3) were imported into the ImageJ software, and the total visible buccal surface area of crowns were mea- sured three times by a single and blind examiner to obtain the means and standard deviations. A tool of the software was used to contour the perimeter of the teeth. A maximum variance of 4% was established for the reliability use of the intra-oral images measurements (Baseline)4. These same procedures were performed to obtain experi- mental casts’ images (Figure 4). The average area of each cast was compared with the Baseline values and the difference between them was expressed in mm2. Figure 1. Custom acrylic resin partial tray. To standardize the thickness of the impression material (2.0-mm relief), the seating position, and to limit the pressure over the tray, extensions were made on the right maxillary lateral incisor and second molar (arrows). The trays were obtained and maintained in distilled water at 37ºC one week before impressions. Figure 2. View of the standardizing device/radiographic positioner with occlusal registration coupled to the camera lens to standardize the angle, focal length and framing. The occlusal registration (Pattern Resin LS, GC America) was made over the positioner, not compromising the area to be digitized. 4 Messias et al. Data were submitted to Shapiro-Wilk’s and Levene’s tests, followed by two-way repeated-measures ANOVA (α=.05). Results No statistically significant differences were observed for the Impression Techniques (P=.525), Double Pouring (P=.281), and their interaction (P=.809) (Table 2). For the nature of this investigation, since the power was 85%, the sample size was considered adequate. Figure 3. Intra-oral photograph. Note the ends of the digital caliper (arrow) fixed with opening of 1.0 mm for the calibration of the ImageJ software (version 1.47a). Calibration was performed informing how 1.0 mm corresponded to pixels in each image, calculating the total visible surface area (mm2) of the buccal surface through the perimeter contour of the teeth (clinical crowns). Table 2. Mean area (mm2) from the differences between Baseline and casts’ values for each Impression Technique and Pouring. Impression Techniques 1st Pouring 2nd Pouring SS 1.18 -0.91 PVC -2.68 -3.00 BUR -2.33 -3.22 MOV -3.77 -2.45 NR -2.02 -3.24 Figure 4. Cast photograph following the same standardization used intra-orally. The respective radiographic positioner was positioned over each cast. The area measurements from intra-oral photographs (Baseline) was compared with those obtained on the casts photographs of each respective patient. 5 Messias et al. Discussion VPS material allowed double pouring without impairing cast’s accuracy. Probably, the tray’s rigidity and its positioning with controlled pressure reduced the bending and residual stresses in the tray’s walls2. The proximity between Baseline and SS technique may be attributed to the thinner layer of the light-body material in comparison to that of two-step techniques. As higher as the viscosity of the material, smaller dimensional change would be expected5. How- ever, a higher volume of filler content means that there is less elasticity and fluidity, resulting in lower detail reproduction1. Thus, it is highly recommended to use small thickness of light-body material in combination with putty-body one. Despite correcting laboratory bias and minimizing often-clinical steps, multiple pour- ing can provide errors. However, in this study, there were no statistically differences between the casts, regardless of impression techniques and double pouring. Kumar et al.6 also observed no dimensional changes between multiple casts when the elastic recovery time is respected. One of the limitations of this study was to analyze only the buccal surface of the teeth by 2D-measurements. Conversely, this sort of evaluation is supported by authors7, who observed no differences between 2D and 3D-analyzes. Although the major prob- lem of most 2D-techniques is the limitation to single measurement points, both tech- niques (2D and 3D) can show comparable results and are in the range of the values of former studies8,9, which used well-established methods like direct view technique used in this study. Impression techniques and double pouring did not influence the cast’s accuracy. SS presented the closest absolute values to Baseline ones. Acknowledgments This study was granted by the “Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP” (Grants 2011/19165-4 and 2011/19314-0). References 1. Balkenhol M, Ferger P, Wostmann B. Dimensional accuracy of 2-stage putty-wash impressions: influence of impression trays and viscosity. Int J Prosthodont. 2007 Nov-Dec;20(6):573-5. 2. Davis RD, Schwartz RS. Dual-arch and custom tray accuracy. Am J Dent. 1991 Apr;4(2):89-92. 3. Al-Abidi K, Ellakwa A. The effect of adding a stone base on the accuracy of working casts using different types of dental stone. J Contemp Dent Pract. 2006 Sep 1;7(4):17-28. 4. Silva SC, Messias AM, Abi-Rached FO, de Souza RF, Reis JM. Accuracy of gypsum casts after different impression techniques and double pouring. PLoS One. 2016 Oct 13;11(10):e0164825. doi: 10.1371/journal.pone.0164825. 5. Fano V, Gennari PU, Ortalli I. Dimensional stability of silicone-base impression materials. Dent Mater. 1992 Mar;8(2):105-9. 6. Kumar D, Madihalli AU, Reddy KR, Rastogi N, Pradeep NT. Elastomeric impression materials: a comparison of accuracy of multiple pours. J Contemp Dent Pract. 2011 Jul;12(4):272-8. 6 Messias et al. 7. Anadioti E, Aquilino SA, Gratton DG, Holloway JA, Denry I, Thomas GW, Qian F. 3D and 2D Marginal Fit of Pressed and CAD/CAM Lithium Disilicate Crowns Made from Digital and Conventional Impressions. J Prosthodont. 2014 Dec;23(8):610-7. doi: 10.1111/jopr.12180. 8. Contreras EF, Henriques GE, Giolo SR, Nobilo MA. Fit of cast commercially pure titanium and Ti–6Al–4V alloy crowns before and after marginal refinement by electrical discharge machining. J Prosthet Dent. 2002 Nov; 88(5):467-72. 9. Romeo E, Iorio M, Storelli S, Camandona M, Abati S. Marginal adapatation of full-coverage CAD/CAM restorations: in vitro study using a non-destructive method. Minerva Stomatol. 2009 Mar;58(3):61-72.