Branka Trifkovic

Application of Replica Technique and SEM in Accuracy Measurement of Ceramic Crowns

Application of Replica Technique and SEM in Accuracy Measurement of Ceramic Crowns The paper presents a comparative study of the measuring values of the marginal gap related to the ceramic crowns made by dental CAD/CAM system using the replica technique and SEM. The study was conducted using three experimental groups, which consisted of ceramic crowns manufactured by the Cerec CAD/CAM system. The scanning procedure was carried out using three specialized dental 3D digitization systems from the Cerec family - two types of extraoral optical scanning systems and an intraoral optical scanner. Measurements of the marginal gap were carried out using the replica technique and SEM. The comparison of aggregate values of the marginal gap using the replica technique showed a statistically significant difference between the systems. The measured values of marginal gaps of ceramic crowns using the replica technique were significantly lower compared to those measured by SEM. The results indicate that the choice of technique for measuring the accuracy of ceramic crowns influences the final results of investigation.

Accuracy of optical scanning methods of the Cerec®3D system in the process of making ceramic inlays

BACKGROUND/AIM One of the results of many years of Cerec 3D CAD/CAM system technological development is implementation of one intraoral and two extraoral optical scanning methods which, depending on the current indications, are applied in making fixed restorations. The aim of this study was to determine the degree of precision of optical scanning methods by the use of the Cerec 3D CAD/CAM system in the process of making ceramic inlays. METHODS The study was conducted in three experimental groups of inlays prepared using the procedure of three methods of scanning Cerec 3D system. Ceramic inlays made by conventional methodology were the control group. The accuracy of optical scanning methods of the Cerec 3D system computer aided design-computer aided manufacturing (CAD/CAM) was indirectly examined by measuring a marginal gap size between inlays and demarcation preparation by scanning electron microscope (SEM). RESULTS The results of the study showed a difference in the accuracy of the existing methods of scanning dental CAD/CAM systems. The highest level of accuracy was achieved by the extraoral optical superficial scanning technique. The value of marginal gap size inlays made with the technique of extraoral optical superficial scanning was 32.97 +/- 13.17 mus. Techniques of intraoral optical superficial and extraoral point laser scanning showed a lower level of accuracy (40.29 +/- 21.46 mus for inlays of intraoral optical superficial scanning and 99.67 +/- 37.25 mus for inlays of extraoral point laser scanning). CONCLUSION Optical scanning methods in dental CAM/CAM technologies are precise methods of digitizing the spatial models; application of extraoral optical scanning methods provides the highest precision.

In vitro cytotoxicity assessment of 3D printed polymer based epoxy resin intended for use in dentistry

This article was published online first in Vojnosanitetski Pregled in September 2017, available open access at https://doi.org/10.2298/VSP170721127P

Finite element analysis in defining the optimal shape and safety factor of retentive clasp arms of a removable partial denture.

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 analzed. RESULTS The research showed that geometrics of Rapidflex 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 Co-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 improve ment 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.