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PubMed2005

Structure and mechanical properties of the soft zone separating bulk dentin and enamel in crowns of human teeth: insight into tooth function.

The 200-300 microm soft zone of dentin, found beneath enamel in crowns of human teeth, is thought to fulfill important roles in tooth function, but little is known about its structure-mechanical relations. Scanning electron microscopy images of fracture surfaces showed that near the dentino-enamel junction (DEJ), a porous reticulate matrix of intertubular-dentin contains tubules with no peritubular lining. Peritubular-dentin however is found at some distance from the DEJ, and it gradually thickens with increasing depth into the bulk dentin. Concurrently, tighter packing of the collagen fibers is observed with a gradual increase in mineral deposits on and between the fibers. This structurally graded zone is known to be softer when tested for micro-hardness. It undergoes greater strain compared to bulk dentin, when measured using Moiré interferometry. We investigated the deformation and stiffness of this zone by means of non-contact laser-speckle interferometry (ESPI), and nanometer-scale deformations were tracked during compression-testing performed in water. We report a significantly reduced stiffness of this zone compared to bulk dentin, with mid-buccal regions of teeth averaging 3.5 GPa compared with 9.7 GPa in mid-lingual regions. Our results support and expand upon the hypothesis that the durability of the whole tooth relies upon a bucco-lingual asymmetric matching of stiffness by means of an interphase: a cushioning soft layer between enamel and bulk dentin.

Biomechanical Phenomena↗
PubMed2004

Effect of accommodation and pupil size on the movement of a posterior chamber lens in the phakic eye.

PURPOSE: Although a posterior chamber phakic intraocular lens provides effective refractive correction of high myopia and hyperopia, mechanical contact between the implantable contact lens (ICL) and the crystalline lens and inadequate aqueous circulation in the prelenticular space could cause subcapsular opacification. To assess whether and to what extent such mechanical contact occurs, changes in the distance between the STAAR Collamer ICL and the crystalline lens under various conditions were investigated. DESIGN: Open pilot study. PARTICIPANTS: Thirteen eyes of 11 myopic and 2 hyperopic patients with a mean age of 38 years (range, 19-53 years) were examined at least 6 months after ICL implantation. METHODS: A noninvasive, high-resolution biometry technique, partial coherence interferometry, was used to measure distance changes between the ICL and the crystalline lens during subjective accommodation, after instillation of pilocarpine, and under changing light conditions. MAIN OUTCOME MEASURES: Mean distance changes from the posterior corneal surface to the ICL, from the posterior corneal surface to the anterior surface of the crystalline lens, and the distance between the ICL and the crystalline lens. RESULTS: In the nonaccommodated state, the mean distance between the ICL and the crystalline lens was 457 microm (range, 123-924 microm). During subjective accommodation, a significant (P<0.01) decrease and, after topical application of pilocarpine, a nonsignificant (P=0.35) decrease of anterior chamber depth was accompanied by a nonsignificant (P = 0.71) reduction of the ICL-crystalline lens distance. Under photopic conditions, a significant mean reduction (P<0.01) of the ICL-crystalline lens distance of -28 microm (range, -16 to -188 microm) was observed. CONCLUSIONS: Partial coherence interferometry biometry enabled noninvasive high-precision investigation of ICL dynamics. No significant changes between the ICL and the crystalline lens were detected during subjective accommodation and after application of pilocarpine. However, under photopic conditions, with constriction of the pupil, the distance between the ICL and the crystalline lens was significantly reduced. This mechanism might cause inadequate aqueous circulation in the prelenticular space and might be one of the causes of subcapsular opacification in some of the eyes after ICL implantation.

Accommodation, Ocular↗
PubMed1998

In vitro testing of bioprostheses: influence of mechanical stresses and lipids on calcification.

BACKGROUND: Structural valve deterioration of bioprostheses is mainly caused by the progressive development of calcification. Mechanical stresses or lipid deposits in porcine aortic leaflets have been proposed as major factors contributing to the calcification process. METHODS: A new test protocol consisting of nondestructive holographic interferometry, which allows a quantitative deformation analysis of heart valves, and accelerated dynamic in vitro calcification was used. The rapid calcification fluid contained a final combined calcium and phosphorus concentration of 130 (mg/dL)2 in barbital buffer solution. The calcification of 32 bioprostheses donated by different manufacturers (SJM Bioimplant, Biocor standard, Biocor No-React, Carpentier-Edwards SAV, Bravo, pericardial prototype) was assessed after up to 25 x 10(6) cycles by microradiography and the areas of calcification were compared with the holographic interferograms. The distribution of lipid droplets of four porcine prostheses were visualized by Sudan III stain before the calcification process. RESULTS: Most of the tested bioprostheses had areas presenting with stress concentrations, and the dynamic in vitro testing resulted in leaflet calcification corresponding to the holographic irregularities. A strong correlation between calcification and stress distribution or lipid accumulation was found (r = 0.72; r = 0.81, respectively). After 19 x 10(6) cycles, the Carpentier-Edwards SAV and the pericardial valves had significantly less calcification than other prostheses tested (p = 0.003), but the variation among individual prostheses from the same manufacturer was even more pronounced. CONCLUSIONS: Mechanical stresses or lipid accumulation seems to play an important role in the calcification process of bioprostheses. Quality control of bioprosthetic valves using holographic interferometry has the potential to predict calcification before implantation.

Aortic Valve↗
PubMed2002

Laser interferometric method for measuring linear polymerization shrinkage in light cured dental restoratives.

OBJECTIVE: A novel laser interferometric method for monitoring linear polymerization shrinkage in dental restoratives is demonstrated. METHODS: The experimental apparatus consists of a low power Helium-Neon laser, a home-built Michelson interferometer, amplified photodiode detectors, and a computer data acquisition system. The feasibility of using interferometry to measure linear shrinkage was evaluated by measuring the percent linear contraction in five commercially available light cured restorative systems. RESULTS: Five-min interferometric curing profiles were collected for each restorative using a 400 mW/cm2 curing light irradiance. The 'interferograms' were converted into percent linear contraction profiles that revealed the relative kinetics of material shrinkage. The overall percent linear contraction after 5 min compares favorably with literature data for the five commercial restoratives studied here. SIGNIFICANCE: Interferometry offers several advantages over conventional methods of measuring polymerization contraction. These advantages include the inherent sensitivity and accuracy offered by interferometric measurements; the instrument does not need to be calibrated since the wavelength of the laser light source provides an accurate length standard. Also, the ability to collect data at high acquisition rates allows for the real-time characterization of unusually fast photopolymerization reactions. The low cost and relative ease of use associated with the apparatus are also advantageous.

Composite Resins↗
PubMed2001

Poly(methyl methacrylate) model study of optical surface quality after excimer laser photorefractive keratectomy.

PURPOSE: To evaluate lenses produced by excimer laser ablation of poly(methyl methacrylate) (PMMA) plates. SETTING: University research laboratory. METHODS: Two Nidek EC-5000 scanning-slit excimer laser systems were used to ablate plane-parallel plates of PMMA. The ablated lenses were examined by focimetry, interferometry, and mechanical surface profiling. RESULTS: The spherical optical powers of the lenses matched the expected values, but the cylindrical powers were generally lower than intended. Interferometry revealed marked irregularity in the surface of negative corrections, which often had a positive "island" at their center. Positive corrections were generally smoother. These findings were supported by the results of mechanical profiling. Contrast sensitivity measurements carried out when observing through ablated lenses whose power had been neutralized with a suitable spectacle lens of opposite sign confirmed that the surface irregularities of the ablated lenses markedly reduced contrast sensitivity over a range of spatial frequencies. CONCLUSION: Improvements in beam delivery systems seem desirable.

Contrast Sensitivity↗
PubMed2003

Determining postoperative anterior chamber depth.

PURPOSE: To compare measured and calculated postoperative anterior chamber depths (ACDs). SETTING: Department of Ophthalmology and Institute of Medical Physics, University of Vienna, Vienna, Austria, and Department of Ophthalmology, University of Mainz, Mainz, Germany. METHODS: The postoperative ACD was measured in 189 pseudophakic eyes using a laboratory prototype of partial coherence interferometry (PCI). In 6 intraocular lens (IOL) groups, the mean ACD was calculated by ray tracing based on the best-known A-constants of the SRK formulas. In addition, for each IOL type, each measured ACD was compared with a value calculated using the individual spherical equivalent of the postoperative refraction. RESULTS: The measured and the calculated ACD values were close and did not show systematic differences. The ACD values obtained in the study, however, differed significantly from the values published by the IOL manufacturers. A comparison of the PCI-assessed ACDs and the calculated values using the postoperative refraction showed more scattered results for the refraction-based data, which was probably the result of higher measurement errors with the autorefractometer than with PCI. CONCLUSIONS: High-precision interferometry measurements and ray-tracing calculations confirmed each other. The resulting mean ACD values should be used instead of the manufacturers' values. The refractive outcome of cataract surgery can be improved by combining preoperative high-precision PCI biometry and numerical ray tracing for IOL power calculations.

Anterior Chamber↗
PubMed2000

A laser plantar pressure sensor for the diabetic foot.

This paper describes the design and development of a high-resolution pressure sensor for use in the field of foot pressure measurement. The device uses an interferometry technique that involves the use of a laser light directed onto a pressure sensitive plate. The pressure plate compresses when a load is applied, and it is this compression which is measured by the interferometry technique. The interference pattern (interferogram) produced represents the pressure distribution across the plate. The interferogram is inputted into the computer using a high pixel CCD camera and video capture card. A fringe analysis program then converts the interferogram into a three-dimensional image of the pressure distribution. A prototype system is described and the initial results show that the system can produce a high resolution image with dynamic capabilities.

Biomedical Engineering↗
PubMed2006

National Biometry Audit II.

PURPOSE: To determine the change in compliance with the Royal College of Ophthalmologists biometry guidelines since the last National Audit 2 years ago and in particular to quantify the adoption of modern methods of axial length measurement and customization of A constants. METHOD: A structured telephone questionnaire of individuals who perform biometry in all eye departments in the United Kingdom. RESULTS: A biometrist was interviewed in 94 of the 178 United Kingdom Ophthalmology departments. Compared with 2 years ago, nurses alone perform biometry more frequently (67 vs 51%) and junior doctors less frequently (9 vs 15%). More biometrists now attend external training courses (45 vs 37%). The Royal College of Ophthalmologists recommended intraocular lens calculation formulae (SRK-T, Hoffer Q, and Holladay) are used more commonly (30 and 15%) and audit of prediction error is being performed more frequently (78 vs 71%). The routine use of a partial coherence laser interferometry has increased from 35 to 61% in United Kingdom Ophthalmology departments. Currently, only one United Kingdom department is routinely using immersion ultrasound biometry. 'A' constants are customized in 47% of departments. CONCLUSION: Over the last 2 years, there has been improved implementation of the Royal College of Ophthalmologists guidelines on biometry. It is essential that the Royal College of Ophthalmologists guidelines are updated to include current best practice of routine use of partial coherence laser interferometry or immersion biometry and customization of A constants. A benchmark standard of 85-90% of patients achieving a final postoperative refraction within 1 dioptre of the predicted should be established.

Biometry↗
PubMed2004

Cajal bodies, nucleoli, and speckles in the Xenopus oocyte nucleus have a low-density, sponge-like structure.

Nuclear organelles, unlike many cytoplasmic organelles, lack investing membranes and are thus in direct contact with the surrounding nucleoplasm. Because the properties of the nucleoplasm and nuclear organelles influence the exchange of molecules from one compartment to another, it is important to understand their physical structure. We studied the density of the nucleoplasm and the density and permeability of nucleoli, Cajal bodies (CBs), and speckles in the Xenopus oocyte nucleus or germinal vesicle (GV). Refractive indices were measured by interferometry within intact GVs isolated in oil. The refractive indices were used to estimate protein concentrations for nucleoplasm (0.106 g/cm3), CBs (0.136 g/cm3), speckles (0.162 g/cm3), and the dense fibrillar region of nucleoli (0.215 g/cm3). We determined similar protein concentrations for nuclear organelles isolated in aqueous media, where they are no longer surrounded by nucleoplasm. To examine the permeability of nuclear organelles, we injected fluorescent dextrans of various molecular masses (3-2000 kDa) into the cytoplasm or directly into the GV and measured the extent to which they penetrated the organelles. Together, the interferometry and dextran penetration data show that organelles in the Xenopus GV have a low-density, sponge-like structure that provides access to macromolecules from the nucleoplasm.

Animals↗
PubMed2002

Three-dimensional modeling of middle ear biomechanics and its applications.

HYPOTHESIS: This study investigated whether combined technologies of finite element (FE) analysis and three-dimensional reconstruction of human temporal bones could be used to construct a computational model, useful in describing normal and pathologic middle ear sound conduction. BACKGROUND: FE models for biologic systems have been used in ear biomechanics. Three-dimensional reconstructions have also been made, but not in combination with FE modeling and laser interferometry measuring of human temporal bones. Furthermore, an FE model for the human middle ear with its ossicular attachments has not been reported on the basis of temporal bone histologic sections and morphometric reconstruction, to the authors' best knowledge. Because of the size, variability, and complexity of the middle ear, accurate morphologic data and boundary conditions are necessary for accurate FE modeling. METHODS: A fresh temporal bone was decalcified, embedded in celloidin, sectioned and stained, scanned, and digitized, and the normal middle ear was reconstructed. The histologic sections were used to construct a computer-aided design model with ligaments, muscles, and tendons as boundary conditions. The data thus obtained were converted into an FE mechanical model that was validated by comparison with displacements obtained by laser Doppler interferometry on 17 fresh human temporal bones. RESULTS: An FE model was generated, demonstrating dynamic behavior that moderately approximated the laser interferometric data from human temporal bones receiving 90-dB sound pressure level auditory frequencies at the tympanic membrane. CONCLUSION: Accurate FE modeling, incorporating both morphometric and interferometric performance data, predicted both normal and pathologic mechanical performance of the human ossicular chain.

Biomechanical Phenomena↗
PubMed2004

Repeatability of IOLMaster biometry in children.

AIMS: This study compares the repeatability of IOLMaster (Zeiss, Oberkochen, Germany) axial dimension measurements and conventional ultrasonography in children. METHODS: A series of IOLMaster (partial coherence interferometry, optical pachometry) and Echoscan (US 800, Nidek, Tokyo, Japan) (ultrasound) measurements were taken on 179 Chinese children (mean age, 10.6 +/- 0.8 years) taking part in a longitudinal study of myopia development, and the measurements were repeated on 37 of these subjects. RESULTS: IOLMaster axial length measurements showed better repeatability (95% limits of agreement for repeatability, -0.047 to 0.038 mm) than Echoscan axial length measurements (95% limits of agreement for repeatability, -0.85 to 0.67 mm). IOLMaster anterior chamber depth measurements also showed better repeatability (95% limits of agreement for repeatability, -0.053 to 0.073 mm) than Echoscan anterior chamber depth measurements (95% limits of agreement for repeatability, -0.57 to 0.49 mm). IOLMaster measurements were, on average, slightly larger than Echoscan measurements for axial length (by 0.14 mm) and anterior chamber depth (0.09 mm). CONCLUSION: Partial coherence interferometry techniques, such as that used by IOLMaster, should be considered as the standard technique for axial length measurement in children because they are noninvasive, highly precise, and easy to use.

Biometry↗
PubMed2002

Lysozyme crystal growth kinetics in microgravity.

Mach-Zehnder interferometry is applied to quantitatively characterize growth of lysozyme crystals in microgravity. Experiments were performed by the Free Interface Diffusion technique into APCF FID reactors using large seeds. Tracking of the experiments using interferometry allowed to monitor the onset of supersaturation and the seed growth. A large and stable concentration depletion zone around the growing crystal developed, whose time evolution was analyzed. The interferograms were analyzed taking into account finite thickness of the cell by integrating the concentration over the straight lines through the optical path. It was concluded that there may be a quasi-steady state growth mode at the stage when the spacial concentration distribution did not change but its absolute value over all the cell was slowly diminishing. From this portion of the data, an estimate was made of the dimensionless parameter beta R/D where beta is the face kinetic coefficient, R is the effective crystal size and D is the lysozyme diffusivity in solution, as followed from the steady state model. For the assumed quasi steady state data portion, the parameter varies between 0.7 and 0.9 suggesting mixed diffusion-interface kinetic controlled growth.

Animals↗
PubMed2006

Strip meniscometry: a new and simple method of tear meniscus evaluation.

PURPOSE: To investigate the applicability and efficacy of a new and simple method of quantification of the volume of tear meniscus, termed "strip meniscometry," in the diagnosis of the dry eye syndromes in a prospective controlled study. METHODS: One hundred eyes of 50 patients with dry eye (19 males; 31 females) aged between 18 and 76 years (mean, 54.3 years), as well as 80 eyes of 40 normal subjects aged from 15 to 70 years (mean, 50.8 years; 12 males, 28 females) were recruited in this study. The patients and the control subjects underwent strip meniscometry for 5 seconds, tear film lipid layer interferometry, tear film break-up time measurement, and ocular surface vital staining with fluorescein and rose bengal dyes and the Schirmer-1 test. RESULTS: Strip meniscometry scores correlated with tear quantity and stability, ocular surface staining scores, and lipid layer interferometry grades and improved after 2 weeks of punctal plug occlusion. CONCLUSIONS: Strip meniscometry is a swift, noninvasive, promising new method that is expected to find application in the diagnosis and evaluation of the outcome of treatment of dry eye syndromes.

Adolescent↗
PubMed1993

Interferometric measurements of cusp deformation of teeth restored with composites.

A Michelson interferometry apparatus was used for measurement of the displacement of the buccal cusps of premolars after restoration of MOD preparations with composites. The effects of composite type, cavity size, and hydration conditions were examined. Interferometry permitted real-time measurement of cusp movement as it occurred. Contraction occurred very rapidly, about 1/3 of the 60-minute amount within the two-minute period of exposure to the curing light. Cusp movement was smooth rather than interrupted, indicating lack of microfracturing at deformations of 11-46 microns. Contraction, 0.94% for Heliomolar and 1.2% for P-50, was similar to the linear polymerization shrinkage of the resins. Less cusp movement occurred in small cavities than in large cavities. Hydrated teeth had less cusp movement than dehydrated teeth.

Acid Etching, Dental↗
PubMed2002

[Test of thermal deformation for electronic devices of high thermal reliability].

Thermal deformation can be caused by high partial heat flux and greatly reduce thermal reliability of electronic devices. In this paper, an attempt is made to measure the thermal deformation of high power electronic devices under working condition using laser holographic interferometry with double exposure. Laser holographic interferometry is an untouched measurement with measurement precision up to micron dimension. The electronic device chosen for measurement is a type of solid state relay which is used for ignition of rockets. The output circuit of the solid state relay is made up of a MOSFET chip and the power density of the chip can reach high value. In particular situations thermal deformation and stress may significantly influence working performance of the solid state relay. The bulk deformation of the chip and its mount is estimated by number of interferential stripes on chip surface. While thermal stress and deformation can be estimated by curvature of interferential stripes on chip surface. Experimental results indicate that there are more interferential stripes on chip surface and greater flexural degree of stripes under high power. Therefore, these results reflect large out-of-plain displacement and deformed size of the chip with the increase of load current.

Electronics↗
PubMedDate not supplied

[The deformation-strain state of bridgework dentures].

Holographic interferometry was used to study strained deformed status of bridge dentures. The technique of measurements with a small holographic system is described. Dentures made of Cr-Ni steel with a principally new method of crown to intermediate part adhesion were under study, as were other bridge denture designs. The findings evidence that holographic interferometry may be used as a sparing method for checking up the quality of casting and adhesion of abutment crowns and an intermediate part of fixed dentures, as well as the strength of adhesion of the facing material (porcelain, plastic) to the metal base of the denture.

Dental Stress Analysis↗
PubMed1981

[Morphometry of anatomical objects using holographic interferometric technics].

Theoretical basis and results on application of holographic interferometry methods to certain area of the functional and applied anatomy are presented. The possibility to use some topographic methods and methods to study deformities are demonstrated in order to investigate functional characteristics of the circulatory vessels, certain skeletal bones, as well as to apply them in practical medicine, especially in stomatology. A precise quantitative information, obtained by means of the holographic interferometry, surves as an essential supplement to some known methods of biological morphology.

Anatomy↗
PubMed1998

Eye elongation during accommodation in humans: differences between emmetropes and myopes.

PURPOSE: The pathophysiology and pathogenesis of myopia are still a matter of controversy. Exaggerated longitudinal eye growth is assumed to play an important role in the development of myopia. A significant correlation between refraction and amount of near-work has been reported. However, current knowledge of changes of axial eye length with accommodation is limited because clinical ultrasound biometry does not provide the precision and resolution required to thoroughly investigate these phenomena. METHODS: Partial coherence interferometry (PCI), a noninvasive biometric technique, uses laser light with short coherence length in combination with interferometry to achieve precision in the micrometer to submicrometer range and resolution of 10 microm. In the present study this technique was used to investigate axial eye length changes in 11 emmetropic and 12 myopic eyes during monocular fixation at the far and near point. In 7 subjects, the contralateral eye has also been measured to investigate interocular differences in eye elongation. RESULTS: All investigated eyes elongated during accommodation. This elongation was more pronounced in emmetropes than in myopes (P < 0.001). Mean accommodation-induced eye elongations of 12.7 microm (range, 8.6-19.2 microm) and 5.2 microm (range, 2.1-9.5 microm), corresponding to a dioptric change of approximately -0.036 D and -0.015 D, were obtained for emmetropes and myopes. No significant difference in accommodative amplitudes between groups (5.1 +/- 1.2 D [range, 3.8-7.1 D] versus 4.1 +/- 2.0 D [range, 1.0-7.1 D]; P = 0.14) was detected. No significant interocular difference in accommodation-induced eye elongation was revealed (P = 0.86). Also, a mean backward movement of the posterior lens pole of 38 microm (range, 9-107 microm) was observed in both study groups. CONCLUSIONS: The detected eye elongation can be explained by the accommodation-induced contraction of the ciliary muscle, which results in forward and inward pulling of the choroid, thus decreasing the circumference of the sclera, and leads to an elongation of the axial eye length. Finally, it was demonstrated that PCI, in contrast to clinical ultrasound, is capable of characterizing eye length changes during accommodation in humans.

Accommodation, Ocular↗