WO1997002787A1 - Fluoride releasing dental pit and fissure sealant dispensing system and method - Google Patents

Abstract

A fluoride releasing dental pit and fissure sealant dispensing system including a cartridge having a nozzle with a capillary conduit wall enclosing a capillary passage extending to a dispensing opening from a cylindrical chamber enclosing a sustained release dental pit and fissure sealant composition having a viscosity of less than 30,000 cps and including a polymerizable acrylic monomer, fluoride releasing glass particles and a fluoride containing salt. The salt is at least one hundred percent more soluble in water than calcium fluoride. The nozzle has a length to diameter ratio of at least six, and is readily bendable to form an arc of at least 30 degrees between the center line of the cylindrical chamber and the center line of the distal end of the nozzle.

Description

FLUORIDE RELEASING DENTAL PIT AND FISSURE SEALANT DISPENSING SYSTEM AND METHOD

The invention relates to dispensing systems for dental

compositions for sealing pits and fissures in tooth surfaces to

prevent or reduce the formation of decay therein. The invention

provides a cartridge dispensing system for a fluoride releasing

dental pit and fissure sealant having a viscosity less than

30,000 cps, which is directly applied to the outer surface of

natural dental teeth from a bendable nozzle.

Almost all children are plagued with dental surface

imperfections, commonly termed pits and fissures, which tend to

harbor and permit proliferation of microorganisms which can cause

formation of caries. Since normal dental hygiene methods, such as tooth brushing, are relatively ineffective against these physically protected microorganisms it has been the practice of many dentists for a considerable time to attempt to seal the pits

and fissures to eliminate these sites for microorganism growth.

Occlusal caries (decay) account for nearly half of all caries

occurring in the human population. Certain adhesive materials

have been shown to be effective in sealing the pits and fissures

of the occlusal tooth surface, to thereby prevent or reduce the incidence of various attacks. One of the deficiencies of existing pit and fissure sealants is the lack of sustained fluoride

release.

Commonly used pit and fissure sealants are composed of

a polymerizable resin system, such as the polymerizable acrylic

system described by Bowen in U.S. Patent Number 3,066,112, and

Lee et al. in U.S. Patent Numbers 3,815,239 and 3,539,533.

Randklev in U.S. Patent Re. 32,073 discloses a dental filling

composition utilizing zinc-containing inorganic filler. Wilson

et al. in U.S. Patent 3,814,717 disclose poly(carboxylic acid) -

fluoroaluminosilicate glass surgical cement. Jurecic in U.S.

Patent 3,971,754 discloses an x-ray opaque, enamel-matching

dental filling composition. Maxel in U.S. Patent 4,003,368

discloses article transparent to microwaves and process for

making same. Liotta et al. in U.S. Patent 4,028,358 disclose 6-

Fluoro-9-Perfluorobutyl Purine. Lee, Jr. et al. in U.S. Patent

4,032,504 disclose x-ray opaque filler useful in dental and medical restorative compounds. Schmitt et al. in U.S. Patent

4,082,722 disclose pre-mixed dental composition for the

preparation of a dental silicate cement. Tezuka et al. in U.S.

Patent 4,089,830 disclose setting solution for dental glass

ionomer cements. Crisp et al. in U.S. Patent 4,143,018 disclose cements. Joos in U.S. Patent 4,150,012 discloses discernible

dental sealant. Kohmura et al. in U.S. Patent 4,154,717 discloses

hydraulic dental cement. Gardner in U.S. Patent 4,160,758

discloses method of manufacture of elastomer polyester molding

compounds. Bertenshaw et al. in U.S. Patent 4,174,334 disclose

surgical cement compositions containing alumino borate glass and

a polymer glass and a polymer containing recurring carboxylic or

carboxylate groups. Temin in U.S. Patent 4,188,317 discloses

dental restorative compositions containing titanium silicate.

Panzera in U.S. Patent 4,209,334 discloses porous ceramic seals

and method of making same. Mabie et al. in U.S. Patent 4,217,264

disclose microporous glassy fillers for dental resin composites.

Crisp et al. in U.S. Patent 4,222,920 disclose cements. Stewart

in U.S. Patent 4,224,072 discloses pit and fissure sealant for

teeth. Potter in U.S. Patent 4,243,567 discloses medical

compositions. Anderson et al. in U.S. Patent 4,288,355 disclose

surgical cement composition. Beede et al. in U.S. Patent

4,317,681 disclose modifiers for ion-leachable cement

compositions. Maries et al. in U.S. Patent 4,336,153 disclose a

glass composition for water setting ion-polymer cements. Crisp

et al. in U.S. Patent 4,337,186 disclose hardenable compositions. Muramatsu et al. in U.S. Patent 4,342,677 disclose fluorocomplex

salt-containing liquid for setting dental cements. Randklev in

U.S. Patent 4,350,532 discloses glass composition and articles.

Schmitt et al. in U.S. Patent 4,360,605 disclose a mixing

component for dental glass ionomer cements. Schaefer in U.S.

Patent 4,375,967 discloses dental composition containing x-ray

opaque material. Schmitt et al. in U.S. Patent 4,376,835

disclose calcium depleted aluminum fluorosilicate glass powder

for use in dental or bone cements. Griffith in U.S. Patent

4,378,248 discloses bonding dental porcelain. Smyth in U.S.

Patent 4,401,773 discloses highly reactive ion-leachable glass.

Denton et al. in U.S. Patent 4,492,777 disclose heat treated

barium or strontium glass. Hann et al. in U.S. Patent 4,530,766

disclose method of inhabiting scaling in aqueous systems with low

molecular weight copolymers. Wilson et al. in U.S. Patent

4,569,954 disclose dental cement composition comprising poly

(carboxylic acid) and chelating agent. Bennett et al. in U.S.

Patent 4,659,327 disclose a multiple dosage syringe. Ibsen et

al. in U.S. Patent 4,738,722 disclose dental compositions

incorporating glass ionomers. Gasser et al. in U.S. Patent

4,767,798 disclose polymerizable radiopaque dental composition.

Akahane et al. in U.S. Patent 4,775,592 disclose fluoroaluminosilicate glass powder for dental glass ionomer

cement. Billington in U.S. Patent 4,861,808 discloses glass/poly (carboxylic acid) cement composition. Akahane et al. in U.S.

Patent 4,900,697 disclose glass powders for dental glass ionomer

cements. Huang et al. in U.S. Patent 4,966,934 disclose

biological compatible adhesive containing a phosphorous adhesion

promoter and accelerator. Fischer in U.S. Patent 5,246,371

discloses method and apparatus for delivery of highly filled

thixotropic sealant to teeth. Oxman in European Patent 0,237,233

discloses one-part visible light-curable dentin enamel adhesive.

Blackwell in European Patent 0,363,903 discloses adhesive

containing pit and fissure sealants. Johnson & Johnson, in

Direct Delivery System disclose a clear light curing pit and

fissure sealant. The prior art does not provide a fluoride

releasing dental pit and fissure sealant cartridge dispensing system for a composition comprising a polymerizable acrylic

monomer, fluoride releasing glass particles and a fluoride containing salt which is at least one hundred percent more

soluble in water than calcium fluoride.

It is the object of the invention to provide a system for

dispensing through a nozzle from a cartridge enclosing a

sustained release dental pit and fissure sealant composition having a viscosity less than 30,000 cps and comprising a polymerizable acrylic monomer, fluoride releasing particles and a

fluoride containing salt which is at least one hundred percent

more soluble in water than calcium fluoride.

Viscosity as used herein refers to viscosity as measured by a Brookfield viscometer model number LVT, sprindle number 4,

operated at 6 revolutions per minute (rpm) at 25 'C.

Calcium fluoride has a solubility in water at 18°C of 0.0016 gram of calcium fluoride per 100 cubic centimeters of water.

BRIEF DESCRIPTION OF THE FIGURE

Figure 1 is a partial schematic side view of a dispensing

system for use in accordance with the invention.

SUMMARY OF THE INVENTION

A fluoride releasing dental pit and fissure sealant

dispensing system including a cartridge having a nozzle with a

capillary conduit wall enclosing a capillary passage extending to

a dispensing opening from a cylindrical chamber enclosing a

sustained release dental pit and fissure sealant composition

having a viscosity of 'less than 30,000 cps and including a

polymerizable acrylic monomer, fluoride releasing glass particles and a fluoride containing salt. The salt is at least one hundred

percent more soluble in water than calcium fluoride. The nozzle

has a length to diameter ratio of at least six, and is readily

bendable to form an arc of at least 30 degrees between the center

line of the cylindrical chamber and the center line of the distal

end of the nozzle.

DETAILED DESCRIPTION OF THE INVENTION

As shown in Figure 1, dispenser 10 has handle 12 and

removable cartridge 14. Cartridge 14 has nozzle 16 closed by cap

18, cylindrical chamber wall 20 and piston 24. Chamber wall 20

encloses a light curable extended fluoride release pit and

fissure sealant.

Channel 22 extends through nozzle 16. To dispense extended

fluoride release pit and fissure sealant from cartridge 14, rod

shaped plunger 26 forces piston 24 into the cylindrical chamber enclosed by wall 20. With cap 18 removed, pit and fissure

sealant is forced from the chamber through channel 22 onto a

patient's dental teeth, and then the sealant is exposed to

actinic light to cure the sealant. Preferably, channel 22 has an

inner diameter of from 0.2 to 3 mm. Preferably, nozzle 16 is from 1 to 4 cm in length. Sealant compositions having a viscosity greater than 30,000 cps require substantial force to move the composition in the channel. Such force may breach the

integrity of the system, for example, by breaking the cartridge.

Even such damaging force may be insufficient to move the sealant

entirely through the channel to be applied to a tooth surface.

Preferably, nozzle 16 is readily bendable so that the central

axis of channel 22 is positioned at an angle of from 30 to 90

degrees from the central axis of the cylindrical chamber. Plunger 26 has flange 28. Spring 30 is positioned between flange

28 and wall 32. The user may dispense sealant by holding handle

12 in the user's hand and pressing actuator 40 with the user's

thumb. When actuator 40 is pressed downward, it pivots on pin

42, and cam 44 presses against flange 28, forcing plunger 26

against piston 24.

The invention provides a sustained release dental pit and

fissure sealant composition containing acrylic monomer, fluoride releasing particles and a fluoride containing salt. Fluoride containing salts for use in accordance with the invention are

more soluble in water than calcium fluoride, strontium fluoride

or barium fluoride. Preferably, the fluoride containing salt is

at least one hundred percent as soluble in water as calcium

fluoride. The composition is formulated to have a viscosity that can

be readily handled by the dentist, and will usually have a

viscosity of less than 30,000 centiposes, and preferably, from

about 5,000 to about 25,000 centiposes at 25°C. Suitable resins

include the Bowen monomer bisphenol-A diglycidyl dimethacrylate

(bis-GMA) , bisphenol-A dimethacrylate, triethylene glycol

dimethacrylate, and other similar acrylic monomers which are well

known in the art. Other acrylic formulations suitable for use in

the invention are described in U.S. Pat. No. 3,815,239 and in the

aforementioned U.S. Pat. No. 4,150,012.

In a preferred embodiment, the composition employs a

polymerization catalyst, usually a peroxide catalyst such as benzoyl peroxide. The catalyst is used in the customary amounts.

The system also employs an accelerator to activate the peroxide.

Such accelerators are well known in the art, and are usually

amines, with N,N-bis (2-hydroxyethyl) -3,4-dimethylaniline being

the preferred accelerator.

Stabilizers such as substituted phenols may also be employed in the pit and fissure sealant composition of the invention to

retard or prevent premature polymerization.

In accordance with a preferred embodiment of the invention,

the composition of the invention is provided in one package. The composition includes a light activatable photoinitiation catalyst. Photoinitiators useful in compositions of the

invention are disclosed by Osborne et al. in U.S. Patent

3,759,807, Dart et al. in U.S. Patent 4,071,424.

Sealant compositions, in accordance with the invention,

preferably include from about 2 to 60 percent by weight of

fluoride releasing material including glass which releases

fluoride in water and a water soluble fluoride containing salt.

Preferably, the water soluble fluoride containing salt is at

least three hundred percent more soluble in water than calcium

fluoride. Most preferably, the water soluble fluoride containing

salt is at least one thousand percent more soluble in water than

calcium fluoride. Fluoride containing salts which are at least

ten thousand percent more soluble in water than calcium fluoride are within the scope of the most preferred salts for use in

sealant compositions in accordance with the invention.

Preferably sealant compositions in accordance with the

invention include from about 0.2 to about 5 percent by weight of

a water soluble fluoride containing salt. More preferably

sealant compositions in accordance with the invention include

from about 1 to about 3 percent by weight of a water soluble

fluoride containing salt. Preferably sealant compositions in accordance with the invention include from about 20 to about 50 percent by weight of

fluoride releasing particles, such as glass containing water

leachable fluoride.

The following examples illustrate the practice of the invention:

EXAMPLE 1

Loaded into the cylindrical chamber of a cartridge having

the structure shown in Figure 1 is a fluoride releasing dental

pit and fissure sealing composition. The nozzle is about 1.25

inch in length (3.14 cm). Through the nozzle extends a channel

having a diameter of about 0.01 inch. The fluoride releasing

dental pit and fissure sealing composition is made by stirring

together the amount indicated of each of the components of the

resin blend and the filler blend shown in Table 1. Thus, 19.25

grams of cyclodi-2,2-bis ( (4- [3 methacryloxy-2- (1,12-dioxo-3,10

diazadodecane) propoxyl] phenyl)) propane, 27.53 grams of 2-

propenoic acid, 2-methyl-l,2 ethanediyl-bis (oxy-2, 1-ethanediyl) ester, 0.018 grams of stannous octoate, 0.029 grams of phenol, 2

6-bis{1,1-dimethylethyl-4-methyl) , 0.088 grams of bicyclo (2,2,1)

heptane-2, 3-dione, 1,7,7 trimethyl, 10.55 grams of 2-propenic

acid 2 methyl- (1-methyl) ethylidene bis [4,1 phennyleneoxy (2-

hydroxy-3,1-propanediyl) ] ester, 0.290 grams of N-methyl

diethanolamine, 0.260 grams of moropholino-ethyl methacrylate,

1.170 grams of 2,2,6,6-tetraacryloxymethyl-4,8-dioxa-9-oxo-ll-

undecenyl phosphoric acid, 0.470 grams of methyacryloxy propyl- tetramethyl silane, 37.53 grams of barium alumino fluoroboro silcate glass, 0.130 grams of silicon dioxide, 1.98 grams of

sodium fluoride, and 0.690 grams of titanium dioxide are stirred

to form a fluoride releasing dental pit and fissure sealing

composition having a viscosity of 18,500 cps. The composition

is stored in a bottle and then applied to form a thin layer on the occlusal surface of a dental tooth after etching the tooth

with 30 weight percent aqueous phosphoric acid, rinsing, and

thoroughly drying. The tooth is then exposed to actinic light

for 20 seconds, and the composition polymerizes on the tooth to

form a sustained fluoride release pit and fissure sealant

composition thereon. The polymerized sustained fluoride release

pit and fissure sealant has diametral tensile, water sorption,

compressive strength, tensile strength and bond strength to etched enamel as shown in Table 2. The sustained fluoride release pit and fissure sealant" has static fluoride release shown in Table 3.

Table 1

AMOUNT (grams) RESIN BLEND

19.25 cyclodi-2,2-bis ( (4- [3 methacryloxy-2- (1,12-dioxo-3,10 diazadodecane) propoxyl] phenyl)) propane, sometimes referred to as Low Viscosity NCO monomer

27.53 2-propenoic acid, 2-me hy1-1,2 ethanediyl-bis (oxy-2, 1- ethanediyl) ester, sometimes referred to as Triethylene glycol dimethacrylate

0.018 Stannous Octoate

0.029 Phenol, 2 6-bis (1,1-dime hylethyl-4-methyl) , sometimes referred to as Butylated hydroxy toluene (BHT)

0.088 Bicyclo (2,2,1) HEPTANE-2, 3-DIONE, 1,7,7 trimethyl, sometimes referred to as Camphorquinone

10.55 2-propenic acid 2 methyl- (1-methyl) ethylidene bis [4,1 phennyleneoxy (2-hydroxy-3,l-propanediyl) ] ester, sometimes referred to as Bis GMA

0.290 N-methyl diethanolamine

0.260 Moropholino-ethyl methacrylate

1.170 2,2,6, 6-Tetraacryloxyme thyl-4,8-dioxa-9-oxo-ll-undecenyl phosphoric acid, sometimes referred to as Dipenta- erythritol Pentaacrylate Phosphate

FILTER BLEND

0.470 Methyacryloxy propyl-te ramethyl silane, sometimes referred to as A174 Silane

37.53 barium alumino fluoroboro silcate glass, sometimes referred to as Corning Glass S/F 7726

0.130 Silicon Dioxide, sometimes referred to as Cab-O-Sil TS 720

1.98 Sodium Fluoride

0.690 Titanium Dioxide Table 2

Physical Properties

BEFORE POLYMERIZATION

Appearance White creamy viscous liquid

Viscosity 18,500 cps

AFTER POLYMERIZATION

Depth of Cure 3.83 mm

Diametral Tensile 6812 psi

Water Sorption 1.08 mg/cm² @ 37°C

Uncured Film Thickness 0.60%

Sodium Fluoride 1.80%

Compressive Strength (after 24 hours) 36,058 +/- 5,293 psi

Tensile Strength (after 24 hours) 5,393 +/- 909 psi

Bond Strength to etched enamel 2,910 +/- 1,255 psi (24 hours)

Tag Length (mu) 150

Abrasion Loss (mL X IO^"4) 64.7 +/- 12.8

Table 3 shows, over a period of six weeks, the fluoride released at 37°C from samples of polymerized sealant made as

disclosed in Example 1, and having an average weight of 2.3865

grams, an average diameter of 1.51 centimeters and an average

thickness of 0.103 centimeters.

Table 3

STATIC FLUORIDE RELEASE

Fluoride

Released in

Micrograms

Fluoride Fluoride per gram of

Released Released sample Cumulative

Weeks (ppm) ⁽μg) (μg/g ) μg/gm

1 19.30 212.30 740.90 740.90

2 11.50 126.50 441.50 1182.40

3 6.76 74.36 259.50 1441.90

4 4.72 51.92 181.20 1623.10

5 2.85 31.35 109.40 1732.50

6 2.40 26.40 92.10 1824.60

EXAMPLE 2

A fluoride releasing dental pit and fissure sealing

composition is made by stirring together the amount indicated of

each of the components of the resin blend and the filler blend

shown in Table 1. Thus, 19.25 grams of cyclodi-2,2-bis ( (4- [3

methacryloxy-2- (1, 12-dioxo-3, 10 diazadodecane) propoxyl] phenyl))

propane, 27.53 grams of 2-propenoic acid, 2-methyl-l,2

ethanediyl-bis (oxy-2, 1-ethanediyl) ester, 0.018 grams of

stannous octoate, 0.029 grams of phenol, 2 6-bis (1,1-

dimethylethyl-4-methyl) , 0.088 grams of bicyclo (2,2,1) heptane-

2, 3-dione, 1,7,7 trimethyl, 10.55 grams of 2-propenic acid 2

methyl- (1-methyl) ethylidene bis [4,1 phennyleneoxy (2-hydroxy-

3, l-propanediyl) ] ester, 0.290 grams of N-methyl diethanolamine,

0.260 grams of moropholino-ethyl methacrylate, 1.170 grams of

2,2,6, 6-tetraacryloxyτnethyl-4, 8-dioxa-9-oxo-ll-undecenyl

phosphoric acid, 0.470 grams of methyacryloxy propyl-tetramethyl

silane, 37.53 grams of barium alumino fluoroboro silcate glass,

0.130 grams of silicon dioxide, 1.98 grams of potassium fluoride,

and 0.690 grams of titanium dioxide are stirred to form a

fluoride releasing dental pit and fissure sealing composition.

In more specific detail, a portion of the sustained fluoride

release pit and fissure sealant composition is used to fill an applicator cartridge. The entire occlusal of each tooth is cleaned by polishing with a non-fluoride, oil free paste, such as

Nupro-prophy paste. The tooth is then rinsed with water. A

quadrant of teeth is isolated with a rubber dam and each tooth is

dried at least 30 seconds with an air syringe. Etchant is applied to the entire occlusal surface with a brush. Each tooth is

etched for 60 seconds. The teeth are then thoroughly rinsed for

at least 30 seconds. Any areas of tooth surface that do not

appear frosty and opaque are re-etched for 20 seconds, while not

allowing saliva to contaminate etched surfaces. A rubber dam is

then used to isolate a quadrant and each tooth is dried with an

air syringe for at least 30 seconds. A disposable cartridge

containing sealant composition is then inserted into an

applicator handle. The tip of the cartridge allows access to any portion of either arch. The disposable cartridge contains sufficient sealant composition to treat occlusal surfaces of one

quadrant. The cartridge tip is touched to the occlusal surface.

The lever is slowly depressed while moving the cartridge tip

along fissures to dispense the sealant. Work time is about 45 seconds. All coated tooth surfaces are exposed to a visible

light source for 20 seconds keeping the light exit window about

1-2 mm from the tooth surface. Polymerized sealant appears as a polymerized thin film with color similar to pre-polymerized

liquids.

It should be understood that while the present invention has

been described in considerable detail with respect to certain

specific embodiments thereof, it should not be considered limited

to such embodiments but may be used in other ways without

departure from the spirit of the invention and the scope of the

appended claims.

Claims

What is claimed is:

1. A fluoride releasing dental pit and fissure sealant dispensing

system comprising: a cartridge having a nozzle with a capillary conduit wall enclosing a capillary passage extending through said nozzle from a cylindrical chamber enclosing a fluoride releasing

dental pit and fissure sealant composition having a viscosity of

less than 30,000 cps, said composition comprising a polymerizable

acrylic monomer, fluoride releasing glass particles and a fluoride containing salt, said salt being at least one hundred

percent more soluble in water than calcium fluoride, said nozzle

having a length to diameter ratio of at least six, and being

readily bendable to form an arc of at least 30 degrees between

the center line of said cylindrical chamber and the center line of the distal end of said nozzle.

2. The composition of claim 1 further comprising a photoinitiator and said viscosity is less than 25,000 cps.

3. The composition of claim 1 wherein said photoinitiator is

camphorquinone.

4. The composition of claim 1 wherein the polymerizable monomer is bisphenol-A diglycidyl dimethacrylate.

5. The composition of claim 2 wherein said fluoride releasing

particles comprise from about 10 to about 60 percent by weight of

said composition, and said salt comprises from about 0.5 to about

5 percent by weight of said composition.

6. The composition of claim 5 wherein said particles comprise

containing water leachable fluoride glass.

7. The composition of claim 1 wherein said fluoride releasing

particles comprise a fluoro silicate glass.

8. The composition of Claim 1 wherein said fluoride releasing

particles comprise barium alumino fluoroboro silicate glass.

9. The composition of Claim 1 wherein said salt is readily

soluble in water.

10. The composition of' Claim 1 wherein said salt comprises

hydrogen, an alkali metal or an alkaline earth.

11. The composition of Claim 1 wherein said conduit wall has an inner diameter of less than 2 mm.

12. The composition of Claim 1 wherein said salt comprises from 1

to 4 percent by weight of said composition.

13. The composition of Claim 1 wherein said glass comprises from

20 to 60 percent by weight of said composition.

14. The composition of Claim 1 wherein said salt is at least one

thousand percent more soluble in water at 18°C than calcium

fluoride.

15. The composition of Claim 1 wherein said salt is at least ten

thousand percent more soluble in water at 18°C than calcium fluoride.

16. The composition of Claim 15 wherein said composition is

distributed as a thin layer on a dental tooth surface.

17. The composition of Claim 16 wherein said thin layer of said

composition is exposed to actinic light.

18. The composition of Claim 17 wherein said light activates

polymerization of said monomer.

19. A method of sealing pits and fissures in natural dental teeth, comprising:

providing a fluoride releasing dental pit and fissure

sealant dispensing system comprising: a cartridge having a nozzle

with a capillary conduit wall enclosing a capillary passage

extending through said nozzle from a cylindrical chamber

enclosing a sustained release dental pit and fissure sealant composition having a viscosity of less than 25,000 cps, said

composition comprising a polymerizable acrylic monomer, fluoride

releasing glass particles and a fluoride containing salt, said

salt being at least one hundred percent more soluble in water than calcium fluoride, said nozzle having a length to diameter

ratio of at least six, and being readily bendable to form an arc

of at least 30 degrees between the center line of said

cylindrical chamber and the center line of the distal end of said

nozzle and applying said composition through said nozzle to the outer

surface of a natural dental tooth.

20. The method of Claim 19 wherein said nozzle is held at said angle while said composition is applied to said tooth.

21. The method of Claim 19 wherein said conduit wall has an

inner surface diameter of less than 2 mm.

22. The method of Claim 19 wherein said conduit wall has an

inner surface diameter of less than 1 mm.