Tensometer for simultaneously evaluating polymerization stresses, shrinkage and modulus development
Inventors
Assignees
National Institute of Standards and Technology NIST
Publication Number
US-8857266-B2
Publication Date
2014-10-14
Expiration Date
2031-10-27
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Abstract
The present invention relates to apparatus and method for evaluating the development of PS during polymerization of dental restorative composites, which includes using a tensometer for measuring deflection of a calibrated cantilever beam induced by PS and calculating PS from the measured deflection. A tensometer according to an embodiment of the present invention can be used to quantify PS at varying beam locations and heights, and determine trend in PS development as a function of beam length. More importantly, in the present invention, the development of polymerization shrinkage and the elastic modulus can be simultaneously obtained in real time.
Core Innovation
The present invention provides an apparatus and method for evaluating the development of polymerization shrinkage (PS) during the polymerization of dental restorative composites. This is accomplished using a tensometer that measures the deflection of a calibrated cantilever beam induced by polymerization stress, and calculates the PS from this measured deflection. The tensometer can quantify PS at varying beam locations and heights, allowing determination of the trend in PS development as a function of beam length.
In contrast to previous devices, the beam deflection measured by this tensometer exclusively reflects the specimen deformation due to shrinkage, without including deformation from shrinkage-transmitting rods in the system. The tensometer accounts for geometrical conditions of the beam and allows periodic calibration without undue burden. Additionally, the apparatus enables simultaneous real-time measurement of polymerization shrinkage and development of elastic modulus, which was not possible with prior systems.
The background problem addressed is that polymeric dental restorations often fail due to stresses at the tooth/composite interface originating from polymerization shrinkage. Existing cantilever-beam based instruments lack sufficient sensitivity and do not accurately isolate specimen deformation from rod deformation. Moreover, they require complex calibration procedures and cannot measure polymerization shrinkage or modulus development functionally related to stress. Therefore, there exists a need for a cantilever-based instrument with enhanced sensitivity to specimen shrinkage and beam geometry to measure polymerization stress, shrinkage, and modulus development accurately and simultaneously.
Claims Coverage
The patent contains one independent claim disclosing a method with multiple inventive features related to measuring polymeric shrinkage and modulus development.
Method for determining polymeric shrinkage development
A method comprising curing a first polymeric sample coupled at a predetermined position on a cantilever beam, measuring the deflection of the cantilever beam at predetermined time intervals until the polymer cures, coupling a second polymeric sample at a second predetermined position, curing and measuring similarly, and determining linear shrinkage and elastic modulus of the polymeric material as a function of time.
Calculation and storage of shrinkage stress
The method further includes calculating the shrinkage stress of the polymeric material at each predetermined time interval and storing these stress values over time.
Use of ultraviolet light as curing source
The curing light source used in the method can be ultraviolet light.
Curing via exposure to a light source
The curing steps comprise exposing the polymeric material to a light source to initiate curing and shrinkage.
Detection of shrinkage through beam deflection
Measuring the cantilever beam deflection at predetermined time intervals includes detecting the polymeric material shrinkage induced during curing.
The inventive features together provide a method enabling real-time measurement and determination of polymeric shrinkage, elastic modulus development, and shrinkage stress during polymer material curing using a cantilever beam with samples coupled at different positions, incorporating curing by light exposure and calculation/storage of stress data.
Stated Advantages
The beam deflection reflects exclusively specimen deformation due to shrinkage, improving measurement accuracy.
The invention accounts for geometrical conditions of the cantilever beam, enhancing sensitivity and analytical accuracy.
Periodic calibration of the tensometer can be performed without undue burden, simplifying maintenance.
Simultaneous, real-time acquisition of polymerization shrinkage and elastic modulus development is enabled, providing more comprehensive characterization.
Enhanced sensitivity to subtle differences in polymerization stress compared to existing systems.
Documented Applications
Evaluation of polymerization stresses during curing of dental restorative composites.
Measurement of polymerization shrinkage kinetics and elastic modulus development for restorative dental materials under clinically relevant configurations.
Modeling and simulation of stresses incurred during polymerization of dental restoratives to aid development of new materials.
Measurement of thermal and swelling expansion of polymeric and non-polymeric materials.
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