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

Dugogodišnjim radom mogu se zbog djelovanja vibracija i u stomatologa i u zubnih tenhičara pojaviti određene zdravstvene poteškoće. Svrha rada bila je izmjeriti i usporediti neke parametare u vezi s vibracijama koje utječu na zdravlje stomatologa i zubnih tehničara i to vibracija koje proizvode tehnicki mikromotori sa svrdlima različitih oblika i materijala pri različitim brojevima okretaja. Vibracije su mjerene akcelerometrom postavljenim na tehničkom mikromotoru te na određenim dijelovima tijela ispitanika, uređajem koji se sastoji od piezosenzora, pojačala, filtara i prijenosnog uređaja za snimanje. Dobiveni signali analizirani su računalnim programom SpectraLAB i uspoređeni sa sadašnjim međunarodnim standardima. Statistička raščlamba podataka izvedena je s pomoću programskih paketa: STATISTICA for Windows, Release 5.5 H i SPSS for Windows. Temeljni čimbenik koji utječe na vibraciju jest broj okretaja kojim se služimo tijekom obradbe protetskoga rada. Dobiveni rezultati pokazuju da su vrijednosti ubrzanja vibracija unutar vrijedećih standarda, premda su vrijednosti vibracija radom na 40000 okretaja/min. vrlo blizu gornjoj granici tih standarda. Spektrografska raščlamba vibracija pokazala je da broj okretaja određuje na kojim će frekvencijama biti izražene vršne vrijednosti. Budući da postoje dokazane vibracijske bolesti stomatologa i zubnih tehničara preporučuje se upozoravati osobe koje rukuju takvim alatima na moguće 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

Uspješna endodontska terapija omogućuje da se spase jako oštećeni zubi. Manjak retencijske površine zuba najčešće se nadograđuje metalnim, konfekcijskim ili individualnim nadogradnjama. Problem je te restauracije sivoplava obojenost zubnih struktura. Zato nemetalni kolčići i nadogradnje imaju prednost kao retencijska podloga potpuno keramičkim krunicama, osobito kada se radi o prednjim prelomljenim ili obojenim devitaliziranim zubima. Osim staklo keramike sve češću uporabu kao biomaterijal u stomatološkoj protetici ima cirkonij-keramika zbog dobrih estetskih, kemijskih i mehaničkih svojstava te zbog dimenzijske stabilnosti. U radu će biti prikazan slučaj protetske sanacije prednjeg zbog traume prelomljenog zuba. Zub je endodontski obrađen. Temeljem rtg snimke normiranim je čeličnim i dijamantnim svrdlima odstranjena i izbrušena gutaperka do željene duljine korijenskoga kanala. Odabran je kolčić cirkonijevoga oksida (Biopost, Alfred Bech GmbH, Offenburg, Njemačka) prikladne duljine. Kolčić je nahrapavljen i pjeskaren sa zrncima Al2O3, veličine 150µm te adhezivno cementiran. Preostali dio kliničke krune nadomješten je kompozitom. U gingivni sulkus stavljen je retrakcijski končić. Temeljem dvofaznoga otiska izrađena je potpuna keramička krunica (Empress 2, Ivoclar, Schaan). Krunica je konačno pričvršćena adehzivnim cementom. Provedenom terapijom postignut je optimalan estetski i funkcijski učinak. 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 µm, 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

Rođen je 21. travnja 1923. godine u Varaždinu, gdje je polazio osnovnu školu i gimnaziju. Godine 1945. upisuje Medicinski fakultet Sveučilišta u Zagrebu i diplomira 1952. godine. Nakon liječničkog staža i obveznog terenskog rada (1952.-1954.) započinje na Klinici za maksilofacijalnu kirurgiju kod akademika prof.dr. Ive Čupara specijalizaciju iz stomatologije i polaže specijalistički ispit 1957. godine. U jesen iste godine počinje akademsku karijeru kao asistent u Zavodu za ortodonciju, gdje je bio do umirovljenja. Godine 1964. postaje sveučilišni docent nakon redovitog habilitacijskog postupka i obrane habilitacijskog rada: “Utjecaj jezika na razvoj gornje čeljusti i zubnog luka kod urođenog rascjepa”.Prof. Lapter was born on 21 April 1923 in Varaædin, 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 Čupar, 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 “The Effect of the Tongue on Development of the Maxilla and Dental Arch in Congenital Cleft”

Gradual Loss of Partial Denture Retentive Forces

Djelomična proteza može se fiziološki ispravno prilagoditi fundamentu samo na osnovi poznavanja biostatike stomatognatoga sustava. Velik broj čimbenika utječe hoće li neka sila biti u funkciji fiziološke stimulacije ili će prouzročiti patološke promjene potpornoga tkiva. Ovim istraživanjem namjerava se utvrditi početna vrijednost retencijskih sila lijevanih kvačica, ankera i magneta, te njihov postupni gubitak sile nakon određenoga broja ciklusa vađenja i stavljanja retencijskih elemenata. Mjerenja su provedena u Zavodu za materijale Fakulteta za strojarstvo i brodogradnju Sveučilišta u Zagrebu. Ispitivani uzorci izrađeni su od materijala i gotovih elemenata prema podatcima proizvođača. Odgovaraju kriterijima koje zahtijeva DIN 13912 i DIN 13906-1 i ostalim internacionalnim standardima. Uređajem za mjerenje retencijske sile može se ciklički uključivati i isključivati retencijske elemente i kontinuirano prikupljati mjerne podatke. Ovim mjerenjima istraživao se postupni gubitak sila ispitivanih retncijskih elemenata. Dobivene vrijednosti kvalitativne raščlambe ispitivanih retencijskih elemenata prikazane su grafički i u tablicama. Tijekom ispitivanje došlo se do spoznaje da vrijednost retencijske sile kvačica i ankera postupno opada, a da se sila magnetskih slitina ne mijenja. Temeljni čimbenik koji bitno utječe na veličinu retencijske sile jest trošenje i zamor materijala. Spojnica uz nazočnost sline ima manju silu retencije, ali zbog smanjena trošenja nastat će 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 manufacturer’s 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

Keramički materijali opravdavaju sve češću uporabu u restauraciji oštećenoga žvačnog sustava. »isti keramički sustavi rabe se u izradbi inleja, krunica i mostova manjih raspona. Cirkonijev dioksid je poznat polimorf. Dodatkom magnezijeva ili itrijeva oksida u određenom postotku, ZrO2 je potpuno ili djelomično stabiliziran i time je omogućena njegova uporaba u stomatološkoj protetici. Tetragonski cirkonski polikristal (TZP) stabiliziran s 3mol% itrija ima izvanredna mehanička i estetska svojstva i ima sve veću uporabu u restauraciji endodontski saniranih zuba, izradbi krunica i mostova CAD/CAM sustavom. Očekivati je da će taj keramički materijal nadomjestiti kovinsko-keramičke nadomjestke i u sanaciji gubitka većega 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