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Hybrid acrylic processing

Simple steps to increase predictability in implant-supported cases

by Robert Kryer, CDT .

I have been asked many times, “How do you process acrylic resin for an implant-supported hybrid case?” As we all know, there are various ways to process acrylic resin around an implant bar, but the technique I’m illustrating here provides me with the consistency and desired quality I want. To process using this technique, you must have two implant analog sets: one set for the master cast and another set for investing and processing.

THE TECHNIQUE IN PICTURES: SLIDESHOW
(refer to slideshow for figures)

Post waxup
After completing the wax-up with implant analogs attached with abutment screws to the bar framework, smooth out the wax and seal it around each abutment access hole (Fig. A). I prefer a hard wax (Yeti Dental Solidus 80 or 84, Lincoln Dental) for final wax contouring.

Inject an extra-light-body impression material (Virtual, Ivoclar Vivadent) over intaglio of the wax surface. Before it sets, inject a VPS-based rigid bite registration material (Futar D pink, Kettenbach Dental) over the Virtual and around each implant analog (Fig. B). The VPS-based rigid bite registration material bonds well with the extra-light impression material.

Invest and inject
Invest the finished wax-up with analogs in the first half of a flask and sprue appropriately for the Ivocap Injection process (Fig. C). Fill screw access holes with cotton and then cap with a slight amount of VPS light-body.

Cover the wax with Virtual VPS extra-light impression material to capture gingival detail and prevent tooth movement (Fig D).

Before the Virtual VPS sets, apply a layer of VPS silicone (Sil-Tech Super, Ivoclar Vivadent) to create a rigid surface for the negative mold (Fig E).

After the wax elimination process, remove the implant bar and thoroughly steam clean the VPS positive mold. The Virtual extra-light-body is now visible with the pink Futar D underneath (Fig. F). The implant analogs are visible now with telescopic milled copings (Haechler Esthetic Designs) in the anterior, which provides a very dense and detailed surface to process against and eliminates the problem of stone bonding to the acrylic resin.

The negative mold with teeth now is ready for injection (Fig. G). Characterize the gingival surface using Aesthetic Color Set Easy (Candulor), clean the teeth with heat-cure monomer (SR Ivocron, Ivoclar Vivadent), and inject.

Screw the cast implant bar (Haechler Esthetic Designs) back onto the implant analogs, and fill the access holes with cotton then cap with VPS Virtual extra-light-body material (Fig. H). Sandblast then prime the metal with a metal bonding agent (SR Link, Ivoclar Vivadent). This creates an interface between metal and acrylic resin. Close the flasks and process with the Ivocap Continual Press Injection System. The Ivocap injection compacts the polymer particles very tightly, creating a dense PMMA surface that will have an intimate relationship with mucosal surface when the implant-supported hybrid prosthesis is screwed in place.

Finish and polish
After deflasking, the three types of VPS materials (Sil-Tech Super, Virtual extra-light, Futar D) are visible with implant analogs and sprues for Ivocap acrylic resin (Fig. I).

Cut and peel away the Sil-Tech Super from the processed acrylic resin (Fig. J). Note how clean the surface is, requiring minimal finishing. Implant analogs are still attached because the case was just deflasked. Clean out the VPS cap and cotton in the screw access holes, and remove the screws to disengage implant analogs.

Finish and polish the intaglio surface (Fig. K). The high water designs with increased crown height are no longer preferred on maxillary anterior hybrid prostheses due to impaired phonetics from airflow patterns around abutments and food entrapment.

This finished hybrid prosthesis allows a floss threader to clean between mucosal surface and acrylic resin intaglio (Fig. L). The labial and buccal peripheral borders are beveled to allow enough space (approximately 2 mm) for a floss threader.

For courses or consulting on removable or implant prosthetics, contact Robert Kreyer, CDT, at www.PersonalizedDenture.com.