WO2018056893A1

WO2018056893A1 - Dental composition for dental veneer and method of forming dental veneer using same

Info

Publication number: WO2018056893A1
Application number: PCT/SG2016/050459
Authority: WO
Inventors: Alexander Korsunsky; Tee Khin NEO
Original assignee: Alextania Limited; Primedent Pte. Ltd.
Priority date: 2016-09-21
Filing date: 2016-09-21
Publication date: 2018-03-29

Abstract

A dental composition for a dental veneer (12) and a method of forming a dental veneer (12) are provided. The dental composition includes a ceramic composition and lanthanum oxide, the lanthanum oxide forming a mixture with the ceramic composition. In use, the mixture is applied to a zirconia coping and sintered before being cooled to room temperature, the sintered mixture is further tempered at a temperature of between about 400 degree Celsius (°C) and about 475 °C for a period of between about 4 hours (h) and about 24 h.

Description

DENTAL COMPOSITION FOR DENTAL VENEER AND METHOD OF FORMING DENTAL VENEER USING SAME

Field of the Invention

The present invention relates to prosthodontics and more particularly to a dental composition for a dental veneer and a method of forming a dental veneer with the dental composition.

Background of the Invention

Partially stabilised zirconia is an engineering ceramic material that displays excellent bio-inertness, structural strength and toughness, and aesthetic appearance associated with its stable white colour. Extensive testing of its application in the construction of dental prostheses has revealed excellent resistance of this material to thermal, mechanical and environmental exposure in human oral cavities that can guarantee successful performance of such systems over several decades, free from mechanical failure and degradation in colour and appearance.

Due to the brilliant white colour and exceptionally high hardness of zirconia compared to other materials present in the oral cavity, uncoated zirconia copings are generally not suitable for direct use in restorative dentistry, except in some posterior locations. The high machining resistance of zirconia creates an additional challenge when adjusting an installed prosthesis.

In modern dental practice, porcelain veneers are used to create pearlescent restorations with colours that are adjusted to match the natural teeth of patients. Long-term preservation of pearlescence is an important function of restoration that has significant impact on the perception of freshness and quality of a smile by patients and others. Another important function of porcelain veneering is to allow the finished prostheses to be sculpted to closely resemble the shape of human teeth, and to provide for facile adjustment of masticatory bite after installation.

Clinical experience of using porcelain veneered partially stabilised zirconia prostheses reveal that chipping fracture of the porcelain veneer is one of the most prevalent modes of failure accounting for the failure of restoration in up to 5% of cases. Given the high cost of restoration and installation and the difficulty associated with its removal that is exacerbated by the extreme hardness and machining resistance of zirconia, this mode of failure has become the principal cause of concern to dental practitioners and dental material and equipment suppliers. It is therefore desirable to provide a dental composition for making a dental veneer with improved reliability and resistance to fracture and a method of forming such a dental veneer.

Summary of the Invention Accordingly, in a first aspect, the present invention provides a dental composition for a dental veneer. The dental composition includes a ceramic composition and lanthanum oxide, the lanthanum oxide forming a mixture with the ceramic composition. In use, the mixture is applied to a zirconia coping and sintered before being cooled to room temperature, the sintered mixture is further tempered at a temperature of between about 400 degree Celsius (°C) and about 475 °C for a period of between about 4 hours (h) and about 24 h.

In a second aspect, the present invention provides a method of forming a dental veneer. The method includes providing a dental composition comprising a mixture of a ceramic composition and lanthanum oxide and applying the dental composition to a zirconia coping. The dental composition is sintered and the sintered composition is then cooled to room temperature. The sintered composition is subsequently tempered at a temperature of between about 400 degree Celsius (°C) and about 475 °C for a period of between about 4 hours (h) and about 24 h.

Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a schematic sectional view of a zirconia coping with a dental veneer formed thereon using a dental composition in accordance with one embodiment of the present invention;

FIG. 2 is a schematic flow diagram illustrating a method of forming a dental veneer on a zirconia coping in accordance with one embodiment of the present invention;

FIG. 3 is a graph of a heat treatment schedule to which the dental composition is subjected in accordance with one embodiment of the present invention;

FIGS. 4A through 4D are energy-dispersive X-ray spectroscopy (EDX) microanalysis maps showing the elemental distribution in the dental veneer formed using the dental composition in accordance with one embodiment of the present invention; FIG. 5 is an enlarged schematic view of line arrays of micropillars machined across an interface between the dental veneer and the zirconia coping to test the mechanical properties of the dental veneer; and

FIG. 6 is a graph showing the fracture toughness of the dental veneer formed using the dental composition in accordance with one embodiment of the present invention across an interface between the dental veneer and the zirconia coping compared to the fracture toughness of a conventional porcelain veneer.

Detailed Description of Exemplary Embodiments The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the scope of the invention.

Referring now to FIG. 1 , a section of a zirconia coping 10 with a dental veneer 12 formed thereon using a dental composition in accordance with one embodiment of the present invention is shown. The dental composition for the dental veneer 12 includes a ceramic composition and lanthanum oxide (La₂0₃), the lanthanum oxide forming a mixture with the ceramic composition. In use, the mixture is applied to the zirconia coping 10 and sintered before being cooled to room temperature, the sintered mixture is further tempered at a temperature of between about 400 degree Celsius (°C) and about 475 °C for a period of between about 4 hours (h) and about 24 h. The ceramic composition may be a commercially available veneering porcelain powder. In one embodiment, the ceramic composition is a conventional low temperature fusing semi-vitreous porcelain. Examples of suitable ceramic compositions are shown in Table 1 below.

Table 1

The lanthanum oxide may comprise between about 0.5 percent by mass and about 1 percent by mass of the mixture and may have an average particle size of between about 100 nanometres (nm) and about 400 nm.

The mixture may be sintered according to sintering instructions provided in respect of the ceramic composition. In one embodiment, the mixture may be sintered at a temperature of between about 650 degree Celsius (°C) and about 750 °C for a period of between about 1 minute (min) and about 20 min.

In one embodiment, the sintered composition may be tempered at 450 °C for 24 h. The addition of lanthanum oxide to the base porcelain composition in combination with tempering has been found to achieve superior fracture toughness, resistance to chipping, durability and reliability of dental prostheses.

Referring now to FIGS. 2 and 3, a method 14 of forming the dental veneer 12 on the zirconia coping 10 will now be described. The method 14 begins at step 16 by providing a dental composition comprising a mixture of a ceramic composition and lanthanum oxide. The lanthanum oxide may comprise between about 0.5 percent by mass and about 1 percent by mass of the mixture and may have an average particle size of between about 100 nanometres (nm) and about 400 nm. In one embodiment, micro-doping amounts (<1 %) of lanthanum oxide nanoparticles may be added to veneering porcelain powder by ball milling to produce the dental composition.

Advantageously, the formulation of the dental composition preserves the mechanical properties of the veneer such as stiffness and overall strength, whilst simultaneously improving the translucency, biocompatibility, adhesion, fracture toughness and chipping resistance.

At step 18, the dental composition is applied to the zirconia coping 10. In one embodiment, the dental composition may be applied in the form of an aqueous slurry to dental prosthesis zirconia copings. At step 20, the dental composition is sintered. The dental composition may be sintered according to sintering instructions provided in respect of the ceramic composition. In one embodiment, the mixture may be sintered at a temperature T-i of between about 650 degree Celsius (°C) and about 750 °C for a period ti of between about 1 minute (min) and about 20 min. The dental composition may be sintered in a vacuum.

The sintered composition is cooled at step 22 to room temperature RT. At step 24, the sintered composition is tempered at a temperature T₂ of between about 400 degrees Celsius (°C) and about 475 °C for a period t₂ of between about 4 hours (h) and about 24 h. The sintered composition is subjected to low temperature controlled fusing to produce the veneer. A veneer that displays improved adhesion, fracture toughness and chipping resistance, has excellent aesthetic appearance, and is fully biocompatible for use in humans is thus produced.

Example

0.5 percent by mass of lanthanum oxide (La₂03) nanoparticles with a nominal size of between about 100 nm and about 400 nm was added to a commercially available veneering porcelain powder. Low intensity ball milling was carried out using alumina balls for 24 hours (h) to ensure uniform dispersion.

The resulting formulation was mixed with a small amount of water to form an aqueous slurry. Application of the aqueous slurry of the dental composition onto zirconia copings was followed by vacuum sintering using a ramp up-hold- ramp down temperature profile with a maximum firing temperature of 750°C, followed by a 24 h tempering treatment that followed the heat treatment schedule shown in FIG. 3. The overall mechanical properties of the base porcelain veneer and the lanthanum oxide micro-doped formulation are shown in Table 2 below.

Table 2

expansion (100 - 400 °C)

Glass transition temperature °C 490 ± 10 470 ± 10 645 ± 10 (Tg)

Referring now to FIGS. 4A through 4D, the uniformity of lanthanum oxide dispersion within the fired porcelain veneer was investigated using energy dispersive X-ray spectroscopy (EDX) microanalysis. The microanalysis maps of elemental distribution in the sample of commercially available veneering porcelain powder micro-doped with lanthanum oxide nanoparticles reveal the predominant silica-alumina mixture and the spatially uniform dispersion of La₂03 doping achieved by ball milling and low temperature sintering.

Referring now to FIG. 5, the macro-scale chipping resistance of lanthanum oxide nanoparticle micro-doped veneering porcelain on the partially stabilised zirconia (PSZ) coping was investigated by micro-pillar splitting. Arrays of micro-pillars with diameters of a few micrometres were machined by focused ion beam (FIB) milling in a line across the porcelain/zirconia interface. These were first used to determine the stiffness and hardness of the material at the appropriate resolution. Following that, indentation splitting was used for the samples of standard and modified porcelain veneer to determine the material fracture toughness.

Referring now to FIG. 6, the variation of fracture toughness (in units of MPa Vm) as a function of distance (in pm) from the porcelain/PSZ interface is shown. The profile for standard porcelain veneer is represented by circle markers and the profile for the La-oxide-doped porcelain veneer formulation by square markers. The marked reduction in fracture toughness of the standard porcelain veneer (by a factor of up to 6 times with respect to the bulk value indicated by the straight line) is apparent within a band of approximately 30 pm from the interface. This is associated with local nano-scale voiding in the standard porcelain material. In contrast, in the La-oxide-doped veneer, the fracture toughness level is maintained within approximately 10% of the bulk value everywhere. This finding explains the improved chipping resistance shown by the present formulation. The combination of lanthanum oxide nanoparticle doping with the selection of an appropriate veneer fusing thermal history leads to an improvement in the fracture resistance of porcelain veneer and reduces the incidence of chipping. This conclusion was confirmed by fine scale evaluation of the mechanical properties (stiffness and hardness) using micro-pillar line arrays machined across the porcelain/PSZ interface using focused ion beam (FIB) milling. The comparison of experimental results between base porcelain veneer and lanthanum oxide micro-doped porcelain veneer confirmed that the properties remained consistent down to a spatial resolution of a few microns.

As is evident from the foregoing discussion, the present invention provides a dental composition for making a dental veneer with improved resistance to chipping at the interface with zirconia coping and that maintains excellent bio-compatibility, aesthetic appearance and performance. The present invention also provides a method of forming a dental veneer with the dental composition. While preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to the described embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the scope of the invention as described in the claims. Further, unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising" and the like are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

Claims

1 . A dental composition for a dental veneer, comprising:

a ceramic composition;

lanthanum oxide, the lanthanum oxide forming a mixture with the ceramic composition;

wherein, in use, the mixture is applied to a zirconia coping and sintered before being cooled to room temperature, the sintered mixture is further tempered at a temperature of between about 400 degree Celsius (°C) and about 475 °C for a period of between about 4 hours (h) and about 24 h.

2. The dental composition of claim 1 , wherein the sintered mixture is tempered at 450 °C for 24 h.

3. The dental composition of claim 1 , wherein the lanthanum oxide comprises between about 0.5 percent by mass and about 1 percent by mass of the mixture.

4. The dental composition of claim 1 , wherein the lanthanum oxide has an average particle size of between about 100 nanometres (nm) and about 400 nm.

5. A method of forming a dental veneer, comprising:

providing a dental composition comprising a mixture of a ceramic composition and lanthanum oxide;

applying the dental composition to a zirconia coping;

sintering the dental composition;

cooling the sintered composition to room temperature; and tempering the sintered composition at a temperature of between about 400 degree Celsius (°C) and about 475 °C for a period of between about 4 hours (h) and about 24 h.

6. The method of claim 5, wherein the sintered composition is tempered at 450 °C for 24 h.

7. The method of claim 5, wherein the lanthanum oxide comprises between about 0.5 percent by mass and about 1 percent by mass of the mixture.

8. The method of claim 5, wherein the lanthanum oxide has an average particle size of between about 100 nanometres (nm) and about 400 nm.