” DOUBLE STEP REVERSE ” ( DSR ): A NEW PROTOCOL IN POLYVINYLSILOXANES ( PVS ) IMPRESSION- TAKING PROCESS - TWO CASE REPORTS
Figure 1 . Tooth # 13 with a very old crown
Figure 2 . Post-space impression with Aquasil Ultimate on the left and Aquasil XLV on the right
by means of an Aquasil Ultimate system . The Double Step Reverse technique wants to overcome the limitation of the speed of execution , required by PVS , to keep the same application mode of Putty-Wash 1-step / two-component technique , an is aiming to manage all the issues related to the hasty procedure of the latter . We then aim to compare the Putty-wash 1 step technique with polivinylsiloxanes ( A-silicone ) and the new Double Step Reverse ( DSR ) with the innovative Aquasil Ultimate impression system . In the first study , we took two impressions of each one of a 10-patient group who needed fixed prosthesis ( one or more elements ): one for each technique . Our laboratory then made two prosthesis for each patient . The controls were carried out on plaster models and on the patient ’ s mouth , checked through an optic microscope , “ Fit Checker ” and probing of the closing edge was also done . The 30 elements examined were eligible for cementation without any evidence of dimensional differences ; the closing edge has shown to be clinically acceptable in the range of 40 - 120 μm as indicated by McLean already in 1971 1 . The new DSR technique has shown to be clinically similar to the traditional one . The advantages were : ease of operation thanks to an easier control of the field that is free
from saliva and crevicular fluids during placement of the wash , the respect of the reticulation times even in case of multiple teeth impressions and the elimination of errors due to the proper control of the thrust of the tray material (“ V-shaped ” voids ). Moreover the patient accepted this technique well as shown by the final survey . This work aims to describe a new workflow in the polyvinylsiloxanes ( PVS ) impression taking ( Aquasil Ultimate , Dentsply ). A handpiece connected to the air circuit of the dental unit mixes and dispenses the “ wash ” material pressurized . The system involves the use of a PVS provided in two textures : a “ Type-3 ” ( Aquasil Ultimate Wash ) and a “ Type 2 ” ( Aquasil Ultimate Tray ) according to ISO 4823 . Both the chemical and physical properties of the material allow the adoption of a new protocol in impression taking that leaves the clinician enough time to deliver the PVS in compliance with the working time specified by the manufacturer without having to rush the procedure for multiple preparations . As to do so , it is possible to have a precise control of the field and of the single elements . The new protocol is not found in the literature yet , as this new system has been available for a short time . The procedure , called “ DSR ” ( Double Step
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