Porcelain compositions for low expansion all-porcelain cores...

Details Porcelain compositions for low expansion all-porcelain cores... Porcelain compositions for low expansion all-porcelain cores...

2000-06-30

2003-04-29

Shaver, Kevin (Department: 3732)

Dentistry

Method or material for testing, treating, restoring, or...

Crown

C433S212100, C106S035000

Reexamination Certificate

active

06554615

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to low expansion porcelain compositions, and in particular to relates to low expansion, low maturing temperature porcelain compositions useful for the fabrication of dental restorations.
2. Description of the Related Art
Porcelain materials are used in dentistry in order to obtain natural-looking dental restorations. Porcelains are highly desirable for this purpose since they can be colored to closely resemble the teeth they must replace, resist degradation inside the oral cavity, and remain biocompatible even after years of continuous contact with mammalian tissue. Restorations may be classified as either porcelain-fused-to-metal (PFM) or as all-ceramic restorations.
Typically, PFM restorations are fabricated by applying a dental porcelain powder in aqueous slurry to a metal alloy framework and firing the porcelain at high temperature to form a tight, impervious porcelain layer having the appearance of natural dentition. Those skilled in the art recognize that it is important that the firing temperature of the porcelain must be compatible with the material used for the metal framework. For example, titanium and titanium alloys require overlay porcelain having firing temperatures below the temperature at which the alpha crystalline structure transforms to the less useful beta crystalline structure. It is further important that the thermal expansion behavior of the porcelain be compatible with the thermal expansion behavior of the metal so that no stress cracks are produced in the porcelain layer due to thermal expansion mismatch stress occurring during firing and cooling down.
Today, there is an increasing trend in dentistry toward the use of ceramic cores in lieu of metal alloy frameworks to provide all-ceramic dental restorations. Where a ceramic is employed as the core of a dental restoration, any porcelain applied to the ceramic framework or coping must also possess a coefficient of thermal expansion (CTE) that is compatible with that of the ceramic in order to avoid production of stress cracks in the core and/or porcelain.
Metal alloys and ceramics employed in the manufacture of dental restorations have typically possessed moderately high coefficients of thermal expansion, in the range from about 13×10
−6
/° C. to about 17×10
−6
/° C. Many porcelain compositions are known in the art which are thermally compatible with these moderately high expansion core materials and provide smooth, fused glassy surface on the resulting dental restorations. However, few porcelain compositions are suitable for use with low expansion alloys and ceramics, i.e., those alloys and ceramics having coefficients of thermal expansion in the range of about 7×10
−6
/° C. to about 13×10
−6
/° C.
Accordingly, there remains a need in the art for porcelain compositions thermally compatible with low expansion core materials; having maturing temperatures below about 850° C.; which are chemically and thermally stable; and which provide a smooth, non-abrasive surface when applied to low expansion alloys and porcelains.
BRIEF SUMMARY OF THE INVENTION
The above mentioned drawbacks and disadvantages are overcome or alleviated by a dental porcelain composition comprising an amorphous glass phase with a maturing temperature less than about 850° C., wherein the amorphous glass phase, in one embodiment, comprises:
Component
Amount (wt. %)
SiO
2
55-75
B
2
O
3
2.6-6  
Al
2
O
3
  3-4.9
ZnO
0-3
CaO
0-3
MgO
0.5-3  
ZrO
2
0-3
BaO
0-2
Li
2
O
0.8-2  
K
2
O
  0-6.5
Na
2
O
 2-15
Tb
4
O
7
0-1
TiO
2
0-3
CeO
2
0-1
F
0-2
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A dental porcelain composition which is low fusing and suitable for use with titanium, titanium alloys and ceramic cores, and which provides an extremely smooth surface for dental restorations, comprises an amorphous glass phase with a maturing temperature less than about 850° C. and a coefficient of thermal expansion (25° C. to 500° C.) of about 7×10
−6
/° C. to about 11×10
−6
/° C. The compositions find particular utility as overlay porcelains for veneers, single and multi unit restorations such as dental crowns and bridges (fixed partial dentures), inlays and onlays.
The dental porcelain composition comprises, on a weight percent basis:
Oxide
Range 1
Range 2
Range 3
Range 4
SiO
2
55-75
55-75
55-75
55-75
B
2
O
3
2.6-6  
2.6-6  
2.6-6  
2.6-6  
Al
2
O
3
  3-4.9
3-9
3-9
  2-4.9
ZnO
0-3
0-3
0-3
0-3
CaO
0-3
0-3
0-3
0-3
MgO
0.5-3  
0-3
0-3
0.8-3  
ZrO
2
0-3
0-3
0-3
0-3
BaO
0-2
0-2
0-2
0-2
Li
2
O
  0-8.2
0-2
0-2
0.8-2  
K
2
O
  0-6.5
0.5-4  
  0-6.5
 6-10
Na
2
O
 2-15
 2-15
14.1-17  
 6-10
Tb
4
O
7
0-1
0-1
0-1
0-1
TiO
2
0-3
0-3
0-3
0-3
CeO
2
0-1
0-1
0-1
0-1
F
0-2
0-2
0-2
0-2
Glass Transition
450-600
450-600
450-600
450-600
Temperature, ° C.
Dilatometric Softening
520-650
520-650
520-650
520-650
Temperature, ° C.
Firing Temperature,
Less than
Less than
Less than
Less than
° C.
850° C.
850° C.
850° C.
850° C.
CTE × 10
−6
/° C.
 7-11
 7-11
 7-11
 7-11
(25° C.-500° C.)
The dental porcelain compositions are amorphous glasses that mature at a temperature consistent with the thermal stability temperature of low expansion porcelain cores and alloy frameworks. That is, the porcelain forms a chemical bond with the core and has a thermal expansion value within about 2×10
−6
/° C. of that of the core. Components such as Li
2
O, BaO, F, TiO
2
, ZnO and SnO
2
are added to these glasses to provide wettability and good bonding to the cores used with these porcelains. ZnO and TiO
2
are particularly useful if the porcelain composition is to be used in conjunction with titanium and titanium alloys.
The porcelain compositions are chemically and thermally stable and have sufficient viscosity at firing temperature to maintain the required shape of dental restorations mimicking that of tooth anatomy. The porcelain compositions are fired at temperatures not exceeding about 850° C. The porcelain composition fires to nearly 100% of theoretical density, thus forming a tight impervious surface necessary in the oral environment.
A preferred feature of the present composition is a combination of Al
2
O
3
, B
2
O
3
, and MgO effective to achieve low maturing temperature, while at the same time maintaining low thermal expansion and high chemical durability. While B
2
O
3
often lowers thermal expansion and maturing temperature, it can simultaneously decrease the chemical durability of porcelain if it comprises more than about 3-4 wt % of the total composition. To lower expansion and maturing temperature while maintaining high chemical durability, B
2
O
3
is therefore preferably used in combination with Al
2
O
3
and MgO.
The porcelain compositions can be prepared by melting together sufficient precursor components to yield the compositions shown in the above table. Suitable precursors include silica, alumina, boric acid, feldspar, calcium carbonate, sodium carbonate, potassium carbonate, lithium carbonate or lithium fluoride, or if desired, the actual oxides, blended in proportion to yield the compositions shown in the above table.
The preparation of such materials is well known in the art. After the materials are blended, preferably in finely divided powder form such as powder sufficiently fine to pass through a 200 mesh screen (Tyler series), the precursors and/or oxides are heated to a temperature of at least about 1100° C., and preferably to at least about 1230° C., in a crucible to form a glass.
The molten glass may then be quenched in water, dried, and ground in a ball m

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