Reducing polymerization stress by controlled segmental curing

Details Reducing polymerization stress by controlled segmental curing Reducing polymerization stress by controlled segmental curing

2001-03-15

2004-08-31

Seidleck, James J. (Department: 1711)

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

C427S487000, C427S517000, C427S508000, C522S004000, C522S001000, C522S908000, C433S229000, C433S215000, C433S217100, C433S226000, C523S116000

Reexamination Certificate

active

06783810

ABSTRACT:

TECHNICAL FIELD
This invention relates to a method or technique to cure a polymerizable material with various light sources, particularly light curable materials that are selectively cured using special patterns. The patterns are either placed onto a special mask on the materials or onto the curing light tip, or by employing a special light source. As a result from such a segmental curing technique, the polymerization stress associated with the cured materials is limited or minimized due to extended molecular relaxation promoted by this controlled hybrid curing technique.
BACKGROUND OF THE INVENTION
Light cured materials are well known in the art. For example, it is known in the dental industry to place curable materials into place on a tooth or other dentition to be restored. The materials are then expose to light to effect curing. It has been found that a problem with some such materials is excessive shrinking during the polymerization or cure process.
In the past, many efforts have been made to reduce polymerization shrinkage because it was believed that the lower polymerization shrinkage would always lead to the lower polymerization stress. This is not always correct. For example, rapid polymerization using high powered light indeed resulted in lower polymerization shrinkage for some materials, but was also accompanied by increasing polymerization stresses that could not be relived due to the rapid cross-linked, rigid polymer network developed during fast curing. Recently, it has been understood that it is the polymerization stress that plays a most critical role in determining a successful dental restoration. Therefore, in attempts to reduce stress, various techniques have been explored, including changing the light intensity during curing, changing the spectrum of light distribution, and modulating the curing frequency et al, in addition to new resin development. It should be pointed out that there is one thing in common for all these approaches: one mass of chemically homogenous material is exposed to a relatively homogenous light source resulting in a relatively homogenous curing rate throughout the material.
Light with a defined wavelength can provide proper energy to activate a light curable material and to start polymerization leading a network formation. Such lights used for curing include, for example, visible light and UV light in terms of different frequency or wavelength; there are halogen light, LED light, plasma ARC light, and laser light in terms of different energy. In addition, different light structures, including lamp, filter, light guide have been used in order to change the light output by tuning both spectra and energy distribution. Unless otherwise noted, “light” “light source” and the like refer to any and all such lights, light sources, light guides and the like. Examples of such lights and light sources are discussed by way of example, in U.S. Pat. No. 5,521,392, which is hereby incorporated by reference for such disclosure.
However, with all of these modification, it was noticed that the area exposed directly to such a proper light would always cure first no matter how the light was generated and delivered to the curing surface, which may vary from standard, pulse, ramp to soft-start et al in terms of different curing modes.
It is known that how the materials cure often determines their ultimate performance including polymerization shrinkage, polymerization stress, and their mechanical properties. For restorative dental materials, additional properties like bonding strength, micro-leakage, micro-cracking and post-restoration sensitivity and the like, is believed to be associated with the curing process. Therefore, there has been much effort in the dental industry focussing on the development of new materials and new curing devices.
U.S. Pat. No. 4,385,344 discloses the use a halogen lamp that is filtered to supply light in the range of 400-700 nm. U.S. Pat. No. 5,290,169 discusses a light guide consisting of glass, acrylic, polycarbonate and polystyrene having a head with different concave surface geometry, a tapered section and a curved section to control total light output. U.S. Pat. No. 5,472,991 discloses to generate a light with different wavelengths during two step curing. U.S. Pat. No. 5,634,711 discusses a hand-held LED light with various light energy levels. U.S. Pat. No. 5,879,159 discloses a battery powered hand-held, high power ARC light for fast curing. U.S. Pat. No. 5,912,470 teaches to control total light output in a way to increase light intensity continuously or in stepped form. U.S. Pat. No. 5,975,895 discloses that to generate a series of light pulses at a predetermined frequency, a flash lamp was coupled to the trigger electronics. U.S. Pat. No. 6,008,264 discusses to generate a light with various power, wave form and modulation parameters. U.S. Pat. No. 6,033,223 discloses the use of a laser light and an optical fiber insert to initiate polymerization progressively from a portion thereof adjacent the bottom of the dental cavity towards a surface portion thereof. U.S. Pat. No. 6,079,861 discusses to control total light output from low to very high by two light sources. U.S. Pat. No. 5,229,230 teaches to enhance total incident light intensity on photo-sensitive surface by using new type of photomask with plurality of auxiliary patterns consist of transparent phase shit material spots. U.S. Pat. No. 5,468,577 discloses to increase total light intensity by using new type of photomask with plurality auxiliary patterns of small slots. U.S. Pat. No. 5,835,661 discusses to convert a point-like light into a collimated linear or planar light beam.
DISCLOSURE OF THE INVENTION
This invention relates to a method or technique to cure a polymerizable material with various light sources, particularly light curable materials that are selectively cured using special patterns. The patterns are either placed onto a special mask on the materials or onto the curing light tip, or by employing a special light source. As a result from such a segmental curing technique, the polymerization stress associated with the cured materials is limited or minimized due to extended molecular relaxation promoted by this controlled hybrid curing technique.
With this controlled segmental curing technique, heterogeneous curing zones of polymerization within a chemically homogenous material are created, from which a pre-gel-like behavior is demonstrated during the heterogeneous post-gel stage. The normal polymerization stress generated within those segments initially curing is relieved through stress relaxation within the partially cured or uncured segments adjacent to them. By such segmental stress relief, the severe final stress concentration occurring at the interface between the restorative material and the tooth structure can be avoided. As a result, the associated microleakage and microcracking is limited or minimized. Therefore, this technique can be understood as dividing the stress occurring over the entire composite/tooth interface into a series of incremental stresses over sub-interfaces (composite/composite) that prevents the overall polymerization stress from being transmitted to the composite/tooth interface and/or passed through the interface into the tooth structure. This unique feature is distinguished over other sequential curing techniques, such as soft-start curing, pulse curing, or the like.
An object of this invention is to provide a method by which the polymerizable materials could be selectively cured from the very first surface. As a result of such sectional curing, low polymerization shrinkage and especially low polymerization stress are expected with the cured materials. Because the polymerization stress associated with the cured section could get relief via its adjacent less cured section through normal relaxation.
In general, a method of curing a photo-polymerizable material with light energy from a light source, comprises the steps of exposing at least one selected segment of the material to the light energy while selectively limiting ex

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