Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-10-19
2001-01-09
Szekely, Peter A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C427S226000, C427S535000, C427S536000, C428S543000, C523S105000, C523S113000
Reexamination Certificate
active
06172130
ABSTRACT:
This invention relates to dental prostheses with modified surface.
It also relates to a process for manufacturing these prostheses.
There are 10 million persons in France wearing attached dental prostheses. 38% use a complete set of false teeth, 57% use partial false teeth and 5% use both types of false teeth.
Extrapolating across the European Community, the number of persons using false teeth is probably about 60 million.
Partial and complete resin dental prostheses, particularly made of polymethacrylate, have an intermediate surface energy of between 35 and 45 mj.m
−2
. There are two major disadvantages with these prostheses due to this energy and the porosity of the material:
high adhesion of proteins that causes candidiasis, cavities and prosthetic stomatites, and
insufficient retention for complete sets of false teeth and mainly complete lower false teeth.
Miscellaneous methods have been used to improve retention of these prostheses. Thus starting in the XVI
th
century, springs were placed on prostheses between maxillary and mandibular false teeth. Then in the XVIII
th
century prostheses were treated in a Fauchard vacuum chamber. Finally, repulsive magnets were installed on some prostheses.
More recently, attempts were made to improve prostheses by increasing the surface energy of the component materials. Thus, hydrophile resins were manufactured.
An attempt was also made to cover polymethylmethacrylates with silicon dioxide. However, this process was found to be expensive and the resulting prostheses were unstable.
Patent application EP-0 401 385 (Mitsubishi Rayon Co., limited) describes a treatment for acrylic resin prostheses by a halogen or a halon compound, preferably based on iodine. This treatment has the disadvantages that it modifies the biocompatibility of the resins and increases the volume of the prostheses. Furthermore, this treatment can only avoid the formation of dental plaque, and does not have any effect on the retention of prostheses. Finally iodine, which is the element preferably used, can produce allergies.
The intrados of the prosthesis for complete dental prostheses were also subjected to quartz sanding for 30 to 60 seconds. However, this technique also proved to be unsuitable, due to the considerable increase in bacterial colonization.
Dental adhesives are also used to hold dental prostheses in the mouth. Nevertheless, these adhesives must be used once or several times per day. Furthermore, they are quite expensive.
Resin dental prostheses are also responsible for the development of severe dental plaque. Thus, negative Gram germs are three times more numerous in a person wearing a new prosthesis, and eleven times more numerous in persons wearing old prostheses, compared with a healthy individual with teeth. Enterobacteria are seven times more numerous for a person wearing new prostheses compared with a healthy individual with teeth. Candidiases are eight times more numerous for a person wearing new prostheses and twenty-seven times more numerous for a person wearing old prostheses.
This bacterial plaque creates prosthetic acidosis responsible for cavities, gingivitis, candidiasis and sub-prosthetic stomatitis in persons wearing resin prostheses.
In order to prevent the development of this dental plaque, persons wearing prostheses must maintain strict hygiene and use cleaning products, and must not wear their prostheses at night, which is usually not well perceived by patients.
Therefore, there is no way of providing efficient retention of prostheses, and limiting the development of bacterial plaque to an acceptable level.
The treatment of various objects by cold plasma is well known.
Thus, application FR 2 620 624 (IRAP, CARDIAL, DE LA FAYE) describes various objects designed to come into contact with blood, such as catheters, syringes, parts of vascular prostheses or heart valves, composed of polymers in which the hydrogen atoms present on their exposed surface have been replaced by fluorine atoms or CF
2
or CF
3
groups. Polymers particularly include polyethylene, poly(vinyl chloride) or poly(ethylene terephthalate). The hydrogen atoms are replaced such that the total fluorine represents not more than 10% of the atoms present on their surface. Objects are treated in plasma containing fluoride for a period varying from a few seconds to about 10 minutes at a power varying from 0.1 watts to 2 watts per liter of capacity of the reaction vessel, and at a pressure of the order of 10 to 10000 Pa.
Application EP-0 487.418 (IRAP, FIDOMI Group) describes devices for ophthalmologic use formed by polymeric substrates, in which the hydrogen atoms present on the surface have been replaced by fluorine atoms or by CF, CF
2
or CF
3
groups. The total fluorine represents at least 15% of the atoms present on this surface. Polymers may be polymethylmethacrylate (PPMA), a polymer made of 2 hydroxy-ethylmethacrylate (HEMA) of silicon or a polysulfonate. The devices are treated in appropriate fluoride gases for 1 to 20 minutes, at a reaction vessel emission power of between 3 and 10 watts per liter of capacity of the reaction vessel, and at a negative pressure of between 0.1 and 1 torr.
DEJUN LI and JIE ZHAO (1995, J. Adhesion Sci. Technol., Vol.9, pp 1249-1261) describe the treatment of polyurethane objects by cold argon and nitrogen plasma between 1 and 15 minutes, at a power of 100 watts and a pressure of 0.3 to 15 Pa. The authors demonstrate that these treatments induce reductions in the contact angle of water and an increase in the coagulation time. Therefore, these treatments are obviously intended for applications on objects or devices designed to come into contact with the blood.
Application EP-0 096 573 (The United States of America) describes the treatment of textile fibers by cold plasma. No application to prostheses is mentioned.
GEBHARDT et al. (1995, Proceedings, 12
th
International Symposium on Plasma Chemistry, Minneapolis, Minn., USA, Vol. 1, 155-160) describe the treatment of high density polyethylene sheets (HDPE) by an argon plasma and then grafting of styrene groups and ether 2-(chloroethyl)vinyl groups by exposure to vapors. Therefore, this article does not describe a simple treatment of cold plasma, but a treatment combining a cold plasma treatment step and a chemical treatment step. The authors show that this surface has a better biocompatibility with rat hepathocytes.
An analysis of the state of the art clearly shows that the treatment of dental prostheses by cold plasma has never been described.
Ocular tissues, or blood cells, are quite different from tissues in the mouth. Thus, the buccal cavity contains a much higher number of types of cellular tissues than the ocular cavity. Consequently the characteristics of polymers in contact with these various tissues and of cell types are different, and cannot be transposed from one organ to another.
Therefore, the applicant attempted to determine conditions for treatment of polymers for use in dental prostheses, in order to improve their retention and/or limit the development of dental plaque.
He showed that the treatment of these polymers by cold plasma can solve these problems.
Therefore, this invention relates to dental prostheses composed mainly of a polymer containing hydrogen atoms and with the required mechanical and chemical properties, characterized in that the hydrogen atoms at the surface of the said polymer have been replaced by fluorine atoms, —CF, —CF
2
, —CF
3
, —OH, —CO
2
H, C═O, —OOH, —NH
2
, —C═NH and/or —CONH
2
groups.
According to a first embodiment, the prostheses are complete sets of false teeth to which hydrogen atoms of the said polymer are preferentially replaced by —OH, CO2H, —C═O, —OOH, NH2, —C═NH and/or —CONH2 groups. Preferably, the said polymers are characterized in that their oxygen content has been increased by between 1 and 15%, and even better between 1 and 10%, over a thickness of 30 nm on the surface of the prosthesis.
These polymers are particularly suitable for complete sets of false teeth since they have a higher surface energy
Jacobson Price Holman & Stern PLLC
Szekely Peter A.
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