Evaluation of the elastic recovery of polyvinyl siloxanes contamined, during set, with astringent solutions
aClinical Assistant, Department of Prosthodontics, University of São Paulo School of Dentistry.cProfessor, Department of Dental Materials, University of São Paulo School of Dentistry
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Purpose:It has been suggested that astringent solutions could alter clinically the set and the quality of an impression with polyvinyl siloxanes (PVS). However, investigations seem to charge an inadvertent contamination by latex rubber gloves for these unwanted effects.1,2 In this study, the elastic recovery of two commercial PVS was evaluated, as an indirect way to access the polymerization rate, contamined with astringent solutions.
Materials and Methods:
Three grams of low-viscosity, cartridge-mix, PVS (Aquasil, Dentsply; President, Coltène) were spatuled with 5 µl of a contaminant solution, for 30 s (n=3): G1- physiologic sour (NaCl 3%); G2- Astringedent, Ultradent (FeSO4); G3- Hemostop, Dentsply (Cl3Al); G4- no contamination (control). The material was then inserted in an Muench´s elasticimer device.3 After the manufacturer’s setting time (President: 4 min; Aquasil 4,5 min) an initial standardized deformation of 12% for 5 s was induced4 and then elastic recovery was measured at this time (time 0) and after two and four minutes (figure 1). The results were submitted to ANOVA and Tukey test (p=0,05) – software GMC 7.7 (graphic 1).
Figure 1- Muench´s elasticimer. A-base, B-main shank, C- receptacle´s lock, D-material´s receptacle, E-crossbeam, F-rod, G-indicator e protractor, H-gauntlet´s shank, I-cable
Results:The results showed that there were differences in the elastic recovery for the materials (p<0,001; Aquasil, 98,96% and President, 97,33%), and setting time (p=0.000). The contamination with sour resulted in the lowest elastic recovery values (G1: 97,68%b; G2: 98,63%a; G3: 98,12%ab; G4: 98,16%ab), essentially because of the results of President at the manufacturer´s setting time.
Graphic 01- Elastic recovery at the final setting time (0 minutes), and after two and four minutes; P=President, Aq=Aquasil.
Conclusion:It can be concluded that the astringent solutions tested did not influence the elastic recovery of PVS. As the elastic recovery diminished with time, it can be inferred that setting of PVS should be at least four minutes longer than time indicated by the manufacturers.
1. O’Mahony A, Spencer P, Williams K, Corcoran J. Effect of 3 medicaments on the dimensional accuracy and surface detail reproduction of polyvinyl siloxane impressions. Quintessence International 2000;31(3):201-206.
2. De Camargo LM, Chee WWL, Donovan TE Inhibition of polymerization of polyvinyl siloxanes by medicaments used on gingival retraction cords. J Prosthet Dent 1993;70(2):114-117, 1993.
3. Muench A, Jansen WC. Recuperação elástica de elastômeros em função da idade e da ordem de deformação. Rev. Odont. Univ. São Paulo 1997;11(1):49-53.4. American Dental Association. Revised American Dental Association Specification No. 19 for Non-Aqueous, Elastomeric Dental Impression Materials. J Amer Dent Ass 1977;94:733-741.