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    Technique: Building a better metal-free substructure

    Using Shofu’s TRINIA™ for a new option in substructure work.

    In restoration cases that require a substructure, dentists and laboratories are looking for more efficient and cost-effective alternatives to metal bars cast in semi-precious or precious metals or bars milled in titanium. In the instances where substructures are cast in semi-precious or precious metals, casting can be a tedious process with many steps. There can be distortion, which results in the bar having to be sectioned, indexed and re-soldered, in which case the model will need to be readjusted and an additional try-in will be required. 

    Additionally, substructures cast in precious metals can be quite costly. Bars can also be milled in titanium, but many milling machines owned by laboratories are not capable of milling titanium, so the cases must be sent out for milling, resulting in additional turnaround time and a markup by the laboratory doing the milling step. Titanium is also a relatively expensive choice for a dental substructure. Shofu has a better alternative. 

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    Shofu’s TRINIA™ is the solution for precise, metal-free substructures that can be milled with great precision on most leading wet or dry milling systems using nano-diamond burs. TRINIA is a lightweight, biocompatible material that obtains its tremendous durability and resiliency from multi-directional, interlacing layers of fiberglass and resin. The material has high flexural and compressive strength to facilitate intraoral function and comfort. As an additional benefit, milled TRINIA substructures can be produced at a unit cost far less than the cost of precious metal or titanium bars.

    The following case study is a step-by-step guide for fabricating a full lower screw-retained appliance incorporating a TRINIA bar. 

    01 Once a verified model from a verification jig has been obtained and the case is ready to proceed, the case is mounted and a try-in is prepared. After the try-in has been checked in the mouth and any necessary adjustments are made, a rubber index is prepared that will be used to transfer the teeth from the try-in to the bar. 

    02 Next, UCLA abutments are waxed and cast over the implants (Fig. 1; all figures in video above). Normally, you would use a scan jig when you scan the model and then, from a purchased titanium insert kit, use appropriate abutments and titanium inserts. In this case, because a scan jig was not available to me, plastic UCLA abutments were cast, finished and screwed on the model. 

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    03 The try-in is sprayed with scan spray to reduce glare and reflection and is then scanned. Leaving the model in the same position on the scanner, the try-in is removed and the cast and finished UCLA abutments are screwed onto the model. The abutment screw holes are filled with wax. The metal portions of the abutments are sprayed with scan spray, and then the UCLA abutments are scanned (treating the abutments as if they are copings around which a bar is to be designed) (Figs 2 & 3).

    Next page: Placing the teeth ...

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