WO2009050455A1

WO2009050455A1 - Bow and articulator frame apparatus

Info

Publication number: WO2009050455A1
Application number: PCT/GB2008/003494
Authority: WO
Inventors: Ashraf Ayhoub; Joseph Barbenel; Khursheed Moos; Fraser Walker
Original assignee: Greater Glasgow Health Board
Priority date: 2007-10-15
Filing date: 2008-10-15
Publication date: 2009-04-23
Also published as: GB0720189D0

Abstract

An apparatus and method for accurately measuring and replicating facial dimensions using a face bow and articulator. The apparatus has means for measuring an absolute datum, such as a spirit level, the means being mounted to the bow and articulator frame such that its orientation can be adjusted.

Description

Bow and Articulator Frame Apparatus

The present invention relates to a bow and articulator frame apparatus and, in particular, to an improved method and apparatus for accurately recording and replicating an individual's jaw structure.

A bow, or a face bow, is an instrument that is used to register the positions and orientations of key cranial-facial points of an individual. Traditionally, a face bow is referenced to certain anatomical planes which are defined by touching three anatomical points on an individual's head.

An articulator is conventionally a bench-top rig used in laboratories to assist technicians and surgeons plan the correct repositioning of a patient's jaw(s) before carrying out surgery on a patient with, for example, a congenital facial deformity. The articulator is required to replicate a patient's jaw structure in three dimensions. Often, articulators are used to construct wax moulds which are employed as guides during orthognathic operations as detailed below.

Bows and articulators are used in dental surgery, and in particular in orthognathic surgery - surgery to correct deformed jaws. Such surgery is common on the UK and further afield with over one thousand such operations performed in the UK every week.

People with jaw deformations tend to suffer from malocclusion, that is, their upper and lower teeth do not align or meet satisfactorily making oral functions (such as chewing, breathing and speech) difficult. A common example of the problems caused by malocclusion is given by a person with an "under-bite", who cannot (for example) eat an apple because their incisors do not meet, thus preventing them from biting effectively. Orthognathic surgery is performed when a patient's malocclusion is too severe to be resolved using orthodontic techniques. The operation involves cutting and repositioning either one or both of the maxilla (upper jaw) and the mandible (lower jaw). The results of orthognathic surgery can be quite dramatic, producing a new occlusion and radically transforming facial features. The surgery requires a great deal of commitment from the patient as the whole process, from orthodontic braces through to post-surgical completion, takes a minimum of two years, and at may involve some serious discomfort immediately following surgery.

Therefore it is clear that it is important for any such surgery to be performed with accuracy and care. Whilst there has been considerable refinement in the field of orthognathic surgery since its inception in the 1850's, problems still exist with the absolute accuracy of orthognathic surgery. In particular the face bows and articulators that are used in planning the surgery do not have the level of accuracy that surgical teams desire.

As previously mentioned, face bows are traditionally referenced to certain anatomical planes, these anatomical planes are the maxillary occlusal (MO) plane, and the axis orbital (AO) plane which are defined by touching three anatomical points on an individual's head. The anatomical points are; the head of the articulating joint of the mandible on both right and left sides and the left inferior orbital rim. However, these planes are inconsistent from person to person and using them as a datum introduces error into the modelling process. This problem is exacerbated by face bow manufacturers' incorrect assumption that the plane that the face bow references (the axis orbital plane) and the plane that the articulator is designed around (the Frankfort horizontal) are parallel. Another wrong assumption is that the inferior rims of the orbits are symmetrical

Normally, the face bow and the articulator are two separate instruments. Therefore there is a requirement to transfer measurements made using the face bow to the articulator. In making this transfer there is clearly an associated error which affects the model constructed in the articulator. This in turn affects the accuracy of the so-produced wax guide which has an impact on the accuracy of the operation. Thus it is clear that even a small error in the transfer of measurements from the face bow to the articulator can have a dramatic effect on the outcome of the orthognathic surgery.

Furthermore, as mentioned above, articulators are generally designed around the Frankfort horizontal plane, which in fact is not horizontal (i.e., it does not coincide with the true horizontal (TH) plane) when a person has their head in a "natural" position. The "natural" position for the head is defined as a head position which a person can adopt repeatedly with a satisfactory degree of accuracy. It is achieved by sitting a person so that they are level looking into their reflection in a mirror.

The erroneous principles relating to face bows and articulators routinely lead to final jaw structures that are up to 20° out of the intended position. This can result in errors in pre-surgical planning, and hence in post- surgical outcome.

The following patent publications are indicative of the general background in the field. A face bow designed for denture base or implant treatments is described in EP1 600 117 (WO 2004/082511 - 30.09.2004).

Articulators intended for measuring and or simulating jaw movements are described in US 4 034475, US 4909 737, US 6 109 917, and WO 1992/02192.

An apparatus for recording the movements of the lower jaw in relation to the skull and for transferring upper jaw models into an articulator correctly with respect to the skull is described in US 2005/0251066 A1.

WO 93/14715 describes a face bow which uses two bowl spirit levels one of which is rigidly attached to the face bow, and the other of which is used to define the anatomicocranial reference plane. It can only be levelled by moving the patient's head, thus ensuring that the plane identified by the face bow is horizontal, but eliminating any relationship between the face bow defined plane and the natural head position. The transfer of these measurements to an articulator requires a second bowl spirit level with a Cartesian grid.

The apparatus disclosed in WO 93/14715 can only reproduce an arbitrary orientation depending on the face bow. As the face bow is used with a standard articulator, the lateral tilt of the maxillary occlusal plane cannot be reproduced in patients with vertical and/or horizontal asymmetry of the jaw joints as occurs in normal subjects and as is common in patients requiring orthognathic surgery.

Mounting dental casts using face bow defined planes has been repeatedly shown to be inaccurate. There are numerous reports of inaccurate outcomes of orthognathic surgery that are traceable to the use of face bow defined anatomical planes.

A method for treating maxilla/cranial base to mandibular axis discrepancies in the temporomandibular joints of a patient such as caused by mandibular, temporomandibular dysfunction syndrome or developmental facial/dental deformities without performing an investigative open jaw joint surgical intervention is described in US 2005/0039759 A1. The method described there provides for an orthognathic surgical procedure to be planned by reliance upon a preliminary a craniomandibular orthopaedic repositioning method also described in US 2005/0039759 A1.

None of the documents cited above address all of the problems of the prior art as described herein.

Therefore, it is an object of the present invention to obviate, or at least mitigate, at least some of the drawbacks associated with the prior art.

Another object of the invention is to provide a device useful in preparing for a surgical procedure, especially for the purpose of registering, and modelling a patient's jaw structure to enable orthognathic surgery planning.

Further aims and objects of the invention will become apparent from a reading of the following description.

According to a first aspect of the present invention there is provided a bow and articulator frame apparatus comprising at least one means for recording a datum, wherein said datum is independent of anatomical planes.

In this description a bow and articulator frame is understood to mean a device for registering the positions and orientations of key cranial-facial points of an individual and for replicating the dimensions of a patient's jaw structure in three dimensions.

Advantageously the bow and articulator frame apparatus of the present invention allows cranial-facial measurements independently of anatomical planes. Anatomical planes vary from person to person, whereas a true vertical or true horizontal axis can be established repeatedly and accurately. Furthermore, as the face bow and the articulator frame are combined, the error associated with the transference of measurements from a face bow to an articulator is avoided.

According to a second aspect of the present invention there is provided an apparatus for accurately recording an individual's cranial-facial dimensions and replicating an individual's jaw structure, said apparatus comprising a bow and articulator frame and at least one means for recording at least one absolute datum, wherein the at least one means for recording the at least one absolute datum is removably attached to the bow and articulator frame.

Preferably the at least one absolute datum is a true vertical datum.

Optionally the at least one absolute datum is two perpendicular true horizontal datums. The means for recording the absolute datum may be a rotatably fixable plumb line.

The means for recording the absolute datum may be a rotatably fixable pendulum,

Both the plumb line and pendulum revert to the true vertical under the force of gravity, at which point they can be fixed in position.

The means for recording the true horizontal datums may be one or more spirit levels.

The means for recording the absolute datum or true horizontal datums may be an electrical or electronic goniometer or accelerometer.

The bow frame may be substantially U-shaped.

Preferably the apparatus further comprises a means for receiving the means for recording the absolute datum.

The receiving means may be a recess.

The apparatus may further comprise means for locating condyles.

The means for locating condyles may be attached to rods that are attached to the bow and articulator frame.

Preferably the rods are attached to the bow and articulator frame by adjustable fixing means. Preferably the adjustable fixing means is adjustable in three planes.

The adjustable fixing means may be a cup and ball lock.

Preferably the condyle locators comprise a transparent portion.

The condyle locators may provide a mount point for a mandible replica.

According to a third aspect of the present invention there is provided an apparatus for accurately recording an individual's cranial-facial dimensions and replicating an individual's jaw structure, said apparatus comprising a bow and articulator frame, a base plate adapted to receive the bow and articulator frame, and at least one means for recording at least one absolute datum, wherein the at least one means for recording the at least one absolute datum is removably attached to the bow and articulator frame.

Preferably the base plate comprises an aperture adapted to receive at least part of the means for recording the at least one datum.

Preferably apparatus further comprises a base unit adapted to receive at least part of the means for recording the at least one absolute datum.

According to a fourth aspect of the present invention there is provided a method for accurately recording an individual's cranial-facial dimensions, said method comprising the steps of: registering the cranial-facial dimensions of an individual; and recording a datum wherein the registered cranial-facial dimensions are referenced to an absolute datum. According to a fifth aspect of the present invention there is provided a method for accurately recording an individual's cranial-facial dimensions, and replicating an individual's jaw structure, said method comprising the steps of: registering the cranial-facial dimensions of an individual; recording a datum; replicating an individual's cranial-facial dimensions; wherein the registered and replicated cranial-facial dimensions are referenced to an absolute datum.

Registering the cranial-facial dimensions may comprise registering the maxillary occlusal plane.

Preferably the method comprises the further step of physically fixing the absolute datum.

Preferably the at least one absolute datum is a true vertical datum or true horizontal datums.

Preferably the maxillary occlusal plane is referenced to the true vertical datum or true horizontal datums.

Registering the cranial-facial dimensions may also comprise registering the condylar head positions.

Registering the cranial-facial dimensions may also comprise registering the position of the most anterior maxillary tooth. According to a further aspect of the present invention there is provided an apparatus for accurately recording an individual's cranial-facial dimensions and replicating an individual's jaw structure, said apparatus comprising a bow and articulator frame and at least one means for measuring at least one absolute datum, wherein the at least one means for measuring the at least one absolute datum is adjustably mounted to the bow and articulator frame such that its orientation can be adjusted.

The orientation of the at least one means for measuring at least one absolute datum may be adjustable in at least two orthogonal directions.

The at least one means for measuring at least one absolute datum may be rotatable.

The at least one absolute datum may comprise a true vertical datum and/or a true horizontal datum.

The at least one absolute datum may comprise two substantially perpendicular true horizontal datums.

The means for measuring the absolute datums may be one or more spirit levels.

The apparatus may further comprise condyle locators which are attached to rods, said rods being adjustably attached to the bow and articulator frame.

The rods can be attached to the bow and articulator frame by adjustable fixing means. The adjustable fixing means may be adjustable in three planes.

The adjustable fixing means can be a cup and ball lock.

The condyle locators may provide a mount point for a mandible replica.

The apparatus may further comprise a base plate configured to receive the bow and articulator frame.

According to a further aspect of the present invention there is provided a method for accurately recording an individual's cranial-facial dimensions, said method comprising the steps of: registering the cranial-facial dimensions of an individual; and determining a datum, wherein the registered cranial-facial dimensions are referenced to an absolute datum.

The method may comprise the further step of: replicating an individual's cranial-facial dimensions, wherein the registered and replicated cranial-facial dimensions are referenced to an absolute datum.

The maxillary occlusal plane may be referenced to a true vertical datum and/or a true horizontal datum.

The method may comprise the further step of fixing the absolute datum. The at least one absolute datum may be a true vertical datum or true horizontal datums.

Registering the cranial-facial dimensions may further comprise registering the condylar head positions.

Registering the cranial-facial dimensions may further comprise registering the position of the most anterior maxillary tooth.

It will now be described, by way of example only, various embodiments of the invention with reference to the following Figures, of which:

Figure 1a is a lateral (side) view of the articulator frame apparatus of the present invention in which the lower (mandibular) cast is mounted on a tray supported by the condylar head component of the articulator;

Figure 1 b is an anterior (front) view of the articulator frame apparatus of the present invention in which the lower (mandibular) cast is mounted on a tray supported by the condylar head component of the articulator;

Figure 2 shows the face bow adapted to measure the horizontal datum; and

Figure 3 is an isometric view of the bow and articulator frame apparatus of the present invention.

Referring to Figures 1 a and 1 b, there is shown an articulator frame apparatus at 20, featuring a maxillary (upper) cast 21 which is mounted on an upper maxillary cross member; and a mandibular (lower) cast 22 which is mounted on supports 23. The supports 23 are connected to the adjustable condylar components 24. The two condylar components 24 are mounted on components 25 which allow the adjustment of the position of the condylar components 24 in three orthogonal directions.

Referring to Figure 2, there is shown a face bow apparatus at 30 having an anterior bar 31 upon which a circular spirit level 32 is mounted. Lateral bars 33 connect to the anterior bar 31 by clamps 34 that allow each lateral bar 33 to be rotated and lengthened. Each lateral bar 33 terminates in a calibrated sliding scale 35 carrying a linear spirit level 36 and condylar connector 37. A bite fork 38 is connected to the anterior bar 31.

The apparatus as described in Figure 2 has two spirit levels which are adjustably mounted to the bow and articulator frame such that their orientation can be adjusted. Specifically, the orientation of the spirit levels can be adjustable in at least two orthogonal directions, the spirit levels being both slidable and rotatable. The spirit levels can be used to measure or determine an absolute datum.

Referring now to Figure 3, a bow and articulator frame apparatus is depicted at 1 and has face bow frame 2 connected to condyle rods 3 by cup and ball lock arms 4. The condyle rods 3 support the condyle locators 5 which allow a user to accurately locate an individual's condylar heads. The face bow frame 2 is substantially U-shaped and forms the main structural component of the device. The face bow frame 2 also comprises an additional structural component which forms a recess 6 into which a fixable pendulum 7 can be placed. The recess 6 protrudes from the bottom section of the U-shaped face bow frame 2 and is planar with said face bow frame 2. The fixable pendulum 7 Is located in the in the recess 6 when an individual is being registered. Attached to the face bow frame 2, via an adjustable upright 8, is a removable and adjustable bite fork 9 for placing in an individual's mouth. In use the bite fork 9 is covered in dental wax and is used to register the maxillary occlusal plane and the position of the anterior maxillary tooth.

The cup and ball lock arms 4 allow adjustability in three directions; that is they facilitate vertical, horizontal and lateral movement. The cup and ball lock arms 4 can be locked in a set position to locate and secure the condylar head locations.

In order to model a patient's jaw structure on an articulator, three specific pieces of anatomical information, which correspond to characteristic anatomical features, must be recorded. These are the orientation of maxillary occlusal (MO) plane, the condylar head positions, and the position of most anterior maxillary tooth (which lies on the MO plane).

The MO plane is determined by placing a flat plate over the surfaces of the maxillary teeth (in practice the flat plate is known as a "bite fork"). The MO plane is always registered in reference to another plane in order to orientate the jaws in space,

The condylar head positions are the anatomical hinging points of the mandible. On an average person these are at roughly the same point on either side of the skull. However, in patients with hemifacial microsomia (which affects half of the face) and other facial deformities these points can be asymmetrical.

The position of most anterior maxillary tooth is simply the furthest forward tooth of the top jaw. This is established using the bite fork and dental wax. In use, the bow and articulator frame apparatus is firstly used to register the positions and orientations of key cranial-facial points of an individual. When the registration is taken the MO plane is referred to a true horizontal or vertical axis by way of one or more spirit levels, the fixable pendulum that is acted on by gravity or by one or more electronic or electrical goniometers or accelerometers. The condylar rods are placed on the individual's condyles, thereby registering the condylar head positions. The registration taken is the true orientation of the MO plane when the head is in the natural position. Note that the angle of the bow and articulator frame can be rotated or deviated from normal as this is referenced to an absolute vertical. Therefore, any rotation or deviation from the natural head position is compensated for. When the user is satisfied that they have recorded the MO plane, the condylar head positions and the position of most anterior maxillary tooth, they fix the spirit levels or fixable pendulum in its effective orientation.

Once the MO plane and condylar head positions are taken, the face bow is removed and connected to the articulator frame. The condylar connectors of the face bow are connected to the condylar connectors of the articulator. The position of the condylar connectors of the articulator is adjusted in three-dimensions to centre the maxillary cast of the patient centrally. The position of the condylar connectors of the articulator and the position of the face bow are adjusted until the horizontal or vertical datum indicators show that the position of the MO plane reproduces its relationship to the natural head position.

All the required information to articulate the casts accurately and perform a model operation is now present. In contrast to the prior art, the apparatus of the present invention references the MO plane to reliably accurate, quantifiable and reproducible absolute, or true, plane.

In addition, again in contrast to the prior art, the present invention advantageously accurately reflects the position of an individual's condyles, and their relationship with the maxilla in order to predict the auto-rotation (opening and closing) of the mandible.

Note that it is important for the condylar locators to have three degrees of freedom so that they can locate a condylar head in any position within the three dimensional volume that is the side of an individual's face.

The condylar head locators allow a user to locate an individual's condyles. They condylar head locators are advantageously transparent for improved accuracy over conventional face bows. The transparent condylar head locators allow a user to better identify an individual's condyles and thus provide an improved degree of accuracy in measurement.

Also, the present invention employs adjustable spirit levels and may, for example, comprise a single planar spirit level that is not rigidly fixed to the face bow, but can be rotated around two orthogonal axes. Thus the spirit level can be levelled without moving the patient's head. This ensures that the invention of the present application enables the casts to be mounted on the articulator relative to, and reproducing the posture of, the patient's head.

The invention of the present application is used to mount casts by using the natural head position, thus eliminating the use of inaccurate face bow defined mounting planes. This cannot be done in the apparatus of the prior art which can only reproduce arbitrary orientation depending on the face bow.

The present invention is able to record the required anatomical information (MO plane orientation, condylar head positions and position of anterior maxillary teeth) and has the required adjustability to account for variable anatomy (variable height condyles, asymmetrical skeletal features etc.). In addition, the apparatus of the present invention requires a minimum number of operations by the user. This is in contrast to the bows and articulators of the prior art where increased adjustability has often led to over-complexity, making such devices difficult to use effectively.

Further modifications may be made without departing from the scope of the invention herein intended.

Claims

1. An apparatus for accurately recording an individual's cranial-facial dimensions and replicating an individual's jaw structure, said apparatus comprising a bow and articulator frame and at least one means for measuring at least one absolute datum, wherein the at least one means for measuring the at least one absolute datum is adjustably mounted to the bow and articulator frame such that its orientation can be adjusted.

2. An apparatus as claimed in claim 1 wherein the orientation of the at least one means for measuring at least one absolute datum is adjustable in at least two orthogonal directions.

3. An apparatus as claimed in claim 1 or claim 2 wherein the at least one means for measuring at least one absolute datum is rotatable.

4. An apparatus as claimed in any preceding claim wherein the at least one absolute datum comprises a true vertical datum and/or a true horizontal datum.

5. An apparatus as claimed in any preceding claim wherein the at least one absolute datum comprises two substantially perpendicular true horizontal datums.

6. An apparatus as claimed in any preceding claim wherein the means for measuring the absolute datums is one or more spirit levels.

7. An apparatus as claimed in any preceding claim wherein the apparatus further comprises condyle locators which are attached to rods, said rods being adjustably attached to the bow and articulator frame.

8. An apparatus as claimed in claim 7 wherein the rods are attached to the bow and articulator frame by adjustable fixing means.

9. An apparatus as described in claim 7 wherein the adjustable fixing means is adjustable in three planes.

10. An apparatus as described in claim 8 wherein the adjustable fixing means is a cup and ball lock.

11. An apparatus as claimed in claims 7 to 10 wherein the condyle locators provide a mount point for a mandible replica.

12. An apparatus as described in any preceding claim wherein the apparatus further comprises a base plate configured to receive the bow and articulator frame.

13. A method for accurately recording an individual's cranial-facial dimensions, said method comprising the steps of: registering the cranial-facial dimensions of an individual; and determining a datum, wherein the registered cranial-facial dimensions are referenced to an absolute datum.

14. A method as described in claim 13 comprising the further step of: replicating an individual's cranial-facial dimensions, wherein the registered and replicated cranial-facial dimensions are referenced to an absolute datum.

15. A method as described in claims 13 or 14 wherein registering the cranial-faciai dimensions comprises registering the maxillary occlusal plane.

16. A method as described in claims 13 to 15 wherein the maxillary occlusal plane is referenced to a true vertical datum and/or a true horizontal datum.

17. A method as described in claims 13 to 16 wherein the method comprises the further step of fixing the absolute datum.

18. A method as described in claims 13 to 17 wherein the at least one absolute datum is a true vertical datum or true horizontal datums.

19. A method as described in claims 13 to 18 wherein registering the cranial-facial dimensions further comprises registering the condylar head positions.

20. A method as described in claims 13 to 19 wherein registering the cranial-facial dimensions further comprises registering the position of the most anterior maxillary tooth.