Effect of repeated process of remelting cobalt - chromium alloy to microstructure on metal-ceramic bond

Uvod: Ena najpomembnejših lastnosti zlitin, s katerimi načrtujemo kovinsko-porcelanske restavracije, je sposobnost vezave porcelana na kovino. Vez med porcelanom in zlitino se ustvari na stični površini med njima. Sestava in debelina plasti oksidov predstavljajo ključni pomen za uspešno dolgotrajno vezavo s porcelanom. Močna vez med porcelanom in zlitino je ključna za dober dolgotrajen protetični izdelek. Zelo pogosta tehnična napaka pri kovinsko porcelanski tehniki je, da vez med zlitino in porcelanom oslabi, kar lahko vpliva na lastnosti zlitine in tehnološko izvedbo. Namen: Raziskati vpliv večkratnega pretaljevanja Co-Cr zlitin na jakost kemijske vezi s porcelanskim plaščem. Litje predstavlja postopek oblikovanja kovinskih gradiv. Zlitino stalimo in jo ulijemo v livno votlino forme, v kateri se strdi in obdrži njeno obliko. Torej pri litju zlitina v tekočem agregatnem stanju zapolni formo, se v njej strdi in dobi dokončno obliko. Najbolje se lijejo čiste kovine in evtektične zlitine. Z večkratnim litjem iste zlitine smo raziskovali, kako se spreminja učinkovitost vezi med zlitino in porcelanom. V praktičnem delu smo natančno prikazali vpliv večkratnega litja iste zlitine na kakovost kovinsko-porcelansko vez. Pri raziskavi nas je zanimalo, ali je pri večkrat uliti zlitini vez oslabljena. Metode dela: Glavni vir informacij je pregled sodobne strokovne literature, kot so članki v znanstvenih revijah s področja laboratorijske zobne protetike in dentalnih materialov. Literatura je iskana v knjižnici Zdravstvene in Medicinske fakultete na podlagi predhodnega iskanja v sistemu COBISS. Članke smo iskali po zbirki podatkov PubMed, ScienceDirect ter z iskalnikom Google učenjak in vsebuje tako domače kot tuje strokovno delo. Praktično delo in priprava preizkušancev za preizkus sta izvedena deloma v zobnem laboratoriju in deloma na Naravoslovno-tehnični fakulteti na oddelku za materiale in metalurgijo v Ljubljani. Izdelali smo vzorce za izvedbo metalografske analize vezi med porcelanom in Co-Cr zlitino. Izdelali smo tri vzorce ter nanje nanesli porcelansko osnovo. Rezultati: Predstavljeni so rezultati vrstične elektronske mikroskopije za vsak preizkušanec posebej. Prikazani so slikovni posnetki VEM s pomočjo naprave JEOL JSM-5610, iz katerih sta razvidna spreminjanje debeline oksidne plasti ter vsebnost elementov v njej. Razprava in zaključek: Najpomembnejša lastnost kovinsko-porcelanskih restavracij je sposobnost vezave porcelana na zlitino. Kemijska vez se ustvari na površino zlitine. Čeprav je ta običajno močnejša, ne smemo zanemariti mehanske vezi. Kakovost vezi je najboljša po prvem litju, saj je oksidna plast prisotna in enakomerna po celotni površini. Po trikratnem litju je debelina oksidne plasti še pogojno ustrezna. Na nekaterih mestih je namreč kemijska vez prekinjena, vendar je v povprečju še vedno več oksidne plasti, ki je prisotna. Najslabša kemijska vez je po šestkratnem litju. Oksidna plast je po šestkratnem litju na številnih mestih prekinjena in najtanjša.Introduction: One of the most important characteristics of alloys by which we plan metal-ceramic restorations is the ability to bind the ceramics to the metal. The bond between ceramics and alloy is created on the contact surface between them. The composition and the thickness of the layers of oxides represent the essential significance for the successful long-term bonding with the ceramics. A strong bond between porcelain and alloy is essential for a good prosthetic product. A very common technical flaw in metal-porcelain technique is that the bond between the alloy and porcelain weakens which can influence the characteristics of the alloy and technological performance. Purpose: Within the framework of the bachelor’s thesis, we research the impact of a remelted Co-Cr alloy on the chemical bond strength with a porcelain coat. Casting represents the procedure of forming metal materials. We melt an alloy and cast it into the casting mold cavity where it sets hard and retains its form. Thus, in casting, the alloy in the liquid aggregate state fills the mold, sets hard in it and gets the final shape. Pure metals and eutectic alloys cast the best. By casting the same alloy several times, we researched how the efficiency of bonds between the alloy and ceramics changes. In the practical part, we accurately showed the influence of casting the same alloy several times to the metal-porcelain bond. During the research, we were curious whether the bond will weaken in the alloy casted several times. Methods of work: The main source of information were the review of the scientific literature, such as articles in scientific magazines from the field of laboratory dental prosthetics and dental materials. The literature was sought in the library of the Faculty of Health Sciences and the Faculty of Medicine on the basis of the previous searching in the COBISS system. The articles were sought by means of the data collection PubMed, ScienceDirect, and by the Google Scholar. It includes domestic and also foreign scientific literature. The practical work and the preparation of the test items for the test was performed partly in the dental laboratory and partly at the Faculty of Natural Sciences and Engineering at the department for materials and metallurgy in Ljubljana. We produced samples to test the bonds between the ceramics and the Co-Cr alloy. We have produced three samples and pasted the ceramic basis on them. Results: The results of the linear electron microscopy for every test item individually were presented. The picture recordings VEM were presented by means of the device JEOL JSM-5610. They show that the thickness of the oxide layer and the content of the elements in it. Discussion and conclusion: The most important characteristic of the metal-ceramic restorations is the ability to bond ceramics to the metal. The chemical bond is created to the metal surface. In spite of that that the former is usually stronger, we must not neglect the mechanical bond. The quality of the bond is the best after the first casting, as the oxide layer is present and even on the entire surface. After three-time casting, the thickness of the oxide layer is conditionally appropriate. In some spots, namely, the chemical bond is broken. On the average, however, the oxide layer is present and prevails. The worst chemical bond is present after six-time casting because it is broken on several spots and narrow