Dentistry – Prosthodontics – Preliminary casting – model – or trial denture
Reexamination Certificate
2000-02-25
2004-12-21
Lewis, Ralph A. (Department: 3732)
Dentistry
Prosthodontics
Preliminary casting, model, or trial denture
C433S006000, C264S573000
Reexamination Certificate
active
06832914
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to International Application No. PCT/FR98/00984, filed May 15, 1998, the entire specification of which is incorporated herewith by reference.
FIELD OF INVENTION
This invention concerns the orthodontic or dento-facial orthopedic apparatus sector, particularly those which are precisely adapted to the specific morphology of each patient.
More particularly, it concerns all orthodontic or dento-facial orthopedic apparatuses having a general hollow body which may have one or more openings, variable thickness, and which, due to this particular geometry, cannot be produced from a flat plate.
BACKGROUND OF THE INVENTION
Such apparatuses, which may be removable, may be those intended to maintain a patient's tongue in a given volume, particularly Bonnet's Nighttime Lingual Envelope or N.L.E.
More generally, the invention concerns apparatuses which must necessarily be adapted very precisely to each patient or user in order to fulfill their function and which cannot be manufactured based on a blank in the form of a flat plate due to their final complex shape (open hollow body, variable thicknesses which cannot be obtained by simply shaping a plate, etc.). By contrast, these apparatuses are produced starting from a blank or preform whose shape permits it to be expanded in a mold that reproduces the patient's morphology. This preform has the general shape of a three dimensional hollow body, more particularly, a hollow, tubular or approximately tubular form, more particularly still, a hollow, tubular or approximately tubular form which is cut on the upper anterior part to form an opening.
Traditionally, such apparatuses are tailor-made, created in a laboratory and therefore, piecemeal, starting from formed molds based on research models which have themselves been formed based on an impression or impressions made in the practitioners office by the same.
Several apparatuses are generally necessary during treatment, to follow changes in the patient's morphology. The need to produce a new apparatus during treatment may also come from the need to move the fastening hooks due to a change in the environment (for example, with the appearance of wisdom teeth or with shifting of teeth). Each time a cast must be taken to produce a model, then a mold, and then the final apparatus must be produced.
More specifically, the traditional process for manufacture is a contact molding process. It occurs in four steps:
Construction of the Mold
The practitioner makes a casting of the upper maxilla and possibly a casting of the lower maxilla of his patient, most often with alginates due to their rapid polymerization and biocompatibility properties. These castings act as a base for the production of a model in one or two parts which is most often in plaster, completed using wax that sticks easily and/or is easily deformed. This requires that the technician have great technical proficiency, integrating brief perceptions, dexterity, and experience. The technician, also using wax, positions the fastening systems (or fastening hooks and pins), generally metal wires which shall then be duplicate molded and shall perform the fastening function of the completed apparatus in the patient's mouth as well as any other additional necessary piece.
Contact Molding
A resin with two components is used, a solid powder and a fluid, adapted to contact molding of traditional orthodontic pieces. Work is conducted with successive passes of dampening by the liquid using a pipette and/or dusting with the solid.
However, the shape of the hollow body with variable thickness in certain apparatuses such as the N.L.E. by Bonnet results in special difficulties during production since the different areas of the apparatus have quite varied orientations and curvature radii. Therefore, the technician is confronted with several difficulties.
(i) A compromise must be found between passes that are too liquid or too thin or of such small surface that multiples are needed, thus lengthening the operating time, and passes which are too thick or too pasty which creates irregular upper thicknesses that will then need grinding.
(ii) It is difficult to estimate or measure the deposited thicknesses to inspect ones work as it progresses,
(iii) A choice must be made between molding of all passes in a single operation lasting several minutes or up to a quarter of an hour followed by a single final polymerization or molding with several very brief operations each lasting approximately a minute with as many intermediate polymerization phases in an autoclave pressurized above atmospheric pressure (otherwise gas bubbles arise deterring from the piece's final appearance). In the first case, one obtains a piece having irregular transparency and which is little flattering, in the second case, the production time, and therefore the cost are noticeably higher.
Mold Ejection and Finishing
The blank is ejected from the mold, then finishing takes place using machining and grinding. The shape of the preform being somewhat removed from the final piece, finishing is a long and delicate operation generating noise and dust. Since this pollution is incompatible with a dentist's office, finishing must take place in an area with specific equipment, namely, for example, a suction hood.
There are variations in which the teeth and gums part of the lower maxilla model are used complementing the upper maxilla model. A filler material (for example, plaster) is used to complete the missing part in order to obtain a complete mold. In this case, the mold is completely exterior to the piece to be molded; the general accessibility and visibility are not as poor as in the preceding variation.
The apparatus is then equipped with hooks in order to be attached to the patient's mouth. Currently, there are mainly two types of hooks or claws or fastening systems, hereafter fastening hooks, (Step
1
) used depending on the morphology and the dental age of the patient, in general made of stainless steel orthodontic wires:
Lateral Hooks (Generally Symmetrical, Totaling 2)
They are used especially for young children. They are anchored in the apparatus at one end which is inserted in the lateral wall of the apparatus, the other end being inserted elastically into a diastema to attach the apparatus to the mouth. They are generally cold-formed using the Sahar method, meaning that the beginning of the emerged part has a zigzag shape such that it may be deformed by the practitioner to adjust the tightness of the anchoring when it is first placed in the mouth and on the following visits depending on the changes in the patient's oral environment, all without changing the anchoring, that is, the position of the part of the hook included in the apparatus. In the thickness of the outside wall of the apparatus, a hollow is reserved to lodge this zigzag whose shape changes during the apparatus' life.
The Posterior Hooks (Generally Symmetrical, Totaling 2)
They are anchored in the apparatus such that the wire exits at the rear of the apparatus approximately in the horizontal occlusion plane. The wire then generally follows the contours of the teeth which are farthest back (for example, the 6 year tooth or the 12 year tooth), then it comes to exert pressure from the outside on the tube of a ring. It is formed in such a way that with the slight symmetrical forces of the two posterior right and left hooks pressing upward and outward in reaction to the apparatus it is kept in position against the palate.
This production method offers certain inconveniences. In effect, production costs are high (made to order), the appearance and quality of the product are often insufficient (manual), at times, considerable finishing is needed, delays are excessive. Furthermore, the alginate cast is destroyed when the plaster model is released from the mold. Therefore, the model must not be damaged so that the patient does not have to undergo the procedure again. So, this plaster model is very fragile. It must be handled all
Bonnet Bruno
Bonnet François
Bonnet Maïwenn
Arent & Fox PLLC
Lewis Ralph A.
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