Dentistry – Method or material for testing – treating – restoring – or... – Crown
Reexamination Certificate
2000-01-18
2001-07-10
Wilson, John J. (Department: 3732)
Dentistry
Method or material for testing, treating, restoring, or...
Crown
C433S218000
Reexamination Certificate
active
06257892
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to temporary and provisional dental crowns, and more particularly to flexible dimension crown shells and methods of making temporary and long-term provisional dental crowns using such shells.
Presently, there are three primary methods for fabricating temporary and provisional crowns. In a first technique, conventional prefabricated crown forms or shells, made of a metal such as aluminum or stainless steel, or of a polycarbonate such as the Ion crown forms sold by 3M Corporation, are trimmed and shaped to fit a prepared tooth. Examples of temporary crowns of this type are disclosed in U.S. Pat. No. 4,015,332 (Manne), U.S. Pat. No. 4,678,435 (Long), U.S. Pat. No. 4,778,386 (Spiry), and U.S. Pat. No. 5,458,489 (Tennyson).
A second technique calls for making an impression of the tooth before the tooth is prepared for a crown. After the impression is made, the tooth is prepared and the impression, filled with a bis-acryl material, is placed over the prepared tooth. After the bis-acryl material sets, it is removed from the dental impression, and then trimmed, polished, and seated in the mouth.
A third primary technique, which is used and recommended by Gordon Christenson, is also popular. According to the third technique, a putty-like ball of polymethyl-methacrylate is applied over a prepared tooth. The patient then bites down and the material begins to set. Before it completely sets, the putty-like material is removed from the tooth, trimmed and placed back on the tooth. Once the material sets, it is then trimmed again and the bite adjusted. Finally, the temporary crown is cemented to the tooth. In a variation of this technique, as disclosed in U.S. Pat. No. 5,385,469, a tubular dental form for forming a universal crown in situ is used.
Each of these techniques has various advantages and disadvantages. Using prefabricated forms, as in the first technique, for example, is fast and simple, but the fit of the conventional shell is not very good. The margins, in particular, do not fit well. Specifically, it is hard to get good proximal contact to adjacent teeth, and the contours and occlusion are not always good. Some manufacturers try to overcome these drawbacks by proliferating sizes and shapes of shells, with some selections providing as many as 80 different sizes and shapes of molars and bicuspids. Unfortunately, this attempted solution is expensive in terms of materials and also in terms of the time required for the dentist to pick the right shell.
Manne adds a degree of freedom to the first technique by providing an incisor shell that has slits in the mesio-distal sides to permit the shell to flex in the labio-lingual direction about a hinge axis at the occlusal surface. Long also provides a degree of freedom in this technique by having the mesio-distal sides of a temporary molar crown open to permit the acrylic resin filler material to protrude proximally to contact adjacent teeth. These shells, like others used in this technique, require trimming the free edges of their buccal and lingual sidewalls to ensure a good fit along the gingival margins, as well as a good occlusion. The shells in Long also appear to require substantial trimming of the filler material due to their open mesio-distal sides. Such trimming and fitting is time-consuming for the dentist and the patient.
The second technique gives good contours and bite accuracy, but making an impression is time-consuming. Furthermore, neither the strength nor the durability of temporary crowns produced by this technique are very good. Furthermore, the impression cannot be made if the patient's tooth is already broken when initially treated. The third technique, namely, free-forming a temporary crown of putty-like material, can be accurate and fairly fast compared to the other techniques, but only if performed by a skilled dentist or technician. It, too, however, is more time-consuming than desirable. Another main problem with this approach is that it is very technique-sensitive. A dental technician must be highly skilled in order to accurately carve the tooth anatomy. Another problem with this technique is that special care must be taken to ensure that the patient's mouth is not injured by the exothermal reaction involved in curing the crown material.
As noted, all of the foregoing techniques are undesirably slow. Even the fastest of these techniques generally takes half an hour or more of work for the dentist to fit a temporary or provisional crown to a patient. Additionally, the crowns resulting from the second and third techniques are typically not very durable and are therefore not well-suited for long-term wear. Although the stainless steel shells of the first technique are very durable, it is more difficult to fit stainless steel shells to the patient and to grind the shells' occlusal surfaces to get a comfortable bite.
Accordingly, a need remains in the profession for a way of making temporary and provisional crowns that is quick and accurate, that provides a good fit without substantial trimming, that is durable enough for long-term use, and that is inexpensive.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to simplify the fabrication, fitting, and installation of temporary and provisional crowns.
Another object of the invention is to make temporary and provisional crowns that fit well and are durable enough for long-term use.
A further object is to make crowns that fit well but are inexpensive both in terms of materials and time taken to fit the crowns.
In general, the invention combines two of the conventional techniques, namely, the free-form and specially-designed shell techniques, in a way that takes the advantages of, yet avoids the major disadvantages of, both of these techniques as used individually. Specifically, the shells of the invention have a generally U-shaped window, unbounded along a gingival margin, in at least one of the mesio-distal sidewalls. A putty-like material or resin is used, similar to that used in the free-form technique, but in this case it is shape-controlled by the shell and the windows provided therein. This shape control saves the dentist valuable time in shaping the temporary or long-term provisional crown. The mesio-distal sidewalls each include a recessed area or indentation adjoining the windows for receiving and retaining protruding resin in proximal contact with adjacent teeth. The shells are further designed with short labial and lingual side walls so that no trimming of the shells themselves is needed. This, too, saves the dentist a great deal of time. The shells also give the dentist several degrees of freedom, so that most molars and bicuspids can be fitted with only a limited range of sizes and shapes of symmetric shells.
A particular shell for making a temporary or long-term provisional crown on a prepared tooth includes a top wall, a buccal sidewall; a lingual sidewall, and opposite mesio-distal sidewalls. The top wall defines an occlusal surface of the shell. The mesio-distal sidewalls are each connected to the top wall and to the buccal and lingual sidewalls, and are spaced apart from each other to define a central cavity. The central cavity is configured to receive resin and to fit over a prepared tooth. A window is formed in at least one mesio-distal sidewall to provide a partial opening that allows a portion of the resin to protrude mesio-distally from the cavity to an adjacent tooth. Furthermore, at least one of the mesio-distal sidewalls is shaped concavely to interfit with a convex mesio-distal surface of the adjacent tooth.
Preferably, the top wall of the shell is shaped concavely along mesio-distal edges to form an approximate hourglass shape conforming to a convex shape of mesio-distal surfaces of adjacent teeth, with both of the mesio-distal sidewalls shaped to align with the concavity of the top wall. In this way, the concave mesio-distal sidewall can provide an approximately uniform-width gap between the shell and the convex adjacent tooth and control a proxi
Flexible Dimensions, LLC
Marger & Johnson & McCollom, P.C.
Wilson John J.
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