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Background/Aim. There is limited published evidence on the cytotoxicity of 3D printed polymer materials for dentistry applications, despite that they are now widely used in medicine. Stereolithography (SLA) is one of the foremost 3D processes used in 3D printing, yet there are only a small number of resin materials reported to be suitable for medical applications. The aim of this study was to investigate, in vitro, the cytotoxic effect of the 3D printed resin in order to establish the suitability for its usage in dentistry and related medical applications such as surgical dental guides, occlusal splits and orthodontic devices. Methods. To examine the cytotoxicity of the 3D printed polymer-based epoxy resin, Accura® ClearVue™ (3D-Systems, USA), two cell cultures were used: mouse fibroblasts L929, and human lung fibroblasts MRC-5. The cell viability was determined by the Mosmann's colorimetric (MTT) test and the agar diffusion test (ADT). Results. Direct contact of the tested material with the ADT test showed nontoxic effects of tested material in any cell culture. The tested material showed no cytotoxic effect after 3 days of extraction of the eluate by the MTT, but mild cytotoxic effect after 5, 7 and 21 days on both cell lines. The cytotoxicity increased with increasing the time of the eluate extraction. Conclusion. The 3D printed polymer-based epoxy resin, Accura® ClearVue™ (3D-Systems, USA) is considered appropriate for making surgical dental implant guides according to the cytotoxic behavior. According to the mild level of cytotoxicity after the longer extraction periods, there is a need for further evaluation of biocompatibility for its application for the occlusal splints and orthodontic devices. [ABSTRACT FROM AUTHOR]

Background/Aim. Dental impressions present a negative imprint of intraoral tissues of a patient which is, by pouring in gypsum, transferred extraorally on the working cast. Casting an accurate and precise working cast presents the first and very important step, since each of the following stages contributes to the overall error of the production process, which can lead to inadequately fitting dental restorations. The aim of this study was to promote and test a new model and technique for in vitro evaluation of the dental impression accuracy, as well as to asses the dimensional stability of impression material depending on the material bulk, and its effect on the accuracy of working casts. Methods. Impressions were made by the monophasic technique using the experimental master model. Custom trays with spacing of 1, 2 and 3 mm were constructed by rapid prototyping. The overall of 10 impressions were made with each custom tray. Working casts were made with gypsum type IV. Measurement of working casts was done 24 h later using a coordinate measuring machine. Results. The obtained results show that the working casts of all the three custom trays were in most cases significantly different in the transversal and sagittal planes in relation to the master model. The height of abutments was mainly unaffected. The degree of convergence showed certain significance in all the three custom trays, most pronounced in the tray with 3 mm spacing. Conclusion. The impression material bulk of 1-3 mm could provide accurate working casts when using the monophasic impression technique. The increase of the distance between abutment teeth influences the accuracy of working casts depending on the material bulk. [ABSTRACT FROM AUTHOR]

Background/Aim. Retentive force of removable partial denture (RPD) directly depends on elastic force of stretched retentive clasp arms (RCAs). During deflection RCA must have even stress distribution. Safety factor is the concept which can be applied in estimating durability and functionality of RCAs. This study was based on analyzing properties of clasps designed by conventional clasp wax profiles and defining the optimal shapes of RCAs for stress distribution and safety factor aspects. Methods. Computer-aided-design (CAD) models of RCAs with simulated properties of materials used for fabrication of RPD cobalt-chromium-molybdenum (CoCrMo) alloy, commercially pure titanium (CPTi) and polyacetale were analyzed. Results. The research showed that geometrics of Rapid-flex profiles from the BIOS concept are defined for designing and modeling RCAs from CoCrMo alloys. I-Bar and Bonihard clasps made from CPTi might have the same design as CoCrMo clasp only by safety factor aspect, but it is obvious that CPTi are much more flexible, so their shape must be more massive. Polyacetale clasps should not be fabricated by BIOS concept for CoCrMo alloy. A proof for that is the low value of safety factor. Conclusion. The BIOS concept should be used only for RCAs made of CoCrMo alloy and different wax profiles should be used for fabricating clasps of other investigated materials. The contribution of this study may be the improvement of present systems for defining the clasps shapes made from CoCrMo alloys. The more significant application is the possibility of creating new concepts in defining shapes of RCA made from CPTi and polyacetale. [ABSTRACT FROM AUTHOR]

Background/Aim. Fracture toughness determines functional crown strenght and prevents damages on ceramics during mastication. There is a lack of relevant literature data about fracture toughness of crowns made by feather-edge preparation. Mechanical testing of ceramic samples is supposed to show if feather-edge tooth preparation is a successful method for making ceramic crowns without any risk of reduction of their mechanical properties. This research was done to establish effects of feather-edge tooth preparation on fracture toughness of single zirconia ceramic crowns. Methods. The research was performed as an experimental study. Sixty (60) ceramic crowns were made on non-carious extracted human premolars. Thirty (30) crowns were made on the basis of feather-edge preparation (experimental group I). The group II included 30 crowns made on 1 mm rounded shoulder. Crowns fabrication was executed on a copy mill production system "Zirkonzahn" (Zirkonzahn GMBH, Gais, Germany). The spherical compression test was used to determine fracture toughness, using 6 mm diameter ceramic ball. Fracture load for damaging ceramic crown was recorded on a universal testing machine -- Zwick, type 1464, with the speed of 0.05 mm/min. Results. The results of this research introduced significant differences between fracture toughness of ceramic samples in every examined group. However, fracture toughness of crowns from both group was above 2 000 N, what was double beyond a recommended value. The mean value of fracture toughness in the feather-edge group was 2 090 N, and in shoulder group it was 2 214 N. Conclusion. This research showed a high fracture toughness of zirconia crowns made on feather-edge preparation. The examined crowns showed a fracture resistance at a sufficient distance in relation to the minimum values of functional loads. Further research of functional loads of these crown is necessary, as well as research of marginal adaptation of cemented crowns and gingival inflammatory response. [ABSTRACT FROM AUTHOR]