[Analiza preloma skeletiranih proteza sa livenim kukicama]

Fractures of cast clasps are practically irreparable and impaire both therapeutic and prophylactic value of partial dentures. On purpose to explain causes of this rather frequently occuring damage, examination of fracture surface with optical and electronic microscopes and assessment of stress in the retainers were carried out. Microscopic examinationes comprised fracture surfaces of 30 cast clasps divided into 2 groups: Group I (control group): cast clasps formed and cast \u27under controlled laboratory conditions; Group II (test group): fractured cast clasps. It was found that surfaces of cast clasp fractures had a complex structure containing developed dendrites and separated carbide phases. In contrast to the control group, fracture surface from the test group showed signs of alloy fatigue, increased porosity and presence of new phases. On base of the analysis of partial denture movement it was assessed that stress in cast clasps approached both proportionality and fatigue level. In the conclusion it is pointed to two main factors causing cast clasp fractures: plastic deformation and material porosity.Praktično nemogući za reparaturu, prelomi livenih kukica skeletiranih proteza umanjuju terapijsku i profilaktičnu vrednost proteze. Sa ciljem da se objasne uzroci, ovoj relativno čestoj pojavi, obavljena su optička i elektronsko mikroskopska ispitivanja prelomnih površina i procenjeni su pritisci u retencionim elementima. Mikroskopska ispitivanja su obavljena na ukupno 30 prelomnih površina livenih kukica, svrstanih u dve grupe: 1. grupa (kontrolna) — livene kukice modelovane i livene pod kontrolisanim laboratorijskim uslovima. 2. grupa (ispitivana) — prelomljene livene kukice. Prelomne površine livenih kukica imaju složenu mikrostrukturu sa razvijenim dendritnim granama i izdvojenom karbidnom fazom. Za razliku od kontrolne grupe, ispitivana grupa prelomnih površina pokazuje znakove zamora materijala, prisustvo novih faza i povećanu poroznost materijala. Nakon analize kinematike skeletirane proteze procenjeno je da je pritisak u livenim kukicama u blizini tačke proporcionalnosti i blizu granice zamaranja. U zaključku su izdvojena dva najvažnija uzroka preloma livenih kukica: plastična deformacija i poroznost materijala

Influence of friction on the retention of Cobalt-Chromium partial denture

Dosadašnja istraživanja retencione sile skeletirane proteze pokazuju da ona zavisi od elastičnih svojstava materijala i ugla retencione površine u odnosu na vertikalu. Cilj istraživanja je bio da se utvrdi uticaj trenja na retencionu silu skeletirane proteze i izmeri statički koeficijent trenja za različite dodirne površine. Merenja koeficijenta trenja dodirnih površina su izvršena jednostavnom, ali originalnom metodom. Rezultati istraživanja nedvosmisleno ukazuju da trenje predstavlja važan faktor u retenciji skeletirane proteze livenim kukicama. Kako su vrednosti koeficijenta trenja (µ) različiti za različite dodirne površine, to se u zaključku ističe da se pri planiranju retencionog sistema skeletirane proteze koeficijent trenja, odnosno materijal retencionog zuba mora uzeti u obzir .The hitherto made investigations on the retentivity of cobalt-chromium dentures show that this power depends on the elasticity of material and the angle between the retentive surface and the vertical. The objective of this work was to determine the influence of friction on the retentivity of a cobalt-chromium denture and to measure friction ceoficients of various contact surfaces. Friction coefficient was measured by a simple but original method. Obtained results show clearly that friction is an important factor for the retention of a cobalt- -chromium partial denture by cast clasp. Various contact surfaces have different friction coefficients (ju). Therefore, in the conclusion it is pointed out hat in planing the retention system of a cobalt-chromium denture the friction coefficient, i.e. the abutment tooth material must be taken into consideration

Influence of friction on the retention of Cobalt-Chromium partial denture

Dosadašnja istraživanja retencione sile skeletirane proteze pokazuju da ona zavisi od elastičnih svojstava materijala i ugla retencione površine u odnosu na vertikalu. Cilj istraživanja je bio da se utvrdi uticaj trenja na retencionu silu skeletirane proteze i izmeri statički koeficijent trenja za različite dodirne površine. Merenja koeficijenta trenja dodirnih površina su izvršena jednostavnom, ali originalnom metodom. Rezultati istraživanja nedvosmisleno ukazuju da trenje predstavlja važan faktor u retenciji skeletirane proteze livenim kukicama. Kako su vrednosti koeficijenta trenja (µ) različiti za različite dodirne površine, to se u zaključku ističe da se pri planiranju retencionog sistema skeletirane proteze koeficijent trenja, odnosno materijal retencionog zuba mora uzeti u obzir .The hitherto made investigations on the retentivity of cobalt-chromium dentures show that this power depends on the elasticity of material and the angle between the retentive surface and the vertical. The objective of this work was to determine the influence of friction on the retentivity of a cobalt-chromium denture and to measure friction ceoficients of various contact surfaces. Friction coefficient was measured by a simple but original method. Obtained results show clearly that friction is an important factor for the retention of a cobalt- -chromium partial denture by cast clasp. Various contact surfaces have different friction coefficients (ju). Therefore, in the conclusion it is pointed out hat in planing the retention system of a cobalt-chromium denture the friction coefficient, i.e. the abutment tooth material must be taken into consideration

The fourth industrial revolution's impact on dentistry

Uvod I najveći vizionari nisu mogli da pretpostave kojom brzinom će stomatološka struka i nauka prihvatiti koncept četvrte industrijske revolucije. Po obimu i složenosti ova transformacija je veća od svih do sada poznatih i u literaturi je opisana kao Dentistry 4.0. Digitalna revolucija je stomatologiji omogućila da gotovo sve kliničke i laboratorijske procedure mogu biti podržane digitalnim tehnologijama. Cilj ovog rada je razumevanje uloge četvrte industrijske revolucije u stomatologiji. Metode Pretraživanje baze Medline izvršeno je putem baza podataka PubMed i Google Scholar za termine "četvrta industrijska revolucija", "digitalna stomatologija", "stomatologija 4.0", "CAD-CAM". Takođe su korišćene opcije "srodnih članaka" uz dodatno ručno pretraživanje preglednih članaka i relevantnih tekstova. Rezultati U radu su opisane najčešće dijagnostičke i terapijske procedure koje su podržane digitalnim tehnologijama. Zaključak Sofisticirane tehnologije četvrte industrijske revolucije dovele su do brže i preciznije dijagnoze oralnih oboljenja. Kliničke procedure postaju jednostavnije, preciznije i predvidljivije za lekara, a komfornije za pacijenta. Dugoročno, tu su i ekonomske uštede i očuvanje životne sredine.Introduction Even the greatest visionaries could not have guessed at what speed the profession and science of dentistry would accept the concept of the Fourth Industrial Revolution. In terms of its scale and complexity, this transformation has been greater than any known before and it has been described in the literature as Dentistry 4.0. The digital revolution in dentistry has allowed for nearly all clinical and laboratory procedures to be supported by digital technologies. The aim of this paper is to understand the role of Industry 4.0 in the profession of dentistry and identify its research status today and in the future. Methods An electronic search of Medline literature was performed via PubMed and Google Scholar databases with the terms "fourth industrial revolution," "digital dentistry," "dentistry 4.0," "CAD-CAM." The option "related articles" was also utilized as well as an additional manual search of review articles and the most relevant papers. Results The paper describes the most frequently used diagnostic and therapeutic procedures supported by digital technologies. Conclusion The sophisticated technologies of the Fourth Industrial Revolution have led to more rapid and precise diagnoses of oral diseases. Clinical procedures have become easier, more precise and predictable to the dentist, and more comfortable to the patient. The long-term benefits also include financial savings and environmental protection

The fourth industrial revolution's impact on dentistry

Uvod I najveći vizionari nisu mogli da pretpostave kojom brzinom će stomatološka struka i nauka prihvatiti koncept četvrte industrijske revolucije. Po obimu i složenosti ova transformacija je veća od svih do sada poznatih i u literaturi je opisana kao Dentistry 4.0. Digitalna revolucija je stomatologiji omogućila da gotovo sve kliničke i laboratorijske procedure mogu biti podržane digitalnim tehnologijama. Cilj ovog rada je razumevanje uloge četvrte industrijske revolucije u stomatologiji. Metode Pretraživanje baze Medline izvršeno je putem baza podataka PubMed i Google Scholar za termine "četvrta industrijska revolucija", "digitalna stomatologija", "stomatologija 4.0", "CAD-CAM". Takođe su korišćene opcije "srodnih članaka" uz dodatno ručno pretraživanje preglednih članaka i relevantnih tekstova. Rezultati U radu su opisane najčešće dijagnostičke i terapijske procedure koje su podržane digitalnim tehnologijama. Zaključak Sofisticirane tehnologije četvrte industrijske revolucije dovele su do brže i preciznije dijagnoze oralnih oboljenja. Kliničke procedure postaju jednostavnije, preciznije i predvidljivije za lekara, a komfornije za pacijenta. Dugoročno, tu su i ekonomske uštede i očuvanje životne sredine.Introduction Even the greatest visionaries could not have guessed at what speed the profession and science of dentistry would accept the concept of the Fourth Industrial Revolution. In terms of its scale and complexity, this transformation has been greater than any known before and it has been described in the literature as Dentistry 4.0. The digital revolution in dentistry has allowed for nearly all clinical and laboratory procedures to be supported by digital technologies. The aim of this paper is to understand the role of Industry 4.0 in the profession of dentistry and identify its research status today and in the future. Methods An electronic search of Medline literature was performed via PubMed and Google Scholar databases with the terms "fourth industrial revolution," "digital dentistry," "dentistry 4.0," "CAD-CAM." The option "related articles" was also utilized as well as an additional manual search of review articles and the most relevant papers. Results The paper describes the most frequently used diagnostic and therapeutic procedures supported by digital technologies. Conclusion The sophisticated technologies of the Fourth Industrial Revolution have led to more rapid and precise diagnoses of oral diseases. Clinical procedures have become easier, more precise and predictable to the dentist, and more comfortable to the patient. The long-term benefits also include financial savings and environmental protection

Selektivno lasersko topljenje i sinterovanje dentalne legure kobalt-hrom

Introduction/Objective the objective of this paper is to describe the microstructure and mechanical properties of sintered Co-Cr alloy and to emphasize its advantages and disadvantages with respect to the microstructure and mechanical properties of cast Co-Cr alloy. Methods Base Co-Cr alloy, EOSint M EOS Co-Cr SP2 (EOS GmbH, Munch, Germany), was used for the purpose of this research as the base material for sintering metal structures of metal-ceramic restorations. Metal sintering was conducted by using EOSint M 280 device of German origin in a stream of neutral gas - argon. After that, the alloy was heated over a period of 20 minutes at the temperature of 800°C. The chemical composition of the alloy was determined by energy dispersive spectroscopy. Microstructure of the tested alloy samples was examined under an optical metallographic and scanning electron microscope. Physical and mechanical properties were measured in a universal testing machine. The samples were prepared according to the standard ISO 527-1:1993. Results Chemical composition of the sintered Co-Cr alloy, determined by applying energy dispersive spectroscopy, indicated the same qualitative but different quantitative composition compared to cast Co-Cr alloys. The microstructure of the sintered Co-Cr alloy is lamellar in nature, with two dominant phases: ξ-Co and/or ξ-Cr (fcc - face-centered cubic) and γ-Co (hcp - hexagonal close-packed). Mechanical properties of the Co-Cr alloy obtained by applying selective laser melting technology compared to the cast Co-Cr alloy are superior or approximately the same. Conclusion Selective laser melting of the Co-Cr alloy is a good example of new technologies based on digitization. Together with other digitized procedures, this technology is an introduction to a new era in dentistry popularly called Dentistry 4.0. The advantages of the selective laser melting technology with respect to the conventional technology of casting Co-Cr alloy metal structures are precise metal structure fitting and eco-friendly technology.Uvod/Cilj Cilj rada je opisati mikrostrukturu i mehaničke karakteristike sinterovane legure Co-Cr i istaći njene prednosti i mane u odnosu na mikrostrukturu i mehaničke karakteristike livene legure Co-Cr. Metode U istraživanju je korišćena bazna legura Co-Cr, Eosint M EOS Co-Cr SP2 (EOS GmbH, Minhen, Nemačka) za sinterovanje metalnih konstrukcija metalokeramičkih nadoknada. Sinterovanje metala je obavljeno na aparatu EOSint M 280 u struji neutralnog gasa argona. Nakon toga legura je žarena 20 minuta na temperaturi od 800° C. Hemijski sastav legure određivan je energodisperzivnom spektroskopijom. Mikrostruktura ispitivanih uzoraka legure posmatrana je na optičkom metalografskom i elektronskom skenirajućem mikroskopu. Fizičko-mehaničke karakteristike merene su na univerzalnoj kidalici. Uzorci su pripremani prema standardu ISO 527-1:1993. Rezultati Hemijski sastav uzoraka sinterovane legure CoCr pokazao je isti kvalitativan ali različit kvantitativan sastav u odnosu na legure Co-Cr za livenje. Mikrostruktura sinterovane legure Co-Cr je lamelarne prirode, u kojoj dominiraju dve faze: e-Co i/ili e-Cr (fcc - face-centred cubic) i g-Co (hcp - hexagonal close-packed). U poređenju sa livenom legurom Co-Cr, mehaničke karakteristike sinterovane legure Co-Cr su bolje ili približno iste. Zaključak Selektivno lasersko topljenje legure Co-Cr je dobar primer novih tehnologija zasnovanih na digitalizaciji. Zajedno sa drugim digitalizovanim procedurama koje prethode, ova tehnologija je predvorje novoj eri u stomatologiji, popularno nazvanoj Dentistry 4.0. Prednosti tehnologije selektivnog laserskog topljenja u odnosu na tehnologiju konvencionalnog livenja metalnih konstrukcija od legure Co-Cr su preciznost naleganja metalne konstrukcije i čista tehnologija

Retencija parcijalne proteze sa dvostrukim krunama

The aim of this paper is to explain the mechanisms of retention with double crowns, examine the possibility of improving the process of measuring the forces of separating double crowns and suggest the measures for optimizing the retention forces with telescopic partial dentures. After the manufacturing of a partial denture with double crowns, it can only be established whether if the retention force is strong enough or not, but its nominal value remains unknown. Optimally it should be between 5 and 10N per anchor. Too strong retention force of partial denture causes traumatic damages of periodontal tissues, when taking the denture off, while not enough strong retention force doesn't connect the partial denture to the supporting tissues tightly enough. The paper describes the mechanism of retention with telescope and conus crowns and the way of measuring the force of their separation. For the purpose of optimizing the retention force, the ways of reducing exceedingly strong and increasing insufficient force were described. The necessity of being acquainted with the nominal value of the retention force of telescopic denture and its bringing to within the borders of optimal force is stressed in the conclusion.Cilj ovog rada je objasniti mehanizme retencije kod dvostrukih kruna, ispitati mogućnost unapređivanja postupka merenja sila razdvajanja dvostrukih kruna i predložiti mere za optimizaciju retencione sile kod teleskop parcijalnih proteza. Po završenoj izradi parcijalne proteze sa dvostrukim krunama jedino se može zaključiti da li je retenciona sila dovoljna ili ne, ali njena nominalna vrednost ostaje nepoznata. Optimalno ona treba da iznosi između 5 i 10N po pojedinačnom sidru. Prevelika retenciona sila parcijalne proteze uzrokuje traumatska oštećenja potpornog aparata zuba nosača, pri skidanju proteze, dok nedovoljna retenciona sila ne vezuje parcijalnu protezu za noseća tkiva u dovoljnoj meri. U radu je opisan mehanizam retencije kod teleskop i konus kruna i način merenja sile njihovog razdvajanja. U cilju optimizacije retencione sile opisani su načini redukcije prevelike, odnosno povećanja nedovoljne sile. U zaključku rada se ističe neophodnost poznavanja nominalne vrednosti retencione sile teleskop proteze i njeno dovođenje u granice optimalne sile

Anatomical and histological characteristics of proximal surfaces of abutment teeth

Formiranjem vodećih površina na aproksimalnim površinama retencionih zuba uklanja se deo gleđi. Faktori koji limitiraju moguću redukciju zuba su debljina gledji i nagnutost zuba. Cilj rada je analiza anatomskih i histoloških karakteristika aproksimalnih površina retencionih zuba. Merenja debljine gleđi na 280 preparata zuba, izvršena su na optičkom mikroskopu. Merene su četiri zone aproksimalnih površina zuba, na različitim udaljenostim a od vrha oštrice gleđnog noža. Određivanje dubine podminiranosti 420 aproksimalnih površina zuba izvršeno je na mikro-analizatoru sa preciznošću od 0,05 mm. Poređenjem srednjih vrednosti debljine gleđi, u okluzionim trećinama, i dubine podminiranosti aproksimainih površina zuba može se zaključiti da se i nakon uklanjanja svih prirodnih podminiranosti, formirana vodeća površina nalazi u zoni gleđi.When the guide planes are formed on the proximal surfaces of abutment teeth the part of enamel is removed. Thickness of enamel and inclination of tooth are the fectors that limit the possible tooth reduction. In this report anatomical and histological characteristics of proximal surfaces of the abutment teeth are analysed. Thickness of the enamel has been measured using the optical microscope for 280 prepared teeth. Measurements were performed on four zones of too th\u27s proximal surfaces, on the different distances from the top of enamel edge. Undercut of 420 proximal surfaces of tooth have been determined by micro-analyser with accuracy of 0,05 mm. By compering the mean vallues of enamel thickness, in occlusal thirds, and undercut of proximal surfaces, it is possible to conclude that the formed guide plane remains in the enamel even after the removing of all natural undercuts

Investigation of mechanical and biomedical properties of new dental alloy with high content of Au

The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. The demands which have to be met when developing a new dental alloy are linked with fulfilling the necessary requirements for making the alloy suitable for use in metal-ceramic restorations. Due to the stress generated by masticatory forces, alloys for dental restorations must have corresponding mechanical properties (yield strength, tensile strength, and elongation), hardness, the coefficient of thermal expansion (CTE), and biocompatibility. Namely dental alloy placed in an oral cavity reacts with the environment and deteriorates. New dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86.9Au-9.9Pt-1.5Zn, and about 1,5 wt.% micro-alloying elements (In, Ir, Rh). The dental alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: a1-phase rich in Au (main phase) and a2-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the a1-phase content is about 98,5 wt.% while the content of a2- phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solids temperature of about 1292 K and a liquids temperature of about 1412 K. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Spectral reflectance data from the mirror-polished flat samples of initial Au dental alloy were collected under the CIE standard illuminant D65. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done. According to the results of our research we can conclude that new dental alloy from Zlatarna Celje satisfied all requested standards regarding mechanical properties, hardness and CTE: Rp0.=550 [N/mm2], Rm =610 [N/mm2], A= 9%, 180 HV and CTE (25-600°C) about 14,45×10-6K-1. This new Au dental alloy has a yellow tinge in comparison to conventional Au-Pt-Zn alloys and did not show cytotoxicity when using standard short-term in-vitro assays on an L929 cell.

Preciznost keramičkih kruna izrađenih primenom optičkih metoda skeniranja Cerec3D sistema

Introduction: The results of many years technological development of Cerec® 3D CAD/CAM system, is implementation one intraoral and two extraoral optical scanning methods. Aim: The aim of this study was to determine the precision of ceramic crowns made by optical scanning methods of Cerec®3D system. Methods: The study was conducted in three experimental groups of ceramic crowns in whose manufacturing was applied three optical scanning methods of Cerec®3D system. Control group consisted of metalceramic crowns made by conventional methodology. The accuracy of ceramic crowns was examined by measuring of the marginal gap size between edge of crowns and demarcation by scanning electron microscope (SEM). Results: The research found, that there is a difference in the accuracy of ceramic crowns made by Cerec®3D system. The highest level of accuracy was recorded in the group of crowns made by technique extraoral optical superficial scanning (31,64±9,45μ). Marginal gap size crowns made with technique intraoral optical superficial scanning showed a lower level of accuracy (50,27±31,50μ). Value of marginal gap size crowns made by technique extraoral laser point scanning was 102,58+31,23μ. Conclusion: Ceramic crowns made by Cerec®3D optical scanners show a high and clinically acceptable precision level.Uvod: Dugogodišnji razvoj Cerec®3D CAD/CAM sistema implementirao je u praktičnu upotrebu jednu intraoralnu i dve ekstraoralne metode optičkog skeniranja. Cilj: Cilj rada je bio da se utvrdi stepen preciznosti keramičkih kruna izrađenih primenom različitih tehnika optičkog skeniranja Cerec®3D sistema. Materijal i metod: Ispitivanje je sprovedeno u okviru tri eksperimentalne grupe kruna u čijoj izradi su primenjeni različiti postupci skeniranja Cerec®3D sistema. Metalokeramičke krune izrađene konvencionalnom metodologijom predstavljale su kontrolnu grupu. Preciznost kruna ispitivana je merenjem veličine marginalnog zjapa između ruba krune i demarkacije preparacije pomoću skenirajućeg elektronskog mikroskopa (SEM). Rezultati: Rezultati istraživanja pokazuju da postoji razlika u preciznosti kruna izrađenih primenom različitih metoda skeniranja Cerec®3D sistema. Najviši stepen preciznosti (31,64±9,45μ) zabeležen je kod kruna u čijoj izradi je primenjena tehnika optičkog ekstraoralnog površinskog skeniranja, nešto niži stepen preciznosti (50,27±31,50μ) imale su krune izrađene tehnikom intraoralnog optičkog površinskog skeniranja. Krune izrađene primenom tehnike ekstraoralnog tačkastog skeniranja imale su stepen preciznosti od 102,58±31,23μ. Zaključak: Krune izrađene primenom optičkih metoda skeniranja Cerec 3D sistema pokazuju visok i klinički prihvatljiv stepen preciznosti