Laser interferometric method for measuring linear polymerization shrinkage in light cured dental restoratives (original) (raw)
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Optics Communications, 2007
A fiber optic sensing method based on a Fizeau-type interferometric scheme was employed for monitoring linear polymerization shrinkage in dental restoratives. This technique offers several advantages over the conventional methods of measuring polymerization contraction. This simple, compact, non-invasive and self-calibrating system competes with both conventional and other high-resolution bulk interferometric techniques. In this work, an analysis of the quality of interference signal and fringes visibility was performed in order to characterize their resolution and application range. The measurements of percent linear contraction as a function of the sample thickness were carried out in this study on two dental composites: Filtek P60 (3M ESPE) Posterior Restorer and Filtek Z250 (3M ESPE) Universal Restorer. The results were discussed with respect to others obtained employing alternative techniques.
Time-resolved 2D shrinkage field of dental resins using laser interferometry
Applied Optics, 2015
A Michelson interferometer-based approach was developed to accurately measure the axial shrinkage dynamics and topography of fast curing resin-based composites. The main components of the apparatus consist of a helium-neon laser and a charged coupled device camera with an acquisition rate of 122 frames per second capable of measuring shrinkage rates of up to 19.3 μm∕s at a spatial resolution of 20.6 μm. The accuracy of the data obtained using this approach was determined by comparison with data obtained using spherical concave mirrors of known focal lengths, and with data collected using a photodiode and stylus-based profilometer.
Spectral Fizeau Interferometer applied to dental polymeric resins early shrinkage determination
Optica Pura y Aplicada, 2018
In this work a variant of the well know Fiber Optic Fizeau Interferometer is presented. It is analyzed in the spectral domain and applied to the study of the shrinkage experienced by photocured polymeric resins. This approach, which maintains its main characteristics of being noninvasive and intrinsically self-calibrated, is sensitive to changes in the direction of evolution of the interferometric cavity length which is being measured. The Spectral Domain Fiber Optic Fizeau Interferometer generates typical response curves that must be processed in order to obtain the measurement related to the cavity length for every moment in time. The cavity is formed between the surface of the sample under test and the fiber optic tip itself. Besides, this sensor is used to determine whether or not exothermal effects from photocuring reactions affect the net shrinkage measured in the samples.
Video-controlled characterization of polymerization shrinkage in light-cured dental composites
Polymer Testing, 2008
This study investigated a procedure to measure the intrinsic polymerization contraction of dental resin-based materials. A CCD-camera interfaced with a computer through videointerface hardware measured the coordinates of the centers of gravity of two dot markers stuck on a resin composite cylinder before and after the irradiation. The distances of the centers of gravity, and hence the linear percentage shrinkage, were calculated. The values obtained were compared with those measured by the deflecting disk technique [D.C. Watts, A.J. Cash, Determination of polymerization shrinkage kinetics in visible-lightcured materials: methods development, Dent. Mater. 7 (1991) 281-287.], which assessed polymerization shrinkage through deflection of a glass disk measured by an linear vertical displacement transducer (LVDT). Three resin composites, light-cured for 40 s at 800 mW cm À2 , were tested: Solitaire 2 [SOL2], Tetric Ceram [TECE] and Z100 [Z100]. The data were subjected to the Kruskal-Wallis test (p < 0.05). Whatever the experimental procedure, the three resin composites did not present statistically different polymerization shrinkage, and data obtained with the video-controlled technique were statistically higher than with the deflecting disk method.
Scientific Reports, 2019
traditional polymerisation shrinkage (ps) measurement systems measure average ps of dental composites, but the true local ps varies along the length and breadth of the composite. the ps depends on the curing light intensity distribution, resultant degree of conversion (DoC) and the curing rate. In this paper, optical fibre Bragg grating (FBG) sensing based technology is used to measure the linear post-gel ps at multiple locations within dental composite specimens, and is correlated with DoC and curing rate. A commercial dental composite is used, and its post-gel ps and DoC are mapped using embedded fibre Bragg grating sensors at different curing conditions. The distance between the curing lamp and the composite specimen is varied which resulted in different intensity distribution across the specimen. The effect of curing light intensity distribution on PS, curing rate and DOC are investigated for demonstrating a relationship among them. It is demonstrated that FBG sensing method is an effective method to accurately profiling post-gel PS across the specimen. Focus on aesthetics, toxicity concerns and ease of application has led methacrylate based dental composites to be the preferred restorative material by practitioners around the world 1. Current drift towards 'minimal invasive dentistry' has increased the usage of dental composites at all locations of mouth area. Applications of adhesive restorative composites in dentistry are multifold, ranging from root canal posts, posterior restoration, tooth prostheses and orthodontic devices to cavity liners, inlays, crowns and onlays 1. However, the main drawback is their contraction during/after polymerisation 2. Methacrylate based dental composites are generally photocured under blue-light at a wavelength range of 420-480 nm. During photo-curing, double carbon links (C=C) in monomer are converted to single links (C-C) in polymer; the number of molecules converted to polymer is referred as degree of conversion (DOC) 3. Mechanical and physical performance of dental resin composites are directly dependent on the extent of DOC during polymerisation; higher the conversion, higher are the longevity, mechanical and physical properties. Nonetheless, most of the dental resins show considerable amount of monomers remaining in the cured polymers 4-6 , which could be due to the influence of several factors such as irradiation time, irradiation distance, type of light source, size of light tip, optimum wavelength, power density, type of monomers, size and volume fraction of fillers, refraction coefficients of both organic matrix and inorganic fillers, type and quantity of photo-initiators and co-initiators 7,8. Polymerisation process involves certain amount of polymerisation shrinkage (PS), which could be due to chemical, thermal or post contraction 9. During chemical contraction, the van der Waals distance between the atoms of monomers are reduced from to ~10 4 Å ~1.0 Å, resulting in bulk contraction in cured resin, i.e., volumetric polymerisation shrinkage 10-12. Though the effect of thermal contraction due to exothermic reaction and cooling back to room temperature is minimal, internal stresses could be induced which could be detrimental to the
Contemporary Materials, 2010
Polymerization shrinkage is one of the most critical properties of esthetic resin-based dental restorative materials and may have a negative impact on their clinical performance. As the composite is adhesively bonded, contraction of composite material that occurs during the polymerization causes stress and strain of hard dental tissues. Polymerization shrinkage also affects the maintenance of the bonded interface between the composite resin and dental hard tissues. The aim of this study is to present holographic interferometry as a method for detecting and measuring strain of dental hard tissue caused by the polymerization shrinkage of the dental composite. Materials and methods: Strain was measured experimentally, by real time holographic interferometry, on the maxillary teeth. Strain of dental tissue was determined by counting the interferomentic fringes that appeared during the polymerization process. Results: The deformation was recorded on the coronal dental tissue from 2.25 µm to 5.8 µm. The conclusion is that holographic interferometry is a non-contact, non-destructive, very precise method for measuring deformation of hard dental tissues that is caused by the polymerization shrinkage of dental composite.
Dental Materials, 1991
An instrument for the reproducible measurement of polymerization shrinkage kinetics is described, constructed around a disc-shaped specimen sandwiched between two glass plates. Test specimens of light-sensitive dental restorative materials were irradiated through the lower, rigid plate. The upper, non-rigid plate was readily deflected by an increase of the adhesive stress from the polymerizing and shrinking sample. Deflection was measured by an LVDT transducer and computer-recorded. Dimensional changes were confined to the specimen disc-thickness dimension, such that the fractional linear shrinkage approximated the volumetric shrinkage. Shrinkage data are reported for representative materials: unfilled and resin composites, base-lining materials, and an impression material. Equilibrium shrinkage magnitudes ranged from 0.65%, for the impression material, to 7.9% for the unfilled resin. The kinetic behavior was approximately characterized by an overall time constant, ranging from 12.5 to 280 s, associated with an exponential growth curve, although the initial shrinkage was near-linear in time, for many, materials, due to nonsteady-state concentrations of polymer freeradicals. The test-specimen geometry facilitates rapid and essentially uniform cure and hence the determination of minimum possible time-constants at each ambient temperature and incident light-intensity. Study of hybrid giass-ionomer materials, without spurious dehydration effects, was also achieved.