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Title:
EQUIPMENT FOR DIRECT DETECTION OF DENTAL DIE FROM THE MOUTH OF A PATIENT
Document Type and Number:
WIPO Patent Application WO/2008/050373
Kind Code:
A1
Abstract:
Device for direct survey of dental prints of a patient by means of automatic scanning x,y in the plane of the dental arch, using photogrammetrical o laser methodologies, and in which the position of the teeth is preventively individuated by the device itself by means of linear measurers, on the base of the data obtained from the first manual scanning executed by the physician who individuates the teeth position, viewing them on the monitor, while in the following phase of automatic scanning the same is guided by the previous process of individuation executed by the physician acted by motors, being the same device placed on an arm fixed to the dental arch (upper or lower) of the patient.

Inventors:
MOSCHELLA DEMETRIO (IT)
DANIELI GUIDO (IT)
NUDO PAOLA (IT)
GIUZIO FRANCESCO (IT)
Application Number:
PCT/IT2007/000755
Publication Date:
May 02, 2008
Filing Date:
October 29, 2007
Export Citation:
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Assignee:
DANIELI GIOVANNA (IT)
FRAGOMENI GIONATA (IT)
GATTI GIANLUCA (IT)
COLACINO FRANCESCO (IT)
MUNDO DOMENICO (IT)
PERROTTA PAOLO SALVATORE DOMEN (IT)
PERROTTA ANDREA (IT)
MOSCHELLA DEMETRIO (IT)
DANIELI GUIDO (IT)
NUDO PAOLA (IT)
GIUZIO FRANCESCO (IT)
International Classes:
G01B11/24; A61C9/00; A61C13/00
Domestic Patent References:
WO2006016389A12006-02-16
Foreign References:
US20060154198A12006-07-13
EP0305107A21989-03-01
US5343391A1994-08-30
EP0919784A21999-06-02
US5416538A1995-05-16
US20040130729A12004-07-08
Attorney, Agent or Firm:
PERROTA, Aldo (Soverato, IT)
Download PDF:
Claims:

Claims:

1. Device for direct detection of dental die from the mouth of a patient by means of x,y automatic scanning in the plane of the dental arch, using photogrammetrical o laser methodologies, characterized by the fact that in said device the position of the teeth is preventively individuated by the device itself by means of linear measurers, on the base of the data obtained from a first manual scanning executed by a physician who individuates the teeth position, viewing them on the monitor, while in the following phase of automatic scanning the same is guided by the previous process of individuation executed by the physician acted by motors, being said device placed on an arm fixed to the dental arch (upper or lower) of the patient.

2. Device for direct detection of dental die from the mouth of a patient according to claim 1 characterized by the fact that said device is hooked to a self-balanced system with 5 or 6 degrees of freedom, in order to be able to follow the eventual movements of the head of the patient.

3. Device for direct detection of dental die from the mouth of a patient according to claim 1 characterized by the fact that said device uses a structured light system composed by projector of any type able to project and focus images on surfaces of small dimensions, and a system for detecting images whose focal axis is oriented in an a priori known way and by one or more than one mirrors fixed to the image detection system.

4. Device for direct detection of dental die from the mouth of a patient according to claim 1 characterized by the fact that said device will be moved, with respect to the patient's mouth, by motors allowing to move the scanning element on the dental arch plane along two axes, possibly perpendicular, driven by suitable prismatic joints, through a double threaded bar and female screw coupling, moved by step

motors, while the position within the plane will be supplied by linear measuring devices, placed at sides of the bars, in order to detect the exact position of every tooth during navigation, while the position will be controlled by motors and eventually encoders during robotized scanning.

Description:

1

Equipment for direct detection of dental die from the mouth of a patient

Technical field of invention.

Nowadays, in order to realize dental prosthesis it is necessary to execute a survey of the arch by means of die. Afterwards it is usually brought to another laboratory, scanned and analyzed to transfer it to CAD environment. The whole process needs time, sometimes entire weeks, to obtain the prosthesis to implant to the patient. Nevertheless, the applications which use technologies able to shorten the period of elaboration are still very few.

The systems developed up to now use different methodologies for realizing a 3-D model of the dental apparatus of the patient, obtaining usually medium results by reason of low resolution, of modest acquisition velocity and lack of sterility of the device. The more frequently used systems are based on multi image photogrammetry, laser scanning, structured light and sectioned light. The accuracy of the measuring system is a fundamental aspect. In the sistems previously listed, the structured light followed by the multi image photogrammetry has the best precision; laser scanning produces shadows during the model analysis which leads to out of focus images with a very low resolution. Finally, the sectioned light presents ambiguity when it is necessary to analyse a model which has variations of height. The second factor which obstacles the diffusion is the time of data acquisition and elaboration. The multi image photogrammetry needs different steps to elaborate the image while the other methods present lower time.

Recently, during the development of all these methodologies, the attention was devolved to the devices capable to represent the structure of the entire dental arch of a patient in CAD environment. In fact, a recently developed system has an intraoral probe for the 3 - D scanning of a tooth. This probe detects and records the detected images in

a computer. In this latter the comparison between the non-distorted model projected by the probe and the distorted one reflected from a specific area is made. To avoid any type of ambiguity the process is repeated several times; moreover, during the acquisition the patient must remain immobilized in order to avoid signal losses and, hence, data losses. The system results efficient but presents important limits which must be overcome: the length of the analysis process and the fact that the system does not preview self- balancing.

The present invention tries to overcome the limits previously described defining a structure which is more simple from the mechanical point of view and proposes time of elaboration and realization of 3 -dimensional model inferior to those proposed as well as major accuracy.

Actually, the new method of direct rilevation of 3-D dental die is proposed. It uses the structured light, simple and rapid method of form data acquisition, characterized by a data elaboration process relatively fast, low costs, while the accuracy of the final result is very high. In particular, the data acquisition system could be constituted by passive self-balancing arm or by a combination of constraints (turning chair, mounted on wheels and with adjustable height, which guarantees anyway the 6 degrees of freedom (a lower number of degrees of freedom would limit unusefully the patient movements), fixed on the platform made solid with the dental arch by means of a suitable mask, put in contact with the teeth by means of three or more than three points of contact with the teeth (for example, a steel wire) and fixed to the patient head (or chin) by means of belts and linked to a minisystem of detection of the shape of the teeth which can be moved both in active and passive ways inside the patient mouth, in order to allow both the identification of the position of the dental arch with respect to the x,y reference system

of the minisystem of detection, operated by the physician, and the automatic moving guided by the previous process of identification.

Such minisystem could be constituted by an LCD projector or other luminous source focused in a way to project the image onto a very small surface, from one or more than one mirror suitably positioned and from at least one TV camera in a direct way or by means of optical device eventually assisted by optical fibres, which observation direction is inclined of a certain angle with respect to the projection direction. Projector, mirror and TV camera must be fixed between each other and movable both in active and passive modes with respect to the plane of dental arch to be examined, with micrometrical control of the position in the plane as specified previously. An angular control of the whole system could be added subsequently to such control in the plane, in order to amplify the observation capacity of this system.

In alternative, nevertheless, the detection system (the head) can be constituted by any other form detection system based on the usage of laser or stereophotogrametrical techniques, which is moved inside the mouth in an automatic or also manual way, but, anyway, capable to know its position in terms of relative coordinates. Two of these constraints, mutually orthogonal for semplicity, but not necessarily such, must lay on the last link of the self-balanced system which must be linked by means of opportune elements to the dental arch of the patient, in such a way that the eventual movements of the head of the same patient don't modify the relative position of the examined element with respect to the dental arch. Description of the preferred embodiment.

In particular the detecting system will be composed, in the preferred realization, by four microcameras which observe the scene from different angles directly or by means of optical devices, eventually assisted by optical fibres and connected to a PC. An

opportune system of lenses, fixed to the projector and to the detecting system, will permit concentration and focusing at a close distance of the projected light, while the mirror or the mirrors of the light deflection will be still fixed to the whole structure. Alternatively, the same structure could be realized using optical fibres coupled with TV cameras and projector.

Figure 1 describes a representative scheme of the various elements constituting one possible detection system. To allow to the system to be always positioned in a known position with respect to the dental arch of the patient it is fundamental that it is placed at the end of a cinematic self-balanced chain with 6 grades of freedom (in our case depending from the choice of the constraints of the patent application CS2006A00007, deposed on the 19/04/2006), on a plane fixed to the same dental arch (1) (upper or lower), by means of a mask (Figure 2) blocked with strap to the head or to the chin, fixed by means of metal wires to the top of the teeth or by means of special gum supports on the gum surfaces and blocked with strap to the head or to the chin individuating the plane parallel to the same dental arch. The frontal part of the mask is rigidely linked to the 7° link of the self-balanced structure. Naturally, such cinematic self-balanced chain could be substituted by another mechanism or avoided at all, simply constricting the patient to the immobility.

Figure 3 describes one possible intraoral system, in which TV cameras are placed directly on the final element. The system of reading from the dental arch is placed on the last link of the robotic arm. The position of the four TV cameras (2) is constrained by the clearance of the mirror dimensions (3). The ray reflected from one or more than one mirrors covers a surface of nearly 1 cm 2 , in order to allow the scanning of at least one tooth a time.

The TV cameras must guarantee non-interference with the beam of projected light and an optimal resolution for the registration of the various images. It leads to the fact that the central axis of the focal cone of every TV camera must be not on the tooth surface, but nearly at a half height of the tooth itself (Figure 4) to guarantee a complete covering of the tooth to examine evidencing also the gum region.

Figure 5 the optical detecting system is described: the projector (4) receives in input a signal from the PC and projects a beam of light towards the biconvex lens (5). The ray is directed towards the mirror (7) by means of an opportune biconcave lens (6), which allows to follow the entire beam of light exactly onto the tooth (8) to examine. The b/w pattern of lines having different thickness and direction, is distorted by the tooth shape, allowing the reconstruction of the shape both of the tooth and of the gum. This is necessary for the reason that the observed deformation of the lines, otherwise parallel, permits, by means of a software opportunely calibrated, to correlate displacement of each line from its projection direction with the local depth of observed point. During the projection of the lines, the four TV cameras registrate four images which after being sent to a PC are elaborated by means of software obtaining the visualization of the tooth model examined in a CAD environment.

After having scanned the first tooth it is passed to examine step-by-step the entire dental arch of the patient. All the process is realized thanks to the interposition between the self-balanced system of 6 degrees of freedom and that one dedicated to the detection of the single tooth shape, of a further system which allows the moving on the plane of the dental arch driven by threaded bars and by screw-mother screw coupling, which permits its moving long two orthogonal axis, using, for example the scheme described in Fig. 6 for the passage from the Navigator mode to a Robot mode for a prismatic joint and vice versa. In particular, in Figure 7, every of the two mother screw is divided into

two halves (9), so that when they are open, the screws are free and it is possible to move freely the intraoral system in its plane, allowing, hence to the physician, to observe the entire dental arch. When they are closed the system moves itself only under the engines commands to scan sequently every tooth so as previously individuated by the physician. The system will also be able, from the analysis of the detected data, to correct the position of the scanner to center every tooth, avoiding so eventual imprecision of the physician. The opening and the closure of the mother screws are actuated by a cam system (10), which rotation (clockwise and counterclockwise direction) controls blocking and the unlocking of the mother screws. The two threaded bars rotate thanks to the presence of two step motor (11) placed in an opportune mode on the two lower ends while the control of the angular position of the screws is realized by two digital encoders (12) placed on the other end of the mother screws. Naturally, it will be possibile to guarantee the moving x, y also by the different system of threaded bars and mother screw, in which the mother screw is a whole piece and is placed always on the screws, and the cam system described previously is simply used to block the rotation of the mother screw and to permit the traction of the scanning system. Anyway, it will also be possible to use a system in which the motion is commanded by a system of cables and pulley on every axis. As far as position control on the plane x,y in the navigator mode is concerned it is executed by two linear measuring devices (13) having zero signal and placed on the side of the mother screws (Figure 8).

To execute the scanning of the whole dental arch, the dentist identifies the position of the teeth using the system in the navigato mode. After that, placing the intraoral system to the starting point, the x, y robot moves itself to execute automatically the exam of the dental arch.

Once the scanning is over it is possibile to reconstruct the entire dental arch with the PC. The process needs a post-processing time to eliminate the excessive data and obtain as final result the model of dental arch in 3 - D. Now the dentist has all the necessary information to establish optimal form and position of various prosthesis or of the various prosthesis devices in order to obtain the desired result. The data relative to the 3-D model will be delivered to the numerical control cutter which will produce different prosthesis and eventual models. In such a way the prosthesis can be implanted in the oral cavity of the patient even on the same day, if the numerical control cutter are placed near, and anyway in much more short periods of time than those realizable now. During the whole phase of detection, the mouth of the patient must be well-open and to do it the opening systems already present in commerce can be used. All this permits to execute the exam in a limited but accessable space, especially where the space between one and another arch becomes very small. In fact, about dimensions, the structure results rather small, having a maximum width of 3.5 cm and a height of 1.8 cm. This system should respond to the space available in the oral cavity. And dimensions can be further reduced using telescopical or optical fibres. Besides, the patient, during the scanning process is not constrained to stay immobilized; in fact, the robotic arm moves itself together with the head of the patient.

To execute the test of the dental die the support of the TV cameras must be necessarily introduced inside the oral cavity; it implies that the system can be sterilized. For this reason the support must be constructed in metal material that has to be sterilized at high temperatures. The problem for the TV cameras which will be extracted from their placements does not exist, while the video cameras may be taken away, and repositioned wrapped in single use sterile plastic bags to prevent cameras and relative lenses from being contaminated.

The present invention aims to overcome the limits of the previous methodologies. The main constraint is time. It can be noticed how by means of this system of scanning the time of detecting is rather small because scanning is done only one time for every tooth to cover the whole dental arch.

As far as the foreseen precision is concerned it is observed that even if the actual resolution of the TV cameras (which will increase with time), the representation of the dental surfaces by means of the clouds of points long the lines placed on the distance of 100 μ is still possible. This density can be increased by repeating the projection after a shift of the lines (with standby time of some millisecond) and repeating again the scannings after the displacement of the heads of few steps (5 μ for motor step), obtaining the desired precision and in any event greater than what required by the American Association of the Dentists (40 μ).