Measuring tooth vibrations induced during cavity preparation with time-averaged holography and its influence on near vision acuity in dentists.

The aim of this study was to quantify vibrations and their influence on visual acuity. The study consisted of two parts, laboratory and clinical. Time-averaged holographic interferometry (TAHI) method was used in laboratory for measuring the amplitude of tooth vibrations induced by dental handpiece. The amplitudes of tooth vibrations were measured for the three diameters and three speeds. The larger diameter coupled with increasing speed resulted in greater vibration amplitudes, whereby a maximum amplitude of less than one micrometer was detected. For quantifying the natural visual acuity for the corresponding tooth vibrations, we have used the clinical condition approach with miniaturized Snellen optotype as an assessing tool. Central visual acuity did not display variance in visual acuity at rest or under load. Results indicate that the vibrations induced during cavity preparation are not sufficient to negatively affect visual acuity of dentists.

Effects of Curing Modes on the Microhardness of Resin-modified Glass Ionomer Cements.

OBJECTIVE: This study evaluated the effects of curing modes on surface microhardness of visible light-cured resin-modified glass ionomer cements (VLC RMGIC) and a giomer after different storage periods in comparison to auto-cured resin-modified glass ionomer cements (AC RMGIC). MATERIALS AND METHODS: The following materials were used: VLC RMIC: Fuji II LC Improved, Photac Fil Quick Aplicap, AC RMGIC: Fuji Plus, Fuji VIII and Giomer: Beautifil II. The measurements of microhardness were performed using a Vickers test (100 g loads were applied for 10 s) in the following time intervals: immediately after the recommended cure and after 1, 7 and 14 days of immersion in distilled water. Five samples (d=4 mm, h=2 mm) were prepared for each combination of curing mode and tested material. RESULTS: After 14 days, an improvement of microhardness was evident in all tested materials. The full factorial ANOVA identified a highly significant (p<0.001) effect of the factors "material", "time" and "curing mode ("low", "soft", "high") for the light-cured materials Beautifil II, Fuji II LC and Photac Fil Quick. There was a statistically significant difference in the microhardness between different material types (Beautifil II˃Fuji II LC˃Photac Fil Quick˃Fuji Plus˃Fuji VIII) and curing modes (low ˂soft ˂high). CONCLUSIONS: Material type had the greatest impact on microhardness, followed by the factor of time, while curing modes showed a considerably smaller influence on microhardness of the light-cured materials.

Dimensional Changes of Glass Ionomers and a Giomer during the Setting Time.

OBJECTIVES: The aim of this study was to evaluate dimensional changes of conventional glass ionomer cements, resin-modified glass-ionomer cement, and a giomer during the setting time using digital laser interferometry. Additionally, the influence of different curing modes ("high", "soft", and "low") of a light-emitting diode (LED) curing unit on dimensional changes was evaluated. MATERIALS AND METHODS: Linear curing shrinkage of conventional glass ionomer cements (CGICs): Fuji IX Extra (F9E), Fuji IX Fast (F9F), Ketac Molar Aplicap (KM), Ketac Molar Quick Aplicap (KMQ), resin-modified glass ionomer cement (RM GIC): Fuji II LC (F2LC) and giomer: Beautifil II (B2) was analyzed. All tested materials were of shade A3, while all of the GIC were encapsulated. Discoid specimens (n=10, d=10 mm, h=0.85 mm) were prepared for each tested material and each curing mode (for light-curable materials) according to the manufacturer's instructions. Light-curable specimens were cured with LED curing unit (Bluephase G2, Ivoclar-Vivadent, and Schaan, Liechtenstein). Dimensional changes during curing were recorded in real-time. The results were analyzed by ANOVA, and Tukey post hoc test was used for multiple comparisons (α˂ 1%). RESULTS: All tested materials showed an initial setting expansion and a subsequent setting shrinkage. KM and KMQ had significantly lower setting shrinkage than RM GIC polymerized using any of the three curing modes. B2 showed lower shrinkage compared to F2LC. CONCLUSIONS: The extent of curing shrinkage in RM GIC measured in this study can affect longevity of restorations.

Remineralizing amorphous calcium phosphate based composite resins: the influence of inert fillers on monomer conversion, polymerization shrinkage, and microhardness.

AIM: To determine if the addition of inert fillers to a bioactive dental restorative composite material affects its degree of conversion (DC), polymerization shrinkage (PS), and microhardness (HV). METHODS: Three amorphous calcium phosphate (ACP)-based composite resins: without added fillers (0-ACP), with 10% of barium-glass fillers (Ba-ACP), and with 10% of silica fillers (Si-ACP), as well as commercial control (Ceram•X, Dentsply DeTrey) were tested in laboratory conditions. The amount of ACP (40%) and the composition of the resin mixture (based on ethoxylated bisphenol A dimethacrylate) was the same for all ACP materials. Fourier transform infrared spectroscopy was used to determine the DC (n=40), 20 min and 72 h after polymerization. Linear PS and Vickers microhardness (n=40) were also evaluated. The results were analyzed by paired samples t test, ANOVA, and one-way repeated measures ANOVA with Student-Newman-Keuls or Tukey's post-hoc test (P=0.05). RESULTS: The addition of barium fillers significantly increased the DC (20 min) (75.84±0.62%) in comparison to 0-ACP (73.92±3.08%), but the addition of silica fillers lowered the DC (71.00±0.57%). Ceram•X had the lowest DC (54.93±1.00%) and linear PS (1.01±0.24%) but the highest HV (20.73±2.09). PS was significantly reduced (P<0.010) in both Ba-ACP (1.13±0.25%) and Si-ACP (1.17±0.19%) compared to 0-ACP (1.43±0.21%). HV was significantly higher in Si-ACP (12.82±1.30) than in 0-ACP (10.54±0.86) and Ba-ACP (10.75±0.62) (P<0.010). CONCLUSION: Incorporation of inert fillers to bioactive remineralizing composites enhanced their physical-mechanical performance in laboratory conditions. Both added fillers reduced the PS while maintaining high levels of the DC. Silica fillers additionally moderately improved the HV of ACP composites.

Time-averaged photon-counting digital holography.

Time-averaged holography has been using photo-emulsions (early stage) and digital photo-sensitive arrays (later) to record holograms. We extend the recording possibilities by utilizing a photon-counting camera, and we further investigate the possibility of obtaining accurate hologram reconstructions in rather severe experimental conditions. To achieve this, we derived an expression for fringe function comprising the main parameters affecting the hologram recording. Influence of the main parameters, namely the exposure time and the number of averaged holograms, is analyzed by simulations and experiments. It is demonstrated that taking long exposure times can be avoided by averaging over many holograms with the exposure times much shorter than the vibration cycle. Conditions in which signal-to-noise ratio in reconstructed holograms can be substantially increased are provided.

Digital holography at light levels below noise using a photon-counting approach.

Recording of digital holograms of a weak signal [0.44 counts per second (cps)] hidden below the detector's noise (21 cps) is investigated by employing the high dynamic range of a photon-counting detector. Recording conditions are discussed in terms of the most important holographic measures, namely, the fringe visibility (or contrast) and signal-to-noise ratio (SNR), and in relation to the main holographic parameters. Theoretically evaluated curves are tested by recording holograms for a wide range of the parameter values. We found that (i) the optimum set of holographic parameters can be determined for a harsh signal conditions, (ii) increasing the visibility does not necessarily improve the more important SNR, and (iii) in cases of nearly constant visibility, the SNR clearly reveals differences in the quality of holographic recordings.

Properties of axially loaded implant-abutment assemblies using digital holographic interferometry analysis.

OBJECTIVE: The aim of this study was to (i) obtain the force-related interferometric patterns of loaded dental implant-abutment assemblies differing in diameter and brand using digital holographic interferometry (DHI) and (ii) determine the influence of implant diameter on the extent of load-induced implant deformation by quantifying and comparing the obtained interferometric data. METHODS: Experiments included five implant brands (Ankylos, Astra Tech, blueSKY, MIS and Straumann), each represented by a narrow and a wide diameter implant connected to a corresponding abutment. A quasi-Fourier setup with a 25mW helium-neon laser was used for interferometric measurements in the cervical 5mm of the implants. Holograms were recorded in two conditions per measurement: a 10N preloaded and a measuring-force loaded assembly, resulting with an interferogram. This procedure was repeated throughout the whole process of incremental axial loading, from 20N to 120N. Each measurement series was repeated three times for each assembly, with complete dismantling of the implant-loading device in between. Additional software analyses calculated deformation data. Deformations were presented as mean values±standard deviations. Statistical analysis was performed using linear mixed effects modeling in R's lme4 package. RESULTS: Implants exhibited linear deformation patterns. The wide diameter group had lower mean deformation values than the narrow diameter group. The diameter significantly affected the deformation throughout loading sessions. SIGNIFICANCE: This study gained in vitro implant performance data, compared the deformations in implant bodies and numerically stated the biomechanical benefits of wider diameter implants.

White light reconstruction of image plane digital holograms.

A real-time system is developed that employs a CCD sensor for recording and a reflective high-resolution liquid crystal display for reconstructing of image plane digital holograms. Two types of light sources, namely, the coherent (laser) and white light (LED) are used for optical reconstructions of static and dynamic object wave fronts. As expected, white light reconstructions exhibit improved properties compared to the corresponding monochrome reconstructions. However, these improvements become substantial in cases in which digital holograms are preprocessed by applying the common algebraic operations such as subtraction.

Shrinkage evaluation of composite polymerized with LED units using laser interferometry.

OBJECTIVES: Composite resin materials shrink during polymerization regardless of curing unit or polymerization program used. However, different polymerization programs lead to different shrinkage percentages. The aim of this study was to evaluate linear polymerization shrinkage for five composite materials polymerized with curing modes of two LED curing units. METHOD AND MATERIALS: Bluephase C5 (500 mW/cm2, 20 seconds) and Bluephase C8 (high-power mode-800 mW/cm2, 20 seconds; and soft-start mode-650 mW/cm2 for the first 5 seconds, and 800 mW/cm2 for the next 15 seconds) (both curing units by Vivadent) were used for composite resin photopolymerization. The materials used were two fine-particle hybrid composite resins (Tetric Ceram and Artemis) and a nanohybrid composite (Tetric EvoCeram) of different shades (all by Vivadent). Polymerization shrinkage was recorded during each second of the polymerization process using laser interferometry. The results were analyzed by ANOVA, and Tukey post hoc test was used for finding significance levels. RESULTS: The highest shrinkage values were obtained in the case of composite polymerization using the high polymerization mode of Bluephase C8 curing unit (0.61% for Tetric EvoCeram A1 and A3 and 0.69% for Artemis A2), while the lowest results were observed with the soft-start mode of Bluephase C8 LED (0.48% for Artemis A2, 0.41% for Tetric Ceram A3, and 0.35% for Tetric EvoCeram A3.5) and Bluephase C5 curing unit (0.40% for Tetric Ceram A1 and 0.44% for Tetric EvoCeram A3.5). Artemis A2 showed the greatest overall sample dimension change, regardless of the light-curing source used. The initial expansion was recorded for all composite resins and curing modes during the first 4 to 9 seconds of illumination. CONCLUSION: Negative consequences of polymerization shrinkage and temperature rise can be diminished by applying a polymerization program with lower initial light intensity, which prolongs the pregel phase of the polymerization process.

Undersampled digital holography.

Acceptable signal recovery of the band-pass signals typically used in the off-axis digital holography systems is possible in the undersampling conditions. A typical system is considered in which the angle between two beams represents a variable parameter. For the given signal bandwidth and experimental conditions the hologram reconstruction is constrained by the sampling frequency of the array photo-detector. Reconstructions from the undersampled digital holograms are analyzed both theoretically and experimentally. It is shown how increasing the angle values beyond the Nyquist limits leads to repeatedly folding and inverting the reconstructed object image until the fading of the image. The phase point at the image fading and the non-overlapping intervals for correctly preserving the useful information are defined and evaluated. Amplitude distributions are analyzed on the example of the time-averaged holograms acquired for an oscillating membrane. Based on removing the zeroth-order reconstruction term, significant extensions of these intervals are also demonstrated.

Visualization of marginal integrity of resin-enamel interface by holographic interferometry.

This study determined whether it was possible to detect deformations and fractures in dental hard tissues or in composite material from internal stresses using double-exposure holographic interferometry. On the proximal side of eight intact human permanent premolars, a direct Class II cavity was prepared and restored with a self-etching adhesive (Clearfil SE Bond) and Tetric Ceram, a resin composite. In five of the specimens, Tetric Flow was used as an elastic layer. The samples were illuminated using a helium-neon laser beam, and the holograms of samples were recorded using Agfa 10E75 photographic plates. Hologram reconstructions were captured with an 8-bit monochrome CCD camera and qualitatively analyzed. Deformations and fractures appeared as fringe patterns on all interferograms, where the distribution of fringes provided location information, while the density of fringes gave the amplitude information. Greater fringe densities were observed in samples treated without a flowable composite.

Composite photopolymerization with diode laser.

Under clinical conditions, the time needed for the proper light curing of luting composites or the multi-incremental buildup of a large restoration with halogen curing units is quite extensive. Due to the development of high power curing devices, such as argon lasers and plasma arc lights and, in order to decrease curing time, halogen and LED devices have developed a high intensity polymerization mode. This study compared the degree of conversion using Fourier Transform Infrared Spectroscopy (FT-IR) of two composite materials: Tetric Ceram and Tetric EvoCeram polymerized with three polymerization modes (high, low and soft mode) of a Bluephase 16i LED curing unit and blue diode laser intensity of 50 mW on the output of the laser beam and 35 mW/cm2 on the resin composite sample. Descriptive statistic, t-test, ANOVA, Pearson Correlation and Tukey Post hoc tests were used for statistical analyses. The results show a higher degree of conversion for the polymerization of composite samples with all photopolymerization modes of the LED curing unit. However, there is no significant difference in the degree of conversion between the LED unit and 50-second polymerization with the blue diode laser. Tetric EvoCeram shows a lower degree of conversion regardless of the polymerization mode (or light source) used.

Enhanced sensitivity digital holographic interferometry.

Corona discharges are generally characterized by a low optical density whose detection is often near or under the limits of interferometric techniques. In this paper, we propose a method of digital holographic interferometry that enables detection with enhanced sensitivity. This sensitivity increase is obtained by post-processing the digital holographic recordings with a set of point-wise image operations. The procedure is described mathematically and illustrated experimentally. Examples are given for an opaque object and for DC corona discharges generated in the symmetrical point-plane geometry.

Comparison of composite curing parameters: effects of light source and curing mode on conversion, temperature rise and polymerization shrinkage.

This study analyzed the degree of conversion, temperature increase and polymerization shrinkage of two hybrid composite materials polymerized with a halogen lamp using three illumination modes and a photopolymerization device based on blue light emitting diodes. The degree of conversion of Tetric Ceram (TC) (Ivoclar Vivadent) and Filtek Z 250 (F) (3M/ESPE) was measured by Fourier transformation infrared spectroscopy at the surface and 2-mm depth; temperature rise was measured by digital multimeter, and linear polymerization shrinkage was measured during cure by digital laser interferometry. Composite samples were illuminated by quartz-tungsten-halogen curing unit (QTH) (Astralis 7, Ivoclar Vivadent) under the following modes: "high power" (HH) 40 seconds at 750 mW/cm2, "low power" (HL) 40 seconds at 400 mW/cm2 and "pulse/soft-start" (HP) increasing from 150 to 400 mW/cm2 during 15 seconds followed by 25 seconds pulsating between 400 and 750 mW/cm2 in 2-second intervals and by light emitting diodes (LED) (Lux-o-Max, Akeda Dental) with emitted intensity 10 seconds at 50 mW/cm2 and 30 seconds at 150 mW/cm2. A significantly higher temperature increase was obtained for both materials using the HH curing mode of halogen light compared to the HP and HL modes and the LED curing unit after 40 seconds. Significantly lower temperature values after 10-second illumination were obtained when LED was used compared to all halogen modes. For all curing modes, there was no significant difference in temperature rise between 20 and 40 seconds of illumination. Results for the degree of conversion measurements show that there is a significant difference in the case of illumination of resin composite samples with LED at the surface and 2 mm depth. For polymerization shrinkage, lower values after 40 seconds were obtained using LED compared to QTH.

Real-time monitoring of vibration fringe patterns by optical reconstruction of digital holograms: mode beating detection.

A new technique capable of monitoring two-dimensional vibration fringe patterns in real-time is presented. It is based on optical reconstructing of time-averaged digital holograms. Recording of the holograms is realized in a quasi-Fourier off-axis setup whilst reconstructing in an extended Fourier transform setup capable of spatial filtering of the hologram reconstructions. The effectiveness of the proposed device, tested on a silicon wafer, was verified by performing operations such as monitoring of vibration modes, adjusting the hologram recording parameters, or searching for resonant frequencies. Additionally, mode beating between two distant vibration frequencies is observed and reported. The proposed technique is suitable for various scientific and industrial applications.

Measurement of linear polymerization contraction using digital laser interferometry.

Polymerization shrinkage is an unavoidable consequence of resin composite photopolymerization and is one of the most important factors in determining the clinical quality and durability of composite filling. Many different methods of measuring polymerization shrinkage are described in the literature. Digital laser interferometry is a method that enables direct observation of polymerization shrinkage in real time. This study used the digital holographic interferometry method to measure the linear polymerization contraction of composite materials: Tetric Ceram (Vivadent), Spectrum TPH (Dentsply) and Valux Plus (3M Dental Products) polymerized with three different curing modes of the Elipar Trilight (ESPE) halogen curing unit. The highest polymerization contraction was recorded by "standard mode" (ETS) (1.24 +/- 2.66% lin), and the lowest by "medium mode" (ETM) (0.40 +/- 0.41% lin) during 40 second illumination. The "exponentional mode" (ETE) showed the highest expansion during the first 10 seconds of illumination. Curing units with initial low intensity enable better inner adaptation of composite material, preventing the detachment of material from dentin during polymerization and avoiding the negative consequences of polymerization shrinkage.

Dynamic modal characterization of musical instruments using digital holography.

This study shows that a dynamic modal characterization of musical instruments with membrane can be carried out using a low-cost device and that the obtained very informative results can be presented as a movie. The proposed device is based on a digital holography technique using the quasi-Fourier configuration and time-average principle. Its practical realization with a commercial digital camera and large plane mirrors allows relatively simple analyzing of big vibration surfaces. The experimental measurements given for a percussion instrument are supported by the mathematical formulation of the problem.

Detection of hidden stationary deformations of vibrating surfaces by use of time-averaged digital holographic interferometry.

A method of detecting displacements of a surface from its steady-state position to its equilibrium position while it is vibrating has been developed by use of time-average digital holographic interferometry. This method permits extraction of such a hidden deformation by creating two separated systems of interferogram fringes: one corresponding to a time-varying resonantly oscillating optical phase, the other to the stationary phase modification. A mathematical description of the method and illustrative results of experimental verification are presented.

Refined fourier-transform method of analysis of full two-dimensional digitized interferograms.

A refined Fourier-transform method of analysis of interference patterns is presented. The refinements include a method of automatic background subtraction and a way of treating the problem of heterodyning. The method proves particularly useful for analysis of long sequences of interferograms.

Subtraction digital holography.

Overlapping of the desired (first-order) and undesired (zero-order) terms originating from the recorded primary-fringe patterns in digital holography is a problem without a real-time solution. We propose a procedure for suppressing the zero-order disturbance that is realizable in real time. The procedure is based on the stochastic change of the speckles in the primary-fringe patterns and on the subtraction of two such subsequent patterns. The theoretical description of the procedure is given and experimental results presented.