Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-11-23
2001-08-07
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S115000, C523S213000, C524S430000, C524S442000, C524S444000, C524S492000
Reexamination Certificate
active
06271282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to ceramic network materials used for restorative material and for various devices such as posts, implant abutments, orthodontic brackets, or blocks.
2. Description of Related Art
Referring to
FIG. 1
, natural tooth enamel
10
is a hard, vitreous substance that covers the outer portions on a tooth crown
1
. Hardness is an important enamel property because enamel
10
provides a protective covering for the softer underlying dentin
12
. Enamel
10
also serves as a masticatory surface on which food is crushed, ground, and chewed. Specifically, hardness is a measure of the ability of tooth enamel to withstand deformation by indentation or scraping, or the like, and mature enamel demonstrates a Knoop hardness number (KHN, i.e., the ratio of a given load to an area of indentation expressed in Kg/mm
2
) in a range of about 200 to 500 KHN.
Because enamel is semitranslucent, the color of enamel depends in part upon its thickness. For this reason, enamel may assume the various colors of its underlying structures. Thus, when enamel is thicker, and consequently more opaque, it may appear grayish or bluish white reflecting more of its inherent coloration. When enamel is relatively thin, however, it may be yellow-white in appearance, reflecting the underlying generally-yellowish dentin.
As demonstrated by
FIG. 1
, dentin
12
may constitute the largest single component of tooth structure, extending almost the entire length of the tooth. Dentin
12
is covered by enamel
10
on the crown
1
and by cementum
14
on the root. The internal surface of dentin
12
forms the walls of a pulp cavity
16
which primarily contains pulpal tissue
18
. Further, the walls of pulp cavity
16
may closely conform to the outline of the external surface of the dentin
12
.
Dentin and bone in general are natural ceramic-composites. Chemically, dentin
12
is composed of organic and inorganic matter. As noted above, the inorganic matter includes calcium phosphate in the form of hydroxyapatite (Ca
10
(PO
4
)
6
(OH
2
)). The organic matter is primarily collagenous material. The hydroxyapatite crystals are bonded to themselves to create tubules through which collagen fibers run and these may be attached to the dentin.
Restorative materials generally are tested on three criteria: sufficient hardness, adequate fit, and acceptable aesthetics, e.g., color match. Of these three, however, aesthetics often are the deciding factor in the choice of restorative materials. Composite resins and ceramics are in widespread use due in part to their ability to match the color of a patient's natural teeth. Composite resins may be composed of a glass in a polymer matrix. This combination, however, may result in rapid wear of the restoration, as the softer polymer is lost, and the glass filler pulls out of the remaining polymer. High wear rates are associated with rapid loss of restorative strength. Restorative ceramics may also be problematic. Despite relatively high strength and hardness, ceramic materials also are generally brittle, such that they may withstand only minimal deformation without failing. Thus, wear in current composite resin materials and catastrophic fracture of ceramic restorations are significant limitations of currently available restorative materials.
On the other hand, direct filling composite resin restorations are widely used to fill decayed teeth. These materials consist of a glass and/or ceramic particles placed into a resin to create a paste. The paste is placed directly into the tooth and cured.
Orthodontics involves movement of teeth by applying force to the teeth via wires which are tied to brackets mounted on the teeth. Most brackets are fabricated from metal which is not aesthetic. New brackets fabricated from alumina are more aesthetic but tend to fracture prematurely and also wear the opposing teeth. Alumina brackets also have high friction with the archwires which slows the tooth movement and prolongs treatment time. Plastic brackets deform and thus decrease the force transmitted to the teeth, prolonging treatment.
SUMMARY OF THE INVENTION
A process for preparing a ceramic network for fabricating stronger, more aesthetic, and better wearing restorative materials. A restorative material may be based on monomer, glass, or metal infusion of a ceramic network, or monomer infusion of a partially, glass infused ceramic network may present advantages over currently available restorations, such as composite resin and ceramic restorations, with respect to wear resistance and strength. It is a technical advantage that such a restorative material may have improved wear resistance and flexibility with respect to conventional composite resins and ceramics. It is a further technical advantage that in restorative materials made according to this invention, the masticatory surface, e.g., the coronal portion, may be glass infused to provide a hard, wear resistant restoration. For example, a glass layer may have a hardness in a range of about 300 to 600 KHN and an elastic modulus in a range of about 70 to 80 GPa. In addition, it may have a flexural strength of about 200-500 MPa, and the monomer infused interior may have a flexural strength of about 150-80 MPa and an elastic modulus of 15-25 GPa.
One embodiment of the invention includes producing implant abutment parts which may be machined directly from resin infused ceramic or the ceramic mixed with a binder which may be directly molded to form the part. The binder is burned out and the ceramic is sintered, infused and then cured.
Additionally, endodontically treated teeth often require crown restorations. Resin infused ceramic may be used to fabricate posts, or post and cores may be milled directly from a block or can be molded into custom or prefabricated parts. Advantages of this material include its increased strength, improved translucency and cementing ability.
Furthermore, orthodontic brackets which are resin infused have the advantages of improved fracture toughness, aesthetics and decreased enamel wear. They also have decreased friction with orthodontic arch wires which eases tooth movement and decreases treatment time. These brackets may be fabricated by machining a block of resin infused ceramic or by pressing the powder/powder plus binder into a mold. The binder is burned out and the ceramic is sintered. The ceramic is then infused with a resin.
Yet another embodiment involves direct filling composite resin restorations which are widely used to fill decayed teeth. These materials consist of a glass and/or ceramic particles placed into a resin to create a paste. The paste is placed directly into the tooth and cured. An application of this technology involves fabricating blocks of resin infused ceramics and then grinding these blocks into a powder, the powder is then mixed with a resin to form a paste which can be inserted into the tooth and cured. The advantage of this process is that the filler material contains ceramic particles which are joined, whereas all of the particles in a conventional composite resin are unjoined. The latter creates increased wear of the resin as the particles pull out of the resin. In this formulation bonding of the filler particles should be enhanced because there are interconnected ceramic particles already partially filled within the resin. Filler pull out is more difficult resulting in decreased wear.
Other objects, advantages, and features will be apparent when the detailed description of the invention and the drawings are considered.
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paten
Cain Edward J.
Samuels Gauthier & Stevens
Trustees of Boston University
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