DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0023] The present invention incorporates a digital dental model into a three-dimensional CT model, thereby obtaining a computerized composite skull model of both the highly accurate bone information obtained by the CT process and the accurate digital dental model data.

[0024] Three-dimensional CT models as shown in FIG. 2 have been used in craniofacial and maxillofacial surgery, since CT imaging provides an excellent representation of bone structure. CT scanners capture images layer by layer, and data between the image layers is conventionally reconstructed by mathematical algorithms. A significant disadvantage of CT, however, is that it is not capable of accurately representing the teeth. A scattering of the CT image as shown in FIG. 2 may be due to orthodontic metal brackets, dental fillings, or prosthesis. The technique of the present invention creates a three-dimensional computerized composite skull model which represents both the fine bony structures and precise dental structures. Using this model, diagnosis and treatment planning may be significantly improved.

[0025] To form the composite skull model of the present invention, a set of digital dental models as shown in FIG. 3 may be made on the patient's dentition in a conventional manner, but with the addition of fiduciary markers 20 . The digital dental models may then be positioned as shown in FIG. 4 . Digital dental models may be conventionally obtained by laser surface scanning of the dental impressions. The fiduciary markers may be inserted into the radiolucent full-arch dental impression tray, as shown in FIG. 9 . Titanium balls may be used as suitable fiduciary markers. A triple-tray may be used to take simultaneous impressions of the maxillary and mandibular arches. Four fiduciary markers may be mounted on the tray, with one pair for the left and right canine region, and the other pair for the left and right molar region. The dental impressions with the four fiduciary markers may be scanned using a 3-D laser surface scanner to obtain the digital dental model. The digital dental model provides for highly accurate occlusion relationships.

[0026] A three-dimensional CT bone model of the skeleton may be taken on the same patient with the same set of fiduciary markers, as shown in FIG. 5 . The CT skull model is constructed from the CT scan of the skull. Using computer programming, the four fiduciary markers may be located in the same position for both the CT data and the digital dental model data. Interactive alignment of the corresponding fiduciary markers thus provides alignment between the bone model and the digital dental model. The fiduciary markers may then be removed to create a precise composite of the skull model 26 , as shown in FIG. 6 . By incorporating the digital dental model into the CT skull model through alignment of the fiduciary markers, a highly accurate computerized composite skull model may be obtained. Digital dental model information is incorporated into the computerized CT bone model to accurately represent both bony structures and teeth. By establishing the dental occlusion, it is possible to precisely formulate a computerized surgical plan and simulate outcomes prior to surgery. Treatment planning with the composite model may replace the need for traditional plaster dental models, and will help the surgeon reduce operative time and improve surgical outcomes.

[0027] The composite computer model may be displayed, so that one or both of the upper jaw and the lower jaw are selectively repositioned relative to the skull to a planned position computer model. With the computer model, surgeons may move and rotate bone segments to any desired position. Recognizing that the lower jaw “floats” with respect to the skull and the upper jaw, the upper and lower jaws may be positioned in the composite computer model so that the jaws come together with desired alignment of the jaws and the dentition. Using the upper and lower jaw planned position computer model, the dental splint may be formed to receive the teeth. The computerized composite skull model may thus be used to generate a stereolithographic model of the patient's craniofacial skeleton and dentition. The techniques of the present invention allow a surgical plan to be employed which includes a digital dental model to establish the occlusion and fabricate surgical splints. Using the composite CT model of the present invention, surgical planning will thus be optimized to produce the desired surgical outcome.

[0028] After the digital dental model as shown in FIG. 4 has been incorporated into the CT model as shown in FIG. 5 to produce the computerized composite model 26 as shown in FIG. 6, a computerized horseshoe wafer 28 may be generated, as shown in FIG. 7 . This wafer may then be placed between the digital maxillary and mandibular dental arches of the computerized composite skull model, and the lower jaw moved to indent the wafer with both the upper and lower teeth. After Boolean operations to subtract the teeth from the wafer, it produces a digital dental splint 30 . A physical dental splint 32 may then be fabricated with the SLA machine using the digital dental splint 30 as a model. The treatment plan may thus be transferred from the computer to the patient to form both intermediate and final surgical splints generated according to the techniques of the present invention.

[0029] To test the accuracy of the composite model of the present invention, a complete dry skull was used to generate a composite skull model, with both CT bone and digital dental data. On the computerized skull model, three-dimensional measurements were taken between bones and between teeth, and from bone to tooth. These same dimensions were manually taken from the dry skull. The results indicate that the computerized composite model accurately represented bone structures from the CT data, but also reproduced accurate dentition from the digital models.

[0030] FIG. 8 is a block diagram of a suitable process according to the present invention for fabricating a surgical splint. As discussed above, impressions of the dentition may be made for both upper and lower teeth using an impression tray, with fiduciary markers secured to the tray. Using the dental impression tray, a digital dental model may be obtained by laser scanning the dental impressions with the fiduciary markers in place. Using the same dental tray and with the fiduciary markers in place, a CT scan of the patient may be obtained to create a CT bone model of the craniofacial skeleton with the fiduciary markers in place. The CT bone model, which is highly accurate in depicting bone structure, is then combined with the digital dental model, which accurately depicts the dentition, by alignment of the fiduciary markers. The teeth in the CT bone model are thus replaced with the digital dental model, so that when the fiduciary markers are removed a composite skull bone model is created which accurately displays both the bony structure and the teeth.

[0031] Using this composite skull model, a surgical plan may be developed. In many applications, that plan will include making one or more cuts in the upper jaw or lower jaw, so that the bony segments of the jaw may be moved to desired positions. Once a selected position is obtained, a computerized pressure horseshoe-shaped wafer may be placed between the upper and lower teeth to fabricate a digital surgical splint model, as shown in FIG. 7 . Using the digital surgical splint model, a physical surgical splint may be generated using an SLA machine.

[0032] According to a preferred embodiment of the invention, a stereolithographic apparatus (SLA machine) is preferably used to fabricate the dental splint from the computer model surgical splints. It should be understood, however, that various types of computer controlled rapid prototype machines may be used for accurately fabricating surgical splints once supplied with the proper surgical splint computer information

[0033] To test the accuracy of the technique for forming surgical splints according to the present invention, a surgical splint was fabricated for each of a number of volunteers. One stereolithographic and one conventional acrylic splint was generated for each volunteer. The air space between the teeth and the splint was quantified. The air spaces were recorded by impression materials and sliced cross-sectionally. Corresponding areas of the cross-sectional airspaces between the stereolithographic and the acrylic splints were then measured and compared. The results indicated that the techniques of the present invention were highly accurate.

[0034] According to the present invention, diagnosis, surgical planning and simulation, and surgical splint fabrication may be accomplished at the computer and computerized splint fabrication machine. Patients with craniofacial and maxillofacial deformities may be CT scanned, and their dentition may be laser scanned. Computerized virtual osteotomies may be performed on the computerized skull model, and the treatment plan transferred from the computer to the patient through the intermediate and final surgical splints. Accordingly, traditional plaster dental model surgery may be replaced by the more cost effective and versatile techniques of the present invention.

[0035] A desired workstation according to the present invention is shown in FIG. 10 and preferably includes the components required to form the computerized composite models and the surgical splints. The workstation 50 includes a CT scanner machine 52 , a scanner 54 for obtaining a digital dental model, and a computer with software 56 for combining the data from the CT machine and the digital dental scanner. Software for aligning the digital markers and for creating the computerized horseshoe wafer may be obtained commercially from various sources, including Discrete, Inc. in Montreal, Canada, marketed as 3D Studio Max. A screen, monitor 58 or other device displays the composite model. A keyboard, mouse, or other input command mechanism 60 to the computer allows the clinician to reposition at least one of the upper jaw and the lower jaw relative to the patient's skull to form the desired position computer model. Using this desired position computer model, a computer model surgical splint may be generated, and the data from the computer model surgical splint then input into an SLA machine or another computer-based manufacturing machine 62 for fabricating a surgical splint. With the improved surgical splint, teeth on the patient may be positioned within the splint, and plates, screws, and other mechanisms then conventionally used to fix the upper and lower jaw in place during the surgical technique.

[0036] While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptions of the preferred embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.