A novel laser-based method for controlled crystallization in dental prosthesis materials

Abstract

Glass-ceramic materials are increasingly becoming the material of choice in the field of dental prosthetics, as they can feature both high strength and very good aesthetics. It is believed that their color, microstructure and mechanical properties can be tuned such as to achieve an optimal lifelike performance. In order to reach that ultimate perfection a controlled arrangement of amorphous and crystalline phases in the material is required. A phase transformation from amorphous to crystalline is achieved by a heat treatment at defined temperature levels. The traditional approach is to perform the heat treatment in a furnace. This, however, only allows a homogeneous degree of crystallization over the whole volume of the parent glass material. Here a novel approach using a local heat treatment by laser irradiation is presented. To investigate the potential of this approach the crystallization process of SiO 2 -Li 2 O-Al 2 O 3 -based glass has been studied with laser systems (pulsed and continuous wave) operating at different wavelengths. Our results show the feasibility of gradual and partial crystallization of the base material using continuous laser irradiation. A dental prosthesis machined from an amorphous glassy state can be effectively treated with laser irradiation and crystallized within a confined region of a few millimeters starting from the body surface. Very good aesthetics have been achieved. Preliminary investigation with pulsed nanosecond lasers of a few hundreds nanoseconds pulse width has enabled more refinement of crystallization and possibility to place start of phase change within the material bulk.

Bioactive and inert dental glass‐ceramics

“…For instance, it was recently demonstrated that new nano‐glass‐ceramics with a notably high ZrO 2 content can be synthesized using sol‐gel methods . The technology required to achieve this goal could rely on chemistry‐based and applied nanotechnology. New or improved sintering/crystallization processes, such as microwave heating, laser crystallization, spark‐plasma sintering, biomimetic assemblage of crystals, textured crystallization, and electron beam crystallization, should be further developed. Chemical strengthening of RDGCs by ion exchange, as tested by Kawai et al and Fischer et al, is a promising route and should be further pursued. Glass‐ionomer composites are widely used in restorative dentistry. We believe that glass‐ceramic powders, including bioactive formulations, can also be used as inorganic fillers in these composite restoratives.…”

“…3. New or improved sintering/crystallization processes, such as microwave heating, 159 laser crystallization, 160,161 spark-plasma sintering, 88 biomimetic assemblage of crystals, textured crystallization, and electron beam crystallization, should be further developed. 4.…”