GB2297928A - Epoxy-coated fibre-optics - Google Patents

Description

END COATED FIBER-OPTICS 2297928

Field of the Invention

The present invention relates to fiber-optics which have improved moisture resistance. The invention also relates to methods for improving the moisture resistance of f iber-optics, as well as instruments employing such'f iberoptics.

Backqround of the Invention Modern dental handpieces and surgical instruments include fiber-optics to generate spot sources of illumination onto a work site. For example, a typical dental handpiece projects one or more light beams through fiber-optics onto a drill or burr of the handpiece. Light from a remote light source can be transmitted through an is optical light path in the handpiece through fiber-optics disposed in an exit port of the handpiece. Handpieces which employ fiber-optics are disclosed, for example, in U.S.

Patent No. 5,003,434. Handpieces described in U.S. Patent No. 5,003,434 are available from Den-Tal-Ez, Inc., Valley Forge, PA under the trademark COLORightO.

After use, dental handpieces and medical instruments must be sterilized. There are several conventional procedures for sterilizing handpieces and medical instrume nts. One procedure involves a so-called chemiclave in which the handpiece is subjected to biocidal chemicals in a hot pressurized environment. In the chemiclave, a vapor phase of alcohol is used, and a percentage of water usually (12-15 percent) is present. In is another procedure, a handpiece is subjected to steam at elevated temperatures, typically about 2400C - 2750C, at super-atmospheric pressures in an autoclave. Repeated exposures of the end surfaces.of the glass fiber-optics to the steam cause the glass in the fiber-optics to absorb moisture which causes degradation of the fiber-optics. Also, when the fiber-optics are employed in a bundle, they separate when the binder employed to bond the fiber-optics degrades due to moisture absorption from the steam. As a result, the light output of the fiber-optics is reduced.

A new handpiece typically has a useful life of more than 2000 sterilization cycles. On average, an approximate 35 reduction in light output from the fiberoptics occurs after 200 sterilization cycles in an autoclave. Thus, with respect to autoclave sterilized handpieces and medical instruments, a user perceives a decrease in the light output from the fiber-optics very early in the life of the handpiece or medical instrument. This reduction in light output is undesirable because it reduces the useful life of the handpiece. ' Since the cost to replace the fiber-optics is typically about fifty percent of the value of a new handpiece, the expense associated with fiber-optic replacement is unacceptable.

A need therefore exists for fiber-optics which have improved moisture resistance, especially when exposed to high temperature, superatmospheric steam. A further. need exists for dental handpieces and surgical instruments having fiber-optics with improved moisture resistance.

Summarv of the Invention The invention provides moisture resistant fiberoptics and a method of their manufacture. The fiber-optics according to the invention have a layer of a substantially transparent, hydrophobic epoxy resin on all of their end surfaces. The method for manufacture of the moisture resistant fiber-optics involves applying a layer of a transparent, or substantially transparent, hydrophobic polymeric resin onto each of the end surfaces of the fiberoptics, and heat treating the resin layer to cure the resin as well as to bond the resin to the end surfaces of the fiber-optic.

In another aspect, the invention provides instruments such as dental handpieces having light input and light output ports which house fiberoptics having a layer of a hydrophobic, resin on all of the end surfaces of the fibers.

Brief Descriotion of the Drawinqs The foregoing summary, as well as the following detailed description of preferred embodiments-,of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings, like numerals indicate like elements throughout.

Fig. 1 is a perspective view of a dental handpiece which includes fiberoptics having a protective layer of polymeric resin over the fiber-optics.

Fig. 1A is a side view of the handpiece of Fig. 1.

Fig. 1B is a partial vertical cross-sectional side view of the exit port of the handpiece of Fig. 1 after application of resin prior to cutting and polishing.

Fig. 2 is an enlarged, partial cross-sectional view of the exit port of the handpiece of Fig. 1 having a protective epoxy layer thereon.

Fig. 3 is a graph comparing the change in light transmission of fiberoptics'which have a protective epoxy resin layer on an end surface to fiber-optics which do not have a protective epoxy resin layer.

Detailed Descriotion of the Invention Referring now to the drawings, Figs. 1 and 1A illustrate a dental handpiece 10 which includes fiber-optics 22 therein. In the illustrated embodiment, handpiece 10 includes a drill member 40 and light emission ports 14. As shown in Figs. 1A and 1B, fiber-optics 22 having distal ends 20 are positioned in light emission ports 14. Light can be provided proximally to fiber-optics 22 by an electricallypowered lamp (not shown). Conveniently, the lamp can be housed in handle 16 of handpiece 10.- Light from the lamp can be transmitted to fiberoptics 22 by an optical path provided by a series of endwise disposed, opt ically- transparent elements (not shown) located in handle 16 of handpiece 10. Handpieces which employ this type of optical path are available, for example,. from DenTal-Ez, Inc., Valley Forge, PA under the Trademark STAR Model 430 SWL.

In accordance with the invention, and as can be understood by reference to Fig. 1B., a transparent, or substantially transparent layer 24 of a hydrophobic, heat resistant polymeric resin 30 is applied to distal (output) ends 20 (as well as proximal or input ends - not shown) of a bundle of fiber-optics 22 in port 14. The polymeric resin is chemically stable to at least 400OF after heat curing of the resin. The resin must also meet safety requirements for human toxicity where trace amounts of the resin may come in contact with mucous membranes.

Preferably, the polymeric resin is a thermosetting resin, most preferably an epoxy resin having a viscosity of about 2000 to about 2200 cps. Preferably, the epoxy resin is an anhydride-curable epoxy resin such as TRA-BOND F202 available from Tra-Con, Inc., Medford, Mass. TRA-BOND F202 is a two-part epoxy that has separate resin and hardener components. When ready for use, the resin and hardener components are mixed in measured quantities. When mixed, is the epoxy resin remains usable for application during a period of about 24 hours.

Anhydride-curable epoxy resins which remain clear after curing may be applied to.end surfaces of the fiberoptic. Preferably, epoxies such as TRA-CON F202.which have a pH of about 7 are applied to the end surfaces of the fiber-optic. Epoxies which have a pH other than 7, however, also may be applied.

Fiber-optics which can be treated in accordance with the invention include glass fiber-optics such as those available from the Volpi Manufacturing Co., Auburn, New York, under Schott glass product designations LF-5, F2 and F7. As used herein, fiber-optics means a glass fiber (or fibers), used to transmit light or images from a source to a specific target surface'.

The polymeric resin can be applied to single fiber-optics as well as to bundles of fiber-optics, preferably to bundles of fiber-optics. Prior to applying the polymeric resin to the end surfaces of the fiber-optics, the end surfaces are preferably cleaned with a cotton swab soaked in a solvent such as isopropyl alcohol or other fastdrying de-greasing agents to remove any oils or debris on those end surfaces. The following description of the method of applying the polymeric resin will be with respect to the preferrd use of an epoxy resin, it being understood that minor modifications may be necessary when using other resins.

For each step in the procedure below, and as can be understood by reference to Fig. 1B, epoxy resin 30 is preferably applied with a 0.01311 diameter syringe tip (not shown) attached to an epoxy resin reservoir which is attached to a pressure metering unit (not shown). After port 14 is cleaned, fiber-optics 22 are inserted into port 14 for bonding of f iber-optics 22 to port 14 as well as to each other by the epoxy resin. The epoxy resin is then applied after heating fiber-optics 22 and port 14 from room temperature to a maximum temperature of about 1150C. While maintaining the temperature at about 1150C, drops of epoxy resin are applied by the syringe tip to distal ends 20 of the fiber-optics 22. During application of the epoxy resin, the epoxy resin is absorbed into voids between adjacent fiber-optics 22, as well as into any space existing between fiber-optics 22 and port 14. Epoxy resin is applied until voids between fiber-optics 22 are filled, whereupon the epoxy resin begins to pool on the surfaces of the fiberoptic distal ends 20 to create a layer of epoxy resin 30 that has a glossy appearance. Application of epoxy resin is then halted and the assembly is heat cured in a closed oven. The resulting structure generally corresponds to that shown in Fig. 1B. It will be understood that epoxy resin should also be applied to the proximal end of the fiber-optics 22 in a similar manner, since during sterilization of the instrument, both ends of the fiber-optics ar e subject to degradation by moisture.

The epoxy resin then is heat cured. Heat curing is performed by heat treating epoxy resin layer 30 to increase the temperature of the epoxy resin from room temperature to about 1350C 50 over about 7 minutes. The temperature of about 1350C 50is maintained for about 60 minutes, followed by heating to increase the temperature of the epoxy resin from about 1350C to about 1750C 50C over about 10 minutes. The temperature of about 1750C is maintained for about 90 minutes, followed by cooling to reduce the temperature of the epoxy resin to about 180C over about 13 minutes.

After heat curing, additional epoxy resin can be applied following the procedure above to voids in epoxy resin layer 30 on distal ends 20. The additional epoxy resin then is heat cured using the procedure described above.

After the epoxy resin is heat cured, those portions of fiber-optics 22 which extend beyond end face 19 is of port 14, as can be understood by reference to Fig. 1B, are severed flush with end face 19. Distal ends 20 of fiber-optics 22, as well as end face 19 are then polished to ensure maximum light transmission. Distal ends 20 and face 19 are then cleaned following the procedure employed above in preparation for receiving protective epoxy resin layer 24.

Fixturing of the f iber-optics 22 in the handpiece is performed by holding port 14 and fiber-optics 22 therein in a horizontal position, and applying a drop of epoxy resin to distal ends 20 of fiber-optics 22 as well as to end face 19 of port 14. The drop of epoxy resin creates a smooth protective epoxy layer 24 that has a convex shape which covers both distal ends 20 as well as end face 19 as shown in Fig. 2. During application of the epoxy resin to fiberoptics 22 to form protective layer 24, the dispensing tip of the syringe remains in contact with the epoxy resin to prevent trapping air within the epoxy resin.

The applied, protective epoxy resin layer then is heat cured as described above. The heat cured epoxy resin layer is smooth and optically clear with a visible light transmission between- about 95!k and about 10011k, preferably greater than about 95V when measured at a thickness of about 0. 010". Light transmission is calculated using a calibrated light source and photometer. The light source is first measured directly to determine source foot-candle output. Then the light source is placed at the proximal,end of the fiber-optics and a photometer is placed at distal end of the fiber-optics. The foot-candle output through fiber-optics then is recorded.

In another aspect, an adhesion promoter may be applied to distal ends 20 and face 19 after fiber-optics 22 severed as described above but prior to applying epoxy resin to form convex layer 24. Useful adhesion promoters include TRA-PRIME 1192 available from TRA-CON, Inc. TRA-PRIME 1192 is a clear, 100k solids adhesion promoter which contains - 8 reactive epoxy and silane functional groups. TRA-PRIME 1192 is soluble in organic solvents and hydrolyzes to form aqueous solutions. The adhesion promoter can be applied after distal ends 20 and face 19 have been cleaned with solvent. The adhesion promoter can be applied by well-known methods such as brushing to achieve a coating thickness of about one micron.

The epoxy resin can be applied at any time to form a protective epoxy resin layer 24 on distal ends 20 of fiber-optics 22 during the life of the handpiece. Preferably, the epoxy resin is applied when the handpiece is manufactured. If, however, the fiber-optics are damaged through mishandling or normal wear, the epoxy resin layer may be removed by grinding and polishing and reforming a new protective epoxy layer following the above-described procedure.

Fiber-optics w ' hich have been provided with a protective epoxy resin layer thereon in accordance with the invention have improved moisture resistance. This improved resistance is apparent from substantially reduced light loss after the fiber-optics are exposed to repeated sterilization cycles in an autoclave. Without wishing to be bound by any theory, it is believed that reduced light loss is achieved because the protective epoxy resin layer reduces the tendency of metal present in the fiber-optics to react with the moisture present in super- atmospheric steam to cause deterioration of the fiber-optics.

To demonstrate the ability of the invention to provide fiber-optics which have improved moisture resistance, and consequent reduced light loss, handpieces were subjected to repeated sterilization cycles in an autoclave. The handpieces tested were identical except for presence of the protective layer of epoxy resin on distal and proximal ends of the fiber-optic. The sterilization cycle entailed placing a dental handpiece into an autoclave at room temperature and raising the temperature to about 2500F. The rise in temperature causes the pressure in the autoclave to increase to about 32 psi, wherein the atmosphere in the autoclave is nearly look water vapor by weight. The handpiece is retained in the autoclave for 15 minutes after which time the pressure is returned to atmospheric. The handpiece is removed and cooled to room temperature.

The light transmission from the fiber-optics of the handpieces is measured using a calibrated standard lamp source and EG & G 880 spectroradiometer light measurement system which is calibrated and traceable to a National Bureau of Standards standard lamp. Repeat testing for comparative purposes yielded a light testing accuracy which is repeatable within 6k of an average value. The results is are shown in Table I.

Table 1

Number of % Light Fiber-ODtie' Sterilization Transmittance Cycles Retained TRA-BOND F202 epoxy 200 87 resin layer of 0.010 inch thickness TRA-BOND F202 epoxy 900 77 resin layer of 0.010 inch thickness Without epoxy resin 200 65 layer W thout epoxy resin 900 46 layer Schott F-7, available from Schott optical Glass Co., Durea, PA The results shown in Table I indicate that fiberoptics which have a protective layer of epoxy resin on the input and output end surfaces of the fiber-optic has improved moisture resistance. This improved moisture resistance is shown by the ability of the epoxy resin coated fiber-optics to retain about 77V of the light transmittance of as-manufactured, fiber-optics which are free of the epoxy resin layer after 900 autoclave sterilization cycles. In contrast, fiber-optics which did not have a protective epoxy resin layer on both ends retained only about 46k of the light transmittance of an as-manufactured, uncoated fiberoptic after 900 sterilization cycles.

While the epoxy resin layer can be applied to a single end surface of a fiber-optic to provide improved moisture resistance. Maximum moisture resistance is realized, however, by applying the epoxy resin layer to both end surfaces of the fiber-optics which provides a lenscap over those fiber-optics.

Fig. 3 illustrates the percentage loss in light transmission as a function of sterilization cycles. Samples No. I and No. 3 do not have a protective epoxy resin layer on either end thereof. Sample No. 2 has an epoxy resin layer on the input and output ends thereof. As shown in Fig. 3, Samples 1 and 3 which do not have a protective epoxy resin layer experience a much more rapid rate of light loss than Sample 2 which has a protective epoxy resin layer on its input and output end surfaces.

While the present invention has been described particularly with respect to a dental handpiece, it should be apparent that it has applicability to other instruments utilized in dental and medical applications, including endoscopes, laryngoscopes, laproscopes, and the like which incorporate fiber-optics and which require periodic sterilization. Accordingly, while a preferred embodiment of the invention has been described in detail, various modifications, alterations and changes may be made without departing from the spirit and scope of the present invention as defined in the appended claims.

is 1 claim:

1. A glass fiber-optic having improved moisture resistance comprising, glass fiber-optic, and layer of a hydrophobic, substantially transparent polymeric resin on end surfaces of said fiberoptic.

The glass fiber-optic of claim 1 wherein the 2. polymeric resin is an epoxy resin.

3. The glass fiber-optic of claim 2 wherein said epoxy resin is an anhydride-curable epoxy resin.

4. The glass fiber-optic of claim 2 wherein said layer of epoxy resin has a thickness of about 0.001 inch to about.020 inch.

S. The glass fiber-optic of claim 1 wherein said polymericresin is chemically stable attemperatures of about 4000F.

6. The glass fiber-optic of claim 2 wherein said fiber-optic having said layer of epoxy resin thereon, after having been subjected to about 900 exposures of steam at about 250OF and about 32 psi, wherein each of said exposures extends for about 15 minutes, has a light transmittance that.is at least about 77V of the light transmittance of an as-manufactured fiber-optic which is free of said layer of epoxy resin.

7. A method for manufacture of a glass fiberoptic having improved moisture resistance comprising, providing at least one glass fiber-optic having input and output end surfaces thereon, appl ying a hydrophobic, substantially transparent polymeric resin to said end.surfaces to form a layer of said polymeric resin on said end surfaces, and heat treating said layer of said polymeric resin on said end surfaces of said fiber-optic to yield a fiber-optic having improved moisture resistance.

8. The method of claim 7 wherein said polymeric resin is an epoxy resin which is anhydride-curable after applying to said end surface.

9. The method according to claim 8 further including a step of treating said end surfaces with solvent prior to applying said epoxy resin.

10. The method of claim 9 wherein said polymeric resin is applied by contacting said end surfaces with said polymeric resin until said end surfaces achieve a glossy appearance.

11. The method of claim 8 wherein said heat treating comprises heating said epoxy resin to increase the temperature thereof from about room temperature to about 1350C over about 7 minutes, maintaining said epoxy resin at about 1350C for about 60 minutes, heating said epoxy resin to increase the temperature thereof from about 1350C to about 1750C over about 10 minutes, maintaining said epoxy resin at about 1750C for about 90 minutes, and cooling said epoxy resin to reduce the temperature thereof to about 180C over about 13 minutes.

12. The method of claim 9 further compr ising treating said end surface with an adhesion promoter after treating said end surface with solvent prior to said applying of said epoxy resin.

13. The method of claim 12 wherein the adhesion promoter contains reactive epoxy and silane functional groups.

14. An instrument having glass fiber-optics for transmitting light onto a work location comprising at least one glass fiber-optic having input and output end surfaces and a layer of a hydrophobic, substantially transparent polymeric resin on said end surfaces.

15. The instrument according to claim 14 wherein said polymeric resin which is an epoxy resin which is chemically stable at temperatures of about 4000F.

16. The instrument according to claim 15 wherein said 'epoxy resin is an anhydride- curable epoxy resin.

17. The instrument according to claim 15 wherein said layer has a thickness of about 0.010 inch.

18. The instrument according to claim 14 further comprising an exit port for housing said fiber-optic, wherein an additional layer of said polymeric resin is present over said exit Dort.

19. The instrument according to. claim 16 wheiein said fiber-optic having said layer of epoxy resin, after having been subjected to about 900 exposures of steam at about 250OF and about 32 psi, wherein each of said exposures is for a period of about 15 minutes, has a light transmittance that is at least about 77 of the light transmittance of an as-manufactured fiber-optic which is free of said layer of epoxy resin.

20. A glass fiber-optic having improved moisture resistance, substantially as hereinbefore described with reference to the accompanying drawings.

21. A method for manufacture of a glass fiber-optic having improved moisture resistance, according to claim 1 and substantially as hereinbefore described.

22. A method for manufacture of a glass fiber-optic having improved moisture resistance, substantially as hereinbefore described with reference to the accompanying drawings.

23. An instrument having glass fiber-optics for transmitting light onto a work location, substantially as hereinbefore described with reference to the accompanying drawings.