Dentistry – Apparatus – Having means to emit radiation or facilitate viewing of the...
Utility Patent
1999-09-22
2001-01-02
Lucchesi, Nicholas D. (Department: 3732)
Dentistry
Apparatus
Having means to emit radiation or facilitate viewing of the...
C433S226000
Utility Patent
active
06168431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of polymerizing a photo-polymerizable composition for dental use, which may be used in filing treatment of dental caries, and also to a beam illuminator for use in filling treatment of the dental caries with the photo-polymerizable composition.
2. Description of the Prior Art
In recent years, the polymerizable dental compositions (composite resins) comprising a polymerizable monomer, a polymerization initiator and an inorganic filler have been improved in physical strength resistance to wear color rendering and reproducibility of a tooth morphology and has therefore been used widely not only in dental filling treatment of dental caries and as a material for dental crowns, but also in many other applications. Among others the photo-polymerizable composite resin which initiates polymerization with visible light irradiation has expanded its market because of its ease to use and handle and is now one of the most popular products.
However, the polymerizable composite resin has been found having its own problem, that is, polymerization shrinkage. Specifically, when the photo-polymerizable composite resin undergoes polymerization, a considerably large shrinkage stress develops, resulting in formation of a gap between the eventually polymerized composite resin and the cavity wall. The shrinkage stress is related to a pain that a patient may feel during the dental treatment, and the gap between the polymerized composite resin and the cavity wall often constitutes a cause for loss of the dental filling and generation of secondary caries. Accordingly, attempts have been made to avoid formation of the gap, but have not yet been successful.
With regard to the light-curing apparatus, the currently utilized popular light-curing apparatus comprises a light source installing a halogen-tungsten lamp, a control means including a switch for controlling the light source and a timer for setting the duration of irradiation, a cooling means with a cooling fan, and a light guide means including optical fibers bundled to a diameter of 6 to 16 mm, and is so designed as to irradiate downwardly the photo-polymerizable composite resin filled in the dental cavity with a broad light of a high intensity. Polymerization of the photo-polymerizable composite resin with the above-mentioned light-curing apparatus has been found making it difficult to eliminate the problem of the gap and cracking resulting from the polymerization shrinkage of the photo-polymerizable composite resin.
By way of example, when the photo-polymerizable composite resin filled in a cylindrical dental cavity is irradiated from above by the visible rays of light emitted from the light-curing apparatus, an upper portion of the photo-polymerizable composite resin will be cured upon polymerization to close the cavity photo-polymerizable composite resin proceeds deep into the dental cavity. The formation of the gap and cracking is, however, found unavoidable because of the polymerization shrinkage. The higher intensity of the light to irradiate, the quicker the photo-polymerization. Accordingly, the quicker the photo-polymerization, the faster the shrinkage of the photo-polymerizable composite resin and, hence, the easier the formation of the gap and cracking.
Also, with the method in which the photo-polymerizable composite resin filled in the dental cavity is irradiated from above the dental cavity, it is impossible for a dentist to ascertain whether or not the photo-polymerizable composite resin in the dental cavity would have been completely polymerized to cure, and it has often occurred that the bottom portion of the photo-polymerizable composite resin in the dental cavity remains unpolymerized. Once this occurs, there is a risk that a monomer component of the unpolymerized composite resin will penetrate in a high concentration into the dental pulp.
In view of the foregoing problems, the Japanese Laid-open Patent Publication No. 64-15037, published in 1989, discloses a shrinkage-compensated differential photo-polymerizing method. According to this publication, two kinds of photo-polymerizable composite resins sensitive to different wavelengths of light were prepared. The first photo-polymerizable composite resin is applied to the wall of the dental cavity, followed by filling of the second photo-polymerizable composite resin. Thereafter, the second photo-polymerizable composite resin is first polymerized by irradiation, followed by photo-polymerization of the first photo-polymerizable composite resin. The method disclosed in the publication is described effective to minimize any possible adverse effect brought about on the teeth by the shrinkage occurring upon polymerization within the cavity.
It appears that the method disclosed in the publication referred to above has the following two features: In the first place if the second photo-polymerizable composite resin, which is the major filling material, is first polymerized prior to curing of the first photo-polymerizable composite resin which corresponds to a material for protecting the cavity wall and which is used in a relatively small quantity, the polymerization shrinkage occurring in the second photo-polymerizable composite resin can be compensated for by flow or deformation of the first photo-polymerizable composite resin so that shrinkage of the second photo-polymerized composite resin can complete without adversely affecting the teeth.
In the second place, even though the first photo-polymerizable composite resin used in the relatively small quantity, is polymerized subsequently, an averse influence on the teeth which would be brought about by shrinkage of the first photo-polymerizable composite resin would be minimal so long as it is used in a small quantity.
However, not only has the publication referred to above failed to specify particular materials and compositions used for this purpose, but also the processes disclosed therein are indeed complicated, and therefore, the technical effectiveness of the method disclosed therein is questioned. Specifically, considering that the polymerizable dental composite resin is in the form of a slurry or a paste, and even though the cavity wall is protected by the first photo-polymerizable composite resin, an attempt to fill up such a small hole as the caries cavity with the second photo-polymerizable composite resin is quite difficult to accomplish without allowing the first photo-polymerizable composite resin to flow or deform, and the portal edge of the cavity would be more or less covered by the second photo-polymerizable composite resin. In other words, when the second photo-polymerizable composite resin is cured first by polymerization, such composite resin will form a cover over the opening of the dental cavity, making it difficult to avoid developing polymerization shrinkage stresses inside the dental cavity.
In addition, the first and second photo-polymerizable composite resins are described as initiating polymerization upon irradiation with the respective light of different wavelengths. However, the photo-polymerization initiator is generally not sensitive selectively to a certain single wavelength, but sensitive to a relatively broad band of wavelengths. Further in the light-curing apparatus utilizing a halogen lamp, the light emitted therefrom have a broad band of wavelengths. Accordingly, it is difficult to assuredly prevent the first photo-polymerizable composite resin from initiating its polymerization when the second photo-polymerizable composite resin is photo-polymerized and therefore, it is not avoidable that the second photo-polymerizable composite resin eventually forms a cover over the dental cavity opening.
By the reasons as discussed above, the suggestion disclosed in the publication referred to above appears having numerous problems left unsolved.
On the other hand, the inventors of the present invention have conducted a series of experiments in which with the use of a light dispersive rod (LUCIWEDGE. available from Howe Ne
Hino Ken-ichi
Ihara Masahiro
Narusawa Hideaki
Ohtani Fumihiko
Kuraray Co. Ltd.
Lucchesi Nicholas D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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