18.1 Laser for Joining Metals

The laser first became popular in dental laboratories in the early 1990s. With the broad introduction of titanium as a framework material, a suitable joining option had to be found. Laser welding was the easiest method.

The alternatives at that time were mainly bonding. The typical adhesive materials were plastics and therefore usually not heat-resistant. The temperature-resistant variants made of glass or ceramics were cumbersome and time-consuming to process. In addition, adhesives require a relatively large amount of space to guarantee a high mechanical load-bearing capacity. However, the “passive fit” is better than with all other alternatives.

Some laboratories tried to solder titanium (Fig. 18.1). For this purpose the workpiece was placed under a glass dome, which was first sucked out by a vacuum pump and then flooded with argon. This prevented the embrittlement and formation of the alpha-case layer that occurs when heating titanium in a normal atmosphere. A highly focused infrared beam was now directed through the glass onto the workpiece prepared with solder and flux and heated until the solder began to melt. It was an incredibly complex process, and if the preparations were not perfect, the procedure had to be repeated.

Both joining options, bonding and soldering, were more than questionable, however, as far as the biocompatibility question, which really made titanium “in”, was concerned. Laser welding enabled us to join parts together with one and the same material.

Laser welding has remained an indispensable joining method for metal to this day. The laser can be used for almost all metals used in dental technology. Porous surfaces can be sealed with the laser or missing contact points can be created without great effort. Countless ready-made anchors and attachments are lasered onto all possible bases. With extensions, the laser makes it possible to attach retentions to model casted frameworks without destroying the surrounding plastic.

The main risks of laser welding are severe distortion and embrittlement of the material or its destruction (e.g. in titanium, if argon is not flooded enough). The different melting temperatures, thermal conductivity and surface reflection must also be taken into account.

18.2 CAD/CAM Laser as Scanner

At the turn of the millennium, lasers were used in large numbers as scanners, for example, in the Sirona Cerec system. At Sirona, in the early days, a small plaster model was attached to the workpiece holder and optically scanned with a small laser, mounted on one of the grinding motors (Fig. 18.2). Thus, smaller impressions could be digitized and further processed accordingly.

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