482 research outputs found
Structural analysis of high-rpm composite propfan blades for a cruise missile wind tunnel model
Analyses were performed on a high-speed composite blade set for the Department of Defense Propfan Missile Interactions Project. The final design iteration, which resulted in the CM2D-2 blade design, is described in this report. Mode shapes, integral order excitation, and stress margins were examined. In addition, geometric corrections were performed to compensate for blade deflection under operating conditions with respect to the aerodynamic design shape
Shot peening for Ti-6Al-4V alloy compressor blades
A text program was conducted to determine the effects of certain shot-peening parameters on the fatigue life of the Ti-6Al-4V alloys as well as the effect of a demarcation line on a test specimen. This demarcation line, caused by an abrupt change from untreated surface to shot-peened surface, was thought to have caused the failure of several blades in a multistage compressor at the NASA Lewis Research Center. The demarcation line had no detrimental effect upon bending fatigue specimens tested at room temperature. Procedures for shot peening Ti-6Al-4V compressor blades are recommended for future applications
Examining Vibrations in Dental Procedures
DugogodiÅ”njim radom mogu se zbog djelovanja vibracija i u stomatologa i u zubnih tenhiÄara pojaviti odreÄene zdravstvene poteÅ”koÄe.
Svrha rada bila je izmjeriti i usporediti neke parametare u vezi s vibracijama koje utjeÄu na zdravlje stomatologa i zubnih tehniÄara i to vibracija koje proizvode tehnicki mikromotori sa svrdlima razliÄitih oblika i materijala pri razliÄitim brojevima okretaja.
Vibracije su mjerene akcelerometrom postavljenim na tehniÄkom mikromotoru te na odreÄenim dijelovima tijela ispitanika, ureÄajem koji se sastoji od piezosenzora, pojaÄala, filtara i prijenosnog ureÄaja za snimanje. Dobiveni signali analizirani su raÄunalnim programom SpectraLAB i usporeÄeni sa sadaÅ”njim meÄunarodnim standardima. StatistiÄka raÅ”Älamba podataka izvedena je s pomoÄu programskih paketa: STATISTICA for Windows, Release 5.5 H i SPSS for Windows. Temeljni Äimbenik koji utjeÄe na vibraciju jest broj okretaja kojim se služimo tijekom obradbe protetskoga rada. Dobiveni rezultati pokazuju da su vrijednosti ubrzanja vibracija unutar vrijedeÄih standarda, premda su vrijednosti vibracija radom na 40000 okretaja/min. vrlo blizu gornjoj granici tih standarda. Spektrografska raÅ”Älamba vibracija pokazala je da broj okretaja odreÄuje na kojim Äe frekvencijama biti izražene vrÅ”ne vrijednosti.
BuduÄi da postoje dokazane vibracijske bolesti stomatologa i zubnih tehniÄara preporuÄuje se upozoravati osobe koje rukuju takvim alatima na moguÄe posljedice, a dobiveni rezultati mogu biti korisni da bi se prevenirale takve bolesti i upotrebljavale brzine okretaja koje proizvode najmanje vibracija.Certain health problems may appear both in dentists and dental technicians due to long periods of exposure to vibrations.
The aim of the study was to measure and compare some factors related to vibrations which affect the health of dentists and dental techicians, particularly those produced by mocromotors with drills of different shapes, made of different materials rotating at different speeds.
Vibrations were measured by an accelerometre which was placed an the technical micromotor and on various body parts of subjects. The device consists of a piezosensor, an amplifier, a filter and mobile recording device. The obtained signals were analysed by the SpectraLAB computer programme and consequently compared with presently valid international standards. Statistical data analysis was carried out by PC software, STATISTICA for Windows, Release 5.5 H and SPSS for Windows, Release 7.5.
The main factor that effects vibration is the rotation number used in the course of prosthetic replacement processing.
The obtained results point to the fact that the vibration acceleration values are within accepted standards, although the vibration values at 40000 rotations per minute approach the maximum limit of these standards. The spactral analysis of vibration revealed that the rotation number determined the frequencies of the maximum values. Since there is strong evidence to support vibration related illnes in dentists and dental technicians, it is recommended that individuals who use such devices be warned about the possible harmful effects. The obtained results may be used in prevention of such illness. They are also recommended to use rotation speeds which produce the least vibrations
ZrO2 Ceramic as an Esthetic Post
UspjeÅ”na endodontska terapija omoguÄuje da se spase jako oÅ”teÄeni zubi. Manjak retencijske povrÅ”ine zuba najÄeÅ”Äe se nadograÄuje metalnim, konfekcijskim ili individualnim nadogradnjama. Problem je te restauracije sivoplava obojenost zubnih struktura. Zato nemetalni kolÄiÄi i nadogradnje imaju prednost kao retencijska podloga potpuno
keramiÄkim krunicama, osobito kada se radi o prednjim prelomljenim ili obojenim devitaliziranim zubima.
Osim staklo keramike sve ÄeÅ”Äu uporabu kao biomaterijal u stomatoloÅ”koj protetici ima cirkonij-keramika zbog dobrih estetskih, kemijskih i mehaniÄkih svojstava te zbog dimenzijske stabilnosti.
U radu Äe biti prikazan sluÄaj protetske sanacije prednjeg zbog traume prelomljenog zuba. Zub je endodontski obraÄen. Temeljem rtg snimke normiranim je ÄeliÄnim i dijamantnim svrdlima odstranjena i izbruÅ”ena gutaperka do željene duljine korijenskoga kanala. Odabran je kolÄiÄ cirkonijevoga oksida (Biopost, Alfred Bech GmbH, Offenburg, NjemaÄka) prikladne duljine. KolÄiÄ je nahrapavljen i pjeskaren sa zrncima Al2O3, veliÄine 150Āµm te adhezivno cementiran. Preostali dio kliniÄke krune nadomjeÅ”ten je kompozitom. U gingivni sulkus stavljen je retrakcijski konÄiÄ. Temeljem dvofaznoga otiska izraÄena je potpuna keramiÄka krunica (Empress 2, Ivoclar, Schaan). Krunica je konaÄno priÄvrÅ”Äena adehzivnim cementom. Provedenom terapijom postignut je optimalan estetski i funkcijski uÄinak.
Sve faze slikovno su prikazane.Successful endodontic therapy allows patients to retain severely damaged teeth.
A minor retention surface is usually restored with metallic, commercial or individual posts.
Silver-gray color posts is an esthetic problem in reconstruction of antetior teeth. Nonmetallic posts in combination with all-ceramic crowns are esthetically preferable for the restoration of endodontically treated anterior teeth with fractured or discolored coronal aspects.
Glass ceramics as well as zirconimum oxide ceramik have been used as biomaterials in prosthodontics.
Zirconium has good esthetic, chemical and mechanic properties and is dimensionally stable.
In this study, a clinical case with prosthetic restoration of an upper fractured incisor has been discribed. After endodontic and radiograph treatment , the root canal was prepared with specific cylindrical steel and diamond burns. Gutta-percha was removed to the optimal depth of the root canal. Zirconium oxide post (Biopost, Alfred Becht GmbH,
Offenburg, Germany) was chosen of suitable lenght. After roughening and sandblasting the surface of the ZrO2 post with particles Al2O3, size 150 Āµm, the post was adhesively cemented. The clinical crown was built with composite. Retraction thread was placed in gingival slucus. Monophase impression was taken. An all-ceramic crown, Empress 2 (Ivoclar, Schaan, Lichtenstein) was made. The ceramic
crown was fixed with adhesive cement. Good esthetic and functional effect was achieved. All phases of the therapy have been illustrated by figures
In memoriam Prof. Vladimir Lapter 1923 - 2002
RoÄen je 21. travnja 1923. godine u Varaždinu, gdje je polazio osnovnu Å”kolu i gimnaziju. Godine 1945. upisuje Medicinski fakultet SveuÄiliÅ”ta u Zagrebu i diplomira 1952. godine. Nakon lijeÄniÄkog staža i obveznog terenskog rada (1952.-1954.) zapoÄinje na Klinici za maksilofacijalnu kirurgiju kod akademika prof.dr. Ive Äupara specijalizaciju iz stomatologije i polaže specijalistiÄki ispit 1957. godine.
U jesen iste godine poÄinje akademsku karijeru kao asistent u Zavodu za ortodonciju, gdje je bio do umirovljenja.
Godine 1964. postaje sveuÄiliÅ”ni docent nakon redovitog habilitacijskog postupka i obrane habilitacijskog rada: āUtjecaj jezika na razvoj gornje Äeljusti i zubnog luka kod uroÄenog rascjepaā.Prof. Lapter was born on 21 April 1923 in VaraƦdin, where he attended primary and high school. In 1945 he enrolled at the School of Medicine University of Zagreb and graduated in 1952. After obligatory medical practice and fieldwork (1952-1954) he began specialising in dental medicine at the Clinic of Maxillofacial Surgery under Academician Prof. Ivo Äupar, and passed the specialist examination in 1957.
In the autumn of the same year he started his academic career as Assistant in the Department of Orthodontics, where he worked until retirement. In 1964 he became Senior Lecturer after defending his thesis āThe Effect of the Tongue on Development of the Maxilla and Dental Arch in Congenital Cleftā
Gradual Loss of Partial Denture Retentive Forces
DjelomiÄna proteza može se fizioloÅ”ki ispravno prilagoditi fundamentu samo na osnovi poznavanja biostatike stomatognatoga sustava. Velik broj Äimbenika utjeÄe hoÄe li neka sila biti u funkciji fizioloÅ”ke stimulacije ili Äe prouzroÄiti patoloÅ”ke promjene potpornoga tkiva.
Ovim istraživanjem namjerava se utvrditi poÄetna vrijednost retencijskih sila lijevanih kvaÄica, ankera i magneta, te njihov postupni gubitak sile nakon odreÄenoga broja ciklusa vaÄenja i stavljanja retencijskih elemenata.
Mjerenja su provedena u Zavodu za materijale Fakulteta za strojarstvo i brodogradnju SveuÄiliÅ”ta u Zagrebu. Ispitivani uzorci izraÄeni su od materijala i gotovih elemenata prema podatcima proizvoÄaÄa. Odgovaraju kriterijima koje zahtijeva DIN 13912 i DIN 13906-1 i ostalim internacionalnim standardima. UreÄajem za mjerenje retencijske sile može se cikliÄki ukljuÄivati i iskljuÄivati retencijske elemente i kontinuirano prikupljati mjerne podatke.
Ovim mjerenjima istraživao se postupni gubitak sila ispitivanih retncijskih elemenata. Dobivene vrijednosti kvalitativne raÅ”Älambe ispitivanih retencijskih elemenata prikazane su grafiÄki i u tablicama. Tijekom ispitivanje doÅ”lo se do spoznaje da vrijednost retencijske sile kvaÄica i ankera postupno opada, a da se sila magnetskih slitina
ne mijenja.
Temeljni Äimbenik koji bitno utjeÄe na veliÄinu retencijske sile jest troÅ”enje i zamor materijala. Spojnica uz nazoÄnost sline ima manju silu retencije, ali zbog smanjena troÅ”enja nastat Äe i sporije smanjenje retencijske sile.A partial denture can be oppropriately accommodated physiologically on the denture base only with good understanding of the stomatognathic system biostatics. A force can either act as a physiological stimulus or can lead to pathological alterations in supporting tissue, wich depends on a great number of factors.
The aim of the study was to determine the initial retentive force values of cast clasps, anchors and magnets as wel as their gradual loss of force after a certain number of retentive elements, extraction and insertion cycles.
Measurement were carried out at the Materials Department, School Engineering and Naval Architecture, University of Zagreb. The examined specimens were made of materials and ready-made elements in accordance with the manufacturerās declaration. They satisfy the DIN 13912 and DIN 13906-1 criteria and comply with other
international standards. The device for retentive force measurement can periodically both include and exclude retentive elements thus continually collecting measurement data.
Gradual loss of the examined retentive element forces was analysed by these measurings. The obtained values of the examined retentive elements qualitative analysis are presented in graphs and tables.
In the course of analysis it was dicovered that the retentive force value of both clasps and anchors gradually decreases whereas the magnetic force of the alloys remains unchanged.
The key factors which have a great impact on the retnetive force value are wear and material fatigue. A clasp in a wet environment (saliva) has less retentive force, but due to decreased wear the retnetive force decrease will progress more slowly
A Quantitative Evaluation of the Distal Displacement of the Gingival Zenith in the Maxillary Anterior Teeth
The aim of this study was to quantify the specific distal displacement of the gingival zenith in the maxillary anterior dentition. Bilateral measurements, taken with a digital caliper in maxillary stone casts were recorded in six maxillary anterior teeth to evaluate distal displacement of the gingival zenith in relation to the long axis of the crowns. The gingival zenith was distally displaced between 0.45 and 1.01 mm in 90%, 85% and 60% of the central incisors, lateral incisors and canines, respectively. Contralateral comparisons between the tooth groups revealed significantly larger distal displacement of the zenith in left canine (p<0.05). Ipsilateral comparisons revealed that the lateral displacement of the zenith was significantly larger in central than in lateral incisors (p<0.05). Similarly, the zenith of lateral incisors was displaced significantly more distal than that of canine teeth (p<0.05). Comparisons of the frequency of coincidence of the position of the gingival zenith with the long axis of the tooth revealed that it was significantly greater in canines than in lateral and central incisors (p<0.05). The frequency and magnitude of distal displacement is tooth-dependent and larger in central than in lateral incisors, which in turn, is larger than in canines. These data could be used as reference points during esthetic anterior oral rehabilitation, especially in case of porcelain laminate veneers
Zirconium Oxide Ceramics in Prosthodontics
KeramiÄki materijali opravdavaju sve ÄeÅ”Äu uporabu u restauraciji oÅ”teÄenoga žvaÄnog sustava. Ā»isti keramiÄki sustavi rabe se u izradbi inleja, krunica i mostova manjih raspona. Cirkonijev dioksid je poznat polimorf. Dodatkom magnezijeva ili itrijeva oksida u odreÄenom postotku, ZrO2 je potpuno ili djelomiÄno stabiliziran i time je omoguÄena njegova uporaba u stomatoloÅ”koj protetici. Tetragonski cirkonski polikristal (TZP) stabiliziran s 3mol% itrija ima izvanredna mehaniÄka i estetska svojstva i ima sve veÄu uporabu u restauraciji endodontski saniranih zuba, izradbi krunica i mostova CAD/CAM sustavom. OÄekivati je da Äe taj keramiÄki materijal nadomjestiti kovinsko-keramiÄke nadomjestke i u sanaciji gubitka veÄega broja zuba.Dental ceramics justifies more frequent use in prosthetic restoration of damaged dental status. Inlays, crowns and three-unit bridges have been made of all-ceramic system. Zirconia dioxide is a well- known polymorph. The addition of stabilising oxides like MgO, Y2O3 to pure zirconia, makes it completely or partially stabilized zirconia which enables use in prosthodontics. Tetragonal Zirconia Polycrystals (TZP) stabilized with 3mol % yttria, has excellent mechanical and esthetical properties. Fixed prosthetic appliances of this ceramic have been made using CAD/CAM techniques. It can be expected that zirconium oxide ceramics will replace metal-ceramics in restorations that require high strength
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