In the field of dental implants, patient comfort and the efficient use of a dentist's time are paramount. Likewise, precision alignment of the prosthetic components is essential. The need to match upper and lower teeth to within a few microns and provide accurate mating of the prosthesis with existing teeth requires accurate replication of oral structures when making dental impressions. It is possible with the introduction of an intra-oral scanning apparatus to scan the oral environment and precisely display a working virtual model on a computer screen and to generate a physical model in accurate detail. Alternately, the more direct method of creating a physical stone model is still preferred by the majority of dentists.
To create accurate stone models for fitting the final prosthesis, a matched upper and lower impression can be obtained simultaneously with the jaw in the closed position and the teeth in the interdigitated position (centric occlusion). Currently, the tall impression transfer posts used to register the implants to the upper and lower jaws prevent the full closure of the mouth while making the simultaneous upper and lower scans and impressions. The present invention remedies this oversight for both virtual scanning and physical modeling.
Existing practice has been to perform the following procedures. After dental implants have healed into the underlying bone structures of the mandible or maxilla and the soft tissue has healed around a protective healing cap or healing screw, a full set of upper and lower impressions of the mouth are made using individual full or partial arch upper and lower trays. A separate bite registration elastomeric impression is also made in centric closure. Positive casts of the upper and lower impressions are poured, mounted on a dental articulator and aligned in centric occlusion by means of the separate elastomeric bite registration.
In more detail, the prior art performs the following steps to make an accurate impression, the healing caps are removed from one or more dental implant fixtures and standard length impression transfer posts are accurately placed with retaining screws on each implant fixture. An impression tray filled with a self-hardening elastomeric impression material is pressed over the region of the dental arch containing the impression transfer posts.
After a few minutes, the elastomeric impression material has set. The tray is gently removed from the mouth leaving the tall standard impression posts still attached to the implant fixtures. The screw retaining the standard impression transfer post is removed and the tall impression post is attached to an implant analog. The impression post and attached implant fixture analog is reinserted in the elastomeric compound. Taking care to seat the impression post accurately. The pratitioner or a dental lab casts a stone model embedding the implant analog. The implant fixture analog is thus fixed accurately within the stone model. The stone model serves as the platform to craft the prosthesis. The healing cap is replaced on the dental implant fixture in the mouth. Another impression of the mating jaw is taken by the same method. A third elastomeric cast is made of the teeth in centric closure to insure later alignment.
The stone models of the upper and lower mouth structure with dental implant analogs exactly aligned and retained are molded in hard plaster stone from the separate impressions. These models are separately placed upon a dental articulator to mimic the actual jaw motions. The separate upper and lower stone casts are aligned in centric closure with the elastomeric bite cast. The final prosthesis is built and tried in for a non-interfering, good fit. This prosthesis relies upon proper replacement of the tall standard impression post to insure the properly aligned position.
With the optical scanning apparatus, a virtual three dimensional image of the whole oral environment can be created in a minute or two. The virtual image file can be transmitted electronically to a lab and a physical model of the upper and lower jaw can be printed in rigid polymer with a three dimensional printer.
Applicants offer an impression post serving the needs of both the physical casting techniques and the virtual scanning methods.
Applicants, in order quickly to make an accurate, simultaneous impression of the upper and lower teeth in the correct alignment use a dual arch impression tray such as the Triple Tray™. This tray consists of a molded plastic or metal assembly with a handle connected to a set of confining dams and a thin open screen mesh. The mesh is oriented horizontally and is to be placed between the mating occlusal surfaces of the teeth while the jaw is in the closed or centric position. The mesh is thin enough to allow complete centric closure. The mesh is flexible and porous to trap and retain an elastomeric impression compound.
The buccal and lingual dams are molded to the mesh. A paste of quick-setting elastomer is placed on both sides of the mesh within the confines of the dams. The mouth is closed with the upper and lower teeth in the closed or centric position while embedded within the curing elastomer. In this manner, a matching set of aligned upper and lower impressions along with the proper bite registration are made simultaneously.
The elastomeric impression materials, such as polyvinylsiloxane or polyether, are dimensionally stable, but need adequate thickness and surface area in contact with the impression transfer post to ensure accurate positioning and replication of the implant within the models mounted upon an articulator. Currently, long tapered impression transfer posts are used, which have adequate surface area to accurately register the elastomeric impression to the dental implant analog, but interfere with the use of a dual arch impression tray by preventing closure.
In prior art Neal B. Gittleman U.S. Pat. No. 6,213,773 Reduced Height Dental Impression Post, and Neal B. Gittleman U.S. Pat. No. 7,632,096, with all reference made therein, a low profile wing impression post is taught. The impression post is of reduced height to allow complete closure to obtain a triple impression of the upper and lower dentition as well as the dental occlusion. This impression post is removably attached to an installed implant fixture and remains embedded within the triple impression compound, when the impression is removed from the mouth. The winged coronal top of the impression transfer post has sufficient volume and surface area to remain accurately fixed and stable within the impression compound. An implant fixture analog is mated with the impression transfer post and cast in the stone model. The prosthesis is accurately built upon implant fixture analog, with a matching manufactured abutment.