WO1984003143A1

WO1984003143A1 - Optical probe to measure the depth of a cavity

Info

Publication number: WO1984003143A1
Application number: PCT/GB1984/000029
Authority: WO
Inventors: Lewis Arnold Simon
Original assignee: Ljs Practice Management Ltd
Priority date: 1983-02-03
Filing date: 1984-02-03
Publication date: 1984-08-16
Also published as: EP0163645A1; GB8505501D0; GB2155628A

Abstract

An instrument for measuring e.g. the depth of periodontal pockets comprise a light source (109), an optical fiber (102) arranged to conduct light from the light source toward a free end (105) of the fiber to be inserted into the pocket to be measured, and a photo detector diode (114) arranged to detect light reflected back along the optical fiber wherein the free end of the optical fiber tapers. The instrument is also capable of measuring characteristics of liquids such as their content of light absorbent constitutents.

Description

OPTICALPROBETOMEASURETHEDEPTHOFACAVITY

This invention relates to measuring instruments e. g. for measuring the depth of cavities or a characteristic of a liquid such as its depth. In particular, but not exclusively, the invention relates to instrument for measuring the depths of dental cavities or gum pockets (periodontal pockets).

In modern dental care, increasing importance is being placed on the treatment of gum disease. An important measure of gum disease is the depth of the cavities or periodontal pockets which are the spaces between the gingival tissues (gums) and the teeth. The most usual method presently used for measuring the depth of these pockets is to provide a solid probe, graduated in millimeters, which the dentist inserts to the base of the cavity, and then takes a visual reading of the number of graduations visible above the top of the cavity. Not only is this method somewhat inaccurate, and time consuming, it also requires the assistance of a second party, for example a dental nurse, to note down the readings as they are read out by the dentist. A number of more sophisticated instruments have been proposed, for example an instrument comprising an handle having a tubular sheath, and a probe adapted for movement inside the sheath, such that the end of the sheath, may be rested on the margin of the cavity, and the probe extended to the base of the cavity. The depth of the cavity is then read from a scale on the handle of the instrument. Although this probe is an improvement on the type of probe described above, it does not overcome the major problem that an assistant is required to provide a manual record of the investigation.

Various attempts have been made to automate measurement when ^"using dental probes. For example, US Patent No. 3058225 describes a dental instrument in which the degree of extension of -a probe within a sheath is indicated on an electrical meter. Not only is this probe clumsy in use, but also it does not provide any solution to the above-noted problem that an assistant is required to record results.

US Patent No. 3943914 describes an arrangement which goes some way towards solving this problem, in that an instrument is used which produces an electrical signal indicative of the depth of a cavity, and this signal is used to provide a print-out of the readings measured. However, this instrument suffers

O PI from a number of disadvantages. For example, the arrangement in the instrument described is such that a probe is first positioned at the base of the cavity in question, and a slidable sheath is then moved along the probe until it contacts the gum margin. This is likely to result in damage to the delicate tissue at the base of gum cavity. Furthermore, no means are provided in the instrument described for providing a permanent machine-readable record of readings obtained, to enable changes in the values obtained for a particular patient to be readily observed.

United States Patent Specification 4287427, describes the use of an optical fibre having a core and a cladding for detecting the level of a liquid. Light is passed from a source at one end of the fibre to a detector at the other end. A section of fibre exposable to liquid has its cladding thinned or removed to promote light loss to liquid when liquid contacts the fibre. The amount of light lost between the source and detector serves as a measure of the level of liquid present. Such a construction would be too cumbersome for use in an extremely restricted space such as a periodontal cavity because access is needed to both ends of the fibre.

OMPI United States Patent Specification No. 4342919 relates to measuring liquid levels in the petroleum industry and describes the use of an optical fibre having a light source and a detector coupled to one end thereof. Light is directed down the fibre, reflected back up from a free end thereof and detected. Means is provided to be pressed against the fibre by liquid pressure when the fibre is partially immersed, which means transmits light out of the fibre: The amount of light thus lost is a measure of depth. In place of such a means for transmitting light from the fibre, the liquid itself may be relied upon. However, such a construction is not effective on a scale suitable for use in measuring periodontal pockets.

According to a first aspect of this invention, there is provided an instrument for measuring the depth of a cavity, comprising a handle member, a probe connected to the handle member and adapted for insertion into the cavity, means for emitting light at a plurality of points spaced along the probe, and means for example, on or adjacent the handle member for viewing the probe to determine the number of the said light- emitting points visible, thereby to determine the depth of insertion of the probe into the cavity.

JUREA₍ OMPI The light emitting means may preferably comprise a light source associated with the handle member and a plurality of optical fibres leading from the light source to the said plurality of points spaced along the probe. The means for viewing the probe portion may comprise a sensor, for example a light-sensitive diode, or a photocell directed at the probe, for measuring the intensity of light emitted from the points. The light source preferably emits in the infra-red region of the spectrum, in order to minimise interference with the sensor by ambient light, and a laser source may preferably be used.

The instrument may preferably be connected to a computer for recording readings of pocket depths obtained from a patient. Means operable by the clinician, for example a foot-pedal, or a push-button on the instrument, may be provided for indicating to the computer when a depth reading is to be registered. It is normal practice for six depths readings to be taken on each tooth, and the computer may preferably be programmed and arranged to record a predetermined number of readings, for example six readings, as being associated with each tooth of the patient, before moving on to the next tooth. According to a second aspect of the invention, there is provided an apparatus for measuring the depth of a cavity, comprising a dental instrument including a handle member, a tubular sheath extending from the handle member, a probe adapted for longitudinal movement inside the sheath, means on the handle for causing longitudinal movement of the probe in the sheath, sensing means for producing an electrical signal indicative of the longitudinal position of the probe in the sheath, the apparatus including a computer connected to the sensing means for recording readings of pocket depths obtained from a patient, means operable by a clinician for indicating to the computer when a depth reading is to be registered, the computer being programmed and arranged to record a predetermined number of readings as being associated with each tooth of a patient.

Periodontal pockets are filled with saliva. Their depth may therefore be measured by measuring the depth of liquid in the pockets. Other characteristics of such liquid may also be of interest, e.g. the presence of red blood cells.

In a third aspect, the present invention provides instruments for use in measuring a characteristic of a liquid some of which may be used for measuring liquid depths, for instance in periodontal pockets, and some of which may be used for measuring other characteristics of liquids. Accordingly, the present invention provides an instrument for measuring a characteristic of a liquid comprising a light source, an optical fibre arranged to conduct light from the light source toward a free end of the fibre to be contacted with liquid to be measured, and light detection means arranged to detect light reflected back along the optical fibre away from said free end, wherein at the free end of the optical fibre there is a progressively thinning portion. Preferably, the progressively thinning portion is a conical or frusto-conical taper.

Preferably, the tip of the fibre at the free end is provided with a mirror coating.

Preferably, the progressively thinning portion extends over a length of up to 12 mm along the fibre. Preferably, except at a portion at the free end the optical fibre comprises a core and a cladding, the cladding having a refractive index lower than that of the core. Preferably, the light source comprises a laser.

Alternatively the light source may be a light emitting diode (LED).

In use, the free end of the optical fibre may be inserted as a probe down to the bottom of a periodontal cavity. Light transmitted down the optical fibre from the light source will to some

-SfRE O ? extent be scattered and reflected back up the fibre to the detector. Some light however will pass through the walls of the fibre and be lost. Where the tip of the fibre is immersed in liquid the light will be lost proportionately more than where the fibre is exposed only to air. This is because the liquid will have a refractive index higher than that of air and, generally, higher than that of the optical fibre. The amount of loss of light will accordingly provide a measure of depth first of the liquid and secondly of the pocket.

In order to measure the quantity of a coloured material in a liquid, or simply to detect its presence, one may use a light source producing a frequency that is particularly strongly absorbed or reflected by the material in question. For instance, the presence of blood in fluid in a periodontal cavity may be detected and its concentration measured by using as the light source a source of green light strongly absorbed by blood.

Whilst measuring apparatus according to the invention may be made particularly adapted to the measurement of periodontal pockets or the measurement of another characteristic of liquid therein, the invention is not limited to apparatus for these purposes. Apparatus according to the invention may be used for measuring liquid depths generally and will often be particularly suitable for use in measuring the depth of liquid in extremely confined pockets similar to periodontal pockets. Also, apparatus according to the invention may be used for measuring characteristics of liquids in general, e.g. measuring the concentration of substances present therein having a pronounced frequency or frequency range of light absorbtion. The invention includes methods of measurement in which are used apparatus or instruments of the invention as defined above.

The present invention includes a process for the measurement of a characteristic of a liquid, such as its depth or the content of a species therein, which comprises the use of apparatus as described herein.

A preferred embodiment of each of the two above- described aspects of the invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a schematic diagram of the tip of a probe according to the first aspect of the invention, Figure 2 is a section on A-A of Figure 1, and Figure 3 shows a dental instrument for use in conjunction with the second aspect of the invention described above;

O ?I Figure 4 is a plan view of the probe of Figure

3;

Figure 4a is a transverse section on the line B-B of Figure 4. Figure 5 is schematic view of a probe according to the third aspect of the invention.

The probe shown in Figure 1 comprises a hollow casing 1 of diameter sufficiently small to enter gum pockets or cavities of the size usually encountered. The casing contains a plurality of fibre optic strands 2 which lead at their proximal ends to an infra-red laser light source, housed in the handle of the instrument, and at their distal ends to a plurality of microprisms 3 in the tip of the probe. The microprisms 3 are preferably each part of a single plastics structure constructed in away similar to a "fresnel" lens, to direct light exiting from the ends of the fibre optic strands onto a photo-receptor 4. The photo-receptor 4 is mounted on the instrument, and arranged to produce an electrical signal which varies in accordance with the number of microprisms 3 which are able to direct light onto it. Thus, as the microprisms 3 are occluded by insertion of the probe into a cavity, the signal output by the photo- receptor will vary. The probe is received in a handle member 5 schematically shown in the drawing. The analogue output obtained from the receptor 4 is converted by an analogue-to-digital convertor to digital form, which is then fed into a computer for further processing, as described below. As an alternative, no outer sheath 1 may be utilised, and the probe may be formed simply by bonding together a bundle of fibre optic strands.

Figure 3 is a sectional view of an instrument for use with apparatus according to the second aspect of the invention. The instrument comprises a body portion including a handle member 10 having a disposable plastics sheath 11 affixed thereto by a screw-threaded portion 12. A flexible probe 13 is adapted for longitudinal movement within the sheath 11 , and has its innermost end received as a friction fit in a boss 14 mounted to slide in opposed channels 22. A slide control 15 projects from the boss 14 to the exterior of the handle 10, for operation by the index finger of the dentist. The boss 14 also carries the wiper of a rheostat or variable resistance 16. Lead-out wires 17 from the rheostat 16 are passed to the exterior through a removable cap 18 provided at the end of the handle 10.

A particularly advantageous feature of the instrument shown is the provision of a spring 19, which provides an approximately constant resistance against which the dentist may advance the probe 13. This greatly assists the accurate placing of the probe 13 at the base of a cavity.

A foot-control, indicated schematically at 23, is provided to indicate to a computer 21 when readings are to be registered. An analogue-to-digital converter 20 converts readings from the rheostat 16 to digital signals which can be interpreted by the computer 21. The computer is programmed to associate six consecutive readings with the six pocket depths measurements usually -made on a single tooth, and subsequent batches of six consecutive readings with consecutive teeth. The readings for a particular patient are stored using a medium such as magnetic tape or magnetic disc, and can readily be recovered for comparison by the computer at a future date.

It should be appreciated that a large number of other arrangements are possible within the scope of the invention, in addition to the specific arrangements described above. In particular, the fibre-optic type probe may be utilised for measuring cavity depths otherwise in connection with dentistry. As shown in Figure 5, a probe 101, shown on a greatly exagerated scale, comprises an optical fibre 102. One end of fibre 102 is free and is ground down to a frusto-conical shape at portion 103. The very tip of the fibre is plane and circular and is provided with a metallic coating to form a mirrored end surface 105. The fibre 102 is over most of its length composed of a core of higher refractive index and a cladding of lower refractive index. The cladding however stops just short of the frusto conical portion 103.

The fibre 102 is provided over all but the free end portion thereof with a protective sheath of flexible opaque material 104.

Adjacent the free end of the fibre 102 is a hand grip 106, the scale of which is greatly reduced compared to the fibre. Grip 106 is shaped to bend the sheathed fibre 102 to a convenient shape for use as described hereafter.

Probe 101 is connected to a connection fitting 107 on a housing 108 such as an SMA connector. Within housing 108 is contained a light source such as laser 109 arranged to direct light through a suitable optical system such as lens 110 onto an inlet facet at the end of a optic fibre 111. Lens 110 is suitably a 30 mm focal length biconvex lens. Optical fibre 111 and a similar further optical fibre 112 form a Y junction with a larger optical fibre 113 of a similar type to fibre 102. Fibre 113 is connected to connection fitting 107 by means of which- continuous light path is made between fibres 113 and 102. Fibre 112 leads from fibre 113 to a photo detector diode 114 or other light detection means. The output of diode 114 is amplified by amplifier 115. An output signal from amplifier 115 is processed via a logic circuit 116, computer interface 117 and read out interface 118 to provide an output 119 to a computer and an output to a read out device 120 such as a printer or LCD display unit.

In operation, light from the laser 109 is passed through lens 110 or other optical system to impinge on the entry facet of fibre 111 from which it passes down fibre 102 to the tip 105. Much of the light will be reflected back up the fibre 102. The major part of the returning light passes up fibre 112 to detector 114 and produces an input signal for amplifier 115 dependant on the light lost in the probe 101.

If the frusto-conical tip 103 of the probe is inserted into a periodontal pocket to the bottom thereof, that portion of the probe within the cavity will be wet with liquid in the pocket. More light will be lost as a result of the contact with the liquid and the size of the signal produced by diode 114, will be inversely dependent upon the liquid depth and hence the depth of the pocket. The purpose of the tapered end of the optical fibre is to promote loss of light to the liquid when the fibre is partially immersed.

Logic circuitry 116 may have an input from a control such as a foot pedal to signal when a reading is to be taken, as described above with reference to Figure 1. The output from the amplifier may be provided, under the control of logic circuitry 116 to a computer via interface 117 and to display 120 via a suitable interface 118. The purpose of the and characteristic of the computer may be as described with reference to Figure 1.

The laser is preferably a helium neon laser producing from half to one milliwatt at a frequency of 632.8 nm. Other suitable light source include light emitting diodes. In particular an infra-red light emitting diode may be used. The use of infra-red frequencies helps to overcome interference caused by stray light. Alternatively a green emitting diode may be used, as is described in greater detail hereafter. The optical fibre 102 preferably has a core diameter of about 200 microns and a total diameter, including the cladding, of about 400 microns. Fibres 111 and 112 may each be smaller, e.g. have a diameter of about 125 microns. They each may be joined to the end of fibre 113 by a butt joint, thus avoiding - 16 - problems of alignment between the fibres and avoiding some sensitivity to vibration.

By virtue of being attached to the light source and detector unit in housing 108 by connector 107, fibre 102 may be made removable for cleaning, e.g. by autoclaving.

In a modification of the apparatus described with reference to Figure 5, the laser shown is replaced by a source of green light, such as a green laser or a green emitting diode. The apparatus is then used to detect blood in the saliva in a periodontal pocket.

Probe 101 is advanced into the pocket to a predetermined depth and readings are taken. Light will be lost to the cavity by a combination of routes. Some light will be lost by transmission into the liquid contacting the end region of the probe. This may be minimised by choosing the refractive index of the core of the fibre 102 to be greater than that .of saliva. Light will also be lost by being absorbed at the interface with saliva because of the saliva containing red blood cells. Losses from the first cause may be kept constant by keeping the depth of probe insertion constant so that variations in light loss are due to varying blood cell concentration. The apparatus according to this aspect of the invention is not restricted to apparatus for use in

-ξJREA, OMPI - 17 -

dentistry. The depth of liquids generally, and of liquid filled cavities or pockets generally may be measured in the same way. Alternatively, apparatus of the invention may be used as a sensor simply to indicate whether a liquid level is above or below a level at which the end of the probe is exposed.

Similarly, apparatus of the invention may be adapted for measuring the concentration of species other than blood cells by the absorption of visible, infra-red or ultra-violet light.

Instead of a light source producing essentially a single frequency, a broad band source may be employed together with suitable filters. Filters may be placed before the entry facet of fibre 111 or before detector 114 in the apparatus described previously.

The invention is not restricted to the specific embodiments described above and many variations and modifications may be made without departing from the scope of the invention.

.-^ORE r OMP

Claims

1. An instrument for measuring a characteristic of a liquid comprising a light source (109), an optical fibre (102) arranged to conduct light from the light source toward a free end (105) of the fibre to be contacted with liquid to be measured, and light detection means (114) arranged to detect light reflected back along the optical fibre away from said free end, characterised in that at the free end of the optical fibre there is a progressively thinning portion (108).

2. An instrument as claimed in claim 1 further characterised in that the progressively thinning portion (103) is a conical or frusto-conical taper.

3. An instrument as claimed in claim 1 further characterised in that the tip (105) of the fibre at the free end is provided with a mirror coating.

4. An instrument as claimed in claim 1 further characterised in that the progressively thinning portion (103) extends over a length of up to 12 mm along the fibre.

5. An instrument as claimed in claim 1 further characterised in that except at a portion at the free end the optical fibre comprises a core and a cladding, the cladding having a refractive index lower than that of the core.

6. An instrument as claimed in claim 1 further characterised in that the light source is selected from the group consisting of a laser and a light emitting diode (LED).

7. An instrument for measuring the depth of a cavity, comprising a handle member (5) and a probe (1) connected to the handle member and adapted for insertion into the cavity, characterised in that ther are provided means for emitting light at a plurality of points (3) along the probe, and means (4) for receiving light emitted by said means for emitting light to determine the number of the said light- emitting points visible, thereby to determine the depth of insertion of the probe into the cavity.

8. An instrument as claimed in claim 7 further characterised in that the light emitting means comprises a light source associated with the handle member, and a plurality of optical fibres (2) leading from the light source to the said plurality of points (3) spaced along the probe.

9. An instrument as claimed in claim 7 further characterised in that the light emitting means emits in the infra-red region of the spectrum.

10. Apparatus for measuring the depth of a cavity, comprising a dental instrument including a handle member (10), a tubular sheath (11) extending from the - 20 - handle member, a probe (13) adapted for longitudinal movement inside the sheath, means on the handle member (15) for causing longitudinal movement of the probe n the sheath, sensing means (16) for producing an electrical signal indicative of the longitudinal position of the probe in the sheath, the apparatus including a computer (21) connected to the sensing means for recording readings of pocket depths obtained from a patient, means (19) operable by a clinician for indicating to the computer when a depth reading is to be registered, the computer being programmed and arranged to record a predetermined number of readings as being associated with each tooth of a patient.