Tatjana Puskar

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.

A Comparative Analysis of the Corrosive Effect of Artificial Saliva of Variable pH on DMLS and Cast Co-Cr-Mo Dental Alloy

Dental alloys for direct metal laser sintering (DMLS) are available on the market today, but there is little scientific evidence reported on their characteristics. One of them is the release of ions, as an indicator of the corrosion characteristics of a dental alloy. Within this research, the difference in the elution of metals from DMLS and cast (CM) samples of Co-Cr-Mo dental alloy in saliva-like medium of three different pH was examined by inductively-coupled plasma mass spectrometry (ICP-MS). The obtained results show that the metal elution in artificial saliva from the DMLS alloy was lower than the elution from the CM alloy. The release of all investigated metal ions was influenced by the acidity, both from the DMLS and CM alloy, throughout the investigated period of 30 days. The change in acidity from a pH of 6.8 to a pH of 2.3 for the cast alloy led to a higher increase of the elution of Co, Cr and Mo from CM than from the DMLS alloy. The greatest release out of Co, Cr and Mo was for Co for both tested alloys. Further, the greatest release of all ions was measured at pH 2.3. In saliva of pH 2.3 and pH 4.5, the longer the investigated period, the higher the difference between the total metal ion release from the CM and DMLS alloys. Both alloys showed a safe level of elution according to the ISO definition in all investigated acidic environments.

Comparative analysis of structure and hardness of cast and direct metal laser sintering produced Co-Cr alloys used for dental devices

Purpose – The purpose of this paper is to analyse structure and measure hardness of Co-Cr dental alloy samples made with two different technologies, conventional casting method (CCM samples) and additive direct metal laser sintering technology (DMLS samples), and to compare the results. Design/methodology/approach – CCM samples were made in a conventional casting machine, using remanium 800+ Co-Cr dental alloy (Dentaurum, Ispringen, Germany). DMLS samples were fabricated out of EOS CC SP2 Co-Cr alloy (EOS, GmbH, Munich, Germany) using DMLS technology. Samples for structural analysis were plate-shaped (10 × 10 × 1.5 mm3) and for the hardness test were prismatic-shaped (55 × 10.2 × 11.2 mm3). Structure was analysed via an inverting microscope and colour metallography method. Findings – CCM samples have a dense, irregular dendritic mesh, which is typical for the metallic phase of the Co-Cr dental alloy. DMLS alloy has a more homogenous and more compact structure, compared to CCM. Metals, the alloy basis cons...

THE DIMENSIONAL STABILITY OF ELASTOMERIC DENTAL IMPRESSION MATERIALS

High accuracy dental impression is usually a first step during fabrication of indirect restorations that have to be seated in or on prepared teeth. The dimensional stability of the impression material could have an influence on the accuracy of the final restoration. Elastomeric materials (addition- cured silicones and condensation- cured silicones) are most frequently used as the impression material in fixed prosthodontics. The composition and the type of the chemical reaction determine the urgency to cast or digitize the impression. The aim of this study was to asses the dimensional stability of addition and condensation - cured silicones in time. Stainless steel model of two cylinders with the spherical top was fabricated. First, individual tray of acrylic resin was made according to the standard procedure. Addition and condensation cured silicon impressions were taken using monophase technique in acrylic tray. Impressions were cast in type IV dental stone after different periods of time, and dental stone replica models were made. Master model and dental stone replica models were scanned using Carl Zeiss Coordinate measuring machine Contura G2 with associated volumetric probing tolerance of 1µm. Processing was done using Calypso software. Addition and condensation cured silicon impressions were cast after different periods of time. Master model and dental stone replica models were scanned and the differences between the models were measured. The dimensional differences between the master model and the replica models occurred due to the dimensional instability of the impression material. The differences were significantly greater when condensation cured silicon impression material was used comparing to the addition cured silicon impression material. Both condensation and addition silicon showed satisfactory dimensional stability if cast according to the manufacturer’s instructions. If so, the linear dimensional changes did not exceed 1%.

Comparative analysis of Full Frame and APS-C camera sensors on 3D digitization results

Image based 3D digitization methods, as an input data, use a digital photographs for reconstruction of 3D objects. Today, digital cameras are common devices used for capturing of digital photographs. Every digital camera is equipped with one of two types of digital sensors — CCD or CMOS. One of important features of these both types of sensors is their physical size. This paper presents results of comparative analysis regarding the influence of Full Frame and APS-C sensor size on 3D digitization results obtained with photogrammetric Structure from Motion (SfM) method. Comparative analysis also included influence from obtained data on accuracy with the use of auto calibrated andpre-calibratedphotographs.

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