WO2002067803A1 - Method and apparatus for dental drilling - Google Patents

Abstract

A method for drilling an access hole into a tooth, comprises the steps of directing a waterjet nozzle (18) at a point on a tooth where it is desired to drill an access hole, generating a waterjet (16) in the nozzle at a pressure insufficient to penetrate the healthy dentin of the tooth, introducing abrasive articles into the waterjet in the nozzle, and drilling the access hole by means of the waterjet and abrasive particles.

Description

Method and Apparatus for Dental Drilling

This invention relates to a method and apparatus for drilling teeth. More

particularly, this invention relates to a method and apparatus for dental drilling in which a high

pressure abrasive waterjet is used to drill small openings in a tooth to provide access to a

chamber or cavity containing dental caries.

Background of the Invention

U.S. patent No. 6,164,966 entitled Removal of Dental Caries with High Speed Waterjet discloses the use of a fine, high-pressure waterjet for removing dental caries from an

internal cavity in a tooth. The waterjet stagnation pressure is set low enough ( < 10,000 psi) that no damage is done to sound dentin surrounding the cavity as a result of the procedure, yet high

enough that the waterjet can penetrate the soft caries in the cavity creating an internal pressure sufficient to expel the caries material and to wash away the caries material clinging to the walls.

U.S. patent No. 6,164,966 is incorporated by reference into this specification.

In most cases, a hole must be made through the enamel and dentin to gain access

to the chamber or cavity containing the caries. The natural entry to the chamber may be a crack,

or a hole too small or awkwardly positioned to be accessible to dental tools and metal fillings. The standard technique is the use of drills and burrs to produce an entry hole, usually relatively

large. However, small holes are desirable because they take less material, preserve the integrity

of the structure, and have reduced chance of exposing a nerve. Air abrasion units have been used

to create small entry holes and their use gave rise to the term microdentistry (small hole filling techniques) to characterize the procedure. Special non-metallic materials allow filling through a small hole. Less heat is generated and heat translates into pain; less vibration translates into

fewer enamel cracks or cracked teeth. However, air abrasion systems cannot be used to remove

caries.

It is possible to use an air abrasion beam to produce a small access hole in a tooth

and then direct a waterjet beam through the access hole to remove the caries within the tooth. It

would be preferable, however, to use the waterjet both to produce the entry hole and remove the

caries. This would avoid the need for separate air abrasion equipment and would make possible

the use of the same equipment to remove stains, drill access holes and remove carious material from the exposed cavity.

Accordingly, the object of this invention is to provide a method and apparatus for

drilling small holes through enamel and dentin in a tooth using a waterjet.

Another object of the invention is to provide a method and device employing a

waterjet for providing access to teeth cavities which can also be used to effect stain removal and the removal and rinsing away of carious material from teeth.

A further object of the invention is to provide a method and device for drilling

access openings into teeth using a waterjet in such a way that unintended injury to healthy dentin

and enamel can be avoided. Summary of the Invention

According to the invention, an abrasive powder is introduced into a waterjet. Any

hard abrasive material such as aluminum oxide or silicon carbide may be used. The maximum

particle size is dependent in part on the diameter of the waterjet. Commercially available particle

sizes may be used although it is preferred that the particle size not be greater than about 10% of the beam diameter. The waterjet is then used to drill a hole in a tooth to provide access to the

caries. The stagnation pressure is set at a level which is insufficient to drill through healthy

dentin without the abrasive particles. The Drawing

The drawing is a schematic illustration of a waterjet nozzle showing how the

abrasive particles may be introduced into the waterjet beam.

Detailed Description

The drawing shows schematically the elements of a waterjet. A stagnation

chamber 12 receives water under high pressure through a conduit 13. The water is forced

through a small opening or orifice 10 in ajewel (e.g. sapphire) to eject a beam 16 through nozzle

18. Beam 16 is launched with a velocity dependent on the pressure of the water within the stagnation chamber 12. The structure of the waterjet nozzle and stagnation chamber are

conventional and are not described in detail herein.

In accordance with the invention, abrasive powder is introduced into the nozzle

region through a conduit 14. The powder mixes and is incorporated into the waterjet 16 which is

propelled from the orifice 10 through nozzle 18.

There is considerable airflow within the nozzle 18 due to the interaction of the waterjet with the surrounding air. The air at the perimeter of the waterjet is accelerated by

collisions with boundary water droplets and moves along with the jet. The pressure of the air is

reduced by virtue of its rapid motion (Bernoulli effect). Also, air is pumped out of the nozzle by

virtue of the waterjet-accelerated motion. Hence, air must be drawn either into the nozzle opening (it travels near the inside perimeter of the nozzle) or through the abrasive inlet to compensate. Abrasive particles introduced through conduit 14 are injected into this air stream

and enter the waterjet. This is called the mixing space. As used herein, "abrasive waterjet"

means a waterjet containing abrasive particles.

The size and material of the abrasive particles are important. The most important

physical quality of the material is its hardness which can be related roughly to the velocity of

sound in the material. The higher the velocity of sound the greater the hardness of the material.

When a high speed abrasive particle impacts the tooth surface, the process is ballistic. The energy of the incident abrasive particle is instantaneously dissipated, gouging out a crater in the

material. The greater the particle energy, the larger the crater. Cutting consists of producing a

high density of contiguous craters and then creating the new surface. By way of example,

suitable abrasive materials for use in the invention include aluminum oxide and silicon carbide. The particle size will depend in part on the diameter of the waterjet beam. The beam diameter for dental drilling may range from 20 to 250 um (microns) with a beam diameter of 33 to 50 um

being optimum. It is preferred that the size of the particles of the abrasive powder be equal to

about 10% of the beam diameter. Thus, the maximum particle size may range from about 2 - 25 um. If the particles are too large, it may be difficult to accelerate them sufficiently to create a

ballistic impact. On the other hand, if the particles are too small the increased air resistance may

hinder the ability of the particles to mix with the waterjet beam. The area to volume ratio of a

microjet beam is typically large which enhances incorporation of the particles which surround the

jet into the beam. The incorporation of the abrasive particles into the waterjet beam makes it

possible to cut the hard healthy dentin and enamel at relatively low waterjet pressures

comparable to those used for caries removal, without creating adverse effects within the material

of the tooth itself. For example, the pressure in the stagnation chamber may be between 5 and

10 kpsi. At a stagnation pressure of 10 kpsi, the speed of the water just beyond the orifice of the

jet nozzle is about 330 meters per second (m/s). After incorporation and acceleration of the

abrasive particles, the speed would be reduced to about 300 m/s.

It is not critical that the amount of abrasive material in the waterjet beam be high

since productivity is not important for simply drilling a hole. There are, however, techniques

which can be employed to increase the density of the abrasive particles. For example, injected

air can be used to bring the abrasive particles into closer proximity with the microjet beam. Because of the lower stagnation pressures, a longer nozzle may be used since the coherence of

the beam is longer at lower pressures. Also, the particles may be driven in a spiral path within

the nozzle to increase the area in which they interact with the beam. The nozzle may be provided

with apertures to increase turbulence and thus mixing.

As indicated above, the same waterjet apparatus can be used to drill the access hole into the tooth and to remove the caries from within the tooth since the stagnation pressure is

insufficient to drill healthy dentin or enamel without the abrasive particles. Once the drilling is

complete (as determined by the dentist), the flow of abrasive particles through conduit 14 can be

terminated and the waterjet used for caries removal, for example, as described in patent No. 6,164,966. The hole drilled through the dentin should be wide enough to permit the waterjet to flush caries from the cavity through the hole. Waterjet pressure may be increased for caries removal so long as it is maintained below the level which would damage healthy dentin or

enamel.

Claims

In the Claims

1. A method for drilling an access hole into a tooth, comprising the steps of:

directing a waterjet nozzle at a point on a tooth where it is desired to drill an

access hole; generating a waterjet in said nozzle at a pressure insufficient to penetrate the

healthy dentin of the tooth; introducing abrasive particles into the waterjet to form an abrasive waterjet; and

using the abrasive waterjet to drill the access hole.

2. A method according to claim 1, wherein said abrasive particles are introduced into

the waterjet in said nozzle.

3. A method according to claim 2, wherein the introduction of said abrasive particles

into said waterjet is discontinued after a hole has been drilled providing access to dental caries

within the tooth.

4. A method according to claim 2, wherein the waterjet has a diameter in the range

of about 10 to 250 microns and wherein the maximum size of said abrasive particles is no greater

than approximately 10% of the beam diameter.

5. A method according to claim 3, wherein the waterjet without abrasive particles is

used to remove dental caries after the hole has been drilled.