U ovom radu ispitivana je vidna oštrina na blizinu liječnika dentalne medicine u simuliranim kliničkim uvjetima na Stomatološkom Fakultetu u Zagrebu, te u laboratorijskim uvjetima u Laboratoriju za koherentnu optiku Instituta za fiziku u Zagrebu, i to metodom vremenski usrednjene holografske interferometrije. Ispitanici su bili studenti Stomatološkog fakulteta (50) koji su dobrovoljno pristali sudjelovati u istraživanju, urednog očnog statusa i vidne oštrine 1.0. U simuliranim kliničkim uvjetima, ispitivana je vidna oštrina na blizinu bez korekcije, i to s pomoću naglavne lupe 1,5x te binokularnih magnifikacijskih pomagala koja koriste Galilejev optički sustav 2,5x/350 mm i Keplerov optički sustav 3,3x/450 mm i 4,5x/350 mm. Vidna oštrina se ispitivala na minijaturnom vidnom testu, izrađenom u suradnji s Hrvatskim državnim arhivom u Zagrebu, a postavljen je u kavitet molara dentalnog fantoma. U laboratorijskim uvjetima mjerena je amplituda zubnih vibracija medotom vremenski usrednjene holografske interferometrije, mijenjajući brzine mikromotora i dijametar karbidnih svrdla u eksperimentalnom laboratorijskom postavu. Rezultati kliničkog dijela istraživanja Wilcoxon Signed Rank testa pokazuju da je distribucija mjerenja vidne oštrine korištenjem magnifikacijskih pomagala (grupe VNL, VGA 2,5, VKP 3,3 i VKP 4,5) sadržavala veće vrijednosti izmjerenih vidnih oštrina u odnosu na korištenje naturalnog vida bez magnifikacijskih pomagala (VSC) (p < 0,001 za usporedbu s VNL, VGA 2,5, VKP 3,3 i VKP 4,5 grupama). Najveće i statistički znatno povećanje vidne oštrine na blizinu postiže se Keplerovim teleskopom 4,5x/350 mm.Vibracije zuba korištenjem triju karbidnih svrdla (promjer: 1.0, 1.6, 2.3 mm) i triju brzina mikromotora ( 100, 450, 800 rpm) bile su u skladu s očekivanim vrijednostima. Veće amplitude vibracije zuba javljaju se povećavanjem dijametra svrdla i brzine okretanja mikromotora. Korištenjem magnifikacijskih pomagala na blizinu u kliničkim radnim uvjetima liječnika dentalne medicine postiže se veća vrijednost vidne oštrine, poboljšanje vizualiziranja oralne šupljine te se pridonosi postizanju optimalnih ergonomskih uvjeta u radu stomatologa.
In this dissertation, the near visual acuity in dentists was examined under the simulated clinical conditions at the Faculty of Dental Medicine in Zagreb and under the laboratory conditions of the Laboratory of Coherent Optics of the Institute of Physics in Zagreb, by the method of the time-averaged holographic interferometry (TAHI). Visual acuity plays an important role in dentists’ vision, which requires fine discrimination of detail in oral cavity in daily clinical routine. Dental competence requires good perceptual and visual skills for judging position, distance and the size of the object, as well as various shapes, in a small operating field .Using rotating instruments in everyday dental work, causing vibrations of the tooth surface and possible consequential structural changes in a tooth, could cause deterioration of the central visual acuity and thus not precise enough dental treatment. So far, TAHI was not used to measure vibrations generated in the tooth by using rotating dental instruments.
The participants are students of the School of Dental Medicine (50) who voluntarily agreed to participate in the study, having normal eye status and visual acuity of 1.0. Under the simulated clinical conditions, the visual acuity was examined at a close proximity and without correction, by application of 1.5x head magnifying glasses and binocular magnifying devices using Galileo's 2.5x/350 mm optical magnification system and Kepler 3x/450 mm and 4,5x/350mm optical system. The visual acuity was examined by means of a miniature visual test that was made in cooperation with the Croatian State Archives in Zagreb and placed in the molar cavity of a dental phantom. A sample of A4 Snellen optotype was created in the high resolution and printed and after that copied to 35mm BW microfilm. What was used is the microfilm camera for shooting, the Zeutscheu storage device, and the highest possible reduction of 28,5x was compared to the initial size of the sample of the A4 Snellen high-resolution optotype. The size of the miniaturized Snellen optotype for the examination of near visual acuity in the work of dentists is 5.2 x 2.8 mm and the optotype dimensions are varying from 0.05 to the biggest of 0.6mm. Under the laboratory conditions, the amplitude of tooth vibrations was measured by a time-averaged holographic interferometry, by altering the speed and diameter of the turbine in the experimental laboratory set up. TAHI is a method suitable for analyzing the modal structures of object vibrations because it turns vibrations into a fringe pattern visible in the recorded hologram We constructed an experimental system, consisting of a coherent source of light (He-Ne laser, MKS Instruments, Inc. Newport, USA, 25 mW, wavelength of 632 nm), a fixation press including a sample carrier, a charge coupled device
(CCD) detector connected to a computer, and an instrument for mechanical cavity preparation (Maillefer NiTi system, Dentsply Tecnika, Ballaigue, Switzerland) with a micromotor with 16:1 of torque (WD-75 M,W&H Dentalwerk Bürmoos GmbH, Bürmoos, Austria). The sample carrier is a three-jaw lathe chuck which allows certain flexibility in fixing the samples. An extracted molar with a cavity was used as a sample and cemented within the sample carrier. The amplitude of vibration h can be calculated from the argument of the zero-order Bessel function, ℎ𝑛=[𝜆(4𝜋)⁄]𝑥𝑛 , where ℎ𝑛 is the amplitude produced by the n-th dark fringe. Thus, the zeros of the Bessel function, 𝑥1≈2.4, 𝑥2≈5.5, 𝑥3≈8.7, etc., can be used to calculate the vibration amplitudes experimentally obtained by the TAHI method. The outcome of the part of the clinical research referring to Wilcoxon Signed Rank test shows the distribution of measurements of the visual acuity undertaken by application of the magnifying devices (VNL, VGA2,5, VKP3,3 i VKP4,5) contained higher values of visual acuity than those received by the use of natural vision, without any magnifying aids (VSC) (p < 0.001 for the comparison with VNL, VGA2,5, VKP3, and VKP4.5 groups). The biggest and statistically significant increase in the visual acuity is achieved by Kepler telescope 4.5x/350mm. The tooth vibrations, occurred by using of three turbines (diameter: 1.0, 1.6, 2.3 mm) and three speeds (100, 450, 800 rpm) were consistent with the expected values. Number of fringes in hologram increases with the size of drill diameter and increased frequency. Smaller diameter drills, at lower frequencies, produced almost not a single clearly visible fringe. Smaller diameters at higher frequencies, as well as larger diameters even at lower frequencies, produced only one, barely visible fringe.Number of fringes increases to maximum number of 3 at higher frequencies and larger drills .The three visible fringes are the highest number of fringes we managed to obtain by measurement, which result in less than 1 μm amplitude of vibrations.The higher amplitudes of tooth vibrations occur by increasing the diameter and the rotation speed of the turbine. The application of magnifying devices under conditions of dentist’ clinical work result in a better visual acuity and improved visualisation of the oral cavity, thereby simultaneously contributing to the optimal ergonomic work conditions of a dentist. The laborqtory results obtained indicated that the vibrations caused by the dental handpiece during cavity preparation are not sufficient to influence visual acuity.