Welding telescopic/double crowns with laser connection elements

In the past, cast partial bases on telescopic crowns were usually modeled directly approximally or orally flat in classical dental technology if a subsequent soldered connection was planned. Even in the casting technique, this solution proved to be extremely unsuitable for a welded connection.

On the one hand, it is almost impossible to produce a distortion-free welded joint with a good fit in this way. The bigger problem, however, is the long-term stability of the joint.
With this type of design, all forces occurring would always be transferred directly into the welded joint, which would greatly increase the likelihood of the joint breaking due to fatigue and result in costly repairs downstream.

Regardless of whether a hybrid telescopic prosthesis is to be cast, fabricated using CAD/CAM techniques or a combination of the two, care must be taken during the planning stage to ensure that the masticatory forces are transferred to the construction and that the welding merely ensures a stable, positive connection between the components. This is the classic type of shear distributor.

Only a few design options are shown schematically below; there are certainly other conceivable alternatives. These can be constructed individually, from ready-made wax parts or possibly from a database, depending on the tools available.

The dimensioning of the connectors should be as delicate as possible in accordance with the available space and individual circumstances (e.g. bruxism), but absolutely as stable as necessary.
Common to all variants is the need for the tertiary construction to fit the secondary parts as precisely as possible in order to avoid possible distortions during welding right from the start (e.g. through clearance fit in contrast to preparation for an adhesive connection, where a small gap for the adhesive is absolutely necessary), as well as design-related tilting moments that could affect the subsequent weld seam.   

When welding, one telescope at a time should be completely welded, not several at the same time. This gives you better control over the fit of the work on the model.

It is advisable to select lower welding parameters for the first welding points. These are only intended for fixing the components and should be set from both the occlusal and basal sides.

The parameters can then be increased. Only a guideline value could be a connection of a secondary crown made of a high gold alloy with a CoCr cast partial:

Material CoCr->Au – Power 40 % – Pulse duration 7 ms – or also

It is advisable not to weld a continuous weld seam from one side at a time, but to place the welding points individually, always alternating diagonally opposite each other, until the seam is complete. This procedure allows any stresses that may arise to be compensated for directly. The work is always placed back on the model to check that it fits correctly so that any necessary corrective action can be taken. If necessary, certain areas can also be reinforced with laser welding wire. No major finishing of the welded work is necessary.