U.S. patent application number 13/201142 was filed with the patent office on 2012-02-09 for determining position and orientation of a dental implant.
This patent application is currently assigned to Straumann Holding AG. Invention is credited to Frank Homann, Uwe Lawitschka, Benjamin Straub.
Application Number | 20120035889 13/201142 |
Document ID | / |
Family ID | 40750872 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120035889 |
Kind Code |
A1 |
Lawitschka; Uwe ; et
al. |
February 9, 2012 |
DETERMINING POSITION AND ORIENTATION OF A DENTAL IMPLANT
Abstract
Method for determining a position and an orientation of a dental
implant includes scanning a surface of a scan body connected to the
implant wherein a plurality of data points is determined which
correspond to positions of points that are located on the surface
of the scan body. The method further included reconstructing at
least three planes based on the data points, reconstructing
intersection information of the reconstructed planes, where the
intersection information includes the reconstruction of straight
intersection lines and of intersection points, and determining the
position and the orientation of the implant based on the
reconstructed intersection information.
Inventors: |
Lawitschka; Uwe; (Berlin,
DE) ; Homann; Frank; (Graefelfing, DE) ;
Straub; Benjamin; (Village-Neuf, FR) |
Assignee: |
Straumann Holding AG
Basel
CH
|
Family ID: |
40750872 |
Appl. No.: |
13/201142 |
Filed: |
February 11, 2010 |
PCT Filed: |
February 11, 2010 |
PCT NO: |
PCT/EP10/00854 |
371 Date: |
October 26, 2011 |
Current U.S.
Class: |
703/1 ;
702/150 |
Current CPC
Class: |
A61C 9/0053 20130101;
A61C 8/0001 20130101; A61C 13/34 20130101 |
Class at
Publication: |
703/1 ;
702/150 |
International
Class: |
G06F 15/00 20060101
G06F015/00; G06F 17/50 20060101 G06F017/50 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2009 |
EP |
09001983.7 |
Claims
1. A method for determining a position and an orientation of a
dental implant the method comprising: scanning a surface of a scan
body connected to the implant, wherein a plurality of data points
is determined, the data points corresponding to positions of points
that are located on the surface of the scan body; or loading a data
set having a plurality of data points corresponding to positions of
points that are located on the surface of a scan body connected to
the dental implant; the method further comprising: reconstructing
at least three planes based on said data points; reconstructing
intersection information of the reconstructed planes, the
intersection information comprising one or more straight
intersection lines and/or one or more intersection points; and
determining the position and the orientation of the implant based
on at least part of the reconstructed intersection information.
2. The method of claim 1, wherein determining the position and the
orientation of the implant comprises one, two or all of the
following: associating reconstructed planes with physical plane
areas on the surface of the scan body; associating reconstructed
straight intersection lines with physical edges of the scan body;
and associating reconstructed intersection points with physical
corners of the scan body.
3. The method of claim 1, wherein the positions of all points which
are used for the reconstruction of planes are located inside plane
areas on the surface of the scan body.
4. The method of claim 1, wherein the determination of the implant
position is based on at least one, two or three reconstructed
intersection points and at least one, two or three reconstructed
straight intersection lines and/or at least two, four, six or eight
reconstructed intersection points and/or at least two reconstructed
straight intersection lines, wherein at least two of said straight
intersection lines intersect each other.
5. The method of claim 1, wherein reconstructing the planes
comprises fitting a plane through a subset of the data points.
6. The method of claim 1, wherein determining the position and the
orientation of the implant is further based on the previously known
dimensions of the scan body and/or the implant and/or or other
parts in between the scan body and the implant, such as an adaptor
piece.
7. The method of claim 1, the method further comprising: generating
a digital model, wherein the digital model is three-dimensional,
and wherein the digital model models at least in part the implant
inside the mouth of a patient.
8. The method of claim 7, wherein the digital model comprises
modelling of neighbouring teeth next to the implant and/or
modelling of the gingiva (17) next to the implant (12).
9. The method of claim 1, wherein the scanning of the surface of
the scan body is performed while the scan body is located inside
the mouth of a patient or wherein the scanning of the surface of
the scan body is performed while the scan body is attached to a
physical model, wherein the physical model preferably reflects the
situation of part of a patients mouth.
10. A computing device for executing the method, and/or a computer
readable medium having stored thereon computer-executable
instructions for performing the method, of claim 1.
11. A scan body for determining a position and an orientation of a
dental implant, the scan body comprising: a bottom end with means
for connecting the scan body with the implant, wherein the scan
body is connected directly to the implant or wherein the scan body
is connected with the implant via an adaptor piece; and a top end
having a scan geometry wherein the surface of the scan geometry
comprises a plurality of plane areas, wherein from every possible
point of view there are at least three of said plane areas
(visible, wherein a possible point of view is located at the same
level or above said scan geometry, where a point of view is located
above said scan geometry in case the orientation of the scan body
is such that the top end points up and the bottom end points down
and the point of view is located at any position higher than the
topmost end of the scan body.
12. The scan body of claim 11, wherein the scan geometry is
polyhedral with one, two, three or all of the following features:
the scan geometry comprises at least two or at least three types of
plane areas having different orientation angels with respect to the
longitudinal axis of the scan body, wherein the longitudinal axis
of the scan body connects the top end and the bottom end of the
scan body; the scan geometry comprises at least two or at least
three types of plane areas, wherein the number of corners of the at
least two or at least three types of plane areas is different; the
scan geometry comprises at least one type of plane areas, where one
particular plane area of said type has a plurality of sides,
wherein all side lengths of said plane area are equal, or wherein
said plane area comprises at least two or at least three sides with
different lengths; and the scan geometry comprises a first corner
and at least three additional corners, wherein at least three of
the additional corners define a plane, and wherein the first corner
lies outside said plane.
13. The scan body of claim 11, the scan body further comprising a
coding associating the scan body with a particular type of implant
and/or with a particular type of adaptor piece.
14. The scan body of claim, wherein the coding is located such that
the coding is visible from every possible point of view, where a
possible point of view is located at the same level or sideways
above said coding, where a point of view is located sideways above
said coding in case the orientation of the scan body is such that
the top end points up and the bottom end points down and the point
of view is located at any position higher than the topmost end of
the scan body.
15. The scan body of claim 13, wherein the coding comprises one or
more ribs and/or channels and/or coloured rings.
16. The scan body of claim 11, wherein parts of the scan geometry
are light reflective and/or parts of the scan geometry are
non-light reflective.
17. The method of claim 2, wherein the positions of all points
which are used for the reconstruction of planes are located inside
plane areas on the surface of the scan body.
18. The method of claim 17, wherein the determination of the
implant position is based on at least one, two or three
reconstructed intersection points and at least one, two or three
reconstructed straight intersection lines and/or at least two,
four, six or eight reconstructed intersection points and/or at
least two reconstructed straight intersection lines, wherein at
least two of said straight intersection lines intersect each
other.
19. The method of claim 2, wherein reconstructing the planes
comprises fitting a plane through a subset of the data points.
20. The method of claim 2, wherein determining the position and the
orientation of the implant is further based on the previously known
dimensions of the scan body and/or the implant and/or or other
parts in between the scan body and the implant, such as an adaptor
piece.
Description
FIELD OF THE INVENTION
[0001] The invention concerns a method, which can be executed by a
computing device and/or can be stored in the form of computer
executable instructions on a computer-readable medium, for
determining a position and an orientation of a dental implant.
Further, the invention concerns a scan body for determining a
position and an orientation of a dental implant.
BACKGROUND
[0002] In the field of artificial tooth replacements where one
tooth or even several teeth have to be replaced, the corresponding
dental prosthesis are usually fixed in a patient's mouth via a
dental implant which is fixed (e.g. like a screw) in the bone of a
patient's jaw. Whereas there is usually plenty of space for placing
a dental implant between two neighboring teeth, for instance, the
situation is more tricky for the corresponding dental prosthesis.
In order to achieve a qualitatively and aesthetically good result,
a dental prosthesis has to fit almost perfectly between neighboring
teeth on one hand and the connection between the dental prosthesis
and the implant has to be very firm on the other hand, which can be
achieved if the connection has basically no play. Besides the final
location of a dental prosthesis within an oral environment it is
also beneficial to ensure that a dental prosthesis can actually be
inserted in between two neighboring teeth and, at the same time,
can be connected with the implant.
[0003] In order to achieve the above-mentioned tasks and
requirements, a possible solution is to determine the position and
the orientation of a dental implant with respect to neighbouring
teeth and the gingiva between these neighbouring teeth with a
certain precision. Typically, this determination has to be
performed in a situation, where the implant is not directly visible
(e.g. the implant is below the upper edge of the gingiva).
[0004] In the prior art, the position and orientation of a dental
implant is determined by attaching a scan body to the implant,
determining the position and orientation of the scan body (e.g.
with an optical scanning method), and determining the position and
orientation of the implant relative to the position and orientation
of the scan body. In some cases, the scanning procedure is carried
out with help of a model which represents the situation of a
patient's mouth or in other cases, the procedure is carried out
directly in a patient's mouth. In the state of the art, various
types of scan bodies with different geometrical properties are
used. Once the positions and orientations of a scan body are known,
this information is used to obtain the orientation and position of
said implant. Whereas dental implants and scan bodies can be
produced with high precision, the above-mentioned scanning
procedure can be less precise, particularly in situations where
distinctive parts, such as corners or edges, of a scan body are
only partly visible.
SUMMARY OF THE INVENTION
[0005] Therefore, a problem to be solved by the present invention
is to determine the position and orientation of a dental implant
with a high precision. At the same time, it is desirable that the
scanning procedure is relatively simple, especially in case the
scanning is performed directly in a patient's mouth where a
long-lasting scanning procedure should be avoided.
[0006] The method for determining a position and an orientation of
a dental implant in one embodiment is a combination of a scanning
procedure and a reconstruction procedure. During the scanning
procedure, the surface of a scan body which is connected to an
implant is scanned by determining a plurality of data points which
correspond to positions of points that are located on the surface
of the scan body. In another embodiment an already existing data
set, having a plurality of data points corresponding to positions
of points that are located on the surface of a scan body, is loaded
in order to perform the reconstruction of a position and an
orientation of a dental implant. Such a data set can be obtained by
a scanning method as is mentioned above or below. During the
reconstruction phase, these data points are used for reconstructing
at least three planes. From the reconstructed planes, intersection
information is determined. The intersection information comprises
straight intersection lines where at least two planes intersect
each other and/or intersection points where at least three planes
intersect each other or where a straight intersection line
intersects a plane or where at least two straight intersection
lines intersect each other. Using the above-mentioned reconstructed
intersection information, the position and orientation of the
implant can be determined. This determination can be based only on
part of the reconstructed intersection information or it can be
based on all available reconstructed intersection information which
allows an even higher precision since the position and orientation
of the implant is over-constrained. In a preferred embodiment an
intersection point is reconstructed directly from the at least
three reconstructed planes.
[0007] It is noted that the scanning points on the surface of the
scan body do not necessarily have to correspond to corners or
edges. Any point within a planar area can be used for the
above-mentioned reconstruction procedure which simplifies the
scanning procedure (e.g. scanning of a relatively moderate number
of points is sufficient). Preferably, only those points are used
for the reconstruction of planes that lie completely inside the
corresponding area (i.e. the points, used for the reconstruction of
planes, are not located at the corners or edges of the scan body).
For the determination of the position and orientation of a dental
implant only a minimum of nine points have to be scanned.
Typically, more than nine points are scanned, for instance between
twenty and one hundred points, in order to make sure that there is
a sufficient number of good quality points available for the
reconstruction phase. In principle, there is no upper limit of
scanning points. The time to perform a scan, however, increases
with an increasing number of points. Therefore, the number of
scanning points should be less than ten thousand or even less than
one thousand.
[0008] In a preferred embodiment, the determination of the position
and orientation of the implant comprises associating reconstructed
geometrical elements with physical geometrical elements of the scan
body. For instance, reconstructed planes can be associated with
physical plane areas of the surface of the scan body.
Alternatively, or in addition, reconstructed straight intersection
lines can be associated with physical edges of the scan body and/or
reconstructed intersection points can be associated with physical
corners of the scan body. It is noted that physical corners (and
also edges) are not perfect corners in a mathematical sense, but
are rounded corners (or edges) with a bending radius that is
typically less than 0.05 mm. It should be understood that the
reconstructed geometrical objects correspond to physical
geometrical objects of a part of the scan body that actually has
been scanned.
[0009] In order to be able to determine the position and an
orientation of the implant, a minimum of information is required.
One possibility is to reconstruct the position and orientation of
the implant using one reconstructed intersection point and one
reconstructed straight intersection line and/or two reconstructed
intersection points and/or two reconstructed straight intersection
lines which intersect each other. Further, it is possible to
determine the position of the implant based on the above-mentioned
minimum information plus additional information or to determine the
implant position directly based on at least, three reconstructed
planes. Preferably, the reconstruction of planes from the data
points is performed based on a sub-set of data points. In case
there are only three data points available, a corresponding plane
is simply calculated. However, in case there are more than three
points available for reconstructing a plane, it is possible to fit
a plane through the data points. For this purpose, a standard
fitting procedure can be used (e.g. a .chi..sup.2 based fitting
procedure). Further, the determination of the position and the
orientation of the implant is typically based on information
regarding the dimensions of the scan body and/or the implant and/or
other parts in between the scan body and the implant in addition to
the reconstructed geometrical information. Such a part which is
located between the scan body and the implant is, for instance, an
adaptor piece, which allows to use the same scan body with
different types of implants. Further, an adaptor piece can be used
to adjust the height of the scan body (e.g. in case the top of the
scan body is too far below the occlusal plane), or in some cases,
an adaptor piece is useful to adapt the angle of the scan body with
respect to the implant (e.g. in case the implant orientation is
considerably off vertical).
[0010] In another embodiment of the present invention, the method
for determining a position and orientation of a dental implant,
further comprises the generation of a digital/virtual model of at
least a part of the implant inside the mouth of a patient. The
digital/virtual model is preferably three-dimensional so that the
model can be viewed from different angles which is useful to study
the insertion of a dental prosthesis, for instance. The
digital/virtual model can further reflect information about
neighbouring teeth and the gingiva in the neighbourhood of the
implant if this information is available (e.g. also determined
during the scanning procedure or obtained from some kind of
database).
[0011] Typically, the scanning procedure is performed on a physical
model which has been made by a dentist and a dental technician,
respectively, and which reflects the situation in a patient's mouth
and comprises an implant analog which corresponds to an implant in
a patient's mouth. Usually, only the relevant part of the patient's
mouth is modelled. Making use of a physical model allows testing
the insertion procedure of a dental prosthesis, for instance, or
allows performing of the scanning in a dental laboratory where a
patient is not required to be available. Alternatively, the
scanning procedure can be performed directly in a patient's mouth
where the implant is already fixed in the bone of a patient's jaw
and the scan body is attached to the implant.
[0012] The invention further concerns a computing device that is
capable of performing the above-mentioned method steps. For this
purpose, a scanning device is typically connected to the computing
device and the scan data (e.g. data points) are directly
transferred to the computing device. However, it is also possible
to render the scanning information in a different way such as using
an IR transmission, a telecommunication system or transferring the
data with the help of a data storage means. Further, the invention
concerns a computer-readable medium having stored thereon, computer
executable instructions for performing the above-mentioned method
steps when said instructions are executed. Furthermore, there is
the possibility that the computing device and/or computer readable
medium is part of a scanning device.
[0013] Another aspect of the invention is related to a scan body
for determining the position and orientation of a dental implant.
The scan body has a bottom end that allows connecting the scan body
with an implant where the scan body is typically connected to the
implant via an adaptor piece but there are other embodiments where
a scan body is connected directly with an implant.
[0014] Further, the scan body has a top end with a scan geometry
that is scanned during the scanning procedure. The scan geometry is
characterized in that its surface comprises a plurality of plane
areas where at least some of said plane areas have to be partly
visible during the scanning procedure. This means that from every
possible point of view, at least three plane areas have to be at
least partly visible. In case the top end of the scan body points
upwards and the bottom end of the scan body points downwards, a
possible point of view is either located above the scan body or at
the same level (beside) of said scan geometry. The idea of these
visibility requirements is to ensure that at least three plane
areas are at least partly visible from any point above the level of
the scan geometry or at the same level of the scan geometry because
the scan information of these at least three plane areas is used to
reconstruct at least three planes which are needed in one
embodiment for determining the position and orientation of a
corresponding dental implant which is connected to the scan body.
Requiring the possibility that at least three planes of the scan
geometry are visible from the side is in particular useful in cases
when the location of the implant is determined with respect to
neighbouring teeth from the opposite side jaw of a patient (e.g.
when the teeth of the upper jaw and the teeth of the lower jaw
touch each other, to ensure that a patient will be able to properly
bite with a new dental prosthesis).
[0015] There are various types of scan geometries thinkable which
are typically polyhedral. The overall shape of a scan body is
approximately cylindrical where the longitudinal axis of the scan
body connects the center of the top end with the center of the
bottom end of the scan body. Since a plurality of plane areas are
required to be visible from different angles with respect to
longitudinal axis of the scan body, in a preferred embodiment of
the invention at least two of the at least three visible plane
areas are required to have a different angular orientation with
respect to the longitudinal axis, preferably there are even at
least three types of plane areas with different orientation angles.
Advantageously, the orientation angle with respect to the
longitudinal axis of at least one type of plane area lies within
the range of 30.degree. to 60.degree. or 40.degree. to 50.degree..
Further, there is preferably one type of plane area that is
perpendicular to the longitudinal axis of the scan body and/or
there is preferably one type of plane area that is parallel to the
longitudinal axis of the scan body. In a further embodiment, it is
required that there are at least two or three types of plane areas
with different numbers of corners and/or a different number of
sides and/or sides with different lengths, respectively. In another
preferred embodiment, the scan geometry comprises at least four
visible corners such that three of said four visible corners lie
within a plane and one of said four corners lies outside said
plane. The requirements regarding the number of types of plane
areas having different features and/or the number of visible
corners in a certain constellation help to ensure that the at least
three required plane areas are easily visible from every possible
point of view. Further, the above-mentioned requirements lead to
scan geometries with a number of planes that is typically above
eight or fifteen and/or a number of corners that is typically above
five or eleven, respectively. In principle, there is no upper limit
in the number of planes and corners respectively. In case the
number of planes/corners is large, however, the size of individual
planes will in turn become small, which can lead to a more complex
scanning procedure. Therefore, an upper limit of twenty, thirty,
fifty or one hundred plane areas and/or thirty or fifty corners,
respectively, is desirable. Further, the scan geometry comprises
different types of plane areas with different shapes, such as
triangles and/or squares and/or pentagons and/or more complex
shapes.
[0016] In another embodiment of the invention, a scan body
comprises a coding associating the scan body with a particular type
of implant and/or with a particular type of adaptor piece. For this
purpose, typically, ribs and/or channels and/or coloured rings are
located just below the scan geometry. The coding or the area where
a coding would be expected, has to be visible from every possible
point of view during the scanning procedure, where a possible point
of view is defined correspondingly to a possible point of view
regarding the scan geometry with the difference that the coding
does not have to be visible from directly above but only sideways
above the coding or scan body, respectively. In case the coding is
not visible during the scanning procedure, the coding information
or the respective identification information can be obtained
"manually" (e.g. by a user looking at the coding and looking up the
corresponding information that is represented by the coding).
Further, the coding can comprise letters and/or numbers and/or
other symbols.
[0017] The coding may also be part of the adaptor piece and refer
to a particular implant which means that by scanning the coding on
the adaptor piece the e.g. type or size of the implant can be
determined.
[0018] In a further embodiment of the present invention, the scan
geometry of the scan body is such that some parts of the scan
geometry are light reflective and/or some parts of the scan
geometry are non-light reflective, for instance, only a part of a
plane area is light reflective and the rest of the plane area is
non-light reflective (e.g. the inner part of a plane are is light
reflective whereas the border area of a plane area is non-light
reflective). In this way, it is possible to simplify the
recognition of plane areas during the scanning/reconstruction
procedure. Alternatively, it maybe sufficient to have different
regions with different reflection coefficients in order to allow an
easy detection of the plane areas.
[0019] The invention also refers to a scan body in combination with
a set of adaptor pieces, with which the scan body can be attached
to different implants by different adaptor pieces. Preferably each
adaptor piece corresponds to a particular implant and for different
implants different adaptor pieces are provided. Preferably each
adaptor piece is provided with a coding that can be optically
scanned, wherein the coding allows to identify the type of implant
or the size of the implant which corresponds to the adaptor piece.
An adaptor piece is typically fixed on top of an implant with help
of a screw or a catcher. If a permanent connection is desired, the
adaptor piece can also be glued to the implant.
BRIEF DESCRIPTION OF THE FIGURES
[0020] Further aspects of possible embodiments of the invention
become clear from FIGS. 1, 2a to 2e and 3a to 3f:
[0021] FIG. 1 shows the overall situation when a position and
orientation of a dental implant is determined.
[0022] FIGS. 2a to 2e show various embodiments of scan bodies.
[0023] FIGS. 3a to 3f illustrate steps related to the determination
of a position and an orientation of a dental implant.
DETAILED DESCRIPTION
[0024] In FIG. 1, a possible set-up for determining a position and
an orientation of an dental implant 12 is illustrated. The set-up
either reflects the situation in the mouth of a patient or reflects
the situation in a model of a patient's mouth. An implant 12 is
fixed in the bone 18 of a jaw. Above the bone 18 there is layer of
gingiva 17. A scan body 11 is attached to the implant 12 via an
adaptor piece 13 which is located partly above the level of the
gingival 17. To the left and to the right of the scan body 11, two
neighbouring teeth 16 are illustrated. However, in some cases,
there is only one neighbouring tooth 16 next to the implant 12. It
should be noted that the longitudinal axis 15 of the scan body 11
and/or the implant 12 and/or the adaptor piece 13 is not
necessarily exactly vertical or is not exactly perpendicular to the
surface of the bone 18, respectively. Further, when scanning the
scan geometry 21 of the scan body 11, the point of view 14 of the
scanning device is not necessarily located exactly above the scan
body 11, but the point of view 14 can be located sideways and/or at
the side of the scan geometry 21 of the scan body 11. In order to
be able to achieve good scanning results, the topmost part 23 of
the scan body 11 lies at or just below the level of the occlusal
plane 19 which is defined by the height of the neighbouring teeth
16. Typically, the distance between the surface of the bone 18 and
the occlusal plane 19 is about 9 mm to 11 mm which means that the
scan body 11 should have a length less than these values. If
however, the scan body 11 is too short (to low with respect to the
occlusal plane 19), it is possible to extend the length by using a
suitable adaptor piece 13. On the other hand, if a scan body 11
would be too long (e.g. would lie partly above the occlusal plane
19) then it would likely to be out of the scan corridor, which is
adapted to scan teeth or residual tooth portions. The typical size
of a scan corridor is 15-20 mm.times.15-20 mm with a length between
25-50 or 30 to 45 mm. The scan corridor may have a square or
rectangular cross section (in a section perpendicular to its
length).
[0025] The scenario, illustrated in FIG. 1, is only one
possibility. There are many other scenarios possible, too. For
instance, there could be two teeth missing, which would result in a
larger gap in between the two neighbouring teeth 16. The latter
scenario would typically comprise two dental implants 12, of which
the relative position and orientation of the implants 12 to each
other could be determined using two scan bodies 11, where each one
would be connected to one of the two implants 12. Other scenarios
could comprise three or even more implants 12 and several scan
bodies 11, respectively.
[0026] FIGS. 2a through 2e show several embodiments of scan bodies
11, each scan body 11 having a bottom end 22 which can be attached
to an implant 12 or an adaptor piece 13, and a top end 23 which
comprises a scan geometry 21. The scan geometry 21 comprises
several plane areas 24 which have corners 25 and sides 26 where the
sides 26 can be also considered as edges 26 of the scan geometry
21. In the particular case of FIG. 2a, the scan geometry 21
consists of six squares and six triangles as plane areas 24.
However, there are other types of scan geometries 21 possible, such
as is illustrated in FIGS. 2d and 2e, for example. The scan
geometry 21 of FIG. 2d consists of three types of plane areas 24,
namely, one square plane area 24, four pentagonal areas 24 of a
first type and four pentagonal areas 24 of a second type. In case
of FIG. 2e, the scan geometry 21 comprises two types of plane areas
24, namely, ten triangles and six pentagons. In FIGS. 2b and 2c,
the scan body 11 of FIG. 2a is shown with additional codings 27
just below the scan geometry 21, but it would be also possible for
the coding 27 to be part of the scan geometry 21. In FIG. 2b, the
coding 27 is a single channel surrounding the scan body 11 and in
case of FIG. 2c, the coding 27 consists of two ribs. As for the
scan geometry 21, the coding 27 or the area where one would expect
a coding 27 (e.g. in case there is a void coding 27) has to be
visible from every possible point of view 14, such that, during the
scanning procedure, the scan body 11 can be identified by
scanning/recognizing the coding 27.
[0027] In FIGS. 3a to 3f, several steps of the scanning procedure
and data processing are illustrated. FIG. 3a shows an exemplary
plane area 24 which is scanned by taking an array of (data) points
31. The points 31 which lie inside the plane area 24 (possibly also
including the borders), are used to reconstruct a plane 32.
Typically, plane 32 is reconstructed with help of a fitting
procedure which can include accepting and rejecting of data points
31 using certain selection criteria (e.g. points 31 which are too
far from a first estimate of plane 32 are rejected). If two planes
that intersect each other have been reconstructed, a straight
intersection line 33 can be determined as is shown in FIG. 3c.
Further, in case there are two straight intersection lines 33 which
intersect each other, an intersection point 34 can be reconstructed
as is illustrated in FIG. 3d. An intersection point 34 can also be
determined from the intersection of three, or. even four, five or
more, planes 32 with those planes 32 corresponding to plane areas
24 neighbouring a corner 25 to which the intersection point 34
corresponds. The latter case does not require the explicit
reconstruction of straight intersection lines 33, and therefore the
step, illustrated in FIG. 3c, may be omitted. Implicitly, the
reconstruction of one intersection point 34, requires at least
three reconstructed planes 32 or three plane areas 24,
respectively. In FIG. 3e, the correspondence of physical
geometrical elements and reconstructed geometrical elements is
determined. For instance, intersection point 34 corresponds to
corner 25 and part of straight intersection line 33 corresponds to
side/edge 26. Further, part of plane 32 corresponds to the physical
plane area 24. Using this correspondence information, a
digital/virtual model of the plane area 24 can be built. The
virtual plane area 24' consists of several virtual corners 25'
which correspond to reconstruction intersection points 34 and of
several virtual sides 26' which correspond to parts of
reconstructed straight intersection lines 33. In this way, it is
possible to create a model of the whole scan geometry 21 or even to
create a digital/virtual model of the whole scan body 11, the
dental implant 12, the adaptor piece 13 and even of part of the
patient's mouth, respectively. In the latter case, however,
additional scanning information and/or additional stored
information (e.g. coming from a database) is necessary.
[0028] The procedure, described in context with FIGS. 3a to 3f, can
additionally involve one or more optional steps which are described
in the following. After a set of points 31 has been obtained by
scanning the surface of a scan body 11, the surface of the scan
body can be approximately described using finite elements such as
triangles, for instance (in the following the example of triangles
is used, but in general other finite elements than triangles such
as rectangles, quadrangles or other polygons may be equally used).
The finite elements can be used to form a mesh (based on the set of
points 31) which describes the surface of the scan body. Each
triangle has three corners, and the orientation of each triangle is
described by a normal vector of the plane in which the triangle
lies. In a consequent step, a person/user can explicitly select a
plane area 24 of the scan geometry 21 by clicking on a triangle
which lies in said plane area 24. This kind of user selection helps
to associate a detected plane area with a real plane area 24 of the
scan geometry 21. In particular, such a user selection of a plane
area 24 is helpful in case said plane area 24 is a single plane
area 24 at the top end 23 of the scan geometry 21, as is the case
for the scan bodies 11 shown in FIGS. 2d and 2e. In this case the
normal vector of said plane area 24 is parallel to the longitudinal
axis 15 of the scan body 11. Since this particular type of plane
area 24 allows a precise determination of the position of the top
end 23 and the orientation of the scan body 11, this plane area 24
helps to determine the position and orientation of a dental implant
12 with a high precision. In addition, the user selection of said
particular type of plane area 24 can simplify (and therefore speed
up) the determination of position and orientation.
[0029] Upon a user selection of a triangle in the further
processing preferably only those triangles are used which are
within a sphere with a radius between 2 and 3 mm since in this way,
neighbouring triangles, which are located inside the sphere,
ideally describe the entire surface of the scan geometry 21, which
can be taken into account when determining the position and
orientation of the corresponding plane area 24, scan body 11 and
implant, respectively. More specifically, the (visible) plane areas
24 of the scan geometry 21 can be described by considering all
triangles inside the above mentioned sphere and by grouping the
triangles according to their orientation (normal vectors). Those
triangles which have similar normal vectors can be considered to
describe the same plane area 24 and therefore belong to the same
group.
[0030] Thereafter, for each group of triangles a plane 32 can be
reconstructed (e.g. by performing a fitting process of a plane to
the corners of the triangles, i.e. the points of the mesh) that
corresponds to a plane area 24 of the scan geometry 21. The
reconstructed planes 32 can then be used to reconstruct
intersection points 34 corresponding to corners 25 of the scan
geometry 21. Three such reconstructed planes 32 can be used to
determine one intersection point 34. Triangles (or corners of
triangles) of the finite element description of the surface of a
scan geometry 21, which correspond to parts of the surface that are
located close (e.g. closer than 0.1 mm) to the edges or corners of
a plane area 24, are preferably not taken into account in the plane
32 fitting procedure, because these triangles might be tilted or
shifted up or down with respect to the corresponding plane area 24,
which could result in a less precise fitting result. For example
only the triangles or corners of triangles may be used which are
located within circle around a mean location of triangles or
corners of triangles of a group. The radius of the circle is chosen
sufficiently small such as to ensure that only triangles or corners
of triangles which are on the same plane 24 are taken into account
for one plane fitting procedure. It is noted that even though a
single triangle is sufficient to define/determine a plane 32
corresponding to a plane area 24 of a scan body 11, it is
preferable to take the average over multiple triangles (e.g. more
than 100, 200, or 500 and/or less than 1000 or 10000) for the
definition of a plane 32 in order to increase the precision of this
determination.
[0031] After the reconstruction of intersection points 34 and the
association of the reconstructed intersection points 34 with
physical corners 25, there is the possibility to compare the
spatial positions of the reconstructed intersection points 34 with
the expected spatial positions of points which, for instance, can
be part of a digital model of a scan body. The latter comparison
can be performed just as a consistency check, or it can be used for
applying corrections to the position and orientation of a scan body
11 or an implant 12, respectively.
[0032] In case that the longitudinal axis of the scan body can be
determined otherwise (e.g. from a global match which tries to fit
the entire scan body into a scanned data set) this longitudinal
axis can be used for verifying that the user has selected a
triangle on the top plane area of the scan body by checking the
position of the triangle with respect to its location along the
longitudinal axis. If it is not almost on the most outward position
along the longitudinal axis, an error message may be provided
indicating that the user has not selected a triangle on the top
plane area of the scan body.
[0033] In order to obtain a more detailed picture of the dental
environment or a more complete virtual model, respectively, the
scanning procedure can involve scanning of a scan body 11 within a
dental environment from different points of view 14 and different
perspectives (e.g. a top view and two side views), respectively.
The information of multiple scans can be combined by identifying
overlapping regions (e.g. of the scan body 11) and by merging
information derived from individual scans. In this way, a basically
complete three dimensional model can be created, which can be
rotated and looked at from every thinkable point of view. Making
use of combined data of different scans typically leads to more
reconstructed straight intersection lines 33 and possibly also to
more reconstructed intersection points 34 corresponding to physical
corners 25. Hence, the number of determined corners 25' can be more
than one, typically more than three, five or seven. The plurality
of determined corners 25' can then be used to be fitted into a
model of the scan body 11 or its corners 25 respectively, in order
to determine the position and orientation of a corresponding dental
implant 12.
[0034] It is noted that for the reconstruction of straight
intersection lines 33 and of intersection points 34, it is not
necessary that physical corners 25 or physical edges 26 are visible
during the scanning procedure. For the reconstruction of plane 32,
it is sufficient that at least three data points can be taken which
lie inside one particular plane area 24. Therefore, the scanning
and reconstruction procedure also works well if the data points 31
are not located closely to physical corners 25 or edges 26.
Moreover, since no points on corners 25 or edges 26 are required
for the determination of the position and the orientation of an
implant 12, it is possible to take less points 31 during the
scanning procedure, which allows the scanning to be performed
faster. Further by reconstructing the planes data points can be
taken into account that actually lie on the corresponding plane
areas of the scan body. Trying to find corners or edges of the scan
body is less precise since there may be only few data points which
actually lie on such edges or corners. In summary, the
determination of the position and orientation of a dental implant
12 of the present invention is more reliable and at the same time
allows for a simpler scanning procedure.
[0035] The determined position and orientation of the implant can
be used for modelling an abutment to be fixed on the implant or any
other part to be fixed on the abutment or the implant such as a
bridge, crown or the like. Also the insertion direction of the part
to be fixed onto the implant or abutment can be determined from the
information obtained.
* * * * *