GB2513097A

GB2513097A - Dental instrument

Info

Publication number: GB2513097A
Application number: GB1302954.1A
Authority: GB
Inventors: Robert Finch
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-02-20
Filing date: 2013-02-20
Publication date: 2014-10-22
Also published as: GB201302954D0

Abstract

A dental instrument 1 for measuring a prepared tooth 103 for mounting a dental crown comprises a handle 2, a head 3 and a jaw 4. Jaw 4 comprises a static 4a and moveable 4b arms; the distance between the two arms 4a, 4b can be varied. Each arm 4a, 4b may have inclined surfaces 12, 13, the angles of inclination of which can be varied. There may be indicator markings (31, 32 fig 6A) which may be used to gauge the angle of inclination of flexible indicators (24a, 24b fig 6A). Moveable arm 4b may have a slider 5 retained within the handle 2. Handle 2 may have apertures 8a, 8b and lugs 11a, 11b extending through them. Arms 4a, 4b may each have a pair of feet 20a, 20b at their distal ends which may extend at an angle. Handle 2 may include a feeler gauge (15 fig 7) which may pivot around a point on the handle 2. The angle of convergence can be measured using this instrument.

Description

DENTAL INSTRUMENT

The present invention relates to a dental instrument and, in particular a dental instrument for assisting dentist in preparing a dental crown.

A dental crown is a dental restoration which provides a cap or covering over the natural crown of a tooth or a dental implant. Preparing a tooth for a dental crown requires the natural crown of the tooth to be prepared by removing a portion of the natural crown of the tooth above the gum so that it resembles a tapered stump onto which the dental crown is mounted. A shoulder around the base of the tooth against the gum line is also prepared and upon which the dental crown sits. Tooth preparation is a task that is often done by eye' without any detailed measurement. This means that the quality of the dental crown can vary from practitioner to practitioner and with varying degrees of success. The parameters that are particularly important for a successflul dental crown are: the taper angle of the tooth i.e. the angle at which the prepared tooth tapers from the gum line to the top of the tooth, the width of the shoulder around the base of the tooth at the gum line and the inter-occlusal space, that is the space between the top of the prepared tooth and any opposing tooth on the opposite jaw.

According to an aspect of the present invention, there is provided a dental instrument for measuring a prepared tooth for fitting a dental crown thereon and comprising: a body with a handle portion and a head portion, ajaw arrangement extending substantially orthogonally from the head portion, the jaw arrangement comprising a static arm and a moveable arm configured for translational movement relative to the static arm to adjust the distance therebetween.

The static arm may have a first inner inclined surface having an angle of inclination configured for pivotal movement to adjust the angle of inclination.

The static arm may have a first flexible member which includes the first inner inclined surface, and the head portion includes a first set of indicator markings and the first flexible member has an indicator reference at the free end of the first flexible member, whereby pivotal movement of first flexible member results in movement of the indicator reference relative to the first set of indicator markings.

The movable arm may have a second inner inclined surface having an angle of inclination configured for pivotal movement to adjust the angle of inclination.

The angle of inclination may be between 0° and 14°. More preferably, the angle of inclination may be up to 200, up to 150, up to 100, up to 50, up to 4°, up to 3°, up to 2° or up to 1°.

The movable arm may have a second flexible member which includes the second inner inclined surface, and the head portion includes a second set of indicator markings and the second flexible member has an indicator reference at the free end of the second flexible member, whereby pivotal movement of second flexible member results in movement of the indicator reference relative to the second set of indicator markings.

The second flexible member may have a bent profile a portion of which defines the second inner inclined surface.

The static arm may include first and second struts formed with the head portion and terminating in a base section, the first flexible member being connected to the base section at a point of fixation for pivotal movement thereround, the first flexible member being fixed to the base section between the first and second struts.

The moveable arm may have a slider attached thereto, the slider being retained within the handle portion and having a mechanism for manual translation of the moveable arm.

The second set of indicator markings of is provided on the slider.

The movable arm may include first and second struts formed with the slider and terminating in a base section, the second flexible member being connected to the base section at a point of fixation for pivotal movement thereround, the second flexible member being fixed to the base section between the first and second struts.

The first and second struts of the movable arm and static ann may have a curved profile.

The movable arm and the static arm may be 5mm to 15mm, and more preferably 10mm in height.

The head portion may have one or more apertures around the head portion and the mechanism may include one or more tabs extcnding from slider and configured for insertion within the one or more apertures.

The head portion has at least one elongate aperture and the operating mechanism is at least one lug extending through the at least one aperture.

The static arm and the movable arm each include a pair of feet at their distal ends.

Each foot of the pair of feet extends at an angle from the respective static arm or movable ann. The angle may between 0° and 10°, and preferably 5°.

The feet may be formed on the base section, The base section may have a curved recess.

Notches may be provided on the struts and on the feet to indicate predetermined measurements.

The dental arm includes a feeler gauge. The feeler gauge may be secured to the handle at a pivot point and configured to pivot around the pivot point.

The feeler gauge may be a flat sheet having an end portion with a frusto-conical lengthways profile. -4.-

The handle portion may be at an angle to the head portion. This may be between 10° and 300 preferably between 15° and 25°, and more preferably20°.

The present invention has the advantage of providing an instrument that can be used to more easily measure parameters of tooth preparation without having to rely on experience and the eye. It can be a useffil teaching aid for student dentists.

According to another aspect of the present invention, there is provided a method of measuring a prepared tooth for mounting a dental crown thereon using a dental instrument, the method including the steps of moving the movable arm away from the static arm so that the arms can fit around a prepared tooth, moving the movable arm towards the static arm until such time as movable arm and the static arm engage the outer surfaces of the prepared tooth and taking required measurements.

Preferably, the movable arm is moved towards the static arm until such time as the first and second inner inclined surfaces engage the outer surfaces of the prepared tooth and run along the tooth surface.

Preferably, the method may include the step of reading out the angles of taper for the prepared tooth by comparing the position of indicator references on the dental instrument with respect to the indicator markings on the dental instrument.

Preferably, the method may include the step of placing the feet of the dental instrument on the shoulder of the prepared tooth to compare the angle of the feet to see if they match with the angle of inclination of the shoulder.

Preferably, the method may include the step of comparing the shoulder width of the notches provided on the feet of the prepared tooth.

Preferably, the method may include the step of resting the feet of the dental instrument on the shoulder of the prepared stump, and comparing the height of the prepared tooth against a notch provided on the struts of the dental instrument.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic illustration of a prepared tooth with a crown mounted thereon; Figure 2 is a perspective view of a dental instrument of the present invention; Figure 3 is a side view of the dental instrument of Figure 2; Figures 4A and 4B are cross-sectional views of the dental instrument of Figure 3 with the jaw arrangement in a closed and open position respectively; Figures 5A and SB are detailed side views of the head portion of the dental instrument of Figure 2 with the jaw arrangement in a closed and open position respectively; Figures 6A and 6B are detailed perspective views of the head portion of the dental instrument of Figure 3 with the jaw arrangement in a closed and open position respectively; Figure 7 is a schematic perspective view of the end of the dental instrument of Figure 2 showing the inter-occlusal space measuring gauge; and Figure 8 is a schematic illustration of the placement of the movable and static arms of the instrument of Figure 2 placed around a prepared tooth for carrying out required measurements.

In order to mount a dental crown 101 on a tooth, the tooth needs to be prepared. Figure 1 illustrates schematically a prepared tooth 100 held within the gums or gingiva 102. The natural crown is filed down to a tapered stump 103 with a reduced height. The tapered stump 103 has an angle of taper, ci", and a height, h. The dentist will also prepare a portion of the tooth 100 around the gingival diameter of the tooth 100 to form a shoulder 104 upon which the dental crown 101 rests. The dental crown 101 is then placed over the tapered stump 103 and secured in place. Typically, the angle of taper, a" should be between 40 and 70, giving a preparation convergence angle of 8 tol4 degrees The shoulder 104 slopes outwardly at a small angle, subtending an angle, F", to the horizontal (see Figure 1) and should have a shoulder width, w, of around 1.5mm, depending on the type of crown required. Typically, the shoulder angle i" will be around 5°. This is well known to persons skilled in the art and need not be described in any further detail herein.

The dental instrument 1 of the present invention can be used to more accurately determine the parameters referred to above and is will be described in further detail below.

The dental instrument 1 includes a main body having a head portion 3 and a handle portion 2. The handle portion 2 is elongate and angled with respect to the head portion 3. In the embodiment described herein, the handle portion 2 subtends an angle of 20° to the head portion 3 to allow easy access to all areas of the mouth. The head portion 3 is also elongate and both the head portion 3 and the handle portion 2 are of a circular or oval cross-sectional profile with the handle portion 2 being configured to be held in a user's palm and gripped for manipulation. Typically, the dental instrument 1 will be held in the same way as a writing implement.

The overall length of the dental instrument 1 is around 16cm.

The head portion 3 has an elongate cavity 9 into which is received a slider 5. The elongate cavity 9 is open at an underside section of the head portion 3. A pair of matching grooves 8a, 8b is provided towards the forward end of the head portion 3 on either side of the head portion 3. A set of three grooves 7a, 7b, 7c are provided towards the rear end of the head portion 3 spaced around the side and upper regions of the head portion 3.

The head portion 3 also has an internal opening 10 at the forward end of the head portion 3 and a gap 34 at the front opening into the internal opening 10.

The slider 5 has an elongate body configured and dimensioned to be inserted into the elongate cavity 9 so that it can slide longitudinally within the elongate cavity 9.

At a forward end of the slider 5, on opposing sides, are orthogonally extending lugs 1 la, I lb which are inserted into corresponding one of the pair of matching grooves 8a, Sb.

Towards the opposite, rear, end of the sliderS, three tabs 6a, 6b, 6c extend orthogonally from the sides and upper surface of the slider 5 and which are configured for insertion into corresponding one of the set of three grooves 7a, 7b, 7c. The engagement of the lugs 1 Ia, 1 lb within their respective grooves 8a, 8b and the tabs 6a, 6b, 6c within their respective grooves 7a, 7b, 7c serve to retain thc slidcr 5 within the cavity 9 while enabling slidable movement of the slider 5 within the cavity 9. The grooves 7a, 7b, 7c; 8a, Sb also serve to limit the extent of the slidable movement of the slider 5 within the cavity 9 by acting as stop surfaces for the respective lugs 1 la, 1 lb and the tabs 6a, 6b, 6c.

The forward end of the slider 5 has an orthogonally extending arm 4b formed therewith.

The extending arm 4b is therefore movable as the slider 5 slides within the cavity 9.

The forward, free end of the head portion 3 has an orthogonally extending arm 4a formed therewith. The extending arm 4a is a static with respect to the movable arm 4b.

The two arms 4a, 4b therefore form a jaw arrangement 4 which extends substantially orthogonal from the head portion 3 and which comprises the static arm 4a and the moveable arm 4b. The movable arm 4b is configured for translational movement relative to the static arm 4a to adjust the distance between the two arms 4a, 4b, as the moveable arm 4b is moved towards and away from the static arm 4b under manual control using the tabs 6a, 6b, 6c The static arm 4a comprises first and second outer struts 22a, 23a with a first flexible indicator member 24a between the first and second outer struts 22a, 23a. The first flexible indicator member 24a inclines inwardly within the internal opening 10 of the head portion 3 as is shown in Figures 5A, SB, 6A and 6B, with an angle of inclination which, in the embodiment described herein is 100 The first and second outer struts 22a, 23a are formed integrally with the head portion 3. The flexible indicator member 24a defines a first inclined inner surface 12 for the static arm 4a. The first flexible indicator member 24a, and the first and second outer struts 22a, 23a terminate at the distal end of the static arm 4a in a base section 30a to which they are fixed. The first flexible indicator member 24a terminates at its free end with a cross piece that is shaped to form a first indicator reference 25a. The first flexible indicator member 24a is flexible so that it can pivot slightly around the point of fixation on the base section 30a between the inclined orientation to an orientation in which it is substantially parallel to the first and second outer struts 22a, 23a i.e. over a range of around 100, The gap 34 in the head portion 3 accommodates the first flexible indicator member 24a.

The base section 30a of the static arm 4a is formed to provide a pair of extending feet 20a at each end underneath the respective outer struts 22a, 23a, the feet 20a extending outwardly in a direction away from the movable arm 4b. The base section 30a has a curved recess 21 a between the two feet 20a.

Each of the pair of feet 20a are inclined at an angle 3, with respect to the struts 22a, 23a -and therefore from the static arm 4a -to complement the angle f3" of the prepared shoulder 104.

The curved recess 2la has a radius of curvature of 2.5mm and is provided so that the dental instrument 1, and particularly the static arm 4a, avoids contact with the neighbouring tooth during use.

The movable arm 4b is formed in a similar way as the static arm 4a. It is formed with the slider 5 and comprises first and second outer struts 22b, 23b with a second flexible indicator member 24b between the first and second outer struts 22b, 23b. The second flexible indicator member 24b inclines inwardly within the internal opening 10 of the head portion 3 as is shown in Figures 5A, SB, 6A and 6B with an angle of inclination which, in the embodiment described herein is 100. The first and second outer struts 22b, 23b are formed integrally with the slider 5. The second flexible indicator member 24b, and the first and second outer struts 22b, 23b terminate at the distal end of the movable arm 4b in a base section 30b to which they are fixed. Unlike the first flexible indicator member 24a of the static arm 4a, the second flexible indicator member 24b has a dog-leg shaped or bent profile as is shown in Figure 4A and 4B. The second flexible indicator member 24b therefore has a bent profile that is formed from a first inclined section which defines a second inclined inner surface 13 for the movable arm 4b, a return portion 26 and then a second inclined section 27 which is substantially parallel to the first inclined section 26.

The second flexible indicator member 24b is shaped at its free end to form a second indicator reference 25b. The second flexible indicator member 24b is also formed to be flexible so that it can pivot slightly around thc region of fixation 30b between the first and second outer struts 22b, 23b between the angled orientation to an orientation in which it is substantially parallel to the first and second outer struts 22b, 23b i.e. over a range of about 100.

Thus, the static arm 4a and the moveable arm 4b have inner, inclined surfaces 12, 13 that diverge towards their remote distal ends. These two inner, inclined surfaces 12, 13 are used to facilitate a measure the angle of taper a".

The provision of the bent second flexible indicator member 24b enables the movable and static arms 4a, 4b to get to a 3mm separation at a minimum for the present embodiment.

Similarly, the base section 30b of the movable arm 4b is formed to provide a pair of extending feet 20b at each end underneath the respective outer struts 22b, 23b, the feet 20b extending outwardly in a direction away from the static ann 4a. The base section 30b has a curved recess 21b between the two feet 20b.

Each of the pair of feet 20b are inclined at an angle (3' with respect to the struts 22b, 23b -and therefore from the movable arm 4b -to complement the angle (3 of the prepared shoulder 104.

The curved recess 21b has a radius of curvature of 2.5mm and is provided so that the dental instrument 1, and particularly the movable arm 4b avoids contact with the neighbouring tooth during use.

Each of the extending feet 20a, 20b are provided with a notch 28a, 28b at 1.2mm distance from the free ends of the extending feet 20a, 20b indicating a preferred minimum shoulder width for certain dental crowns.

Both the static arm 4a and the movable arm 4b have a length of 10mm to accommodate most dental crown heights.

Each arm 4a, 4b has a respective notch 33a, 33b provided therein at a 3mm height position to indicate where there is a 3mm tooth height. This height is generally accepted to be the minimum height of tooth acceptable to retain a crown successfully long term ("the minimum amount of ferule").

The first and second outer struts 22a, 23a of the static arm 4a have a curved cross-sectional profile -widening towards head portion 3 with a large graduated radius. This provides additional rigidity for the static arm 4a while avoiding interference with neighbouring teeth. This is shown in Figures 5A and SB.

The first and second outer struts 22b, 23b of the movable arm 4b also have a curved cross-sectional profile -widening towards the head portion 3 with a large constant radius (typically 4mm) while avoiding interference with neighbouring teeth.

These profiles provide maximum resistance to distortion when in use without getting in the way of tooth preparation.

A first set of indicator markings 31 are provided on the head portion 3 adjacent the front region of the internal opening 10. These indicator markings 31 are used to gauge the angle of inclination of the first flexible indicator 24a as it flexes and the first indicator reference 25a moves relative to these indicator markings 31 and thus to provide an indication of the angle of taper a of the prepared tooth 103.

The first and second set of indicator markings 31, 32 are provided to indicate 10 changes in angle of inclination of the respective flexible indicators 24a, 24b.

Two sets of second indicator markings 32 are formed at the point where the first and second outer struts 22b, 23b of the movable arm 4b are formed with the slider 5. These second indicator markings 32 are used to gauge the angle of inclination of the second flexible indicator 24b as it flexes and the second indicator reference 25b moves relative to these indicator markings 32 to thus provide a further indication of the angle of taper cx' of the prepared tooth.

In use, and as the movable arm 4b is moved towards and away from the static arm 4a so that the distance, X, between the distal ends of the two arms 4a, 4b can be varied. The distance is typically between 3mm and 12mm. Figure 4A shows this minimum distance in which the static arm 4a and the movable arm 4b are in contact and the two inner inclined surfaces 12, 13 define a V-shaped region 29.

At the free end of the body portion 2 there is provided a feeler gauge 15. This is not illustrated in Figures 1 to 6, but is shown in Figure 7. The feeler gauge 15 is used to measure the inter-occlusal space. The feeler gauge 15 is a flat sheet which is pivotably secured to the free end of the handle portion 2 and can pivot in the longitudinal plane of the handle portion 2 as indicated by the double-headed arrow in Figure 7. The end portion 34 of the feeler gauge 15 has a frusto-conical lcngthways profile which enables the feeler gauge 15 to measure different tooth width spaces so that wide or narrower gaps can be measured in one go. If the dentist cannot pull it back out when the patient bites together then there is not enough room, somewhere, then the dentist can inspect visually. In the embodiment described herein, the feeler gauge 15 has a total length of 14mm, the frusto conical section 34 has a length of 10mm. The narrow end of the feeler gauge 15 is 2mm wide, and the feeler gauge t5 has a thickness of 1.5mm.

To measure the various parameters required for good tooth preparation, the dental instrument 1 can be used as follows, This is described with particular reference to Figure 8.

To measure the angles of taper a, a' of opposing sides of the tooth the dentist moves the movable arm 4b by holding the dental instrument 1 in one hand and using the finger to move the slider 5 using the tabs 6a, 6b, 6c. The dentist moves the movable arm 4b away from the static arm 4a so that the arms 4a, 4b can fit around a prepared stump 103. The movable arm 4b is then similarly moved towards the static arm 4b until such time as the first and second inner inclined surface 12, 13 engage the outer surfaces of the prepared stump 103 and run along the tooth surface. This engagement causes the first and second flexible indicators 24a, 24b to flex and pivot about the point of fixation with their respective base section 30a, 30b and with a consequential movement of the first and second indicator references 25a, 25b with respect to the indicator markings 31, 32. The dentist is then able to read out the angles of taper a, a' by comparing the position of the indicator references 25a, 25b with respect to the indicator markings 31, 32. The indicator markings 31, 32 will have a range marked in colour which will indicate a range in which the angle of taper is sufficient for purpose. In practice, a dentist will only need to have the references 25a, 25b within this coloured range rather than needing to know an exact measure.

To measure whether the shoulder width of the prepared stump 103 is correct and that the angle of the shoulder 104 is correct, the feet 20a, 20b are placed on the shoulder 104 to compare the angle, 3' of the feet 20a, 20b to see if they match with the angle of inclination of the shoulder 104. The dentist is also able to compare the shoulder width of the notches 28a, 28b provided on the feet 20a, 20b. The dentist is then able to adjust the shoulder accordingly.

While the feet 20a, 20b are resting on the shoulder 104 of the stump, the dentist is also able to compare the height of the prepared tooth against the notch 33a, 33b provided on the struts 22a, 23a; 22b, 23b and carry out any ifirther tooth preparation that can be required.

The feeler gauge can be used to determine whether the inter-ocelusal space is sufficient.

The dental instrument 1 can be made of any suitable rigid plastics material with the body and slider being injections moulded. The feeler gauge 15 can be made of any suitable flexible material.

It will be obvious that variations are possible within the scope of the present, particularly with regards to dimensions and materials of manufacture.

Claims

CLAIMS1. A dental instrument for measuring a prepared tooth for mounting a dental crown thereon comprising: a body with a handle portion and a head portion, and a jaw arrangement extending substantially orthogonally from the head portion and comprising a static arm and a moveable arm configured for translational movement relative to the static arm to adjust the distance therebetween.
2. A dental instrument according to claim 1, wherein the static arm has a first inner inclined surface having an angle of inclination configured for pivotal movement to adjust the angle of inclination.
3. A dental instrument according to claim 2, wherein the static arm has a first flexible member which includes the first inner inclined surface, and the head portion includes a first set of indicator markings and the first flexible member has an indicator reference at the free end of the first flexible member, whereby pivotal movement of first flexible member results in movement of the indicator reference relative to the first set of indicator markings.
4. A dental instrument according to any preceding claim, wherein the movable arm has a second inner inclined surface having an angle of inclination configured for pivotal movement to adjust the angle of inclination
5. A dental instrument according to claim 4, wherein the movable arm has a second flexible member which includes the second inner inclined surface, and the head portion includes a second set of indicator markings and the second flexible member has an indicator reference at the free end of the second flexible member, whereby pivotal movement of second flexible member results in movement of the indicator reference relative to the first set of indicator markings
6. A dental instrument according to claim 5, wherein the second flexible member has a bent profile
7. A dental instrument according to any preceding claim, wherein the moveable arm has a slider attached thereto, the slider being retained within the handle portion and having an operating mechanism for manual translation of the moveable arm.
8. A dental instrument according to claim 7, wherein handle portion has at least one elongate aperture and the operating mechanism is at least one lug extending through the at least one aperture.
9. A dental instrument according to any preceding claim, wherein the static arm and the movable arm each include a pair of feet at their distal ends.
10. A dental instrument according to claim 7, wherein each foot of the pair of feet extends at an angle from the respective static arm or movable arm.
11. A dental instrument according to any preceding claim, wherein the handle portion includes a feeler gauge.
12. A dental instrument according to claim 11, wherein the feeler gauge is secured to the handle at a pivot point and is configured to pivot around the pivot point.
13. A method of measuring a prepared tooth for mounting a dental crown thereon using a dental instrument as claimed in any preceding claim, the method including the steps of moving the movable arm away from the static arm so that the arms can fit around a prepared tooth, moving the movable arm towards the static arm until such time as movable arm and the static arm engage the outer surfaces of the prepared tooth and taking required measurements.