A method of producing a dental restoration fastened to a jawbone
Description
Field of the invention
The present invention relates to a method of producing a tooth-like dental restoration fastened to a patient's jawbone, of the kind specified in the preamble of claim 1. Such a method comprises the prior art steps of fastening an implant screw in the jawbone and applying a pin to the implant screw for providing a means adapted to indicate the direction of the screw, and thereafter taking an impression and making a plaster model. In its head the implant screw is provided with an open cavity constituting a seat for supporting an abutment.
Background of the invention
When a three-dimensional object is to be given a shape having a concave zone the machining thereof may pose a problem since the tool used for the machining must be smaller (have a smaller radius) than the radius of curvature of the concave zone. However, the size of the tool cannot be below a certain minimum since the tool must have a reasonable structural strength. Consequently, the smallest feasible tool diameter will be a limiting factor for the concave shapes that can be made by the tool.
When the object to be machined is a coping for an artificial tooth (dental restoration) and this coping is to have an internal concave shape with a small radius of curvature, it will not always be possible to perform the necessary machining. Furthermore, if the coping is made of ceramics or some other hard material, the rate of wear for the tool may become unacceptable, especially when the tool to be used for the machining has (or must have) a small diameter. When the object to be machined is an abutment for an artificial tooth, the same problems as mentioned above may of course be encountered if the abutment is to be provided -with e.g. a narrow internal cavity or bore for a fixing screw used to attach the abutment to an implant screw. Consequently, such cavity or bore is therefore preferably a preformed one, so that the abutment will require only external machining. Tools with much larger diameters can then be used for the machining, which of course is favourable from a wearing point of view.
Objects of the invention
When the tooth-like dental restoration to be produced requires a coping (e.g. for covering the mouth of a through bore in an abutment), a first object of the invention is to avoid the necessity of machining the interior of the coping, so that only exterior surfaces on the coping have to be machined.
A second object of the invention is to avoid the necessity of machining interior surfaces in the abutment.
Summary of the invention
According to the invention the above objects are attained by the steps of the method defined in the enclosed claim 1. Supplementary steps further developing the claimed method are defined in the dependent claims 2 - 7.
In the context of the present invention it is to be noted that the gist of the claimed method (being primarily thought for producing a single tooth restoration) is in fact equally useful for producing a dental restoration in the form of a bridge.
This goes for a bridge (or a part of a bridge) which is to be fastened to a patient's jawbone by means of preferably two or more implant screws in the jawbone. In such a method the steps a) and b) would of course refer to one or more implant screws, each having a polyhedral seat. As to the rest of such a bridge-producing method at least the majority of the steps c) to h) would be applicable.
According to the claimed method the plaster model is being scanned (e.g. by laser- scanning) and the scanned data (comprising i.a. information on the screw direction- indicating pin and the shapes of the teeth adjacent to the artificial tooth to be produced) is used to determine the angle between the implant screw and the artificial tooth to be formed and fastened to the patient's jawbone. The exterior for a coping to be used and/or for a reduced crown shape is then designed, preferably using a CAD-program. Furthermore, a preformed abutment blank is provided to be used either directly as a tooth-forming means or as a support means for a coping, which is to be fitted onto the abutment. The chosen abutment blank is to have a preformed external anchoring portion, which fits into the seat in the implant screw, and a preformed through bore for a fixing screw, which is to be used for attaching the abut- ment blank to the implant screw.
By using the method according to the invention, the need of performing a problematic interior machining of the abutment and/or coping is eliminated, and only exterior surfaces on the abutment and coping will have to be machined.
In certain cases no coping will be needed for producing a tooth-like restoration. A reason for this may be that the mouth of the through bore in the abutment blank is situated on a rear side (lingual side) of the tooth to be produced. Since the mouth of the bore in such case is situated on an abutment surface facing inwards into the oral cavity, no coping is required to cover the mouth of the through bore.
Under these circumstances an external reduced crown shape may be machined (in a desired, predetermined direction) directly on a tooth-forming portion of the abutment blank on a side thereof being more or less opposite to the side on which the anchoring pin is situated. On the other hand, if a coping is required, e.g. for covering a through bore mouth on the front side of the abutment used for producing the tooth, a coping blank is provided, which blank has a preformed polyhedral inside seat adapted to fit on a matching polyhedrally shaped support-forming portion on the abutment blank. The external shape on this support-forming portion of the abutment blank is being machined in a desired, predetermined direction on it. The exterior of the coping blank is then machined either to an external desired tooth form or to an external reduced crown form. In the latter case this reduced crown form is subsequently covered with a porcelain crown, which completes the exterior of the tooth. Preferably, a CAD- program is used to design the exterior of the coping blank.
When the abutment has been attached to the implant screw by means of a fixing screw in the through bore, the bore is closed with a suitable material, preferably a composite material. The coping may thereafter be cemented onto the support- forming portion of the abutment.
A timesaving and cost-effective method is obtained by using an abutment blank having at a first end thereof a preformed external anchoring portion and at a second end a pre-machined support-forming portion extending in a direction which is to be chosen in relation to the direction of the anchoring portion that the abutment blank together with a matching coping blank provides the required angle between the implant screw and the tooth to be formed. The machining of the external shape of the support-forming portion of the abutment blank as well as the machining of the exterior of a coping blank, if needed, are preferably made by milling and/or by grinding. The milling action may be a suitable CNC-milling.
By using an abutment blank having a preformed external polyhedrally shaped anchoring portion fitting into a corresponding preformed polyhedral inside seat in the implant screw, an almost perfect fit can be obtained between the abutment and im- plant screw. Description of the drawings
The invention will now be further elucidated referring to the attached drawings, which schematically and not to-scale depict method steps and necessary appurtenant structural means utilised in a method according to a preferred embodiment of the present invention.
On the drawings:
Fig. 1 shows a space for a dental restoration between two teeth in a lower jaw; Fig. 2a shows an implant screw;
Fig. 2b shows an abutment blank to be inserted in a seat in the screw shown in
Fig. 2a; Fig. 2c shows a fixing screw for attaching the abutment blank of Fig. 2b to the implant screw of Fig. 2a; Fig. 3 shows a vertical cross section through a jawbone with a fastened implant screw and abutment blank; Fig. 4 shows a display device with an attached computer; and
Fig. 5 shows in an exploded view a set of dental restoration elements comprising an implant screw, an abutment and a coping blank, to be used together for producing an artificial tooth.
Description of a preferred embodiment
As shown in Fig. 1, a basic step in the method of the invention will be to fasten an implant screw 2 in the jawbone 4 of a patient, at the position of a required dental restoration.
In the head portion of the implant screw (cf. Fig. 2a) there is preformed a cavity 6 constituting a polyhedral inside seat having e.g. a hexagonal cross section. A pin 8 (see Figs. 1 and 3) is applied to the implant screw 2 to indicate the direction of the screw and showing the orientation of the screw's inside seat cavity 6, which is adap- ted to support a matching preformed anchoring portion 10 of a preformed abutment blank 12 (see Fig. 2b). The direction of the pin 8 will provide relevant information during a subsequent scanning process (see below). The anchoring portion 10 of the abutment blank 12 is shaped to fit exactly into the seat 6 in the head portion of the screw 2. If the screw 2 had no indicating pin 8, there would be a certain risk of inserting/mounting the abutment blank 12 in an incorrect insertion position in the polyhedral inside seat cavity 6, whereby the blank might be inclined in a wrong direction.
A bite impression is then made of the space containing the screw 2 with pin 8 as well as adjacent teeth 14, 16. A model, preferably a plaster model, is subsequently made from the bite impression, and information about the topology of the model is retrieved and stored during a scanning process, preferably using a laser scanning apparatus and a computer. The scanned data is used to determine an angle α be- tween the direction Is of the implant screw 2 and the direction It of the artificial tooth to be formed (see Fig. 3). If a coping 18 is required, or the shape of a reduced crown will be needed, the exterior of the coping 18 or reduced crown 18' is then designed using CAD-software and the information about the topology of the model, stored in a computer 19 (as very schematically indicated in Fig. 4).
The preformed abutment blank 12 is selected from a set of preformed abutment blanks with different shapes. As mentioned above, the abutment blank 12 has a preformed external anchoring portion 10 adapted to be fitted into the seat 6 of the implant screw 2. The seat is a polyhedral seat, e.g. a seat with a hexagonal cross section. Furthermore, the abutment blank 12 has a preformed through bore 20 for a fixing screw 22 (see Fig. 2c). This fixing screw is used to attach the abutment blank 12 to the implant screw 2 when the anchoring portion 10 of the abutment blank has been fitted into the seat 6 in the implant screw 2.
As shown in Fig. 5, the abutment blank 12 is also provided with a support-forming portion 24 opposite to the anchoring portion 10. According to the method of the invention, a polyhedral external shape 25 is being machined, in a desired predetermined direction, on the support-forming portion 24. This machined polyhedrally shaped support-forming portion 24 constitutes a coping receiving portion, the exte- rior shape 25 of which is designed to correspond to the shape of a preformed cavity 26 inside a selected coping blank 28.
The coping blank 28 is selected from a plurality of blanks having preformed differently shaped cavities 26. The shapes of the cavities in the various blanks are prede- termined, and the cavities are adapted to receive the support-forming portion 24 of the abutment blank 12. The particular chosen coping blank is selected using the information about the topology of the model of the bite impression and the intended exterior of the coping 18.